Soundcraftsmens lack of bass. Feedback cap?? - diyAudio
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Old 14th September 2012, 02:51 AM   #1
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Location: MN
Default Soundcraftsmens lack of bass. Feedback cap??

While I am trying to nurse my sick Zen Lights back to health, I grabbed my trusty old Soundcraftsmen PCR-800 amp from the closet and hooked it up. and wow again those zen lights just KILL everything in terms of clarity! But to my point....

I remember comparing my PCR-800 to a Bryston 4B and hooking up the Bryston was like adding a subwoofer! there was another octave on the bottom end! I had that same experience hooking up the PCR-800 tonight. where is the bottom end? even the Zen Lights have more low end?

Now the PCR has a 25uf input coupling cap so that should be plenty big. and the feedback circuit has a 220uf cap to ground. which I would think would be big enough. how do you calculate the LF corner??


Here is a crappy copy of the schematic R15 is 680 ohms and R14 is 22K
The pro version of this amp changes those values to R15 - 1600 and R14 16K which I am assuming changes the gain??
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Old 14th September 2012, 04:53 AM   #2
RJM1 is offline RJM1  United States
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F = 1/( R*C ) will give you the -3db point of the RC network. I can't really see the schematic but if your feedback network has the 220uf cap in series with the 680 ohm resistor this would give you a 3db point of 1/(.00022*680) = 6.7Hz. Maybe your input or feedback caps have gone bad?
My guess would be the 220uF 16V caps to ground in the feedback network. I've never trusted 16V caps and always replaced them with 25V caps.

Last edited by RJM1; 14th September 2012 at 05:08 AM.
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Old 14th September 2012, 10:24 AM   #3
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Thanks for the info. the 680ohm is in series from the output to the negative side of the diff pait and the 22K is in series with the 22uf cap to ground.
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