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kevin gilmore

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How would you know if you need to adjust to 1.1Kohm?

If you cannot get the tubes' offset adjusted with the 1k trimmer and the 1k5 resistor, try resizing the 1k5 resistor down to give more adjustment range.

From what Geoff was mentioning it sounds like a tube to tube variation problem, it may or may not be needed on an individual amp. First see if you can get the offset properly adjusted with the 1k5 resistor.

BTW Geoff, that photo looks nice. Quite inspiring! Working on my Mouser parts order as I type.

Thanks for the PCB group buy.

And thanks to Kevin and Birger for the design and prototyping.

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The issue with the trim pot is also present in the KGSSHV or any other amp like this.  Components have different specs even if they are working as they should


What is a suitable pot for volume control? It has to be a 4 gang, 50k, log pot?


Any pot will do.  We use 50K mostly to cater to any source that is out there but 10K is most often more than enough. 

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You are right. Considering the Kevin recommendation and the Headincloud experience the total resistance (R20+VR2) should be less than 1K5, so, a solution is to use the 1K trimmer and a 750R resistor. BTW, in case of using the 1K5 resistor, 1/2W is not enough ( the dissipation with 10+10 mA is 0,6W).

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It wasn't quite finished when I took this.  The little 0.1 caps are missing. 




I put the trimpots as indicated on the silkscreening (both facing each other) but now that I think about it, I should have put them going the same way to make adjusting them easier.


Edit: To clarify, on the amp board silkscreen, the 1K trimpot has the adjusting screw on the right and the 2K trimpot has the adjusting screw on the left.  I wasn't thinking when I put them in and just followed the silkscreen.

Edited by chiguy
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