I just re-flowed one of the PCBs and no change.
I checked the DC voltages at the output with a multimeter and an oscilloscope. The channel I've been doing work (right) on is -30mVDC and the left is +4mVDC.
Next week I will see if I can plug in a bench-top lab power supply for the rails... and if that changes anything.
I checked the DC voltages at the output with a multimeter and an oscilloscope. The channel I've been doing work (right) on is -30mVDC and the left is +4mVDC.
Next week I will see if I can plug in a bench-top lab power supply for the rails... and if that changes anything.
It should be clear by now that just replacing parts everywhere you can, gets you nowhere. The issues are as pointed out in #6. This is an unusual construction, some models using damping materials that break down and there is a grounding issue here with the input stages. It should not be necessary to ground the power supplies as the floating DC supply may be a design feature which obviously worked OK on new products. Perhaps there is also a previous owner's meddling to correct?
Have you actually replaced the main electrolytics yet? Yes, the big expensive can ones but you can fit smaller value, cheaper types with the same or higher voltage rating temporarily, to prove a point. Since there are likely problems there, you can also test the transformer's effect, faults or mounting problems by unmounting it and resting it securely on a piece of timber etc.
Why not also apply a little logic, by first removing the signal input and ground wiring to the PCB to track down where that noise source really is. If, when you short the inputs you get higher noise level, there is definitely a grounding problem there. That should not be the same ground as the chassis either.
Maybe it's time to read a little about amplifier ground wiring and construction rather than looking at components as the only culprits. Check the ground isolation of input sockets, too.Here's one place to start looking - there's a mass of material on amplifiers spread over several sections and general topics. Look at earthing/grounding issues for a start. If nothing else, you can't help but benefit from the practical information.
Have you actually replaced the main electrolytics yet? Yes, the big expensive can ones but you can fit smaller value, cheaper types with the same or higher voltage rating temporarily, to prove a point. Since there are likely problems there, you can also test the transformer's effect, faults or mounting problems by unmounting it and resting it securely on a piece of timber etc.
Why not also apply a little logic, by first removing the signal input and ground wiring to the PCB to track down where that noise source really is. If, when you short the inputs you get higher noise level, there is definitely a grounding problem there. That should not be the same ground as the chassis either.
Maybe it's time to read a little about amplifier ground wiring and construction rather than looking at components as the only culprits. Check the ground isolation of input sockets, too.Here's one place to start looking - there's a mass of material on amplifiers spread over several sections and general topics. Look at earthing/grounding issues for a start. If nothing else, you can't help but benefit from the practical information.
Ian
thanks a lot for this detailed post! Now it is pointing toward some sort of a grounding issue as in post #6
I didn't want to but I will unmount the transformer and see how it behaves ouside the case. I did completely disconnect it from the circuits and it hummed by iself. I also retightened every bolt on it, and there doesnt seem to be any dampening on it since it is not a thoroid.
I also disconnected the big caps and hooked up 10,000uf 85V caps in their place and there was no change :/. I might redo that test again to make sure.
Also yes you are right, I never got to diconnecting the signal inputs and the single grounding wire.
Here is my to do list now:
0) Replace the large caps again and double check.
1) disconnect inputs and ground and check for noise humming out of the speaker and with the scope.
2) unmount the trafo, remount externally and examine.
3) remount the trafo to the Muse and examine
4) use external power supply to power the rails
And yes I do lack amp design bacground, and thank you for that reference. The more this thing pisses me off the more I want to fix it an understand. Definately a good learning experience!!!
thanks a lot for this detailed post! Now it is pointing toward some sort of a grounding issue as in post #6
I didn't want to but I will unmount the transformer and see how it behaves ouside the case. I did completely disconnect it from the circuits and it hummed by iself. I also retightened every bolt on it, and there doesnt seem to be any dampening on it since it is not a thoroid.
I also disconnected the big caps and hooked up 10,000uf 85V caps in their place and there was no change :/. I might redo that test again to make sure.
Also yes you are right, I never got to diconnecting the signal inputs and the single grounding wire.
Here is my to do list now:
0) Replace the large caps again and double check.
1) disconnect inputs and ground and check for noise humming out of the speaker and with the scope.
2) unmount the trafo, remount externally and examine.
3) remount the trafo to the Muse and examine
4) use external power supply to power the rails
And yes I do lack amp design bacground, and thank you for that reference. The more this thing pisses me off the more I want to fix it an understand. Definately a good learning experience!!!
update:
0) Replaced the large 10,000uf Caps - No change. Still had the white noise, hiss, and small crackles when I put my ear about 2-3 inches away from the speaker
2) unmount the trafo
- The mechanical transformer humm is gone and there is no mechanical buzzing coming from the amp! You guys were right about the trafo mounting! I just took the trafo outside the case and set it to the side. I didn't bother mounting it o a piece of wood and just set it on my table (look at pic). I though the amp wasn't ON at the beginning, it was so quiet! As for the sound when I hooked up my speaker I didn't notice much difference. There was still the hiss and random popping noises. It might have been less loud and there might have been less buzz/60hz but I'm not sure.
Also when I plugged in an RCA cable (just the cable no source) the buzzing was horrendous, but my trafo wires were close to the input. Moving the wires around and the trafo a bit seemed to make a difference, up to a point, and than it wouldn't change much but it was still very loud. (look at the pic)
So I need to remount the trafo now... but I had all the bolts tightened before! How do I remount it now so the mechanical buzz wouldn't come back?
It looks like ground noise is being coupled from the RCA inputs. I think the RCA ground wires, that go to the Star Ground connection, cross the AC return lines and noise couples trough there?!? Still I now need to remove the RCA plugs from the chassis and disconnect that ground to see what happens.
Also the right channel heat-sinks seem to get warmer than the left ones when there is no speakers connected. I still have -30ma on the right channel (the one i replaced components). How do I fix that? There is only one bias Pot on each channel and I am not sure how to adjust it yet.
0) Replaced the large 10,000uf Caps - No change. Still had the white noise, hiss, and small crackles when I put my ear about 2-3 inches away from the speaker
2) unmount the trafo
- The mechanical transformer humm is gone and there is no mechanical buzzing coming from the amp! You guys were right about the trafo mounting! I just took the trafo outside the case and set it to the side. I didn't bother mounting it o a piece of wood and just set it on my table (look at pic). I though the amp wasn't ON at the beginning, it was so quiet! As for the sound when I hooked up my speaker I didn't notice much difference. There was still the hiss and random popping noises. It might have been less loud and there might have been less buzz/60hz but I'm not sure.
Also when I plugged in an RCA cable (just the cable no source) the buzzing was horrendous, but my trafo wires were close to the input. Moving the wires around and the trafo a bit seemed to make a difference, up to a point, and than it wouldn't change much but it was still very loud. (look at the pic)
So I need to remount the trafo now... but I had all the bolts tightened before! How do I remount it now so the mechanical buzz wouldn't come back?
It looks like ground noise is being coupled from the RCA inputs. I think the RCA ground wires, that go to the Star Ground connection, cross the AC return lines and noise couples trough there?!? Still I now need to remove the RCA plugs from the chassis and disconnect that ground to see what happens.
Also the right channel heat-sinks seem to get warmer than the left ones when there is no speakers connected. I still have -30ma on the right channel (the one i replaced components). How do I fix that? There is only one bias Pot on each channel and I am not sure how to adjust it yet.
Attachments
Hi,
Does the RCA input connector grounded to the chassis? Did you ever try to ground the input at the amplifier board were the cable it is connected?
Does the RCA input connector grounded to the chassis? Did you ever try to ground the input at the amplifier board were the cable it is connected?
Change the internal wiring of the RCA to a 2+shield cable and do not route it from near the outputs.
Gajanan Phadte
Edit: Hope your RCA is not connected to the chasis.
Gajanan Phadte
Edit: Hope your RCA is not connected to the chasis.
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The RCA seems to be isolated with nylon spacers from the chassis but there is a black wire on the solder lug that connects to the Star Ground.
It seem that the RCA input is grounded to the PCB board as well as the Star Ground... by design.
Do you mean my cable or the RCA input on the amp?
Here how it is wired.
The RCA input connector has four wires. One for the Center Conductor (red), and three to the shield/ground lug (2x Black and one Blue). The RCA input socket seems to be isolated with a nylon spacer from the chassis but one of the black wires connects to the Star Ground of the Amp.
Red goes to the pcb board. The Blue and one Black go to the PCB as well and the Blue and Black both connect to PCB ground. The 2nd Black goes to the star ground on one of the Main Big Capacitors. The chassis is also grounded to the Star ground.
I've loked at other pictures of the amp and the RCA input sockets seem to all have this 4 wire scheme.
Hi,
Has a test I would remove the wires that goes to the capacitor and the wire that goes to the chassis. Let only the wire that goes to the PCB board. See if the hum stop. Another test it is to remove all the RCA wires connections from the board, chassis and from the capacitor and short the amplifier input at the board and if you still has the hum then the problem it is not input wires.
Has a test I would remove the wires that goes to the capacitor and the wire that goes to the chassis. Let only the wire that goes to the PCB board. See if the hum stop. Another test it is to remove all the RCA wires connections from the board, chassis and from the capacitor and short the amplifier input at the board and if you still has the hum then the problem it is not input wires.
So I played with the input tonight and no change and I managed to blow my test speaker.... which is actually a pretty nice speaker.
I took off the RCA input on the right channel and nothing happened. I played around with the wires and disconnected the wire that goes to the star ground... big mistake, and blew my speaker with 58VDC... so yeah this floating power supply design is looking like **** to me, wtf?
Like I don't know if it's my inexperience but isn't it **** to route your ground trough your RCA input??????!?!?!?
and when I touch the shield of the RCA the noise gets less.
There has to be some ground loop or something somewhere or one of the boards has something wrong with it and it is shorting somewhere?
I also remounted the transformer to the chassis again and it's humming mechanically again. Check this out, the traffo mounts to the face plate with 4 screws and than 2 screws to the bottom steel chassis plate. Than the face plate mounts to the two heatsinks via 2 screws per heat sink. there is a gap between the face plate and the steel chassis bottom and when i press against the face plate the mechanical humming almost stops. I can feel the vibrations from the front faceplate btw. Granted everything is not tightened completely but it was super tight before.
Anyways, any advice on mounting the transformer back? any insulation that I can put?
I took off the RCA input on the right channel and nothing happened. I played around with the wires and disconnected the wire that goes to the star ground... big mistake, and blew my speaker with 58VDC... so yeah this floating power supply design is looking like **** to me, wtf?
Like I don't know if it's my inexperience but isn't it **** to route your ground trough your RCA input??????!?!?!?
and when I touch the shield of the RCA the noise gets less.
There has to be some ground loop or something somewhere or one of the boards has something wrong with it and it is shorting somewhere?
I also remounted the transformer to the chassis again and it's humming mechanically again. Check this out, the traffo mounts to the face plate with 4 screws and than 2 screws to the bottom steel chassis plate. Than the face plate mounts to the two heatsinks via 2 screws per heat sink. there is a gap between the face plate and the steel chassis bottom and when i press against the face plate the mechanical humming almost stops. I can feel the vibrations from the front faceplate btw. Granted everything is not tightened completely but it was super tight before.
Anyways, any advice on mounting the transformer back? any insulation that I can put?
Your pcb is connected to the RCA with a braid. I mean this wire to be changed to 2+shield.
Ground connection of RCA, fitted on the chasis, should not be fitted to the chasis without an insulator if there is one more chasis connection.
But if you check as suggested in post#28 by tauro0221, it will make things much clearer.
Gajanan Phadte
Ground connection of RCA, fitted on the chasis, should not be fitted to the chasis without an insulator if there is one more chasis connection.
But if you check as suggested in post#28 by tauro0221, it will make things much clearer.
Gajanan Phadte
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GD, are you saying just touching the outer of the rca socket reduces hum. Is this with it on the chassis or not?
Remember to ALWAYS power up via a bulb tester EVERY time you change ANYTHING !!!!!!!!! With the bias turned up the bulb will glow brightly even with only one channel connected.
You have a quieter left channel.
Measure the output noise on the 199.9mVac scale with the input open and the input shorted to signal ground. Use a spare RCA plug with a wire soldered across from Hot/Signal to Ground/Barrel.
Disconnect the Power and it's ground from the right channel.
remeasure the two noise levels in the left channel.
Now disconnect the left channel from it's Power and Ground.
Measure the noise from the right channel. It should be zero !
Reconnect power and ground to Right channel.
measure noise with open and shorted input.
How do these single channel measurements compare to the four stereo measurements?
Was the disconnected Right Channel completely silent, i.e. 0.0mVac?
You have a quieter left channel.
Measure the output noise on the 199.9mVac scale with the input open and the input shorted to signal ground. Use a spare RCA plug with a wire soldered across from Hot/Signal to Ground/Barrel.
Disconnect the Power and it's ground from the right channel.
remeasure the two noise levels in the left channel.
Now disconnect the left channel from it's Power and Ground.
Measure the noise from the right channel. It should be zero !
Reconnect power and ground to Right channel.
measure noise with open and shorted input.
How do these single channel measurements compare to the four stereo measurements?
Was the disconnected Right Channel completely silent, i.e. 0.0mVac?
I think I know what you are saying about the braid and shield. I will see if I have that type of wire laying around. And YES the RCA input fitten on the chassis is insulated via a Nylon spacer.
Yes! Both while on the chassis and outside.
I have re-mounted/Resoldered the RCA socket and shorted the two RCA inputs via an RCA cable and the buzzing decreases by half. Touching the RCA shell and the chassis doesn't make much of a difference. If anything it is slight.
When I have an open, ie connect an open RCA cable to either input I get the loud buzzing and touching the shell and even the heatsinks decreases the buzzing!
Perhaps there is something up with one of the boards. I am thinking of removing power supply lines (disconnecting the PCB basically) from one of the boards and testing fro the buzzing in the other channel. Thought?
Yep lesson re-learned, measure first than connect :/. In my defence I was doing that but I was making too many "on/off measure" that at one point it got annoying... hehe
Yep that what I am goint to do tonight if time permits!
200W = 23.01 dBW
100W = 20.00 dBW
You are correct if it does output 200W at 4ohms! Nice catch, the stereophile review has the spec wrong.
Ok here are my tests as of now... disappointing again...
*** Both Boards Connected **
**Right Channel**
*RCA Cable Connected and Open:
- -21mVDC
- 30mVAC
- noise, buzzing (loud)
*no RCA cable, RCA input open:
- -22mVDC
- 2mVAC
- low noise, I need to get my ear about 2" away from the speaker
*RCA plug, shorted RCA input
- -27mvDC
- 0.6mVAC
- lowest noise level, year to the speaker to hear slight soft hum
**Left Channel**
*RCA Cable Connected and Open:
- 3.7mVDC
- 63mVAC
- noise, buzzing (loud)
*no RCA cable, RCA input open:
- 2.4mVDC
- 0.6mVAC
- low noise, I need to get my ear about 2" away from the speaker. Less than the right channel
*RCA plug, shorted RCA input
- 0.4mvDC
- 0.4mVAC
- lowest noise level, year to the speaker to hear slight soft hum
NOTE: The right channel heat-sink is hotter than the left! Even when there is no load to the right channel it is hotter!
*** Right Board Disconnected**
**Right Channel**
- no readings at the speaker output or RCA
- I only disconnected the + and - floating rails but the GND connection from the PCB into the RCA into STAR Ground was let as is.
**Left Channel**
- my DC values began to fluctuate from my multimeter. I think it is running out of batteries.
*RCA Cable Connected and Open:
- fluctuates around 0 mVDC, from -4mVDC to +7mVDC
- 25mVAC
- noise, buzzing (loud). Same as with both PCBs?
- on the scope I can see two harmonics possible. One is spiky with high peaks and the other is sinusoidal looking.
*no RCA cable, RCA input open:
- 1mVDC but fluctuates again
- 0.3mVAC
- low noise, I need to get my ear about 2" away from the speaker. Same as with both PCBs?
*RCA plug, shorted RCA input
- 3.5mvDC, but it fluctuates again due to meter maybe
- 0.4mVAC
- lowest noise level, year to the speaker to hear slight soft hum. Same as with both PCBs?
... I wasn't able to do the other channel yet...
What do you make of this??? Weird?
I was hoping that when I plugged in the open RCA cable I wouldn't get the noise so I can isolate to the Right PCB :/
As a brave soul I decided to plug in my iPhone via the RCA jack and have a listen on the Left channel. The noise was very low like the RCA terminal was open. I played some music and it seemed fine, during pause the noise was small too. I tried adjusting the volume during pause but that didn't change the noise/hiss level out of the speaker. Still slight hiss at about 2in away on the small test speaker I am using.
*** Both Boards Connected **
**Right Channel**
*RCA Cable Connected and Open:
- -21mVDC
- 30mVAC
- noise, buzzing (loud)
*no RCA cable, RCA input open:
- -22mVDC
- 2mVAC
- low noise, I need to get my ear about 2" away from the speaker
*RCA plug, shorted RCA input
- -27mvDC
- 0.6mVAC
- lowest noise level, year to the speaker to hear slight soft hum
**Left Channel**
*RCA Cable Connected and Open:
- 3.7mVDC
- 63mVAC
- noise, buzzing (loud)
*no RCA cable, RCA input open:
- 2.4mVDC
- 0.6mVAC
- low noise, I need to get my ear about 2" away from the speaker. Less than the right channel
*RCA plug, shorted RCA input
- 0.4mvDC
- 0.4mVAC
- lowest noise level, year to the speaker to hear slight soft hum
NOTE: The right channel heat-sink is hotter than the left! Even when there is no load to the right channel it is hotter!
*** Right Board Disconnected**
**Right Channel**
- no readings at the speaker output or RCA
- I only disconnected the + and - floating rails but the GND connection from the PCB into the RCA into STAR Ground was let as is.
**Left Channel**
- my DC values began to fluctuate from my multimeter. I think it is running out of batteries.
*RCA Cable Connected and Open:
- fluctuates around 0 mVDC, from -4mVDC to +7mVDC
- 25mVAC
- noise, buzzing (loud). Same as with both PCBs?
- on the scope I can see two harmonics possible. One is spiky with high peaks and the other is sinusoidal looking.
*no RCA cable, RCA input open:
- 1mVDC but fluctuates again
- 0.3mVAC
- low noise, I need to get my ear about 2" away from the speaker. Same as with both PCBs?
*RCA plug, shorted RCA input
- 3.5mvDC, but it fluctuates again due to meter maybe
- 0.4mVAC
- lowest noise level, year to the speaker to hear slight soft hum. Same as with both PCBs?
... I wasn't able to do the other channel yet...
What do you make of this??? Weird?
I was hoping that when I plugged in the open RCA cable I wouldn't get the noise so I can isolate to the Right PCB :/
As a brave soul I decided to plug in my iPhone via the RCA jack and have a listen on the Left channel. The noise was very low like the RCA terminal was open. I played some music and it seemed fine, during pause the noise was small too. I tried adjusting the volume during pause but that didn't change the noise/hiss level out of the speaker. Still slight hiss at about 2in away on the small test speaker I am using.
Looks like you have issues due to the leaking transformer flux. This can be addressed by shielding the transformer.
You may have to use a snubber across the secondary of the transformer.
Gajanan Phadte
You may have to use a snubber across the secondary of the transformer.
Gajanan Phadte
Hi,
At the beginning of your thread you mentioned that you changed all of the capacitors. Did you check the resistors to see if they read withing the marked values ? By shorting the input and you still have the problem for me means that there it is another problem causing it. I maybe wrong but your are concentrating in the input and it maybe not the problem. This is an observation.
At the beginning of your thread you mentioned that you changed all of the capacitors. Did you check the resistors to see if they read withing the marked values ? By shorting the input and you still have the problem for me means that there it is another problem causing it. I maybe wrong but your are concentrating in the input and it maybe not the problem. This is an observation.
Gajanan,
I will try and hook up a benchtop PSU on the rails this week and disconnect the trafo and see if that makes a difference. Like I said tho, the trafo is buzzing against the case. I will probably eliminate the trafo when I hook up the PSU to it. Hope there will be some change.
Still tho the noise is more on the right channel. I will do my test with the rigght channel today and disconnecting the left and see how it is just in case.
tauro,
Yes I changed all the elctrolytic caps on the pcb as well as some diodes, zenners, and all of the small value transistors.
No I did not check the resistors, should i just test them in-circuit?
By the way when I short the input there is almost NO noise coming out from the speaker and I litteraly have to almost press my ear against the speaker to hear a very slight humm. The noise level is MUCH better with the shorting plug than if the input is left open with the RCA cable.
When I plug an open ended RCA cable I get the ANNOYING buzz.
When I plig a shorting RCA Plug I almost get NO noise.
When I leave the RCA input open I get slight humm from the speaker at about 3in away.
Also, I believe my slight DC offset at the output is due to mismatched small level transistors. To my knowledge there is no offset pot and only a bias pot that I am scared to touch.
Anyways, PSU test is in order. I will plug a benchtop DC PSU to the big caps and remove the thoroid from the circuit next.
I will try and hook up a benchtop PSU on the rails this week and disconnect the trafo and see if that makes a difference. Like I said tho, the trafo is buzzing against the case. I will probably eliminate the trafo when I hook up the PSU to it. Hope there will be some change.
Still tho the noise is more on the right channel. I will do my test with the rigght channel today and disconnecting the left and see how it is just in case.
tauro,
Yes I changed all the elctrolytic caps on the pcb as well as some diodes, zenners, and all of the small value transistors.
No I did not check the resistors, should i just test them in-circuit?
By the way when I short the input there is almost NO noise coming out from the speaker and I litteraly have to almost press my ear against the speaker to hear a very slight humm. The noise level is MUCH better with the shorting plug than if the input is left open with the RCA cable.
When I plug an open ended RCA cable I get the ANNOYING buzz.
When I plig a shorting RCA Plug I almost get NO noise.
When I leave the RCA input open I get slight humm from the speaker at about 3in away.
Also, I believe my slight DC offset at the output is due to mismatched small level transistors. To my knowledge there is no offset pot and only a bias pot that I am scared to touch.
Anyways, PSU test is in order. I will plug a benchtop DC PSU to the big caps and remove the thoroid from the circuit next.
My 200 is similarly louder on the right channel, though it's a completely different design internally, and uses a toroid. I'll try shorting rca inputs with plugs and see how it affects mine. It does have the rca/xlr input board which can be switched to give two separate inputs.
louder as in louder noise or louder in general?
Check the DC offset on your speaker outputs. I am curious to know what your numbers are.
Also disconnect your speakers and turn the amp on. Let it sit for 5-10min and touch the heatsinks... is one hotten than the other?
I expect when you plug in your short, your amp will get almost dead quiet like mine.
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