Boogie Quad Pre volume difference fix ch.1 & 2?

[Markedman]

What do I need to do to fix the Master volume level on ch. 2? For some reason Boogie designed the unit this way, they do weird shit like that. What can I do to fix it besides sending it out to Petaluma? I took the Quad to the area authorized tech and he had it for several months and it sat and sat and sat, etc. and I love the thing too much to have it gone again for months.

I'm 57 years old and have only a limited time here on Earth to enjoy playing damn it. I could live with it this way, my amp goes to 11, a Strategy 400, so it's a luxury problem, but I'd like to fix and if I know what to get or tell anther tech so I can wait in the car while they fix it, I'd be in heaven. If it's easy enough, like changing a pot or resistor, I have soldered lots of guitar pick ups/switches and such.

Here's a schematic - https://elektrotanya.com/PREVIEWS/63463 ... .pdf_1.png

http://www.kobra.hr/Schematics/Mesa%20Boogie/s-main.gif

Thanks in advance.

By the way, the Quad Pre amp is a real animal, I own a lot of Boogies and can play any one of them but they pale next to the Quad/400 set up. I like Dimebag, Randy Rhoads, Jimi Hendrix, Slayer, Van Halen type guitar tone that is in your face and extremely clear without mufflers/pillows over my tone.

 

[glpg80]

Just as I suspected, there are LDRs in both channels that control which channel is selected and which is disabled. LDRs are LED controlled resistors. They are current controlled resistances essentially. The problem with LDRs is that they eventually lose their ability to maintain high impedance in the on state. What you’re hearing isn’t just channel 2, it’s also the performance difference of channel 1 to channel 2, as well.

Mesa did offer LDR replacements and Tremoverbs as late as 1994-ish were subjected to the same LDR defects.

I bet with a verification that the tubes are not to blame first, and then replacement of the LDRs, it will be good as new.

You’ll likely need to recap the power supply by now as well if it hasn’t been done.

 

[stephen sawall]

Many Mesa amps have the LDR. In most cases there is never a issue. Personally I would send it to Mesa if you believe there is a issue.
You never actually mentioned what the problem is in your original post.

 

[Markedman]

Garey Noble (MESA/Boogie)
Aug 13, 2020, 9:00 AM PDT

Hi John,

If the pots were changed it will oscillate with gain and ch2 master cranked up.

They thought it sounded right with the 10K master on ch 2, that is the reason ch2 is so much quieter.

You can turn the A and B output LVL knobs up and get more ch 2 and then turn ch 1 down.....
Please let me know if you have any questions or need assistance in any way. Thanks!

MESA Customer Service
Mesa/Boogie, Ltd.
1317 Ross Street | Petaluma, CA 94954 USA
www.mesaboogie.com

707-778-6565

 

[fusedbrain]

.... I took the Quad to the area authorized tech and he had it for several months and it sat and sat and sat, etc. and I love the thing too much to have it gone again for months. ......

Off topic, but FUK me, I see this kinda shit over and over and over again. What the FUK are these "techs" doing.....
When people ask me to work on their shit, I either tell them "it'll be a week to 10 days" and then deliver on that, or "sorry but I'm swamped right now. Take it somewhere else."
I don't take their shit, then keep it for months on end and never look at it or work on it. WTF!!!!!

Sorry for the rant. Carry on

Oh, and in regards to servicing Mesa amps..... they are a bitch to work on, and some of the replacement parts are really hard to find.
Unless it's something simple, you are almost always better off sending the amp to Mesa in Cali.
NOT the local authorized tech.
Send the damn amp to Cali.
It will get fixed right, and sent back on time, with NO drama.
They have all the parts, and they know how to fix the amps.
YMMV

 

[SpiderWars]

I am interested in this because I had heard that the Triaxis has a bazillion LDRs and that over time it needed to be 'tuned' (for lack of better word) to account for LDR drift. But my experience agrees with Stephen, my IIC+ seems fine and the few amps I've built with them (the oldest is only ~15 years old) are fine.

I did build an XTC-inspired amp and the different ON/OFF times made the amp volume swell for an instant when switching from dirty to clean. Do the ON/OFF times drift as well?

 

[Markedman]

Garey Noble (MESA/Boogie)
Aug 14, 2020, 8:11 AM PDT

“It was about the way it sounded with a particular pot value and taper! Tone before all else!”

 

[stephen sawall]

There is a really simple modification that resolves the issue.

Loosen the screw on the knob that believe is at the wrong level. Turn the knob to whatever you think is the right number reading. Tighten the screw on the knob.
It will now read whatever number you want.