Hi Guys
I have a Yaqin MS-22b phono stage with a hum. I have shorted out the input phonos and the hum is still there. I disconnect the input leads from the circuit boards easy to do because of the connectors and shorted both pins of the connectors on the board and the hum stopped. I examined the cable from the inputs to the board and it is 2 pair unscreened. Do you think that this should be screened cable and the screen earthed. Any other ideas would be welcome. I have tried all the normal things moving it around, changing cables etc. This last test was done using a different amplifier. You only notice the hum when there is no music playing.
Many thanks
I have a Yaqin MS-22b phono stage with a hum. I have shorted out the input phonos and the hum is still there. I disconnect the input leads from the circuit boards easy to do because of the connectors and shorted both pins of the connectors on the board and the hum stopped. I examined the cable from the inputs to the board and it is 2 pair unscreened. Do you think that this should be screened cable and the screen earthed. Any other ideas would be welcome. I have tried all the normal things moving it around, changing cables etc. This last test was done using a different amplifier. You only notice the hum when there is no music playing.
Many thanks
Are the RCA jacks isolated from the chassis? If they are not isolated this creates a ground loop that would be responsible for the hum you hear. Twisting should normally be sufficient if inside a metal chassis and not near the power transformer and choke, otherwise low capacitance shielded cable can be used.
Hi
I checked the RCAs both input and output and they are insulated from the metal case. There is also an earth terminal and this is also insulated from the metal case. I disconnected the earth from the board and desoldered an earth that looks like it came from the transformer - none of these worked the hum was still there. I also wrapped the input cables in metal foil to simulate a screen and earthed that but the hum was still there. Does anybody have any other ideas?
Many thanks
I checked the RCAs both input and output and they are insulated from the metal case. There is also an earth terminal and this is also insulated from the metal case. I disconnected the earth from the board and desoldered an earth that looks like it came from the transformer - none of these worked the hum was still there. I also wrapped the input cables in metal foil to simulate a screen and earthed that but the hum was still there. Does anybody have any other ideas?
Many thanks
I'll be interested to know the answer to this too as I have the same issue... 🙁
I have attached the schematic of the MS 22B
I used a multimeter to control the 12AX7s heater voltage and here is what I got:
11.7VAC & 25VDC, are these ok ?
I have attached the schematic of the MS 22B
I used a multimeter to control the 12AX7s heater voltage and here is what I got:
11.7VAC & 25VDC, are these ok ?
Hi
Following on the the above.
1) Used shorted phono plugs on the input - hum still there.
2) Disconnected the inputs from the PCB using the on board connectors.
3) Made up some flying leads with a socket on one end and connected it to the PCB on board connectors - hum all but gone - only the noise you would expect from a cartridge turned up full.
4) After a lot of head scratching traced the leads back to the phonos and found that both the earth/ground L & R were connected together. Split these to make two seperate circuits - Hum gone - same niose as above.
5) Connected my input phono leads shorted them out and hum gone. Connected up my DIY SUT and hum returned - so now trying to sort that out. Pretty sure it will be a ground loop - but it does take time.
Hope this helps
Please let me know.
Regards
Following on the the above.
1) Used shorted phono plugs on the input - hum still there.
2) Disconnected the inputs from the PCB using the on board connectors.
3) Made up some flying leads with a socket on one end and connected it to the PCB on board connectors - hum all but gone - only the noise you would expect from a cartridge turned up full.
4) After a lot of head scratching traced the leads back to the phonos and found that both the earth/ground L & R were connected together. Split these to make two seperate circuits - Hum gone - same niose as above.
5) Connected my input phono leads shorted them out and hum gone. Connected up my DIY SUT and hum returned - so now trying to sort that out. Pretty sure it will be a ground loop - but it does take time.
Hope this helps
Please let me know.
Regards
Hey,
Thanks for this explanation.
Would have pix of what you've done?
I m not sure I get the step 3 and 4
Thanks for this explanation.
Would have pix of what you've done?
I m not sure I get the step 3 and 4
btw, I made an error in typing earlier, I meant:
"I used a multimeter to control the 12AX7s heater voltage and here is what I got:
11.7VDC & 25VAC, are these ok ?"
"I used a multimeter to control the 12AX7s heater voltage and here is what I got:
11.7VDC & 25VAC, are these ok ?"
Phono cartridges generally use a 'floating' connection so the signal return wire should only be grounded once at the preamp input - typically at the point the signal connects to the circuitry. The separate 'ground' connection is for grounding the arm/deck, not the cartridge.
Hi
Reference my previous post. If you disconnect the leads from the input phonos to the circuit board by using the PCB board connectors. You will see two pins on each connector. With the volume control on the amp turned up with a small screw driver short each out. Just like putting two shorted phono plugs in the input sockets. The hum should disapear. This means whatever is casing the hum is further down the line. After reconnecting the PCB connectors I found the problem.
As I said I tracked it down to the common earth returns on the input sockets as soon as I split these making effectively two seperate circuits the hum went away.
Hope this helps
Reference my previous post. If you disconnect the leads from the input phonos to the circuit board by using the PCB board connectors. You will see two pins on each connector. With the volume control on the amp turned up with a small screw driver short each out. Just like putting two shorted phono plugs in the input sockets. The hum should disapear. This means whatever is casing the hum is further down the line. After reconnecting the PCB connectors I found the problem.
As I said I tracked it down to the common earth returns on the input sockets as soon as I split these making effectively two seperate circuits the hum went away.
Hope this helps
So basically, you removed the ground from the 2 original (black) cables on the input and connected the ground directly from the input RCA to the chassis ?
No, the opposite of that! The incoming phono cable should not be connected to any chassis anywhere. It should connect to the preamp circuit, and use whatever ground arrangements that has. The RCA sockets should be isolated from chassis so only grounded via the internal cable and the preamp circuitry.
humm ok, any particular place where I could solder then the input ground on the circuit?
A photo of your circuit maybe ? 😛
A photo of your circuit maybe ? 😛
What do you mean by input ground? Are you asking about how to connect the incoming phono signal to the circuit ground? If so, I have already answered that - it goes to the circuit ground, not the chassis.
If you are asking about the circuit ground then that depends on your circuit, not my circuit!
If you are asking about the circuit ground then that depends on your circuit, not my circuit!
As mentionned above, I just tried to disconnect the 2 input sockets from the pcb and tried the pre amp like this.
Unfortunately, the humm is still here and even slightly louder... 🙁
Here is the schematic of the pre amp:
Unfortunately, the humm is still here and even slightly louder... 🙁
Here is the schematic of the pre amp:
The signal return (or screen) of the phono cable should connect to the bottom end of R11/R14 as that is the point which sets the input signal ground reference.
If wired incorrectly it is possible that C15 injects ripple at this point.
If wired incorrectly it is possible that C15 injects ripple at this point.
Guys,
Got it !
If you look at one of the pix I sent, there is a ground yellow cable that is going from the pcb ground to the chassis.
I disconnected it from the chassi and that's it: no more hum !!!! ;-) (so happy now)
I don't know why the hell YAQIN put this cable here !
However, I still have this "poc" in my speakers when I m changing channels from aux to phono...
Steph
Got it !
If you look at one of the pix I sent, there is a ground yellow cable that is going from the pcb ground to the chassis.
I disconnected it from the chassi and that's it: no more hum !!!! ;-) (so happy now)
I don't know why the hell YAQIN put this cable here !
However, I still have this "poc" in my speakers when I m changing channels from aux to phono...
Steph
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Hi
What I actually ment was that if you look at the input phono connections your'll see that the ground/negatives are soldered together. I split these apart from each other and the hum was gone.
I tried disconnecting the wire to the chasis but in my case it did not make any difference.
Still trying to trace the source of the hum from my DIY SUT - you wouldn't think it would be so difficult. However trial and error I suppose.
Regards
What I actually ment was that if you look at the input phono connections your'll see that the ground/negatives are soldered together. I split these apart from each other and the hum was gone.
I tried disconnecting the wire to the chasis but in my case it did not make any difference.
Still trying to trace the source of the hum from my DIY SUT - you wouldn't think it would be so difficult. However trial and error I suppose.
Regards