my amp is working like a transducer!!?

macwanj · 03-15-2008, 03:33 AM

I have an EL34 stereo amplifier that I recently cured of a bad buzz. But now even stranger things are happening: for a few seconds today I had the amp connected to a cd player and with no speakers connected the amp is playing back the music!! I suspect that the OPT's are playing back and working like a speaker.

Overall the amp still plays back music like it normally does. Any ideas whats going on? Are the OPT's busted? The circuit is basically cathode biased EL34 Sigle ended driven by a cathode biased 6SL7. The power supply is CLC filtered with a 5U4G rectifier. All my voltages measure right and grounding looks fine and anyway I don't think the problem is here. I'm tied at the moment as I've never seen such a thing happen before.

Enzo · 03-15-2008, 04:53 AM

Are the OPTs busted? No, but they will be soon enough if you keep playing the amp without a speaker load. That us THE way to kill a transformer.

Your OT laminations are "singing," mehcanically vibrating from the currents flowing through them. Don't do this any longer.

Paul P · 03-15-2008, 04:56 AM

Funny, I just noticed the same thing in my amp today while running some
tests. With the volume turned to zero I could still hear my signal generator
tone and figured it was just some signal leaking through the circuit. But then
I disconnected my speaker to run into a dummy load and the sound kept
on going. The higher the frequency the louder the sound. Since you can't hear
it when the amp is played normally I figured it wasn't a problem but I'd also
like to know if this is normal or not.

[Edit, just saw Enzo's message] I was running into a 8 ohm 50w dummy load
(big resistor) and could hear my OT (it wasn't very loud, but noticeable).

Paul P

macwanj · 03-15-2008, 06:22 AM

Hey PaulP, see what these guys have to say about it:
http://www.diyaudio.com/forums/showt...hreadid=119457

My transformer doesn't do it with dummy loads but I suspect that in my case its the audio signal modulating the magnetic lines. My amp still sounds pretty nice through speakers so I'm going to ignore the singing OPT's for now atleast.

03-15-2008, 03:33 AM	#1
macwanj Junior Member Join Date: Nov 2007 Location: Walla Walla, WA Posts: 17	my amp is working like a transducer!!? I have an EL34 stereo amplifier that I recently cured of a bad buzz. But now even stranger things are happening: for a few seconds today I had the amp connected to a cd player and with no speakers connected the amp is playing back the music!! I suspect that the OPT's are playing back and working like a speaker. Overall the amp still plays back music like it normally does. Any ideas whats going on? Are the OPT's busted? The circuit is basically cathode biased EL34 Sigle ended driven by a cathode biased 6SL7. The power supply is CLC filtered with a 5U4G rectifier. All my voltages measure right and grounding looks fine and anyway I don't think the problem is here. I'm tied at the moment as I've never seen such a thing happen before.

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03-15-2008, 04:53 AM	#2
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,289	Are the OPTs busted? No, but they will be soon enough if you keep playing the amp without a speaker load. That us THE way to kill a transformer. Your OT laminations are "singing," mehcanically vibrating from the currents flowing through them. Don't do this any longer.

03-15-2008, 04:56 AM	#3
Paul P Senior Member Join Date: Jun 2006 Posts: 439	Funny, I just noticed the same thing in my amp today while running some tests. With the volume turned to zero I could still hear my signal generator tone and figured it was just some signal leaking through the circuit. But then I disconnected my speaker to run into a dummy load and the sound kept on going. The higher the frequency the louder the sound. Since you can't hear it when the amp is played normally I figured it wasn't a problem but I'd also like to know if this is normal or not. [Edit, just saw Enzo's message] I was running into a 8 ohm 50w dummy load (big resistor) and could hear my OT (it wasn't very loud, but noticeable). Paul P

03-15-2008, 06:22 AM	#4
macwanj Junior Member Join Date: Nov 2007 Location: Walla Walla, WA Posts: 17	Hey PaulP, see what these guys have to say about it: http://www.diyaudio.com/forums/showt...hreadid=119457 My transformer doesn't do it with dummy loads but I suspect that in my case its the audio signal modulating the magnetic lines. My amp still sounds pretty nice through speakers so I'm going to ignore the singing OPT's for now atleast.

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