Improving the E1 Circuit in a 370/12RM
Posted: Mon Dec 17, 2018 12:52 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
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