New build: Supro 1624T in a Marshall Lead 12 donor amp

[klooon]

Time for some refinements...

Although, the amp responds well with my Les Paul, I have to set the tone control full open otherwise there is not enough treble. Initially, I have chosen for one input per channel (due to space limitation in my donor amp) and took the 'second input' which has the 100k input instead of the RC (5nF/100k). I am trying to understand the difference. I see that the 5nF/100k combination, gives a corner frequency of 318Hz, so it limits the bass input. Not sure if I will get more treble on tap in the tone control section by changing it to the 5nF/100k input???

Further, is there a simple way to modify the circuit to allow for more treble/high frequency response (and maybe mids)? Change the capacitor of the tone control or so???

I am looking forward to your responses!

[mozz]

I don't know what volume you are playing at, but if you increase the 500pf capacitor across the volume control to 680pf or higher, you will get more highs the lower your vol control is turned. It's a bright cap and increasing it's value will give you more highs (or higher mids) if your vol control is not maxed out.

[klooon]

Thanks. Usually I put the volume at (almost) max and use my picking to control the volume and amount of overdrive. Which is exceptional in this amp. You don't (or hardly) have to use the guitar volume control to have more/less overdrive... So maybe the bright cap is not bringing much then. Which also explains my lack of treble...?! What elke is there to play with? I see a lot of "alternative" values on this schematic link.

[mozz]

Maybe someone can explain the 500pf on the grids of each preamp tube? Maybe that is taking some high freq to ground?

[Enzo]

What else is there to play with? The speaker. The speaker is THE one thing with the most effect on your sound. Maybe you;d like a brighter speaker.

Remember when reading reviews: to one guy a speaker might be shrill, but to another it is bright and defined. Then a different speaker to one guy is smooth and mellow, but to another guy it is dull and edgeless. Read between the lines.

[klooon]

What else is there to play with? The speaker. The speaker is THE one thing with the most effect on your sound. Maybe you;d like a brighter speaker.

Remember when reading reviews: to one guy a speaker might be shrill, but to another it is bright and defined. Then a different speaker to one guy is smooth and mellow, but to another guy it is dull and edgeless. Read between the lines.

Fully agree with that. I went from an Emi Ramrod to this Weber 10A125, which I found too bright (even fizzy) in the micro Bassman amp, but in this amp it is not too bright at all. Usually I find the (Weber) alnicos not edgy enough, too 'nice' sounding - especially in a band setting where it needs to cut through a bit more, like my 12A150 in my Tweed Tremolux, but at home absolutely wonderful though. But in the Supro it is absolutely fine!

[klooon]

Maybe someone can explain the 500pf on the grids of each preamp tube? Maybe that is taking some high freq to ground?

I don't see these 500pF on the grids... you're referring to the 5nF (5000pF)? These form a RC high pass filter with the 100k, I believe... But there are a lot of 500pF around... not sure what they all do... And of all the values in brackets in the schematic which ones are giving the most high end response?

[mozz]

Input tube grids.

[klooon]

Finally, after not being happy with the amp at all, I rechecked everything. It couldn't be that the amp should sound this "dark", and yes bingo. I found out that i placed one 500pF treble cap on the volume pot to ground and a second was not mounted at all. Arghhh. I changed this, and also the tone cap from 10nF to 5nF. Now it sounds beautiful, really nice. Enough treble, nice bold overdrive. Strong tremolo. Great!

[loudthud]

I had to review the pics earlier in this thread. Looks like a cool project. Glad you got it running as it should.