Well the ipod is one device where this is happening. Since the device has internal vc could be considered a pre-amp of sorts. Problem happens when ipod is directly connected to amp.
I have an all analog Adcom GTP-500 pre-amp same problem.
In my theater, I am using a Denon AVR-4308ci as a pre-amp same issue.
I have an older Sherbourn pre-amp for HT and get the same issue.
When different amps are used with any of these devices the problem does not exist. So my reasoning says the issue lies within the amp.
I have an all analog Adcom GTP-500 pre-amp same problem.
In my theater, I am using a Denon AVR-4308ci as a pre-amp same issue.
I have an older Sherbourn pre-amp for HT and get the same issue.
When different amps are used with any of these devices the problem does not exist. So my reasoning says the issue lies within the amp.
Does it make the noise if you just power the amp up with no inputs connected ?
If it's silent then perhaps there is a problem on the input side of things, again to see a circuit would help greatly.
Try that anyway. If the noise has gone then it could be a cap on the input that's leaky etc and the input resistance of the source is then causing a small current to flow through a faulty cap etc.
If it's silent then perhaps there is a problem on the input side of things, again to see a circuit would help greatly.
Try that anyway. If the noise has gone then it could be a cap on the input that's leaky etc and the input resistance of the source is then causing a small current to flow through a faulty cap etc.
No noise, without signal coming in. Just silence. Resoldered input wiring. No noise so far but the problem is that intermittent that I have no idea if the problem is fixed. Kinda crazy to think that all this money is spent on RCA cables for it all to come down to a cat-5 sized conductor and clipped into a board.
By some versions of the AW-100 (Ampliwire 100 AW100) from Electrocompaniet I discover often this problem and I must remove. Here are pictures of AW100 and the sockets between amp and power supply PCB :
http://www.diyaudio.com/forums/swap...ctrocompaniet-aw100-dmb-amplifier-boards.html
Question... does the power amp have a volume control ?
the model in post #1
Google Image Result for http://www.hometheatersound.com/equipment/pics/sherbourn_51500.jpg
"appears" not to have. Is it JUST a power amp.
You say the noise is affected by volume setting... yes ?
the model in post #1
Google Image Result for http://www.hometheatersound.com/equipment/pics/sherbourn_51500.jpg
"appears" not to have. Is it JUST a power amp.
You say the noise is affected by volume setting... yes ?
Yes, that is the amp I own. I use an amp and pre-amp configuration. I have several different amps and pre-amps in different rooms and the commonality is that no mater what pre-amp I use these amps have the scratching noise. Also when I use those exact pre-amps and a different amp, no noise. The noise is affected by the volume in that it occurs at low volumes most often, perhaps because I start listening sessions at low volumes and then increase volume as I move on. When they are turned up, they still make the same noise just louder.
Thank you in advance for you expertise.
Thank you in advance for you expertise.
I think we are gong to have to see a circuit.
What happens if you apply shorting plugs (signal to ground) across the inputs to the power amp. Does it make the noise then.
It's sure to be something really simple, but without seeing a circuit it's all guesswork.
Is there an input coupling capacitor on each power amp input that you can identify ?
The odd thing is you saying it's affected by volume setting... and the only thing that makes sense is that the problem is in the input network of the power amp, and that the different impedance a volume control presents as it is turned affects the noise... perhaps a leaky input cap.
You say no noise with inputs disconnected. Be sure !
Connect to a pre amp that you say is OK and noise returns.
Do you see ?
What happens if you apply shorting plugs (signal to ground) across the inputs to the power amp. Does it make the noise then.
It's sure to be something really simple, but without seeing a circuit it's all guesswork.
Is there an input coupling capacitor on each power amp input that you can identify ?
The odd thing is you saying it's affected by volume setting... and the only thing that makes sense is that the problem is in the input network of the power amp, and that the different impedance a volume control presents as it is turned affects the noise... perhaps a leaky input cap.
You say no noise with inputs disconnected. Be sure !
Connect to a pre amp that you say is OK and noise returns.
Do you see ?
This noise is signal related, no signal present = no noise, more signal worse noise. The first place to look IMHO is at any electrolytic capacitors directly in the signal path. (I have had similar problems with other ss amplifiers, and it was due to deteriorating electrolytic caps.)
Identify whether or not these amplifiers have electrolytic coupling caps in their input and feedback circuitry. These would be amongst the smaller electrolytics on the pcb. I would simply replace them with good quality elna silmics or similar.
Another thing to be aware of is that the connectors carrying the audio signals to the pcb from the rca jacks may be corroded - this is not necessarily visible to the naked eye unless extreme. Try a cotton tip swab and a little contact cleaner. This is probably a long shot, but worth a try.
As Mooly says a schematic would be helpful, as would really good close up pictures of the amplifier modules.
Identify whether or not these amplifiers have electrolytic coupling caps in their input and feedback circuitry. These would be amongst the smaller electrolytics on the pcb. I would simply replace them with good quality elna silmics or similar.
Another thing to be aware of is that the connectors carrying the audio signals to the pcb from the rca jacks may be corroded - this is not necessarily visible to the naked eye unless extreme. Try a cotton tip swab and a little contact cleaner. This is probably a long shot, but worth a try.
As Mooly says a schematic would be helpful, as would really good close up pictures of the amplifier modules.
So its very difficult to troubleshoot with no amp connected as the amp shuts off after several minutes. It has auto sensing on the inputs for power. So far I have never heard the scratching noises unless the amp is playing something looking into your other comments and calling company for diagrams.
Lol this is getting confusing. We are just guessing.
Circuit and piccys... and try it with the inputs shorted.
Ok, so I talked to one of the engineers and he said that all the amplifiers of this model and age are having the very same issues. He said for each channel the relay will need replaced and is going bad and the caps have gone bad due to drying out. He said when you remove them you can actually shake them and hear the parts rattling around. I asked what I could do to warm them up a bit and he mention the following items. This is the part where I got lost.
Unit currently uses
LF353 and or TL072
Could replace with Burr Brown
OPA604 or 2604 because Bi-Fet input, Dual IC, rather than conventional transistor.
What source do you all recommend for 80v 10000uF caps? Relays? Any thoughts would be great!
Unit currently uses
LF353 and or TL072
Could replace with Burr Brown
OPA604 or 2604 because Bi-Fet input, Dual IC, rather than conventional transistor.
What source do you all recommend for 80v 10000uF caps? Relays? Any thoughts would be great!
Relays... will have to be correct type to physically fit the PCB. They may be a "common" outline and type but you need to look, measure, look at the contact arrangement and coil voltage and current to pick a substitute.
LF353 and TL072 are common FET opamps.
Again would have to see circuit... they may not even be in the audio path and may be used as DC servo etc in which case swapping is totally pointless. The TL072 is perfect for that application.
If they are in the audio path the OP2604 is a personal favourite of mine for sound quality as the spread of distortion it produces favours the even harmonics. OPA604 is a single opamp.
The big caps... no idea in the US where you would get them
Can you not get the specific parts via the engineers you are talking too ?
LF353 and TL072 are common FET opamps.
Again would have to see circuit... they may not even be in the audio path and may be used as DC servo etc in which case swapping is totally pointless. The TL072 is perfect for that application.
If they are in the audio path the OP2604 is a personal favourite of mine for sound quality as the spread of distortion it produces favours the even harmonics. OPA604 is a single opamp.
The big caps... no idea in the US where you would get them
Can you not get the specific parts via the engineers you are talking too ?
OK, so I found the part number for the relay's from Mauser 526-R22-1D16-24. I ordered Qty: 14 capacitors directly from Sherbourn. I spent many hours looking everywhere online and capacitors of this type are nearly impossible to find. So I just went with OEM parts. I still need to order the Relay's which I plan to do tonight. I also spoke with the engineer again today regarding switching the Opamp chips. I am excited at this idea. I am going to order two chips and start with the two channel amp and try some listening tests. My nature tells me to go with the best chip OPA627, but in the interest of warming things up I am going to order the 2604 as this characteristic is the most important to me. Any thoughts on the matter?
But what do the chips do ? What are they used as ?
If they are servo/PSU etc you are wasting time/money and may even cause problems with stability etc. The OPA627 is a very high speed device and needs to be implemented correctly.
You have to see the circuit to make an informed descision
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