ESL Direct Drive SS amp

[kevin gilmore]

ok, here it is.

http://gilmore.chem.northwestern.edu/koss.gif

no apologies for the mess it is in. I wanted to know
why it sounded so lousy, now i know.

For speaker use, increase the number of p and n channel
fets, use much bigger ones, and bias for a few watts of
standing bias. Change the opamp to something decent.

 

[wessol]

I came across this link for a Direct coupled amp:

http://www.audiocircuit.com/9041-esl-circuit/Diy/Experts/NeilMckean-NM/9041DENM-HVA.htm

 

[jan.didden]

I've been checking transformers - Plitron makes a 60v (120VCT) transformer, and a 175v (350VCT). The 60v gives me a 80ish rail, the 175 gives me a 240ish rail. Either much smaller than or much higher than the 200v Exicon max.

jdwinner,
be carefull, each device must widthstand the total rail-to-rail voltage. If the output swings toward one rail, the other device sees the total rail voltage. That means with 200V devices you are limited to +/- 100v rails absolute max. The 80V rail would not be that bad for these devices. Unless you want to go to cascade topology.

Cheers, Jan Didden

 

[jgwinner]

Doh!

Thanks, I was thinking of ground as being the 'low' point for the voltage, almost made a big mistake.

+/- 100 is a bit tight, I'd prefer at least 10% margin there.

I'll look at cascade I guess.

 

[hilbren]

Old topic (but interesting)

what do you think about my own design?

An externally hosted image should be here but it was not working when we last tested it.

it's very simple (I know)

 

[djk]

Ohh, an oscillator!

(inputs on opamp swapped)

 

[hilbren]

oops, but if it's connected the right way, is this going to work?

 

[SY]

I can see a few potential problems, other than oscillation.

Limited swing. 500V won't get most panels playing at anything above very low background music levels.

The 900K feedback resistor is going to be problematic because of stray and input capacitance.

The power resistor will need to be at least 50 watts. It's throwing off a pile of heat. Likewise, Q1 will be a significant heat source.

Distortion reduction will be less effective because of the high closed-loop gain.

 

[hilbren]

thanks for the comment,

Are there already some succesfull amplifires, this topic is quite old and I hoped that someone did build an amplifier for direct-drive esl

 

[SY]

There have been successful designs in the past (I built a small prototype which works quite well, albeit not at the voltages I need), but they've all been tube. You can find the Acoustat schematics on the web- they used a rather flaky output tube, but some people have gotten them to work reliably by changing that part of it.

 

[hilbren]

yeah I found that circuit, i think im going to give it a try.
Ill let you know if it works...
what part do i need to replace with what?

 

[SY]

IIRC, some of the modders replaced the 6HF5s with 6LF6s. The output circuit has to be completely reworked to do this and I don't know the details. If it were me, I might think about using 572Bs or one of the other high voltage RF triodes.

 

[djk]

"oops, but if it's connected the right way, is this going to work?"

Yes, but it is not practical.

Stax sold a headphone amplifier that had two of these per channel bridged.

They worked quite well for phones.

The SOA will not work with transistors for any real power.

Audio Amateur has a proven 900W class AB design using a big power triode, 125W in class A if I remember correctly.

The back issues are on CD for $29.95 (the first ten years worth) thru september 2

http://www.audioxpress.com/bksprods/books/cdaa70s.htm

 

[JohnW]

IIRC, some of the modders replaced the 6HF5s with 6LF6s. The output circuit has to be completely reworked to do this and I don't know the details. If it were me, I might think about using 572Bs or one of the other high voltage RF triodes.

The Acoustat Amps I have use 6HB5's not 6HF5's the only real problem I had with the amps is the "Valve Base's" which uses the PCB as the Base - with turned pin sockets - after time the PCB is damged by the heat of the Valve - also I Lost a "HV diode" once.

 

[hilbren]

"oops, but if it's connected the right way, is this going to work?"

Yes, but it is not practical.

Stax sold a headphone amplifier that had two of these per channel bridged.

They worked quite well for phones.

The SOA will not work with transistors for any real power.

Audio Amateur has a proven 900W class AB design using a big power triode, 125W in class A if I remember correctly.

The back issues are on CD for $29.95 (the first ten years worth) thru september 2

http://www.audioxpress.com/bksprods/books/cdaa70s.htm

but im not paying 29 dollar for one artikel, if someone has this artikel please mail me doot11@hotmail.com

@JohnW
thanks, this makes it more atractive to build it