#002 Steel String Singer - almost there

[martin manning]

Spanky! Are your step filters original or the updated version?

[Richard1001]

I think it is best to wire the connector grounds together. I didn't see this in the video. The amp sounds nice!

IMG_20210530_184653~3.jpg

[erwin_ve]

Here is a quick demo:



Cheers
Gerhard

Congrats, sound great!

[bepone]

Here is a quick demo:

very nice tones, complex and special

[Lothy]

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

[martin manning]

Hmm. That doesn’t sound right. You should be getting something very noticeable,12 dB difference top to bottom.

[Lothy]

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:
when they fail because of overload, they fail almost always to short. (0 Ohm -> safe for OT)
and they give you two ways of alarm:
They release a fog with a stink of old fish and glow orange

I have them in my other builds. But more like this:

Screenshot 2024-03-10 212913.png

https://www.premierguitar.com/the-immor ... -mods-pt-3

Cheers
Gerhard

[Lothy]

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:

Screenshot 2024-03-11 075244.png

It's very subtle...

I think, I missed something here.

Cheers
Gerhard

[Roe]

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.

the speaker jacks should be grounded together with the phase inverter if you use negative feedback.

[martin manning]

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...

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.

[Lothy]

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-high
- red comes from pin 7 at filter low.

IMG_20240311_120726.jpg

Here are the connectins on the board:

IMG_20240311_120743.jpg

Maybe I'm expecting too much. I can measure different values, but I can barely hear any difference, when I switch the positions.


Cheers.
Gerhard

[bepone]

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

[bepone]

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?

[Roe]

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

yes, see here https://www.valvewizard.co.uk/Grounding.pdf

EDIT: "A separate wire
... should then run from the negative connection of the speaker jack back to an
appropriate star. ...If global feedback is used then the speaker ground
should be returned to the local star of whichever stage the feedback happens to be
applied to, which is usually the phase inverter (e.g., fig. 15.14)."

[bepone]

yes, see here https://www.valvewizard.co.uk/Grounding.pdf

yes, but also no need, if you think that voltage feedback used in guitar amps has + and - terminal, and it is FEED BACK to the preamp stage,
both terminals need to be FEED BACK, + and -,

so plus or speaker live terminal returns over the NFB resistor, and MINUS terminal to the - of the preamp stage, and in our case gnd leg of tail resistor (PI), wires must travel together .

Spk jack must be not "grounded" of course, it will be grounded in PI gnd capacitor node.

And you are hearing in 90% of the cases speaker terminal is GROUNDED to the chassis..