Gold M8 - another Marshall JCM800 with FETs

[Renegadrian]

Ok M8s, I had some FETs around and they were begging to be used - So I first took a look at the Marsha Valve (which actually is only the first triode, so half a tube) and made a layout of it, then I went further putting another FET for the other triode, so the first preamp tube is covered.  
Dunno if this has been already made (I looked at Marsha and Electritabs, which is the complete preamp with FETs) so this stands in between I guess...Sounds great (as expected)
Vero layout below, I'll post the schem tonight (but hell it is the standard JCM you easily find googling)
Nothing new I know, but maybe someone could use this as a way of having fun on a boring August night (as it was for me!)

[azrael]

Cool! How does it sound?

[deadastronaut]

+1

nice one adriano... me too....any clips?..can we have the gain section too..

[Renegadrian]

More stages?! Well, you got electritabs circuit! Go for it!!!  
As for the clips, guys gimme a couple of days, I am gonna spend midsummer day with my GF family so I guess I won't be able to play or solder or record...What can I just say for now...How does it sound you ask...Well, it's very very close to a JCM!!! Eheheheh well, it overdrives the signal in a great way, I like it so much...

[Renegadrian]

time to post the schematic and I'm off to bed...4 am here...(put sleepy smiley here...)




Voltage applied can go from 9V to...I don't know, I used 24V too and it rocked!!!

[deadastronaut]

More stages?! Well, you got electritabs circuit! Go for it!!!  

done it ha ha...one of my first projects..

hmmmm wonder how this would be going into a mid gain distortion?....hmmmm.....

[gregwbush]

I realize this thread is nearly 2 years old... but

As it happens, i recently found electrictab's jcm-800 emulation schematic, want to build it, but don't have all the parts atm

So i built this Gold M8 "front end" as per the schematic the other night. Something to do, ya know


How does it sound? Well i tried it at 19.3 volts regulated, biased the first fet to roughly half of that... and it sounded not bad, a little grit, closer to clean than heavy.

I then went on to power it at 9v, biased the fet at about 4.5v..... and guess what... it farted and cut out and sounded like $h!t. I put this down to having a fixed drain bias on the second fet of 100k. Worked for higher voltage but no good for 9v (with the j201's i happen to use, of course)

LAST NIGHT...

i decided to build another portion of the jcm-800 emulation... The Last (output) section which is very (very) similar to that found at runoffgroove / thundercheif

Here is the perfboard layout i made

(a100k pot at output, 1 meg pulldown resistor in front)
by itself, it's NQR....

Put any kind of buffer (...low output impedance) in front... and it's great! i really like this...

I mucked around with stuff... put ROG tonemender "bass mid treb" pedal in front... and it sounds like a cranked valve amp! (ish, of course)....

What i realized was this output section of the jcm/thundercheif circuit likes to be pushed into distortion... but not too  much. There is a sweet spot. The gain control of the buffer in front let me know this

I also tried my (trusted) amz minibooster (npn buffered version) in front with really good results. I love the mini boo by it self but pushing this circuit gave it an output stage, ya know! sweet, sweet tones are there.

How hard it's pushed is crucial i've learned.

Sooooo.... when it comes to building my jcm-800 emu'.... i will be mindful of this

[gregwbush]

Said schematic

[Renegadrian]

THX for sharing your experiments - I had and sold some M8s and had great results with a regular 9V PS...

[gregwbush]

That being said... I'm going to have to re-visit the M8 now 

[roseblood11]

Said schematic

This looks similar to the PAL 800 JCM Emulator...
How could a presence control be added to this circuit?

[anotherjim]

The upper of the two 4k7 R's at bottom right. Make that a pot with a small value cap off its wiper to the junction with the lower 4k7 (guess 10n more or less to taste). That should give some upper lift.

[willqen]

Isn't this schematic of the "JCM800 Marshall Emulator" a Runoff Groove "Thunderchief" basically? There are a couple of minor differences. Or, did the JCM800 Marshall Emulator come first? Anyone know? Does it matter?
Will