M
mandoblast
New member
I bought one of these last fall to try with the expectation of learning from it as well as using it, but ended up tossing it in a heap in the attic till last weekend. I was completely discouraged with it after replacing the opamps (2134) and the tube (still hissy and hummy) and then taking the transformer out (better, but not enough) and damaging the on/off switch in the process. Now it would be more trouble to resell. So it sat.
To be fair, I have a better mic now (rode nt1a) than I had then, and I think that has a lot to do with why I was more impressed with the sound when I pulled it out of the attic last week for a listen on impulse. My other mics were a very noisy TOA condenser and a rather hummy ATM13. I'm still working on the mods, but here's where I am now:
Transformer stays out
opa2134's across the board
Power supply upped to +/-15v from 12v, separate tube heater supply, both main caps 3000/16v
Ground connections severed to high side of gain knob, reconnected with 4k7 resistor. Slightly less full gain (still plenty) but now very linear control and quieter. This is a feedback loop volume control, with high-gain setting dumping the feedback to ground.
Low EQ cap (c35) changed to 10nf (from 150nf?) resulting in a change in corner from infrasonic (it seemed) to about 250. Now it's like dialing in proximity effect. Subtle, not boomy on guitar. HI eq cap (39) from 47 nf to 29nf. Just happened to have it around--I think it's a bit high. I'll replace with around 35 when I order again. I think a 10k boost is like sandpaper, but this is a bit too subtle. I think changes in opamps AND voltages have changed how the eq reacts a bit, though it doesn't make sense to me. Unless it's about input impedances.
So far, result is very nice. Still to come:
input transformer, new blocking caps, and meter lights.
Roger Stevens
To be fair, I have a better mic now (rode nt1a) than I had then, and I think that has a lot to do with why I was more impressed with the sound when I pulled it out of the attic last week for a listen on impulse. My other mics were a very noisy TOA condenser and a rather hummy ATM13. I'm still working on the mods, but here's where I am now:
Transformer stays out
opa2134's across the board
Power supply upped to +/-15v from 12v, separate tube heater supply, both main caps 3000/16v
Ground connections severed to high side of gain knob, reconnected with 4k7 resistor. Slightly less full gain (still plenty) but now very linear control and quieter. This is a feedback loop volume control, with high-gain setting dumping the feedback to ground.
Low EQ cap (c35) changed to 10nf (from 150nf?) resulting in a change in corner from infrasonic (it seemed) to about 250. Now it's like dialing in proximity effect. Subtle, not boomy on guitar. HI eq cap (39) from 47 nf to 29nf. Just happened to have it around--I think it's a bit high. I'll replace with around 35 when I order again. I think a 10k boost is like sandpaper, but this is a bit too subtle. I think changes in opamps AND voltages have changed how the eq reacts a bit, though it doesn't make sense to me. Unless it's about input impedances.
So far, result is very nice. Still to come:
input transformer, new blocking caps, and meter lights.
Roger Stevens