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RE: Dynaco 400 left channel crackles when furnace cycles

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In Reply to: RE: Dynaco 400 left channel crackles when furnace cycles posted by ttone007@gmail.com on December 28, 2010 at 09:44:28

I'd suspect a power supply issue somewhere, letting through a transient in the AC when the furnace cycles. Since the 400 uses a common power supply for both channels, and given the noise happens with both amps, I doubt it's your amps. I'm wondering if it's something upstream causing it.

- Do you have a preamp or source that 1) is feeding both 400's, and 2) has separate power supplies for left and right channels?

- Is the noise affected by the 400's volume controls?

- Does it happen if you have nothing connected to the amps (other than your speakers)?

A little experimentation and simple deduction should help isolate the cause...

Follow Ups:

RE: Dynaco 400 left channel crackles when furnace cycles - ttone007@gmail.com 10:19:40 01/13/11 (1)
Jon,

Thanks for the response! These are good ideas to try to isolate my issues with both amps.

FYI one Dynaco 400 is directly connected to my audio mixing console. The console has "A/B" switching for two sets of speakers and amps such as my larger JBL 4311 monitors and smaller nearfield JBL Control Ones. The console outputs appear to be clean.

The other Dynaco 400 is in my listening room powering B&W DM110's and downstream from an Adcom preamp. In both cases the crackle happens at a low level and unrelated to mixer or preamp output levels. I will test as you suggest and post the results soon.

Thanks!
Mike
- RE: Dynaco 400 left channel crackles when furnace cycles - ttone007@gmail.com 11:46:08 12/11/16 (0)
  Hello again Dynaco folks,
  
  Well, I still have had the low level lefty channel furnace cycle noise after all these years.
  
  Now my older of the two Stereo 400's has a constant low level static or crackle in the left channel. This noise goes away by turning down it's input pot. So I'm guessing I'll be diving in on the PC29 card? I have already done the Vishydale resistor mods on both amps back in 2008 on the PC28 cards.
  
  I guess I should re-cap and re-semiconductor all three cards (both pc28s and the pc29)plus the PC30 while I'm in there? I can get all the parts from our ebay source: quy-co. I also have the uprated relay kit from updatemydynaco standing by.
  
  Anything else to consider here?
  
  Thanks! Mike

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