It might be normal for Jolida but I would stand clear of it. Humming bothers me and I won't stand for it. To me an amp humming has no place in high end audio.
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Humming through the speakers is not the same as a noisey tranny which is a mechanical noise which does not produce a hum through the speakers.
The unit has a hum problem which may be a ground loop issue or power supply caps that need replacing. Perhaps even some other issue. Hard to say if it will happen in your home or system if it is a ground loop issue. My experience suggests your best to assume you will have the very same noise issues. I would stay away and purchase another amp.
Having seen reports of humming trannies
Mechanical vibrating noise from the transformer itself.
All transformers hum to some degree.
What the seller describes in his reply has nothing to do with transformer mechanical humming noise.
Also I would add what the seller describes in his response would be normal in many audio systems if the sound he is hearing is actually white noise and not humming.
Try his test on your existing audio system......
Email the seller back and explain to him what you want to know is if he can hear the power transformer humming with his ears, say, 3 ft from the amp.
Also ask him about his test.... Was the sound he was describing, with the volume cranked up all the way, hum or white noise?
"With the speakers connected to the 302B, I can hear a very faint hum from the speakers, but you have to put your ear right against the speaker grill to hear the hum. Turning the volume knob on the 302B has no effect on the amount of hum - the sound level remains constant regardless of the volume setting. Again, I must stress that the volume of hum is so slight, I doubt if anyone in a silent room will notice it, even when standing close to it.
Now, with a CD player hooked up to the Jolida, the hum level increases as you increase the volume on 302B. When the volume dial is turned down to minimum, the level of hum is very faint (same level as if cd player was not connected).
When the volume is turned to MAXIMUM, the hum becomes noticeable as you approach the speaker (about 3 feet away). In addition, when the CD player is on, and the input selector on the 302B is set to other than CD (such as AUX), turning the volume knob has no bearing on the hum level - it stays constant at the barely audible level.
Just bet the seller is confusing white noise with hum.....
Humming to the speakers is because the AC filament supply to the 12AU7 is making it into a buzzy microphone.
Spent MONTHS on my previously modded 302B to fix the problem by taking out the center tap for the filament which had become intermittent, and building a 100Ohm--100Ohm center tap, and elevating the filament center to about 70V.
Most modders who know about filament elevation for SRPP gain stages would know how to do this.
Remember hum through the speakers can be caused by cable tv issues, interconnects etc. or other external issues that have nothing to do with the amp itself. Also, if there is a bit of hum through the speakers, and it is amp related, the loudness of the hum will also be a function of the sensitivity of the speaker. If your speakers are more efficient than the owners the hum could be louder. How old is this amplifier?
Of course, cos the hum is not from the input jack or internal wire, its from the filament supply.
Most modern power amps or integrated amps with reasonably high gain have DC filaments (read: no hum)
Regardless of AC or DC filament, the textbook treatment if you have a totem pole (SRPP or stacked triodes the call) configured first stage the filament MUST be raised to preserve tube life.
Those who throw NOS tubes at these Chinese amps you are flushing money down the toilet.
properly modded this amp is wonderful. tranny is overbuilt, lots of space to put in oversized components.
However, most modders simply put in new caps and new diodes and completely ignore this serious flaw of filament supply.
If " barely audible" is something acceptable when the input is shorted with nothing, no CD connected, then go for it and fix the CD player, likely a ground loop or a bad RCA cable.
If "barely audible" is a buzz reagrdless of volume and it annoys you, then its the filament supply that really should be fixed.
Well I guess if the OP would find himself putting his ear up close to the speaker grill obsessively then he should pass on this amp.....
I must say I have never listened to a Jolida integrated amp and know beans about them.
I will say reading the email of the seller I believe he was being honest as possible.
I would also bet the seller does not have shorting plugs plugged into the unused inputs on the amp. That alone can add noise....
What did this amp sell for new? Under a $1000 bucks?
All, can't thank you enough. The seller has most graciously let me back out. Amazingly honorable person.
Shipping to the nearest tech would be prohibitive, living with it would not work for this overly particular buyer, and spending the time to learn and fix it myself isn't an option. I need to get my hifi set, so I can return to studying jazz guitar, or I'll never be able to play a tune.
Thanks again. This place is amazing.
Hum is bad. Stay away.
Best case, it's possible a ground loop issue or something along that line in the current setup that might vanish in yours, but unless that could be determined for certain up front, I would look elsewhere.
Worst case is damaged or defective boards or other components internally in need of repair.
Yes, hum is bad!
The seller should identify the issue in the listing now that it has been detected and confirmed and the item should be rated and priced accordingly. As the buyer, it may even be risky to assume the unit can be repaired, but for the right price, that risk might be justified. IF the seller can reliably confirm the issue has been resolved somehow, that is a different story.
Of course buyer beware, but if we believe the seller's description of the hum, I wouldn't worry about it. "very faint hum" with ears pressed up against speaker is a cause for concern? I think not. I have a Music Reference rm10 tube amp that is known for its quietude and I get the same thing through my system. It may not be the amp's fault but given the faintness of the hum I'm not too worried about tracking it down (which can be a nightmare).
To be honest, I used to be, but then again I was being neurotic.