My OR120 MV Is squealing like mad.

[Frank_Jeeves]

I just got my Or120 back from the shop. I had to replace the output transformer. Get a new standby switch and New tubes.

I started playing it at home and the first thing I notice is that it would give me feed back way easier then before it needed to be repaired. When I put just one pedal behind it it started giving me squealing feed back from my Mustang that it never did before I needed to get it repaired. The Output transformer was not the same model and was taken I believe a Th100.

Is this sort of thing normal after getting a new transformer and fresh tubes?

[Gladmarr]

What does the feedback sound like? Does it sound like normal guitar feedback, or does it sound like some really high-frequency ear splitting stuff?

If it's the latter, the tech might've wired your output transformer backwards so your negative feedback line is now giving you positive feedback.

Did you have any tubes replaced?

[Frank_Jeeves]

Most of it is normal guitar feedback that I normally didn't get before. But with my Fender Mustang it's ear splitting squeals at about 4feet away and it fades away a little further away from the amp. The only fresh tubes are the power tubes

[Gladmarr]

Okay, then ignore the whole bit about the output transformer being wired backwards. Did the tech tell you why you needed a new output transformer?

If you truly needed one, I suppose the difference in sound should be night and day. Either that or your old power tubes were so beat to death that they had no brightness left to their sound. That might explain the difference.

[a.hun]

? oscillation from internal wiring having been slightly re-routed? Sometime a problem with these amps I've read. If so the tech would have to have a rethink about exactly where the leads go, especially in relation to the transformer(s).


Andy.

[Gladmarr]

That's what my initial comment was about, but that wouldn't account for proximity of the pickups to the amp. This is a loudness/brightness issue, not a lead dress issue.

[Frank_Jeeves]

Yes. i don't remember the specifics. But basically it was because the voltage was all off and the problem ended up being the ouput transformer. It's weird because he first changed the tubes in the guitar and that didn't do much to the sound but the new transformer has made this thing feedback like no tomorrow when I engage a pedal.

The squealing noise seem to only occur with single coil pickups especially the bridge of my mustang. But it also manage to do it with my Squier Jazzmaster and my Strat. Feedback did occuer with humbuckers but not a squeal.

I'm going to test it out again. The only other thing that I noticed was the FAC knob doesn't pop like it used to when changing settings. I think that's because he changed the way the standby switch worked. Something about the old one made it tax certain parts. I know I'm not giving enough detail here.

[Frank_Jeeves]

I did do a little more testing. Feed back tends to occur when the volume is all the way up and the gain is at about 9:30 and that is with my Jazzmaster with both pickups on and hum cancelling. Could the preamp tube be microphonic?

[Gladmarr]

Just to be clear, does it indeed get worse as you get closer to the amp and better as you get farther from the amp? If so, that's not really microphonic anything. That's just hotter gain at the amp. I think single coil pickups are brighter than humbuckers, so that is probably part of it. I really don't think there's anything wrong with the amp, I think you just have a different sound now that you have the new output tranny and tubes.

[Frank_Jeeves]

In the last test I had the Jazzmaster 20 Feet away and it got really loud.

[Gladmarr]

It's possible that that output transformer from a Thunderverb is just not a good match for that amp. Did your tech look into getting an OR 120 output transformer from Mercury magnetics? If the Thunderverb transformer is a lighter-duty transformer, you might have a more screechy Marshall-like tone now.

[jontheid]

PEDANT ALERT!

Isn't the TH100 the Thunder 100, not the Thunderverb 100.
I don't think there ever was a Thunderverb 100.

This post http://forum.orangeamps.com/viewtopic.php?f=2&t=43430" onclick="window.open(this.href);return false; states that the 'Thunder' amps don't have the extended low frequency response that the 'Thunderverb' amps do, which could well be down to different output transformers.

I too am surprised that the tech didn't get a proper OR120 type transformer from mercury.

[Chackbay]

Its possible that the repair tech who installed the OT didn't re-connect the NFB. I am not sure if that connection is made by physical wire or by PCB trace on this amp, but if it isn't connected, the amp will have tons of high frequency on tap make squeal at high gain settings.

[Gladmarr]

Its possible that the repair tech who installed the OT didn't re-connect the NFB. I am not sure if that connection is made by physical wire or by PCB trace on this amp, but if it isn't connected, the amp will have tons of high frequency on tap make squeal at high gain settings.

It's a wire, and on the OR120, it's connected from the 16ohm tap of the output transformer to a point on the PCB marked "NFB" on the 90s reissue amps. The point is unlabeled on the 70s PCBs.

[Frank_Jeeves]

Do you guys recommend that I get a Or 120 transformer. He talked to Orange and they gave him the TH100 transformer.