amp: croan macro-tech 400
symptoms: crackling in the left channel, and unplugging the preamp doesn't affect it.
It does change with volume, louder, softer, etc.
I put it on the bench and cannot hear it.
I suspect the power caps, any suggestions?
In another case:
amp:
crown d150
symptoms, right channel has distortion. Dostortion clears away as amp is turned off, but for a brief period. I suspected the caps, here, also, but changed them and it still occurs. Output transistors?
Is there a definitive book on troubleshooting transistor amps?
Tube amps are easy, these are a PIA., but I would still like to learn.
tools?, no problems, there.
symptoms: crackling in the left channel, and unplugging the preamp doesn't affect it.
It does change with volume, louder, softer, etc.
I put it on the bench and cannot hear it.
I suspect the power caps, any suggestions?
In another case:
amp:
crown d150
symptoms, right channel has distortion. Dostortion clears away as amp is turned off, but for a brief period. I suspected the caps, here, also, but changed them and it still occurs. Output transistors?
Is there a definitive book on troubleshooting transistor amps?
Tube amps are easy, these are a PIA., but I would still like to learn.
tools?, no problems, there.
Hi, One would normally suspect the volume control first.Give it a
good cleaning with contact cleaner and test again.If it fails then
do a visual inspection of pcb and components for loose solder joints.
After this fails then get an oscilloscope and poke around the inputs and outputs and anything in between.You should be able to see something(noise)
but finding the source of the problem may take experience and knowledge
of electronic circuits. Good luck.
good cleaning with contact cleaner and test again.If it fails then
do a visual inspection of pcb and components for loose solder joints.
After this fails then get an oscilloscope and poke around the inputs and outputs and anything in between.You should be able to see something(noise)
but finding the source of the problem may take experience and knowledge
of electronic circuits. Good luck.
crackling noise
Oh, I think I have reasonable knowledge of electronic circuits.
My 2 degrees are in ELT and Computer science.
I am 59 and have not trouble shot any transistor circuits, since the late 1980's.
I design oilfield automation gear, and computer interfaces. I have written software for major oil companies and the above for the last 30+ years. This is not the same thing, but some of the same things apply. I took up building and repairing tube amps about 12 years ago, when I was asked to by a local music shop. I have never had an amp returned for anything other than a tube change and/or re-biasing, or maybe a tonal change in one or both channels. I hand build my own cabinets, and they are probably better than you can buy.
I was looking for help, but if you have to call names, by saying it may take a tech with electronic circuit knowlwdge,I can go elsewhere, no problem.
I thought I made clear that I have been working on tube amps for some time (as in "tube amps, no problem, but these are a PIA"). But I see I was mistaken.
Cleaning volume pots, on either amplifier will not cure the problem. That would have shown up the first time I tried to turn the amp up or down, and would have been oine of the first things I checked.. As I said in my first message, the volume control affects the volume of the crackling, in the macrotech indicating it is elsewhere in the circuit and not just a dirty pot, although it does go away, somewhat after playing for a minute or 2, but it does return.
The distortion in the d150 is not affected by volume, but goes away when power is shut off, as the caps discharge. In other words I can hear a clean sound as it gets to a certain discharge point.
Next, you don't actually reference any one of the amps, specifically.
The crown macrotech has a totally different problem than the d150.
Poking around on transistors will not help, either, as they either work or they don't. They do not "get weak" as tubes do, but are usually fairly stable. You can't normally "poke" a transistor and get it to work. Other parts, such as Capacitors dry up, resistors change value, sometimes, ....diodes go open or short, and can be measured, even with a resonably good dvm, such as my fluke rms meters, possibly even my old Simpson 260 ananlog meter.
Transistors rarely do. If they do, they fail (short or open).
I am able to use a scope ,but it has been a while. But I can re-learn anything. I do own 2 Hitachi dual-trace scopes.
I will leave this forum and go back to techs with knowledge, who are willing to help, not make fun or tell me things I already made clear. Thanks for your input, anyway.
I'm sorry I bothered any of you.
I can "shotgun" replace all of the transistors on the offending side and be done with it, along with resistors, caps, etc as there are minimal components on/in the d-150. That serves no pourpose, other than what it says "shotgun " that side of the amp. It teaches me nothing.
I just sold all of my NTE stuff (over 110 transistors) but I can obtain them almost anywhere.
again, thanks anyway.
Oh, I think I have reasonable knowledge of electronic circuits.
My 2 degrees are in ELT and Computer science.
I am 59 and have not trouble shot any transistor circuits, since the late 1980's.
I design oilfield automation gear, and computer interfaces. I have written software for major oil companies and the above for the last 30+ years. This is not the same thing, but some of the same things apply. I took up building and repairing tube amps about 12 years ago, when I was asked to by a local music shop. I have never had an amp returned for anything other than a tube change and/or re-biasing, or maybe a tonal change in one or both channels. I hand build my own cabinets, and they are probably better than you can buy.
I was looking for help, but if you have to call names, by saying it may take a tech with electronic circuit knowlwdge,I can go elsewhere, no problem.
I thought I made clear that I have been working on tube amps for some time (as in "tube amps, no problem, but these are a PIA"). But I see I was mistaken.
Cleaning volume pots, on either amplifier will not cure the problem. That would have shown up the first time I tried to turn the amp up or down, and would have been oine of the first things I checked.. As I said in my first message, the volume control affects the volume of the crackling, in the macrotech indicating it is elsewhere in the circuit and not just a dirty pot, although it does go away, somewhat after playing for a minute or 2, but it does return.
The distortion in the d150 is not affected by volume, but goes away when power is shut off, as the caps discharge. In other words I can hear a clean sound as it gets to a certain discharge point.
Next, you don't actually reference any one of the amps, specifically.
The crown macrotech has a totally different problem than the d150.
Poking around on transistors will not help, either, as they either work or they don't. They do not "get weak" as tubes do, but are usually fairly stable. You can't normally "poke" a transistor and get it to work. Other parts, such as Capacitors dry up, resistors change value, sometimes, ....diodes go open or short, and can be measured, even with a resonably good dvm, such as my fluke rms meters, possibly even my old Simpson 260 ananlog meter.
Transistors rarely do. If they do, they fail (short or open).
I am able to use a scope ,but it has been a while. But I can re-learn anything. I do own 2 Hitachi dual-trace scopes.
I will leave this forum and go back to techs with knowledge, who are willing to help, not make fun or tell me things I already made clear. Thanks for your input, anyway.
I'm sorry I bothered any of you.
I can "shotgun" replace all of the transistors on the offending side and be done with it, along with resistors, caps, etc as there are minimal components on/in the d-150. That serves no pourpose, other than what it says "shotgun " that side of the amp. It teaches me nothing.
I just sold all of my NTE stuff (over 110 transistors) but I can obtain them almost anywhere.
again, thanks anyway.
Hi, Geez your are rather sensitive,have some confidence ,what with
your tech qualifications it even impresses me.🙂 When I said poke with a
scope I mean look for the source of noise that you hear as in signal tracing.
That should help you zero in at some part of the amp.With your tools available I'm sure you will find it.Be patient those that have direct
experience with these amps will help.I understand your apprehension at
age 59 with not so good eyesight looking at tiny black bits of transistors.
Just be a little careful and you will do fine.To be frank crackling noise
can be easy or hard,you just have to be systematic and eliminate one
by one.Unless someone has the same problem as you have it's difficult
to pin point anything for sure. good luck.Pete Millet's site have some
electronic trouble shooting books as a reference do download them
for free.
your tech qualifications it even impresses me.🙂 When I said poke with a
scope I mean look for the source of noise that you hear as in signal tracing.
That should help you zero in at some part of the amp.With your tools available I'm sure you will find it.Be patient those that have direct
experience with these amps will help.I understand your apprehension at
age 59 with not so good eyesight looking at tiny black bits of transistors.
Just be a little careful and you will do fine.To be frank crackling noise
can be easy or hard,you just have to be systematic and eliminate one
by one.Unless someone has the same problem as you have it's difficult
to pin point anything for sure. good luck.Pete Millet's site have some
electronic trouble shooting books as a reference do download them
for free.
- Status
- Not open for further replies.