Need some help with an Overdrive Project.

[Izzy]

Hello guys,

I am very happy to be back to this forum. Finaly my intense semester is over!
I learned a lot about transistor this semester. Infact one course was completely about transistor. And it really helped me to understand AC signal analysis for transistor.
Man I feel so happy. 

Anyway I am going to work on another project. A friend of mine want to design him an overdrive pedal. And he wants me to put a separate switch for more Sustain.
What can I do to increase sustain without increasing much gain? Changing the Diodes to from Si to Ge might bring noticable change. So I dont want to do that.

Does anyone know?

[Meanderthal]

 Hmmm... a bit complicated, but you could always build a compressor circuit, stuff em both in one box...

[petemoore]

  It sounds like you maybe want a 'hard compressor' with a touch of dirt..I use a modded Dyna Comp, it fakes sustain at low volumes convincingly [8-10 seconds worth of constant signal level], but with a bit of compressor 'huffing/puffing' soon after attacks.
  Getting sustain from OD is simple...turn the volume up.
  But that's the catch, without volume you're going to have to mess with dynamics, and then it will be possibly a less dynamic OD sound.
  Harder clipping relates to compressing also, have him try more of a 'distorter', something where even small notes induce hard clipping on diodes or transistors etc.
  You can do that by adding gain via booster or mod to existing topology, or reducing the diode clipping threshold...which reduces output volume [can be recovered] and sounds different...
  Here I am rambling and I don't know anything much about the circuit.
  what I'm getting at is that if he likes the sound of the OD, perhaps sticking fairly close to that...maybe try simple assymetric clipping [if it's symmetric now]..mess with the diodes and max gain set components.
 

[Barcode80]

a good boost on the input, like a mosfet boost, will increase the gain considerably and thus the sustain, but i'm afraid that as far as my newb self knows, the only way without adding more disortion or clipping is with a compressor. you can fit an OD and a compressor in a BB though

[Izzy]

Hmmm thanks guys.
So there is no other way to have sustain then?
Only three ways are

1. Increasing the gain
2. Using diodes with less threshold voltage
2. Adding compressor

I really dont want to add a compressor. But Let me ask him if its fine to add gain when he switches SUSTAINER button ON. 
Or may be switiching Ge diodes from Si? (but the tone might change drastically??)

Or may be adding another gain stage with 5-10 gain with Ge diodes?

[newbie builder]

Or may be adding another gain stage with 5-10 gain with Ge diodes?

That might be the method that requires the least amount of extra work if you just wanna increase gain/sustain. Just do that and have a 100kA pot at the end of that stage (make it like a separate pedal within the pedal so that it's a separate boost switch) and then you can dial it in for the right volume and have it be more gainy/sustainy.

[Izzy]

Does anyone has any other opinion?

[Meanderthal]

Or may be adding another gain stage with 5-10 gain with Ge diodes?

Yes, along with its own volume control... I believe that would definitely add sustain, but would be a much more saturated sound. Would be nice to kick in for leads...

[markm]

How about doctoring up the BigMuff circuit......it sure does sustain and perhaps messing with some of the bias and resistor values you could make it sound more "overdrivey"......just a thought.

[Izzy]

I am actually planning to make first gain stage with Jfet and Ge diodes and then second gain stage with opamp and Mosfet clipper. I dont know how well its gonna work. Basically I wanted to make tubey sound. 
And markm I will again be counting on you for PCB work.

[Izzy]

Hello , I need some help here.
My friend asked me to make an OD pedal for him. And this is my first time using JFets and Mosfets so I am kinda confused.


Schematics:
http://img503.imageshack.us/img503/5154/schematiczk5.jpg

Graph:
http://img247.imageshack.us/img247/8532/graphht4.jpg


GREEN: Signal After the first JFET
BLUE: Singal After second JFET
YELLOW: Signal After the opamp.


I wanted to have soft clipping from the first Jfet itself and clip it with GE diodes fron the second Jfet's feedback. I kept diodes in second Jfet because I guess if I put them on the first one it will screw the input Impedence.

But my question is why is the negetive wave of the signal not clipped (Soft)  by the first Jfets? And why is the AC swing not that high? I though it should be  between 0-9v from 4.5 being the midpoint.

And why the diodes are not clipping the Wave in second Jfet?
The wave form are same even if I remove those Diodes. Ok I can see that the top wave is clipped at 0.7V from 4.5V (I guess By First JFET). But diodes should have clipped the negetive wave, shouldn't they? (Since the Negetive wave is more than 0.7v fron 4.5V)

Or am I using them in a wrong way? And also the Mosfets in the feedback of that opamp is not clipping signal at all. Why?



Thanks in advance.



Note: Please disregard those Capacitor Values for now. They are there just block DC and Let AC pass through. And Also those diodes in the first Jfets are supposed to be GE diodes but I coulnt find any model in Pspice.

[Izzy]

Anyone?

[Izzy]

Still Waiting.

[Izzy]

Common guys 
I need some help.