Missing Step from Stereomour II manual dated 07-06-15 or earlier

fullheadofnothing · 6017

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Offline fullheadofnothing

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The instructions for how to use the hum balance pots was left out of the Stereomour II manual. Manuals dated 09-21-18 or later will have these instructions.

Connect the black lead of the meter to the black binding post of the right channel. Connect the red lead of the meter to the red binding post of the right channel.

To find the lowest possible position on the hum pot, you will also need to connect a speaker to the binding posts

Set the meter to read AC volts. If your meter does not autorange, set it to the lowest AC millivolt (mV) scale. Turn the volume pot all the way down to short the input. This will help keep outside electrical interference from affecting the reading on your meter.

Install all tubes into their respective sockets.

Turn the amplifier on let it warm up for a minute or two. Then slowly adjust the hum balance potentiometer behind to the four pin tube socket to get the lowest reading possible on the meter. This should be between 0.8 and 2.0 mV depending on the tube used.

Repeat this process for the left channel tube.

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Offline Karl5150

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Reply #1 on: November 24, 2018, 07:36:57 AM
Finally got around to adjusting the pots. I had originally done it by ear and by placing my phone with dB meter app in front of the subs.
When I hooked up the meter (which in AC only reads V with 3 decimals) I got 0.002 and 0.004. I was able to get both to read 0.000, so less than 1mV, the low end of the as advertised performance. I centered each by feel between the 0.001 readings.
I did noticed some scratchy sound through the speakers when I first started fiddling with the pots that did not go away with exercise.
The final adjustments were made with the MourQuiet at max attenuation.
As I suspected most of the audible hum I hear with my ear near the subs is from the addition of the Dayton plate amps.   

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Offline jbrahen

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Reply #2 on: November 27, 2021, 07:57:59 PM
That's funny, my meter cannot read mV, so I just cranked the volume with sensitive speakers and adjusted to the lowest hum. Curious if maybe that's a common way to do it?

Josh B.

Online Paul Birkeland

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Reply #3 on: November 28, 2021, 04:50:21 AM
The hum level shouldn't change with the volume all the way up.  You may pick up some extra noise with an open input and the level control all the way up, and the null of that plus the hum may be different than the null for the hum itself, so I wouldn't recommend doing that.

If you have some clip leads and some cheap headphones, that can be helpful if your meter can't resolve AC mV.

Paul "PB" Birkeland

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