Do SLOs Hum?

C

cliffc8488

Active member
I just bought an SLO off eBay and the lead channel hums quite a bit. Seller says it was fine when he shipped it and that I have to file a claim with UPS. There's no evidence of shipping damage.

The amp looks to be in great shape. Just hums like mad.

Swapped all the preamp tubes. No difference. Haven't tried the power tubes yet.
 
I had one and it did not hum at all. I bought mine brand new. Sounds like a problem to me...

Steve
 
On another note, Cliff - please model this schem for the Axe-FX, ok:

arredondo1.jpg


Steve
 
Did you try it in different locations?

My XTC hums at home but not at rehearsal. Think the grounding in my home sucks. Apparently the XTC puts a lot of switching power supply noise on ground or something, I was told ... :confused:
 
Could very well be the power tubes. I have had a few amps that were humming like crazy when i got them, and a fresh set of power tubes fixed the problem!
 
Maybe a microphonic tube or bad power coming in.

Try plugging into a power strip with a surge protector.
 
SLO's do not hum but aside from the power tubes I would also take a look at the preamp tubes. If you it is a preamp tube I would guess that it is a Russian. If you have any questions please feel free to call me.

Good luck! :)
Trace
 
voodooamps":16dziq29 said:
I would also take a look at the preamp tubes. If you it is a preamp tube I would guess that it is a Russian.
Click to expand...
According to this:
cliffc8488":16dziq29 said:
Swapped all the preamp tubes. No difference. Haven't tried the power tubes yet.
Click to expand...
..he did. You should go out of the preamp section (Loop - send) into an external Poweramp
(like your VHT 2-50-2).
Make sure you have a speaker load on your SLO ;)

Then you will see if the hum comes from the preamp stage or the power tubes. :yes:
 
I think it's in the preamp because it's proportional to the Master volume. If I turn the Master down the hum goes away. I would think if it was in the power amp it would hum regardless of the Master setting.

I replaced all the preamp tubes but it still hums.

Everything inside looks fine. The amp is in really excellent condition aside from the hum issue. It's also a rare black chassis version.

Does anyone have a layout? I have a schematic with reference designators but there's none on the PC boards so it's a bit of a pain trying to troubleshoot it.
 
cliffc8488":1ef0yjkn said:
I think it's in the preamp because it's proportional to the Master volume. If I turn the Master down the hum goes away. I would think if it was in the power amp it would hum regardless of the Master setting.

I replaced all the preamp tubes but it still hums.

Everything inside looks fine. The amp is in really excellent condition aside from the hum issue. It's also a rare black chassis version.

Does anyone have a layout? I have a schematic with reference designators but there's none on the PC boards so it's a bit of a pain trying to troubleshoot it.
Click to expand...

SLO's have a lifetime warranty - DONT touch or change anything yourself. contact Mike Soldano and he will fix it for free. all you pay is shipping there.

as soon as you try to troubleshoot it yourself you void the lifetime warranty. its not worth it imho.
 
The warranty isn't voided, but they will charge you to put it back to stock, then repair under the warranty.

Pretty cool, really.
 
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