1176 and cheap Mouser VU Meter

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Arrigotti

Well-known member
Joined
Jun 3, 2004
Messages
187
Location
California
I built 2 1176's using MNATS boards and a couple of cheap Modutec Mouser VU Meters (part # 541-MSQ-AVU-AW).

Once I got it up and running (with much help from you all) I went to adjust it. I think I was able to figure out the Q bias adjustments....good.

My problem is that I can't get the VU to 0 in GR mode. It gets to about -3db with the trimpot all the way CCW, and interestingly, the GR Tracking trimpot affects it also. Actually, if I totally screw up the Q bias, I can get it there, but I don't think that's the way to go.

I am getting .938 volts at the meter switch PCB (+ and - for VU) and 187mv after the goo-covered rectifier that came with the VU Meter (just before the VU meter). Could this be the problem?

Also, the output setting for the meter is about -15db off. This probably goes hand in hand with the other problem.

I have been checking the actual output through the computer (Sound Forge) from an Apogee Rosetta.

Everything else seems to be functioning as expected. I get compression, attack and release work as expected as do the input and output adjustments.
 
That little VU meter is pretty poor. I have one here and decided that I would never use it. The FSD of the meter itself is about doouble that of a typical VU meter, so I suspect that you're correct. You could try losing the series resistor (3.6K?) and see if that improves matters, but it's really not a good VU meter and I'm highly suspicious that it might be at the root of your problem.

Keith
 
Yes, I think I will try bypassing the series resistor.

Also, I wonder if maybe the little bridge rectifier that the supply could be the problem.

BTW, what does FSD stand for? Sorry for the ignorance.

I have heard that some have built bridge rectifiers to make a non-VU meter into a VU meter. Has anyone here done that?

Thanks.
 
Well, here I go replying to myself....

I tried to bypass R59 (3.9k) and it helped with the output levels. It was actually too much, so I can just find a value that works there by using a potentiometer to find the correct value and install a resistor of that value.

Bypassing R59 had no effect on the GR value. The needle was still a few db away from zero and I couldn't make it get any closer.

Any ideas on how to adjust that? I've been looking at the schematics and the only resistor I see in the Zero Adjustment part of the circuit is R56(10K). Could I adjust this to help my cause? Up or down?
 
FSD=Full Scale Deflection. I haven't checked the schematic for the Gyraf, but do they have a meter series resistance (mine are the UREI version, with alternate 8.2K and 3.6k resistors for +10 and +4dB respectively)

Basically if you can make the meter more sensitive in GR mode by reducing any series resistance, it might do the trick... A 'better' VU meter would probably work without the mods though.

Keith
 
After trying to change resistors, and testing, etc....I still couldn't get the meter to work correctly. I was able to get it to zero out, but the gain reduction tracking would not work very well at all.

So, I did the smart thing and hooked up the VU I used for my LA2A (a good one) and after realizing I had to take to other meter out of the circuit too, the LA2A was behaving very well.

So, the bottom line here is that those Mouser Modutec VU Meters are CRAP!!, at least for this application.

I guess I'll be buying a couple of Sifam's. Anyone got 2 for sale at a good price?

Maybe Mouser will take these pieces of $%^&# back.

Thanks for your help SSLTech and Allessio.

Once again I learned something because my project didn't work straight away.....Don't buy crappy components...Get the good stuff.
 
Back
Top