Boogie Monster: picking the J201s

[micmac]

Hi all!

I'm gonna get started on the Boogie Monster soon, tomorrow I suppose. I have a cheap transistor tester that shows Vg(off) and Idss and about 20 J201s (SMDs on adapters). So far I measured 10 and they have Idss from 1.1 to 1.4mA and Vg from 553 to 799mV.

I read a post somewhere here on the forum earlier that suggested that depending on what part of the circuit a JFET is in it may be prudent to use higher Vp or lower Vp. I.e. if it's where headroom is important, place a higher Vp JFET, otherwise lower Vp. I'm hitting myself in the head right now because I can't find this post anymore.

Boogie Monster build doc

I don't know much about schematics, but I guess Q1 and Q2 look a bit similar in the sense that they're both connected to Vcc on their drains. Q3 and Q4 look similarly connected to Vdd. And the Q5 looks different again. But really I have no clue

Could a kind soul please give me a hand here?

Kind regards,
Seb

 

[spi]

The reason for all the trimmers in this circuit is so you can adjust the bias for the transistors, accounting for the variations in their specs. You'll be fine, they're all roughly close enough to not impact headroom.

 

[temol]

If you have genuine SMD J201's I'd pick random pieces. Maybe except Q1 - I'd pick one with rather higher Vp - 0.7-0.8V.
Use sockets, do not solder transistors directly to the pcb.
Vdd and Vcc - no magic here. It's a positive supply rail. Vcc has one filtering stage (R101 + C100), Vdd has two filtering stages (R101+C100 and R102 + C101+C102).

 

[Fuzz Wizard]

Why the SMD J201 if you don’t mind me asking? It seems like everyone here uses the SMD over the thru-hole. I ordered some thru-holes for my boogie monster, should I reconsider?

 

[owlexifry]

the transistors don't really need to be 'selected' for this build.
as @spi mentioned, each transistor (except q5) has it's own bias trimmer for adjustment.

you may want to look into trying out this build with a higher supply voltage.
it sounds ok at 9V... I guess most people are pretty happy with it that way.

i wasn't too satisfied, so i built a charge pump circuit that has 17V, 25V, 33V outputs available.

IME, the more voltage, the better it sounds

Why the SMD J201 if you don’t mind me asking? It seems like everyone here uses the SMD over the thru-hole. I ordered some thru-holes for my boogie monster, should I reconsider?

because SMD is a lot easier to get.

nothing wrong with thru-hole, use those, they're great!

 

[spi]

The main problem with through-hole is that these days a lot of the ones you can find are either out-of-spec or outright fake. Totally fine to use if they are ok, just make sure you check they are valid.

 

[temol]

I have a cheap transistor tester that shows Vg(off) and Idss and about 20 J201s (SMDs on adapters). So far I measured 10 and they have Idss from 1.1 to 1.4mA and Vg from 553 to 799mV.

Idss readings seem to be rather high. For MMBFJ201 you should expect somewhere around 0.5-0.7mA (1mA max, according to the datasheet). What kind of meter is this?

 

[micmac]

Hi all!

Thanks very much for all of your replies! I didn't expect that many! I'll take your suggestions to heart and not worry so much about the JFETs in the Boogie Monster. I checked and found some sockets that I can use in my tool box, so I'll use them here for the transistors so I can swap them out quickly and not damage them while soldering.

temol I got this "T7" tester for 25€ on the Internet. That's what I used for the values in my first post. I agree the Idss values look too high.

I bread-boarded the ROG Fetzer Valve Vp/Idss tester last weekend and the Idss values I measured with it were in the ballpark you mentioned, 0.5-0.7mA. So I think the Idss values measured with the T7 tester might be off a bit. But the Vp values it spits out are about the same that I got with the bread-boarded tester.

Also, while it looks like the T7 can find out which leg is the drain and which is the source, actually when you turn the transistor around in the test socket then the result is actually not the same and S and D are reversed But anyway, I like to test with the T7, it's very handy and can check also caps, resistors, LEDs etc. Can't complain considering it only cost 25 bucks.

Have a good day everybody! Wish you all the best and catch you later!

Seb

 

[micmac]

Oh forgot to mention something. Today the Boogie Monster kit arrived. And to my surprise it didn't contain the SMD J201s but instead Musikding put TO-92 J201s with an "F" marking on them and also a string saying "BAI7", or maybe "BAT7" or "BA17". And they measure at a bit higher Vp than the SMD J201s I have: 0.7 - 0.85 V. So I think I'll try these first with the Boogie Monster. The kit came with a sticker on the bag suggesting it was packaged in December 2022. So it looks like Musikding still has a few TO-92 J201s around Although their Vandal From Hell kit I got recently did contain SMD J201s. Anyway. Sorry, hope I don't bore anybody with these details. Sorry! Bye!

 

[temol]

These cheap LCR meters are useful, but they usually have problems with JFETs. ROG Fetzer Valve JFET tester is reliable and easy to build (vero, breadboard).
I guess you can use any J201 (THT/SMD) and not worry too much about their parameters (as long as they are in the Vp range of roughly 0.6-0.8V). You have trimmers so there will be no problem with setting the drain voltages. Additionally - I don't think there are (or at least I've never seen) specific target drain voltages. There are only suggestions and reports from people who built drBoogie. You start with 1/2 Vcc - if it suits you, leave it as is. Or you are looking for your own settings.

 

[micmac]

Hi all,

It worked out fine. I went with the through-hole J201 from the kit and put highest Vp to lowest (0.8 to 0.6) from Q1 to Q5. And then I set the drains to a bit over 6V at Q1 till Q4 as per ROG calculator.

It sounds amazing. Never played anything with this much gain in my life. Always wanted the real thing but the prices are insane (at least in EU).

I was a bit afraid because I read some threads here in the forum about it squealing. But this one doesn't squeal and it's eerily quiet (noise-wise) while having tons of gain and volume.

Would have been even nicer if it had a clean channel as well, as I run it into the fx return. And why the tone stack knobs are reversed I'll never understand But hey, it's still a great pedal.

Thanks again!
Seb