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DIY Amp Prob - Help?

post #1 of 13
10/23/09 at 7:10pm
Thread Starter 
I built a small mains powered headphone amplifier using two NE5534's.

The sound is very distorted. It may sound ok at very very low levels but it's really difficult to tell as it's so quite. Funny thing is, if I switch the power off from the mains the sound is PERFECT for a few seconds then it goes all distorted and eventually dead (of course)..

Ground fault? Gain problem? No idea myself Just a noob passing the time. I couldn't find a schematic on using NE5534's as a headphone amp.

(I thought maybe too much "ripple" of along those lines, I do have large cap's in the PSU though.)
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post #2 of 13
10/23/09 at 7:22pm
Well, what schematic did you use?
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post #3 of 13
10/23/09 at 7:33pm
Thread Starter 
None really, just bits and bobs mostly taken from Cmoy schematics and adapted it to the 5534's.

I've got 2 electrolytic caps between the rectifier and the voltage regulators, but I don't have any after the regulators if you know what I mean. If that helps. Don't think I need more than that but I thought I'd mention it.

Edit: I've been turning it off and on. I don't know if it was some sort of "timing magic" but Ive got it powered and sounding how it should at the moment, well almost.
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post #4 of 13
10/23/09 at 8:42pm
The place to start is power and go from there. What do you have from V- to ground (virtual? I don't know how you rigged this up so just guessing at this point), and V+ to ground. Check it on both opamps. I assume that NE5534s are single opamps, so V- would be pin 4 and V+ pin 7. Are your voltages exceeding the specs for these opamps?
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post #5 of 13
10/24/09 at 6:27am
Thread Starter 
I'll draw up a schematic today of how I did it then I'll post it up here. I know it's difficult to say without "seeing" it.

Shouldn't be exceeding the voltage for the opamps, the power supply was working fine. +14.8v and -14.8v.
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post #6 of 13
10/24/09 at 7:09am
Thread Starter 
Here you go:



Hope that helps.

(I work out the gain to be 3.2 (ish).. I think that should be ok?)
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post #7 of 13
10/24/09 at 7:14am
Thread Starter 
As I say when I switch the power off it sounds great for a few seconds. I'm assuming then that there must be a problem in the supply somewhere. When it gets switched off there's no more "live" current and it's jut using the stored energy from the two large caps and sounds fine. Then it goes to shot and dies again as the caps energy is used up.

EDIT: A link wire was loose and I think possibly it shorted out as it went dead. I've fixed that now and there's an loud buzz through the headphones when powered up. The sound is there though! and sounds good behind the buzzing.. i.e. I think it's working but a component has now failed? buzz.. the two 6800uF caps in the power supply? When I power off it dies within 3 seconds where-as before it was about 8-10 seconds.
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post #8 of 13
10/24/09 at 8:13am
need pictures of the build.
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post #9 of 13
10/24/09 at 8:26am
Thread Starter 
changed the caps and still buzzing. I reckon it must be the 7815 as it's only putting out 12.5v now, the 7915 is putting out -14.8v.

I wont be able to provide pics as I don't have a good camera. My phone is crap as it's fixed focus and can't do any sort of close-up shots.
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post #10 of 13
10/24/09 at 9:24am
It sounds like a virtual ground problem if you are getting 12.5 and 14.9 volts, if it was me I would disconnect the power section and use 2 x 9volt batteries to make basic vg circuit (pic from Tangents site) and see if the problem disappears
LL
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post #11 of 13
10/24/09 at 11:20am
Thread Starter 
Thanks Fred, will check it out and get back to you.
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post #12 of 13
10/24/09 at 3:49pm
He's not using a virtual ground, at least from his power supply schematic. You mention a loud buzzing from the phones now? Check your output DC offset, as I think you may be in danger of trashing a set of phones. At least from TI's datasheet on an NE5534, you are right at its voltage limit of 30V (+/- 15V).
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post #13 of 13
10/24/09 at 7:38pm
Yes he is it the centre tap, so he's useing (+15) - 0 - (-15)
and 0 is virtual ground
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