mk Iv strange nosie...

[Shep]

when i turn my mk iv A 92' on there is this strange hum coming from the back of the head...it not that loud and it could also classifly as a very VERY light vibration.It does Not come out of the speakers ..it really sounds like the best sounding amp i have ever had...so it sounds good..lol

i turn the fan off for a second to see if it was the fan vibrating..no luck..it sounds like it is coming from the output tranny...it could be the normal hum that it has always got and i just heard it so that could be possiable..

Also just a note i transform 240v to 120v ..meaning that its a US head and i use it in AUST with aust power...


is there anything i should be worryed about....?

Thanks Tom

 

[Russ]

Yeah, mine from 90 makes no sound except the fan. Without the fan plugged in it is dead quiet. There is the usual associated tube hum through the speakers but you can't get rid of that. Otherwise, your amp should not make any sound that is not coming from your speakers with exception to the fan.

 

[Shep]

i have a really high quaitly audio amp ( ampzilla GAS ) and it does the same thing and thats running aust power...

 

[Russ]

My Mark IV says 117v on the chassis inside. Typical US household current is between 110-115, sometimes this can vary as high as 120. Is there any way to dial down the 120 on your converter? You might try another converter too as the one that you have may be slightly faulty. That would be cheaper than assuming that the amps you are running are the culprits. To replace those would cost way more than replacing a little converter. Also, these amps are sensitive to bad power. If your power is not consistent it can cause adverse affects also.

I once had a different amp that had a grounding issue that made some humming that I couldn't get rid of. Luckily it barely would come through the amp as audible noise. Eventually it got worse though. It ended up being a short that caused the amp to fail. If the humming doesn't go away on another converter maybe have the amps checked out.

 

[screengrid]

Hi Tom,

what outlet voltage frequency is common in australia? Is it 50 Hz ? I'm not sure if the difference between the net frequenzy in USA ( 60 Hz ) could be the probleme, but it should be considered.
Otherwise, if the hum really doesn't come from the speaker or from some other vibrations, like the fan, I would look, if the power tranny is sitting tight to the chassis.
The next good way, is to check the value of AC current on the primary of the power tranny. So you could see, if the current is in a normal range by the given outlet voltage. The power tranny of my MK IV combo is wired for 220 V AC (Export model ) but there is a sticker at the tranny, which tells 120 V 60Hz 2,5 A !
In order to make sure, that there is no problem with the power tranny ( in worst case, for example a winding short ), one should measure all voltages on the primary and secundary side of the tranny.
But a slide hum / vibration comming from the tranny should be normal, IMO. So it is with my MK IV since I got the amp in January 1991. BTW, it is also normal, that the power tranny becomes fairly warm during operating, especially when operating in full power modus !
Regards and good luck

Arno

 

[Shep]

did those mk iv trannys come with a 240 v coil tap? can i rewire it so it's 240v.. the transformer i am using is a Steed STIG it's pretty much the best tranny you can buy in AUST and it new so i don't thing it's that...the 50hz over 60 hz can that be a problem?

 

[screengrid]

Hi, according to the mentioned schematic I have, the export model should have a transformer with a 240 V tap. But I can't say it for sure, because until today there was no need to take the chassis out of the combo housing.
Regarding the 50 Hz to 60 Hz operating, basically there is a difference of course. A 60 Hz transformer normally should operate with 60 Hz, because with 50 Hz the inductive reactance is less, which can result in a higher current flow.
If it could be a problem,surely is a question, how the manufacturer has designed the technical specs and tolerances of the transformer. I guess, with a orignal power transformer from Mesa Boogie, it should be no problem.
Remember the mentioned sticker ( 120 V~ 60 Hz 2,5 A ) at the export transformer ( wired for 220 V~ ) of my MK IV.

regards
Arno

 

[Shep]

yeah..if the different of the 120v and 240v was a different coil tap i don't think the 50hz/60hz would be a such big problem at all.. is that right..