Hum problem

Hey Swamp….

Sorry to hear this.

Maybe I’m preaching to the choir but your post did not account for:

You said “… for a while” expressly focusing on the 30/30. What was checked or swapped out upstream to put the finger right on the amp?


Using a diff preamp. Got another preamp to try?

Using a diff amp. Got another amp around there? Does this occur with any amp in the system?

As well, Got another pair of speakers? Hook them up and try it again, using the exact same spkr wires, etc. .

These ought to eliminate one aspect. Hope so, but I’m not all in on that one though it seems an area to check out and its easy enough to do I’d think.

You said your tech looked at it but could not replicate the situation in what I suspect was his shop.

Something loose inside the amp? Moved during travel?

I’d suspect he set It up as I stated above before breaking out the multi meter or scope.

Before Al chimed in I thought ‘volume control’ ckt. Or upstream is developing an issue somewhere.

Thought loose connections on spkr wires too. And if using bare wires, a single strand loose and touching the case.

Have a hard time counting on a ground suddenly arising from an IC, or when one had not been there previously eg., CATV, Dimmers, etc. save for a now failing device..

Re-reading the post, the hum is there from the jump but more noticeable once power ala tubes warm up so I’d agree on swapping out what ever tubes, one by one, could be pretty revelatory.

The mystery for me is the ‘tech’ did his investigations with the same tubes in it, I presume.

Might be as simple as the soft start relay is failing. Moving parts with make & break or vice versa contacts do pose issues with time and use. The coil in the relay could just be ready to quit. Insulation break downs, poor conductivity from pitted or dirty contacts, contacts not fully opening or closing, etc.

Depending on what the tech says elec and visually testing it, Relays often have enough info on them so a replacement can be ordered pretty easily… if you just want to see prior to making any major moves… and provided it ain’t the tubes as was said.


If bad have VAC send a new one. I’d sure look into that before packing it in and sending it to the Sunburn state for a look see.

swampwalker

1. Hum not present when Atma S30 amp in system.
For me, interchanging in and out amps would be enough for me to point a finger right at where the issue resides. All else being equal and it appears so.

That move alone should resolve any suspicion of wires or speakers, or upstream gear, or even household effects as culpable items of interest.

My long ago EXP in fixing electronics points me towards the practical common sense sied of things as the approach I used back in the stone age, as a rule.

Guessing out loud as its all I can do here….. I’d say whatever is wrong is wrong in the VAC amp and quite immediately. ‘why’ it becomes more and more pronounced is due to the amp coming into a more stable operating posture so some devices are in play right off and if failing or failed, one would think the amp would either not work at all or work poorly.
Capacitors have terribly quick rise times individually. A bank of them even in parallel takes a tick longer to come up fully but no more essentially.

https://www.electronicproducts.com/Passive_Components/Capacitors/Failure_modes_in_capacitors.aspx

Caps don’t always create an open ckt. Preventing current or voltage transference 100% and hence, a lack of system wide operation. Caps don’t usually become the culprits either…. But nothing lasts forever man. Even caps.. a failing cap might be in play here.

I’d have ?? take a closer look at them IMO.

Also, to lessen or possibly prevent shipping it out, in the DIY vein, depending on just how exciting you want this step to become you can either unplug the amp from power, or leave it plugged in.

Tift the cover from the amp and leaving all tubes in place, as systematically as I could use a bottle of compressed air to clean it out. Or a vacuum cleaner with a thin tipped accessory or merely some pretty good small paint brushes to ensure nothing has gotten into the amp causing the issue. Just a thought. Dust + humidity + heat & repeat causes issues indeed.

Beyond a step by step front to back visual inspection of connections, boards, for issues with attention to excessive heat areas, where insulation or insulators may be compromised, or merely loosened, I’d say something is telling you it is sick and about to quit… but wants to surprise you with the timing of its exodus. Kind of a thoughtful thing if you think about it.

Although, an abrupt failure to operate would probably be less frustrating.

Deep regrets. Best of all possible speedy solutions.

@Atmosphere > “…. capacitors in the power supply that are failing. It could also be a bad ground somewhere that relies on a mechanical connection, but at any rate it sounds like you're going to have to send it out for repairs.”

Blindjim > As I alluded to these two items earlier(caps & grounds), and you have been more specific as to which caps, wouldn’t those devices which have physical movement associated with their functionality be more suspect for abnormal operation of the amp? Eg., relays, power sw, etc., generally speaking?

Just wondering out loud. Thanks.

@swampwalker
I reckon its just a matter of time and well, you know, now. My deepest condolences and best wishes.
I dig a thorough systematic eval to ensure the or those, physical components which have failed, and or are failing to be found out and replaced is in order.

Thanks Ralph. Good to know.