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ryanstreber

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Jan 7 14 10:10 PM

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My Studer 900-series console has been perfect for my setup in many ways, but one major limitation is that it doesn't have direct outputs and isn't an inline-style board.  Currently, when I want to use the mic preamps on the board, I have to "insert" Pro Tools with the channel sends feeding the PT inputs and (assuming I want to monitor from Pro Tools) the PT outputs feeding the channel returns. This causes a whole bunch of awkwardness and limited functionality that I would love to eliminate by adding direct outs before the input select switch on the channels.

On the mic input circuit diagram (see below), it looks like there is some kind of dedicated mic "to TB" feed which is immediately before the channel's input select switch and which has its own pin on one of the channel card's connectors. As far as I can tell, that pin isn't used for anything on the console. Am I right in thinking that I could use this as an unbalanced output directly off of the microphone input? What potential problems would need to be addressed in a modification like this?  Would it be better to run that "to TB" signal to a transformer in order to better interface with an AD converter's input? Or am I being stupid and missing something obvious?

My ideal scenario is simply that I could wire these new direct outs to the patchbay and be able to use the board's mic pres independently of whatever else the channel is doing (as determined by the position of the input select switch.)  

Thanks in advance for any suggestions!

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Last Edited By: ryanstreber Jan 7 14 11:29 PM. Edited 2 times

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ryanstreber

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Jan 7 14 11:17 PM

(Just realized the image I originally used was saved as a TIFF, trying a JPEG now which will hopefully work better.) 

Here's the complete block diagram for the input channel.  (My board has the transformer-balanced mic input, not the "trafoless" one in the box below.)  And if you're curious, the schematic for the input section can be seen here: http://www.oktavenaudio.com/Studer/900_Op_Serv-Input_Schem.jpgimage

Last Edited By: ryanstreber Jan 7 14 11:35 PM. Edited 7 times.

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Mike Rivers

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Jan 8 14 6:50 AM

ryanstreber wrote:
My Studer 900-series console has been perfect for my setup in many ways, but one major limitation is that it doesn't have direct outputs and isn't an inline-style board. 

On the mic input circuit diagram (see below), it looks like there is some kind of dedicated mic "to TB" feed which is immediately before the channel's input select switch and which has its own pin on one of the channel card's connectors. As far as I can tell, that pin isn't used for anything on the console. Am I right in thinking that I could use this as an unbalanced output directly off of the microphone input? What potential problems would need to be addressed in a modification like this?  Would it be better to run that "to TB" signal to a transformer in order to better interface with an AD converter's input?



 

It certainly wouldn't hurt to try one channel and see what signal level you get at that point and what tying a lead over to your patchbay and on to your A/D converter. An actual schematic might be helpful in guessing how it'll work, but if that point in the circuit is easy to access, it's just as easy to hook it up. You won't blow anything up.

OK, I found the schematic from your link. It looks like that TB point is coming off the output of a 5534 IC, which should be pretty stable, but sometimes an op amp can turn into an oscillator, often at a couple of megahertz where you can't hear it but where it can do some damage to your signal. A 100 ohm resistor at the op amp output in series with that long lead to the patchbay might be a good safety measure. But checking for an oscillation with an oscilloscope when everything is hooked up would be a good idea.

Here's a better and simpler idea. It apparently has channel insert sends and returns. I think those are the two leads that go upward following the "phase" switch. Why not use the insert send as your direct output? This is fairly common practice for recording a console's mic preamp output when there's no direct output connector. Not to compare your Studer with a Mackie but that's how people with Mackie/ADAT studios used to work.
 



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Last Edited By: Mike Rivers Jan 8 14 7:06 AM. Edited 1 time.

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ryanstreber

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Jan 8 14 8:17 AM

Hi Mike,
Thanks for your response!  I mentioned back in my first post that I do currently use the insert sends and returns for this purpose, but I would like to get around the limitations that come with this setup. For example, the insert point is before the PPM meters, so I lose metering on playback unless I physically re-patch every time I switch from record to playback.  Also, the channel filters and eqs as well as auxes (when set to pre-fade) are all pre-insert, so overdubbing and punching can be cumbersome. Generally, I would just like a little more flexibility with how things can be routed.  And of course, it would be nice to keep the inserts free for other duties when tracking.

I will likely just hook up a channel as you suggest and see how it goes, but it would be great if any one else has any ideas about how best to accomplish this.

Thanks!

 

Last Edited By: ryanstreber Jan 8 14 8:22 AM. Edited 1 time.

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Mike Rivers

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Jan 8 14 10:56 AM

ryanstreber wrote:

Thanks for your response!  I mentioned back in my first post that I do currently use the insert sends and returns for this purpose, but I would like to get around the limitations that come with this setup. For example, the insert point is before the PPM meters, so I lose metering on playback unless I physically re-patch every time I switch from record to playback.  Also, the channel filters and eqs as well as auxes (when set to pre-fade) are all pre-insert, so overdubbing and punching can be cumbersome.

 

Well, that's why people use recorders rather than Pro Tools.  ;)  I wasn't sure whether, in your original post, you were talking about the channel inserts on the console or the "inserts" in Pro Tools. I assumed the latter and I guess you mean the former. I'm probably missing something by not being there or not having a console like yours so pardon my musings and "I already know thats" if they don't apply.

The "old school" way of setting up a system like this is to use the console insert outputs (sends) to feed a multi-channel audio interface, and assign the track outputs to interface outputs, and connect those to the console insert inputs (returns) so you have one track per output and if you use the DAW mixer at all, it's for things like monitor mixes or effect sends. You can then pretend that it's an in-line console and monitor what comes back into the console channels from the DAW. But this requires as many inputs and outputs on your interface as you want to use simultaneously, and it also requires essentially no-latency input monitoring on the part of the DAW. Most new ASIO interfaces are pretty good about this with a well tuned computer, but older ones will have you checking your calendar to see when it's time for the signal to come back into the console. Latency is, of course, of no concern for mixdown but it can really complicate punch-ins.

The newer-school way of setting up a system like this is to use the insert sends (or direct outputs) to feed the DAW inputs, then use the DAW mixer to play a rough mix of your tracks back into a couple of spare inputs on the console. When overdubbing, turn off "input monitoring" on the DAW and monitor the input directly from the console, mixed with the DAW playback. Send that mix to the headphones on the player doing the overdub so that he won't have to deal with the latency, and let the DAW's latency compensation put the new track in the right place so that it lines up with the previously recorded tracks. Essentially you're using the DAW as an insert effect in the console signal path.

If you have the console insert sends and returns wired to your patchbay, you probably have them half-normalled so that patching the send to a DAW interface input won't break the channel signal path. That way you can monitor the input when recording and monitor the track playback when overdubbing or mixing, but you'll need to do some switching and patching.

This is something that requires considerable thought and some messing around before you get something that works. It's why a lot of people just use the console for mixing and monitoring and patch outboard mic preamps to the interface when recording. But it's all possible. You might be able to get the console metering to display what you want with some clever switching, though if the console just wan't built for this kind of work, you may need to modify it, or search for jumpers that will let you configure it as you want it.

 



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ryanstreber

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Jan 8 14 3:47 PM

Hi Mike,
Thanks for the suggestions.  I already have a setup working with mostly outboard preamps that I'm happy with, so I'm just looking to find a way of using the console preamps that integrates a little more elegantly into my current configuration.  
Thanks,
Ryan

 

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ruairi

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Jan 8 14 6:25 PM

Can you explain what it is about your current set up that doesn't work when using the Studer Pres? It seems to me that the preamp feeding the insert out acts like any other outboard unit you'd have, is the the fact that you are missing trims and polarity flip on your insert return when using it as a line in?

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Mike Rivers

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Jan 8 14 9:13 PM

ruairi wrote:
Can you explain what it is about your current set up that doesn't work when using the Studer Pres? It seems to me that the preamp feeding the insert out acts like any other outboard unit you'd have, is the the fact that you are missing trims and polarity flip on your insert return when using it as a line in?

That's what you get when you use a hookup like this, unless the console has "tape returns" that go through the full input path when you push the "mixdown" button. The DAW way of thinking is that what you put back into the console for mixing is what you recorded, which is essentially the same thing as recording straight to stereo except that you have as many chances to mix it right as you need. The DAW is where your channel trim control is now, as well as your polarity switches, along with any signal processing that you don't have enough of as analog hardware.

 



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ryanstreber

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Jan 8 14 9:39 PM

Hi Ruairi,

That's part of it.  The insert snd / rtn setup works fine for lots of tracking scenarios, but again I would like to have the ability to use the preamps independently of the rest of the channel for some situations.  

As an example, I did a session recently with a large-ish jazz group with around 22-24 inputs, where the producer wanted to only use the console preamps (no outboard preamps.)  Patching the insert sends to PT was ok for tracking, but on playback and running quick mixes on the board, it was frustrating that the console channels became so limited (no metering, no filters, eq, polarity, limited ability to patch in outboard gear on the inserts, audio unavailable on the aux sends so that musicians in the liveroom were unable to listen to playback on their headphones, etc.) without physically repatching all of the channels. We were recording a lot of numbers in one day and jumping back and forth between record and playback frequently, so it was a bit tedious.  Not the end of the world, but if a simple modification could make this more seamless I'd be happy.  That's kind of the point of an inline console, right?

In short, having the ability to keep the channels set on PT out or at least be able to switch easily between sources without having to repatch so much is what I'm after.  Also, keeping the inserts free for patching outboard or sending things to other destinations would be nice as well.

I generally like to set up monitor and cue mixes from the console (rather than in Pro Tools), and that becomes difficult particularly with cue mixes when overdubbing or punching given the location of the insert point being after the aux sends.  Yes, there are other ways to set this up.  I'd just like to have a particular way that I like working available to me.

Another thing (last I'll mention) is that I would like to possibly have the console pres half-normalled at the patchbay to AD inputs (which is how I have all of my outboard pres) so that they're available in Pro Tools simply by selecting the appropriate input.  Not an urgent need, but again it's nice to have this stuff quickly and reliable ready to go without having an additional set of patches to make. I can't do this with the inserts of course because the sends need to be normalled to the returns.   

Last Edited By: ryanstreber Jan 8 14 9:43 PM. Edited 1 time.

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ryanstreber

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Apr 12 17 4:49 PM

Sorry to rehash an old thread. I did finally work with my tech to set up preamp outputs from a number of chanels on the console, taking a line from those "to TB" outputs on the channel cards to connectors on the real panel of the board. It works, but I'm running into problems with them being unbalanced outputs: the output is 6dB down, they're prone to noise issues, and seeming to have trouble driving some inputs.

I'm interested in adding transformers on these outputs to balance them. Can anyone recommend a good transformer that would do the job and won't cost a fortune in quantity (I will need at least 16 of them)?

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ssltech

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Apr 12 17 8:19 PM

If you're having trouble driving certain loads, then transformers may not be the answer. They may actually make things worse.

You should add an active drive circuit to drive the transformers if this is the case; and if you tried to regain the 6dB by using transformers with a 1;2 ratio, then I would most certainly say this should be necessary.

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John Eppstein

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Apr 12 17 9:44 PM

ryanstreber wrote:
(Just realized the image I originally used was saved as a TIFF, trying a JPEG now which will hopefully work better.) 

Here's the complete block diagram for the input channel.  (My board has the transformer-balanced mic input, not the "trafoless" one in the box below.)  And if you're curious, the schematic for the input section can be seen here: http://www.oktavenaudio.com/Studer/900_Op_Serv-Input_Schem.jpgimage

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waltzingbear

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Apr 13 17 11:48 AM

what are you driving with them that is problematic? The most benefit from balancing is on inputs, nice to have balanced out too, but not as important and can be done as "impedance balanced".

As Keith said, just adding a transformer may not help if you have drive problems, That is a 5534 as an adjustable 12db gain stage driving that point, there should be no problem with loads per se.

I would be more curious about return path connections at this point.

I also note that the output cap is two 100uF in series, resulting in effective 50uF, are you experiencing LF loss into low impedance inputs?

There is also a gain strap that can be set, which position is it in for your needs.  ( pins 104, 105, 106)

Alan

Alan Garren
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Last Edited By: waltzingbear Apr 13 17 11:56 AM. Edited 1 time.

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zmix

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Apr 13 17 12:31 PM

waltzingbear wrote:
what are you driving with them that is problematic? The most benefit from balancing is on inputs, nice to have balanced out too, but not as important and can be done as "impedance balanced".

As Keith said, just adding a transformer may not help if you have drive problems, That is a 5534 as an adjustable 12db gain stage driving that point, there should be no problem with loads per se.

I would be more curious about return path connections at this point.

I also note that the output cap is two 100uF in series, resulting in effective 50uF, are you experiencing LF loss into low impedance inputs?

There is also a gain strap that can be set, which position is it in for your needs.  ( pins 104, 105, 106)

Alan
Page 199 of the Service Manual.

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ryanstreber

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Apr 23 17 12:50 PM

Thanks for your responses, and sorry I haven't posted a reply sooner. I'my probabl mis-diagnosing the problem. I'm finding that when I connect these outputs to my AD converter (Burl Mothership), the preamps' headroom seems to be surprisingly low with very significant distortion at modest input, and there's also low level hum that is steadily present as soon as a physical contact is made at the patchbay between the preamp output and AD input patch points. I haven't had a chance to elimintate variables and trouble shoot this more, but I'm hoping to spend some time with it this coming week and will update with what I find. Thanks again for your suggestions.

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