[jedgar]

I switched out the tubes for the transcendence 10 preamp and left the cover off to test the system.  It was very good though the hum did not totally disappear.

Later I put the cover over the unit but did not screw it in place.  Then all heck broke loose, with microphonics and ringing initiated when I touched the cover reflected back though the speakers. Ouch! That resolved once I screwed down half of the 16 screws.  Notice too that the front and back of the cover are indistinguishable.   I thought 16 was excessively Frank but maybe not.

SO, as I said the hum was reduced and not eliminated.

Now a new discovery, after coming home late last night from hearing Margo Price at First Av. (really good but not as exciting as the tour when launching Midwest Farmer's Daughter) I played some jazz on headphones using the preamp's builtin amplifier. No hum! 

There is no hum when only the amp (Van Alstine solid state Synergy 240)  is on, no hum when only the preamp is on. 
Hum only when preamp and amp are both on, and regardless of whether source (TT, CD, Wifi) are powered on or off.

Happily not enough to hear when playing music but wonder what others think.  Try different tubes?  I will also unplug and replug all lines and spin some Lindsey Buckingham later today.

[Charles Xavier]

is this a new problem or have you always had the hum.

[jedgar]

Some "hssss" for months, greater hssss recently. 

[SJ David]

Seems like tube(s) issue without knowing a whole lot about the situation. Even if there is still something else causing the hum you hear it makes sense to sort out the tubes first.

The microphonics described sounds significant and you should not use that tube in a preamp circuit, at all.

I don't know how AVA set up the headphone amp in the pre but I would be surprised if the phones amp is not totally separate from the line stage, sharing only the volume control. Don't know for sure but this may be why no noise when listening to headphones.

Fiddling with tubes is all part of the fun of using tube equipment. Right?

[Doublej]

I offer generic thoughts.

From web pictures it appears that the Transcendence 10 has a ground switch on the back. Does anything change if you flip it on or off?

Are both pieces plugged into the same outlet? If not try plugging them into the same outlet. If they are plugged into the same outlet, try plugging them into different outlets and if possible different outlets on the separate sides of the breaker box.

In each case flip the ground switch and see if anything changes.

You can also temporarily try adding ground lift adapters to the ends of your power cords.

[danielgk]

jedger

You stated "There is no hum when only the amp (Van Alstine solid state Synergy 240)  is on, no hum when only the preamp is on."

This tells me that the power amp is fine.  The way we test power amps for noise is to ground the input (which in your case, I believe, is the same as turning the preamp off).
Note that an open input is NOT the same as a grounded input.  Most AVA power amps will be quite noisy if the inputs are open (even though they do have pull down resistors).

That leaves a noisy preamp or a ground issue.

Number one suspect would be a tube in the preamp.  There is a strong possibility that this would only cause the noise in one channel though.

Number two would probably be ground:  in a typical stereo chain - source, preamp, power amp, speakers - one, and only one, component should be connected directly to earth ground.  If multiple components are each connected to earth ground there is a possibility of a ground loop.  You can disconnect the component from earth ground by flipping the ground switch (down = off) on most AVA gear or by using a 3 to 2 prong adapter cube thingie (which is the same as old school cutting the ground prong off -which you are not suppose to do anymore).


Dan

[jedgar]

Thanks all.

I used the ground switch on rear of preamp yesterday with no effect.

I went back to things today and found that with the "new" tubes the ringing came back after a few minutes of operation.  Both channels, though worse on one side.

I put the older (AVA-sourced) JJ6922 tubes back in and have no ringing but audiible hsss at 9 feet when no source is playing.  So, back to the local tube retailer, who on the past have been easy to work with.  Unless they have a proposition, I will return them and order the plain Jane JJs  from AVA.

I will look up Frank's flow chart for isolating problems and see if that gives me something to explore beyond the tubes as source of the HSSS.

Ah ha I was smart enough to print it out and at the bottom of the page I get: "pre-amp line stage defective, power supply, oscillating, or possibly defective cables."  Now I assume Frank assumed we would be aware of possible defective tubes along with those possibilities. 

[jedgar]

Replacement replacement tubes installed.  Reduced hssss and no macrophonics.  After I have rested up and cleaned my glasses I will put the dozen plus screws back into the assembly, unless Lindsey Buckingham shows up and volunteers to do it for me.