500 series blue face 1176 rev A - Help thread

[mutterd]

first 2 level circuit board - getting close now...

 

[mutterd]

hey everyone...

I just finished putting all this together but I'm having some trouble...

I have supply coming out of the 16-30 pcb, and 0V/-10V/+30V at the molex going to the CA PCB. I also have -10 and +30 on the meter pcb

but Im not get any output gain or any gain reduction…

If i run -18db of 1khz in, it passes it - and the input pot is working - but the output gain knob doesn't do anything and I'm not getting anything past that.

when I start it up i hear the whiz and the meter pegs to the right and stays all way to the right no matter what position any of the switches/pots are in…

anybody here have any gain/gain reduction issues with this?

I contacted David, will keep you guys posted when I hear from him....

thanks.
T

 

[rob_gould]

I'm also struggling with this one.  I get signal at the input pot, I get signal at the other side of the input transformer (junction of R5 and R4) but the signal just seems to disappear on the other side of R5.  I get nothing on my scope.

I've checked the circtuit over and over, David has verified that all the component measurements etc I've made are OK.  The FETs and transistors both seem to be OK.  There don't seem to be any solder bridges or anything.

So there's a possibility that I am measuring wrong somehow, or there's a very subtle fault with a component being short circuited but that seems very unlikely.

The next step for me is to build an audio probe rather than using my oscilloscope, thus removing the possibility that I'm measuring something incorrectly.

 

[Ferry Alons]

Hi All,

Also some challenges over here. Input and output controls are good, but the unit distorts very fast and the output sounds like there is a huge boost in the low end and the higher frequencies are gone. Like a -20db shelf filter up from 200hz or something.

Checked all components, power supply and voltages. I tried swapping the transformers and all transistors and FET's for new ones, no success. Then I contacted David.

Yesterday evening I measured with an audio probe and scope. I'm having a clean and good signal from the input till the source of Q4. The drain and gate is the point where it is getting interesting, there's definitely something going wrong over there. When put the audio probe on the gate or drain I hear the same distorted and filtered audio as on the output.

I'll keep you all posted on this.

 

[mutterd]

ALRIGHT!!!

so, for me - I had the polarity reversed on the T-pad - stupid - but, I guess that's what happens when you stay up all night tinkering with this sort of stuff...

checked the main board and found a few cold solder joints using this, which was mentioned a number of times in the thread:
http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

now all those little bits in there are singing in unison and it sounds great...

Also, ran the lead from the +16v pin with an 820R resistor to the + side of the meter and grounded the other and now have the meter lit - looks great...

my last question - when im "all buttons in" I'm getting the expected compression and excitement, but my meter is pegged hard to the right, so after signal swings it down, it really smacks back up to +3 pretty hard...

anybody else notice this?

thanks David - this is going in my live rack right in front of my Laz LA3A and I couldn't be happier...

 

[rob_gould]

ALRIGHT!!!

so, for me - I had the polarity reversed on the T-pad - stupid - but, I guess that's what happens when you stay up all night tinkering with this sort of stuff...

So please can you tell me... Exactly which wires did you have crossed?  And when you fixed this, did it stop the meter pegging over to the right when you turned it on?

The symptoms you describe in your first post sound quite like what I've got...

 

[Unit7]

http://groupdiy.com/index.php?topic=20058.msg640043;topicseen#msg640043

 

[mutterd]

http://groupdiy.com/index.php?topic=20058.msg640043;topicseen#msg640043

thanks for that!
T.

 

[mutterd]

ALRIGHT!!!

so, for me - I had the polarity reversed on the T-pad - stupid - but, I guess that's what happens when you stay up all night tinkering with this sort of stuff...

So please can you tell me... Exactly which wires did you have crossed?  And when you fixed this, did it stop the meter pegging over to the right when you turned it on?

The symptoms you describe in your first post sound quite like what I've got...

Hey Rob,

Instead of the two "In -" and "Input -" wires connecting to the left pin of the middle section of the T-pad, I had the "In +" and "Input +" going there...

but even after i fixed that and touched up the cold solders, my meter still pegged, and did until I went thru the Q Biasing, Tracking and Meter calibration - nothing really made sense, or seemed to work until i went thru that...

and even after it took me a second to understand the gain structure - it seemed really noisy so i was troubleshooting that - but the reality is, there is so much gain on the back side of this I can't really imagine ever needing to go past 12 or 1 o'clock...

I have to leave for tour on Monday - but if you need any specific measurements let me know...

how did your voltages compare to the Mnats schematic?

let me know if i can help...
T.

 

[barbaroja]

Would love to hear some vocal audio clips. Even better if compared to a rev D!

 

[Unit7]

Would love to hear some vocal audio clips. Even better if compared to a rev D!

http://realgearonline.com/thread/840/urei-1176-clone-vocal-shootout

 

[brewbacca]

Has anybody else had an issue where their unit starts squealing again (I'm assuming this is the power converter gadget) after about 30-45 minutes of being on? Could this have something to do with the heat sink coming off or overheating?

 

[brewbacca]

I'm trying to run a pair of these stereo linked and they never stop the squealing in the first place, but work fine when not linked. Anybody have ideas what might be causing this?

 

[brewbacca]

Got it! My 51x VPR power supply seems to be putting out less than 16+V, which can vary depending on the modules I have hooked up. I'd assume that my U76's weren't getting enough power for the 30+V conversion. I took out a few modules, and they seem to be working now.

 

[slegg]

Hi,
Is there anybody know why "Don Classics" doodled with black pen "RED" and "BLU" output transfo on U76 PCB ?

Thanks

 

[mutterd]

yeah - there was a change in the screen on the board - its in the manual on page 12...

 

[slegg]

Thanks a lot Mutterd, I forgot to read this page .... It's because I'm french !!! ah ah ah !!!

 

[goetzmd]

I finished mine yesterday – what a great project! This was my second diy electronics project ever.

I encountered two minor errors I have read here before – maybe this will help someone:

- very quiet sound, no low frequencies: the resistor-leg I used to connect the 3 middle pins on the input pod was loose on one pin
- very loud constant tone: I mixed up the violet and grey transformer wire

And yes, you'll get distortion if you feed a mastered track with 0dBfs through this thing! 

The sound:
It looses a little bit low end (maybe 2-3 dBr – is this normal?) but strong compression sound much smoother and less annoying than with a software plug-in.

 

[drew571]

Hey everyone, been contemplating doing this build but I noticed there were several components in BOM from mouser that are backordered and discontinued. 

I'm not smart enough to figure out alternatives. 

For you guys who are currently going through the ordering process, can you share with me the Mouser Cart that you end up with or explain the best way to get the components that are missing? 

Thanks.

drew

 

[rob_gould]

Which components are missing?