Decadence Preamp Modification

G

guntedn

New member
I built this for a friend but he isn't sold on the sound. He says the volume is low, but I'd already swapped the resistor. I can't really hear what he's hearing but has anyone tried to change the pre and post pots to logarithmic and gotten a better result? I also changed the op amp to a JRC instead of the TI and I tell myself it sounds better whether it really does or not.:ROFLMAO: Any other mod suggestions would be appreciated. I'm willing to try anything to get a bigger sound out of this thing.
 
With hard clipping right before the output, it's only going to be so loud, regardless of the circuit previous to it.
You could swap the clippers for LEDs or use 2 diodes in series each direction but it will feel a bit different as there will be more headroom between non-clipping and clipping.
 
Pulling the diodes and installing a on/off/on switch would probably be the way to go. Center position would be no clipping and would be pretty damn loud. Then put si and LEDs on each ON position.
I'd be more apt to do that than swap for LED straight out. I don't like the transition of the higher Vf of LEDs as hard clippers typically.
if I need higher Vf on hard clipping, I'm more apt to use Ge Si(with a lower Vf, like bat41) in series. The softer knee of the Ge helps soften the transition and the Si mitigates the leakage of the Ge
 
I finished one recently too. I was surprised to see a 10k pot as the volume knob instead of a 100k so I assume it just doesn't have the volume on tap.
 
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jwin615 said:
With hard clipping right before the output, it's only going to be so loud, regardless of the circuit previous to it.
You could swap the clippers for LEDs or use 2 diodes in series each direction but it will feel a bit different as there will be more headroom between non-clipping and clipping.
Click to expand...

Might be a good candidate for infrared LEDs as clippers.
 
Am I right that R20 limits the max volume to 1/3rd of what can go through the final hard clippers?
I'd be curious to see what jumpering this resistor does -- I would expect it to increase the volume range 3x?
It is my understanding that op amps can drive lower impedences, so presenting IC1.2 with 10k instead 32k (R20 22k + VOL B10K) should not alter the tone -- but that's worth checking. At least I often see a 10K or even 5K volume pot in circuits with an opamp buffer or gain stage on the output. Check the Maleficent mids for example...
 
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