Build Thread:MS76

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karloff70

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So I have arrived at the blend pot. The pot has the three normal pins, which I have wired to the 3 pin Molex that says blendpot. Assuming that isn't wrong already, what do I do with the two contacts named A and C on the switch and how do I get the relay involved? I see the hole marked 'blend switch return' on the board, but have no idea what to do now?
 

rtron

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So I have arrived at the blend pot. The pot has the three normal pins, which I have wired to the 3 pin Molex that says blendpot. Assuming that isn't wrong already, what do I do with the two contacts named A and C on the switch and how do I get the relay involved? I see the hole marked 'blend switch return' on the board, but have no idea what to do now?
Wire a 12V wire (from the 12V header on the main pcb) to the blend pot/switch contact (doesn't matter which one). Then run a wire from the other contact on to the blend switch return of the the main pcb.

Also, for the blend pot connections, I did board pin 1 (red wire) and went to pot pin 3, board pin 2 (brown wire) to pot pin 2, and board pin 3 (black wire) to pot pin 1 and it worked out correctly. Note that I define my pot pins like this: https://sound-au.com/pots-f5.jpg
 

karloff70

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Wire a 12V wire (from the 12V header on the main pcb) to the blend pot/switch contact (doesn't matter which one). Then run a wire from the other contact on to the blend switch return of the the main pcb.

Also, for the blend pot connections, I did board pin 1 (red wire) and went to pot pin 3, board pin 2 (brown wire) to pot pin 2, and board pin 3 (black wire) to pot pin 1 and it worked out correctly. Note that I define my pot pins like this: https://sound-au.com/pots-f5.jpg
Amazing, thank you! Looks like I need to swap 1 and 3, but now I know what to do with the 12V. Thank you very much!
 

JMan

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Hey All,

I ordered one of Gustav's last spare boards -- now just to wait out the long shipping times between Germany and the US... 🙃

I took a look at the schematic, which I think is the only way for me to put together a BOM. (I guess since this was previously offered as a full kit, there is no published BOM?). I see that the M/S encoding and decoding sections use THAT 1240 chips. I was just looking things up on Mouser to kill time, and I see that there's a 0dB version and a -6dB version of this IC. Is one or the other preferred? EDIT: Never mind, I see that the -6dB one has a slightly different part number that I didn't catch in the sea of results that Mouser gave me.

More questions to come, I'm sure, whenever the package arrives and I have a chance to start working on it.
 
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karloff70

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Ok, so I have it powered up. It passes signal, the VU's work. But it does not compress. At all. And when you put the meter in GR the needle goes to the bottom and stays there as opposed to zero. Everything else seems to be working.

If you smell a specific diagnosis of what fudgery I have committed based on that description I would very much appreciate learning about it. :)
 
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karloff70

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Looks like I am on my own and with the 'schematics' provided my tech can't help either. Great. Any chance you could help me finish this, Gustav?
 

rtron

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Ok, so I have it powered up. It passes signal, the VU's work. But it does not compress. At all. And when you put the meter in GR the needle goes to the bottom and stays there as opposed to zero. Everything else seems to be working.

If you smell a specific diagnosis of what fudgery I have committed based on that description I would very much appreciate learning about it. :)
Did you follow the calibration procedure? My meters did weird things too, before I calibrated it...
 

karloff70

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I didn't but the tech did, so technically it is calibrated. But mostly it doesn't compress at all regardless what the meters are doing.
 

Gustav

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Looks like I am on my own and with the 'schematics' provided my tech can't help either. Great. Any chance you could help me finish this, Gustav?
HI Karloff

There is a full schematic in the folder on the site - its separate for the main board/aux boards, and you can "overlay" the aux boards on the main board to see connections and continuity in signal flow.

If your tech cant read them, I would recommend trying to find someone else to try to help you.

Unfortunately, its impossible to solve your problem based on the symptoms you are describing. They are simply too general. From what you are saying, the GR is triggered hard, regardless of setting, by indication of the meter, so we can suspect you have something pushing it. It could be a short to a supply, so you have DC flowing in, but it could also be a number of other things.

For trouble shooting, start by verifying all voltages. The main supply voltage values are printed on the board - and in addition to that, you can check the voltages around the transistors, which are printed on the board (we dont expect them to be spot-on, but in the general area of what is printed).

Thats always the first step for trouble shooting, so do that, get back, and we can help you look further into the problems you are experiencing with the build! :)

Gustav
 

Gustav

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I didn't but the tech did, so technically it is calibrated. But mostly it doesn't compress at all regardless what the meters are doing.
After replying to your earlier post, I saw this.

I dont know if this means, the GR meter is no longer pegged, and your are seeing compression action on it!? I sort of assume it does.

If so, please note, the metering here is done by shadowing what goes on in the signal path. The transisor in your signal path may still be bad/blown, even though the meter is responding. I would start crudely by replacing the 2N5457 in the signal path. (its less likely, if you are experiencing this in both channels, of course).

There are test points scattered throughout the signal path.

1. pure input after the 1206
2. after the input gain
3. after the output gain.

(double check these on the schem, Im going by memory, but it will be obvious when working with the unit).

Check if those are working/if you are seeing any compression.

Another reason why you may not be seeing compression could be, that the blend circuit is not set up properly - double check that as well.

Hope that helps!

Gustav
 

karloff70

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Hi Gustav,

Well, the tech is Mick Hinton at DAV/ex Decca, so I don't think I 'need a new tech'. He seemingly can't work with those schematics though, unfortunately.

The meter is not pegged, just slowly falls to the bottom when switching to GR after working as expected on in or out. There is no compression happening.

I will try your suggestions best I can as soon as I can, as about to start moving house. Maybe this thing can finally come alive in the next address.
 

Gustav

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Hi Gustav,

Well, the tech is Mick Hinton at DAV/ex Decca, so I don't think I 'need a new tech'. He seemingly can't work with those schematics though, unfortunately.

I understand its frustrating, that your unit is not working, and you need help.

I would suggest you find a tech who can help. Alternatively, I would be happy to lend Mick a hand.

He may have just missed the tag on the end of the input section/start of the amp, end of the amp, start of the output section.

All sections are named, and drawn in sequence, and as mentioned, you can overlay the aux.

I will try your suggestions best I can as soon as I can

Sounds good. I hope you get it working! :)

Gustav
 

ho-fi

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Apr 18, 2015
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switzerland
Here's my Issue:
I finished the build but now i’m running into problems calibrating the ms76.
PSU-voltages are fine and of course i’m sticking to the calibration-guide :)

CH1:
Input-meter works fine.
when trying to calibrate the q-bias, i’m unable to adjust the output-level to 0dB, maximum is about -20dB on the MS76-Meter
in my DAW the input reads 10dB less than the DAW-output.
when trying to adjust zero, the meter stays at around -7dB, it doesn’t move at all when adjusting the zero trimmer.

CH2:
In VU-In mode, the needle jumps to maximum right, even if there’s no signal present.
when trying to adjust zero, the meter stays at around -7dB, it doesn’t move at all when adjusting the zero trimmer.
VU-Out max. Level is also around -20dB on the Meter, in the DAW it’s almost 10dB less on the input.


Unfortunately I’ve made a silly mistake when hooking up the PSU. I accidentally connected -15 to GND, +15 to -15, +30 to +15, -10 to +30, +12 to -10 and GND to +12
Well, this is what happens when you’re almost done and get careless.
I could hit myself for doing this...

FYI: i’ve added the LL5402 in my build.


And here's Gustavs reply (by mail):

In the areas around the transistors, there are approximate voltages. Check those first.
Then, I would look for fried ICs.

Your note on the Q-bias seems odd, maximum is -20? You should set it, so reading is +1, and you adjust it Down to 0 in GR mode.



If that doesnt Work out – try adjusting the q-bias out of the way, then calibrate the meter, and try Again.
 

Mugge

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May 14, 2020
Messages
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Hello,
I'm building this nice machine, but I cannot seem to find the LM7910 available anywhere... So, is there another voltage reg to use in stead?
Also, I was wondering whether it's possible to add a stereo link option in this one like on the MS HOL for instance?

Thanks in advance

/Marcus
 

rtron

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May 16, 2014
Messages
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Where the silkscreen says lm7910 you should use an lm7912 (I am using the latest pcb set). I had emailed Gustav about this and he confirmed it. So you should have a 7812, 7912, 7815, 7915, and 317 on the psu board.
Hello,
I'm building this nice machine, but I cannot seem to find the LM7910 available anywhere... So, is there another voltage reg to use in stead?
Also, I was wondering whether it's possible to add a stereo link option in this one like on the MS HOL for instance?

Thanks in advance

/Marcus
 

JMan

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Joined
Oct 26, 2019
Messages
298
Location
Chicago
Hello,
I'm building this nice machine, but I cannot seem to find the LM7910 available anywhere... So, is there another voltage reg to use in stead?
Also, I was wondering whether it's possible to add a stereo link option in this one like on the MS HOL for instance?

Thanks in advance

/Marcus
In regard to the stereo link, I’m sure Gustav can elaborate, but basically I think the M/S matrix is replacing the stereo link here, since 76-style compressors are notoriously bad at linking. This is an effort to correct the associated tracking errors. Maybe someone else can jump in and be a bit more specific (or, I think Gustav has written about it in his various MS____ project threads).

EDIT: ah, I see that you referenced the MS HOL in your post. Even in that design, the link is described as “unreliable.” I have to imagine it would be as much so or worse here. But it might be interesting to hear about it if you attempt it.
 

Gustav

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Also, I was wondering whether it's possible to add a stereo link option in this one like on the MS HOL for instance?

Thanks in advance

/Marcus

The MS is great for linking it in stereo, but you can search this forum and find the typical link for two 1176 units.

I cant really think of any units that had this MS matrix set-up done before I built it into this, but it was fundamentally an idea based on linking, not so much aimed at manipulating the MS balance. That aspect was, at first, a fun side effect, and I did get all giddy about it. Its just really something new, when you havent explored it much (this was 2012, before the plugins were doing it, and we mostly knew it setting up 3 channels on the console for an MS recording mattrix).

Many years later, I still consider the MS stereo linking a great solution, to avoid the dodgy L/R tracking, but - I am not the biggest fan of the MS balance manipulation, and what happens to phase and sonics as a result.

So basically, I would make link it MS, make sure the balance in MS mode is set for phase and balance, not use for MS balance manipulations, and if its done, keep the footprint light!

Gustav
 

Gustav

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Joined
Jun 4, 2004
Messages
2,146
Location
DK
Here's my Issue:
I finished the build but now i’m running into problems calibrating the ms76.
PSU-voltages are fine and of course i’m sticking to the calibration-guide :)

CH1:
Input-meter works fine.
when trying to calibrate the q-bias, i’m unable to adjust the output-level to 0dB, maximum is about -20dB on the MS76-Meter
in my DAW the input reads 10dB less than the DAW-output.
when trying to adjust zero, the meter stays at around -7dB, it doesn’t move at all when adjusting the zero trimmer.

CH2:
In VU-In mode, the needle jumps to maximum right, even if there’s no signal present.
when trying to adjust zero, the meter stays at around -7dB, it doesn’t move at all when adjusting the zero trimmer.
VU-Out max. Level is also around -20dB on the Meter, in the DAW it’s almost 10dB less on the input.


Unfortunately I’ve made a silly mistake when hooking up the PSU. I accidentally connected -15 to GND, +15 to -15, +30 to +15, -10 to +30, +12 to -10 and GND to +12
Well, this is what happens when you’re almost done and get careless.
I could hit myself for doing this...

FYI: i’ve added the LL5402 in my build.


And here's Gustavs reply (by mail):

In the areas around the transistors, there are approximate voltages. Check those first.
Then, I would look for fried ICs.

Your note on the Q-bias seems odd, maximum is -20? You should set it, so reading is +1, and you adjust it Down to 0 in GR mode.



If that doesnt Work out – try adjusting the q-bias out of the way, then calibrate the meter, and try Again.

Not much to follow up on, until you report back/try the suggestions!
:)

Gustav
 

Mugge

New member
Joined
May 14, 2020
Messages
2
The MS is great for linking it in stereo, but you can search this forum and find the typical link for two 1176 units.

I cant really think of any units that had this MS matrix set-up done before I built it into this, but it was fundamentally an idea based on linking, not so much aimed at manipulating the MS balance. That aspect was, at first, a fun side effect, and I did get all giddy about it. Its just really something new, when you havent explored it much (this was 2012, before the plugins were doing it, and we mostly knew it setting up 3 channels on the console for an MS recording mattrix).

Many years later, I still consider the MS stereo linking a great solution, to avoid the dodgy L/R tracking, but - I am not the biggest fan of the MS balance manipulation, and what happens to phase and sonics as a result.

So basically, I would make link it MS, make sure the balance in MS mode is set for phase and balance, not use for MS balance manipulations, and if its done, keep the footprint light!

Gustav
Thank you very much for the thorough explanation! I'll keep it as it is - really excited to hear it in action!
 

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