Looking for schematics for Girardin MT series mixers...

[soapy_goat]

I have 2 6 channel mobile mixers from the 60s, MT.67 and MT.68, and I'd like to get direct outs out of them. Does anyone have documentation on these?

here is the MT.67, it gets to sit in first class!

 

[guy_4]

Hello soapy_goat,

I worked on a few Girardin in the past.
They were built with no expenses cut ( our taxes ! ) for French Government Radio and TV stations.
I have never found documents and/or schematics.
They are modular and easy to get inside, fix it and do some mods too.
Bad point is they are 12V DC and so a limited dynamic range.
Good luck with yours.

Best,
Guy

PS : MCI 636 is a nice shelf for a Girardin !

 

[Evertide]

I have 2 6 channel mobile mixers from the 60s, MT.67 and MT.68, and I'd like to get direct outs out of them. Does anyone have documentation on these?
View attachment 107862
here is the MT.67, it gets to sit in first class!

https://fr.audiofanzine.com/console-analogique/girardin/mt68/medias/photos/

 

[zamproject]

MT48 just added in the tech doc

stereo version like MT67/68 should be the same but 2bus and more input modules

https://groupdiy.com/threads/girardin.83770/
Best
Zam

 

[soapy_goat]

MT48 just added in the tech doc

Thank you!

 

[zamproject]

You'r welcome

I know (have) at least two different input modules type, which differ by the EQ section
On have high boost OR presence boost in the same selector, and low cut on the second selector.
While the other version have high boost/cut and low boost/cut selectors

The change is mainly at selector assembly, as RC network is PTP soldered to them

At some point in the production I suspect they switch from Ge to Si transistor
My lovely MT47 is Germanium

Cheers
Zam

 

[Dreams]

Eyyy that's Hidden Fortress isn't it

 

[soapy_goat]

Eyyy that's Hidden Fortress isn't it

yes!!

 

[Whoops]

Those Mixers look pretty cool

 

[zamproject]

Those Mixers look pretty cool

Yes they are

Now for the OP question

I'd like to get direct outs out of them

There is already pre-fader (post EQ), called -reprise- at the modules connectors (pin 6)
Then depending of the version/option it act like an aux send or direct-out
There is no bus on those lines, each channel go to a card inside the frame with individual buffers (transistor)
Option 1 (MT47 ?) there is pot for each lines and then summed to mono -reprise- like an AUX
Option 2 (MT48 ?) no pot, each buffer out go to a miltipin connector like Direct Outs

Moding one to another should not be that difficult

Cheers
Zam

 

[pierrebe]

I have 2 6 channel mobile mixers from the 60s, MT.67 and MT.68, and I'd like to get direct outs out of them. Does anyone have documentation on these?
View attachment 107862
here is the MT.67, it gets to sit in first class!

Hello, my father can get you the documentations of the MT 67 and 68 (schema) contact him on his mail : [email protected]
Pierre (from France )
Kind regards

 

[pierrebe]

I have 2 6 channel mobile mixers from the 60s, MT.67 and MT.68, and I'd like to get direct outs out of them. Does anyone have documentation on these?
View attachment 107862
here is the MT.67, it gets to sit in first class!

Hello, my father can get you the documentation for MT 67 and 68, you can contact him on his mail : [email protected]
Pierre (from France )
Kind regards

 

[copacetest]

Hello, my father can get you the documentation for MT 67 and 68, you can contact him on his mail : [email protected]
Pierre (from France )
Kind regards

I've sent him an e-mail. Hoping to hear back soon

Yes they are

Now for the OP question

There is already pre-fader (post EQ), called -reprise- at the modules connectors (pin 6)
Then depending of the version/option it act like an aux send or direct-out
There is no bus on those lines, each channel go to a card inside the frame with individual buffers (transistor)
Option 1 (MT47 ?) there is pot for each lines and then summed to mono -reprise- like an AUX
Option 2 (MT48 ?) no pot, each buffer out go to a miltipin connector like Direct Outs

Moding one to another should not be that difficult

Cheers
Zam

I'm wanting to get DOs on my MT-67 as well and tested this out today. I noticed that the output from the direct out had a significantly lower amount of gain than the normal mix output. Is that to be expected? Potentially due to not using the output transformer? Or am I just doing something wrong. If anyone has some more details or ideas on how to perform this mod I'd love to hear them.
I would like to preserve the high gain that this mixer has available if possible.
Thanks

 

[zamproject]

@pierrebe , not sure it's a good idea tu put private mail on a public forum, especially if it's not your...
If it's your father, better ask yourself the doc and add it to the technical doc section, where I already open a Girardin topic

I noticed that the output from the direct out had a significantly lower amount of gain than the normal mix output. Is that to be expected?

Look expected to me, signal is picked prefader from input modules, -25dB for a +12dBu nominal input.
As -reprise- buffer is unity you get -13dBu.

In any modern AD converter you should probably increase the sensitivity to match level, or add a 25dB gain makeup circuit, or just don't care as you -only- lose 4 bit (considering a 24 bit converter). Can't say now which one is better for S/N

Cheers
Zam

 

[copacetest]

Thanks for clearing that up for me Zam. I tried adjusting the sensitivity on my interface and in doing so became aware of a ground hum. Adding a small 10k:10k transformer I had mostly fixed this but I'm wondering if there might be a better (cheaper) option to eliminate the hum?

I found a better grounding point on the "Alimentation" board which quieted the hum somewhat, but is there some other non-transformer circuitry I could add that may help? I'm not very familiar with things like this, so I could use some extra help if possible. Thanks

 

[zamproject]

in doing so became aware of a ground hum

Can't say, what is the hum level, S/N ?
This is old school (60') broadcast germanium mixer, low voltage rail, with noise floor far from modern standard I suppose...
Mine is also noisy at high gain setting, still never try it on battery, but only with the originally fitted PSU trafo box (recaped).

 

[copacetest]

The hum was very overpowering at any usable gain setting, so not just a higher than usual noise floor.

However its good you brought up the power supply! I don't have an original one and had purchased one off ebay which looked promising, but it seems it is the culprit for the hum. I switched to my bench supply and the hum is gone!

This is the ebay supply btw 50VA HIFI Ultra-low Noise Linear Power Supply DC5V 9V 12V 15V 19V 50W LPS PSU 24 | eBay
Looks like I need to open it up and investigate why it would cause this issue.

 

[zamproject]

Is it hum at 50/60 ? or 100/120Hz ?
I just have a very quick look at your link...main IEC connector seem to have the safety earth unconnected ?!?
Probably not your issue but...

There is no power consumption data in the service manual and I don't know for the MT 67/68, but it's just 2 more input channels than my 47, where the fuse is rated at 600mA.
Which mean @ 12V the mixer take less than 7.2W, your 50 VA is probably over rated and maybe don't handle well the under load condition ?
Check with an A meter at the -12V input

Also in addition to 0V and -12V there is a third banana socket for grounding the desk, long time I don't open mine, so not sure how it's wired inside, but probably everything is floating inside the frame/chassis. You may try hooking this to a safety ground ?

By the way did you recap de console ? despite quality build and component I wont trust the lytic after 60+ years...

Cheers

 

[copacetest]

Thanks for helping look into this, and yes it's 60hz hum.

I haven't had the chance to look at the supply yet, but will make sure to check on those things and maybe try the ground jack on the mixer. I didn't realize until I saw on some other pictures online that that jack is for ground. It's not labeled on mine.

I recapped the entire mixer shortly after I got it. There was a few things that weren't working quite right so recapping seemed like a good idea, and luckily doing so fixed those issues.

 

[copacetest]

I did some testing with the grounding jack on the mixer and found that connecting it to the earth from the IEC inside the power supply fixed the 60hz hum
For a more permanent solution I disconnected one of the two power outputs inside the supply and connected both pins to the IEC earth. So now a cable with a banana jack can be connected from that to the mixer nicely.

You are right that the supply is overkill for the mixer, but it was cheaper than buying the parts and building one from scratch so it seemed worth trying. Luckily it seems to working perfectly now with a bit of modification.

I just finished putting together the D-sub to XLR snake cable, so now I just need to wire in the D-sub inside the mixer and I will have my direct outputs!