Stereo connections for 2-1176

[ChuckHanning]

Hi all,
I have two channels of Eddie Ciletti & Scott Liebers Neve 1176 project that had been set aside in my basement. I am now trying to design the enclosure and design functions for the unit which will have two channels in a 2U enclosure.
I also bought hairball’s stereo interconnection boards for when in stereo and a vu buffer for when the vus are measuring output (not gain reduction). The boards already have a built in buffer for gain reduction.

My main question is I would like to set up like a 2-1176 rather than 1178, where I have two independent channels or a stereo unit in which the attack and release are controlled by channel 1. Does anyone know how to do that?

Unfortunately I have not found a schematic for a 2-1176 or 1178, so am not sure what UREI originally did. I believe the hairball stereo boards Avery the two signals and then share them in the side chain, if I understand it correctly.

More minor question:
1. I was going to insert a sc rolloff choice? I have seen some compressors that have multiple choices but what is the consensus for just one frequency? 120 or 200 Hz or something else?


Thanks in advance for your help and opinions!!
Chuck

 

[JohnRoberts]

It is difficult to maintain good stereo imaging when linking two such mono devices together. The gain laws of the two individual units do not track very accurately causing stereo images to wander.

JR

 

[scott2000]

Yeah, it seems just running dual mono would be best.... They still sell this gizmo it looks like....
not sure what the deal is with it...
Schematic in manual
https://vintageking.com/universal-a...MI7YXynLXcigMVvaNaBR2BCTeYEAQYASABEgJvzfD_BwE

 

[Michael Tibes]

Wasn’t there a stereo link pcb somewhere on the forum?
I have used selected fets for my units to have a chance for better / easier stereo linking, but it haven’t tried it yet. The original urei unit was basically a battery and a pot if I recall correctly. In my understanding it was designed like that to achieve an absolute noise free dc voltage. As I remember it is not so much about the actual tracking but the different dc operation points of the individual fets - which were obviously not selected for different units, hence my thought to get away with the selected fets.

 

[scott2000]

I think the TTX OP76 project here mentioned the deal with matching fets in the build guide... Not sure what link method was used in that project if any at all apart from maybe a pad to add something....
It was based on Igor's op amp 1176 so maybe there is something different in there....

 

[JohnRoberts]

Wasn’t there a stereo link pcb somewhere on the forum?
I have used selected fets for my units to have a chance for better / easier stereo linking, but it haven’t tried it yet. The original urei unit was basically a battery and a pot if I recall correctly. In my understanding it was designed like that to achieve an absolute noise free dc voltage. As I remember it is not so much about the actual tracking but the different dc operation points of the individual fets - which were obviously not selected for different units, hence my thought to get away with the selected fets.

If it was as easy as matching Vgs they'd already do that, while of course that doesn't hurt.== Back last century when Peavey offered a dual mono tube limiter (VCL/2) we had customer requests for a stereo link mode. I had an engineer put one on the bench as see how it worked when the side chain was linked (not very good). We gave the customers a simple mod but warned them that stereo imaging would suffer.

This might be an interesting application for a MCU (microprocessor). Read and learn the gain laws of the two individual mono units, then compute precise tracking offsets for use in stereo linked mode..... or not.

JR

 

[scott2000]

This might be an interesting application for a MCU (microprocessor).

I think FMR Audio uses microprocessing in their stuff... not sure and how it is used if it does ...

oh..
https://www.fmraudio.com/rnc.html

 

[JohnRoberts]

I think FMR Audio uses microprocessing in their stuff... not sure and how it is used if it does ...

oh..
https://www.fmraudio.com/rnc.html

I just said it would be interesting to look at, not necessarily do.

DSP use in dynamics processing has been around for decades.

JR

 

[dmp]

Years ago, I built a pair of 1176 rev D with stereo tracking option and it involves both connecting the sidechain voltage together (with the stereo link circuit) and matching the FETs between the two units. I bought a large amount of the FETs and tested/sorted them to obtain 4 as close as possible.
The stereo link is described here

 

[MarkHorn]

Here is my hand-scrawled schematic for the 1176-SA stereo adapter that I made thirty years ago, and the UREI calibration instructions. It can only match the gate turn-on voltages but the gain laws of the FETs will usually be a little different hence substituting matched FETs. One unit will turn on sooner than the other so it may be necessary to swap the connections for the threshold matching to work.

The Brook F-96 solves this by using an internal interface board to match both threshold and gain so parameter spreads between the same type of FET are compensated for.