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Pure sound 20th April 2013 04:27 PM

cyrus aca7.5 help
Hi all, again im back with another problem.
Before i start can anyone point me in the direction of what parts i should be changing or checking.
The problem is with the pre amp,i am getting noise on one channel like a rustling noise / crackling noise ,not all the time but most of it.
Its does not change when i turn the volume up,nor does it change when i unplug all inputs or change from cd to tuner.

Is it a cap drying up ?????

Thanks Help would be most appreciated!!!:D

Ian Finch 20th April 2013 09:45 PM

Post a schematic or link to one and someone will be able to at least make suggestions.

Pure sound 21st April 2013 01:31 PM

I cannot find schematic so im stuck. What i have done is took out and tested the 2 largest caps in the pre amp 4700uf 50v and they are reading 3900uf thats on the limit!!! could this be causing the noise??

Ian Finch 24th April 2013 07:56 AM

Changing power supply caps won't hurt if the quality you fit is as good as original but it is unlikely to help in a preamp. - It is not old enough nor would it get hot enough to suspect caps, tbh. Taking stabs in the dark using hearsay as a basis for a faultfinding is not sensible either. How did you decide the 7.5 preamplifier was the problem?

Obviously the noise starts after the volume control and that eliminates the input circuits and their switching. That leaves the line buffer and any muting relay, circuit etc.
The issues with preamps start with the voltages to the relevant line amplifier(s), connections and switching; including relays, CMOS switches, FETs and MCUs. To check these you need a schematic or a Cyrus service tech who knows the model.

Occasionally, small signal transistors, opamps and electrolytics become noisy but good quality film caps will last a lifetime and high temp. electrolytics are not far behind if used at reasonable case temperatures, <50C. This model Cyrus teamed with their monobloc amplifiers doesn't seem to be widely distributed, which might explain the lack of pirated schematics on the web. Cyrus are pretty tight on their technical backup and use just a handful of sevice agents so I can understand the difficulty - I can't get a scrap of info. for my Cyrus 5 integrated even. OTHOH, the very popular old Mission Cyrus 1,2,3 schematics are everywhere.

I don''t know your level of expertise but I think, considering the likely overall value of the system, that professional Cyrus service would be a sensible option. Even though it seems to a trivial fault, Messing with high value gear using DIY techniques and budget without proper instruments like a 'scope or even a simple signal tracer and schematic is not likely to be satisfactory, IMHO.

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