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i have two ps audio delta 100 amps. one of them has a hum problem when both inputs are connected. i found an old post on this forum that described the problem well posted by chris in oct. 2005. if anyone has had this problem and knows the fix please let me know.
thnx,
tim
from chris in 10/2005
"I posted this on the mail amp page but thought it may be better to put it here in the Ps Audio section... Please let me know if any of you have any ideas...
Ok, I am at wits end now and this is driving me up a wall! For the past few weeks I have noticed a very low volume hum coming out of my speakers. To notice it you have to have no music playing or have it at super low levels. It sounds like a grounding hum / loop to me but I can't for the life of me figure it out.
Originally I had though it was the Preamp since once I disconnected the amp the noise went away. After further testing I have found that it will occur with any source so long as BOTH channels are plugged in. If I unhook one channel the hum disappears in both channels.
I have tried things such as floating the ground, plugging the amp power directly into the wall, unplugging other devices on the same power run (other than stereo sources, ie lamps, fan...) and even plugging the amp directly into my iPod through an 1/8 RCA adaptor... All still resulted in the hum... Even with the iPod, the amp was silent with the RCAs until the iPod itself was plugged in (there was still a hum when the iPod was plugged in but not powered up)
Sonically the sound is still good and clean so long as you can have the volume loud enough to block the hum.
Any suggestions would be great!"
Follow Ups:
Obviously a ground loop. The clue is that neither amp does it alone.
I would start by taking an RCA cable and connecting it between the two amp's inputs. This would mean no actual input, you are just tying the two input grounds together through the single RCA cable between the amps. I am assuming the hum will appear. If it appears in both amps then you should be able to get rid of it through disconnecting the AC grounds. If it is only in one amp and always the same amp, then you might have to have this amp looked at.
Use this as your baseline. Try cheating the 3d prong on both amps, just one, etc.
sorry i didn't explain better. i bought the second amp because the original one had the hum. the hum only occurs when both input channels have an rca connector plugged in. the older post that i copied described the same problem. my question was/is does anyone know the fix. i sent it to a shop in the new orleans area but no luck.
Did you try my suggestion? Take a single RCA cable and connect the two inputs together and see if it hums. Let me know what you find.
sorry for the delay. i had to assemble things.
the amp still has the hum/buzz with inputs linked together. i had a shop in the new orleans area inspect the amp and they eliminated some of the buzz/hum but not all of it. (it was more pronounced in one channel)
i suspect power supply caps. this looks like the earliest model delta 100. i know there are at least three design changes. all three have different placement of the caps and rectifiers with the oldest being closest to the circuit boards. i guess i have to call cullen...
Why don't you have the caps replaced?
i'll probably have that done but i'm getting to the point of diminishing returns.
this version of the amp is the one with four 6800uf 63vdc caps per channel soldered directly to the circuit board. replacement may drive the price of the amp above the threshold however what is it worth as is?
thank you very much for your time and advice. it means a lot when someone with your credentials takes the time to help with questions.
tim
Thanks. I just like to make sure all of our products continue to bring enjoyment to people for many, many years. Let us know if we can help.
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