VU meter hum problem

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VU meter hum problem Empty VU meter hum problem

Post by terrydec on Sat May 04, 2013 4:40 pm

I'll try and post photos if necessary.
First some info. I have a studio that consists of a Tascam 464 Portastudio that I use as a mixer. The output feeds a BlueMax compressor/limiter. That output feeds a series of jacks wired in parallel inside an aluminum box. That box feeds the inputs to a cassette deck, a reel to reel, a monitor amp and a Ramsey FM25 transmitter. The limiter is like an AVC, smoothing out the signal for the transmitter. Also in the chain is a home made VU meter system consisting of 2 WBS 4 inch meters with lamps. There are two LM 386 op amps to drive the meters. The amps are powered by a simple biamp power supply. It consists of a 12VAC center tapped transformer, the center tap is not used. The rest of the supply is 4- 0.1 mf film caps, 2- 1,000mf electrolytics, 2 1N004 diodes and two 12 volt regulators- 7809 and 7909.

I take the 12 volts for the lamps straight off of the secondary of the transformer before the power supply. The amps attach directly to the meters by "L" brackets.

Problem- every time I plug the VU meters into the RCA jack strip it causes hum in the transmitter.
The transformer and power supply are in the same cabinet and sit in between the VU meters and amps.
So-options: Move the power supply out of the cabinet? Build a separate DC supply for the lamps, or use a separate transformer? Use a 3rd,(ground), wire connected to the center tap? Get a separate low power amp to drive the meters? Just let the box sit there with the lights on to look cool? Question

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Post by Resistance is Futile on Sun May 05, 2013 3:55 pm

You might wand to use shielded cable for the lamps. Question, does the hum go away if the lamps are not inserted?
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Post by terrydec on Sun May 05, 2013 6:48 pm

Resistance is Futile wrote:You might wand to use shielded cable for the lamps. Question, does the hum go away if the lamps are not inserted?
Thanks-
It will be easier to do anything else but remove the lamps. They are epoxied to a spring that holds them in place.
I'm going to try and use two conductor shielded wire for the power leads to the power supply and move the transformer
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