mxr microamp want to modify for better tone

[stopstopsmile]

I have an mxr microamp.  Its a nice loud booster but a little vanilla.  Very very plain. I wish it had a little more sparkle and personality.
I like it but after comparing it to a klon I just found that there was a little something missing.

I know the klon is so much more and much more cash.  But there has to be a way to tweak the microamp for a little klon like boosting response?

I am also using a modified TS9 and just want a little more personality with the microamp. 

[Mark Hammer]

Try building my Crank circuit, but omit the clipping diodes.  Or whip up your own approximation of the same principle.

The "problem" with the Microamp is that it uses a single op-amp gain stage to produce all the gain.  That places a number of challenges on the chip.  One of them is that if you use the ground leg to adjust gain (i.e., decrease the resistance of the path between the "-" pin and ground/vref), and you aim for a lot of gain, you tend to lose bottom end as gain is increased.  Conversely, if you use the feedback path to produce more gain, and you have a feedback cap in place to keep oscillation and hiss under control, you tend to lose top end as you increase gain.

What I did with the Crank was to simply use two cascaded noninverting gain stages, and split the overall gain up between them.  One stage uses the ground leg to produce its gain, and the other uses the feedback path.  Because neither change in resistance is all that dramatic, and because gain is multiplicative (overall gain = gainA * gainB), you can achieve high output without having to sacrifice top or bottom.

The Crank, stock as shown ( http://img.photobucket.com/albums/v474/mhammer/TheCrank.gif ), provides a maximum gain of 42-ish.  The Microamp, stock, provides a maximum gain of just under 22.

Just a note that as one starts to introduce greater amounts of gain, it is useful to provide greater amounts of hum rejection into the circuit.  Using what is essentially the same basic circuit design, the Distortion+ used a capacitor value replacing C3 ( http://www.generalguitargadgets.com/diagrams/microamp_sc.gif ) which resulted in a low-end rolloff starting around 720hz at maximum gain.  People complain about the thin sound at max gain, but maybe that's because there is not as much audible 60hz hum for them to complain about instead.

This is the long way of saying that the cap values one might wish to select for the parts shown as .47uf in the Crank schematic, might be usefully reduced to .33uf.  These would provide a bass rolloff around 102hz in stage 1 and 71hz in stage 2, reducing the amount of gain applied to any 60hz hum sneaking in with the guitar signal.  When gain is reduced, and the risk of audible hum is decreased, more bass is recovered.

Finally, the TL061 trades off hiss vs current consumption against the TL071.  The 61 uses less current but is a tad noisier.  If current is not a major concern, and you want to stick with the Micro-Amp, switch to the TL071, or an even "better" BiFET op-amp.  Note as well that 15uf is not exactly a standard value these days.  You can use a 22uf cap instead, or maybe even a 10uf, without sacrificing anything.