Found this cool little thing at DIYSB. A fairly simple high gain circuit which is supposed to emulate a cranked Marshall using three MOSFETS with a J FET buffer up front. There is a simple treble roll of at the end of the circuit.
Write-up, schematic and a demo HERE
I built this, but it’s not working as is. Is the pinout for the j112 correct on this one? The source is on the middle leg on j112’s that I have. Could I just sub in another jfet that has a pinout that matches the layout, or just twist the legs? Also, does the big 470uF capacitor span 2 rows or 3? It’s hard to tell
ReplyDeleteDoh! Pinout of the J FET was wrong. It should be DSG as most western world J FETs. As it is a buffer the part number isn't very important since there is a unity gain buffer. Yhe 470uF cap should have 2 row spacing.
DeleteHi fuzzhead. The resistor R3-4,7k of Q3 drain, must go to B8,not A8
DeleteAh, yes it should! Thanks! Updated the layout.
DeleteHi fuzzhead. The R8 resistor in M12-J12 is 8,2k,not 10k.
DeleteThe Q3 drain resistor moving down a row was the fix for me. It’s working now, with the 10k resistor in place for R8. I‘ll sub in the 8k2 when I can to see if there’s a noticeable difference. What about the 220uf capacitor? In the schematic it looks like a 220nf to me.
ReplyDeleteGosh, I need to get some glasses:-/. 220nF subbed 220uF.
DeleteI know what you mean, I was actually using a magnifying glass to read the schematic. With the changes made, it seems to be working as it should. I did notice that there’s a fourth 10uf capacitor on the schematic, but the layout as posted now is working, so I’m not sure about what it’s for.
ReplyDeleteCool, so would you consider it verified by now?
DeleteI would say so. It sounds pretty much like the demo, which isn’t a bad sound at all. I’m a sucker for the cranked Marshall sound, so I’ve built a bunch of the “Marshall in a box” pedals. This one falls somewhere in the middle for me, it’s not the best or the worst, but it’s an easy build that sounds how it should. Plus it uses easily available bs170’s, which is a big plus as the jfets get harder to find.
ReplyDeleteCheers! it is tagged. Yes, the use of BS170's is one of the things that made it appealing to me.e
DeleteJ201 / 2n5457 work?
DeleteYes, but for Q1 only. Q2 to Q4 is MOSFET transistors.
DeleteGreat sounding crancked Marshall !
ReplyDeleteI used 6k2 for the drain resistors, that gave 6v on the drains (should be 6 to 6,75v according to Jonny Reckless). 4k7 gave 6,8v which was ok, but lacking a tiny bit of gain for my taste