Improving the E1 Circuit in a 370/12RM

Non-Rickenbacker Guitars & Effects

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Improving the E1 Circuit in a 370/12RM

Postby (Very Occasionally) » Mon Dec 17, 2018 1:52 am

I just got the RM signature guitar and am finding some fault with the circuit design. It's basically the MXR Dyna Comp CA3080 circuit, but without an output (volume) control and a sensitivity control. For those interested, the IC is a CA3080 or NTE996 and the xstrs are 2n5088's. I've attached the schematic - hat tip to Mark Tefler who posted it in 2008. My guitar is not exactly the same, but close enough to make no material difference. Also posted are 2 MXR DynaComp schematics.

The 1st issue - decreased overall volume compared to the non-compressed settings - can be remedied with a 100k, or 50K, pot where the 82k resistor sits, or by simply jumpering that resistor (R16) and lifting the ground on R17 (On the circuitboard of my guitar R12 is not present).

The 2nd issue is there is no way to control the amount of compression in the circuit. Although the instructions that accompany the guitar tell you it can be adjusted with a trim pot (1k variable resistor on the PCB, R23), that pot really is a "set and forget" that works best in the 12 O'clock position and does nothing to vary the amount of compression. And there is an insane amount of compression in this circuit.

If you compare the E1 schematic to the DynaComp, you see the E1 has a 33k resistor from the Emitter of Q5 to pin 5 of the IC, where the Dyna has a pot (in front of a 27k resistor on electrosmash schematic, and no resistor on the GG schematic) going to the same pin. I suppose Roger liked a super-smashed sound, so the designer left out a real sensitivity control, but I find I prefer to be able to reduce (or increase) the effect, depending on the song, etc. So then the question becomes how to implement the mods without compromising the integrity of the pickguard and circuit board.

Any suggestions?

~ Steve
Attachments
mxr-dyna-comp-schematic.jpg
MXR-DYNACOMP.jpg
Rickenbacker 370-12RME1 Circuit.gif
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Re: Improving the E1 Circuit in a 370/12RM

Postby (Tube_Fan) » Mon Dec 17, 2018 7:29 pm

If you want to add a sensitivity control without drilling more holes in the pick guard, you could try putting in a stacked dual concentric pot and use one pot for the control that was there and the other pot for the sensitivity control.

CA8080 datasheet
https://www.intersil.com/content/dam/In ... 3080-a.pdf

Applications
https://www.experimentalistsanonymous.c ... AN6668.pdf
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Re: Improving the E1 Circuit in a 370/12RM

Postby (Very Occasionally) » Tue Dec 18, 2018 6:39 am

[quote="Tube_Fan"]If you want to add a sensitivity control without drilling more holes in the pick guard, you could try putting in a stacked dual concentric pot and use one pot for the control that was there and the other pot for the sensitivity control.

Hi John, thanks for your suggestion; much appreciated. Take a look at the pic and you'll see the controls are hard-soldered to the circuit board, so it's not possible to install a stacked pot.

What I am considering is having a spare lower guard made so I can mod without destroying the original. In that case I may use a couple mini-switches to give me some more options as presets for higher output and stepped levels of compression.

I did reduce the compression about 25% by inserting a 150k resistor in series between the 33k resistor and pin 5 on the 3080. And I increased the output of the E1 with a 10K in parallel with the 82k to the output, leaving R17 (10K to ground) in the circuit. Totally easy to remove these mods to put it back to original spec. So far I'm finding it more useful than stock.

~ S.
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IMG_0649 web.jpeg
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