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Spencerleehorton

Re: 500 series blue face 1176 rev A - Help thread
« Reply #200 on: February 03, 2016, 05:23:10 AM »
Hi, I'm looking for a cheap alternative that works well for the input T attenuator and came across  this

https://www.surplussales.com/Potentiometers/PBM-Shafted/PBM-Shafted-3.html

Panel Bushing Mount Pot
1k Ohm

(RCV) BAS1213-033
3 gang panel bushing mount pot. 1k ohm, 2 watt. 1/4" shaft. 1" diameter body. Made by Centralab.

If the outer two pots were connected with 2 X 500 ohm resistors would this be pretty close?
It's only $6 which seems good, they do have another section with cheaper T attenuators.

Spence.


mica

Re: 500 series blue face 1176 rev A - Help thread
« Reply #201 on: February 03, 2016, 06:17:29 AM »
Well, took it apart looking for wrong components or bad solders, but didnt find anything. Its passes audio allright, and the input/output seems to work, but im getting a very loud hizzing noise from the unit even without audio. I have ruled out the extender cable, because its equally noisy when inserted directly in the 500-rack. The noise increses when i turn up the output, but all the way up, the signal/noise seems to disappear. What could i look for?

http://soundz.dk/U76-2.mov

mica

Re: 500 series blue face 1176 rev A - Help thread
« Reply #202 on: February 07, 2016, 08:21:48 AM »
Ok, so heres a rundown of my problems. The in/put knobs seem to work, but I cant get very much volume from them. 10 DB max, and im supposed to get 50.. Also theres a horrible distortion coming from the unit, that disappears when i touch the TDK box on the PS16Vto30V PCB:

http://soundz.dk/U76-3.mov

The noise:
http://soundz.dk/U76/noiseU76-2.mp3

My rig doesn't have grounding problems, because if i switch the U76 for another 500 unit, its dead quiet:
http://soundz.dk/COLOUR.mov

Pics:


























Also, my multimeter tells me that these two point are touching (possible short) Is that a problem? They are very close together by design, so kind of difficult keeping them apart.


mica

Re: 500 series blue face 1176 rev A - Help thread New
« Reply #203 on: February 08, 2016, 02:25:37 PM »
For reference for other novice builders: Some of the noise was removed by adding a wire between pin 1+5 and adding a wire from the DCDC chassis to pin 13. Thanks to DON himself for the advice. :) The weird input/output thing at the beginning was due to a broken off pin on the input knob (they are very fragile) and the very low DB gain was a overlooking on my part in my setup. The line input was at +4dbu on my soundcard.

Still having problems with static noise though and low gain. Can only get around 20DB gain..
« Last Edit: February 10, 2016, 04:48:07 PM by mica »


 

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