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Don Allen's Latest Push-Pull Designs.................

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Posted on October 3, 2009 at 22:54:01
Todd Krieger
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 I realize this is "SET Asylum", but I think this new push-pull design is something special...... It has all the SET magic, with push-pull power....... The new design is a convergence of transparency and magic. With a soundstage and midrange to die for.

The new design uses a new driver circuit, using the 12AX7 tube...... Previous designs were around the 6BQ7 driver. My 6W6 push-pull stereo amp might displace the mighty KT88 SE monoblocks. (My 6W6 PP amp is the standard black case with illuminated lightning bolt.) The amp is light enough to lug around like a Cakepan. (And the power tubes are inexpensive.) I might also try it with the Fritz, which might be happy with its twelve watts........

I listened to two other fabulous push-pull amps, based on the same driver design. One was a rebuild of the Bogen DB130 monoblocks (about 25 WPC), the other custom 60 WPC KT88 push-pull monoblocks using Hashimoto output iron, one of the very best amplifiers I've ever heard. All now use the same 12AX7 driver circuit.


another Don PP convert so to say, posted on October 13, 2009 at 22:10:41
2chJunkie
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 Hey Todd

Been busy moving and other things with my son... so been out of touch with audio and Don lately, just found this post.

As a happy owner of Don's Bogen and Personal PP design I have to agree, Ive found a new love. They do it all and Im in heaven. I think I wont be buying any more amps (now dont hold me to this...) but really Im out for a while (maybe ever) now. Im happy and finally have it all, power to spare and the detail to match.

Would like to add, prob wont ever sell my Don 300B set stereo amp but really love this new topology and have not felt the need to go back.

Dont feel Ive become the anti.... just found something I like more than any other design.

Will be in touch with Don soon and wanted to add that these new PP amps Dons been doing are certainly worth the hype.

Dave
push-pull versus parallel output stages (Single ended), posted on October 7, 2009 at 07:14:18
FenderLover
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 Todd JOC, how do these push-pull amps sound in comparison to parallel output stage SET amps? Is it easier to build and maintain the push-pull versus multiple output tubes in an SET topology?


Thanks!

RE: push-pull versus parallel output stages (Single ended), posted on October 7, 2009 at 22:55:36
Todd Krieger
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 "Todd JOC, how do these push-pull amps sound in comparison to parallel output stage SET amps? Is it easier to build and maintain the push-pull versus multiple output tubes in an SET topology?"

I'm not sure what you mean by "parallel"...... Don has modified a Golden Tube SE40 to run "parallel SET" (as in parallel output tubes- I forgot the tubes used- About eight WPC), but it sounds mighty fine too. The SE40 apparently has some killer iron in it. (If it weren't for the 6W6 PP, I'd probably try that amp.)

What makes the PP designs special is the new 12AX7 driver stage. The catch is I think it's only viable in PP mode, but it gives the amps a "spooky" transparency that makes one forget about SE vs. PP...........


RE: push-pull versus parallel output stages (Single ended), posted on October 8, 2009 at 00:46:29
FenderLover
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 So, you like the tone of this push-pull topology versus SE with parallel output tubes (say one which runs two or three 300B).

Much thanks!

RE: push-pull versus parallel output stages (Single ended), posted on October 15, 2009 at 00:24:50
Todd Krieger
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 "So, you like the tone of this push-pull topology versus SE with parallel output tubes (say one which runs two or three 300B)."

VEERRY close....... I might get one of those mod parallel SE40s too...... But I need something w/ power for the main system first.


RE: push-pull versus parallel output stages (Single ended), posted on October 7, 2009 at 12:24:02
drlowmu
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 Hi,

I'm not Todd, but PSE should be superior sonically to P-P, as it is lower Z, has far better peak current capability, and does not require a phase inversion process(or) to be part of the circuit.

Downside is the SE output transformer gets a bit large, limiting bandwidth, but it still should be technically / sonically superior.

Jeff Medwin

RE: push-pull versus parallel output stages (Single ended), posted on October 10, 2009 at 03:06:48
Peter H-son
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 "PSE should be superior sonically to P-P, as it is lower Z, has far better peak current capability"

Wrong. PSE and PP have exactly the same z. PP has better peak current capability.

"Downside is the SE output transformer gets a bit large, limiting bandwidth, but it still should be technically / sonically superior."

Exactly how would it be superior? The PP transformer is smaller, has significantly higher inductance (we are talking a factor of 10 here) and does not need to be made lossy.

"Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord: And the prayer of faith shall save the sick, and the Lord shall raise him up"
--James 5:14-15
RE: push-pull versus parallel output stages (Single ended), posted on October 10, 2009 at 21:38:10
Paul Joppa
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 See the notes below about transformer impedance. The P-P transformer primary has four times the impedance of the PSE transformer, so the PSE makes twice the current at half the voltage. At the output side of the transformer, you are of course correct about the PP peak current capability if you allow it to go into Class AB.

Personally, I agree with you when we look at the output side of the transformer which I think is the right way to look at it. I always like to normalize things to nondimensional parameters - resistance ratios rather than just resistances.

As for losses and inductance, both are quite complex subjects when it comes to transformer design. I would not totally agree with anything simple enough to fit in a forum post!

RE: push-pull versus parallel output stages (Single ended), posted on October 11, 2009 at 03:57:31
Peter H-son
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 No. For parallel tubes you use one primary winding. For PP you use two.

Say you have a PSE amp with a 2k transformer. For the PP amp you would use 2+2=8k.

Say you make a 6S45P spud amp with input step-up transformer. But you want more power and want to use two tubes. You can go SE or PP. A PP amp is simply two SE amps in parallel, one half being inverted. In case of the 6S45P "spud" amp, you simply use the input step-up transformer as a phase-splitter for PP. Benefits are cost, little DC offset, reduced distortion, PSRR.

A/B has no place in serious audio as far as I'm concerned.

But since the 2nd order will be cancelled (more or less), you can use a transformer with lower primary impedance. You get 20W from a pair 300Bs in PP Class A1 with a 4k transformer according to the datasheet.

Transformers are complex, indeed. But we can make some generalizations. A MC step-up transformer is normally superior to a 25W SE output transformer.

"Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord: And the prayer of faith shall save the sick, and the Lord shall raise him up"
--James 5:14-15
RE: push-pull versus parallel output stages (Single ended), posted on October 11, 2009 at 08:22:50
PakProtector
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 -----Say you have a PSE amp with a 2k transformer. For the PP amp you would use 2+2=8k.

That is not exactly what should be done. Go for 4k a-a, which presents each tube with a 2k load until you take one out of the picture by cutting it off( AB ). Each end sees half the a-a as long as we're in class A. So, we only need twice the PSE number of turns. 2k:8 SE, is 1.414 times the turns ratio of a 1k:8 PSE, and the 1k:8 primary will be doubled for the 4k a-a PP.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: push-pull versus parallel output stages (Single ended), posted on October 7, 2009 at 14:33:07
PakProtector
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 -----but PSE should be superior sonically to P-P, as it is lower Z, has far better peak current capability...

Assuming both the PP and the SE are loaded equally and the PP is running Class A from the same operating point, the peak current under control by the finals is *EXACTLY* the same.

-----Downside is the SE output transformer gets a bit large, limiting bandwidth, but it still should be technically / sonically superior.

What constitutes 'technically' superior? Does full bandwidth not matter( given your past responses, I think you will answer that it does not)? Also the SE opt for a big PSE amp is going to be well past the point where its sonics are no longer recoverable, it is the same with PP though the power output a PP can deliver is far larger...allowing smaller, better sounding OPT's at *ANY* power level...:)
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: push-pull versus parallel output stages (Single ended), posted on October 7, 2009 at 22:42:01
Paul Joppa
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 Allow me to point out that in parallel feed, the core size demands on the output transformer are exactly the same with Class A push-pull or parallel single ended. The only differences are:

1) The SE transformer has a primary with half the single tube impedance, while the P-P transformer has twice the SE impedance, for a total of 4:1 impedance ratio. This means the SE transformer can have significantly better performance.

2) The P-P transformer will have the additional constraint of matching leakage and capacitive parasitics end-to-end if it is to perform well. This usually means a much more complex design, more difficult to wind and with other compromises in performance.

RE: push-pull versus parallel output stages (Single ended), posted on October 8, 2009 at 14:53:39
PakProtector
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 That's about right. PSE cuts the turns by root2/2 v. the single tube loading. The PP has exactly twice as many, though each half has exactly as many turns on each side of CT as the PSE. It is quite easy enough to drop leakage L, and winding capacitance to acceptable levels IME.

In any case, the series feed SE is going to need more turns to establish a proper low frequency phase characteristic( primary inductance ). Go parafeed and you've now( likely ), got a choke to put signal across...more an' more turns and C_winding...an' two inductors in parallel. Doesn't look like there is any advantage to one or another on these rather narrow basis-es...get a better OPT coil with good magnetic material and either one can stand out above the other.

Now, why not have a comment on this:
but PSE should be superior sonically to P-P( from among others )has far better peak current capability...

or won't you go and contradict another SE-ist?
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: push-pull versus parallel output stages (Single ended), posted on October 8, 2009 at 11:58:38
Ray Moth
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 Paul,

how about the net DC in the primary of an SE OP transformer, requiring a gap and a much bigger core to compensate, relative to PP? Or are you assuming parafeed?

RE: push-pull versus parallel output stages (Single ended), posted on October 8, 2009 at 14:44:17
PakProtector
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 hey-Hey!!!,
It should also be disclosed that in order for parafeed to really have a smaller core, its primary load has got to be an Iron-free. Resistive, or CCS of some sort. Do parafeed with a choke, and you're impressing signal on even more iron than with series-feed.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I don't think the KT88 amp in question is operating in class A, posted on October 8, 2009 at 05:51:37
Frihed89
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 I remember reading on the Amp/Preamp forum that the power out 80 Watts, according to the owner. Isn't that way too high for a 2 x KT88/channel system?
"What did the Romans ever do for us?"
Doug's comments were re: Class A., posted on October 8, 2009 at 11:40:45
Paul Joppa
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 I was just responding to Doug's comments on transformer design restrictions, not to the original post. Sorry for any confusion.

RE: Doug's comments were re: Class A., posted on October 8, 2009 at 14:41:40
PakProtector
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 Do please run an equally thorough explanation on the 'PSE controls more current' comments.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: Doug's comments were re: Class A., posted on October 8, 2009 at 12:46:18
drlowmu
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 Thanks Paul,

You can always express yourself so well !!

What was overlooked (and is seldom discussed by P-P proponents) is the negative sonic result of forcing a 180 degree phase inversion upon the audio signal, a process totally absent in SE amps.

Less is more. KISS.

Jeff Medwin

RE: Doug's comments were re: Class A., posted on October 10, 2009 at 12:50:31
Ray Moth
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 Jeff,

Would you like to discuss "the negative sonic result of forcing a 180 degree phase inversion upon the audio signal"? Perhaps you would be prepared to explain to Don Allen where he's going wrong?

Your post seems glibly to assume that there is a negative result, but such assumption needs to be backed up by some sort of explanation, otherwise it's just bombast.

RE: Doug's comments were re: Class A., posted on October 15, 2009 at 22:42:05
Todd Krieger
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 "Perhaps you would be prepared to explain to Don Allen where he's going wrong?"

Don has gotten such comments lots of times...... But what's often "wrong" in theory ends up being right in practice....... And not just sonically, but with measured performance, stability, tube compatibility, and tube life.


RE: Doug's comments were re: Class A., posted on October 18, 2009 at 06:42:22
drlowmu
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 Todd,

Ray is just an armchair theorist with too much retirement time on his hands.

Jeff Medwin

RE: Doug's comments were re: Class A., posted on October 18, 2009 at 08:14:35
Ray Moth
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 Jeff,

I'm not retired yet, just resting between engagements ;)

Beside, you shouldn't try to divert attention from your unfounded statmentt "What was overlooked (and is seldom discussed by P-P proponents) is the negative sonic result of forcing a 180 degree phase inversion upon the audio signal, a process totally absent in SE amps." by using a silly insult.

Your comment makes no sense. A phase splitter does not cause any harm to a signal - why should it? There are some very respected practitioners whom you would probably dub "proponents of PP" based on their successful PP designs - not only Don Allen but many others too. I don't think they would have attained their good reputations if your statement were true.

RE: Doug's comments were re: Class A., posted on October 9, 2009 at 15:35:15
Caucasian Blackplate
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 A standard voltage amplifier forces a 180 degree phase inversion on the signal. Am I missing something?

RE: Doug's comments were re: Class A., posted on October 10, 2009 at 06:44:02
drlowmu
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 CB,

Yes, a phase inversion function obtains both a positive and negative signal.

Jeff Medwin

LMAO!!!!, posted on October 8, 2009 at 14:39:55
PakProtector
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 Dude, they sound different for good reason; there is not much point in attempting to lable one better. The only thing you're going to get is better for me; attempting a 'better for you' is rather silly. IME, exactly what lots and lots of folks look for and develop in SE just drives me nuts.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: LMAO!!!!, posted on October 8, 2009 at 23:52:55
tube wrangler
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I think if you're driving power-hungry speakers, then you need Push Pull, and in that case, it will sound better than S.E. if the P/P is a good design.

S.E. begins to outperform Push/Pull (assuming series-feed) at close to under 2 watts continuous average power in most cases.

I can well understand the need and preference for P/P amplification for power needs above two watts.

What I still don't understand (and RMAF 2009 proved it once again) is why anyone would use a speaker-- for any reason-- that has to have more than two watts.

---Dennis---
RE: LMAO!!!!, posted on October 9, 2009 at 07:17:49
PakProtector
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 -----What I still don't understand (and RMAF 2009 proved it once again) is why anyone would use a speaker-- for any reason-- that has to have more than two watts.

So what kind of speaker is this? What sensitivity?
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Do you have a schematic? nt, posted on October 5, 2009 at 06:42:24
Bas Horneman
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 no text at all.
To infinity and beyond!!!
No [nt], posted on October 6, 2009 at 19:08:38
Todd Krieger
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Thanks nt, posted on October 7, 2009 at 02:33:19
Bas Horneman
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 .
To infinity and beyond!!!
RE: Don Allen's Latest Push-Pull Designs................., posted on October 4, 2009 at 09:52:58
Jottow2@yahoo.com
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I agree with Todd about Don's new KT88 amp. While I love SET amps this amp is truly special. It has a cross between a SET amp sound and the PP sound. It has the best of the two world.

Todd mentioned the soundstage which is truly remarkable, but there is separation of instruments I like nothing I have ever heard before. Part of it is due to the fact that there is extremely low distortion, so low that it was unmeasurable on the scope.

While I own five great SET amps this is my favorite. I have attached pictures of the amp. The pictures show one of the monoblocks.

RE: Don Allen's Latest Push-Pull Designs................., posted on October 9, 2009 at 03:55:43
gortnipper
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 Didnt Don make a KT88 SET amp as well? How does this compare to it?

RE: Don Allen's Latest Push-Pull Designs................., posted on October 10, 2009 at 11:31:05
Todd Krieger
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 "Didnt Don make a KT88 SET amp as well? How does this compare to it?"

Yes..... I own the KT88 SET monoblocks..... I think until Don finds a way to get an "equivalent" driver stage for the SET, the PP has the edge now. The driver stage is the difference.


RE: Don Allen's Latest Push-Pull Designs................., posted on October 6, 2009 at 10:22:47
jgdebelen@sbcglobal.net
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 Where can I buy this amp? Does it come in kits or factory manufactured? How much Does it cost? Please give more info about it, I'm really interested on it. Thanks.

RE: Don Allen's Latest Push-Pull Designs................., posted on October 7, 2009 at 16:31:06
Jottow2@yahoo.com
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 There are no kits available. Don is located in Phoenix and make each amp. Send an email and I will provide his contact information. He can also provide more information and a price.

RE: Don Allen's Latest Push-Pull Designs................., posted on October 8, 2009 at 07:12:32
Athos56
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 What i want to know is where he gets his chassis mounted test points?

RE: Don Allen's Latest Push-Pull Designs................., posted on October 8, 2009 at 20:00:25
Jottow2@yahoo.com
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 Don't know, but they work great.

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