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Perry Babin 11th September 2020 12:20 PM

The regulation for the rails is working. The 317/337 are fed from the rails so if that voltage is stable, their heating should be the same.

objext 12th September 2020 04:56 AM

Did some further checking. After first turn-on I got the following:

In: 29.1V
Out: 14.5V
Adj: 13.4V

Out: -12.9V
In: -29.1V
Adj: -11.4V

Is there anything to learn from those numbers? I also noticed the solder joints look cold/cracked on the 317, and I'm getting a high frequency vibration from, I assume, the transformer when I first power it on. I didn't notice that before switching power supplies.

Perry Babin 12th September 2020 05:03 AM

It's important that you post accurate numbers. The values for the 337 should all be negative.

High frequency vibration?

The values indicate that the regulators are a bit out of tolerance but it's not a big deal. For a healthy regulator the difference between out and adj will be 1.25v.

objext 12th September 2020 05:10 AM

Corrected, sorry.

Vibration, coil whine perhaps? Here's a 5 second video. It stops as soon as the amp fully powers up.

September 11, 2020 - YouTube

Perry Babin 12th September 2020 05:11 AM

I don't do videos. No exceptions.

Is the problem getting into the audio?

It's not likely with the mute delay.

objext 12th September 2020 05:23 AM

No problem, I understand. I haven't tested the audio output in a while. I can check it tomorrow. I didn't notice anything before, however.

objext 14th September 2020 06:59 AM

1 Attachment(s)
Audio output from all channels still seems fine at low volume, and you're correct that the whine stops before the mute delay lifts. I reflowed the cracked looking solder joints on the regulators, and also some similar looking joints on the output fets. Still getting plenty of heat from the regulators. My measurements were slightly different, but that may have been my meter battery was dying.

In: 28.5V
Out: 14.2V
Adj: 12.9V

Out: -12.5V
In: -28.5V
Adj: -11.1V

Hard to believe this could survive in a hot car environment. This was taken with about 77F ambient with a light ceiling fan breeze

Perry Babin 14th September 2020 08:36 AM

You are on the tab. If the tab is hotter than the heatsink, add some heatsink compound.

I don't know what's normal for these. There could be a load that heavier than it should be.

Are any of the op-amps running hot?

objext 15th September 2020 04:32 AM

Yes, but I was getting similar readings off the back of the heatsink.

Q6, Q8, Q13 are definitely heating more than Q5, Q7, & Q12. About 125F compared to about 100F.

U202 is heating as much as 117F give or take, and similarly U402 next to it. It's difficult to get accurate readings. The other TL072 chips are getting warm also, but these are the hottest as far as I can tell.

objext 15th September 2020 04:56 AM

I just noticed if I take a voltage reading off pin 1 or pin 2 of the TL494 I get the same coil whine as when the amp is powering up. Not sure if that's relevant but figured I'd mention it.

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