My vote is a Zendrive clone

Given that the caps in the HT power supply are rated at 350V, I would guess they are running the filtered DC to the plate resistors at around 300 volts. Most Marshall preamps run this voltage between 245 and 350 volts, so it seems in the ball park.

You might try bypassing each side of the switch with a 1M-2M2 resistor. So from common to each pot wiper connection. That should maintain the DC bias across the switch but limit the signal when disconnected.

Just a shot

It's an on-off-on switch The LEDs are always connected and active when in the center switch position. The center lug of the switch is connected to ground. The other sets of diodes are connected to the respective outside lugs. The lower Vf diodes will take over from the LEDs when they are activated. ...

I find SW2 on the input of the LT1054 to be interesting . It's not mentioned in the documentation and is not on the pcb.

I've been looking at this a bit more yesterday, and found the OD880 which is quite similar to a RAT with opamp buffers, but without the voltage doubler. what I don't understand is why on both the OD880 and the OD820 the output buffer/gain recovery is inverting? Maybe there is a good reason for this...

Did you use R13?

Baja,

Maybe a silly question, but how are you accounting for the asymmetric clipping in early gain stages of the real amp?

Thanks!

Sounds like the fet might be leaky and need replaced. damaged gate junction or something the like.

BlueMeany wrote:Hi Baja, cool stuff! What is going on with the tl062 stage? Looks interesting.

I believe it is modeling the output stage behavior

The toggle is a on/off/on, so no clipping diodes in middle position? I do believe that is correct. This should correspond to the 100W mode, described as "cleaner, loud". I was under the impression that the louder setting were the LEDs , the lowest setting were the Schotky's and the middle...

The toggle is a on/off/on, so no clipping diodes in middle position? I do believe that is correct. This should correspond to the 100W mode, described as "cleaner, loud". I was under the impression that the louder setting were the LEDs , the lowest setting were the Schotky's and the middle...

Schematic.png Here ya go, I'll upload a pinout for the 3PDT shortly. I have PCBs ready to go for this if anyone wants em. I'm aware that Q5 appears to be upside down, I reconfirmed this multiple times, it is correct. Since these are 2N5457 the Drain/Source is interchangeable. thank you very much in...

I was wondering why Friedman and others have Vbias going through an op amp? Is there an advantage to this like less noise or is this just something you do with unused op amps? screenshot.642.png It provides a low impedance bias rail that is very stable. Plus it's something to do with that left over...

C12 could be a 1n capacitor, as noted by Pakrat in his post: https://www.freestompboxes.org/viewtopic.php?f=7&t=27775&start=80#p264115 C12: 12pf MLCC? ( Marked "CDM 102 +/-5%") ...even if, in the following post he says: Correction, C12 is indeed 120pf silver mica. Sorry about that...

Yes wired in anti-parallel, like normal to ground clippers, it is just the body diode that does the clipping. If you want the internal zener clipping of the mosfet, you have to wire them like zeners.

@rmroza - just in case you missed this earlier reply. Also, it may be the angle of the pic but to me LED3 and LED4 by IC3 look like they are facing the same direction. They should be facing opposing directions. One flat down, one flat up. Same with the 2 LEDs next to IC1. The cathodes should face op...

Interesting, what difference does it make? It guarantees you a stiff 4.5v dc bias voltage - the op amp has a very low output impedance compared to the high impedance (5k in this case) from the 2 x 10k voltage divider. I think the fried man (or whoever laid the board out) made a stupid layout mistak...

I do Tayda for pots however small bear and mammoth are great as well for hardware :applause: Biggest issue with Tayda and pots is they don't carry a wide variety of pcb mount right angle pots. Especially in anti-log. Which is why I suggested Mammoth. Steve at Small Bear carry just about everything ...

rmroza wrote:Thanks. I was just about to it myself since I have the time....now

What about the PCB pots? I'm having a hard time locating all the necessary variations in the states from my sources!!!

Mammoth Electronics has them all