Quick Cleaver question

[Jonnytexas]

I don't have any 2n5458s. Do have 2n5457, j112, j113, 2n5457 among others. Could I use any of these? I assume the goal is to bias to 1/2 of the 9v supply? Thanks in advance.

 

[spi]

Yeah, I think any jfet should work in that circuit. Since you have options, try socketing them and try out different pairs. You might even mix and match for a cool combo.

 

[Jonnytexas]

The circuit is working with j113s. I want to make sure I am biasing correctly. I biased both fets to around 4.6 volts, is this the optimal way to bias? Can't bias by ear or my neighbors will call the police.

 

[spi]

I have a similar boost with a j113 (but only one stage rather than two). The guidance for that circuit was to bias between 4.5-6V.

 

[Jonnytexas]

I have a similar boost with a j113 (but only one stage rather than two). The guidance for that circuit was to bias between 4.5-6V.

Thanks

 

[Jonnytexas]

I guess my question is whether this one needs to be biased differently because it has the charge pump.

 

[spi]

Oh, good point. I would suspect yes, but I don't know what the target voltage should be.

 

[Jonnytexas]

Can anyone chime in on this?

 

[Chuck D. Bones]

Shoot for around 1/2 Vcc. In this case, 18V / 2 = 9V.

 

[Jonnytexas]

Shoot for around 1/2 Vcc. In this case, 18V / 2 = 9V.

Thanks so much Chuck. I had already biased to 9v after poking around on the web. If it's not too much trouble, would you explain why most boosts bias to 1/2 of Vcc? Thankd. I am trying to learn.

 

[Chuck D. Bones]

Maximum headroom (largest undistorted signal) occurs when 1/2 of the power supply voltage is dropped across the transistor. When distortion does occur, you get symmetrical (or nearly symmetrical) clipping. Not all pedals sound best with this bias setting, but it's a good starting point.