Popping Selector Switch

ptlud · 5178

0 Members and 1 Guest are viewing this topic.

Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
on: February 12, 2015, 03:05:23 PM
I been running my new Stereomour 45 for a couple of weeks, and it has developed an annoying pop as I rotate the selector knob.  I sprayed a little contact cleaner.  Could it be the very dry conditions of our house in the winter, or  a defective switch?

Also the selector switch has six click positions, but only three are used.  Is that normal?

Thanks,

Paul
« Last Edit: February 12, 2015, 03:12:19 PM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #1 on: February 13, 2015, 11:13:22 AM
Have been doing some additional research, and the popping could be caused by a number of other issues.  How do I determine what is the root cause of the popping.

The popping did not start until several weeks after the amp was built.

The popping does not happen when there are no inputs to the amp.  The popping occurs when either or both the CD player or Airport are connected.

I swapped the 12AT7.  The popping continues.

Thanks for your help!

Paul
« Last Edit: February 13, 2015, 11:16:46 AM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #2 on: February 13, 2015, 12:26:52 PM
I checked the 12AT7 grid voltage with the CD player attached and on.  Zero DC voltage, so it appears as though there is not DC bias riding on the signal.

Also, the DC voltage on the 12AT7 grids does not vary from 0.00V while the selector switch is rotated.

Does this makes sense?

Thanks,

Paul
« Last Edit: February 13, 2015, 12:45:43 PM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline galyons

  • Sr. Member
  • ****
    • Posts: 626
  • Geary Lyons
Reply #3 on: February 13, 2015, 01:54:49 PM
Paul,
I would look for grounding faults, (loose connection or cold solder joint), or something mechanical within the switch is shorting. The switch should be set for 3 positions. There is a tabbed key to do that, but you would need to remove the switch from the chassis.  Might be a good idea to check the assembly.

Cheers,
Geary

VPI TNT IV/JMW 3D 12+Benz LP-S>  Eros + Auralic Aries + ANK Dac 4.1 >Eros TH+ Otari MX5050 IIIB2 > BeePre >Paramount 300B 7N7 > EV Sentry IV-A

Thorens TD124/Ortofon RMG-212/SPU >Seduction > Smash^Up> Paramour 45 MQ >K12's


Offline Doc B.

  • Administrator
  • Hero Member
  • *****
    • Posts: 9641
    • Bottlehead
Reply #4 on: February 13, 2015, 02:26:05 PM
The popping does not happen when there are no inputs to the amp.  The popping occurs when either or both the CD player or Airport are connected.

Do either of them use a three wire power cord? It sounds like there might be a ground potential issue between the amp and the source gear.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #5 on: February 13, 2015, 03:15:23 PM
Both the AirPort and the CD player only have two-pronged AC plugs.

Set the rotary switch to only have three positions.  It only pops when I rotate the switch to a position that is connected to a source.

Note:  I can't find anything in the manual at describes how to set the switch to three positions.
« Last Edit: February 13, 2015, 04:11:09 PM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #6 on: February 13, 2015, 03:44:22 PM
How do you set the number of positions to three on the Alpha rotary switch?  Figured it out.
« Last Edit: February 13, 2015, 04:06:25 PM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #7 on: February 14, 2015, 02:04:28 AM
I went through the wiring and warmed up all joints I could access without taking the whole amp apart.  The popping still occurs.

Is this just an annoyance?  Does it indicate a fundamental problem with the amp?

Any suggestions?

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #8 on: February 14, 2015, 04:01:55 AM
I removed all the sources and connected my iPhone, which is battery powered.  The popping is almost negligable.  My speakers are very efficient at 100dB/m/W.

So I think this is a ground loop issue.

Any suggestions on remidying the problem?
« Last Edit: February 14, 2015, 04:04:13 AM by ptlud »

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline Doc B.

  • Administrator
  • Hero Member
  • *****
    • Posts: 9641
    • Bottlehead
Reply #9 on: February 14, 2015, 05:27:50 AM
Some interconnect cables have the shield connected to the signal cold at both ends and that can create a ground loop. A cable with the shield connected to signal cold at only one end is a better design and might help. You might start with the connected end plugged into the Stereomour and the other end into your source component, then swap ends to see if it makes a difference.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #10 on: February 14, 2015, 06:46:09 AM
Doc,

Thanks for the suggestion.  My plan is to add a three-terminal IEC socket to my modded Toshiba 3950, as well as my Marantz receiver. 

I also plan on purchasing an Uber BiFrost DAC which comes with a three-terminal IEC.  The digital feed from the AirPort and CD player will be "isolated" from the individual components.

Finally,  at some point I plan on upgrading the selector switch to a Grayhill 4P-3T-1D.

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20


Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 5822
Reply #11 on: February 14, 2015, 02:34:19 PM
I suspect the problem is (as noted by Doc B) one of ground currents. A device that is not safety-grounded (3rd wire of the power cord) will have a ground voltage that is not the same as that of the Stereomour, whose signal ground is tied to safety ground. This will cause a pop when switched in or out.

You can test this by measuring the voltage difference between the RCA jack grounds on the two devices when they are NOT connected. It's almost certainly AC voltage, not DC - but always interesting to check. Usually the impedance behind that voltage difference is high, so the resulting current  when the grounds are connected will be small - you can try to measure that as well, but it may be too small to measure easily. fortunately the current is so small that there is no damage to the switch or other components - unless the speakers are making excessive movements  :^)

If you can, try reversing the 2-wire power plugs to see whether one orientation makes less voltage or current.

"Ground loop" hum is a result of that current, which is why we switch the grounds. Otherwise any source with a ground current will create hum even when that source is not selected. The alternative is to leave all grounds connected (unswitched), which should eliminate the pops but risks creating a new source of constant low-level hum. If the available ground current is small enough to not make a problem hum, then the alternative might actually work better, at least until a source with a noisier ground is added to the mix. You can get some clip-leads and use them to temporarily connect the grounds, checking to see if that does indeed stop the pops.

Paul Joppa


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19694
Reply #12 on: February 14, 2015, 04:47:58 PM
You can get some clip-leads and use them to temporarily connect the grounds, checking to see if that does indeed stop the pops.
This has always worked well for me.  Clip lead a screw on the chassis of the source and clip it to a screw on the Stereomour plate. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline ptlud

  • Jr. Member
  • **
    • Posts: 33
Reply #13 on: February 23, 2015, 10:15:16 AM
I added a grounded IEC socket to my modded Toshiba 3950.  No more pop as I roll the selector switch to CD.  Yeah!

Paul

Stereomour 2A3
Modded Toshiba 3950 DVD Player + Schiit Uber Bifrost DAC
JVC A40 Turntable with AT95e + Schiit Mani Preamp
Klipsch KLF-20