Look at this Boss MD-2 schematic: what a strange circuit!

[Steben]

What the...?
Look at this distortion section:
Opamp clipping followed by strange tranny stage (like a split version of the Push-Pull Fuzz?):

http://experimentalistsanonymous.com/diy/Schematics/Distortion%20Boost%20and%20Overdrive/Boss%20MD-2.jpg

[WGTP]

Interesting, I don't fully understand, but why would you have a discrete op amp followed by 2 stages of non-discrete???   

[Sir H C]

Noise.  Often times you can get lower noise with discrete devices.  Once you have some gain, the rest of the stages noise contributions matter far less.  That would be my guess.

[Steben]

Nah, modern opamps have better noise rates than discrete designs. The decent way is the other way around. In -> High gain low noise Opamp -> Ge trannies.

But I wondered more about the following stages, not the difference in opamps.

[WGTP]

I don't know enough to comment on the part your talking about.   I've been interested by Boss' use of the discrete op amps in some of there other pedals, so I found it curious the way they were doing this one.  Looks like there are 2 gain stages, the discrete and the non.  Since it is a Metal Pedal, and their chart shows it on the left/metallic side, I'm assuming that the op amps may all contribute to the distortion along with the push pull section, which is probably an attempt at duplicating a tube output stage (obviously).

Does anyone remember the PP stage that Joe Davidson had up a year or so ago?

Also interesting tone section.   Thanks for posting it. 

[Johan]

Interesting, I don't fully understand, but why would you have a discrete op amp followed by 2 stages of non-discrete???   

..looks to me like a push-pull amp, but clearly not intended to push current..so Im guessing, to simulate the last stage in a push-pull amp..just guessing thou...

johan

[Paul Marossy]

Yeah, it kind looks like a push-pull arrangement. It looks to me like they are amplifying the hell out of the positive and negative cycles and then recombining them or something like that... 

[DDD]

1. Capacitors at the input and output of the weird transistor stage are NOT polarized enough to work properly with the input\output AC signal that is approximatrly equal to "rail-to-rail" voltage. So they should distort the signal somehow.
2. Emitter follower at the output of the stage should distort also due to the high level of the signal and its own slight asymmetrical bias.
3. The stage itself adds some asymmetric distortion due to the difference of PNP and NPN trannies' properties.
All the above mentioned features together give some weird sound.

[lovekraft0]

Looks to me like it'll probably generate some crossover distortion, and maybe cancel some 2nd harmonic content, like a real class AB tube amp pushed too hard - I wonder if it sounds anything lke the real deal. 

[Paul Marossy]

Looks to me like it'll probably generate some crossover distortion, and maybe cancel some 2nd harmonic content, like a real class AB tube amp pushed too hard

I think you're onto something there lk...