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I have a little Fender Excelsior which is a cool little amp but I’d love to see what I could do to stiffen up the feel somewhat. It sags a lot and I’d love to tighten it up. Now I’ve never really done any amp mods before but I do know how to drain the filter caps to be able to work on it.
Can anyone here tell me which caps I’d need to replace to give it a stiffer feel?
Pic attached. I’m
Assuming C12, C29,C26, C28 is the main filter caps?
They are all 22uf 450v, would I go something like 30uf instead?
Would you just do one or some or all?

I’d forget about the caps - they’re not the reason for the sag. Just off the left of your snipped schematic image are two 270 ohm 7W resistors between the bridge rectifier and the 1st cap (c28). Change those resistors out for something lower, depending on how much less sag you want. You could drop them to 10ohms if you want virtually no sag, or 100ohm if you want some sag (but less than at present).

You beat me to it... I was just about to say its got plenty of filtering already and the sag is likely "designed" into the circuit using those 2 resistors. They limit the current so that the filter caps take time to recover.

There’s certainly some options to increase stiffness

RectifiedAmps wrote: ↑Fri Jun 02, 2023 6:23 pm I’d forget about the caps - they’re not the reason for the sag. Just off the left of your snipped schematic image are two 270 ohm 7W resistors between the bridge rectifier and the 1st cap (c28). Change those resistors out for something lower, depending on how much less sag you want. You could drop them to 10ohms if you want virtually no sag, or 100ohm if you want some sag (but less than at present).

Thank you, that’s really helpful as I don’t know anything about this really. So in this pic R22 and R30?

Reg18 wrote: ↑Fri Jun 02, 2023 9:11 pm So in this pic R22 and R30?

Yep! They’re the ones.

RectifiedAmps wrote: ↑Fri Jun 02, 2023 9:16 pm

Reg18 wrote: ↑Fri Jun 02, 2023 9:11 pm So in this pic R22 and R30?

Yep! They’re the ones.

2 questions, looks like they are up off the board to dissipate heat?
Also is this 10watt 100ohm from jaycar suitable?
https://www.jaycar.co.nz/100-ohm-10-wat ... r/p/RR3364

I was going to suggest trading it for a younger model if you want less sag.

Also keen to know where the negative feedback resistor might be, and which bits I could change to alter the tone switch values to be less dark on the dark setting and less bright on the bright setting (preferably without replacing the switch with a pot)
Link to schematic here.
https://drive.google.com/file/d/0B94M9u ... V243ZilJgw

10w resistors will do the job provided they’ll fit.

This amp doesn’t have a negative feedback loop as far as I can tell.

C2 and C19 are the caps to reduce to make the switching less bright and dark (respectively).

I had an Excelsior and it has an undocumented middle position on the tone switch which cuts out the tone stacks,so that there is no need to mod it.

There is a lot of info on modding them here: https://www.tdpri.com/threads/the-excel ... ge.322527/

So after a quick trip to Jaycar this morning I’ve done the mods. Due to the size I ended up trying 47ohm 10watt resistors and 10ohm 10watt resistors (which I settled on)
The 100ohm ones were 11.5cm long!
The 10ohm was a slightly more manageable 4.7cm.
There’s not a night and day difference but certainly has a more immediate feel. I’d be interested to know if people can actually hear the difference as well?
Bright/dark switch I altered the dark cap from 10nf to 2.2nf with a subtle difference but slightly better.
I’d try and even lower one but it was a bitch of a spot to get a soldering iron too so not gonna try again.
Here’s a video of the changes.

[youtube]https://www.youtube.com/watch?v=D-UzMjI ... YXllcnM%3D[/youtube]

This was recorded through an IR and load box, having a quick go through its 15” speaker it could do with some more bass at lower volumes now. It doesn’t saturate untill around noon which is too loud for home use in real
Life. Any suggestions on where to alter bass in the circuit and where would I install a PPIMV?

Lowering those resistors will raise the voltages, this will probably give you more headroom. You may need to increase the value of the dropper resistors to get the voltages lower in the pre-amp, thus allowing that to break up at lower volumes. Guitars amps are quite simple but every change has an impact on other parts of the circuit. PPIMV may effect the tremolo circuit, a simple master vol across R25 may give you what you need - trial and error is often the case