From: trevor@rageaudio.com.au   
      
   On 1/10/2022 1:12 am, JC wrote:   
   > Trevor Wilson wrote:   
   >> I have a Meyer Sound 833 control unit on my bench. It has a weird   
   >> fault that appears to centre around a 15kHz oscillation that affects   
   >> one channel, directly, but is bleeding through to the other channel.   
   >>   
   >> Meyer Sound refuses to supply a schematic. They will repair it for a   
   >> set charge of US$592.50 (nice round figure). That's a bitter pill to   
   >> swallow, but it gets worse. I (and my customer) are here in Australia   
   >> and I figure on the freight charges to blow that figure out to around   
   >> US$1,000.00 or so.   
   >>   
   >> I am hopeful that someone has some experience with this product. Maybe   
   >> even schematics.   
   >>   
   >> TIA   
   >>   
   >> Trevor Wilson   
   >>   
   >>   
   >   
   > not familiar with the amp and not an audio guy but:   
   > 15Khz sounds like switching supply noise? Bad caps on power rails?   
   > JC   
      
   **Not power supply noise. The power supply is as clean as a whistle.   
      
   All electros have been replaced with high quality (Panasonic and   
   Nichicon) components.   
      
   The unit is pure analogue. NO digital stuff to be seen.   
      
   There are 25 dual OP amps (5532), a handful of bipolar transistors, 2 X   
   dual gate MOSFETs, four Vactrol opto-isolators and here's the big one:   
   27 preset pots. Every single one has been moved from factory settings by   
   a previous tech. Without access to factory service data, I have no   
   chance of restoring this thing to anything resembling normal operation.   
      
   I have been able to stabilise one channel (though I still have a low   
   level 2MHz oscillation to deal with). I was able to measure the   
   frequency response curve and fell confident that I can duplicate the   
   curve using a a 32 band, digital parametric EQ. I won't have the ability   
   to use the speaker feedback section, but that should be a concern, give   
   that the system is designed for sound reinforcement use, but will be   
   used in a domestic application. The speaker feedback system is designed   
   to protect the HF drivers under very high power operation. MY solution   
   should work well and will cost my client much less cash.   
      
      
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