Solid State amp with output transformers

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#22
Magura said:



And the point of adding distortion being?
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Hi,
I don't mean it will be a benefit. I was being a little sarcastic. Forgive me.

BudP said:


I am just asking that you query him in a polite manner John, while he shows you what is actually possible, beyond off the cuff, knee jerk answers, and no, you do not know it to be true, you just surmise it from past experience and all other published commentary. He did not do this due to stupidity or lack of rigor.
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Hi again Bud,
Let's not jump the gun here. I am as interested in this as anyone else. Don't worry, I won't scare him off.

An output stage running at high voltage, low current would need an output transformer, right? I don't have a problem with that concept, it's something I wouldn't mind trying.
I'd like to know what the potential benefits are though. Will the output devices run cooler? Would it be more stable? The obvious one is the DC protection for the speaker and the easier load on the amp itself.
 
#26
BudP said:
Gary Pimm's Tabor
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Bud, from the map on Gary's site the Tabor is input trafo -> 6AU6 LTP direct coupled to a pair of 1624s...

http://home.pacifier.com/~gpimm/1624.gif

I am very interested in this amp.

John Swenson, i believe, is also getting very good results from SS output stage with OPTs... Susan Parker's Zeus also gets good press.

Despite the "common knowledge" that transformer coupling can't do any good, there are some pretty amazing devices that use them, and many of those from designers that couldn't get similar results using more common cap or direct coupled citcuits. Probably due to the elimination of a lot of capacitors, which are still the "weakest" passive device we have in our parts box.

dave
 
#27
It's 2007 and you still use output autoformers in your amp.

Why?

Can drive any impedance to full power. 16 ohms, fine. 1 ohm, fine. 0.25 ohms, fine (MC2300 in mono no less).

How many amps can direct drive those ribbons?

I used to take out the 3 ohm series resistors and the 120V lightbulb out of the big Koss electrostats. Without that stuff they were actually efficient (and less than 1 ohm).

Distortion?

You're talking out of your hat. McIntosh measure as low as the direct coupled amps, about 0.002% midband (SoundTechnology 1700) at moderate levels (10W).

It's all about what you select for core material, and how you wind it. McIntosh bought their power transformers, but they made their output autoformers.

What kind of bandwidth and distortion performance can you get out of a transformer?

The more nickel in your core, the less distortion you will have. It is possible to get distortion dropping below 0.001% above 50hz. Cheap M6 steel cores have 10X (+20dB) this distortion, what does this sound like? It adds some 'warmth' to the sound. Some expensive studio gear uses M6 as part of their 'sound'.

How low can they go?

McIntosh only specs full power down to 10hz, it's a cost trade-off. Jensen make ground-loop isolator transformers that the spec is -0.25dB at 2hz, and they are typically -0.11dB
 
#28
The quad 50E used output transformers and was well received at the time ! They still fetch a fair price
The fact that they can match almost any impedance and can drive a floating load could also be an advantage
I have also come across an early sansuiE pa amplifier that used an output transformer
regards trev
 
#29
BudP said:
vizion

Gary Pimm's Tabor is sensationally good, in either tube or solid state. He uses the same outputs and different interstage's in both. He has not updated his site to reflect any of his usual information, but you might try contacting him to see what sort of help he would provide you for a DIY build.

http://home.pacifier.com/~gpimm/
Bud
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Bud, Gary's tube design work is very absorbing and I am sure that there are many like myself who would be very interested and grateful if he could contribute to this thread.

Has Gary published the schematic of the solid state version of the circuit?
 
#30
I am pretty sure that the reason for using output transformers is:
1) to get improved sound quality
2) to make the amp drive a wider range of loads

As of 1 there is probably not much to measure, but it is a common fact in pro-audio, that a well-made transformer in a mic amp, compressor or something - improves the sound. Being technically correct or not, most sound engineers just looooove the sound of the old NEVE mic amps, wich are running a decent idle current throug an output transformer (line-level), and also uses an input balancing transformer. Actually Rupert Neves expertise originated from making signal transformers for BBC.

As you can read in test of MacIntosh amplifiers in hifi magasines, there is one thing they always mention, as a trade mark of MacIntosh: Dynamics!

Being the only wideavailable ss amp with output transformers, this unique sound can only be caused by that one thing: Output transformers.
 
#31
Here is a link to a thread where our very own EC8010 weighs in on OPT characteristics. A few posts further on he shows just how good even a mains toroid can be.

The first post is from an M6 core OPT, built to our level one standards, the toroid is an unknown, but may actually have even lower grade core material.

http://www.diyaudio.com/forums/showthread.php?postid=1330746#post1330746

Appears G Pimm is off auto crossing and may not be back until Sunday night. I will persevere.

Meanwhile, keep those examples coming!

Bud
 
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