modifying the mxr micro-amp

Started by any, May 23, 2006, 08:37:28 AM

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any

I'm still looking for the most promising way to splice in a tone control into the micro amp...  :icon_wink:
Anyway, my vision would be a 3 way DPDT on/off/on switch that would do a bass cut/nothing/treble cut.
Since it's a on/off/on I might foresee some problems since I can only use the tone control parallel to the signal.
Looking at the schematic (from GGG: http://www.generalguitargadgets.com/diagrams/microamp_sc.gif )
and assuming it is virtually the same as the commercial MXR micro amp;
I was wondering if switching a cap parallel with the cap at C5 would give me a useable bass cut.
(The high cut would be much easier to solve with a "parallel switch" approach, so less worries there.)


Suggestions are indeed welcome!
It's supposed to sound that way.

any

To follow up on my own thread, after a lot of queries on the micro amp subject I finally found a post by Mark Hammer (as far as I can recall)
about parallel cap's to change the bass and treble cut frequencies.

What I've done is slightly modified his proposed idea and ccame up with the following:

- The 47pF cap got paralleled with a switchable cap that I mounted in a socket to alow adjustment
  to the treble cutoff frequency.
- The 4.7uF cap was removed and replaced with a socket containing a 0,15 cap and was also
  paralleled with another switchable cap also in a socket. (now containing a 1.0uF

pretty much as discribed, apart from placing all vital caps in sockets wich I mounted on the back of
the original MXR PCB (drilled holes to mount the sockets and connected them with the various points on the board.)
This way the caps can be replaced without disasembly of the board.

The switch I used was a 3 way on/off/on wired in the following way:


This way the switch in up position cuts treble by the amount set with the socketed cap,
the middle position cuts bass to the amount set with the second socketed cap.
The bottom position is "standard" with the third socketed cap bringing the bass back up
to the original value. (so when more bass cut is needed the second cap needs to be adjusted as well
to balance out the "standard" position.
Does that make sense?
I works like a charm! I get treble or bass cut or unaltered sound with only one 3 way on/off/on switch...  :)
It's supposed to sound that way.