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Crown IC150a L phono "popping" when in auto-return or set to phono2

M

mariusl

New Member
Hi folks,
I'm new to the forum and might have missed something on this in my searches, in spite of trying. Hoping someone can nudge me in the right direction here

I found two D150a power amps and an IC150a, still in original boxes and in great shape, having been stored since the 80's sometime. After cleaning switches and pots to clear up some popping and scratching, there remains a rhythmic popping sound when set to phono 2 on the left channel. When using phono 1, there is no such problem until the TT is in auto-return, then the same characteristic rhythmic popping sound is heard, only on the left channel. I've tested with another pre-amp and the two D150a's and don't get the problem, so I'm thinking that there is something in the integrated crown phono pre-amp. - Any suggestions?

I'd like to fix the IC150a phono if that's the problem, but I suppose I can also use a separate phono pre-amp with the D150a's. Any suggestions on a phono pre-amp, or perhaps replacing the phono pre-amp in the IC150a?

Thanks for any guidance
 
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With phono 2 selected and no TT connected is the popping still present ?
 
Thanks for that fast response! :)
Yes, the same rhythm when the selector is set to Phono 2 and no TT connected.
 
It seems so, but I wonder if it is not some combination of issues in the TT during auto return and the phono pre-amp module in the IC150a. When using the TT with another amp, there is no problem, either playing or in auto-return. With the IC150a, the problem is only apparent in auto-return on phono1 (plays fine), or at anytime when set to phono2
 
If I remember correctly the Crown IC 150A had shorting plugs in the unused phono input. Maybe your problem has something to do with them.
 
There are some caps on the phono 2 inputs, but they are not linked. I tried with these caps removed and nothing connected and also with the TT connected to phono 2, with no change in the results. Are the shorting plugs somewhere inside?
I asked the fellow I bought the amps from and he said all the capacitors had been replaced in the IC150a at some point, so maybe there is some fallout from that.
 
Long shot -- Try cleaning the input select switch.
mariusl said:
all the capacitors had been replaced in the IC150a at some point,
Click to expand...
Including films and ceramic disc's ? Or just the electrolytic's which is usually the case.
 
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