anthony wrote:

I am calculating crossover scenarios for the HF Channel (Channel F) and am hoping that you can remember a reasoning for using a 20K LPad instead of a larger value such as 30K or even 50K?  As the larger impedance is used the value of the capacitors reduces and the size of the inductor increases, which I would have thought to be a good thing in terms of the actual performance of the inductor compared to its design specifications.  Unless your aim was to minimise the inductor size or you were just using the LPad that you had available? I am not sure how increasing the LPad from 20k to 50k would affect the operation of the filters in the other channels.

Romy the Cat wrote:

There is no aspects of minimization of the inductor size. You can go to 30K, or 50K, or 100K input LPAD. The LPAD (which is not inductive switched attenuators with good resistors) anyhow sites behind the filter, so the input impedance of the attenuators will be “visible” by other channels only at HF, so the value of the attenuators is semi-irrelevant. The reasons why I went with 20K is because I would like to keep the value of the resistors that formed the attenuators lower. If I use S102 resistors that have no inductance of any kind then the value of the resistors would be absolutely irrelevant. I use very good resistors for attenuator (RN/CMF55/60), they are metal film and non-indicative but they still have “some” residual inductance and my presumption was that higher value the more inductance. I warn you that this is such an irrelevant minor thins that we can talk about it but I very confident that it has no practical impact to the sound you will get out of it. So, in term of the input attenuators for HF you can do anything you want.

anthony wrote:

I am not sure how large to make the filter caps for the DHT channel.  At this stage I think I will start at 3000uF and perhaps try altering it a little up or down once the system is stable.

anthony wrote:

On another point, I got to Sydney a couple of weeks ago and listened to Tax's 'Koshka' Melquiades running a heavily modified AG horn system.  I did enjoy my visit and am now quite confident that the Melquiades will suit my objectives.  Of course this is a few hours listening in a new room but I heard a lot of things that I like.

Romy the Cat wrote:

anthony wrote: I am not sure how large to make the filter caps for the DHT channel.  At this stage I think I will start at 3000uF and perhaps try altering it a little up or down once the system is stable. Hm, it is depends how stupid you are. The 3000uF is an average level of stupidity. In my amp I went for 36000 I believe that was accessibly stupid. In some amp DIYers make SETs with 8uF that is unsufficiently stupid. It is about how much you wiling your transformers, chokes and the rest PS and filter to be impactful to sound. Some folks make vintage tube rectification, use super-duper components in filtration and use very small last cap of a special type, let say paper in oil… Then the sound of the amp is 50% of the sound of PS. I do not say that it is bad and with proper tweaking all of it you can get fine result. I do not like this approach and I prefer to use large electrolytic to cancel out any sonic PS contribution. In my amp it is not about the contributive sound of passive elements but rather about unadulterated sound of active elements. Use the filtration to drive ripples to let say 1-3mMv and it would be good start.

Romy the Cat wrote:

anthony wrote: On another point, I got to Sydney a couple of weeks ago and listened to Tax's 'Koshka' Melquiades running a heavily modified AG horn system.  I did enjoy my visit and am now quite confident that the Melquiades will suit my objectives.  Of course this is a few hours listening in a new room but I heard a lot of things that I like.  It is nice to hear BUT: if you heard the Tax's installation then how you concluded that sound you heard was result of “good Melquiades” but not the result of Tax’s heavily modified AG horn system? What I am asking is how you in the sound that you heard you were able to attribute what you liked to the amps but not to numerous other aspects?

anthony wrote:

Hi Romy, So it is time to think about the bass output transformer in my DSET.  My bass channel will be 8 x 25W/8565-00 each side set in a sealed box and will cover the frequency range below say 100Hz.  These drivers can be wired anywhere between 1R and 64R which gives quite a bit of flexibility for adjusting the amplifier/speaker system damping factor.  Reading your threads about your Scanspeak arrays it is evident that the system damping factor is important for the bass channel and is influenced by the OPT decisions, how the 6C33C is loaded and most likely by how the speaker is wired.   I propose to wire the drivers in parallel so that they present a nominal load of 1R to the amplifier which in effect will maximise the system damping of the drivers, which from what I take from your writings could be a good thing.  Then I will have a bass OPT wound with a secondary of 1R or 1.1R that will pass 450mA and cover say 5Hz - 800Hz before rolling off. Romy, given your experience with the amplifier and the drivers, are you able to offer any advice regarding the OPT or wiring of the drivers before I give the transformer winder my final specs?

Romy the Cat wrote:

Output transformer. Here is what the thing become complicated. Of you drive ultra-low impedance with step down transformer then your secondary turns will decrease. They primary will have whatever they have for all case but secondary will go lover and lower as load impedance drop and might even become foil-made. That is for sure will make the transformer faster and better for transients BUT your need LF DSET transformer it means you need inductance. As you will be losing your turn on secondary you will be losing inductance and the only way to get it back would be to increase the core size.  You need to put your transformer maker on the task and see if you will be able to obtain a transformer core for half amper gap, no secondary turns and 5Hz at full power. That will be a small refrigerator size piece of iron and it might be very expensive.

Romy the Cat wrote:

Cables. Driving 1R you will be driving current. Driving 64R you will be driving voltage. Some of the cables/connectors behave differently under voltage vs current conditions. Also if you drive 1R with low voltage then you might pick some on like interferences.

Romy the Cat wrote:

Drivers. If you go with 8 x 25W/8565-00 then make sure that your make the right boxes and over dump them. I would use 4 individual boxes by 2 drivers each. I do not think that drivers would care how they are connected. The difference would be in case of driver mismatch. In real world all drivers will be slightly different. You are not a large speaker builder and you won’t be able to pick among 100s driver the best matching drivers. So, if one driver has Fs 20Hz and another 24Hz then the question is: would it be betters for them to be connected in parallel or not. I do not know the answer and I am not informed enough to make a guess. You need to consult with somebody else, BTW, if you do them post a received answer.

Romy the Cat wrote:

Usability. That is bitch. First thing first: how do you know how much your tube need to be loaded? Pretend that it is 6C33C and pretend that you need to load it with 600R to get a balance MF sound. Idle tube more you dive you less harmonics, faster sound, in a way over-burned transients. Loading the tube more five you “slower”, more euphonic sound and more power. That would be true for MF but at LF you will have much less negative impact of tube idling and you might find VERY beneficial to load your 6C33C with 1 kR or 1.2kR. That are not exact number but I just give you an idea. Also, the differences at 1R load are huge. Each change of 0.1R loading will give you a large difference in sound. You will need to hit very prissily and you as you start will not know where to aim. I can only presume that you will be in the realm of 1200-1500R, or perhaps higher but with “odd” transformer and a few other variable it is very hard to predict anything. Do not also forget that with limited wiring on the secondary you will have very limited opportunity to have multiple taps on your transformer as the filling of the barbing will be suffering.

Romy the Cat wrote:

Usability continue. There are more ugly things: as you ideal more your bass tube and get better sound (to a degree) you will be losing power. Even with 8 drivers and let say a single 6C33C you will need a sealed room of let say no more than ~300sq feet or you will be driving your 6C33C into A2, which is a clipping for this tube.  If you have a normal listing room of 600+ with open floor plan then you are way out of your DSET capacity with 6C33C unless you super load the tube and then you have shity sound. Even if you did resolve your problem with power somehow then the ugly truth that it will take time for you to understand what type of bass you need. My estimation that it would be good to stay with properly doe bass for 2-3 months in order to “get” where/how to move next with bass.

Romy the Cat wrote:

So, from all that I said above if I were in your position I would not go final DSET solution with bass now but rather did it incrementally.  Make your bass sections, connected them conventionally, let say 16R each and drive them with some kind of SS amp. Then take the SET that you would like to use as DSET and drive it into the bass channel. Play with loading, find the best configuration and make a judgment about sufficiency of power. Then go for a DSET that would be against a conventional load. 4x16R in parallel = 4R. That would be a conventional load and you can use many different amps to try, including your SET, If you test everything with your SET, find a proper loading and get conformation about power then you can converts the found transformer ratio to any another load. That is basically what I did over the time and this is what I would do if I do it again. Do not forget that your situation might be very different from what mine was in my old city home. Your bass channel will be running under 100Hz and your room dissipation at 100Hz might be very different then at 40hz, so you might need much more power than you might think. It is nice to learn about it experimenting with SET then to pay a lot of money for DSET OPT and then learns that you have not enough DC gap to add another tube in parallel or that you need to lose another 10% turns on secondary and the cost of shipping of the transformers will cost more than a pair of new one.

anthony wrote:

Romy, I have seen you mention setting speakers up across the long wall before but never got to the base of your reasoning?  Could you please elaborate?  Is it to do with the delay of first reflections?

Romy the Cat wrote:

Interesting. with sealed 280 sq feet and 8 drivers per side along a long wall you very much migh be able to use a singe 6C33C. With proper loading, good trasformer, DSET and these drivers you should be able to get bass that I doubt you will be able to get from any SS amp.

noviygera wrote:

Romy,why do you feel the SS amps will not provide as good bass as tube amp? Since there is such a big selection of SS amps, also hybrid one, is it a general rule, regardless of amp power and type? Is it the type of distortion that's inherent to tube amps that makes them specially enjoyable in the bass region?

Romy the Cat wrote:

Output transformer. Here is what the thing become complicated. Of you drive ultra-low impedance with step down transformer then your secondary turns will decrease. They primary will have whatever they have for all case but secondary will go lover and lower as load impedance drop and might even become foil-made. That is for sure will make the transformer faster and better for transients BUT your need LF DSET transformer it means you need inductance. As you will be losing your turn on secondary you will be losing inductance and the only way to get it back would be to increase the core size.  You need to put your transformer maker on the task and see if you will be able to obtain a transformer core for half amper gap, no secondary turns and 5Hz at full power. That will be a small refrigerator size piece of iron and it might be very expensive.

anthony wrote:

My transformer winder has completed the first prototype DSET bass OPT.  He was quite excited when he called me and used the word "phenonomenal" to describe its performance into a reflective 1R load.  At 4Hz it is down 0.5dB and at 10kHz and 20KHz it is down 1dB and 3dB respectively.

Romy the Cat wrote:

anthony wrote: My transformer winder has completed the first prototype DSET bass OPT.  He was quite excited when he called me and used the word "phenonomenal" to describe its performance into a reflective 1R load.  At 4Hz it is down 0.5dB and at 10kHz and 20KHz it is down 1dB and 3dB respectively.     That all make sense ONLY if we are taking about max power. You will not get from your transformer 0.5dB at 4Hz and 3db at 20KHz at max power and the fact that your guy gives you the numbers at a fraction of power does not make me too happy about him….