Dual Recto Loop Produces "Bad" Distortion

[kruzty]

Hi, I've searched this forum and elsewhere and can't find anyone that has a similar issue. I also called Mesa support and the guy seemed very knowledgeable, but said he had never heard of anything like it. So, I'd like to describe what I'm hearing and see if anyone else has experienced this on a 3 channel Dual Rectifier.

When the fx loop is active, I can sometimes get an almost chorusy, ghost-note, bad distortion type sound. It is most prominent on the clean channel (only because of the intended distortion on the other channels) and if I play somewhat hard. I don't actually have anything in the loop, I just use it for the output level and solo boost. Here have been my attempts to isolate and diagnose the problem:

- When I turn the loop off on the back of the amp, this problem does not exist.
- I've changed V1, V2, and V4 (the loop tube) and there is no difference.
- I've changed the Send level from very low to very high and everywhere in between and it doesn't seem to make much of a difference (although, when it is really high it might be a bit more noticeable).
- I've changed the Output level without a significant difference.

I'm just wandering if this is normal. After hearing the cleans with the loop turned off, it is hard to go back. I would just leave the loop off, but I really need the Solo boost function. One other note about my setup is that I pulled the two center power tubes and rectifier to reduce output power (per the manual). That shouldn't affect the loop, but who knows.

By the way, great forum - I hope to be hanging out here often.

Thanks for any help,
Andy

 

[mikey383]

Wow man. That's odd.

The 3 channel heads have a boatload of stuff in them. There are some transistors in the effects loop, and an IC chip. I'm gonna go out on a limb here and say that one of them went bad. It's probably time for a visit to a tech.

Sorry I can't be of more help.

 

[R_ADKINS80]

Sounds to me like the guy above said.....you're getting some oscillations from one of the hard parts or solid state components in the loop circuit. Could be anything from a faulty transister, cap, IC, or pot to a bad solder connection. Either one of those could cause symptoms like you are experiencing. Ya need to have it looked at by a tech who know's that circuit.

 

[kruzty]

Well, I just got my amp back from the tech. He went through and tested everything and cleaned all the pots and said it sounded fine to him. So, I had him plug it in at the shop and it did sound good. I still want to test it at home and see if I notice it anymore. He said sometimes just taking thing apart and putting them back together can clear up some of the odd gremlins. I don't really like that because there is no definitive answer, and I had to pay for the work since there was nothing "wrong" as far as warranty work goes. However, if it is sounds good when I get it home, I guess I won't care...

 

[Old BF Shred]

He said sometimes just taking thing apart and putting them back together can clear up some of the odd gremlins. I don't really like that because there is no definitive answer, and I had to pay for the work since there was nothing "wrong" as far as warranty work goes. However, if it is sounds good when I get it home, I guess I won't care...

CONTEST THAT CHARGE! If it is truly under warranty, you do not owe anything!!
He even admits that "sometimes just taking thing apart and putting them back together can clear up some of the odd gremlins"....so there was something wrong after all! :shock:

Call Mesa and complain BIG TIME. :evil:
They will not like you being charged for their warranty work. They will "have words" with that tech and possibly pull his service station status if they find he is pulling this crap!!

You need to FIGHT this! :x :mrgreen:

Best of luck!

 

[fluff191]

Isn't the V4 preamp tube position the Loop tube? Try replaces that.

 

[kruzty]

When I picked it up he asked about it being covered and he was kind of surprised and didn't know it was warranty work. I called Mesa before I took it in and they said he would look up the S/N, so I thought I didn't need to do anything, but maybe I needed to state it up front.

I don't think the tech was trying to get away with anything. They guy is the best in the area and has been doing this for many years, so I'll give him the benefit of the doubt, but you never know... If it all sounds good when I get it home, I'll contact Mesa and see if I can clear it up.

 

[kruzty]

Isn't the V4 preamp tube position the Loop tube? Try replaces that.

That was one of the first things I tried - didn't make a difference.

 

[Old BF Shred]

I wish you luck with that, either way.
I really think Mesa will stand behind you on this all the way. The last thing they want is the reputation that their service centers charge for warranty work. :shock: :roll:

The economy is bad enough and this could hurt their future sales.
The tech should always ask or check for warranty status (although you may be asked to present your receipt or other proof of purchase/warranty).

Please let us know how this turns out.

Take care!

 

[MrBoggles]

Thats a tough one.. sounds to me almost like an out of phase problem (like you can get when recording) Would you describe the sound as almost Hollow?? or tubular?? usually you would get a sound like that from having the dry signal return from the fx you may use in the loop. most rack pieces should offer a kill dry option.
but seeing how you don't use any.. Hmmm
I set my loop to send - 11 o'clockish and return - to 1 o'clockish without any probs.
one thing you could try is convert the loop to a series loop. I think i read here somewhere that you can do it without losing the solo function. that might solve your prob. but I'd get it checked out by a tech that knows mesa amps.

 

[pino0105]

Hi, I'm having similar issues (drastic tone change, to my ears at least) with both of my RK's (I+II)

http://forum.grailtone.com/viewtopic.php?f=24&t=41065

Maybe a design issue...