Blumenstein and Stereomour

[Doc B.]

Try mV

[thdewitt]

I would like to start by saying than you to everyone for their help.  I am having so much fun with my Bottlehead projects.  I will be buying some Paramounts and a Beepree soon.

Anyway, I love to post pictures.  I am sure I have it right this time.  When hooked up to the Fluke meter on the mV setting it jumps from 2.0 to zero.  Here is a short movie of what happens.



Here is what the readings are with the oscilloscope.
(https://dl.dropboxusercontent.com/u/38833957/2014-06-13%2010.06.03.jpg)
(https://dl.dropboxusercontent.com/u/38833957/2014-06-13%2010.06.27.jpg)

[Doc B.]

The scope says 0.57mV rms of ripple. That is excellent.  Up closer to 1mV is more common.

[Grainger49]

Tom,

Ok, you have a good zero of the AC imbalance when your meter reads 0.000V AC.  And we all agree this is not a normal situation.

Since the sub has extended response that the Orca doesn't at 60 Hz it will hum louder.  What I was trying to check is if it is a ground loop in the Stereomour or in the Orca/Dungeness setup.

So we have that the Orcas hum a little and the Dungeness is louder. 

One more thing, are you shorting the input of the Stereomour when making the hum balance adjustment? 

When you use shorting plugs do you have the hum?  If you get no hum this points to your Solos or the interconnects from it to the Stereomour.

[Clark B.]

Tom, good catching up with you on the phone Friday and sorry to hear about the hum problem in your system.  If you still have problems with it or have a hunch its somehow a malfunctioning amp in the dungeness then please let me know and I'll fix it for you. 

Otherwise, I'm sure there are many people wondering: how's the sound of the stereomour/orcas?

[thdewitt]

OK, First, thank you to Clark and Molly at Blumenstein Audio.  They have been fantastic.  From advice on the type of amp, to speaker placement, to just talking me through their offerings.  Also, the craftsmanship and service are second to none.  I absolutely love my new Orca Deluxe's and Dungeness sub.  For me they are a piece or art that will live in my house as long as I do.  My only concern now is what am I going to buy from them next.  I see some great new products on the horizon.  Probably will pick up a second Sub ASAP.  Clark is currently working on my amp bases for my Crack, Stereomour, and Submissive in Chocolate Bamboo to match.  They system will look sweet when they arrive and I will post some pictures.

BACK to MY QUESTIONS about hum on my Stereomour.  I am a big dummy.  I figured out that the probes on my Oscilloscope where set to 10X but my scope was set to 1X.  After testing on both my scope and my Fluke Meter with the proper settings, i am getting readings of about 1.5 mV after adjusting the Hum pots. 

Grainger and all.  Is there something to look for that would cause this?
Answers to your questions:
I am sure I am testing AC mV on all the right settings.
I am shorting with RCA Plugs as recommended in one our your posts. (I cut up an old RCA twisted together and soldered.
I do have the hum when using shorting plugs.
Also, I do not get any hum in the sub when it is not connected to the Stereomor.  When I connect one speaker side the hum starts, gets louder when second side is connected.
If I adjust the pots with the speakers connected I definitely get to a clear minimum as asked by Paul.
I have looked closely at all solder joints.  I have reflowed any suspect joints.  I have tested the continuity on all the grounds in the circuit and they seem to be fine. 
Could there be a problem with the tubes?
Not sure if I should do anything else or just leave it alone and enjoy the amp/speakers with a slight hum.

Tom

[Paul Birkeland]

  After testing on both my scope and my Fluke Meter with the proper settings, i am getting readings of about 1.5 mV after adjusting the Hum pots. 

That sounds about right.

Have you set the levels on your sub amps?  If they are up all the way, then the level of hum will appear to be artificially high.

-PB

[Doc B.]

Another potential issue is that the subs may be sitting in a spot in the room that is accentuating the hum. You might try moving them around a little to see if you might be setting off a room mode where they are now. Usually moving them about a foot at a time is a reasonable.

[thdewitt]

Have you set the levels on your sub amps?  If they are up all the way, then the level of hum will appear to be artificially high.

-PB

Yes, When I adjust the sub gain to the 10 O'Clock position recommended by Clark the hum is minimized but still slightly audible. 

When the system is first turned on, the hum starts very loud and then reduces for a few seconds to barely audible.

Tom

[Natural Sound]

Remember, the Stereomour has AC heaters. It will never be perfectly quiet. I have a pair of the discontinued Paramour II amps. The circuitry is similar and I even upgraded the iron to use the Stereomour/S.E.X. iron. I had 2A3's installed originally and later modified the amp for 45's. I always had a bit of hum that you could hear if you were right next to the speaker. Sitting in my listening position it was much less noticeable. And when music was playing you don’t hear the hum at all. I noticed that when I went from 2A3 to 45 the hum was lessened quite a bit. To me that would indicate too much gain. Additional padding in my pre-amp helped even more. In your case you are controlling the volume with the submissive. You could try dumping some of that gain with the pot on the Stereomour. Have tried hooking your source directly into the Stereomour? You might be introducing hum with your interconnects.

[thdewitt]

Well, I hooked up the Orcas and Dungenus to two other amps and got zero hum even at 100% gain on the sub.

[Doc B.]

Is the 1.5mV you measured on the scope peak to peak or rms? If it is peak to peak (Vpp) then you are well below the hum spec for the amp. If it is rms then the hum is slightly higher than average, but low enough that you would probably only get it lower by swapping out tubes until you find a particularly quiet set. The place to start might be the 12AT7.

You could also reduce the hum slightly by wiring the transformers for 4 ohms output rather than 8 ohms. However this will limit your headroom a bit.

[thdewitt]

Thanks Doc, I am measuring RMS.  I will take a look at the tube.  Maybe wire the transformers for 4 ohms as well.  I am in a small space.

[Doc B.]

The 4 ohm thing would only be a liability if you run the system loud enough that it seems to run out of steam on loud passages. If you are not running that loud it should work fine. Also the hum may reduce a little as the tubes burn in. It's usually worth it to touch up the hum balance after a few hours play when you have new tubes.

[thdewitt]

I am lucking for a replacement tube on ebay right now.  Any suggestions.  The stock one I got was pretty beat up.  Pens a little bent so it may be suspect.  Do you have a recommendation for a generally accepted high quality replacement.  Cost is not a big issue.

Thanks,