Push-pull Tube Amps and autoformers

Never tried what you are doing, but perhaps email Dick Olsher, who wrote this article?

First, my apologies to Paul for getting the spelling of his name wrong, Its, Speltz, not Speltzer.  And next, @hilde45, thanks for that link.  I have read Osler’s fine article/review  and saw he felt low-powered amps, (but particularly OTLs) might benefit from the Zeros, though he did try something I wouldn’t,  using the Zero between  a DIY SET and  high impedance speakers:  (“T-Rex 300B SET, a DIY design project in the works (still unpublished) using Plitron output transformers with only 8-ohm taps, and the Lowther DX4 BassZilla - a 97dB efficient loudspeaker with an 8-ohm nominal impedance rating”).  His results were kinda predictable and he admitted it was a push to go in that direction.  So, I expect different results, if not necessarily better, as I’m going to use the Zeros between  low-powered push-pull amps (4 ohm tap) on the 84db 4 ohm Maggies.  I really don’t know what I’ll get, but I’m still waiting to hear from anyone else that  may have already tried this or something similar.  Thanks though, I agree it’s a good article to start with.  

the auto former wont help, most push pull conventional tube amplifiers will play fine at most impedances it is the lack of power that is an issue you need 100-200watt tube amplifier or a tube preamp with a solid state amplifier

Dave and Troy

audio intellect NJ

40 year audio veterans

@audiotroy 

Why would that be if power required loudness (without distortion ), is dependent on the how the speaker and amp communicate ohms. Doesnt the autoformer tell the speaker that it’s getting more ohms (8, 16) to allow higher volume with less or no distortion?  

no loudness is dependent on power of the amplifier and sensitivity of the loudspeaker a tube amplifier load matches via an output transformer so any additional device is un necessary

only otl amplifiers would need this

assistance

@audiodidact I think the best way to use the ZEROs is to use the 16Ohm taps on your Quicksilvers if they have one.

Then use the ratio on the ZEROs that seems to sound best. Keep the speaker cables as short as possible and as heavy as possible between the ZEROs and the speakers. You can use longer cables between the amps and ZEROs and they don't have to be so heavy.

This might give you more bass extension since most output transformers become less efficient when using the lower impedance taps and they often lose low frequency bandwidth at the same time. You might also get less distortion- if so the system will sound less bloated, more relaxed and you might hear more detail.

If you add a crossover, you can roll off the bass on your Maggie’s at around 60hz and add a subwoofer that rolls in at around 50hz, you’ll have more than enough power to make those Maggie’s sing and I mean sing loud!

All the best.

@atmasphere, Thanks for the encouraging words, however, the Quicksilver M60 only has 1, 4 and 8 ohm taps. Is that end-game?  

@audiodidact with your particular tube amplifiers you do not need the Speltz Zeros, as I am surprised Ralph is saying it is ok. They were created for OTL amplifiers. If I am understanding you correctly, I agree with audiotroy. Get a robust and beefy solid state amplifier " that you like " to drive your Maggies. There are some speakers that do better with the muscle of a great solid state amp. Enjoy ! MrD.

@mrdecibel and @audiotroy, thank you both for the heads-up. I’m aware that the Zeros were initially meant for OTLs (I noted such above, in my opening post), but I did speak with Paul Speltz and while he is not promising anything, he felt it would be worth trying to see if the Zeros might help the QS with the Maggies. I actually have a pretty beefy SS amp (Parasound A21+), still in the system, that I switch between it and the QS with a Luxman switcher. The QS produces a lovely detailed sound at lower listening levels, especially at night (I’m talking 65-70db). The SS is for everything above 80db when I want slam. The Zeros may very well not pan-out, but they’re on their way and I’m going to try them at various taps and settings and see what happens. And i’ll be quick to post the results, whatever they are, good or bad, when I’ve finished.  Yes, I hope to get just a teeny bit more from the tubes, and yes,  it just may not be in the cards, but the proof of the pudding is in the actual eating, so, I’m going to take a bite and see for myself, though I had initially hoped to find  someone here who’s actually tried something like this. But, thanks again, everyone!

Oh, I should mention that I modified the  1.7i Maggies recently with GR Research external crossovers.

I’m a very happy customer. The autoformers allow me to use the 8 Ohm tap on my ARC 75SE. SQ is excellent, at higher volumes the amp is working effortlessly. I’m also using an analog crossover at 60hz for my subs.

Yours is a perfect application for autoformers. And not an uncommon one.

I recommend you let your ears be the judge.

I used the Zeros for about 4 or 5 years with a PP Elekit TU 8340  and various tubes(EL 34, KT 77 and KT 120) driving ML Electromotion ELS, Quad 63s and ET LFT 8s. The Zeros were most effective with the Quads and the Martin Logans.

YMMV

with your particular tube amplifiers you do not need the Speltz Zeros, as I am surprised Ralph is saying it is ok. They were created for OTL amplifiers.

@mrdecibel The ZEROs can really help solid state amps sound better driving lower impedances- they aren't just for OTLs!

Ralph, can you point me in the direction of someone using a beefy solid state power amplifier that are using the Speltz zeros, so I may hear from them their opinion. Mcintosh continues to use autoformers in many of their designs, but a Krell, Boulder or even a Parasound are able to handle the impedance dips in most speakers. It is my opinion, and this will not change, that the Speltz units are band aids for tube amplifiers, such as you OTLs. A properly designed amp should be able to handle this task. I see no need for a speaker with very low impedance dips, nor of low efficiency. Can we just leave it at that. My best, always, MrD. 

"It is my opinion, and this will not change..." 

There's a lot of that going around. 

Perhaps Autoformers are band aids for inefficient speakers?

Ralph, can you point me in the direction of someone using a beefy solid state power amplifier that are using the Speltz zeros, so I may hear from them their opinion.

@mrdecibel Yes- talk to Steve McCormack of McCormack Audio.

Perhaps Autoformers are band aids for inefficient speakers?

No- its more for reducing the distortion of an amp driving a lower impedance. All amps make more distortion into lower impedances; the ear interprets this distortion as greater harshness and lack of detail. This is why low impedance speakers are not the best investment if you want to get the most out of your amplifier dollar investment.

By increasing the load impedance on the amp, you get smoother and more detailed sound (because distortion is reduced). You might also get less power if the amp is solid state. I see the 3dB increase in power you get with 4 Ohms with a solid state amp as a rather weak rationalization since in high end audio, its usually about the presentation rather than the sound pressure.

Ralph, I am not the one who stated " Perhaps autoformers are band aids for inefficient speakers?" rhg3 stated that. I know autoformers are for impedance matching. I stated both, speakers with low impedance dips AND low efficiency are of zero interest to me. My best, MrD.

@atmasphere Thank you for your informative answer.

@mrdecibel Yes, that comment was not directed at you.