I have the following problem with my Adcom GFP-565 preamp. It seems tp have
developed recently. I don't recall this in the past.

If I have the 'record selector' set to CD, and also the 'listen selector' set
to CD, I get audible pops under the following circumstances:

1. as I move the listen selector into or out of the CD position

2. when I cue my CD player to the next track (!) or hit the pause button (very
odd)

I generally have the same problem any time the record selector is set to a
source that I want to listen to.

For example if the record control is set to tuner, and I switch the listen
control to tuner I get a pop when I move the listen selector.
This happens regardless of whether I use the 'lab' or 'norm' main outs on the
Adcom and happens with more than 1 power amplifier.

Has anyone experienced similar problems? I'm wondering if it might be cold
solder joints on a ground somewhere, or possibly the listen or record selector
in need of replacement.

Any suggestions will be apreciated!!
Peace
Steve

Sounds more like a bad coupling capacitor or op-amp IC in the pre-amp.

Mark Z.


"Northamusi" wrote in message
...
I have the following problem with my Adcom GFP-565 preamp. It seems tp
have
developed recently. I don't recall this in the past.

If I have the 'record selector' set to CD, and also the 'listen selector'
set
to CD, I get audible pops under the following circumstances:

1. as I move the listen selector into or out of the CD position

2. when I cue my CD player to the next track (!) or hit the pause button
(very
odd)

I generally have the same problem any time the record selector is set to a
source that I want to listen to.

For example if the record control is set to tuner, and I switch the listen
control to tuner I get a pop when I move the listen selector.
This happens regardless of whether I use the 'lab' or 'norm' main outs on
the
Adcom and happens with more than 1 power amplifier.

Has anyone experienced similar problems? I'm wondering if it might be cold
solder joints on a ground somewhere, or possibly the listen or record
selector
in need of replacement.

Any suggestions will be apreciated!!
Peace
Steve

Do you have a component connected to the tape out? If so, disconnect it to make sure that the external tape deck (or whatever it is) is not contributing to the problem

- Jeff


Northamusi wrote:

I have the following problem with my Adcom GFP-565 preamp. It seems tp have
developed recently. I don't recall this in the past.

If I have the 'record selector' set to CD, and also the 'listen selector' set
to CD, I get audible pops under the following circumstances:

1. as I move the listen selector into or out of the CD position

2. when I cue my CD player to the next track (!) or hit the pause button (very
odd)

I generally have the same problem any time the record selector is set to a
source that I want to listen to.

For example if the record control is set to tuner, and I switch the listen
control to tuner I get a pop when I move the listen selector.
This happens regardless of whether I use the 'lab' or 'norm' main outs on the
Adcom and happens with more than 1 power amplifier.

Has anyone experienced similar problems? I'm wondering if it might be cold
solder joints on a ground somewhere, or possibly the listen or record selector
in need of replacement.

Any suggestions will be apreciated!!
Peace
Steve

Good point. Jeff. I disconnected the tape deck (and cables) from the preamp but
the problem remains. Also I tried this with headphones and was able to observe
two things:
1. the problem also occurs on the Adcom's headphone output.
2. The left side exhibits the pop, but the right side is clean. This is true
for phones and amp/speaker.

Hmmm....any other ideas?
Thanks,
Steve

So it really kinda looks like it is in the front end of the preamp somewhere. If it is an electrical component, I couldn't help, but one thing that I personally would try is some contact cleaner on the selector switches.

Note that this is probably a long shot as it seems an electronic section is most likely at fault. Also, the 565s are getting a bit old now so the possibility of bad caps or cold solder joints are increasing. However, I've fixed a lot of weird problems by just cleaning contacts and it's cheap and easy to try.

- Jeff


Northamusi wrote:

Good point. Jeff. I disconnected the tape deck (and cables) from the preamp but
the problem remains. Also I tried this with headphones and was able to observe
two things:
1. the problem also occurs on the Adcom's headphone output.
2. The left side exhibits the pop, but the right side is clean. This is true
for phones and amp/speaker.

Hmmm....any other ideas?
Thanks,
Steve

Hi Jeff:
Thanks again... First I cleaned the switches using a Chemtronics contact
cleaner, and then I resoldered all of the connection pins on both the 'listen'
and 'record' selector. Unfortunately there is no difference. I'm thinking about
changing the electrolytic caps that are in the audio section in case any of
them have failed (I haven't been able to spot any that were leaking).

Oh well...
peace
Steve

hmm,

Well, you've covered most of the easy stuff. Before going through all the caps, it sounds as though you are proficient with a soldering pencil, so you might want to go through and touch all the solder joints on the front end components of the bad channel (one last look for cold joints). If I remember correctly it is a single op-amp. Careful with the heat of course.

- Jeff


Northamusi wrote:

Hi Jeff:
Thanks again... First I cleaned the switches using a Chemtronics contact
cleaner, and then I resoldered all of the connection pins on both the 'listen'
and 'record' selector. Unfortunately there is no difference. I'm thinking about
changing the electrolytic caps that are in the audio section in case any of
them have failed (I haven't been able to spot any that were leaking).

Oh well...
peace
Steve

Oh, by the way, I forgot to ask, you DID try substituting a different CD player or putting a tuner in that input to confirm that the CD player itself isn't the problem didn't you?. You might be getting some DC leakage out of the CD player which might explain the behavior seeming to occur at the preamp selector as well as the pause and track operation on the player!

- Jeff


Northamusi wrote:

Hi Jeff:
Thanks again... First I cleaned the switches using a Chemtronics contact
cleaner, and then I resoldered all of the connection pins on both the 'listen'
and 'record' selector. Unfortunately there is no difference. I'm thinking about
changing the electrolytic caps that are in the audio section in case any of
them have failed (I haven't been able to spot any that were leaking).

Oh well...
peace
Steve

I'm a strong believer that you can break things while trying to fix them--especially using shotgun approach on things that might not be broken.

That being said, I have been known to use such strategies :-)

It sounds like the problem may be in the player itself (aren't you glad you didn't go and replace all of those expensive caps in the preamp??) I'd probably try a few more tests to confirm.

1) disconnect the player completely. Does everything work properly now (even when connecting the tuner to the CD inputs)? I'm assuming that it will.

2) disconnect all other input and hook the CD player up. Does the problem still occur when only the CD player is attached? I assume that this is also the case but should confirm.

3) swap the left and right channel inputs from the CD player to the preamp. Note: swap the cables at the CD end and not the preamp end. Does the problem also go from the left channel to the right? I assume that it will. (Note: if it doesn't then there may be a problem with one of your cables)

If all of the assumptions above prove to be true, then there is something wrong with the left output channel of the CD player. This now gets into a realm that I am not real familiar with. The first thing that comes to mind is some kind of DC leakage to the outputs. It might also be some kind of foul-up on the biasing of the output driver.

I'm not familiar with what kind of problems typically happen there. I know enough to be dangerous here :-) First, I'd likely try carefully touching all of the solder points in the output driver area with a soldering pencil. If there is a cold joint, this might be a fast way of finding it. If that didn't help, I would probably try and get a schematic (or at worst, i'd trace the circuit and create a schematic of my own) and then I'd compare the voltages at various points around the output stages of the left and right channels to find a descrepancy that might point to a particular component (starting at the actual output to the cables). An oscilliscope would be handy but you might still be able to learn about the biases with a decent DMM.

Other than that, someone else here with experience in this area might have some suggestions.

Hope this helps some.

- Jeff


Northamusi wrote:

Hi Jeff:
I didn't have a different CD player but I did swap the CD and tuner with their
respective inputs. Interestingly, the problem follows the CD player - a Marantz
CD63 SE. The Marantz unit is (I believe) approaching six years old and has
about 10 electrolytic caps in each channel of the DAC section.

Now you have me thinking: perhaps the problem is one of these caps. I took a
lookie and could not find any leaky caps, but I was unable to check the 'solder
side' of the circuit board, as it's a project to get the main circuit board out
to do so. Now I'm thinking 'DC passsing through the analog output due to a
faulty cap.' Perhaps I should just change out the 20 or so capacitors?

what do you think?

Thanks again for your help!
peace
Steve