Duende Booster Jfet Sub

[AM]

I am planning on building Tim Escobedo's Duende Jfet Booster. I have a couple of questions. Any answers are highly appreciated.

1. I only have a couple of MPF102 around. Would it be OK to use instead of the J201 and adjust the 25kOhm trim pot for the best sound? Do I need to make any further changes in the circuit?
2. Is the 22uF for filtering? Can I use a 47 uF instead and a 1N4002 diode?

Thanks for reading this.
Link to layout:
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Duende_JFET_Layout.gif.html

[PRR]

> MPF102 around. Would it be OK

The trimmer then needs to be 4K to 100 ohms, use a 5K trim-pot. Trim for 2V-8V at the VR1-C2 junction, then fine-trim to taste.

The hottest MPF102s may give short battery life.

The 22u cap value is utterly un-critical. The thing will work with no cap but there may be a little "dirt" as the battery weakens. 22,000u will work but won't fit in the case. 10, 20, 50u are all reasonable values.

D1 is also optional. Without it, if you get the battery backward.... hey, nothing bad happens, it just won't work. (Oh, after a while C1 goes blooey.) With it, your battery or wall-wart dies to save the pedal. I know D1 is customary, and I have lost elaborate boxes because I failed to consider reverse-voltage and idiot helpers (me in the morning), but in this case, I'd leave it out.

[AM]

Thanks for the reply. Based on some research I did I think I should get a measure of around 5V between drain and ground. Should I adjust by ear? Meaning leave the trim pot where I get signal without distortion?

I know that the diode is for polarity protection and both diode and cap could be omitted. It doesn't also protect the Jfet from spikes?
If I would have to choose between frying this circuit or my regulated power supply I would probably prefer the first. The circuit has very few parts which definitely cost less than my power supply.

[PRR]

> I think I should get a measure of around 5V between drain and ground.

An amplifier's output point is "usually" run about halfway up the supply voltage.

5V is near half of 9V and a "good" value.

I'm not sure if this is a "clean boost" or a "BOOST" or if it is supposed to color the sound. You get a wee bit more boost if you trim the drain as low as possible before it just quits (perhaps 2V-3V), but then it distorts earlier. If you trim on the high side (7V-8V), it has a bit less boost but more color.

So yeah. 5V is the safe first bet. But for -musical- uses, feel free to experiment.

> protect the Jfet from spikes?

The JFET appears to be rated to 30V in about any likely direction. If your "9V" supply has spikes to 30V, something aint right. A 9V supply probably doesn't have 30V in it. It could happen in a lightning-strike, when the "120V" wall zings-up to 2,000V for an instant, but when that happened to me I had a lot more damage than a pedal or power-pack.

> a 1N4002 diode?

Oh, yes. Actually on another forum I would say use 1N4007. They are all the same except from 50V to 1000V rating. Back in the old days, '4007 cost more than '4001, so we used good-enough. Today, in small bags, they all cost the same, so I advise just buying '4007 for powering anything from one-chip to two big tubes. I guess in this 9V world, you can use 50V 1N4001 or 100V 1N4002 for anything.

[petemoore]

Should I adjust by ear?
  That you should.

[AM]

I'm not sure if this is a "clean boost" or a "BOOST" or if it is supposed to color the sound. You get a wee bit more boost if you trim the drain as low as possible before it just quits (perhaps 2V-3V), but then it distorts earlier. If you trim on the high side (7V-8V), it has a bit less boost but more color.

It's supposed to be a full range clean boost. I bit of hair wouldn't bother me though. Unless it's nasty sounding. By "a bit less boost but more color" you mean it emphasizes certain frequencies?