Guitarist and Amp in separate rooms?

Nope, no clippers in the circuit shown. D1 is a biasing diode and keeps V1b cathode at about 0.6volts.

This is a very "hot" bias and V1b will pass about 4mA and with a 407k anode load there will be very little anode voltage. I would expect the stage to give a lot of distortion....OR! R7 could be a misprint and be 47k in which case V1b has a Va of some 100V and would work fine.

Interesting to see the channel switching unit is just a chip array of bipolar transistors! "We" at least use FETs for signal switching and the valve snobs even criticize that!

Dave.
 
It's actually 470k! Okay so no "diode clipping" on the split-channel JCM 800? So what jams it's gain up so high on the lead channel?

What about this one? This is the JCM 900 Dual Reverb - regarded by many Marshall cork-sniffers as the ugliest sounding bastard Marshall ever made. I personally don't think they're that bad, and lots of pro players use this amp.
jmp52-02-iss10.gif
 
yes Greg that looks like a diode clipper, BR2. No idea if that is causing the "ugliness"!

My first bet would be on the input op amp, IC1a since it has a gain of about 17dB and probably clips on peaks. A further problem with the TL0 series is that they can "latch up" (down?) to the negative supply when overdriven and that sounds nasty.

And fork! You said "our" series ones were complicated?? LOT o bloody op amps in the 52!

Dave.
 
ecc83 said:
yes Greg that looks like a diode clipper, BR2. No idea if that is causing the "ugliness"!

My first bet would be on the input op amp, IC1a since it has a gain of about 17dB and probably clips on peaks. A further problem with the TL0 series is that they can "latch up" (down?) to the negative supply when overdriven and that sounds nasty.

And fork! You said "our" series ones were complicated?? LOT o bloody op amps in the 52!

Dave.
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Yup, a lot of nonsense in there, and that's probably why they don't sound as smooth and organic as the older, simpler designs. I mean, I don't pretend to fully understand that schematic, but there's a lot of shit in there you won't find on a 1959 or 2203 circuit diagram. The 900 DRs have a harshness to them that isn't particularly pleasing to most people. The cleans are great, the "crunch" is okay, but the overdrive sound is grainy and brittle. I don't think they're that bad in the right hands, but I don't want one. That was an awkward time period for Marshall.

And to be fair, I do criticize your Blackstar amps sometimes, but I'm not crazy about many of the modern era Marshalls either.
 
Greg_L said:
Haha, I have a 100w Marshall 1959 Super Lead feeding a Greenback loaded cab rated for 100 watts. Some Super Leads have been measured at approx 170 actual watts when driven to the max. I know one day it's all gonna blow spectacularly. At that point I will rebuild and do it all over again. Rock and fucking roll. :D
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That's actually pretty common, because amp output ratings are usually published in reference to some percentage of THD.
 
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