Marshall Micro Stack (Lead 12 / 2005) Treble Cut???

[Chris Brown]

Hi, I have one of the marshall lead 12 micro stacks from the 80s and it's a cool little ss amp but it's the treble content is too much for my tastes.

Heres the schem: http://www.drtube.com/schematics/marshall/3005.gif

Some one is going to look at this and know immediately what to do...

Take a look at this schematic and tell me if you see a simple way to cut out some of the fizzy high end that this thing has, please 

I realize it's not a stompbox but the preamp part of the circuit isn't much different than one.... an audio circuit is an audio circuit, right?

I've tried  a 250pf and a .001uf cap from lug 1 to 3 over the volume pot for a quick fix but I didn't notice an audible difference.

Best, Chris Brown

[bancika]

that thing has small speakers, right? maybe you could try to tame them a bit. Try wiring 1u - 4.7u 63V poly cap across speaker lugs.
That's easy enough to try...if you don't like it just remove the cap(s)

[anchovie]

The distortion is solely from op-amp clipping so it's going to be harsh. Try a larger value for C5 - 220p would give a treble roll-off point of about 3.3KHz.

[Chris Brown]

Thanks a bunch for the tips!!! Changing C5 worked perfectly.

I found that different amounts of treble cut sound better depending on where you the gain control is set so I did a spst on-off-on switch with a 100pf cap and a 220pf cap in parallel with the original 100pf cap in the respective on positions of the switch.

Again, thank you so much for the easy solution.

I put together a mod sheet for anyone that has one of these and wants to try this out.

Here are some pics and the mod sheet:







Best regards, Chris Brown

[anchovie]

Awesome, glad you're happy with the results!