a couple of Stereomour II questions

[Jay]

My new stereomour II is up and running with a new pair of 98db speakers.  there is some hum even with the hum pots optimized, so I'm eager to install the dc filament supply.  What is a proper amount of time to wait to decide the Stereomour is good to go for modification?

Also, I blew a fuse while hooking components to it.  What is the best order to turn things on?  i.e. source->Eros->Stereomour, or Stereomour->Eros->source etc.

Thanks,
Jay

 

[Rocketman248]

Always start and finish at the source.  Turn on in this order:  Source > Preamp > Amplifier.  Turn things off in the opposite order.  Amp first, then preamp.

 

[Doc B]

Do you mean you blew a fuse in the Stereomour II? It's pretty unlikely that a Stereomour fuse would blow simply from connecting another piece of gear to it. You might have an intermittent connection inside the Stereomour.

 

[Jay]

Yes, the Stereomour fuse blew.  It had passed all resistance and voltage tests so I replaced the fuse and it has been working well tonight.  No smoke or funny smells.  Should I recheck the tests right away, or is it ok to see how it goes for a while.  Certainly I'll redo the voltage and resistance tests before installing the DC filament supply.
Jay

 

[Paul Birkeland]

You can also tap kind of hard on the chassis plate while music is playing.  If you have a funky connection, you can sometimes hear the amp make some noise as this connection is physically jarred.

 

[Jay]

Update:  I took my stereomour II back to the work room and hunted for any stray leads, loose connections etc.  I found two joints which I had failed to solder.  I corrected those and returned the unit to service.  It worked without a hitch for four days or so, though still with the fairly prominent hum.  Otherwise it was sounding great.

This am, I installed the DC filament upgrade.  Now, it is *dead*  *silent* (except of course for beautiful music)

Two questions:  No matter where i position the hum pots, it remains quiet.  How do I know where to set the hum pots?  Does it even matter now?

 

[Paul Joppa]

There is a very small 120Hz hum residual in the DC board output, which can be cancelled with the pot. You may need to use sensitive headphones to hear it.

The hum pots also will allow you to reduce (and optimally, eliminate) signal current through the capacitor bank on the DC board. Some people think those capacitors cause a subtle loss of quality. If that is true, and if it is due to signal current through the caps, then the hum pot would be able to help. There is virtually no solid data to tell if those assumptions are true. I have not heard this problem myself, but a search of the forums will find many who prefer AC power in spite of the hum. In these days of fake/false news, I am becoming more suspicious of things I have not heard myself.

Note that in the Stereomour, the control now gives you the range of 40% to 60%; you cannot get to one end of the range or the other. Try the control in the middle and at either end to see what you hear, if anything. It will shift the operating point slightly, which might also make an audible difference.