Just spent 30 minutes with a Dirty Shirley...

CrazyNutz":3vxs1pet said:
Rdodson":3vxs1pet said:
I would assume that the Dirty Shirley has much less negative feedback than a BE100, so that is what gives it a less "tight" feel but also what makes the transition from clean to distortion so smooth.

I haven't really analyzed the circuits, but other than the tube rectifier in the DS, I would guess than the NF and power amp filtering go from less to more with the DS, SB, then BE. I think that is why the NF is getting backed off in the latest circuit revision of the BE, but I'd be interested in Dave commenting on the filtering. The power section of the DS is really special.
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The DS has the exact same NFB circuit as the BE. Differences are in the preamp, and the tube rectifier. The preamp has .022uf (BE uses .0022uf) coupling caps, this gives it a fatter tone, the cathode bypass caps are lowered to .47uf to keep it tight, and the preamp filtering is lowered, also keeps it tight. The first gain stage has a 220k plate resister, this makes the gain get gnarly, also makes it tight.
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.1uf power couplers also....aka JTM. Where are you getting your info from on the .47uf cathodes? I thought the same thing also based on a hand drawing layout of the DS until I opened up my DS once I got it. It has .68uf cathodes. I asked Dave if the DS had ever had the circuit changed or updated and confirmed it had not, only an addition of the structure switch and efx loop.
 
BrentSP":15scde1g said:
.1uf power couplers also....aka JTM. Where are you getting your info from on the .47uf cathodes? I thought the same thing also based on a hand drawing layout of the DS until I opened up my DS once I got it. It has .68uf cathodes. I asked Dave if the DS had ever had the circuit changed or updated and confirmed it had not, only an addition of the structure switch and efx loop.
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Yes, .1uf on the PI output, however on the mini I believe they are .022uf. The .47uf cathodes I mentioned were probably from the same hand drawn schematic that you are talking about.

I've built the DS preamp circuit (or modded other preamps to it) a few times, on one the .68uf cath bypass sounded better, on the other the .47uf sounded better.

At any rate If the man himself says they have always been .68uf then who I'm I to argue that :)
 
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