Hairball Audio: 1176 Stereo Linking PCBs Support Thread

[germoju]

Hi,

Yes I got 2x rev D inside and i buyed the Stereo kit on hairballlaudio. So I think FETS are matched by Hairball...
When I send a signal in one board, i can find it on stereo board but one is louder than the other.
The response is not the same between all ratio. Maybe i got a problem on my ratio boards ? But I dont think so,  cause in mono the response are the same with pots at same position etc.
The only components i'm not sure are the 3391 and 3708... Maybe they are not matched as it should.Thanks for your help Mike !

OK !!! I changed all the 3708 on both cards and replace with matched 3708 ! It works great !! same response in stereo mode now So happy

 

[mrerdat]

OK !!! I changed all the 3708 on both cards and replace with matched 3708 ! It works great !! same response in stereo mode now So happy

I did the same yesterday and the stereo response is MUCH better now.  I bought a junk $5 multimeter that had a hFE test because I didn't have that functionality on the other one that I used for my build last month. 

Before, I was getting good stereo response at 4:1 or 8:1, but it got worse after that and was totally unusable in all-buttons-in mode.  It sounded very lopsided and kind of cool actually, but wasn't very usable for many things.  It was bad to the point where I had a better stereo response by putting the unit in dual mono mode when going 20:1 or all-buttons-in.   

Now after matching 3708s with the batch of 20 or so I had left, the tracking works great for all ratios! Now I think I have only a very, very slight deviation.... like a dB or less in all-buttons-in mode because I couldn't be super picky with matching the limited amount of FETs I had lying around.  Nothing that the slight tweak of a knob won't fix. Also very happy  ;D

One thing I should mention is that after replacing the 3708s is that one of my channels had a very low level and wouldn't work well until I passed a loud signal through it.  That fixed it completely and it felt like there were audio cobwebs in the transistors or something...

 

[100WChris]

Hi!
Finished my Stereo-1176 with mnats Rev-D boards and hairball Stereo Linking.

looks wild, but the unit is totally quiet

transformer and link-boards are under the main-pcbs

 

[100WChris]

Hi!
OK, because Mnats had mentioned it in Hairball/Mnats-Stereo-Support thread i have to ask:
Whats the best grounding scheme for a Stereo-1176 unit?
In my build i have done the following:
- All XLRs are grounded to chassis via Pin1
- IEC, all (four) boards, and PSU are grounded individually to the starground-point near IEC
- three LEDs are grounded via PSU-ground-terminal to the start ground.
Can this be improved? Unit works and is really quiet, but if it can be done better...
Cheers
Chris

 

[mnats]

Hi!
OK, because Mnats had mentioned it in Hairball/Mnats-Stereo-Support thread i have to ask:
Whats the best grounding scheme for a Stereo-1176 unit?
In my build i have done the following:
- All XLRs are grounded to chassis via Pin1
- IEC, all (four) boards, and PSU are grounded individually to the starground-point near IEC
- three LEDs are grounded via PSU-ground-terminal to the start ground.
Can this be improved? Unit works and is really quiet, but if it can be done better...
Cheers
Chris

My comment in the other thread was about the XLR grounding. As mentioned by Neil Muncy et. al. pin one should go directly to the chassis rather than to a wire connected to the star ground. I think that is what you are describing above.

 

[morls]

Hello,

I'm having a hard time getting the stereo link to work. I have 2 revision D units, and both work great in dual mono. However, when I link them there is no gain reduction happening. A signal is still passing through, and the meters work in VU mode, but no compression takes place.

I've got a couple of questions regarding the wiring, which might be where I've gone wrong...

1. The TRS female sockets I'm using have the terminals marked as 1, 2 and 3. I'm grounding 1 to chassis, and using the other 2 for input/output and output/input respectively. Is this correct?

2. When I'm connecting the loop terminal to the output pot, using a single core shielded cable, do I need to attach the shield to the pot as well?

Can anyone offer any advice please?

Thanks

Stephen

 

[morls]

So, I have an update, with progress of sorts...

I've been tracing the audio through the compressors. There is only a signal at the 'link' pad, coming from the output pot. Tracing this through the stereo link PCB, there is something I'm not sure of at R202 and R203. There is no signal crossing these two resistors - it's there on the 'link' pad side but not the other. This is the case on both stereo PCB's so I don't think it's bad resistors...

Can anyone please help?

Thanks

Stephen

 

[mnats]

1. The TRS female sockets I'm using have the terminals marked as 1, 2 and 3. I'm grounding 1 to chassis, and using the other 2 for input/output and output/input respectively. Is this correct?

A search fails to turn up any standard numbering system for these connectors. Please specify tip, ring and sleeve, a manufacturer's data sheet or how those numbers relate to the agreed upon terms.

I've been tracing the audio through the compressors. There is only a signal at the 'link' pad, coming from the output pot. Tracing this through the stereo link PCB, there is something I'm not sure of at R202 and R203. There is no signal crossing these two resistors - it's there on the 'link' pad side but not the other. This is the case on both stereo PCB's so I don't think it's bad resistors...

Not sure what you mean by crossing, but if there is a signal coming from the link pad (which is, after all, the output of the Stereo Link Board circuit) then something must be going in either from one or the other units that feed the simple mixer based around A201b. If the signal there makes it through the link switch to the input of the ratio board (R78 on the Rev D) then I can't see why it shouldn't be working.

 

[morls]

Hi mnats, and thanks for the great 1176 PCB's!

As far as the TRS connectors, 1 is sleeve, 2 is tip and 3 is ring.

I've also made a mistake in my earlier post - I get a signal only at the "loop" pad, and none of the other pads. Sorry for the confusion.

As far as my trace, I'll try to be more specific:

I'm running audio through the 1176, using the signal tracing probe from Mark Burnley's site http://web.archive.org/web/20050310014839/http://www.diyfactory.com/data/mbsignaltracing.htm

Here's where I get audio:
"loop pad"
into R201
out of R201
into C201
out of C201
into R202, but NONE out of R202 - ground point, so maybe all ok?
into R203, but NONE out of R203
into R204
out of R204
lastly, pin 3 of A201a

this seems to be the case on both stereo link PCB's.

I think my next step will be to check R203 on both boards. I verified and tested all resistors when I put the boards together, but I'll check again.

If you can help in any way I'd be very grateful. It's very generous of you to offer this support already, so many thanks.

Stephen

 

[mnats]

Hi mnats, and thanks for the great 1176 PCB's!

As far as the TRS connectors, 1 is sleeve, 2 is tip and 3 is ring.

I've also made a mistake in my earlier post - I get a signal only at the "loop" pad, and none of the other pads. Sorry for the confusion.

As far as my trace, I'll try to be more specific:

I'm running audio through the 1176, using the signal tracing probe from Mark Burnley's site http://web.archive.org/web/20050310014839/http://www.diyfactory.com/data/mbsignaltracing.htm

Here's where I get audio:
"loop pad"
into R201
out of R201
into C201
out of C201
into R202, but NONE out of R202 - ground point, so maybe all ok?
into R203, but NONE out of R203
into R204
out of R204
lastly, pin 3 of A201a

this seems to be the case on both stereo link PCB's.

I think my next step will be to check R203 on both boards. I verified and tested all resistors when I put the boards together, but I'll check again.

If you can help in any way I'd be very grateful. It's very generous of you to offer this support already, so many thanks.

Stephen

You stopped at the crucial moment. So no output from the first buffer? Is it the correct IC (dual rather than single)?

Measure the DC voltages of A201 at pins 8 and 4 using the virtual ground as reference at the junction C301/302.

 

[morls]

Thanks,

I have identified the problem. I have incorrectly installed A201 and A302 on both boards, they need to be swapped. An inevitable mistake I think given my level of (in)experience.

Your help is much appreciated. I'll let you know how I go once I correct this problem.

Stephen

 

[morls]

OK, I'm very happy to report success. I ordered a new stereo link kit, and have just installed both the stereo link boards. It all seems to work very nicely.

Thanks again for the help, I really appreciate it.

Stephen

 

[DUDE GUY]

Hello,

I just installed the link PCB's in two mono hairball 1176 kits. Both compressors work fine on their own, however, when linked, I'm having a similar problem that Boris (Stephen) mentioned previously:

Both compressors continue to pass signal (and meter fine in VU), but I see no gain reduction on my meters when in GR mode. I can turn up the level of the audio passing through the compressors, using either the input or output controls, but no compression occurs (no GR on the meter, no audible compression). I've triple checked the components on my link PCB's and I'm pretty sure everything is in order.

I believe I have used proper shielding techniques. The signal leads are shielded up to link PCB's and the ratio PCB's. I tied together all shields at the SPDT switches (but floating, not connected to the switches) and connected the shields to the right pin of the output pot (looking from the back), which then connects to GND at pad 16 on the main PCB, in the signal preamp area. I'm not having any noise issues, which would seem to imply that my shielding is good. Yes? No?

I'm using an SPDT switch in each unit (on the front panel) to minimize cable lengths. Thins means I have to engage the stereo link on both compressors, as opposed to using a DPDT switch installed in one compressor to engage the stereo link. I'm using the TRS link method described in the hairball stereo link guide, with tip and ring swapped at the link PCB's. I have the jumpers installed and my IC's are in the correct positions.

I'm grounding the link PCB's to one of the bolts on the output transformer, which is grounded to the chassis. I connected the +30 pad on the link PCB's to the +30 VDC test point on the main PCB. I'm measuring 29.72 VDC across  the +30 pad and chassis ground.

Any help is appreciated. I'm stumped. Please let me know if you need additional info.

Thanks very much.

-Kevin

 

[mnats]

Both compressors work fine on their own, however, when linked, I'm having a similar problem that Boris (Stephen) mentioned previously:
...
Any help is appreciated. I'm stumped.

So did you try signal tracing like moris did?

 

[DUDE GUY]

Good call. Thanks, mnats. I'll build that and see what I find.

Thanks for the boards, btw.

-Kevin

 

[dmnieto]

transformer and link-boards are under the main-pcbs

Hi Chris, I have one question... where do you find those L-shaped hinges (where you mount the output transformer)? I am trying to build my dual stereo board witha similar configuration as yours, but I have no clue about where to find that

 

[100WChris]

transformer and link-boards are under the main-pcbs

Hi Chris, I have one question... where do you find those L-shaped hinges (where you mount the output transformer)? I am trying to build my dual stereo board witha similar configuration as yours, but I have no clue about where to find that

Hi!
I found them at the local hardware store, nothing special...
Chris

 

[dmnieto]

My local store sucks them do they have a particular name?

 

[100WChris]

My local store sucks them do they have a particular name?

sorry, i dont´n know if they have a dedicated name... i´d call them aluminium L-profile or L-brackets. i found them in length of 1 meters at the hardware store and just cut of two small brackets to mount the transformers.
Chris

 

[DUDE GUY]

Both compressors work fine on their own, however, when linked, I'm having a similar problem that Boris (Stephen) mentioned previously:
...
Any help is appreciated. I'm stumped.

So did you try signal tracing like moris did?

I tried signal tracing and it seemed to be an issue with one of my SPDT switches. I swapped out the switch and the problem persisted. Before I try anything else, I want to make absolutely sure my wiring is correct. Please see the attached diagram. I included the MAIN PCB wiring (pads 16, 15, 17) that are connected to the output pot. All of the green "boxes" around the red lines represent the shield. Hopefully you can see how all the shields are connected. Please let me know if this looks correct or if I'm way off.

Thanks very much.

-Kevin