Very Low Output Volume on Stereomour II [resolved]

[HughFisher]

I finally got the time to finish my Stereomour II. All the voltage checks were in specification. The amp sounds good through my Pipettes but the volume is extremely attenuated. In order to get the sound to normal listening level I have to turn the volume all the way up. There are no pops, hum, anything. Dead quiet, just very low output. Thoughts welcome!

Hugh

 

[Paul Joppa]

What is your source?

 

[HughFisher]

What is your source?

I tried both my CD player and my Aurender music streamer. I pulled them off of my main system (Line Magnetic 518IA). I have no experience with 2A3B tubes. How much do they glow? There is some glow at the top, but that's it. By contrast, the 845's in my LM-518IA practically light the room. Just curious if they are outputting properly.

 

[Paul Joppa]

The Line Magnetic is about 22dB more sensitive than Stereomour - it makes 6 times as much power for 1/5th the input voltage. That may be all the difference you experience.

 

[HughFisher]

The Line Magnetic is about 22dB more sensitive than Stereomour - it makes 6 times as much power for 1/5th the input voltage. That may be all the difference you experience.

That can't be it. At 50% volume on the Stereomour barely anything comes out of the speakers. At 100% it is what I would consider listening volume.

 

[HughFisher]

The Line Magnetic is about 22dB more sensitive than Stereomour - it makes 6 times as much power for 1/5th the input voltage. That may be all the difference you experience.

Dunno. Maybe. At 50% gain it is at low background music level. At 100% it is listening level. If that's all I get out of it I suppose it's fine since this amp goes in the dining room for background music. But I'm surprised...

 

[Paul Birkeland]

Can you play a 60Hz tone through your source, then use your meter to measure the AC voltage that appears across one of the RCA cables coming from your source? This can be helpful in determining if/where there may be an issue.

 

[HughFisher]

Can you play a 60Hz tone through your source, then use your meter to measure the AC voltage that appears across one of the RCA cables coming from your source? This can be helpful in determining if/where there may be an issue.

If I'm doing it correctly, it is .63 volts. I should say that it does sound very nice. It renders the music well, and I never expected it to have the depth and range of my big Line Magnetic going through DeVore Fidelity speakers. It sounds exactly how I thought it would. I'm just reacting to the output level.

 

[Paul Birkeland]

You'll really want to find a stronger source to drive the Stereomour, or look up the specified output of your source and see if you're getting all the output. The vast majority of DACs on the market these days put out 2V RMS at minimum, and many go above that. You're really going to want 1.5V of signal coming into the Stereomour to get full output out of it, though I'd suggest a DAC with at least 2V of output.

 

[HughFisher]

Paul, that was it! It was a setting on my Aurender. It's pumping out now. Thanks much! Issue resolved.

 

[Paul Birkeland]

I appreciate your willingness to dive into measuring that and figuring it out.