500 series blue face 1176 rev A - Help thread

[Echo North]

About 3 weeks!

 

[Marc Duchesne]

Just received my hairball parts.. nice !

 

[qmp audio]

The pins aren't used for anything at the moment. Just mechanical for 51X. As there's no +30V rail in a 51X, I thought if I'm gonna have to make one, I may as well make it from the -+16V to make it compatible in any lunchbox.  Of course, if you wanted to bump up your 51X PSU to have a +30V rail, you could fly a wire straight in from the +30V pin.  DIY.. the possibilities are endless... 

I'm planning on taking this approach ( though w/ the standard 24v ).
So basically,  if i am understanding the schematic correctly, i will need to populate the section of the 16vto30v PCB that sends out the -10V.
I can eliminate everything on this PCB that comes after psC2.
I can fly a lead from the +24v pin to the +30v molex connector on this PCB to send +24V to the rest of the circuit.

Anyone have any additional recommendations?  Will I need to attached a diode ane/or fuse (f1/f2) to the +24v lead?

I,m just starting to sketch it out but don't want to over think it,  or potentially miss something. ( I'm not an expert EE ).

 

[onlymeeee]

The -10V rail is made on the main PCB.  The only thing the ps16vto30v does is create a +30V rail..  so all you need to do is leave that out completely. 
You may need to adjust a couple of resistors on the main PCB to adjust for the lower voltage into the amps.
I wouldn't put a diode as you'll lose even more voltage.  A PTC fuse could be worthwile however.. Up to you really.

 

[qmp audio]

The -10V rail is made on the main PCB.  The only thing the ps16vto30v does is create a +30V rail..  so all you need to do is leave that out completely. 
You may need to adjust a couple of resistors on the main PCB to adjust for the lower voltage into the amps.
I wouldn't put a diode as you'll lose even more voltage.  A PTC fuse could be worthwile however.. Up to you really.

Thanks for the info.  I was assuming that section of the schematic ( w/ the -10v ) was all on the converter pcb.
Since it will most likely be pretty easy to add the 30V conversion later,  i want to try doing as 51x first.  Igor's rev f style f76 i have built runs @ 24v and I'm very happy w/ it's performance.  I will report back when i get closer in case anyone else is interested in doing as 24v/51x too.

 

[tonycamp]

The -10V rail is made on the main PCB.  The only thing the ps16vto30v does is create a +30V rail..  so all you need to do is leave that out completely. 
You may need to adjust a couple of resistors on the main PCB to adjust for the lower voltage into the amps.
I wouldn't put a diode as you'll lose even more voltage.  A PTC fuse could be worthwile however.. Up to you really.

Thanks for the info.  I was assuming that section of the schematic ( w/ the -10v ) was all on the converter pcb.
Since it will most likely be pretty easy to add the 30V conversion later,  i want to try doing as 51x first.  Igor's rev f style f76 i have built runs @ 24v and I'm very happy w/ it's performance.  I will report back when i get closer in case anyone else is interested in doing as 24v/51x too.

pardon me if i missed it, but what is the advantage of doing this?

thanx
T

 

[qmp audio]

The -10V rail is made on the main PCB.  The only thing the ps16vto30v does is create a +30V rail..  so all you need to do is leave that out completely. 
You may need to adjust a couple of resistors on the main PCB to adjust for the lower voltage into the amps.
I wouldn't put a diode as you'll lose even more voltage.  A PTC fuse could be worthwile however.. Up to you really.

Thanks for the info.  I was assuming that section of the schematic ( w/ the -10v ) was all on the converter pcb.
Since it will most likely be pretty easy to add the 30V conversion later,  i want to try doing as 51x first.  Igor's rev f style f76 i have built runs @ 24v and I'm very happy w/ it's performance.  I will report back when i get closer in case anyone else is interested in doing as 24v/51x too.

pardon me if i missed it, but what is the advantage of doing this?

thanx
T

For me, the advantage is save around $40 in parts, and utilize existing +24v rail in 51x rack. 

 

[TheJames]

I think you would need to scale the resistors in the amp stages (and meter circuit)to make the circuit work 100% properly with the lower voltage.  Not to say it couldn't work...But it's something that needs to be considered when designing the circuit.  Igor is a sharp guy and I'm sure he took this into consideration when he did his project.  While I haven't spent much time reading up on his project specifically, a few comments here and there that I've read seem to indicate that it's more inspired by the 1176 than an actual recreation.  While completely valid...it's a different approach than what David has done with the u76a.

I built a pair of NV73's in 51x and omitted the converter circuitry.  I'm rolling with the u76's with the converter.

All that said...I got the bulk of my parts in last week and started building mine yesterday.  Aside from a couple of "Uhhh...How's that go?" moments, everything went together really smoothly and I'm all done minus the Hairball parts kit which has gone on sale today.  Get yer parts now!! 

As a build related note, it appears that there's one mounting hole for the main board that's off on the metal tray. 

 

[Nauraushaun]

Howdy all I'm relatively new to audio DIY and completed my U76 a few weeks ago and just have to say it sounds fantastic!!!! Absolutely love what it does definitely has the feel of any 1176 I've ever used
Just a question maybe someone can help me? just wanna
Be sure i haven't messed up haha
Ok so when I use my U76 as an insert in pro tools brilliant can get excessive compression before intentional distortion
But used when tracking following a pre amp can barely get any input on before distortion happens?

So input all the down output all the way down an undistorted signal -18 to -12dbfs (checked without compessor in chain) slowly raise input until 0.5db gain reduction bring output up until it reads the same as pre compressor and it's distorted not massively but it gets worse the more I add can barely get 3-5 gain reduction before distortion but as I say as an insert in pro tools i can crank this baby (compressor in) all day and no distortion
Any ideas?

 

[Marc Duchesne]

The 0 dbu analog is roughly -18 dbfs... When recording, you should set your pre's to around -18 dbfs in order to use outboard efficiently and keep your peaking levels down.
.

 

[onlymeeee]

Doesn't sound right.  You should be able to squash a -18dBFS signal no problem. (Obviously with output pot quite low to not distort the DAW)

How much gain does the unit have?  Input max, output max, compression off.

This only happens when being fed with a -18dBFS signal from a preamp? Not when you feed a -18dBFS signal from the DAW?


TheJames:
"As a build related note, it appears that there's one mounting hole for the main board that's off on the metal tray.  "

How much is it off?  I've not had any problems with any of my builds.  Can it be rectified by loosening the others off a little and tightening them all together?  Or is it a faulty L-Bracket?  If so, I can send you another, if you give me an email.

 

[TheJames]

A quick note...

When I first powered up one of my u76's, I only used a +/- 16v PSU connected to pins 12-14.  I made the assumption that all of the grounds were connected on the boards.  After not getting good voltages when powered this way, an email exchange with David proved this to not be the case at all as the grounding scheme is meant to be determined within the rack/PSU/wiring arrangement.  So if you're going to power this up outside of a rack, make sure you tie together at least pins 13 and 5 on the edge connector.  You'll save yourself some head-scratchin.

 

[TheJames]

Another note...

Even though it isn't explicitly mentioned anywhere related to this project (that I've seen at least), the 8035 meters from Hairball have LED lighting in them.  Tack an 820ohm resistor off that guy and fly a couple of wires to the +16v and power GND and you'll have your meter lit.

I've got one of mine built and calibrated sitting next to a pair of NV73's and a slew of VP312's.

Time for another rack.

 

[rob_gould]

Even though it isn't explicitly mentioned anywhere related to this project (that I've seen at least), the 8035 meters from Hairball have LED lighting in them.  Tack an 820ohm resistor off that guy and fly a couple of wires to the +16v and power GND and you'll have your meter lit.

Thanks for this info.  I'll defo be giving this a go.

By the way, for European builders...  My Hairball parts kit came in with a €42 customs charge   Just to give you some idea of what to expect....

 

[slegg]

Hi,
I have finished my first U76 Don Classics ! I love the sound to much ! But look at my measures ... I think I made a big mistake ! Isn't it ?
Slegg

 

[dbonin]

Hi,
I have finished my first U76 Don Classics ! I love the sound to much ! But look at my measures ... I think I made a big mistake ! Isn't it ?
Slegg

You should be doing a sweep from 20hz to 20khz just to be safe, but the attenuation at each ratio looks good.  Just make sure there isn't something funky happening above 10k - it looks like it's rolling off a little around 20k, but it's not at all bad.  I think you're good!

 

[slegg]

Hi Dbonin,
Thanks for your answer. I'm ok for the frequency response. But look at the Ratio !!!! There is more compression with 4:1 than other ratios. With same input signal of course.

 

[kante1603]

Hi Dbonin,
Thanks for your answer. I'm ok for the frequency response. But look at the Ratio !!!! There is more compression with 4:1 than other ratios. With same input signal of course.

Hello,

if I remeber correctly I had the same "issue" when I built Igor's F76s.
I think it is by design,not something going wrong.

Best,

Udo.

 

[baadc0de]

IIRC, any 1176 will change its threshold too when changing ratio, so that could be the culprit?

 

[dbonin]

Hi Dbonin,
Thanks for your answer. I'm ok for the frequency response. But look at the Ratio !!!! There is more compression with 4:1 than other ratios. With same input signal of course.

If you apply a steady test tone and you keep the input pot in the SAME position as you cycle through the ratios this is VERY typical of what you will see.  You are golden and have done nothing wrong.
Do some more reading on how the 1176 ratios work - it's all about how the input level effects the compression threshold... 

"The calculation of the "real ratio" was made measuring the relative change in Output for a corresponding relative change in Input at 0dBu (ΔInput/ΔOutput)."...
Check out this guys explanation  - scroll down to section 9 and you will see your curves match the typical response.
http://www.masonaudio.org/diy/comp1176