The Amp Garage

I've found it and it's a shame: IMG_20240312_200048.jpg 4k7 instead of 470k at the LNFB. What a bummer, so stupid 😂 Now the filter works as expected. I think, I'll change the switches anyway. These are so bulky and hard to rotate... like an old oven... The amp sounds totaly different now. It had a l...

Richard1001 wrote: ↑Tue Mar 12, 2024 12:52 am i dont think new switches will make a difference.)

I don't know what else to do. The only thing thats left are the switches.

Marked up layout is here: https://ampgarage.com/forum/viewtopic.php?p=463579#p463579 Thanks Martin. That's exactly what I've done. Except some small value differences 1n instead 1.5n, 1m, 100k... I think, somethings wrong with that switches and everything on it. Time to start from scratch. I'll ord...

martin manning wrote: ↑Mon Mar 11, 2024 8:25 pm Ryan C's layout and Erwin V's pcb marked up for the modified filters.

Thanks Martin.

Maybe I'm expecting too much. I can measure different values, but I can barely hear any difference, when I switch the positions. I used Erwin's boards and Martins filters and the difference between switch positions is easy to hear. Shouldn't your first cap on the switch (orange drop) be connected t...

That's a good question, since some of the filter components are on the boards. Maybe Erwin can look into that? I would be happy to check for problems, but I don't have his pcb files or even a picture of the traces and component positions. Maybe they are the same as Ryan's eyelet board layout? Ill d...

Maybe I'm expecting too much. I can measure different values, but I can barely hear any difference, when I switch the positions. If everything is good up to the points where the red/green/white leads connect to the filters (but check that), then the problem must be within the R and C arrays and/or ...

the speaker jacks should be grounded together with the phase inverter if you use negative feedback. correct, and it is the only truth.. people here using just random grounding for almost everything, or what they see from other people (the worst way), multiplying noise collected from the chassis dir...

That schematic seems to be correct. R29 and R32 values were tweaked from the earlier version, but that isn't going to make the difference you describe. There must be some wiring error. I think, I've done it right. Here you see the 3 wires. - white goes to the cap-bundle - green to commons at filter...

martin manning wrote: ↑Sun Mar 10, 2024 8:23 pm Hmm. That doesn’t sound right. You should be getting something very noticeable,12 dB difference top to bottom.

I just checked it. I've done it like this, except R29 100k, R32 1M:
It's very subtle...

I think, I missed something here.

Cheers
Gerhard

a cheap way to protect the OT against secondary open condition is a MOV (metal oxyd varistor) just solder it directly over one of the output windings. The rated voltage approx. 2x the highest expected output voltage. They look like a disk with about 15…20mm diameter. The good thing with this MOVs: ...

martin manning wrote: ↑Sun Mar 10, 2024 3:53 pm Spanky! Are your step filters original or the updated version?

Your step filters. But they are not very effective, more subtle. I don't know if this is right, or if I have done something wrong. I'll check it one more time.
Cheers

Here is a quick demo:



Cheers
Gerhard

When I lift R64 NFB resistor, the hum is almost gone. Did I miss a ground some where? OT secondary/speaker ground? Thats it... those damn speaker jacks got no connection to the chassis, even with lock washers. Thanks god, the OT ground was wired to the jack I'm still using. Otherwise bye bye OT. Th...

martin manning wrote: ↑Sun Mar 10, 2024 12:41 pm
What happens if you ground the PI input (wiper of the MV pot)? If it goes silent that eliminates the PI.

No change.
When I lift R64 NFB resistor, the hum is almost gone.
Did I miss a ground some where?