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MESA/BOOGIE .50 Caliber FX-loop problems

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1/23/2000 7:14 PM

MESA/BOOGIE .50 Caliber FX-loop problems

Mesa/Boogie .50 Caliber EL-84 non lead master model.

Hi guys, for who wants to know i'm still waiting for the
desired parts to smooth out the lead mode.
Meanwhile i've started to look into the FX-loop of this thing.
It sends out extremly strong and overloads the effects-unit
very quickly.
The input of my Lexicon MPX-100 and/or my Rocktron Replifex
must be set very low (not higher than 2)leaving very little
volume to the return input of the amp.
I have tried the effect-units with several other amps (Boogies also!)
this works fine with those.
Can anyone tell me what would be an acceptable value (m.volts or something)
and/or how to check this.
I have already checked the resistor values in this area and they seem to be
oke.
I've noticed in the schematic that the send and return is reversed.
A mistake from the draftsman,this is also wrong in the .22 Studio schematic!

Andy

1/24/2000 4:48 PM

The BEST way to deal with the ultra hot signal you have would be to start off installing a trimpot at the SEND. That way, you're guaranteed to have the proper level for your particular FX box as well. Of course, since you will be taming the signal at the FX SEND, you willhave to up the signal after the FX RETURN point so that the PI sees the same level, otherwise you will lose power.

Typically, I shoot for arond 0dBv at the FX send. No better way to do with than using a guitar and typical settings though, but you could use a 1KHz input signal at 100mV and then measure the voltage at the FX send and shoot for 1V RMS. That would be ballpark.

Gil

1/24/2000 9:28 PM
Andy	Thanks Gil Do you mean it's common knowledge for older(standard) Boogies to be difficult with effects? Anyway,how should i tame the return in my amp? Maybe you can instruct me with help of the image i've sent you of the send & return section. I'm practicly new at working on tubeamps, but i find it to be very interesting.(especialy Boogies!) Regards Andy

1/24/2000 9:39 PM

I don't know about the 50 Caliber series. The old (late 70s) Mark IIBs had a very hot FX loop, but by the time they got to the Mark IIC+, they had it right, and I never had any problems while I had that amp.

You know, it's not that you have to TAME the return of the FX loop, Andy, quite the opposite. If you lower the signal level at the SEND, you should make up for the difference at the return port. I don't even have a schematic in fornt of me at the moment, so I don't even know what the 50 Calibers architecture looks like.

But assuming there is no added stage that gets kicked in when you use the loop, look at the reisistive network that precedes the send, and lower the signal level there (by lowering the voltage divider effect), and do the converse on the return stage, or up the gain of the stage that follows it.

If anything I am saying makes no sense to you, then maybe this wouldn't be the project I would recommend tackling for the first time. I will see if I can have a look at a 50 Caliber shcematic tonight and get back with you here if I do.

Gil

1/24/2000 9:43 PM
Andy	Gil, i could mail you the schematic myself. Andy

1/24/2000 10:04 PM
Gil Ayan	Please do, you have my adress. Gil ayan@earthlink.net

1/24/2000 10:05 PM

quote:
"Please do, you have my adress.

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