The Amp Garage

Thanks, Martin. I do plan to swap the plate resistors.

That lead me to recall some prior discussions here that you are not really balancing the PI as much as the whole power amp. Is that a fair statement or am I misunderstanding? You are correct. The best approach is to arrange the power tubes to get the best DC balance, and then use the PI trimmer to ...

I think with 51k/47k plate loads and 22k tail as shown in the 2nd Gen layout, a perfectly matched 12AT7 would have very nearly balanced outputs. Any particular tube might be off in either direction, so keeping the original offset in place with a +/- capability via the trimmer would be the way to go...

While waiting on some parts to arrive I "balanced" the PI. Scare quotes because with the 5K trimmer I installed and the tubes in the amp, I could get close using the ampeg method but not all the way to a 0v offset. It settled around 1.7. I do have another 12AT7 and may try that to see if it gets me...

Glad you got everything working!

-Dan

While waiting on some parts to arrive I "balanced" the PI. Scare quotes because with the 5K trimmer I installed and the tubes in the amp, I could get close using the ampeg method but not all the way to a 0v offset. It settled around 1.7. I do have another 12AT7 and may try that to see if it gets me ...

Ok, hopefully I can get this thought out in some sensible fashion. After comparing the layout, schematic, board plans, and re-reading my questions about the changes - I think I might see where I went wrong. Bear with me because I still struggle with how these things flow from a theory POV - so I ma...

Yes, the pot side or rather the opposite of the tube side. The coupling caps block DC so you can set a scope or meter to measure AC and check at that end of the coupling cap leg.

Hey Raoul, this build is looking great! If you post some more pics of the relay board, effects loop jacks, and channel masters we may be able to help you spot something. When signal tracing, I always start after the coupling cap of each stage. If you find signal at one but not the next, you know the...

Seemed like I had a better balance between the channels too but that required maxing out the volume and keeping overdrive around 50%. Was a low dB test though and may not be reflective of normal playing levels. More fun later tonight after work.... I ran a simulation including source impedance for ...

Forgot to pay the "tax" with an updated gut shot: PXL_20240517_023439314.jpg Your tone controls should work now! Forgot to pay the "tax" with an updated gut shot: PXL_20240517_023439314.jpg Any difference in the tone stack? Yes, had a quick test this morning. Treble and middle function as expected ...

Forgot to pay the "tax" with an updated gut shot:

Thinking about this more and running some numbers here is what I've come up with. Voltage dividers are linear (though a pot may have a different taper) meaning if you think of the divider as attenuating a certain percentage of signal voltage, it does not matter if that input is 10V or 50V, the rati...

Hey Dan, Regarding your tone stack being underwhelming, check your slope resistor. You have a 100R instead of a 100K. Credit goes to Jelle for spotting it :D Thank you Ian and Jelle! I will get that swapped out before any other changes. You guys are awesome! -Dan Swapped in the proper slope resisto...

ijedouglas wrote: ↑Thu May 16, 2024 2:53 am Hey Dan,

Regarding your tone stack being underwhelming, check your slope resistor. You have a 100R instead of a 100K.

Credit goes to Jelle for spotting it

Thank you Ian and Jelle! I will get that swapped out before any other changes. You guys are awesome!

-Dan