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Home » Melquiades Amplifier » Valve Preamplifier for Macondo/DSET (75 posts, 4 pages)

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08-16-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	51
Post ID:	25919
Reply to:	25917

Three preamps compared

Now that all three are on the same absolute polarity and have been listened to quite a bit I thought it time to write down my impressions. From least preferable to most:

(3) Neurochrome Universal Buffer set to invert polarity and with 12dB gain. No volume control and no input selector: Dac >> Buffer >> DSET's. A really high performer given the low price with a lot of good things going for it, including its tremendous flexibility. Unfortunately, although it does drive the DSET better than pretty much every other preamp and buffer I have tried and trialled, it is not as capable in this task as the next two preamps. There is a whiteness introduced to the mids that is noticeable on vocals and some strings which may have to do with the capacitive load of some of the filters at the input to the amplifiers. An easier load and I am quite sure this whiteness will disappear and what is left is nothing but neutral. Very good soundstaging, excellent clarity, loads of frequency extension at both ends.

(2) Placette Active Linestage. 12dB gain added with Neurochrome Universal Buffer. Dac >> Buffer >> Placette >> DSET's. This is better. Whiteness is gone (probably thanks to the 18kR resistive load of the Placette) and a softness or delicacy has found its way to the presentation, more like real instruments. Even though input selection and volume control are added to the signal path, this is a more complete, balanced, enjoyable experience. There does not appear to be anything missing. Vocals are lovely, strings better, more definition and clarity in all instruments and softness in the bass.

(1) 10y breadboard preamplifier. Dac >> 10y >> DSET's. I am trying so hard to overcome my obvious biases here, and for a while today I almost convinced myself that the Placette was marginally better in this role with the DSET's, but in the end I cannot deny that the 10y plays with a little more delicacy, or consideration, tenderness, or however I am failing to describe it. Think of the difference as how two musicians can play the same notes but sound slightly different, a softer touch here, a little more firmness there, seemingly more time between the notes, a slight calmness...that is what the 10y is doing compared to the Placette. There is just a little more variation in the notes that makes things just a little more dimensional and less flat. It is quite close though. Both reveal very fine nuances and sounds but the Placette is not quite able to articulate things quite as well as the valve pre. The soundstage feels very wide and expansive with all three preamps with the Placette more three dimensional than the Buffer but the 10y is a little different. I cannot decide if the Placette stage is noisier or more noisless than the 10y. With the Placette it feels like things are presented on a huge screen about 5m wide and 2m high, but with the 10y I do not have the illusion of a screen, where you think there is glass or something see-through where there is no apparent sound appearing. The 10y just puts the images in the same places as the Placette, with a little more 3d or little more depth (they pop), but the illusion of the "screen" is not there rather just sounds appearing in their place with nothing below or above them. It is strange, and I have not decided which, if any, I prefer.

Dinner is on the table. I will add some more comments later.

08-16-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	52
Post ID:	25920
Reply to:	25917

More thoughts...

Romy the Cat wrote:

Another a very valid thing to try is to see of the same difference with the same recordings happens with different DACs, preamps the you will take care of the absolute phase.

To date, my listening has been with my favourite dac, the Phasure NOS1a. The other dacs here don't really compare, and if listening with digital I will always go Phasure otherwise for background I might stream Tidal from my work computer via a Focusrite Scarlett 2i2, which is quite befuddled compared to the more expensive dac.

Romy the Cat wrote:

You see, different DACs topology have different post DAC filters and they send different amount and different type of UHF into the upstream chain. Your 10Y is UHF limited and in a way acts as low pass filter, which is not necessarily a bad thing. Placette is wide open monster in UHF, in fact it might run a video signal with is very good for it but not necessarily good for music. I in a past observe a phenomenon that Placette was very much picky to what I used in DAC output filters. I have some CDs that if I play them with Bidat vs. Lavry Gold DACs they sound like very much different recordings and the difference is VERY different than a typical delta between Bidat vs. Lavry. If do the same experiment with a different preamp then the difference will be between the DACs but in completely different way. In most of the cases TLO-Lavry Gold with Placette has too much “resolution” and too ferocious dynamics that is superbly impressive to thrill audiophiles but not so musical and I tend do not use this combination.

The Phasure dac is completely filterless...nothing, nada, zip. The digital filter is applied in the computer software and sent to the dac in 32/768 which just plays the file NOS without additional filtering at all. As such the Phasure dac is wide open frequency wise. Plus the BNC cables I use are video spec and have something like 1dB attenuation over 100m at 6GHz and they are not filtering any UHF either.
"Ferocious dynamics" is not something that I am associating with the sound that I am getting here from this dac, and sometimes I might correlate that sort of sound to washed out or white mids with an emphasis on highs, but the sound here seems very well balanced.

08-16-2020

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	53
Post ID:	25921
Reply to:	25920

The last paragrapher worth to read a few times...

anthony wrote:
Have put all my DHT's on the curve tracer to see if pairs can be matched for preamp duties.

It was very interesting to read about all of it. If you have a socket for YO186 then you can accommodate all 4V tubes and I site like them If you do have a chance, try the a pre-WW2 RE604. This is a day of all 4V stube, and I do like it for full range applications. It is expensive nowadays however. In Milq you do not use then in full range however.

anthony wrote:
Now that all three are on the same absolute polarity and have been listened to quite a bit I thought it time to write down my impressions. From least preferable to most:
….
Dinner is on the table. I will add some more comments later.

Again, it was very interesting, but… Let agree that methodologically you did not try Placette as it performance was masked out by you need to use your Neurochrome buffer to get gain. Your chain will sound as the worst element is and in case of 10Y you have the worst element removed. I do have high high probability that if you were able to run Placette and 10Y directly then they will sound identical as the same volumes. I think it is simple to test. I do not know what output in your Phasure DAC. Get any DAC with a op-amp in output stage, most of them are. Find where a feedback provided to the output op-amp and reduces it to gain10-12dB more gain from the DAC. If Phasure DAC has no op-amp in output stage, then get any other DAC. The quality of the DAC is not import you need it purely foe prove the methodological concept. Then repeat the experiment. I think that you will find then Placette will hold his own.

anthony wrote:
The Phasure dac is completely filterless...nothing, nada, zip. The digital filter is applied in the computer software and sent to the dac in 32/768 which just plays the file NOS without additional filtering at all. As such the Phasure dac is wide open frequency wise. Plus the BNC cables I use are video spec and have something like 1dB attenuation over 100m at 6GHz and they are not filtering any UHF either.
"Ferocious dynamics" is not something that I am associating with the sound that I am getting here from this dac, and sometimes I might correlate that sort of sound to washed out or white mids with an emphasis on highs, but the sound here seems very well balanced.

Anthony, this exactly answer all questions then. You need to reinterpret at the result of your experiments in context of what I will be writing now. You see, there is school of thinking that if a DAC operate at very high sampling rate then the post DAC filter is not necessary, or a file might be very shallow as all post DAC nastiness will be at very high frequency that is very far from auditable range, It is very legitime way of think and indeed some of the systems do sound spectacular wit DACs like this. I did a LOT of looking into it. The excessive HF that is sent by DAC works out ONLY if later one in the chain you have some kind of lowpass filter the strips that HF component. I your case use you 10Y buffer you have via the auto-former that is bandwidth limited. Placette is the worst in your case as Placette has a huge bandwidth, as I told it runs video signal. So, in case of Phasure + Placette you have the whole HF nastiness HF from DAC sent directly to Milq. A reasonable question would be why Power Amps filters do not act as the power is frequency limited as well. The legitimate question to ask but unfortunately it does not work in this way. I have written about it years back. My theory was that audio components get “poisoned” by excessive HF and they have a memory of that poisoning. Do not ask me to explain it, I do not know how, I am just a practitioner and the depth of electronics design is not a feld that I am interested in. Anyhow. What I say is very easy to test it. Wake your phono stage and disengage your RAAI filter. Play music for an hour. It will be a horrible HF only sound, but you do need to play it laud. Then put the phono filter back and play it normally. It will be sound horribly because you power amp is “poisoned” by HF. It will take a good day of a normal operation to recover good sound from your amp until the HF “poison” will de dissolved.

So, I do think that in your case, considering the DAC you are using in case you use too HF transparent preamps you “poison” you power amp with HF. You can put a simple first order low pass subtraction filter before Placette and you will have better sound.

So, where it lives you. Obviously if you have frond-end with more output then I am very convinced that Placette will fulfill all your expectations, I am not kidding it is very hard to beat it. However, if you had this arrangement then you most likely would not like you DAC as much as via Placette it would sound not too gentle enough. If you willing to use your DAC then keep your 10Y preamp as it acts a great low pass filter for your system. If you would like to use Placette then you need a DAC with a post conversion filtration (preferably analog) and more output voltage.

What is very important to understand that in case you have both of the scenarios implemented then you should have identical result the end. Another very important message you might consider is that in case of your 10Y the main beneficiary to sound is not the quality of tube or your auto-former but a presence of preamp that acts and post-DAC low pass filter.

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

08-16-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	54
Post ID:	25922
Reply to:	25921

All sources

Romy the Cat wrote:

Again, it was very interesting, but… Let agree that methodologically you did not try Placette as it performance was masked out by you need to use your Neurochrome buffer to get gain. Your chain will sound as the worst element is and in case of 10Y you have the worst element removed. I do have high high probability that if you were able to run Placette and 10Y directly then they will sound identical as the same volumes. I think it is simple to test. I do not know what output in your Phasure DAC. Get any DAC with a op-amp in output stage, most of them are. Find where a feedback provided to the output op-amp and reduces it to gain10-12dB more gain from the DAC. If Phasure DAC has no op-amp in output stage, then get any other DAC. The quality of the DAC is not import you need it purely foe prove the methodological concept. Then repeat the experiment. I think that you will find then Placette will hold his own.

Yes, true. A few more observations about the listening:

Having one preamp playing for extended periods always gave me the best sound, whether that was the Placette with the Buffer or the 10y. When the 10y was in for extended periods I thought it worked better than when swapping them in an out to do relatively quick comparitive listening. Likewise, when the Placette was in for extended periods I thought it sounded better than when swapping it in an out for quick comparitive listening. Psychoacoustics? Probably. There are guys here that buy into the whole cable settling theory but I do not know...all I know is that when swapping things in and out that the sound was not quite as good as when things were left in place for hours or longer...perhaps it was my mood at having to change all those cables.

The quick comparitive listening was a little confounding. When in for the long run I thought the 10y held a larger advantage than when doing the quick comparitive listening. Swapping things in and out more quickly the sounds became more or less the same and I was really struggling to hear the 10y as being any better than the Placette at all. I used my observations from the longer term listening as a starting point in the short term stuff and they just were not observable to the same degree. As I reported, there was not much in it. Perhaps it is the dac HF issue and DSET poisoning you mentioned earlier. Sounds like it. Maybe there is just very little between the two, which is an excellent outcome for me.

I the past few weeks I have purcased a Pioneer UDP LX-500 universal disc player so that I can listen and watch my Bruckner and other DVD's and Blu Rays. Well, like pretty much everything these days it is 2Vrms output and needs some gain to get loud enough. I played that Gogol Suite CD you mentioned earlier in the thread (to scope out how much gain I might really need) and used pretty much the entire 18dB the 10y had to offer...through the Placette without any gain it was like trying to listen to whispers. Anyway, point here is that I need gain from my dac, disc spinner, phono stages, even from the little dac I use to stream Tidal because none of them give more than 2Vrms output. That is my issue.

To my ears there is very little separating the Placette and the 10y. I think I may be able to improve the 10y once it is boxed up with a more ideal layout and perhaps also with an unregulated power supply. The Placette could possibly be improved by using a different dac and by using one of Guys buffers for gain which in essence is exactly the same concept as the Buffer I am using. Guy has made it clear that nothing more is going in the case of my Placette and that if I need gain there will be another box for his buffer. How that works for multiple sources I have not yet figured out.

In the end I have breadboarded a preamp with gain that at least runs in the same league with the Placette. Two things about this were certainly not expected: firstly, I did not expect to be able to get the Placette working as well as it does now, but sorting out the power supplies has really helped as has the polarity thing with much of the digital music I listen to; secondly, I did not expect the valve preamp to be so immediately successful. Sure, it is a proven design with SS output and I did my reading between the lines to choose a valve that drew enough current, was not microphonic, and gave a sound that was not overtly sweet or warm, but I only gave the project a 50% chance of success and even then after much, much more effort than has gone in thus far. That a DHT is so neutral and transparent and can compare to modern engineering such as the Placette is extraordinary.

Romy the Cat wrote:

So, where it lives you. Obviously if you have frond-end with more output then I am very convinced that Placette will fulfill all your expectations, I am not kidding it is very hard to beat it.

Three weeks ago I would not have agreed with this statement, but now I do. The Placette is very hard to beat. If both systems were optimised, I am not sure the 10y will beat it, but they will be more or less equivalent.

Romy the Cat wrote:
What is very important to understand that in case you have both of the scenarios implemented then you should have identical result the end. Another very important message you might consider is that in case of your 10Y the main beneficiary to sound is not the quality of tube or your auto-former but a presence of preamp that acts and post-DAC low pass filter.

I am certainly not ruling that out, and will mull over consequences and actions in relation to HF and dacs, but I do need gain from all my sources.

08-16-2020

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	55
Post ID:	25923
Reply to:	25922

I think you are done then

Well, you can’t use Gogol Suite as some kind of reference in term of gain. The Gogol Suite was record by Pope Music at very high dynamic range they have very little compression. It feels like very soft volume recording as a result.

Architecturally for your system, considering that you have low voltage souses the 10Y sounds as a better solution. If you were able to make your 10Y to sound comparable to Placette then your preamp is operating very close to how preamps should sound and you do not need to look any further. Make sure that the fain you have from your preamp does not flood your input stage and does not max out your output stage. Is your AC voltage at input is under the DC voltage of your bias at 0dB digital level then you are all set. It is important do not drive the driver tube to A2 operation. The same goes with output tube, make sure that it does not go for A2 operation and it will clip very hard.

Another aspect. You know now what are the loads of your channels and they are fixed impedance. Now you need to assure that your amp is properly set power-vice. Drive your power amp at 0dB digital and max out your preamp. Let pretend that you are not clipping, add another preamp and make sure your power amp just beginning to clip. It is very easy to with a generator BTW. Now make sure that when your sinusoid gets clipped then it happens symmetrically atop and at bottom. Probably it will be the most applicable for your LF channel. Idle the LF channel as much as your power permits you (those drivers will sound better with less loading) and set if at symmetrical clipping. You can slightly adjust voltage and current of the output tube operation in order to moderate the top and bottom clipping. If happens the you have not enough power for your room drive the Milq LF in Pure Class A then you have a problem. Let me know if it’s the case. I predict that in your room and with the amount of you LF drivers you would be able to use Milq;s LF with no problems.

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

08-25-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	56
Post ID:	25927
Reply to:	25923

All for nought?

Well, I decided it was time to start using some "proper" interconnects between the preamp and DSET's, ordered them and had them delivered. To date I had been using cheap interconnects from the local electronic shop (literally $6) which should be ok...afterall they are just wire and how easy is it to attach some coax to rca sockets? All my good cables were either too short or too long for the job so the $6 fellows became the interim solution. Have been happy with the sound I am getting, was able to dial in a decent sound quite easily using just the l-pads for the upper channels to get a reasonably flat measured response at the listening position.

Put in the new interconnects and the sound is harsh..not nice. Bass is gone, sound is bleached and irritating even listening at lower levels. It has been a long time since I've had new cables but I never recalled such a change in sound so I turned down the volume and let them play in the background for a few days. No change. Put in the old $6 wires and good sound was back.

This really had me scratching my head so I grabbed the LCR meter and measured both sets of cables. The cheapies measured 0.4ohm DCR and 0.4ohm AC resistance (100Hz - 100kHz) whilst the new cables an excellent 0.03ohm DCR and 0.018ohm AC resistance along with a quarter of the inductance, although both cables have inductance and capacitance under control. The only real difference I could find that may or not influence the sound is the resistance of the wires.

So, with the new interconnects I have had to attenuate the midrange/fundamentals/HF channels and the good sound seems to be back. Early impressions at least. This tuning has only been done by ear, but about 5dB more attenuation has been necessary in the upper channels, give or take, and I will have to find some time to pull out the microphone and measure the frequency response once more.

It seems as though the $6 interconnects really were broken, or at least they acted as a high pass filter for the sound, which means that I should re-visit the preamplifier comparisons to be fair to all contenders with the new interconnects. What a pain.

08-25-2020

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rowuk

Germany
Posts 454
Joined on 07-05-2012

Post #:	57
Post ID:	25928
Reply to:	25927

Your enviable situation

Just think back a couple of years where you read about claims of difference in the sound of cables and wondered if it could be true. Well, in many cases it isn't and those posting document the BS by making claims that simply do not describe what cables do!
Just think about how you wanted a system of such resolution that the cables became "important". Now you can make decisions.
It may be a pain, but I consider you to be one of the lucky ones!
There is no decision more gratifying than one without compromise!

Whenever I feel blue, I start breathing again.

08-26-2020

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	58
Post ID:	25929
Reply to:	25927

Do not ask me how I know it.

I do not know how about 5dB attenuation via cable but for sure cables sound very different. Hey you are talking to a person who have a small fortune spent for wiring my entire system with vintage Dominos and I never felt that it was waste of money. There is so much talk about cables that I do not want to pollute this thread with this subject. I do feel that it is a bit to early for you to worry about cable and you need to setup the major game strategy and then wary about the dribbling. BTW, be advised that the configuration of your system permits you to do some very interesting things in term of cabling. You for instance might DC bias the cables with DC voltage that is very positive impact some of the cables. All you need to do is juts to shut down the positive bios supply and do not set 0VDC at impute. As the preamp is connected the ultra-low Zout of the preamp will ground the negative bios voltage to ground via the 400K grid-bias resistor. This will generate the proper negative bias for the driver tube and the DC voltage will be flowing over your interconnect to preamps output. Very cook configuration. Do not disconnect your interconnects in this configuration while your amp is work as you will be baying need drivers for your speakers and new windows for you house. Do not ask me how I know it.

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

08-27-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	59
Post ID:	25930
Reply to:	25929

No questions asked

Romy the Cat wrote:
I do not know how about 5dB attenuation via cable but for sure cables sound very different. Hey you are talking to a person who have a small fortune spent for wiring my entire system with vintage Dominos and I never felt that it was waste of money. There is so much talk about cables that I do not want to pollute this thread with this subject. I do feel that it is a bit to early for you to worry about cable and you need to setup the major game strategy and then wary about the dribbling.

The circa 5dB attenuation is strange. All that I can think is that the $6 cables were somehow broken. I've never heard such a difference with cables before and hope I do not have to again with this project. I just need some cable of the correct final length so I could keep things tidy and went with something I am familiar with.

Romy the Cat wrote:
Do not ask me how I know it.

You paint quite the picture there Romy...

rowuk wrote:
There is no decision more gratifying than one without compromise!

Yes. What a nice way to phrase the concept.

04-23-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	60
Post ID:	26763
Reply to:	25901

Preamp details

Hi Anthony,
Nice piece, congrats! I'm in need of a good preamp and was thinking of making the same as I have 801A's. If I may,

1. Has the 801A pre stayed in your system? How do you feel about it after the time?

2. What is the OP of 801A, Ale's 200V/20mA/-6V?
3. I understand Slagle's autoformer is at the output, do you decouple it from 801A with a cap? If so how big and what brand.

4. What kind of bias do you use? Resistor, SiC or sth else?
Thanks, Jarek

Cheers,
Jarek
STACORE

06-29-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	61
Post ID:	26821
Reply to:	26763

Oops

Hi Jarek,

Apologies for missing your post.

To answer your questions:

(1) Yes and no. I've bundled the preamp into its new chassis (that I made from scratch) and it does not sound as good as before. There is a grounding problem with the new installation that I need time to track down and I am only getting volume from even numbered volume settings on the attenuator, not the odd settings, which is weird, but related to my grounding issue. The preamp has sat there for some time waiting for work to calm down a little to give me weekends to myself so that I can do this last little bit of work to get the preamp back into use.

(2) I have been using Ales operating point. However, I have a new source that puts out almost 4V and it will drive the preamp input to audible distortion so I will have to bias the 801a/10y deeper, probably around -10V. Once the grounding issue is sorted I will pull out the audio analyser and figure out just where to bias the valve to suit that high input source.

(3) No decoupling with a new cap...although there is already the series cap at the output of the hybrid mu-follower that rids DC from the output.

(4) Initially just sic filament bias. I do have other options here to try once the preamp is operating correctly. Reading descriptions of sound from other builders I think the sic diodes will probably suit Macondo/Melquiades most appropriately but only time will tell.

However, and this is a big however, I personally need this preamp, or something like it, because I have high input amps (4Vrms) and low output sources (1Vrms) and I like to listen loud which Macondo/Melq does unlike anything else I have heard. If you do not need the gain in your system, there are likely to be better preamps about or even a more conventional DHT preamp using a good output transformer and a suitable tube (not the 10 family: perhaps 71a if you can tame the microphonics).

Entire system gain structure is much more important to good sound than any particular qualities of the preamp. If I didn't need the x8 gain from my preamp I would be using a different pre with just the right amount of gain, no more. The 10y/801a is the right tool for my job, but it may not be so for yours.

Listening to the Placette active linestage with my new high output dac is very nice indeed and I do appreciate what Romy values in this setup, and if my sources all put out 4Vrms then I would have no need for the 10y preamp in its current guise, or the 10y tube at all.
Anthony

06-30-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	62
Post ID:	26822
Reply to:	26821

Some more on my needs

Hi Anthony,
Thank you for your reply & explanations.
I actually need only a buffer, perhaps 2x as my Yamaha B2 is very sensitive, but I need a good one. I have right now Yamaha C2 just to have anything and I suspect it kills the sound ('constipated' sound) although it has ample of gain. Placette in EU is very rare to come by to have a listen. I've been looking at 801A not so much for its gain but for to its very good following as a preamp tube. Spoke about it to Ale, he claims it has some special character and betters all he has heard (incl. 46 which I also have and was thinking to use). You seemed to have seconded that initially but now sounds like you are a bit cooler in your perception? I'm being a bit of a parasite here, trying to copy a known good solution - too little time for experiments recently.

My idea is to make sth along Ale's/your lines with the Slagle autoformer at the output to reduce both the gain and the output impedance (the preamp drives 6m interconects). BTW, which model of the Slagle do you have? Does it handle your 4Vrms output well without distorting?

Cheers, Jarek

Cheers,
Jarek
STACORE

06-30-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	63
Post ID:	26823
Reply to:	26822

The known good solution

N-set wrote:
Hi Anthony,
trying to copy a known good solution - too little time for experiments recently.

Well, Romy had great results with the Placette and his Dannoys, so that is the known good solution as far as I am concerned. Sounds like the 10y will introduce far too much gain which you will have to attenuate thus likely ruining the sound. I mentioned system gain structure earlier, and it is very important, more important than the amplification stages themselves.

The 10y is a bitch of a tube. You cannot wind a good output transformer for it...anyone that tells you they can either are deaf or have very low expectations of sound...so for a preamp we are limited to different output topologies including the mu follower which Ale uses. Trouble with the hybrid mu-follower is that unlike an OPT we end up with all the gain of the tube which in my situation is excellent but in yours not so much. Ale does recommend a resistor divider to attenutate some of the gain and perhaps that is an option should you still go with the 10, but it is still attenuation, and resistor attenuation at that which may or may not be better sounding than letting the Slagle Autoformers do all the attenuating work (I have the silver version with the Bent AVC-1 which Dave made for me and John Chapman supplied the control circuitry).

There is talk that thoriated tungsten filaments (as used in most of the 10's along with several other tubes) are where the good sound comes from. I don't know if this is true but all DHT's are very sensitive to the quality of the heater power supply. You are likely limited to using the Coleman regs, which are very good, but I have used a CCS developed locally that is no longer available, and last time anybody checked is better sounding than the previous generation Coleman regs, although the latest version seems to be well regarded but I not heard them. I don't know how much of my sound is due the the over-the-top filament supply, but I reckon a good portion of it.

In terms of me going cool on my preamp, no, that is not true, I've just had trouble putting it in a box. Plus I need to experiment a bit because my one (new) high output source overloads the input of the preamp and I need to bias it deeper. It is still the best sound in my system, but that is my system, and I am not sure it will be the best fit for your system.

07-01-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	64
Post ID:	26825
Reply to:	26823

Yes but...

anthony wrote:
Well, Romy had great results with the Placette and his Dannoys, so that is the known good solution as far as I am concerned.

If I were in US, I'd definitely try it but not here.

anthony wrote:

Sounds like the 10y will introduce far too much gain which you will have to attenuate thus likely ruining the sound. I mentioned system gain structure earlier, and it is very important, more important than the amplification stages themselves.
The 10y is a bitch of a tube. You cannot wind a good output transformer for it...anyone that tells you they can either are deaf or have very low expectations of sound...so for a preamp we are limited to different output topologies including the mu follower which Ale uses. Trouble with the hybrid mu-follower is that unlike an OPT we end up with all the gain of the tube which in my situation is excellent but in yours not so much. Ale does recommend a resistor divider to attenutate some of the gain and perhaps that is an option should you still go with the 10, but it is still attenuation, and resistor attenuation at that which may or may not be better sounding than letting the Slagle Autoformers do all the attenuating work (I have the silver version with the Bent AVC-1 which Dave made for me and John Chapman supplied the control circuitry).

All well understood of course but I'm massaging the idea, possibly wrong, of making effectively a 801A buffer. "Cheating the physics" with: i) the mu follower taking the job of the load and ii) letting the Slagle magnetics do only the stepdown, without the need for the magnetics to do both jobs, which as you mention is an impossible task given the high plate impedance of 801. By that the usual bass/HF compromise that step down transformer have to struggle with is +/- avoided. Autoformer should actually have an excellent HF, at least on paper, as the coupling does not rely on the magnetic flux with leakage inductances limiting the HF. Of course as you point out at the ~18dB attenuation that I'd need from the autoformer, no idea how well would it perform.
How is the performance of your preamp on lower volumes? That might give a hint if what I'm considering makes sense.
Thanks again, Jarek

Cheers,
Jarek
STACORE

07-03-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	65
Post ID:	26826
Reply to:	26825

Damnable Type 10's

Jarek,
If you would like some help with this please get in contact with me and I'll help out any way I can. Probably best to not do it on Romy's forum lest it become a diy audio site...
Anthony

07-03-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	66
Post ID:	26827
Reply to:	26826

Thanks goodness we are not soldering resistors ;)

rather discussing a potential of building a tube buffer around 801/10. I'd appreciate your help very much, especially your sound impressions under various conditions. My mail phixphi_AT_gmail.com
Thank you

Cheers,
Jarek
STACORE

08-04-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	67
Post ID:	27193
Reply to:	26827

801A preamp

After eons of construction, I've finally completed my version of the 801A premap, based on Ale Moglia /Bartola Valves design with his Gyrator anode loads, SiC bias and Rod Coleman filament supplies. 6 inputs, switched by an Elma switch and Dave Slagle / Intactaudio TVC on the output to better drive the 5m long IC cables to B2. I'm sorry I'm too lazy to upload the pics, you can find some here: https://www.facebook.com/groups/164921830213087/posts/6808017412570129/ Expectedly, it is a night and day from my previous Yamaha C2 that was temporarily doing the job. The pre is still breaking-in, missing a proper power cord, etc but man it makes magic! It also shows more accurately how Dannoys work, uncovered some problems with a bass in my space, but that is a separate subject. PS is Romy-style with 3300uF caps. I made my life harder being too lazy to add a shorting resistor on power down so have to wait about 10mins after switching the HV off for the caps to discharge. If anyone follows the design, do make that little effort.
There is a space in the chassis (and a ready PS) for a twin TDA1541A DAC I've been cooking simultaneously, hope to finish within a few eons.
Big thanks to Anthony for the inspiration and help!

Cheers,
Jarek
STACORE

08-05-2023

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Paul S
San Diego, California, USA
Posts 2,672
Joined on 10-12-2006

Post #:	68
Post ID:	27194
Reply to:	27193

With Headphones?

Jarek, congrats on getting a project to where you can listen to it! Are you planning to use this with headpones, or have you used it with headphones? I saw it is "limited" to 5V in, but perhaps enough overall gain with buffer for 'phones"? I realize that 'stats have special requirements; just wondered if this new pre-amp would do yoeoman duty.

Best regards,
Paul S

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	69
Post ID:	27195
Reply to:	27194

Dannoys

Thanks Paul! No, no, it works with Yamaha B2 and my Dannoys. I continue researching this intriguing project. For the Staxes I do not need a preamp. 5V is a plenty enough for B2 which has 1Vmax sensitivity.

Cheers,
Jarek
STACORE

08-05-2023

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Paul S
San Diego, California, USA
Posts 2,672
Joined on 10-12-2006

Post #:	70
Post ID:	27196
Reply to:	27195

Attenuation?

You may remember I also use transformer shunting for attenuation, in my case the taps are selected by "communications" shunts/relays. My output is quite low R, but variable, and only the transformers for isolation (no "active buffer". I was wondering if your new pre would be a "simple attenuator" that would drive headphones. I have not measured output from my radio's headphone jack, but it drives my Sennheiser HD650s well enough, and then some. I have not yet even tried headphones from my TVC/main system.

Paul S

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	71
Post ID:	27197
Reply to:	27196

Electrostats

Paul, my headphones are electrostats that need a separate driver. I use Blue Hawaii amp with a quad EL34. The preamp has a direct output from the selector switch, which will be connected to the headphone amp.

Cheers,
Jarek
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08-05-2023

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anthony
Posts 338
Joined on 08-18-2014

Post #:	72
Post ID:	27198
Reply to:	27193

It is alive!

Nice one Jarek! Glad that you have it going.

I've now switched my autoformer to the input as one of my new sources puts out over 10Vrms and I did not want to increase the bias. No real change in sound as far as I can tell. Enjoy.

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	73
Post ID:	27199
Reply to:	27198

Thank you!

It's quite a marvel from what I can tell now. The overall sound is somewhat on the darker side but the preamp is still breaking in (although I gave it 30h benchtop burn in with the frybaby track). I also suppose it reveals the Dannoy and the room interactions, which Yamaha C2 was masking due to inadequate bass and which I have not optimized yet (the Dannoys sit very close to the floor). The bass is great btw, amazing from such moderate-looking speakers. Plus it's power cord is still burning in and not in the place. And I've been using ordinary, cheap speaker cables. I suspect at this level of resolution all that begins to matter. I'm very happy to have the TVC at the output to run my long cables and given that my sources are not as powerful as yours, in particular TU-X1 tuner needs quite some amplification. I used different parts than you do in some locations, in particular Soviet K40Y-9 and Dale resistors on the gyrator board (Rmu is 5W Mills) and Polish Miflex plastic coupling caps, recommended to me by a prominent Polish audio manufacturer whose sound I know and like (initially I had an eye on the V-caps). The tubes are Hytron VT62, pumping 18mA with 204V on the plates and -6V bias. I also have graphite plate Mazda's 801A, which I haven't tried yet.

Cheers,
Jarek
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08-07-2023

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	74
Post ID:	27200
Reply to:	27199

Get more DB from you tuner

N-set wrote:
…in particular TU-X1 tuner needs quite some amplification….

It is not necessary the case. My TU-X1 has nigh output, no different than all of my other front ends. If you look at the schematics of the TU-X1 then you might find a chip per channel that is responsible for output stage. This chip has feedback and right there will be a trimmer resistor that adjusts the depth of that feedback. I lowered the feedback that sent to this chip and got if I remember correctly 10 or 12 dB more from the TU-X1. Whatever I got I made it to be the same as my Bidat DAC. At that time, I did a lot of experiments to ensure that getting more gain from TU-X1 will not impact its sound. I did not detect any meaningful difference, at least in context of FM broadcasts.

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

08-07-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	75
Post ID:	27201
Reply to:	27200

Not necessary now

Thanks Romy. Given the power of 801A preamp, this correction is not necessary. I simply increase the volume compared to my clone of 834 RIAA or other sources and the autoformer at the output is still in the attenuation mode, providing increased output current to drive the long IC's. It's the beauty of having the TVC at the output, I learned from Anthony.

Cheers,
Jarek
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