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Old 3rd February 2012, 09:49 PM   #1
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Default Please help me with a few questions and a idea for an old PA

Hi guys. Please be patient, as I'm trying to educate myself alittle. I have an old Bogen 50 that I want to play around a little a bit. I was think about something like the Soldano SLO100 preamp section to the old Bogen poweramp. Could you please tell me how to separate the orginal poweramp from the orginal preamp. It is tied into the preamp by pin 6 and 8 of V2b by the circuit I have in question. I have put red arrows pointing out the circuit section that is in question. Could you please tell me what that section does, and how to tie it into the new preamp section I was thinking of. Please feel free to change anything to make it a better design. Image A is part of the orginal schematic. Image B is the circuit in question. Image C is what I'm shooting for. Yes I know that the Soldano SLO is 100 watts, but still shooting for something simular. Thanks, David.
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Old 4th February 2012, 02:05 AM   #2
Enzo is offline Enzo  United States
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The circuit in question is the "negative feedback" circuit of the power amp. Often abbreviated "NFB" in amp discussions. You don;t want to eliminate it until you have a good reason to do so.
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Old 4th February 2012, 03:28 AM   #3
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Well, a good reason might be that the Slo does not use NFB. It does use a LTP rather than the cathodyne but since most of the distortion comes from the preamp section it should not matter too much. That being said, it is tricky to lay out a high gain amp.
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Old 4th February 2012, 04:24 AM   #4
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Thanks Enzo and Printer. Off to do more research. Thanks
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Old 4th February 2012, 07:34 AM   #5
Enzo is offline Enzo  United States
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Printer, that is a good point. I figured that if he didn;t know what it was, perhaps he ought not be yanking it out of the circuit a priori. It may not be part of the Soldano design, but it was part of THIS power amp, and while removing it may cause no grief at all, it also could reveal some stability issues or other artifacts. Easy enough to disconnect and find out, once things are built.
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