500 series blue face 1176 rev A - Help thread

[drew571]

Here's the link to the cart.  Many things are backordered.

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=4fe7f974bc

 

[barbaroja]

Is the output on this rated for a 600ohm load?
Is the input the same?
Got mine ready, thinking about patching it correctly now.
Is there a easy way to mod it to add a full bypass switch on the front panel? I miss that.

 

[rob_gould]

Finally got this finished after spending far to long waiting to resolve a problem with faulty FETs.

It sounds sublime, though since I'm new to 1176 compressors I think it'll take a little while to learn how to get the best out of it.

 

[Bobby Baird]

Um... has anyone else experienced your hairball t-pad causing static sounds as you adjust levels in real time with playback of low frequency material like bass guitar? This is funny because it doesn't happen with playback of vocals. I checked continuity of t-pad bushing with L-bracket all good. Maybe I have a faulty t-pad.

 

[Bobby Baird]

I think all answer my own question. I looked at the main pcb and it seems I omitted the ground connection near the input transformer from the t-pad and audio ground on the edge connector to t-pad. This must be causing the floating reference to ground which is what I'm hearing as I adjust the t-pad. When I referenced the build manual there was no reference to ground connection for the t-pad. Also, I noticed that I have rev.3 boards which have the output polarity flipped, all fix that to while I'm in there. I have to pick up some solder wick and all report back in a day or two with my findings.

 

[mutterd]

Bobby,

I have experienced crunching and crackling while adjusting the T-Pad - but it wasn't source specific - it would make noise even if there was no input signal at all…

I swapped it out with a new one and it was fine, but now my 2nd U76 is doing the same thing…

let us know how it goes…

Timothy

 

[Bobby Baird]

Bobby,

I have experienced crunching and crackling while adjusting the T-Pad - but it wasn't source specific - it would make noise even if there was no input signal at all…

I swapped it out with a new one and it was fine, but now my 2nd U76 is doing the same thing…

let us know how it goes…

Timothy

It's a crackling alright as I adjust the pot on the u76. Thing is on my dual 1176 with mnats boards theres is no need for ground potential on attenuator which has me wondering. I hope to just ground out the 3 pins in the middle of the attenuator and see if that cleans up the crackle. I just hope I don't introduce ground loop. As audio ground will be connected to chassis ground. ???

 

[Bobby Baird]

So I checked the 2-1176 with hairball attenuators and it does the same thing with the bass. I then tried bass guitar direct through a radial jdi into the 1176 with the ground lift and the chatter went away, so something with the ground reference is causing the chatter, crackle what ever you want to call it while adjusting the t-pad. I still want to see if I can hush these t- pad things, but I might have to just use a 1:1 jensen tx between my mesa boogie and my 1176 for peace of mind.

 

[Bobby Baird]

Tried grounding 3 middle pins of attenuator to ground and it didn't provide any improvement to chatter only caused more distortion at full cw position. I will try a product called Deoxit and fader lube sold by Caig company as it's suppose to be safe for plastic conductive pots.

 

[Bobby Baird]

Anyhow units put back together after adding ground wire from edge connector pin 5 audio ground to input transformer. I corrected a plastic standoff with an aluminum standoff near edge connector pin one chassis ground. As well put a wire from edge connector pin 6 link, to pad 7 on main pcb for stereo linking of the side-chain. Swapped the blue and red output transformer wires as I have version 3 pcb as stated in the build manual to have correct polarity. After all that unit seems to be a tad bit quieter on the noise floor. The attenuator doesn't chatter with no audio present or running mono drum buss loops from interface. I believe the problem I was experiencing was coming from my mesa bass preamp. If anyone is interested in a trade of my u76 for a TB550a give me a PM. I have just built a 2-1176 and acquired 2- api 527 and I only have one TB550a that I would like to have a stereo pair. My u76 has plenty of spank. Picture here.

 

[fatheaddrummer]

Hi There,

I hope I am right here, because my question is about the NV73.....

Can I use this part:
http://www.mouser.at/Search/ProductDetail.aspx?R=2N3772Gvirtualkey58410000virtualkey863-2N3772G

instead of that part:
http://www.mouser.at/Search/ProductDetail.aspx?R=2N3055Gvirtualkey58410000virtualkey863-2N3055G

for the NV73....unfortunately the first part is out of stock, and i am not to good with BJT's

Thank you very much!!

Best,
Christian

 

[Bobby Baird]

That looks to be a good substitute. It is always good practice to have an over engineered part than buy an under engineered part. As long as the dimensions are the same as far as footprint and it has over specked amperage. You could post here to ask your question. http://groupdiy.com/index.php?topic=36831.680. Are e-mail David about the part.

 

[fatheaddrummer]

Hey Bobby,

Thank you very much for the quick reply and also for the Link to the right forum!
So, I will take this Part - you helped me a lot, to be a little more sure ;-)

Best,
Christian

 

[Mulmany]

Just completed my build today.

Testing voltages and they are odd... +10v on the +30v and -30v on the -10v supply. Not sure how this is possible.

Anything else to check? I did a visual inspection and a orientation check.

 

[Mulmany]

Got it worked out. It was a grounding issue in the OSA rack. Well I should say it was the lack of grounding in the rack.

 

[emrr]

I made a post about the OSA rack wiring differences here somewhere.

 

[crisotop]

I just saw that I only have 47u / 35V as C18 in stock (in the BOM it is rated with 40V). According to the schematic this cap is between +30V and ground, so 35V should be fine? any objections?

thanks!
Christoph

 

[mica]

Finished assembling and getting +30V and -10V but this happens when i pass it audio and turn up the output knob:

http://soundz.dk/U76.MOV

Second time i turned up the input a little, getting the weird delay thing..

Any ideas what to check for?

 

[onlymeeee]

Finished assembling and getting +30V and -10V but this happens when i pass it audio and turn up the output knob:

http://soundz.dk/U76.MOV

Second time i turned up the input a little, getting the weird delay thing..

Any ideas what to check for?

Sounds like a DAW setup thing to me.. latency/hearing two signals.. pre & post converters.. 

Is the output of the U76a all the way down when we're not hearing the delay?  If so, how come we're hearing the drums at this point?

Does it do it when the U76a isn't in circuit...  ie.  unplug the XLRs of the lunchbox and plug them in to each other..  (careful of volume!)

 

[mica]

yes the delay thing is probably my little test daw setup, but the noise when the input is all the way down is worrying.. I'll try it on the big setup later.. cant find anything wrong when looking at the build. No shorts or wrong components..