MXR Micro Amp and a Variant?

[soupbone]

I have a bone-stock MXR Micro Amp,and one problem I've always had,is it boosts the bass frequencies too much.If there a fix for this?I haven't tried the General Guitar Gadgets layout.So,I don't know if there version fixes this problem.I was looking in the Gallery,and there a pedal called the,Buster 6 with mods.Is this a Micro Amp variant?I was going to socket the opamp,and try some different ones.Maybe,JRC4558D,LM741CN,LF353N,TL071CN.Here's a schematic; www.rockcreekband.com/projects/custom/schematics/html/mxr_microamp.htm

[FUZZZZzzzz]

maybe send these guys an email

https://www.youtube.com/watch?v=fLIZ_qga0fY

[Elijah-Baley]

Hi.
I have just built a micro amp ggg version (on veroboard).
I don't know if there are some differences with the original MXR, but those could be pretty similar.
I noticed it enhanced bass frequency, (and maybe treble too, a bit).

I don't know this Buster 6, I didn't find it, but if you wanna fix your Micro Amp you should replace the C1 capacitor. The original value is 1uF (1000nF). You should try to replace with an 820nf, or 680nF. Under 470nF, I think, is too low.

But I'm looking for a confirm of this mod.

Edit: Sorry! Values wrong! Corrected them now!

[soupbone]

I have a bone-stock MXR Micro Amp,and one problem I've always had,is it boosts the bass frequencies too much.If there a fix for this?I haven't tried the General Guitar Gadgets layout.So,I don't know if there version fixes this problem.I was looking in the Gallery,and there a pedal called the,Buster 6 with mods.Is this a Micro Amp variant?I was going to socket the opamp,and try some different ones.Maybe,JRC4558D,LM741CN,LF353N,TL071CN.Here's a schematic;  www.rockcreekband.com/projects/custom/schematics/html/mxr_microamp.htm

[soupbone]

maybe send these guys an email

https://www.youtube.com/watch?v=fLIZ_qga0fY

Cool!

[soupbone]

Hi.
I have just built a micro amp ggg version (on veroboard).
I don't know if there are some differences with the original MXR, but those could be pretty similar.
I noticed it enhanced bass frequency, (and maybe treble too, a bit).

I don't know this Buster 6, I didn't find it, but if you wanna fix your Micro Amp you should replace the C1 capacitor. The original value is 1uF (100nF). You should try to replace with an 82nf, or 68nF. Under 47nF, I think, is too low.

But I'm looking for a confirm of this mod.

Ok cool!I'll give it a try,and report back.

[soupbone]

Hi.
I have just built a micro amp ggg version (on veroboard).
I don't know if there are some differences with the original MXR, but those could be pretty similar.
I noticed it enhanced bass frequency, (and maybe treble too, a bit).

I don't know this Buster 6, I didn't find it, but if you wanna fix your Micro Amp you should replace the C1 capacitor. The original value is 1uF (100nF). You should try to replace with an 82nf, or 68nF. Under 47nF, I think, is too low.

But I'm looking for a confirm of this mod.

Here's the Buster 6 page; www.aronnelson.com/gallery/main.php/v/waltk/Photos/Buster+6+w-mods.png.html

[Elijah-Baley]

www.rockcreekband.com/projects/custom/schematics/html/mxr_microamp.htm

In this schematic the input capacitor is 0.01uF in GGG, (and probably in original Micro Amp) is 0.1uF. So, you should get further inforomation. Me too.

[italianguy63]

You see that in the original Fuzz Face schematics too.  (.1uF and .01uF).  It does control the brightness.  .1uF would be on the dark side.  So, yeah, head towards the .01uF and experiment.  MC

[duck_arse]

you can also try reducing the 4u7 cap to ground (C3 on ggg) under the inverting input.

[Elijah-Baley]

I think so, too. That, maybe, should get a "light sound".
And eventually C5 cap, 15uF. Obviously with a lower one.

But him could be try just one mod for the moment, and test it. C1?

[Mark Hammer]

Take a tip from the ProCo Rat and run two ground legs, one normal and one for highs.

First, replace the 4.7uf cap with 0.1uf.  Then, run a 1uf/4.7k pair in parallel with that.  This will provide flat response at low gain, but more boost above 720hz than below as you turn up.

[Fender3D]

I wonder how a signal booster with linear frequency response might

(it) enhance(d) bass frequency, (and maybe treble too, a bit).

maybe the issue lies somewhere else...

[soupbone]

Take a tip from the ProCo Rat and run two ground legs, one normal and one for highs.

First, replace the 4.7uf cap with 0.1uf.  Then, run a 1uf/4.7k pair in parallel with that.  This will provide flat response at low gain, but more boost above 720hz than below as you turn up.

Thanks Mark for your reply!Can you maybe go into a little more details about this mod?Thanks!

[Kipper4]

Look at the schematic here

Top left hand corner is what Mark is talking about I think

http://www.electrosmash.com/proco-rat

[Elijah-Baley]

I have a bone-stock MXR Micro Amp,

Sorry, does it mean the pedal is an original MXR pedal, it isn't?

and one problem I've always had,is it boosts the bass frequencies too much.

I finished two days ago a Micro Amp based on ggg schematic, so I just tried it few minutes with my modesty instruments.
I hear more bass when I turn up the pot, on clean sound of the amp. Maybe with a distortion channel or a distortion pedal (after the Micro Amp) I hear no too much increasing of bass frequency. But I'm going to test it again.

I can't say anything about the response of the original Micro Amp. But, following the tonepad schematic of the micro amp (a little different) C1 is a 0.01uF cap. As in the schematic into the first post here.

[Mark Hammer]

Look at the schematic here

Top left hand corner is what Mark is talking about I think

http://www.electrosmash.com/proco-rat

Correct.  Sorry I had to be so short, but I was responding via my tablet, and typing anything on it is a royal pain.

The basic strategy is to provide more gain for the mids and highs than for the lows.  Stock, the unit provides a flat response from sub-audio up to frequencies your amp won't reproduce.  Using this drawing as our reference - http://www.generalguitargadgets.com/pdf/ggg_mamp_sc.pdf - the gain is set by the feedback resistance (R4) plus the ground-leg resistance (R5 + R6)/ divided by the ground-leg resistance.  When the Gain pot is set to zero, then our gain is given by (R4+R6)/R6, or 21.7x.  The low-end rolloff is given by 1 / (2 * pi * C3 * R6+R5).  At min gain, that is less than 1hz.  At max gain, that moves up to 12.5hz - obviously a change you're not likely to notice. 

The suggested changes would provide a max gain of 21.7 for content above 589hz.  That nudges up to around 720hz and a mac gain of 26.5x, if you make R6 2k2 instead of 2k7.  The parallel pair of 1uf/4k7 would have negligible impact when the gain is at min, but as you increase the gain control, the gain is increased more for the mids and highs than for the bottom.  That is, bottom is not rolled off, so much as simply not boosted. 

The 1uf/4k7 pair will result in a max gain of 12.9x for content below 720hz.  With the gain pot set to 10k, the gain is 5.6x for the mids and highs, and 4.8x for lows.  With the gain pot set to 5k, the resulting gain is 8.8x for mids and highs, and 6.8x for lows.  And so on.  YOu can see that the relative gain for lows and mids/highs starts to pull apart as you turn up.

If the suggested values don't yield the degree of bass-restraint you are looking for, then consider making the added resistor 5k6, instead of 4k7.

Also, consider dropping C5 from 15uf down to 2.2uf for even more bass reduction.