Failed voltage checks on Low-current and B-side high current boards

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Offline Paul Birkeland

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DC offset adjustments are typically present in solid state (and some tube OTL amps) with bipolar power supplies and directly coupled outputs.  On a capacitor coupled amplifier, the cap blocks DC and the resistor from the output of each coupling cap to ground ensures that there's no DC present at the output and provides a path for charging on powerup.  The tiny bits of DC that you're seeing at the output could be from the DC voltage on the other side of the cap moving around slightly, and possibly from a tiny bit of capacitor leakage.  Still 0.032V across the 2.2K resistor there is possibly 0.0000145A of leakage current, and with 300 Ohm headphones, the DC appearing at the outputs would drop to 0.0043V, which is even closer to 0 than what you had before.

Paul "PB" Birkeland

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Offline Loading

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Thank you so much, that makes a lot of sense.

From a theoretical perspective then, could you reduce this even further by using caps that are less "leaky"?
« Last Edit: July 17, 2023, 03:22:03 AM by Loading »



Online Paul Joppa

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Very probably.

It's always possible there is some other cause, and replacing the 100uF output cap is an expensive way to test this, but on he other hand it's a popular upgrade mod - and the C2A has room for it.

Paul Joppa


Offline Paul Birkeland

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From a theoretical perspective then, could you reduce this even further by using caps that are less "leaky"?

You could, but this is like driving all over town to buy a car for $19,999.98 rather than $19,999.99. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man