500 series blue face 1176 rev A - Help thread

[Spencerleehorton]

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]

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]

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]

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..

 

[mica]

Ok, got through to the end, but when doing the meter/tracking calibration i was only able to get a max -7db drop witht hte input at full CW, following the guide.  I can see that this has been a problem in other 1176 builds too, not just the 500-version. Anyone know how to fix this?

 

[mica]

So, im getting noise when the CA PCB is connected. The audio is clean until it his the CA board. Anywhere that would be obvious to look for noise there?

 

[wave]

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..

Hello fellow builders,
So is the consensus to jump any of the grounds together at the card edge? I see in mica's post he jumped chassis to AGND. Is any one else making any ground jumps? Other 500 modules I have built have pin 5 (AGND) and pin 13 (PGND) jumped but pin 1 (CHASSIS) is on a header...

Also mica, was the DC/DC chassis you spoke of the TDK part and you soldered a wire to it's metal housing?

Dave

 

[zmix]

I recently purchased a non-working u76A and am in the process of determining why.. 

In the mean time I wanted to check the feasibility of building 5 more..  when I enter a quantity of 5 in the Mouser BOM order, it has some interesting results:

Item 39 shows up with a minimum order of 5000

39

KOA Speer
Mouser #: 660-MF1/4DCT52R1003F
Mfr. #: MF1/4DCT52R1003F2
Mfr.: KOA Speer

Metal Film Resistors - Through Hole 100Kohms 1% 100PPM

Minimum Order 5000.
Must be Ordered in Multiples of 5000.
Similar Product 660-MF1/4D52R1003F

Item 64 shows up with a quantity of  200:

64

Central Semiconductor
Mouser #:610-2N3708
Mfr. #:2N3708

Bipolar Transistors - BJT NPN Gen Pur SS

200 Ships Now

$0.273

$54.60

Items 30, 67, 70 , 76, 97, 100  are all backordered


Item 88 is no longer available:

88
Cornell Dubilier
Mouser #: 598-DSF050J333
Mfr. #: DSF050J333

Film Capacitors .033UF 50V

Not Available

 

[onlymeeee]

If you have a look at the general BOM on the BOM page it should list any alternatives.. 
http://thedonclassics.com/u76a-diy_bom.html
https://docs.google.com/spreadsheet/ccc?key=0AhieSXF0iI98dFI1aU5FQndQdGlXQ1h2bVp3NkhBWHc&usp=sharing

For the backorder stuff:
For 647-UPW1H010MDD1TD, use 647-UPS1H010MDD or 647-UPJ1H010MDD
For 647-UVR1H6R8MDD, use 647-UPJ1H6R8MDD or 667-EEA-GA1H6R8
For 667-ECA-1VM101, use 667-ECA-1VM101I
For 66-RC07GF395J, use RC1/4395JB
For 271-62K-RC, use 71-CCF0762K0GKE36

For the 660-MF1/4DCT52R1003F, you can use the recommended product 660-MF1/4D52R1003F.  (same resistor)

For the longer available 598-DSF050J333, use 80-R82EC2330AA50J

The 2N3708 shows up with the correct 20 quantity here.  Maybe clear basket and add again? 

 

[zmix]

I just discovered that there were 2 terminals on the meter that are used to connect to the internal LED,  I used a 10kΩ resistor in series with the -16Vdc rail to power it, it looks like this:

 

[Teej]

Super noob question: Due to moving around a bunch between projects, I don't have my box of odds and sods left over from previous projects. The U76 needs some hook-up wire to be provided by the builder. Which wire should I order from Mouser?

I'm located in Berlin, Germany, there may be better sources around here, but I need to make another order from Mouser anyway so that keeps it simple.

Thanks!

 

[Teej]

Full idiot mode...assembling two of these, managed to do this section on the first one just fine but then screwed up the second and was trying to remove solder but lifted the pad 

Where do I jump this to? I assume looking at both side of this that I have no option but to jump it? I've looked at the schematic but I can't figure out where this should go.

 

[Teej]

other side

 

[a_)_i]

I'm at the calibration stage of my U76a build. It passes audio and responds to input and output controls but it won't do any metering or gain reduction. Voltages measured:

      G S D
      B C E

Q1       -1.2 0 0             5457
Q2            3.5      4.7 10.3             5457
Q3       10.3 13.9    9.7             3708
Q4       2.8      4.1 17.8             5457
Q5       3.1      28.3    2.5             3708
Q6       2.6      31 1.8             3053
Q7       5        17.3    4.3             3708
Q8       17.3 33.2    16.6             3708
Q9       3.9      17.9    3.2             3708
Q10            17.9 33.2 17.2             3708
Q11       -1 -0.9 16.3             5457

Meter was pegged to the left but as I was able to get it away by adjusting the zero trimmer but I can’t get it any further right in input mode than -20db. The meter doesn’t react to the signal in IN or GR modes.

There is audio signal at the right hand side pin of the 2-way molex connector for the CA PCB.  This is also present at the GR switches. However, I can't trace it any further than that at the moment.

Anyone have experience of the above issue?

 

[leRooie]

Hi guys,

Long time lurker, first time poster here. I was trying to order 2 kits from the Don's Classic website, but apparently they're out of stock. Tried to PM  the man himself, but apparently his inbox is full :-\. Anyone got any news on this?

Cheers!
Sietse

 

[onlymeeee]

Hi guys,

Long time lurker, first time poster here. I was trying to order 2 kits from the Don's Classic website, but apparently they're out of stock. Tried to PM  the man himself, but apparently his inbox is full :-\. Anyone got any news on this?

Cheers!
Sietse

Yes.. I'm currently out of front panels (waiting for a new batch to arrive) but I may have two..  if you email me, I'll check if I have a couple of fronts left..  Contact details on : http://thedonclassics.com/contact.html

 

[leRooie]

Yes.. I'm currently out of front panels (waiting for a new batch to arrive) but I may have two..  if you email me, I'll check if I have a couple of fronts left..  Contact details on : http://thedonclassics.com/contact.html

Awesome, will do, thanks!

 

[MiamiBoy]

Does anybody know the Radial PowerStrip?
https://www.radialeng.com/product/powerstrip/specifications

It has a “stereo link” on/off function on the back.
I wanna know if when the ON is engaged, will I be able to use 2x U76A as a stereo pair, without wiring the 6th edge finger?

I don’t really understand it.

Please see attachment from their website.

 

[dencul]

I just discovered that there were 2 terminals on the meter that are used to connect to the internal LED,  I used a 10kΩ resistor in series with the -16Vdc rail to power it, it looks like this:

Any chance you could offer a diagram or detailed explanation of how to wire this? I'd like to get my meter lit but not sure how to do it.
Shot in the dark here 3 years since your posting but.... thanks!

 

[MiamiBoy]

These are the instructions I got from The Don.
It works. But remember a resistor on the +wire.

“I normally power it with pin 12 (+16V) and pin 5 (ground)..  and wire a resistor in series on the + pin of the meter LED..  normally around 1k5 to 10k depending on how bright you would like it..  The smaller outer pins on the meter are for the LED.”

I hope it helps