#002 Steel String Singer - almost there

[Lothy]

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 directly via nfb loop

Not pretty, but I want it sorted once and for all...

IMG_20240311_130137.jpg

[martin manning]

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 switches. There is no way the effect should be barely audible.

[Lothy]

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 switches. There is no way the effect should be barely audible.

I've checked everything. I get the exact pf and resistance values on from common to the white or red board connection when I rotate the switch.
Do you know someone else who used this filters with Erwins boards?

Cheers
Gerhard

[martin manning]

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?

[Raja_Kentut]

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.

and what about this simplicity, R=47R 5W permanently soldered to the output jack?

you lose always power...and heat the atmosphere the MOV only active in case of a open load condition which won't last for a long time, normally.
and the MOV is small...and a part that could have been used since the 30's so its "authentic"

[erwin_ve]

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 do a screenshot of the pcb, they are the same as Ryan's tho.

Edit; see below

[Lothy]

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 do a screenshot of the pcb, they are the same as Ryan's tho.

Edit; see below

Thanks Erwin.

I have a 1 M instead the 470k after the 1nf. And the 3nf over the 100k to ground after the 820k. I took it off the switch today for testing. The inductor is jumped. That's all.

Cheers
Gerhard

[award70]

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 to the rest of the capacitor "commons" white wire? Yours is grounded.

[Lothy]

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 to the rest of the capacitor "commons" white wire? Yours is grounded.

No, it's the 3nf that is parallel to the 100k to ground at the green line.

Cheers
Gerhard

[award70]

Ok I see.

[martin manning]

Marked up layout is here: https://ampgarage.com/forum/viewtopic.p ... 79#p463579

[Lothy]

Marked up layout is here: https://ampgarage.com/forum/viewtopic.p ... 79#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 order the right switches from Mouser and do it again.

Cheers
Gerhard

[Richard1001]

If you are going to change the switches i can recommend using 11 position switches (blocked at 7 positions) like the original hand drawn schematic.
This way you can make a common bus for the capacitors
like the original schematic is drawn and as is visible on the gutshot of SSS001. (But if you measure the right values, i dont think new switches will make a difference.)

IMG_20200818_113121~2.jpg

[Lothy]

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.

[Lothy]

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 lot of sag with the 4k7. Now it sound really big and responsive. I need to explore it some more the next few days, but I'm sure I will not be disappointed at all.

Again, thank you all for your support, I really appreciate it. Special thanks to Martin for his effort with the drawings.

Cheers
Gerhard