High pitched whine in preamp. Oscilaltion?

Started by marcelomd, June 04, 2023, 06:12:47 PM

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marcelomd

I have them all connected via the enclosure. I didn't get to ground the enclosure yet.

Today I tried all 9V supplies I have. All presented oscillation except for one: I put a 9V buck converter in the box with my little amp. It feeds from the 24V that goes into the TPA3118. Zero oscillation there.

PRR

> I didn't get to ground the enclosure yet.

Might be worth a try??

https://www.adafruit.com/product/1592
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marcelomd

#22
Grounding the enclosure makes the whine almost imperceptible on the clean channel. On the dirty channel it started changing volume with the level knob (!). Previously it was the same volume regardless of level knobs.

I removed the 10uF capacitor near the output stages. No change.

I have a rehearsal tomorrow. Will see how it goes with other amps.

Edit: If I disconnect the (regular 9V) wall wart with the amp on, the whine goes "weeweeweewee" until it fades. Kinda funny actually.

amz-fx

10r for your R13 is too small. It needs to be at least 100r. And keep the 100uf that you added.

Also. the preamp and power amp will probably be happier if they do not share a ground...  i.e. the preamp has a wire connecting it to ground at the power supply jack, and the power amp has a separate wire connecting its ground to the  power supply jack.

regards, Jack

marcelomd

Quote from: amz-fx on June 19, 2023, 10:35:19 PM
10r for your R13 is too small. It needs to be at least 100r. And keep the 100uf that you added.

Also. the preamp and power amp will probably be happier if they do not share a ground...  i.e. the preamp has a wire connecting it to ground at the power supply jack, and the power amp has a separate wire connecting its ground to the  power supply jack.

regards, Jack

Will change the 10r later today if I get the chance. The original prototype had 33r.

About the grounding. I'm confused. These devices share a ground through the cable. How not to do that?
Also, the combination that is oscillation free is when I use a buck converter that is inside the power amp. So sharing ground via input jack AND power supply.