G'day from OZ

Philwait · 27th May 2004, 11:39 AM

Hi...

Just signed up and checking things out.

I'm in the process of building a tube amplifier for 35W per CH based on a little known distortion cancelling technique. I've managed to get 0.04% distortion at almost full power with no global feedback using a SEPP circuit with C-core output transformer. Hope to have it good enougth to post a pic very soon and it sounds real nice to me...but I'm no audiophile-just a crackpot engineer.

I've found this site while trawling for tube links so here I am. I'm also into ham radio and sailing here in Sydney, Australia. Next project is a valve ham rig on AM...now thats weird stuff.

Hope to chat with you guys and gals soon,

regards

Phil

Circlotron · 27th May 2004, 01:40 PM

Mmm.. more information please!!

BTW, were you an EA contributor years ago?

Philwait · 27th May 2004, 02:12 PM

`BTW, were you an EA contributor years ago?'

Hi Cyclotron,

You must be as old as me! Yep that was ETI magazine and about 1978-1980.

The amp uses a sort of a differential circuit around the output stage which cancells out distortion components produced in the output stage. I use two EL509's in each channel (trying to find EL509-2's) and a 12AX7 SEPP input stage. The only downside of this type of circuit is the elevated heaters for the top tubes, and adjustments for bias current, output voltage bias, and distortion cancellation.

Using the distortion cancellation it's possible to dial up the distortion you want from about 0.04 - 0.5% or higher but I haven't done any listening tests with this yet.

It's a very clean sounding amp with low distortion and OK damping factor of about 6 or so. If I use about 6dB of overall feedback the specs improve further but I dont like the sound as much. (except for piano which for some reason i like better with the global feedback)

I'm using some Legend speakers from canberra which seem to match the amp very nicely.

As I said I'm no audiophile and probably wouldn't hear many of the things others can. But to me it's a sweet amp with just a hint of that valve character.

My real job is electronics manufacturing (SMD machines and all that) and I've got half a mind to do a kit like the old ETI days.

phil

Philwait · 28th May 2004, 11:43 AM

Hi CIRCLOTRON......sorry about the spelling of your name on my last post.

I've attached a basic cct of the amp which I hope will come out here OK. It dates from 1960 so is about the time totem pole transistor outouts were around. You can see the likeness.

phil

Circlotron · 28th May 2004, 02:41 PM

Gidday Phil. The attachment must have fallen off... give it another go.

Quote:

But to me it's a sweet amp with just a hint of that valve character.

If you're happy with it then it's a big success.

Philwait · 29th May 2004, 11:21 AM

The attachment has turned up at last!

phil

27th May 2004, 11:39 AM	#1
Philwait diyAudio Member Join Date: May 2004 Location: Sydney	G'day from OZ Hi... Just signed up and checking things out. I'm in the process of building a tube amplifier for 35W per CH based on a little known distortion cancelling technique. I've managed to get 0.04% distortion at almost full power with no global feedback using a SEPP circuit with C-core output transformer. Hope to have it good enougth to post a pic very soon and it sounds real nice to me...but I'm no audiophile-just a crackpot engineer. I've found this site while trawling for tube links so here I am. I'm also into ham radio and sailing here in Sydney, Australia. Next project is a valve ham rig on AM...now thats weird stuff. Hope to chat with you guys and gals soon, regards Phil

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27th May 2004, 01:40 PM	#2
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Mmm.. more information please!! BTW, were you an EA contributor years ago?

27th May 2004, 02:12 PM	#3
Philwait diyAudio Member Join Date: May 2004 Location: Sydney	`BTW, were you an EA contributor years ago?' Hi Cyclotron, You must be as old as me! Yep that was ETI magazine and about 1978-1980. The amp uses a sort of a differential circuit around the output stage which cancells out distortion components produced in the output stage. I use two EL509's in each channel (trying to find EL509-2's) and a 12AX7 SEPP input stage. The only downside of this type of circuit is the elevated heaters for the top tubes, and adjustments for bias current, output voltage bias, and distortion cancellation. Using the distortion cancellation it's possible to dial up the distortion you want from about 0.04 - 0.5% or higher but I haven't done any listening tests with this yet. It's a very clean sounding amp with low distortion and OK damping factor of about 6 or so. If I use about 6dB of overall feedback the specs improve further but I dont like the sound as much. (except for piano which for some reason i like better with the global feedback) I'm using some Legend speakers from canberra which seem to match the amp very nicely. As I said I'm no audiophile and probably wouldn't hear many of the things others can. But to me it's a sweet amp with just a hint of that valve character. My real job is electronics manufacturing (SMD machines and all that) and I've got half a mind to do a kit like the old ETI days. phil

29th May 2004, 11:21 AM	#6
Philwait diyAudio Member Join Date: May 2004 Location: Sydney	The attachment has turned up at last! phil

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