Alesis Midiverb II HElP!!

Q

quadman2007

New member
ovld red LED and signal is always on no matter where the input knob is adjusted to. the leds are on even when nothing is plugged into the back. is there any way to do a factory reset?
thanks
 
Search for a post of mine on this board, I think someone was looking for a key sequence to hard reset a quadra-verb and I posted a link to a site with tons of devices...

I'm at work, and the bookmark is on the home machine
 
what you have is a blown op-amp in the first stage of the thing.... the output is sending DC out and the ovl led is treating it as signal... pretty much guaranteed.... unlikely a coupling cap since the thing is most likely direct coupled... and unlikely to be a supply rail problem ... otherwise would be giving more than just the ovl...
 
im pretty good with circuit boards so is there any way to fix it or do you know the chip or component that needs to be replaced?
 
i would need to see the unit or at the least a schemo of the thing to say which one is likely culprit... but this should be an easy fix even for a rookie tech... check the first and second opamps in the chain... mostlikely dual tlo72 or similar...
 
tlo84 is the lowend of TI's opamps... it's a quad package so the power pins are the middle of each side... (4is + 11 is -) the outputs are the four corners... (1-7-8-14) inverting inputs 2-6-9-13 non invert 3-5-10-12...
first check that the supplies are there and symetrical... the the outputs should be at 0V... or simply replace it and see what happens...
 
The TL074 is the low noise equivalent of the same amp. You could sub it if you want but I doubt very much you'd hear the difference. The difference between the two would be more noticeable in something like a mic preamp where your gain is substantially higher. This is where a low noise amp will make a difference. Don’t let the words LOWEND distract you. We are talking MIDIVERB II here, right.

Dwain
 
it's been awhile since i read the data sheet on those 2 chips but IIRC...

the tlo84 is a bipolar input...
the tlo72 is a fet input...
so if ya swap them ya may need to add some decoupling caps to the supply rails at the chip... which aint a bad idea anyhow...

just about any quad opamp should work ok here... doesnt need to be all that fast... though it wont hurt either... since it's getting hit with line level sigs... it's primary function is "conditioning" before conversion...
 
Both have J-FET inputs so you shouldn't have any issues.

As d-chord stated, pretty much any quad amp with the same package and pin configuration should work. I purchased my MIDIVERB II almost 20 years ago now and it uses two LF347s, which is again, a similar J-FET amp by a different manufacturer.

Although they are not exactly the same, their differences are slight. For practical purposes it doesn't matter.

Dwain
 
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