My Marshall ShredMaster needs a mod ...

[Ron Buckle]

Hello,

I am the proud owner of the discontinued Marshall Shredmaster. I love the sound of this pedal but it lacks treble ...
Even with the treble knob to the max, it sounds more like it is on 12 o'clock.

My questions :
- what component can cut treble when aging ? Tantalium caps ? Cheap resistors ?
- what do you advice to solve this ? Works on the input and add some sort of a treble boost ? Or work on the treble pot circuit and change some values (and then which ones ?)

In Aron's tips I see clues to improve bass response ; what about treble ? :-)

Hereafter a link to the schematics : http://www.harpamps.com/schematics/shrdmstr.pdf

I have already done some DIY pedals (EH Pulsar, John Hollis' Omnidrive), still my knowledge in electronics requires some help !! :-)

Thank you in advance.

Ron.

www.concordesound.com

[Steben]

I think you should change cap C18 to 470pF or something.
It's a high roll-off at around 1,5kHz there with the stock cap.

[Ron Buckle]

Thanks ! I will try that ...

Is it a good idea to change C2 if if want to increase treble at the input ?

[cd]

Remove C13 (or change it to 100pf) as well.  You can also change R14 to a higher value (like 22k) but that will change the sweep of the tone controls as well.  Changing C2 won't do anything unless you change it to something tiny like 1000pf, that will kill a lot of bass and emphasize the treble.

[Mark Hammer]

There are a bunch of spots where high end is "tamed", presumably to reduce fizz and add body.

C3 - 100pf: With the gain maxed this rolls off around 15.9khz, not much additional treble to be gained there.

C7 - 47pf:  In tandem with feedback resistor R9, this rolls off just under 5khz.  A possible candidate.

C13 - 2200pf:  In tandem with listed value R16, this rolls off high end around 328hz.  That just doesn't seem right, but we'll stick this one on the back burner.   I will simply note that if it were 220pf rather than 2200pf, it would roll off around 3.3khz, which seems infinitely more plausible in a pedal of this type.

C18 - 1000pf: In tandem with R21, this rolls off around 1.6khz.

Clearly, the lowest rolloff/treble-cut is created by C18.  I would suggest reducing it to 330-390pf, which would raise its rolloff point to 4.8khz (with 330pf) or 4080hz (with 390pf).  That should give you more unrestrained bite.

I would also suggest tinkering with the value of C14, perhaps increasing it to 2n2 (2200pf).  The network formed around the "Contour" control is essentially a midrange filter.  When the wiper of R23 is shifted all the way over to lug 3, C14, C16, R18, and R19 form a notch filter (mid-scoop) exactly like what Jack Orman has a nice tech paper on.  If you increase the value of C14, you shift the point in the spectrum where the dip occurs.    A bigger cap value will definitely add more bite.  I've increased a similar cap in several pedals and been pleased with the amount of edge it added.

As noted, the posted value of C13 just seem plain wrong.  Either the feedback cap or resistor is shown with the wrong value (2200pf would be fine if the resistor were a low enough value).  My sense is that the value of  C7 is about right for producing lower order harmonics without too much fizz.  Whatever the current value of C13 is, it should probably roll off somewhere around 5-6khz also to keep that brashness but without the fizz.  If you raise that rolloff and also increase C14, then maybe try a 470pf cap in the last stage (C18).  This would give more midrange bite, but keep the accumulated harmonics of harmonics at bay.

[LinuxMan]

Just a note.

The above schematic has an error. C5 should be 68n.

Cheers
LM

[John Egerton]

Anybody got a PCB for this?

hint hint  

[LinuxMan]

Hello...

Something like this: click

This is unverified. I think he uses a different schematics. You could use
and/or change the PCB though.

Cheers
LM