How quiet should the Mainline be?

MikeSattler · 32172

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Offline MikeSattler

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Reply #15 on: August 13, 2024, 07:04:51 AM
Okay thanks for the info, so it seems like that noise level is just normal then?

Is there anything I can do to reduce it a bit with high ohm headphones like the HD800? They sound the best with the impedance set to high but the noise floor is definitely noticeable in a quiet room.


Offline MikeSattler

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Reply #16 on: August 13, 2024, 03:09:33 PM
So just out of curiosity, I measured for AC at the +275 connection on the PSU. I'm getting 20-24 mv of AC 120hz ripple. Is that within spec? Just wondering if something is out of wack with my power supply and it's not totally filtering out the AC.


Offline Paul Birkeland

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Reply #17 on: August 13, 2024, 04:24:04 PM
Power supply noise is 120Hz and you'd want to measure at the OA terminals on the C4S board to see residual power supply noise.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Joppa

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Reply #18 on: August 13, 2024, 06:35:04 PM
The output transformers could (with some difficulty) be re-wired for 8 or 16 ohms, which would buy you another 6 or 3dB respectively.

Paul Joppa

Offline MikeSattler

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Reply #19 on: August 14, 2024, 05:49:50 AM
Oh interesting! Okay well, when measuring at the OA terminals on either C4S board I'm only getting around 100 microvolts of ripple which seems pretty good. I just wanted to make sure the filtering caps in the power supply were working properly since they sat around for a few years before I built the kit. Thanks for the help!


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