Jfet Sorting For Preamps/Overdrives?

[ncusack]

Hello,

I'm wondering about the many Jfet based preamps and overdrives and if anyone can shine some light on the selection of jfets for these designs. For example the Wampler plexidrive calls for 3 J201's. Would Wampler sort these by Idss and Vgs values for a production build of this pedal and how closely might they be sorted?

[smallbearelec]

if anyone can shine some light on the selection of jfets for these designs.

I don't know Brian's spec. I can tell you that we have been consistently selling small quantities of remainders from sorting for phasers:

http://smallbear-electronics.mybigcommerce.com/jfets-low-vp-sorted/

The lower limit for Vp for phasers happens to be around the upper limit for what you would want for boosts. We have--almost literally--a ton of raw stock and a semi-automated test fixture. If we know what you want, we can likely provide it at a decent price.

[Gentle Jack Jones]

I didn't know that the lower good limit for phasers is 1.40, but I bought what, for me, was a figurative ton of 2N5457s from Small Bear, hoping to make many things, but a phaser among them, and I found the Vp using RG's JFET tester below 1.40 on all of them. Do you tend to sort out the > 1.4s before selling loose JFETs?

I do wonder if my JFET tester works properly. I got different readings from .86 to 1.25 on all but two of about 30 2N5457's, but got readings of .72 on all of 10 2N5952s.

[smallbearelec]

Do you tend to sort out the > 1.4s before selling loose JFETs?

The range of 1.4 to 3.5 Vp is a "sweet spot" that R. G. suggested when I asked his advice before going to market. So far, the bag of 2N5457 that we have been picking from has not yielded many parts with Vp over 3.5 volts. So we have been getting a mix of parts that are good for phasers and some on the low end that are more like a high Vp J201. If we start seeing 2N5457 with Vp over 3.5 Volts, those will be another "remainder" line item. If you buy loose JFETs of any type, you will get unsorted raw stock.

[ncusack]

I've recently been working with some surface mount J202's I picked up for pennies a piece. I've populated some on breakout boards. The Vgs ranges from 1.7V to 2.3V and Idss from 2.2mA to 3.5mA on the 50 or so I've done. I see designs like the ROG amp sims and wonder how carefully they would select the jfets used in those designs. Sure trim pots allow you to get the voltages in line but that doesnt mean the gain of each stage will be the same at that voltage. I'd really be curious to hear from any of the larger production builders about how tightly they spec their parts for pedals like this.