Eurocards Part 3 - Audio Cards

Has this week ever gone quickly! Things have been pretty stressful with the move coming up, but I've really been looking forward to getting through the last of the eurocards with you all. I've been spending all of my time working and packing boxes. No sign of the amount of work to do letting up either! Oh well, let's get to it!

2 eurocards left to cover. They are pretty simple, so I don't think this post will be too long.

1.915.914.00 - 4 Bal. Amp 6dB
No before pics on this one. Check out the caps removed in the
top left hand corner though. The light blue caps aren't
aluminum electrolytic so there is no need to replace them.

4) 1.915.914.00 - 4 Bal. Amp 6dB (x3)
This card seems pretty self explanatory. As you can see, the board is divided into four duplicated quadrants. Before researching these modules, I had a bit of help with their function. On the door that opens up to the eurorack cards there are descriptions of the cards. The descriptions for the 3x 4 Bal. Amp 6dB cards are:


- GR 1-4
- GR 5-8
- ∑1+2 / ∑ M

Need I say more? 





Okay, maybe I should say more since I was completely fooled about the function of this card. Before I do though, I would like to let you all know that, despite my best attempt at planning (scanning the pdfs I would need for today's blog a few days ago), I was forced to open a packed box for the SECOND time (once for Monday's post too) to get the manual out. Here was the dilemma. 
Initially, I thought that this card was simply a card to drive the direct outs for the 8 groups and 3 master channels. After looking in the manual for this card, I realized that it is, in fact, for the insert points! 


Here's a little description from the manual:


This circuit board is equipped with four amplifier circuits each of which features its own amplifier with trafoless balanced input and unbalanced output and an amplifier with unbalanced input and trafoless balanced output.


Since this card is not available in the online manual, you can find documentation here:
Studer 900 Series Console - 1.915.914


This board contains 4x combo balanced>unbalanced / unbalanced>balanced amplifiers! 
The issue that forced me to take the manual out from its fully packed box was that the schematic seems to suggest that the card is UNBALANCING the signals to send out of the insert and REBALANCING them on the return. Take a look for yourself... it very specifically says 'ASYM OUTP (TO INSERT)' and 'ASYM INP (FROM INSERT)'. This doesn't seem right. Ideally, an engineer would want balanced inserts. Why convert them from balanced to unbalanced? I decided to dig deeper (into my beautifully packed boxes... sigh).

Without posting too much revealing information from the future, I will say that I found the schematic source of the insert points. They come from the group fader modules and show both a pre and post fader option. I can't check which one I have (since the modules are packed, of course) but BOTH OF THE INSERTS ARE UNBALANCED FROM THE FADER! Detective Ian does it again! This means that signals are most likely balanced and unbalanced with these cards to interface with outboard gear. 

Let me clarify this:
Unbalanced Fader Module > Balancing amplifier (1.915.914.00) > Balanced Insert Out
Balanced Insert In > Unbalancing amplifier (1.915.914.00) > Unbalanced Fader Module


So it seems to make sense, but let's confirm it... let me check the manual to see if I can trace the signal through the module, or at least provide some evidence that the inserts are definitely balanced by these cards...

...hmm, the schematic says the group outputs are transformer balanced... well that's good. It wouldn't really make sense for these cards to be used for that... but it doesn't show a separate set of direct outs. I guess they just hook them up in parallel...  ?

... hmm, there is a complete wiring chart in the back of the manual... OOO! Here is a page that shows the inserts as balanced! Good news!

...and on the next page it describes them as unbalanced.... bad news.

Sigh...

Ok, forget this. I'll just open the back of the console and try to trace some wires and see what I can find. I'll just reach into my toolbo... rrrriiiiiigghhtt. My tools are all packed. :|

So I'm stuck. First time in the blog so far. I blame it on my massive lack of availability to most of the console. All of the modules are packed! I can't even get to my tools to open the ol' boy up.





I'll just leave this section here:

Give me some credit for the pretty picture!
Recapped and cleaned!

The Studer 1.915.914.00 eurocard module is composed of 4 amplifiers which have a balanced>unbalanced component as well as an unbalanced>balanced component each. All evidence suggests that they are used as balancing and unbalancing amplifiers for the inserts for the 8 groups and 3 masters. With that said, I can't physically make sure of this fact until I have a little more access to the entire console. The last thing I want to do is provide incomplete or incorrect information, so I will post an update to this section once I am in the new space and will add the link here >>>______.

 Damn, let's hope I have more luck with...


5) 1.915.304.00 - Monitor Amplifier (x1)

Too much fluff, not enough nerd stuff in the last section:

Manual Description:
The monitor amplifier board 1.915.304 is part of the monitoring system. Isolation transformers and input amplifier for the C.R. monitor and studio amplifier path are built in.

Manual section PDF: Studer 900 Series Console - 1.915.304


Picture:


Studer 1.915.304.00



The Studer 1.915.304 amplifier, indirectly referenced in Part 2 for its relay switching, is a combination audio amplifier and routing unit. 

Basic functions:
- 2x Stereo amplifiers for Control Room and Studio monitors
- Used to switch ∑1+2 master onto Control Room and/or Studio monitor output (see Eurocards Part 2 - Signalling and Switching... Then some big news!... this is the 15th and final signal that can be routed to the monitors)
- Allows the Studio Output to be switched to whatever is on the Control Room Output. 
- Allows meters to be switched between the Control Room Monitor Input (Whatever input is selected on the monitoring section) and the ∑1+2 master output.

That about sums it up! Cleaned, recapped, rubbed the transformers for good luck, and Bob's your uncle!

So that's it for the eurocards (minus the update to #4 in this post which will come soon). I would say that this is the most dry section of the console restoration. If you made it this far, it will be smooth sailing from here on in. The issue with the eurocards is that there isn't any restoration to show! Other than recapping a few capacitors and giving them a quick clean, there is nothing to do but talk about what they do! Future posts will have a lot more pictures and a lot more fun content.




I should mention that there are a few other cards that Studer would provide as an option for 900 series consoles. For example, there is a master limiter card that can be inserted into the signal path on some consoles. With that said, I'm a little glad that I don't have any more because I don't think that I could handle any more eurocard posts! We'll be taking a short break from console topics for the next blog or two to talk about my studio move. Monday's post should be really fun, so be sure to tune in! Blog goes up at 10am.
Wish me luck!