Citation 12 Deluxe Repairs

[tgraan]

Hi all, new to the forum, first post.

Recently acquired a Citation 12 Deluxe in very good physical condition. After running it for a short time I noticed some distortion in one channel when bass demands were high. Tracked it down to a bad power supply capacitor. Replaced all four power supply caps and things are looking and sounding very good. For the record, I replaced the 6000uF caps with 6800uF and everything seems to be fine. Output voltages with inputs shorted are 8 mV in one channel and 12mV in the other.



After searching this forum I found and read the several threads devoted to this amp and common mods. Not sure that I want to build the Nelson Pass Mosfet version yet, but in the mean time I installed his power supply mods.

So here's my questions. I thought that the next relatively simple and inexpensive step would be to replace all of the remaining electrolytic capacitors in the circuit (there are only 10). Does this sound like a good idea?

Second, there is a 250uF cap on the input. Why is it so large? I assume that it is doing something other than blocking DC. Is it important to replace this cap with one the same size?

[Nelson Pass]

Originally posted by tgraan
I thought that the next relatively simple and inexpensive step would be to replace all of the remaining electrolytic capacitors in the circuit (there are only 10). Does this sound like a good idea?

Second, there is a 250uF cap on the input. Why is it so large? I assume that it is doing something other than blocking DC. Is it important to replace this cap with one the same size?

It's a good enough idea to try. The input cap doesn't have to
be that value at all. Use whatever appeals to you, or try direct
coupling it.

[GRollins]

A cap in series with the input blocks DC, which you can think of as 0Hz if you like. The question is not so much whether it blocks DC, but how much AC it blocks. The larger the cap, the lower the frequencies that can get through.
Reducing the size will give you less low end, but given that a 250uF cap against any reasonable input impedance is going to roll off somewhere well under 1Hz, you've got plenty of leeway.

Grey