Chuck D. Bones
Circuit Wizard
Catalinbread skewed the tone stack parts values, presumably to achieve the desired tone.
Tube amp schematic.. to FET pedal?
- Thread starter megatrav
- Start date
jubal81
Well-known member
Right, you'd just do those substitutions for the tone stack and the gain control. It's not strictly necessary, though. I have a lot of A100K pots, so scaling lets me use those instead.
Be interesting to build it both ways and see if one is less noisy. Never actually done that.
Another Edit: BTW, the SFT sounds epic when you crush the input with a Klon.
Chuck D. Bones
Circuit Wizard
Getting back to what Jubal81 said about scaling...
It makes sense to scale the impedances to suit the devices (FETs vs. tubes) and signal levels because higher impedances invite noise pickup. It has to be done carefully because a tone stack loads the gain stage that drives it, the next gain stage loads the tone stack and so forth. I suspect that some pedal builders simply avoid the effort involved in optimizing the design by just copying component values from another circuit whether it's appropriate or not.
Fig, those pot pins are too fat for the protoboard holes and will stretch them out so they are too loose for resistor and cap leads. There's an analogy somewhere in the back of my mind...
It makes sense to scale the impedances to suit the devices (FETs vs. tubes) and signal levels because higher impedances invite noise pickup. It has to be done carefully because a tone stack loads the gain stage that drives it, the next gain stage loads the tone stack and so forth. I suspect that some pedal builders simply avoid the effort involved in optimizing the design by just copying component values from another circuit whether it's appropriate or not.
Fig, those pot pins are too fat for the protoboard holes and will stretch them out so they are too loose for resistor and cap leads. There's an analogy somewhere in the back of my mind...
Man I really would love to see the P1, R1 and maybe S1 on this site. They're such awesome pedals.There's also a question - how close to the original tube preamp do you want to get with jfets or opamps? What's your goal? What are the assumptions and criteria? Matched frequency response and signal envelope?
Here's an example - comparison of the AMT P1 with Peavey 5150.
Yes, but do they sound identical to the originals? On the other hand - does it matter?They're so popular anyway
temol
Well-known member
Also I would not stick to x22 factor. Scale the tone stack values as needed for a particular circuit. x5, x10. As C.D.B said above - it all depend what's in front and after the TS. Remember, you have to scale all the tone stack components - capacitors, resistors, potentiometers. Imagine you have 10k potentiometer (or lower) and apply x22.
It does not look like 1:1 tube->jfet conversion.
It does not look like 1:1 tube->jfet conversion.
fig
Village Idiot
I'll use that tone stack calc as suggested, but now I need to hear it as drawn initially. I know a couple folks who might even help get me get it fine-tuned if I ask nicely.
Thanks to everyone for the explanations and insight, and my apologies to @megatrav for hijacking their thread. Sometimes I see a schematic and something snaps....or clicks?.....maybe it's more like showing the queen of diamonds to Raymond?
Thanks to everyone for the explanations and insight, and my apologies to @megatrav for hijacking their thread. Sometimes I see a schematic and something snaps....or clicks?.....maybe it's more like showing the queen of diamonds to Raymond?
megatrav
Well-known member
No apology necessary. I hope one day it all makes more sense to me. I'm grateful for the educational material.I'll use that tone stack calc as suggested, but now I need to hear it as drawn initially. I know a couple folks who might even help get me get it fine-tuned if I ask nicely.
Thanks to everyone for the explanations and insight, and my apologies to @megatrav for hijacking their thread. Sometimes I see a schematic and something snaps....or clicks?.....maybe it's more like showing the queen of diamonds to Raymond?
fig
Village Idiot
Yes sir, it is a piss-poor way to treat a breadboard.
fig
Village Idiot
I think this is finished. I'll go over it with new eyes later. Note: As Chuck rightly pointed out you shouldn't shove pots in BBs, but this one was kinda at the bottom of my bin anyway. I'm hoping to score some not-so-jankys when they are in stock.
I could have saved a little more space I suppose. I did keep all the power/ground on one side. The pots are the wrong taper, but I'll likely change them anyway as suggested.
I could have saved a little more space I suppose. I did keep all the power/ground on one side. The pots are the wrong taper, but I'll likely change them anyway as suggested.
