ET7 S2 transformer hum

[Matty]

We have progress but have not fixed it.

The transformer has 4 screws attaching it to the side of the back casing.
Checked these and gently ensured they are tight and snug.
One needed a 1/8th at most.
Two just a hint.
Not much but something.
There's just very little so possibly this was it.
So...
Before replacing the cover I put the power lead in which puts it into standby mode.
No hum.
Turned on fully.
No hum.
Great.
Put the cover back on.
Ensured all screws were tight and snug.
Plugged the power cord back in...

Hums back.

Unplugged and took the cover off.

No hum.

Can not see any reason why.
All screws are snug when the cover is on.

The unit is a on a solid glass table for this test.
On Ikea bamboo wood board when in the listening position.

It's the same hum same volume in both places.

Put the cover on without scews.

Hums quietly...maybe 1/3

Take cover off...no hum.

Cover on and gently press the edges of the top cover down.

Hum increases to its normal volume.

Pushing down on each individual screw hole without a screw just the pad of the finger.

Left, top and bottom edges no hum increase.

It's only the right side that increases hum volume.

Gently pressing any of the 5 screw holes on the right side makes the hum increase.
The power cord entry is top right corner as is the transformer.

However, with the top plate on without pressure or screws, it still hums about 1/3rd.

No luck trying Roberto's other suggestion of supporting the unit from the bottom plate rather than rubber feet.

[roberto]

if you put something heavy on top of the preamp, just for a try, do you have hum? It is very important to use pine wood, other kind of wood might make it worse.

Now we know that the top cover is resonating. There are mats that prevents resonance...like this or similar

products:https://www.trimacoustics.co.uk/product ... ing-sheet/

[AnotherJohnson]

That sounds like the transformer is transmitting the mechanical vibration to the casework. The most efficient radiator is the top.

Why is the transformer vibrating is the fundamental question?

Perhaps delamination of plates? I don’t know.

There are three solutions.

Replace the transformer … work through the dealer and official importer to initiate this.

Try to absorb the vibration and dissipate it. Without blocking the vents, put something like a brick sitting on a piece of rubber on the top.

Leave the top off … it won’t hurt anything if you don’t poke around inside. The top is to protect you. So protect yourself.

There may be other ideas. I would go with these three in the order I’ve shared them.

[roberto]

Also, there are rubber made anti vibration devices:

https://www.amazon.com/Silencer-Anti-Vi ... B07FB44FM5

You could mount the transformer and isolate it from the chassis...just thinking how to solve your problem Matt...

[AnotherJohnson]

A $13000 preamp should not require aftermarket engineering or tinkering to make it work.

Instead of figuring out how to cobble together a kluge solution, turning it into what I would call a roach, at least try to get the official importer to fix it correctly. The transformer is not supposed to transmit energy to the chassis.

Here’s a thought …

Perhaps if tightening the mounting screws did not solve the problem, loosening them would.

A free non roach creating activity would be to back the screws off a bit and see if that helps. Perhaps it’s already rubber mounted and the problem was the three tight screws rather than the slightly loose one.

[Matty]

Thank you, Roberto and AJ.

Any pressure to the top plate and the hum increases volume.

There are two separate pitched hums.
A slightly higher pitch that's quieter and from the transformer.
A slightly lower pitch that's a bit louder from the top plate, when pressure is applied or the right side is screwed down tight.

There is the exact same slightly higher pitch hum from the ART SA at a marginally lower volume as the slightly higher pitch hum from ET7.

I can hear both or either individually from 2 meters away in the listing position.

With the right side screws not tight or without any presure on top plate the lower pitch plate hum is gone.

[Matty]

A $13000 preamp should not require aftermarket engineering or tinkering to make it work.

Instead of figuring out how to cobble together a kluge solution, turning it into what I would call a roach, at least try to get the official importer to fix it correctly. The transformer is not supposed to transmit energy to the chassis.

Here’s a thought …

Perhaps if tightening the mounting screws did not solve the problem, loosening them would.

A free nonroach-creating activity would be to back the screws off a bit and see if that helps. Perhaps it’s already rubber mounted and the problem was the three tight screws rather than the slightly loose one.

That is an excellent idea.

I will try again tomorrow and get back to you.

[AnotherJohnson]

The higher pitched sound may be a ground loop.

[admin]

As others mentioned, the case is resonating. I have to admit this is unusual as typically it is the transformer directly that causes hum. It's an off chance, but one more thing I would recommend that has not been mentioned is tightening all the screws that hold the main board to the bottom of the case. If any of them are loose, it can cause decoupling from the housing and increase resonance.

I've used dampening material on my JD9 phono mod, that could be a option to employ on the top cover (as others have mentioned).

A ground loop would cause audible hum in the speaker (at 60 hz) due to the effects on the output signal but I don't see how it would cause the case to resonate.

[Matty]

If the volume is turned way up,
The transformer's higher-pitch hum transfers to the speakers.
With ET7 volume at 70 to 99 you can hear it from speakers....same pitch and same sound as coming from amps.

Admin...will try that tommorow.

[AnotherJohnson]

Ground loop won’t cause mechanical resonance as a rule.

Tightening anything at this point would seem counterproductive because it will just enhance energies transfer to the case.

Field repairs are why Jeff doesn’t authorize field repairs.

Get the official importer involved. Unless this is a parallel import, in which case you’ll probably have to send it to VA.

I’m hoping the buzz is due to over tightening.

[AnotherJohnson]

If the volume is turned way up,
The transformer's higher-pitch hum transfers to the speakers.
With ET7 volume at 70 to 99 you can hear it from speakers....same pitch and same sound as coming from amps.

The higher pitched hum is a ground loop. Or possibly RFI.

The lower pitched is a mechanical resonance.

[Matty]

If it is a Ground loop what's the fix?

Could a ground loop resonance... then in turn... resonate the top plate at the slightly lower pitch?

If it is ground loop or the like....it may seem less when testing with the top cover off as then it's away from the system on the glass table with nothing is plugged into the speakers for any added volume and nor is the ART SA on at the same time.

Will try these things out tomorrow with ET7 on top of the audio rack so can plug things in at same time to see.

[admin]

Ground loop won’t cause mechanical resonance as a rule.

Agree,... or at least I've never seen it happen.

Tightening anything at this point would seem counterproductive because it will just enhance energies transfer to the case.

This would be my intuitive answer as well. However, if there are loose components, it has the potential to change the resonance frequency of the entire unit. In other words, it could potentially present in a non-predictable fashion. At the end of the day, tightening a few screws is low hanging fruit,... so something worth trying in my opinion.

Get the official importer involved. Unless this is a parallel import, in which case you’ll probably have to send it to VA.

This is the best advice of course (although not the least expensive).

If it is a Ground loop what's the fix?

This can get tricky and it often deals with identifying the causative component (which may or may not be the ET7). However, as mentioned above, I've never seen a ground loop cause resonance of a cover plate.

I would do some of the mechanical experiments suggested as step 1 and explore ground loop issues after.

[roberto]

The noise coming from the speakers with the volume up to 70 is when you have the turntable connected? To find the possible culprit of an odd noise, takes some effort. The first thing to do is, disconnect all the inputs, just your preamp connected to your power amp and have a listen.

Then add an input one by one, when the possible noise appears, it is coming from that device...
All power transformers radiates EMI and having proximity devices on top, below or on their sides, the EMI could be contaminated the audio signal.

70 is very loud, while listening on my system, I never go up of 40 level, I am usually listening between 25 to 30. 30 is for my DSD files, and 25 is for my PCM files. Sometimes I do play a little bit louder...but this is unusual for me.

I do get noise at 96...noise is normal, I believe...and it is coming from my tube 6922 Gold Lion gold pins Genalex brand.

[admin]

I do get noise at 96...noise is normal, I believe...and it is coming from my tube 6922 Gold Lion gold pins Genalex brand.

I don't think I've every had my ET7s2 above 35. I think it's fairly common to have some noise when you push the volume up to max. There is going to be some distortion or pickup of small aberrations in the signal.

[roberto]

I do get noise at 96...noise is normal, I believe...and it is coming from my tube 6922 Gold Lion gold pins Genalex brand.

I don't think I've every had my ET7s2 above 35. I think it's fairly common to have some noise when you push the volume up to max. There is going to be some distortion or pickup of small aberrations in the signal.

Yes, you are right Admin, my CLXs are very easy to drive and also my room is small. I don't need to crank it. But just for the fun, I increased the volume level up to 96, and there I got hissing odd noise. This unit has a tremendous good s/n ratio. I don't think that I ever played music over 50 in the level numbers of the ET7V2. This unit has much better S/N than my previous ET7V1.

Remember the value 70...is for HT operation. I don't use the Teather option. EPL1 and EPL 2, I don't use it. I use the aux to connect my HT audio signal, and have the volume open up to 70. This level, is like passing through the audio signal. There is not hissing or humming sound at this level. Here in aux, from the LFront and RFront output of my audio and video processor, I can control the volume with the processor instead using the ET7. I have a three channel power amp (Anthem) that drives my centre and rear channels.

[Joe Appierto]

If the newer CJ pre-amps are like the older ones then Roberto is right on the money. A single click on the volume control is = 0.67dB so at a volume setting of 67 you're at unity gain. If Roberto has to pump the volume to 96 in order to hear any hissing then (a) the pre-amp is dead quiet and (b) the tube(s) he's using are first rate/extremely low in noise.

[AnotherJohnson]

If the volume is turned way up,
The transformer's higher-pitch hum transfers to the speakers.
With ET7 volume at 70 to 99 you can hear it from speakers....same pitch and same sound as coming from amps.

Admin...will try that tommorow.

This is the sound that I was calling ground loop related. It is through the speakers at 50 Hz.

A sound that has a pitch is not tube noise which id broad bands.

Turning the unit up to its highest volume ranges will lead to revelation of whatever tube hiss is present. But any sound with a readily identifiable frequency is not expected. It is likely RFI or ground loop.

[Matty]

Ok...looked again with ET7 in position so able to plug it together as needed, with the top plate off.
The good news is with everything plugged up and on, with the ET7 top plate off....you can hear the transformer right next to it but not from the 2 meters away listening position.
As soon as the top does on it hums so you can hear it.

However the ART SA transformer is just as loud and along with the ET7 top cover hum....can be heard clearly.
It seems to be louder after it's been on for a while.

A new thing today..left Martin Logan 13a electrostatic Speaker emits very quiet crackling and clicking sounds.
Ear to speaker panel to hear it but it's there at times... it's inconsistent.
Only occasionally.

Then every hour or so....loud pops and bangs... from the left side.


Is this the tube or the speaker....?