The Amp Garage

If you are likely to be around 50-100k, I would say go for a 500k trimmer. 10-20% of rotation for the partial boost, and 500k is only about 1 dB down from full lift.

If you are looking at my boards .pdf, you're correct, it uses Com2-NC2 as the path to ground. The layout shows the other set of contacts being used to open the mid pot wiper-CW short, which will have no effect on the PAB if the ground is lifted 22M. Interestingly, if a partial lift is used, then set...

Raoul Duke wrote: ↑Thu Apr 25, 2024 9:10 pm So put the trimmer connecting Com1 and NC1 - one side and wiper?

Yes. You wire the pot as a variable resistor, and when the relay contacts are open it becomes the resistance to ground. If the trimmer is on the bus then there are two ground paths.

The biggest mistake I made when I first started building these amps however many years ago was to try to outwit Dumble with "tweaks" instead of trying to understand his original design intention. It's an urge that I have difficulty with to this day.....but I am working hard not to succumb! To concl...

Yes! Thanks Erwin. Clever way to add that feature.

Reeltarded wrote: ↑Thu Apr 25, 2024 12:48 pm It's always something and always never ends.

This is one of the laws of thermodynamics.

award70 wrote: ↑Thu Apr 25, 2024 3:45 am In a recent YouTube clip he essentially said that if you’re mad that he bought a dumble amp, then the next time one’s up for sale go ahead and buy it.

JB just dropped a notch in my estimation.

Guitarman18 wrote: ↑Wed Apr 24, 2024 6:10 pm This is a really simple and effective way to find the outer foil of your caps.

Sometimes the difference is subtle, so I prefer using a DMM or scope to get a quantitative measurement.

retodellatorre wrote: ↑Thu Apr 25, 2024 8:07 am So i changed the middle pot to a A 10K and removed the 6.8k to ground (just ground)... ... So i replaced the 0.047uf with a 0.022uf - and there we go.

Thanks for the update. Makes sense.

Did Dumble actually do this or is it just another TAG tweak? Excuse me, just another TAG tweak? ;^) I seem to recall seeing a picture of this. It may have been in a HAD amp or maybe it was a mod by one of the commercial D clone builders. Does this mean the full 22M has a negative effect or that it’...

Yes, it's a pot. The switch doesn't remove it from the circuit, just makes it go to the full 1Meg while preserving the setting. Alternatively, a switch in series with the pot could be used to open the bypass circuit and completely remove it, but it would be a good idea to put a large resistor across...

As far as the lift resistance goes - 22M and 72k seem pretty far apart. What’s the best way to figure out where to start that experimentation? Higher value lifts more of the stack? 22M is the full lift, same as open circuit for all practical purposes. I've seen various values for the partial lift, ...

He collects, shares his purchases and sells probably for a profit. His money and no-one suffers any damages AFAIK. And by the way, where would the amp otherwise go? A collector who puts it in a safe or at least doesn't show it to the world? What would we benefit from that? No harm except driving pr...

I believe he means to bypass it like this. I added the cap to block DC, and the bypass switch to get the full 1 Meg for "normal" mode from any partial-bypass setting. There will still be some effect from the tone controls with this bypass technique.

Did I have the connections correct? That’s where I got crossed-up. So I could follow mdroberts’ schematic and it would work the way most/many prefer? You understood the layout connections correctly. They are also shown in my ODS Eyelet Board .pdf. You can use MDRoberts scheme, but you might prefer ...