Noise Problem with Triaxis, need hints please

[SigiZ58]

Hello,

I bought a used Triaxis a couple of weeks ago. Now I got also a used 2:90 and I am experiencing ugly noise problems. I already started to track them down. It is possible to separate different issues.

I) Big AC Hum issue
As soon as I turn up the Volume output of the Triaxis, it starts to hum in the power amp. It is totally terrible when direct connected and becomes a bit better, when I use a transformer to cut ground loops. Nevertheless it hums more then with any other amp I possess. It hums without a guitar cable plugged in and when all values are set to zero (except the output-pot). I can remove all tubes - except tube no 5 and it still hums.

II) Ugly noise in Lead 2 modes. It makes some kind of shhh-plplp-shh-krrrrr, except I put down Lead 2 Drive to Zero. Already exchanged Tubes in position 2 and 4 without effect....

In the web there are schematics, but none for the part with the power transformer. I have learned electrotechnics, but I could really need a bit help from people here. Thank you.

 

[elvis]

Sounds like ground loop to me.

It's always tough to tell where the loop is, and isolation transformers are not an automatic solution. I recommend a one-step-at-a-time approach:

Mount them the way you will use them: if you will have them in a rack, put them in the rack. You don't want to do this twice

Try plugging the Triaxis directly into the 2:90 (one channel only) with ground switches set to ground
Plug a guitar into the Triaxis with guitar volume knob set for no volume
Do not plug in a MIDI switcher or FX boxes
Set the Triaxis for worst-case noise
Lift the Triaxis ground, then the 2:90, then both.
Write down which has the least noise

Put an isolation transformer in between the Tri and 2:90
Try all 4 GND positions (neither lifted, then one, then the other, then both)

If you get a reasonable noise level, great. If not, you may need to use rack rail isolators.
Try the steps again until it is quiet.

Add second channel. NOTE: if you used an isolator for the first channel, you may or may not wind up with an isolator on the second channel.

If you will use a MIDI switcher, add it. If it gets noisy, you may need to go through all the steps again.
Try until it is quiet.

Add FX box (if any)
repeat as necessary
You may wind up with isolation transformers in and out of the FX box. Or only in. Or only out. Or none. Of one channel but not the other. You have to try all combinations. And try all combinations of GND lift with each combination of isolation.

 

[SigiZ58]

Hello elvis,

many thanks for your reply. I almost executed all those steps already. Almost because my setup is smaller

What I have:
The Triaxis is not in a rack now. It stands electrical isolated. There are no effects in the loop. Only one channel with isolation transformator is connected to the power amp. There is no guitar cable plugged in. This means 2 connections: AC-Power and output.
It hums. No difference with or without groundlift. As soon as you turn up the output level potentiometer it starts to hum. It is independent from the channel you choose and it comes either right or left. Of course, when you have the lead channel, the other noise adds to the hum.

Finally I took a h4n and removed the output from the Triaxis to power amp. Instead I connected the Triaxis to the H4n. The H4n is driven by a battery. This cannot be a ground loop. It hums. The hum has a level, when you play normal, you don't hear. But when the note goes away, the hum is there before the note has faded out. And if you turn up volume, you have a remarkable hum as ground noise. Even when you put all settings to zero (then all modes are exactly the same level of hum).

If I remove all tubes, then taking signal at send so breaking signal path. It still hums. This includes the Voicing section with op amps

The opposite game, only using V5 and inserting Signal in Return is hum free, not using op amps

This works of course also with all 5 tubes inserted.

And now: if I take not normal output but record output (using an op amp), the humming is back.
That points to the 15V-0V-15V part of the Power Circuit, or all parts that involve OP-Amps.

 

[j20056]

Sigi,

I have exactly the same problem as you and don't know what to do anymore. Did you ever find a solution?

 

[SigiZ58]

Sigi,

I have exactly the same problem as you and don't know what to do anymore. Did you ever find a solution?

Not yet....

 

[Jonelli]

Anybody ever fix this on their unit?
I am setting one up in a rig now, it's an old version 1, SN# T0449. It's got a 60/120 Hum (louder at 120) that is definitely coming from the unit itself.
It's tolerable only if you never boost any low freq's on anything. It's super annoying on clean settings with LF boost.

Just curious if anybody ever found a solution with the internal grounding or power supplies?

 

[cuzzinmike]

Same problem here, my primary unit bought brand new in '97 just recently started doing it, last year I purchased a back up, no idea of what year it was born but it arrived with same issue, I of corse use 2/90's in both rigs and have had them gone through,

So guys the question is with these being almost antiques, could it be caused by bad caps? or?..

 

[woodbutcher65]

Have these units ever been serviced and had their power supply filter capacitors replaced? If not...they're due. Get it done.

Hum can DEFINITELY be due to failing filter caps.

The 2:90 has a well known issue with burning up a molex connector on board. That needs to be checked for and repaired if it's a present problem.