GoodSoundClub - Romy the Cat's Audio Site - It will be a sheep in wolfs clothing...

06-14-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	26
Post ID:	21703
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It will be a sheep in wolfs clothing...

The fullrange Milq will be built in an oversized chassis with the intention of adding maybe two or more channels down the track and perhaps some line level crossovers. So I will up spec. the mains transformers so they can handle a larger draw and will leave room for more power supplies and more amplification stages. Plus it will be tucked out of the way when it is in the room and a little difficult to get to, so the foot pedal will be much appreciated.

Haha about the wall-wart. You would not be the only one to do that. I have boards for a nice dual rail regulated linear supply that will suit things nicely. It is overkill in that is has infinitesimal noise and is really meant for powering parts of a dac but between the two rails I can get 2A which will be enough for the foot pedal and lights and fans et cetera. Plus I will not have a SMPS putting crap back into the power for other components to pick-up...I would like to remove all SMPS on my audio circuit...next will be the PC.

06-15-2015

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Romy the Cat

Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #:	28
Post ID:	21706
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To a great degree it depends where the Cap is used.

anthony wrote:
Romy, I understand that at some stage you trialled a number of different capacitors and settled upon Electrocube 950B/D not necessarily for the Melquiades but perhaps for some other project. I was wondering if you ever experimented with different coupling caps in Melquiades? Oil caps in particular.

As I mentioned earlier in this thread, these are my first valve amplifier builds so I have not messed around with different coupling caps before but I have heard how caps in speaker crossovers can make quite a noticeable difference, so I am interested in your input here.

As much as caps in speaker crossovers makes deference, so do they make in coupling applications. In Milq the cap is light duty as the amp never goes A2 and the cap is not change the polarity, still the coupling caps do mater a lot. I did experimented a lot with the coupling caps and I like the Electrocube 950B and MultiCaps, the last unfortunately available only by small values. I did not experimented with new German Teflon caps. I do not like oil caps, at least those that I tried. I feel that oil caps are more suitable for high current applications. Also, do not forget that in context of DSET the coupling cap behavior is kind of defend. If you need large coupling cap for LF amp that you do not care how “dry” it sounds at HF. I find that for MF and HF it is better do not have cap at all, that why in my DH channel I use DB coupling, something that I would not do for ULF….

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-18-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	29
Post ID:	21717
Reply to:	21706

Cap rolling...

Romy the Cat wrote:

As much as caps in speaker crossovers makes deference, so do they make in coupling applications. In Milq the cap is light duty as the amp never goes A2 and the cap is not change the polarity, still the coupling caps do mater a lot. I did experimented a lot with the coupling caps and I like the Electrocube 950B and MultiCaps, the last unfortunately available only by small values. I did not experimented with new German Teflon caps. I do not like oil caps, at least those that I tried. I feel that oil caps are more suitable for high current applications. Also, do not forget that in context of DSET the coupling cap behavior is kind of defend. If you need large coupling cap for LF amp that you do not care how “dry” it sounds at HF. I find that for MF and HF it is better do not have cap at all, that why in my DH channel I use DB coupling, something that I would not do for ULF….

Thanks for your insight Romy. I can see your point about not needing to worry too much in the DSET about coupling cap performance at higher frequencies but I would imagine that the crossover filter caps are quite import at those regions though. Have you experimented with something other than the Electrocubes there?

I ask this because the Electrocubes are not easy to get hold of and end up reasonably expensive by the time I purchase them in a quantity that they are willing to manufacture so I have looked around a little for alternatives. Where you use film in the power supplies I am considering the Mundorf MCap Supreme film caps...they seem affordable and reasonably well regarded when used in power supplies. Likewise I think that I will try them for the larger coupling caps.

Regarding the DSET crossover filter caps, I am thinking of using either Jupiter Copper Foil or V-Cap CuTF...they are both reasonably affordable in the small values, particularly the Jupiters. DSET coupling caps I will probably try the Mundorf MCap Supreme film caps for a start and maybe even a small value Jupiter Copper Foil or V-Cap for the UpperBass coupling cap, just to see if there is any difference.

I will be building the fullrange first, so I might try a few different coupling caps in it if I get enough time with it. I have a pair of Duelund Cast 630VDC 2.2uf sitting around here somewhere that I can try as the coupling cap plus I will be able to try the much less expensive Mundorf MCap Supreme mentioned above and maybe a Jupiter Copper Foil as well. It will be interesting to see if any of those caps seem to work well in the fullrange Milq.

Regards,

Anthony

06-18-2015

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Romy the Cat

Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #:	30
Post ID:	21718
Reply to:	21717

Caps, caps, caps....

anthony wrote:
Thanks for your insight Romy. I can see your point about not needing to worry too much in the DSET about coupling cap performance at higher frequencies but I would imagine that the crossover filter caps are quite import at those regions though. Have you experimented with something other than the Electrocubes there?

In my view the Electrocubes do well across the board. When you are taking about “caps at higher frequencies”, then what do you mean? The line level, the speaker level, the line level between? Do not forget that a RL filter is always preferable over C filter.

anthony wrote:
I ask this because the Electrocubes are not easy to get hold of and end up reasonably expensive by the time I purchase them in a quantity that they are willing to manufacture so I have looked around a little for alternatives. Where you use film in the power supplies I am considering the Mundorf MCap Supreme film caps...they seem affordable and reasonably well regarded when used in power supplies. Likewise I think that I will try them for the larger coupling caps.

I had a few Mundorf MCap but I can’t say anything concussive about them. The Electrocubes are not as expensive as you think. If you look their inventory then you can get them for a few bucks each. Alternativly you can look at eBay and you will always find someone has leftover and sell them very cheap, for $1 per 2uF/450V cap/ I have bought quite a lot of this way.

anthony wrote:
Regarding the DSET crossover filter caps, I am thinking of using either Jupiter Copper Foil or V-Cap CuTF...they are both reasonably affordable in the small values, particularly the Jupiters. DSET coupling caps I will probably try the Mundorf MCap Supreme film caps for a start and maybe even a small value Jupiter Copper Foil or V-Cap for the UpperBass coupling cap, just to see if there is any difference.

I will be building the fullrange first, so I might try a few different coupling caps in it if I get enough time with it. I have a pair of Duelund Cast 630VDC 2.2uf sitting around here somewhere that I can try as the coupling cap plus I will be able to try the much less expensive Mundorf MCap Supreme mentioned above and maybe a Jupiter Copper Foil as well. It will be interesting to see if any of those caps seem to work well in the fullrange Milq.

I do not know anything about them. Feel free to experiment. If you want, after you finish the amp, let me know your address and I send you a pair of Electrocubes 2uF/450V just for reference. Anyhow, there are tone of the caps out there you might find something good. Do not discard the vintage caps, some of them are very good. Also, be advised that most topologies of caps do need to be burn in in order to yield the best sound.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-18-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	31
Post ID:	21720
Reply to:	21718

Caps at high frequencies...

Romy the Cat wrote:

When you are taking about “caps at higher frequencies”, then what do you mean? The line level, the speaker level, the line level between? Do not forget that a RL filter is always preferable over C filter.

It was reference to the range of frequencies that the lower frequency DSET channels with coupling caps are required to pass. Like a typical audio moron I have read a few things online recently about different people using different caps for various tasks in various systems with various listening preferences with various...well you get the idea...but the main talking points seem to be midrange or top-end with not a great deal of talk about differences at bass frequencies, which is where the coupling caps are used in the DSET Milq. I am left with the impression that the DSET will be less influenced by the choice of coupling caps than a fullrange Milq, and that I will probably get good results with a solid performer but not necessarily over-the-top cap in those positions.

However, the caps in the line level filters may be a different matter because they are working with the entire frequency range, so perhaps the best quality caps should be used there. As an aside I think that I may have just found a good source for these filter caps in Electrocube 950B's and am waiting for a quote (someone actually has stock of the smaller values - but not of the larger 2uF caps). If it pans out I will sort out the filters with Electrocubes and then when everything is settled try some other brands to see if there can be any improvement.

Romy the Cat wrote:
The Electrocubes are not as expensive as you think. If you look their inventory then you can get them for a few bucks each. Alternativly you can look at eBay and you will always find someone has leftover and sell them very cheap, for $1 per 2uF/450V cap/ I have bought quite a lot of this way.

I have had an eBay alert set for 6 months now and it has not alerted me of any 2uF caps. I don't live in the US so maybe I only get alerted about the ones that ship worldwide.

On the other hand these people that I found with some Electrocube stock do have 1.5uF and 3uF sizes (apparently), so perhaps those values are ok to use instead of 2uF and 1uF in your schematic.

06-19-2015

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Romy the Cat

Boston, MA
Posts 10,160
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Post #:	32
Post ID:	21721
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Do not worry about it for now.

Anthony, I think you take the right this in a wrong way. Sure the quality of the coupling caps is important but you truly shall not be worry about it. Make the amp, get comfortable with it and then change the damn cap. It is very simple to do and I am sure you will find zillion caps to experiment with. Do not worry about it for now. For a full range amp 2uP will be enough. The cap and plate impedance will create low pass filter. You want this filter to be a couple octave under the lower cut off of your transformer. If you get at full power -3dB at let say 18Hz then to cut off for the filter at 7-8 Hz would be sufficient. With 2uF you will be somewhere there… Do not forget that you can always parallel the caps, to bypass the caps… there is a lot that might be done.. but later….

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-22-2015

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anthony
Posts 338
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Post #:	33
Post ID:	21729
Reply to:	21721

Second Stage Half-6C33C impedance

Romy the Cat wrote:
Anthony, I think you take the right this in a wrong way. Sure the quality of the coupling caps is important but you truly shall not be worry about it. Make the amp, get comfortable with it and then change the damn cap. It is very simple to do and I am sure you will find zillion caps to experiment with. Do not worry about it for now. For a full range amp 2uP will be enough. The cap and plate impedance will create low pass filter. You want this filter to be a couple octave under the lower cut off of your transformer. If you get at full power -3dB at let say 18Hz then to cut off for the filter at 7-8 Hz would be sufficient. With 2uF you will be somewhere there… Do not forget that you can always parallel the caps, to bypass the caps… there is a lot that might be done.. but later….

I will do it own the track. Going round in circles I was.

Romy, I am checking crossover filter calculations against your DSET schematic and am having a little trouble determining the high pass filter component of the Upperbass Channel. The 0.022uF coupling capacitor is supposed to roll off the high pass at about 60Hz according to the schematic but without knowing the input impedance to use for the half 6C33C I cannot actually check this and look at what effect different sized caps in there will have on the -3dB point. Using 60Hz as the -3dB point and 0.022uF as the capacitor I end up with an input impedance of about 120kOhm for the half-6C33C as you run it in your DSET Milq. Does this sound about right?

Regards,

Anthony

06-22-2015

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Romy the Cat

Boston, MA
Posts 10,160
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Post #:	34
Post ID:	21734
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I think it is about right.

I think it is about right. The 6C33C for upper base has 100K biasing resistor and 20K to ground in Lpad. That would make ~60Hz. This high pass that unload the LF from the horns that it can’t handle is very important as you do not want driver to pressurize the horn by sound that could not be passed by horn. You need to go with high resolution RTA and plot a low knee of the horn decay, full range. Then you need to get the filter and run it just to be barely visible at the plot. Then drop a half of the octave and it would be your crossover point.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-23-2015

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anthony
Posts 338
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Post #:	35
Post ID:	21743
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More Lpads...

Romy the Cat wrote:
I think it is about right. The 6C33C for upper base has 100K biasing resistor and 20K to ground in Lpad. That would make ~60Hz. This high pass that unload the LF from the horns that it can’t handle is very important as you do not want driver to pressurize the horn by sound that could not be passed by horn. You need to go with high resolution RTA and plot a low knee of the horn decay, full range. Then you need to get the filter and run it just to be barely visible at the plot. Then drop a half of the octave and it would be your crossover point.

I have to admit that I have studied the DSET schematic and I just plain missed the Lpads for the 6C33C bias. Kind of obvious really that they should be there considering the variable resistor in that place on the fullrange Milq schematic, but for some reason I missed it.

Romy, do you use an Elma rotary switch with RN60 resistors for these 6C33C bias LPads (Bass, Upperbass and Injection)? What sort of attenuation step should I be looking for here?

Regards,

Anthony

06-24-2015

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Romy the Cat

Boston, MA
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They are not LPads but they are bitch.

Well, they technically not Lpads but juts regular attenuators even though they connected in “protective mode”. You can go with stabilized impedance to maintain the high pass filter over the coupling capacitor to work properly but I do not feel it is necessary. When you make the real amps you will have the attenuator ruining let say between 35K and 36K to set the real tube bias properly. You will not slide the attenuator from 0 to 50K. The range will be buffered by two resistors up and down and in context of 100K biasing resistor the impedance shift that your coupling cap will see will be near negligible and might manifest a 2-3Hz difference in the slop. Above I told you that I tested the slope with analyzer and I did not detect any meaningful crossover shift while I changed bias.

Now, the type of the resistor is the real bitch question. You do not want rotary switch with great resistors but you rather want a 10-20 turns attenuator. However this is bias and everything you do with bias matters sonically. So, find the best you can get 20 turns attenuators. At the time I did it I had 3 or 4 different types and all of them were as good as fixed resistor. I chose the one that I liked best at that time, I do not remember what it was, I think it was some kind of large 20 turns Vishay for $12. It was however over 12 years back and today you might find better parts. Be advised that quality of soldering and wires and even the layout of the bias wiring in the amp’s chasses is very auditable for whatever reason. I actually was very surprised how sensitive and demanding my 6C33C where for biasing line. I was able to hear the sound change when I loved the proximity of bias wired to mass ground. I am not kidding.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-25-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	37
Post ID:	21747
Reply to:	21744

Bleeders at shut-down...

Romy the Cat wrote:
Well, they technically not Lpads but juts regular attenuators even though they connected in “protective mode”. You can go with stabilized impedance to maintain the high pass filter over the coupling capacitor to work properly but I do not feel it is necessary. When you make the real amps you will have the attenuator ruining let say between 35K and 36K to set the real tube bias properly. You will not slide the attenuator from 0 to 50K. The range will be buffered by two resistors up and down and in context of 100K biasing resistor the impedance shift that your coupling cap will see will be near negligible and might manifest a 2-3Hz difference in the slop. Above I told you that I tested the slope with analyzer and I did not detect any meaningful crossover shift while I changed bias.

Now, the type of the resistor is the real bitch question. You do not want rotary switch with great resistors but you rather want a 10-20 turns attenuator. However this is bias and everything you do with bias matters sonically. So, find the best you can get 20 turns attenuators. At the time I did it I had 3 or 4 different types and all of them were as good as fixed resistor. I chose the one that I liked best at that time, I do not remember what it was, I think it was some kind of large 20 turns Vishay for $12. It was however over 12 years back and today you might find better parts.

Thanks Romy. I should be able to track something down. At this stage I am thinking of Bourns 3590 series pots.

Romy the Cat wrote:
Be advised that quality of soldering and wires and even the layout of the bias wiring in the amp’s chasses is very auditable for whatever reason. I actually was very surprised how sensitive and demanding my 6C33C where for biasing line. I was able to hear the sound change when I loved the proximity of bias wired to mass ground. I am not kidding.

I don't doubt this statement at all. There are a few ideas for wiring and component layout kicking round in my brain but I think they are for a later stage.

In the 6 Channel Version of Super Melquiades thread at post #89 you mention trouble you were having with some NC relays that you were using to disconnect some power supply bleeder resistors when the amp was turned on. When the amp is turned off these relays make contact again and they conduct power to drain the power supplies backwards into high wattage 50R resistors. I can see that this would be a good idea from both safety and cap lifespan perspectives. Could you please share a little more info about this setup? Does it still function?

You mention 50R resistors and bridging two 6A relay contacts for each power supply. What wattage do you use for the resistors?

Regards,

Anthony

06-25-2015

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Romy the Cat

Boston, MA
Posts 10,160
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Post #:	38
Post ID:	21748
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A word of warning

anthony wrote:
In the 6 Channel Version of Super Melquiades thread at post #89 you mention trouble you were having with some NC relays that you were using to disconnect some power supply bleeder resistors when the amp was turned on. When the amp is turned off these relays make contact again and they conduct power to drain the power supplies backwards into high wattage 50R resistors. I can see that this would be a good idea from both safety and cap lifespan perspectives. Could you please share a little more info about this setup? Does it still function? You mention 50R resistors and bridging two 6A relay contacts for each power supply. What wattage do you use for the resistors?

I do not remember the specifics with relay. The driver and bias PS are bled the 6C33C’s PS are not. You might do it if you want. You can do it while the PS is running, that would require some current from transformer to be wasted and I do not know if you have a spare current in there. Also, the elevated current would drive the minimum inductance down and would make your choke to be smaller. You can do alternative and on back side of relay to connect a high power resistor, let say 50W. This all does not matter, you can do whatever you want. Just a word of warning if you use the full-range Milq as reference. In the PS of the driver stage it shown L1 20H. For the 100mA the 20H is barley hit the critical inductance. When I measured the critical inductance it did worked fine but to be at the save side I would go ether with let say 30H choke or to drive over the choke 30-50mA more (can be easily set by dropping the volume of R23 resistor). It is not a big deal but it will be more of save side if you do.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

07-02-2015

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anthony
Posts 338
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Post #:	39
Post ID:	21751
Reply to:	21748

They will light up like a Christmas tree

Romy, thanks for the info on the chokes in the fullrange Milq.

Today I have ordered more Milq parts this time for the power sequencing and bleed down. I decided to go for the relay sequenced bleeders for all four power supplies and figured I would be happy with a bleed down time to 50V of about 20-30 seconds. For the four power supplies this is what I calculated:

40,000uF 200V supply = 500R resistor with initial power dissipation of 80W (purchased 500R 100W)
3,000uF 200V supply = 5K resistor with initial power dissipation of 8W (purchased 5K 10W)
9,000uF 400V supply = 2K resistor with initial power dissipation of 20W (purchased 2K 25W)
8,000uF 400V supply = 1.5K resistor with initial power dissipation of 106W (purchased 1.5K 100W)

I decided to go for large ceramic caps with good power ratings so I could avoid heatsinking and also to not rely on the short term power rating of the resistors to get through the initial high power dissipation period of the discharge. In the end the resistors I purchased are big and over-rated for the task but I am happy that I will not be pushing them anywhere near their limits so they should work well for quite some time. Looking at the calculated initial current draws I have similarly purchased relays with over-specified contact current ratings...I certainly don't want them to weld.

Downstream of each bleeder resistor will be a LED to show that charge is draining, or not. So there will be one LED to tell that AC power is available and the standby DC power supply is running, three more LED's for the power-on sequencing relays and then four LED's that will light up when the bleeder circuits are activated on power-down. That is 8 LED's on each amplifier, which is ridiculous and could make the whole thing look a little like a Christmas tree if I am not careful, but I have chosen low intensity red lights so hopefully they will ruin neither my night vision nor my impatience for bright LED's on audio gear.

Regards,

Anthony

07-03-2015

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anthony
Posts 338
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Post #:	40
Post ID:	21752
Reply to:	21683

More on the "inductive" LPad

Romy the Cat wrote:
anthony wrote:
Sorry Romy, I was not clear enough, but the resistor that I am questioning is in the Fundamentals Channel (not the MF Channel as I believe you referred to in your previous post) between the OPT and the S2.

Ah, the Fundamentals Channel, that is totally different story. I have a regular highly inductive 16R L-pad in there, just at the speaker level. The upper knee of the Fundamentals Channel is second order 1000Hz at line-level and you do want to drive as much as possible HF out of this channel. The additional inductive roll off at top only helps to this Channel, even I do not think that it is truly auditable.

Romy, are you able to give me an example of a regular "inductive" LPad? I am struggling. Those that I can find don't state whether they are inductive or not. I have ordered a cheapy from Parts-Express but I have no idea if it is inductive or not...probably not.

07-03-2015

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Romy the Cat

Boston, MA
Posts 10,160
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Post #:	41
Post ID:	21753
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The LPADs....

What do you mean the example of inductive Lpad? All speaker level Lpads are inductive. The speaker level Lpads work with low voltage and high current and therefore they use wire wound restive elements. Any wire wound components are inductive by nature. In fact most of the non wire wound resistors are inductive and you need to pay premium to get not inductive resistors if you need it. I do not know if cheap Part-Express Lpad would be more inductive then some kind of super-expensive Lpad from other brand. They are inductive not by "bad or cheap making" but by topology of restive wire wound restive element. BTW, I had a few vintage German and British LPAD that I fished on eBay and they were way more inductive then the contemporary LPADs. They were not better sounding ether.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

07-09-2015

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anthony
Posts 338
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Post #:	43
Post ID:	21767
Reply to:	21753

Now that I have had a good look at them...

Romy the Cat wrote:
What do you mean the example of inductive Lpad? All speaker level Lpads are inductive. The speaker level Lpads work with low voltage and high current and therefore they use wire wound restive elements. Any wire wound components are inductive by nature. In fact most of the non wire wound resistors are inductive and you need to pay premium to get not inductive resistors if you need it. I do not know if cheap Part-Express Lpad would be more inductive then some kind of super-expensive Lpad from other brand. They are inductive not by "bad or cheap making" but by topology of restive wire wound restive element. BTW, I had a few vintage German and British LPAD that I fished on eBay and they were way more inductive then the contemporary LPADs. They were not better sounding ether.

...I see what you mean. I found some images of the insides of some of these speaker level L-Pads and they certainly do look like they are inductive. I understood the wiring technique used to make wirewound resistors non-inductive and I assumed that this was available for speaker level L-Pads as well.

One question that I still have regarding the L-Pad on the MF Channel is why you did not lose more gain at the filter before the MF driver stage? By my reckoning a resistor change here would shunt more signal and you would possibly not need the S102 resistors at speaker level. Of course you may have just experimented and found a solution that worked well enough and left it there...or I may have missed something.

Romy, I see that you are a fan of the air-capacitor at high frequencies. It has been interesting reading about where you have been successful (or not) with them and what you have had to do to get them to work. Intriguing even. If you don't mind me asking, what do you look for when selecting an air-capacitor? This is all foreign to me. There are variables such as construction material, number of gangs, air-gaps and voltage ratings. I would assume that it is important not only to shield them from RFI but to seal them so they remain clean. Would you care to reveal your source for these caps?

Regards,

Anthony

07-09-2015

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anthony
Posts 338
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Post #:	44
Post ID:	21768
Reply to:	21754

DIY

Paul S wrote:
The usual "trick" to "stop inductance" of wire wound resistors is the "old double-wound trick", like those offered by Mills:
http://www.soniccraft.com/index.php/resistors-mills-c-29_53

(and I think it is much the same for capacitors, for that matter...)

Shallco makes acceptable attenuators, if this is what you are looking for:
http://www.shallco.com/attenuators.html

I thought part of the "fun" of audio electronics is that any "element" in an active series/circuit is part of a "reactive element"...

How I love DIY!

Best regards,
Paul S

Thanks Paul.

I get the feeling that when/if this DSET build gets across the line that I will have more energy for further refinement of the amplifiers than Romy did at the end of his endeavours. Unfortunately I will not have the benefit of the "thousands of steps" that he has taken and the benefit of hindsight they afford so my efforts are likely to be more wayward than Romy's, but it will be interesting nonetheless. I really don't want to DIY just for the sake of it...I want to get a good result and then be done with it...figuring out what I need to do to achieve an objective is the difficult part because of, as you say, the "reactive" nature of audio electronics and their interplay with what comes out of the speakers.

Cheers,

Anthony

07-09-2015

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Romy the Cat

Boston, MA
Posts 10,160
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Post #:	45
Post ID:	21769
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Better air-caps?

anthony wrote:

One question that I still have regarding the L-Pad on the MF Channel is why you did not lose more gain at the filter before the MF driver stage? By my reckoning a resistor change here would shunt more signal and you would possibly not need the S102 resistors at speaker level. Of course you may have just experimented and found a solution that worked well enough and left it there...or I may have missed something.

Sure, it is completely makes sense to put a Lpad before the Milq driver. There are two “conditions” however. The impedance before the driver is used for bias, so you would need more resistors to separate bias and load-constant attenuation. And the last is that in my situation, with my MF tube and my S2 driver I still feel that mild” but very well controlled inductance is beneficial to my sound.

anthony wrote:
Romy, I see that you are a fan of the air-capacitor at high frequencies. It has been interesting reading about where you have been successful (or not) with them and what you have had to do to get them to work. Intriguing even. If you don't mind me asking, what do you look for when selecting an air-capacitor? This is all foreign to me. There are variables such as construction material, number of gangs, air-gaps and voltage ratings. I would assume that it is important not only to shield them from RFI but to seal them so they remain clean. Would you care to reveal your source for these caps?

I look only for size per volume and ability to hide them. There is some belter air-capacitors, some of them silver with holes, just open some top of the liners HP, or Textronics of RS from 80s. I don’t try them however for sound.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

07-23-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	46
Post ID:	21795
Reply to:	21769

Top Plate Draft #1

I got some time on the PC to start to think about how to layout the DSET. I plan to build it a little like a skyscraper: multiple levels separated by component groups and functions.

So mains transformers, AC socket and perhaps time delay relays on the ground floor wrestled into their own sarcophagus that will use some sort of low frequency suspension/vibration management in an effort to keep mechanical vibrations from reaching the rest of the chassis. Then the AC-DC conversion on the first floor, filter caps and output transformers on the third level with the amplifiers sitting proud on top. I don't want to see any caps or transformers...just valves.

By attacking it this way I think that I will be able to build each "floor" on the bench and the hook them into place with minimal in-situ soldering. Over the top will go a nice wood or metal facade that will leave the valves exposed but cover the workings.

So in an effort to see just what sort of footprint I can get away with (prefer small footprint and tall height) I took to SketchUp and produced the first draft layout for the amplifier plate that will be the very top level. As can be seen below I can get everything to fit in about a foot square...which is great...but I doubt that I will be able to get the iron below into such a small footprint without splitting it over more levels...but we will see. I have tasked well regarded local fellow to produce all the iron that I will need: mains transformers, filament transformers, chokes, inductors, output transformers. We will see what he comes up with but I have not made a final decision regarding this stuff and I certainly as yet do not have dimensions of the gear, so laying out the lower levels is not quite possible at this time.

Here are a couple of images...notice that I have tried to keep the 6C33C's about two to three inches from the smaller tubes and about two inches separated from their brethren.

07-23-2015

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Romy the Cat

Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #:	47
Post ID:	21797
Reply to:	21795

Many options are available.

anthony wrote:
Then the AC-DC conversion on the first floor, filter caps and output transformers on the third level with the amplifiers sitting proud on top. I don't want to see any caps or transformers...just valves.

Possible, even I like more the idea of separation of PS and control circuit on the different chassis. The vertical towers work very well with SS amps. With tube and particularly with input choke DSET you will have a lot of LF vibrating high mass element and you won’ be able to quite them down. But this is juts might personal take. What is non-personal and absolutely certain is that you can’t put the last cap in your PF at the different floor then your tubes. The caps need to be right there in very close proximity to tube. If you chose to have large caps then the accommodations need to be made. If you have unlimited heights then you can make the 2 floor of the caps and the third of the tubes.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

07-29-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	48
Post ID:	21818
Reply to:	21797

Fleshing out the design a little more...

Romy the Cat wrote:
anthony wrote:
Then the AC-DC conversion on the first floor, filter caps and output transformers on the third level with the amplifiers sitting proud on top. I don't want to see any caps or transformers...just valves.
Possible, even I like more the idea of separation of PS and control circuit on the different chassis. The vertical towers work very well with SS amps. With tube and particularly with input choke DSET you will have a lot of LF vibrating high mass element and you won’ be able to quite them down. But this is juts might personal take. What is non-personal and absolutely certain is that you can’t put the last cap in your PF at the different floor then your tubes. The caps need to be right there in very close proximity to tube. If you chose to have large caps then the accommodations need to be made. If you have unlimited heights then you can make the 2 floor of the caps and the third of the tubes.

Yes, I think that the separation of the PS and amplifier is very important to make this all work to properly. I have fleshed out the design a little more.

First of all the footprint has been increased from about 300mm square to about 400mm square as there was just no way to get all of the OPT's close to their power tubes with the smaller size. As it is now there is spare room up top with the valves and I am considering whether to introduce a curved roll-off from the top surface to the sides rather the the square "industrial" look. I am not sure. I will have to draw it to see what it looks like.

As drawn below, each mono-bloc will stand somewhere around 1m tall. I think that this will work well when you consider that the Upperbass Horn will stand about this tall and I plan to snuggle each mono-bloc in behind and immediately beside the horn stack, and with the speaker cables coming out at a little under that 1m height I can keep the speaker cables very short. If I keep the amps in nice and close to the horn stack perhaps all I will see of the amplifiers from my seat will be the tubes thus helping to make a visually large audio system seem a little smaller when seated.

Notice that not all of the components are shown in these sketches. The OPT's (in an off-yellow/light brown) have not been chosen so I do not have exact dimensions and have used cuboid of approximately the right size. All the filter caps are shown, but the smaller caps for the bias are just randomly placed in their approximate positions along with a few of the associated components. There should be plenty of room under the top plate for amplifier components (caps ans resistors) and if necessary I can spill into the vacant space of the layer below for parts of the crossovers.

DSET Tower - Early Days #1.jpg

You can see that I plan to use vibration management in two places on the amplifier: firstly under the entire amplifier with a constrained layer platform sitting on springs so that hopefully vibrations above 5Hz or so are not transmitted from the floor to the amplifiers; secondly using the same system internally for the power supply which I intend to keep highly isolated from the amplifier section above it. The brown three layer sandwich is the constrained layer platform but I have not drawn the springs.

DSET Tower - Early Days #2.jpg

In the shot below you can see the placement of the OPT's. They are very close to the centrally located large filter caps and only a few inches from their respective tubes keeping the B+ voltage lines short. You can also see the Bourns potentiometers (in blue). I plan to have these situated behind two little drop down doors. This way I keep the knobs out of eyesight.

DSET Tower - Early Days 3.jpg

Lastly, this shot shows the location of the smaller filter caps for the bias and a little more of the location of the large B+ filter caps.

DSET Tower - Early Days 4.jpg

AC and DC wiring may be able to be transported from the power supply section to the amplifier section inside one or more of the eight chassis columns. Perhaps run a PVC tube up the centre of the column and glue some rubber grommets at the entry points and the wiring would be neat and tidy. I am not sure sure of the electrical consequences of running the wire inside a number of steel bars, but hopefully it will be ok.

Opinions and insight are appreciated.

Regards,

Anthony
EDIT: Not sure why the images are not showing up properly. Romy?

07-31-2015

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Romy the Cat

Boston, MA
Posts 10,160
Joined on 05-28-2004

Post #:	49
Post ID:	21821
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Interesting but….

Generally I like it but I have some concerns, whatever rubber feet and decompiles you will be using you will not defeat the vibration if you have a few transformers and a few 500A input chose sitting at the bottom. You will take a statoscope and you will clearly have the vibration on the tube floor. Well, you will have noise on the tube floor but how will affect sound is very hard to say. A common sense would suggest that you should not have any vibration in there, and in particularly because you use very fast and relatedly microphoneic tubes (when they cold) in driver stage. But in reality it is not so simple and I have seen when vibrated control unit sounding more stage then fully isolated. Still, I would go for fully isolated control unit (tube floor).

The biggest concern that I have if you have a single chasses with PS at the bottom is that your caps at the mid floor is that your caps, like the rest of your components inside will be greatly over heated. The transformer and choke will be getting hot and your entire amp will be a basic chimney with hit-sensitive caps in the middle. I think it is one more argument to put PS to a separate chasses. You still cat stack the PS and control unit one above another, in the way how I did it:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=2715#2715

…but this way you might have more effective heat and vibration decupling. You will be going over the hell of dealing with connecting cables but you might outsource it and order the connectors and cables to be made for you.

anthony wrote:
Not sure why the images are not showing up properly. Romy?

Do not use “#” in the picture names and the will be shown

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

08-04-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	50
Post ID:	21834
Reply to:	21821

Heating is an issue...

Romy the Cat wrote:
Generally I like it but I have some concerns, whatever rubber feet and decompiles you will be using you will not defeat the vibration if you have a few transformers and a few 500A input chose sitting at the bottom. You will take a statoscope and you will clearly have the vibration on the tube floor. Well, you will have noise on the tube floor but how will affect sound is very hard to say. A common sense would suggest that you should not have any vibration in there, and in particularly because you use very fast and relatedly microphoneic tubes (when they cold) in driver stage. But in reality it is not so simple and I have seen when vibrated control unit sounding more stage then fully isolated. Still, I would go for fully isolated control unit (tube floor).

Yes, I considered running an separate isolation platform for the amplifier section but could not think of an easy way to incorporate it into the design as it stands. Thinking about the weight of these things it will probably be a good thing to be able to break them in two to have some chance of shifting them by hand so I will revisit the design.
The isolation platforms are spring mounted. The springs will be loaded by the components that sit on them and the weight of the platform itself so that when you give it a nudge the unit slowly oscillates at a very low frequency, say a couple of hertz. I dare say that the idea is not so different to the Silent Running Audio stuff that you use. The stethoscope is a very good idea. Much more simple than the accelerometer that I was considering to sort this stuff out.

Romy the Cat wrote:

The biggest concern that I have if you have a single chasses with PS at the bottom is that your caps at the mid floor is that your caps, like the rest of your components inside will be greatly over heated. The transformer and choke will be getting hot and your entire amp will be a basic chimney with hit-sensitive caps in the middle. I think it is one more argument to put PS to a separate chasses. You still cat stack the PS and control unit one above another, in the way how I did it:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=2715#2715

…but this way you might have more effective heat and vibration decupling. You will be going over the hell of dealing with connecting cables but you might outsource it and order the connectors and cables to be made for you.

I was going to seal off the power supply section at that thick platform that is about halfway up the tower and either chimney or fan force warm air out the sides so that it does not affect the amplifier section. This will keep the warm air from the internals of the amplifier section.

Romy the Cat wrote:

anthony wrote:
Not sure why the images are not showing up properly. Romy?

Do not use “#” in the picture names and the will be shown

Understood. Thanks Romy.