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Dual PS - Worth the Trouble?

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Posted on June 16, 2016 at 15:15:54
Triode_Kingdom
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 I'm still considering all the possible options when I finally rebuild my HK A50K on its new chassis. I'll be using the factory power supply topology (voltage doubler), but with modern low-ESR caps. I'm also planning to use VR tubes for the screens of the output tubes, and to add a fixed bias supply in order to apply as much A-K voltage as possible to the output tubes. I thought everything was settled following the prototype with 6L6s a few months back, but now I realize there's one more possible variation. I'm in possession of two HK power transformers for the A50K/A500. This opens the possibility of building a dual supply version. The question is whether it would be worth it, or if I should save the extra transformer for another project? Factory A500s sound pretty good to me, so I probably wouldn't be dissatisfied with a single transformer version. On the other hand, I'm open for anything that's likely to improve sonic performance ("likely" being the key word). Is there any general consensus on this issue?




 

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RE: Dual PS - Worth the Trouble?, posted on June 16, 2016 at 17:08:38
Chip647
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 If you are using the factory power supply I would stick with the single transformer. All of your voltages are going to be affected by cutting the load in half. A big part of the sound of the amp you like is that power supply.

If you want to upgrade the power supply pick your goal (stiffer? quieter?) I find the best power supply upgrades relate to using good chokes if you have the available chassis room.

 

RE: Dual PS - Worth the Trouble?, posted on June 16, 2016 at 17:39:50
TomWh
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 I am probably not the guy to ask because I have a tube choke loaded power supply for every tube in my system. I think in the power amp section it could bring some real benefits. There is something about big and many transformers. Maybe you could semi bread board it to see how it sounds.

Good luck
Tom

 

RE: Dual PS - Worth the Trouble?, posted on June 16, 2016 at 17:44:09
Michael Samra
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 Jack
Believe or not there is big advantage IMHO to using a doubler PS.The secondary wiring is typically thicker with fewer turns and therefore has a lower resistance,so that can play well as far as building a lower impedance power supply.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Dual PS - Worth the Trouble?, posted on June 17, 2016 at 07:37:03
krankkall
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 NO.

Any improvement in sound, will be marginal at best.

Steve

 

yes, yes, and yes..., posted on June 17, 2016 at 14:46:18
Lee of Omaha
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 The Pioneer SX-1250 sounds remarkably better than the SX-1050, and the chief difference is that the SX-1250 has dual power supplies off the same power transformer. We've "dualed" power supplies the same way in tubed and solid state amps always with the same result--better bass, better definition throughout the spectrum.

 

RE: Dual PS - Worth the Trouble?, posted on June 17, 2016 at 15:01:04
xaudiomanx
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 I am not as knowledgeable as most or all of these brainiac audio people but I know what I hear.

My experience with monoblocks as compared to building one huge massive low resistance power supply is that the single power supply in anything I ever built(preamp, amp) was a noticeable difference because things seemed to be more coherent with a single power supply. I even built the same amp(this is going back years ago)in mono's with massive supplies all measuring well within range to each other(voltages super close, current draw super close)and it seemed the single power supply was more coherent than dual. It always seemed that the monoblocks seemed a bit smeared.

Now! With that said! I can't answer for a dual supply in a single amp or preamp but if it has the same principles, then a single power transformer would sound better to my ears.

I am sure there will be those that will disagree but their ears aren't mine.

 

RE: yes, yes, and yes..., posted on June 17, 2016 at 15:02:55
xaudiomanx
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 Hi!

I read your response and correct me if I am wrong(which I usually am). I was under the assumption that a dual power supply had multiple transformers. Not a single one.

 

RE: Dual PS - Worth the Trouble?, posted on June 17, 2016 at 16:11:30
Michael Samra
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 My experience with monoblocks as compared to building one huge massive low resistance power supply is that the single power supply in anything I ever built(preamp, amp) was a noticeable difference because things seemed to be more coherent with a single power supply. I even built the same amp(this is going back years ago)in mono's with massive supplies all measuring well within range to each other(voltages super close, current draw super close)and it seemed the single power supply was more coherent than dual. It always seemed that the monoblocks seemed a bit smeared.

Exactly...When you have the option to build dual mono,it is always going to be better than a single power supply shared between 2 channels. Stereo amps are compromised somewhat and that's the nature of the beast but the new caps do help along with splitting the channels like we do on the Mc240s and Citations with the level 2 mods.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

yes, posted on June 17, 2016 at 17:26:41
Chip647
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 Otherwise it is just a change in a filter.

 

"always going to be better than a single power supply", posted on June 17, 2016 at 17:32:59
Chip647
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 I can 100% state that blanket statements are always false :-)

There is nothing inherently better with 2 versus 1 if designed properly, 1 is most likely better than 2.

 

RE: "always going to be better than a single power supply", posted on June 17, 2016 at 19:14:31
Michael Samra
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 Chip
If you have a dual power transformer and dual separate for each channel,I would agree..

Case in point..I posted a Mac Mc30 the other day pushing 48 watts at.1%. If that was a single supply pushing two channels in a stereo amp at the same time,it would have a hard time making those numbers.
With a big enough power transformer that deliver enough current for two channels and a well isolated supply,you would have a better chance but as a rule commercially designed amps don't work that way. A custom amp is a different story.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: "always going to be better than a single power supply", posted on June 17, 2016 at 20:03:09
Tre'
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 "There is nothing inherently better with 2 versus 1 if designed properly, 1 is most likely better than 2."

Is that your subjective impression or was the statement meant to be a technical assessment?

If technical, can you give us the facts?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: "always going to be better than a single power supply", posted on June 18, 2016 at 08:08:58
Chip647
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 Mainly subjective, I said that both are good however two transformers is not ALWAYS better than one.

Technically, 2 completely independent amplifiers will be un affected by each other so you will get absolute channel independence and no chance of power supply modulation of one amp to the other unless you are dragging down the power line.

However, if trying to recreate a stereo image of a dude playing an acoustic guitar being recorded by a pair of microphones in that sound field, we are trying to reassemble a single image. Having both channels working off the same power supply helps to bring commonality to both channels to make them sound more like one sound, not two separate sounds. I would rather have any power supply anomaly present equally in both channels than one amp sounding different than the other.

I have pure dual mono and shared power supply amps and frankly sometimes the dual mono seems to have a more artificial separation of the channels. If recreating a stereo image close to how it was recorded is the goal, a well designed common power supply will be more likely balanced between the two channels and have fewer chances of ground loop problems. My preference is a big-ass independent power supply to keep the big power transformers away from the signal.

 

Hard to answer but...., posted on June 18, 2016 at 08:34:22
Salectric
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 It is difficult to say with certainty whether monoblocks or a stereo amp sounds better. First of all, it is very hard to make a true apples to apples comparison using the same circuit and identical parts. But in my experience, with homemade tube amps that are nearly identical, the main sonic difference I hear relates to imaging and soundstaging. The monoblocks tend to have a larger soundstage with more sense of ambiance and awareness of space. With monoblocks images are located further outside the edges of the speakers at least with some recordings. On the other hand, images with the stereo amp are more focused and perhaps more tangible in the space between the speakers. In my opinion, this comes down to an aesthetic choice. I happen to prefer the bigger, more transparent sound of monoblocks. Others I know prefer the more focused and tangible sound of a stereo amp.

Whether these differences relate to peak power differences or crosstalk or some other measurement is not of much interest to me. What matters is the sound. Sometimes knowing there is a measurable difference between two components (for example, knowing the monoblocks can produce an extra watt or two on the test bench) can bias the listening results.

 

Thanks (nt), posted on June 18, 2016 at 08:45:04
Tre'
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 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: yes, yes, and yes..., posted on June 18, 2016 at 13:16:13
Lee of Omaha
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 You can use separate transformers or not. If you use one transformer, you use two sets of rectifiers and filters. Typically, if you "dual" a tubed amp, you change to solid state rectification because there's no room for a second rectifier tube.

 

RE: yes, yes, and yes..., posted on June 18, 2016 at 14:35:47
Michael Samra
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 Lee
Tube rectifiers are lossy and with today's very fine Schottky diodes which are ultra quiet,I no longer see diodes at a disadvantage.Now they have high voltage Schottkys where they never had them in years past in the 1.2kv range.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Dual PS - Worth the Trouble?, posted on June 19, 2016 at 08:28:41
Triode_Kingdom
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 "...there is big advantage IMHO to using a doubler PS.The secondary wiring is typically thicker with fewer turns and therefore has a lower resistance..."

I agree, although it's not clear to me whether the original designs (Harman Kardon) were able to take advantage of this. B+ current is extracted from the doubler caps, and the ESR of the older electrolytics was pretty poor. That offsets the lower Z that would otherwise be available looking back into the transformer. This is another reason I'm looking forward to the rebuild. Sonics should be improved considerably just by updating the PS.





limited in this respect due to the



 

RE: Dual PS - Worth the Trouble?, posted on June 19, 2016 at 09:09:24
Triode_Kingdom
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 Thanks for all the great replies! The possibility that a split supply might degrade coherency isn't something I had considered. I don't have time to prototype a fully split version of this, and not enough parts to A-B the two types if I did. So, I'll probably build with a single transformer. The original sonics (including coherency) are very good for this type of amplifier, and there might be more to lose than to gain by making such a major change. Dual supplies aside, as part of the anticipated PS upgrade I'm also thinking about adding a separate filament transformer. That would relieve the power transformer of almost 30W of steady-state power draw. Should be a fun build!

 

Agreed..., posted on June 19, 2016 at 15:15:54
Lee of Omaha
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 The one argument for vacuum rectifiers is that they provide a delayed application of B+ to the other tubes. Since many vacuum rectifiers are directly heated, there just isn't much of a difference, as directly heated rectifiers start to conduct well after just a second or two, compared with 10-20 seconds for indirectly heated tubes. And solid state rectifiers usually don't fail.

I wasn't arguing in favor of tubed rectification, just pointing out that there's usually not room for a second one, so conversion to solid state rectification is usually necessary when converting to dual power supplies.

 

I built a preamp using one Transformer but..., posted on June 19, 2016 at 15:43:18
Cougar
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 with two separate secondary outputs. I used two separate rectifiers and regulators while using one supply for positive and the other for the negative while tying the unused other halfs to ground. worked good for me and sounds way better than with a normal type of PS. This of course was for a SS preamp.

I know this may not be possible but I have read that using multiple rectifiers and regulators for each stage improves the sound dramatically when using multiple stages. I never got the chance to try this but I may try this soon.

 

Guys, this is already solid state..., posted on June 19, 2016 at 16:49:46
Triode_Kingdom
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 It's a Harman Kardon with a voltage doubler. Nearly all their amps and receivers used this topology.

 

as a parting thought, remember the KISS principle!, posted on June 19, 2016 at 18:21:55
vinnie2
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 In almost everything I have done (including diy audio) I have found that the fewer parts I used and the more simple the design I used the better things would go.
Good luck with your project!

 

Thanks, there's a lot to be said for that! (nt), posted on June 19, 2016 at 20:40:11
Triode_Kingdom
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 nada aqui

 

RE: Guys, this is already solid state... We know., posted on June 19, 2016 at 23:38:26
Michael Samra
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 We were just talking about rectifier tubes in general..
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

We're trying a semi-split supply..., posted on June 23, 2016 at 14:29:13
Lee of Omaha
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 We're rebuilding an ST-70, and I'm trying something a little new, at least to me. We going C-(LR)-C-(and then...

For each channel there's: An isolating diode and an additional filter capacitor. I wanted to retail the choke. The resistor is there because we're replacing the vacuum rectifier with solid state rectification. The idea behind the "isolating" diodes is that if one channel has a nice big bass note, say, and the rail voltage drops, that channel's filter cap can't draw current from the other channel's filter cap.

Will let you know if we think it sounds better than our current mod.

 

RE: We're trying a semi-split supply..., posted on June 23, 2016 at 17:36:54
Triode_Kingdom
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 " The idea behind the "isolating" diodes is that if one channel has a nice big bass note, say, and the rail voltage drops, that channel's filter cap can't draw current from the other channel's filter cap."

Several things to consider... Unless the time constant of each channel's filters is very long, both will be depleted anyway. Second, most low bass is monophonic. Both channels are taxed more or less at the same time by the program material itself. Finally, if the supply is sagging so badly that operating points or distortion are materially affected, what's really needed is a better supply. Just food for thought.






 

RE: We're trying a semi-split supply..., posted on June 24, 2016 at 08:42:17
Lee of Omaha
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 The time constant is very long.

It's (C=100uF)-(choke-resistor in series)-(220uF)-
and then 2 x (diode-220uF).

And while nothing will totally eliminate the voltage drop you describe, this should "all but" eliminate it. Time and our ears will tell. If it doesn't make a sonic difference, it will have been an interesting experiment. If it does improve the sound, it will become part of our standard rebuild.

 

Time Constant, posted on June 25, 2016 at 11:06:50
Triode_Kingdom
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 "The time constant is very long. It's (C=100uF)-(choke-resistor in series)-(220uF)- and then 2 x (diode-220uF)."

You've forgotten the impedance of the load (amplifier). That's what drains the supply and determines the time constant. That aside (and in addition to the points I made previously), the diodes will degrade the ability of the supply to maintain voltage at the channel driven hardest. If this happens, does it really matter if the other channel continues to operate unaffected? The channel producing the majority of the sound will fall on its face sooner because it doesn't have access to all the capacitance of the supply. As for sonics, I wouldn't waste the time. The unwanted effects of the diodes can be easily quantified with basic test equipment. Sorry, I know that's not what you want to hear, but this modification will perform in a way that's entirely predictable.

 

RE: Time Constant, posted on June 25, 2016 at 15:19:02
Lee of Omaha
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 Since what we're adding is extra filtering, I don't think we're increasing the impedance of the power supply. But as you alluded, we'll try it and see. If it doesn't sound good, out it goes.

 

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