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Name this pedal!?!?!?!

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9/30/1999 3:25 AM

Name this pedal!?!?!?!

here is what i know:

it is an MXR pedal, very beat up, red, my best guess is that it is at least 15 years old.

two knobs, all the lettering is worn off.

the number on the metal bottom is 101-2004
the box inside is 2-051091
and there is one chip on the circut board its numbers are 003 LM 3080N

i like what is does, all it seems to do is boost my signal, and add distortion. i was led to believe that it is a compressor. but it sure doesnt act that way to me. i like it but it has the most horrible bypass ever. can i use the various millenium bypass schematics out there to correct this.

any suggestions/replies appreciated.

skott

9/30/1999 4:01 AM
Aron	My guess is the MXR Dyna Comp. A compressor. It was very popular. Aron

9/30/1999 6:00 PM
Don Symes	I'm with Aron.. definitely a DynaComp... a slightly broken one. I'm pretty sure Aron or RG (GEO) have a schematic. I'd be looking at the switch as being somewhat busted, then I'd check the solder joints on the wires and especially the envelope detector section (that sets the gain of the LM3080) Very nice, useful box - well respected in its heyday and still.

9/30/1999 7:24 PM

I wish they were all this easy.

Yes, it would be nothing other than a Dyna-Comp.

Two things to note:

1) Like many manufacturers of the time, MXR tended to use the least switch they could. Your stomp switch is likely a SPDT switch that only selects between outputs, resulting in loading of the input at all times and some tone-sucking. Get a *real* bypass switch and install that (Several web-sites show how).

2) The LM3080 is a great chip with lots of possibilities, but it was also VERY fussy about the levels it would accept. There was usually a trim-pot connected to one input pin, and a divider/attenuator on the input to bring down the signal level to the manageable zone. I forget whether there is a trimpot on the Dyna-Comp, but you can check any of the posted schematics and confirm one way or the other. Alternatively, if you open it up and see a little rotary control on the board, then it has one. These can drift from optimal settings over time unless fixed in place by laquer or something. You may be able to improve on the distortion specs if it is set right.

10/1/1999 11:16 PM

thank you all for your replies. the other nite i really got at chance to use the pedal in conjunction with my other equipment at a respectable volume. it didnt sound too bad. the switch seems to be in need of repair as it did not turn off all the way sometimes.

the thing that interested me was the trim pot for the chip? how will turning it affect the sound? what is the ideal function of this pedal? which way do you turn the pot??

any answers will be appreciated

10/2/1999 6:44 PM

It's a Dynacomp. The switch is indeed broken. The trimpot is there not to adjust levels, but to balance the two inputs for minimum "thump" or "breathing" and distortion. On a perfect chip, the correct position is dead center. For most purposes, you can replace the trimpot with two 1K resistors.

The 3080 input can only stand about +/-25mV of signal as Mark notes, so the signal is divided down to about that level before going into the inputs. The trimmer plays a small role in that.

Set the trimmer to center, then play it. If it doesn't distort horribly or have a "thump" when you hit a note, leave it at center. If it thumps, turn it a little bit one way; if the thump is worse, turn it the other way.

10/3/1999 9:14 PM

Thanks for the clarification about the trimpot. Given that one should not normally anticipate a trimpot setting very far from the midpoint, it may be helpful to wire up a 1k trimpot with a 470-ohm resistor on either end to provide more usable range of the trimpot and make it a little easier to find the sweet spot.

Or is this overkill?

On a related note, I've been looking at that same schematic for a few years now, and still haven't figured out what components one would tamper with to alter the time constants to get a different attack or decay time. Is this because two components have to be changed rather than one?

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