Adcom makes pop noise, normal?

bansheesho

So I got my adcom gfa-555 hooked up last night, and everything seems good with it. Caps looked ok, DC offset 3mA Left 27mA Right.

My only complaint is that there is a light popping noise every time an audio source is taken away or on shut-down. So for example if I am watching a tv show and I pause or fastfoward/rewind the DVR there is a audible popping noise. Same thing on a Blu-Ray opening menu when the theme music starts over. It happens any time the audio input is taken away.

I have done a bit of searching and have found a range of explanations from it being normal adcom behavior to adding resistors. My questions are: Is this normal? Will it damage my speakers? Can I fix it?

Thanks for your help

Syndil

I would suspect your pre-amp of being responsible for the pop before I would suspect the amp.

bansheesho

Well it's coming off of the sc-25 pre-outs not a preamp. The problem was not there before the amp, but I don't really have an extra amp or preamp to test it out with.

deronb1

It is not normal. Never had that issue with mine. Try and hook a CD player directly up to the amp and see if there are any strange noises when you change tracks or discs.

bansheesho

Okay, should be easy enough to hook up another source and try it out.

unc2701

Shut down /power up pop is normal. The source change is not. Is everything via digital audio? See if it happens with an analog source.

monepolk

I can say that I haven't had that experience with my Adcom GFA-555. So I agree that the pop is not normal.

leftwinger57

I proposed this question on powering down on my 555.When I shut it down I usually always left that room and went to another part
of the house and never noticed or heard anything.While it was spooling down what can be best described is like a deflating balloon.
Most said it's normal for amps to have power up or down noise quirks. Mind you this is only when spooling down ad not changing
sources.There is no noise what so ever on powering up and it's really instant on and for powering down I think it timed to a minute
or 2.There are other people who also have chimed in this exact question.

bansheesho

The pop on shutdown doesn't really bother me too much, though I suspect that it is related to the source change pop. I will use an analog source tonight to see if it still does it. I am also going to bring a dvom home from my work that is more familiar and much more accurate and will retest the DC offset again. I sent an email to adcom to see if they had any suggestions. Things I also thought of but have yet to try is using an adapter without a ground on, trying a different power plug from the one that the receiver is plugged into, rca ground loop filter.

Syndil

I wouldn't have bothered Adcom at this point yet. You need to eliminate the source/preamp (or in your case AVR) as the potential cause of the problem (which is far more likely) before troubleshooting the amp. The shutdown sound is completely unrelated to this issue.

bansheesho

Adcom just gave a generic statement about the amp being old and it should be taken to a repair shop.

DaveHo

This isn't the first time I've heard of getting popping sounds when switching inputs. I don't think there's neccesarily anything wrong with the equipment. The popping is an artifact of how the SC-25 mutes the output & the Adcom being direct coupled. If you mute the sound on the SC-25, do you get the pop then as well?

bansheesho

Playing with it yesterday I noticed that as I turned the volumIfe up the sound of the pop also increased. When I get home I will turn the volume down and see if the pop is still audible. If it is just an artifact is there any way to filter it out?

nguyendot

Have anything to do with the fact that the 555's don't have turn on/off relays?

unc2701

nguyendot wrote: »

Have anything to do with the fact that the 555's don't have turn on/off relays?

That's the source of the on/off pop that just about everyone with an Adcom knows.

I'm with Daveho on the sc-25 being the source for the other pops. The pausing/channel changing on the DVR, skipping on the DVD player, etc will interrupt the digital stream and make the muting circuits kick in which is passing that pop. The adcom is directly coupled, so you get great bass response but just about anything that presents at the input is at the output. Depending on design, a tube buffer might filter that out.

bansheesho

So I did some tests.
-With a digital source signal and the volume turned all the way down to -79 the pop is still at the same volume as it is when it is at -22
-If you bring the volume one click more down to --- (which I assume is muted completely) there is no popping noises.
-When there is an analog source connected through the receiver there is no popping noises if it is paused, ff, rewind. Though when the source knob is changed it does pop.
-I retested the dc offset with my better dvom. I found 4ma and 18ma so I am fairly certain there isnt a crazy dc offset problem with the amp (though my wife was running the amp a bit before that).

So do these findings mean anything to you guys? If it is just the amp design is there any kind of filter or modification I can do to prevent the pop?

deronb1

Because I have never had the kind of issue you are having with your 555, I cannot say what piece of equipment might alleviate the popping sound. I can tell you however, that after I hooked in a tube buffer, the strange noise after shut down quit.

bansheesho

Hmm. I have been thinking that if I can't get this popping noise sorted out and I can prove that the amp is in good condition then I might look into reselling the amp and going a different direction with my system. I wonder how much it would cost to have someone look the amp over for me.

monepolk

I'm not familar with the Pioneer & Adcom combo, but with my Denon 4311 & Adcom there is no popping when I change sources.

unc2701

reported.

monepolk

reported

Why?

unc2701

monepolk wrote: »

Why?

You missed it- spammer went through with some **** pills or something. The mods deleted them.

bansheesho

Are they suggesting I need a bigger amp to compensate?

bansheesho

I have been thinking about this a little bit, and I was wondering if there is anything that I could put in line between the receiver and the amp that would keep some kind of signal going to the amp? Someone had suggested a tube buffer, I'm not very familiar with these or what they do our how to even begin trying to pick out a decent one. In any case whatever I put in would have to not change the signal too much. Also, would a dac such as the ones from Jolida work as a tube buffer as well as a dac?

Jhayman

That's funny my friend has a Pioneer Elite SC-07 and he started noticing a popping noise just before the pre/outs stopped working and had to send in his unit for repair.
Though he was using Rotel Amps..
Apparently it's a known issue with Pioneer..

PolkieMan

You need to probably just remember to turn it down when changing sources or turning on/off.
I was always in the habit of doing it anyways.
A good example is the computer sound card pops the speakers/ amp when it shuts down using the sound card optical output stopped that but you my not have that choice.

bansheesho

Jhayman, do you have any idea what was replaced in your friend's receiver? I discussed this with pioneer customer service, their 2 suggestions were take it in for the factory firmware upgrade and if that doesn't work then it will need repair. I called the local pioneer repair shop and they said they couldn't get it in until after the holidays. I found the firmware update file online and did it myself it was super easy to bring it up to version 1055. Unfortunately it did not fix the problem, but I had little hope of it doing so anyway.

bansheesho

I have narrowed the source of the pop noise even further. The adcom amp is fine. The pop only occurs when the receiver switches listening modes while it is the device doing the decoding. For example if I am watching TV through the dvr or a movie through the bdp, the receiver is the one processing the signal and every time it is paused, fastfowarded, or rewound the receiver switches from what ever mode it was being processed in to stereo mode, and this change is what makes the pop noise to the speakers. I hooked up the laptop to the receiver through hdmi and sent it the signal via pcm, which does not change if you pause or do anything to the music. No pops at all.

monepolk

I'm glad that you found the problem, now you won't have to get rid of your amp.

bansheesho

Well I found the source of the problem, but I don't know if I can rectify it.