So, this is my first post here so I apologize if I am posting in the wrong place!
I have this vintage SS integrated (amp+pre) stereo with around 35 years old and it stayed out of action for a couple years as I was using another vintage receiver.
A few days ago I brought it back to work and it's great as usual but it is with an annoying issue (that now I remember that it already had it when I put it on the shelf).
Right after I turn it ON if I immediately mess with the volume knob it makes a loud scratchy sound. If I keep messing the knob the scratchy sound keep doing for around 3 seconds but goes fading out until stop and then I have no noise anymore.
The same happens when I turn it OFF. It will make the same noise if I push the power button and immediately mess with the volume knob. I can repeat this process a thousand times and it will happen exactly like this every time. But only during 3 seconds after to power ON or OFF. Very weird.
I suspect that it has nothing to do with the volume potentiometer. Seems to me that it is something with a bad capacitor somewhere. Question is... which one?
Anyway, I made a video showing the issue here:
YouTube
Any clue appreciated!
I have this vintage SS integrated (amp+pre) stereo with around 35 years old and it stayed out of action for a couple years as I was using another vintage receiver.
A few days ago I brought it back to work and it's great as usual but it is with an annoying issue (that now I remember that it already had it when I put it on the shelf).
Right after I turn it ON if I immediately mess with the volume knob it makes a loud scratchy sound. If I keep messing the knob the scratchy sound keep doing for around 3 seconds but goes fading out until stop and then I have no noise anymore.
The same happens when I turn it OFF. It will make the same noise if I push the power button and immediately mess with the volume knob. I can repeat this process a thousand times and it will happen exactly like this every time. But only during 3 seconds after to power ON or OFF. Very weird.
I suspect that it has nothing to do with the volume potentiometer. Seems to me that it is something with a bad capacitor somewhere. Question is... which one?
Anyway, I made a video showing the issue here:
YouTube
Any clue appreciated!
Hey AudioMan, thanks for the tip!
Now I am not exactly an electronic technician but just a very well intentioned DIY person with some small tools (solder iron, an old analog multimeter, etc).
The good news is that I know how to recognize a capacitor when I see one and I think I am right to suppose that we are talking about an electrolytic. However I have no idea how to test those guys to know if they are good or not.
Any advice?
Now I am not exactly an electronic technician but just a very well intentioned DIY person with some small tools (solder iron, an old analog multimeter, etc).
The good news is that I know how to recognize a capacitor when I see one and I think I am right to suppose that we are talking about an electrolytic. However I have no idea how to test those guys to know if they are good or not.
Any advice?
It helps to have a service manual or at least a schematic circuit diagram of the amplifier. Then anyone with some familiarity of circuit symbols can locate the likely parts. Do you have the brand and model number and can you locate a schematic on one of the service manual archives like Hifiengine, Electrotanya or Eservice? If you can't find any information, post the details here and we may be able to find some information for you.
First though, is the scratchy noise the same on both channels? You can narrow the search somewhat if you find that the problem is only in one channel. You can also buy very cheap parts testers from China that would test a signal coupling capacitor for some problems but not necessarily leakage current, which is likely what causes the noise when you operate the volume control. Your meter would probably need to be a bit more sensitive to read this tiny current.
First though, is the scratchy noise the same on both channels? You can narrow the search somewhat if you find that the problem is only in one channel. You can also buy very cheap parts testers from China that would test a signal coupling capacitor for some problems but not necessarily leakage current, which is likely what causes the noise when you operate the volume control. Your meter would probably need to be a bit more sensitive to read this tiny current.
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Nothing to complain about.
A leaky capacitor would *always* make pot crackle ... yours does not.
What´s happening is that *during turn on/off* voltages inside are setting up , from 0 to working voltage or viceversa.
Now a perfectly good cap will pass some DC current while it´s charging/discharging and that current can make your pot crackle.
A leaky capacitor would *always* make pot crackle ... yours does not.
What´s happening is that *during turn on/off* voltages inside are setting up , from 0 to working voltage or viceversa.
Now a perfectly good cap will pass some DC current while it´s charging/discharging and that current can make your pot crackle.
@Ian, thank you very much for the thorough information. I will try to find an schematic (I think that a service manual will be a bit more complicated) and will get back here. My equipment is of a domestic brand (from Brazil) called "Gradiente" that I bet you never heard about. They were very known to use JVC projects specially on cassette decks, but I am not sure that this one is the case. I will check this out.
@JMFahey, I really remember that it wasn't like that before so something went wrong and for certainly can be fixed. I am sure that this is not the natural behavior of this amp otherwise the original project would have included a relay to cut the signal along the turn on like some equipments (although it wouldn't solve the problem at the turn off). I understand when you say that it is not something to complain about, but it's VERY uncomfortable specially when I forget about the issue and mess with the vol pot wearing my headphones.
@JMFahey, I really remember that it wasn't like that before so something went wrong and for certainly can be fixed. I am sure that this is not the natural behavior of this amp otherwise the original project would have included a relay to cut the signal along the turn on like some equipments (although it wouldn't solve the problem at the turn off). I understand when you say that it is not something to complain about, but it's VERY uncomfortable specially when I forget about the issue and mess with the vol pot wearing my headphones.
With no signal input connected and in stereo mode, is the noise effect the same on both channels?
Actually, I have read of Gradiente products through posts here by DestroyerX. They seem like straightforward designs and older models are probably not complicated. There is a listing of some models at HifiEngine, perhaps yours is among them: https://www.hifiengine.com/manual_library/gradiente.shtml
Actually, I have read of Gradiente products through posts here by DestroyerX. They seem like straightforward designs and older models are probably not complicated. There is a listing of some models at HifiEngine, perhaps yours is among them: https://www.hifiengine.com/manual_library/gradiente.shtml
JMFahey has it pretty much covered.
I would just add that I think your issue probably is the pot... a 'good' or more 'perfect' pot would be far less prone to crackle in the presence of DC current flow in the wiper than an old one.
If there is no DC current then a good or bad pot will both be pretty much silent.
I would just add that I think your issue probably is the pot... a 'good' or more 'perfect' pot would be far less prone to crackle in the presence of DC current flow in the wiper than an old one.
If there is no DC current then a good or bad pot will both be pretty much silent.
The noise is on left channel only. Very loud. Cool to know that this brand is known outside Brasil! Anyway, I have found the schematics of it but it looks like Greek to me.
Here it is the link for it (from my Google Drive):
Gradiente_Model_166_Schematics.pdf - Google Drive
I got the service manual too:
Gradiente_Model_166_Service_Manual.pdf - Google Drive
PS: Refer to it as "Model 166" that is the VERY SAME equipment. They only difference is that the IA-II came with a black face while the M-166 was silver finished.
I'm saying that it wouldn't surprise me if the problem was the pot. Having looked at the circuit I would suspect the pot even more...
This is the volume control, and the cap that connects to the wiper of the control is drawn as a non polarised type (so not an electrolytic). 220k pF is 220,000 pF which is more commonly written as 0.22uF
This is the volume control, and the cap that connects to the wiper of the control is drawn as a non polarised type (so not an electrolytic). 220k pF is 220,000 pF which is more commonly written as 0.22uF
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So — and sorry for my ignorance as I am not a tech — in your opinion the best shot at this moment would be simply replace the pot?
The pot is the most likely suspect to me but I wouldn't give you a 100% guarantee without having on the bench in front of me such that I could do other tests and make a more informed judgement. However experience says 'pot'.
Is it of a type that can be cleaned... has it got openings in it or is it all sealed ?
Is it of a type that can be cleaned... has it got openings in it or is it all sealed ?
I got it!
I still didn't remove the cover to look inside. Will do this in the next few days and will get back with further info.
OK
The 166 schematic I'm reading, shows a 1uF electrolytic where the film cap is - it might be worth checking which schematic and which type of cap. applies to the amplifier you have.
A tapped volume pot, as it appears to be for a the loudness function, isn't an easy item to find, since loudness controls were phased out long ago. I suggest first trying to source a tapped, dual 100k ohm volume pot (i.e a log. or audio taper pot.) before trying to remove it.
You can identify tapped pots as having 4 pins instead of 3 for each potentiometer section, or 8 pins in total here. The next problem is to determine whether any pot. you may find will fit the PCB correctly, with suitable pin spacing. If the pot is not fitted to the PCB on your version, so much the better.
A tapped volume pot, as it appears to be for a the loudness function, isn't an easy item to find, since loudness controls were phased out long ago. I suggest first trying to source a tapped, dual 100k ohm volume pot (i.e a log. or audio taper pot.) before trying to remove it.
You can identify tapped pots as having 4 pins instead of 3 for each potentiometer section, or 8 pins in total here. The next problem is to determine whether any pot. you may find will fit the PCB correctly, with suitable pin spacing. If the pot is not fitted to the PCB on your version, so much the better.
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