TAC Scorpion Overhaul Odyssey

[Potato Cakes]

All righty, after putting this project on hold from touring all of last year, I am now able to start to work on getting this console fixed up and put to use. Since last time, I met with a circuit designer here in town to discuss making daughter cards to replace the bus EQ with a 553 circuit using the fancy ones from CAPI down to some smaller, economical options. It seems that I will have plenty of space to fit everything up to the height of a 2520 style op amp. I'm planning on leaving off the transformers as the signal in the console will already be unbalanced. Footprints for stepped and variable gain controls will be included. That might not get finished till after the recapping takes place.

I just went through the PSU and did all the updates in Colin's PSU Fix for the TO-3 sockets. Powered it up and it works great. I do need to find a fan. Does anyone who as done this have any recommendations? It doesn't need to be a quiet one as the PSU will be in another room.

Another thing I'm looking at doing is balanced inserts, however I will be doing this off board. JLM sells a handy PCB that will balance or unbalance signal with very good noise measurements. The only this is I would need 48 of them to handle balancing duties for all 24 channels. I'm looking at some options for DSUB break out PCBs to minimize the additional wiring needed in a rack case as it's all ready going to be quite a bit of soldering for all of the cables from the console, to the balancing units, to the gear and back. This is sometime I may abandon all together and just do inserts directly at the interface. It's just handy to have them directly at the console and not bother with additional software manipulation. Maybe I'll see about getting an all in one board made. Hoping later this week when I finish a mixing the current project I am on that I'll start removing channel strips and breaking in my new desoldering gun.

In the meantime I'm going to go over the information I have been massing for this project and make sure I'm forgetting anything, which I will regardless.

Excited to get back to this project and I'll update along the way.

Thanks!

Paul

 

[Potato Cakes]

Now, that I'm more focused on this project and paying more close attention to the schematics and wiring, I've noticed that pretty much everything on this desk is an unbalanced connection except mic inputs and line inputs. According to the manual, this was to be able to accommodate +4 and -10 gear by which pin on the connector was used. Very smart idea for the time, but now that everything thing is pretty much balanced, the question is how much do I want to make balanced and how much of a pain will that be? I'm going to be using Jeff's ACA board in this project, so that will take care of the L/R outputs, but I would like the bus outputs to be balanced as well. I could add a simple circuit with a DRV134 and trim the level going in to the chip so I would have unity gain on the output. Or I can strap in transformers to do the job and not have to think about the additional load of adding all of those extra ICs.

Anyone here who has gone through this whole procedure have any tips or thoughts regarding the unbalanced outputs?

Thanks!

Paul

 

[john12ax7]

I think the first question is do you really need balanced? In a well behaved studio with short cable runs it's often unnecessary.

Impedance balanced would probably be the easiest to implement as an add on. 

 

[Potato Cakes]

That was one of my first thoughts as well. The problem I that I just thought of is the console outputs aren't just unbalanced, they are different level referenced between the two signal conductors on the same connector, so I would have to make a bunch more cables that only have certain pins connected and then some that have all connections wired. This will cause some confusion and possibly more problems hooking up different pieces of gear via a patchbay. Plus, I will have other mixers use my spot when I'm on the road, so I don't think it would be helpful if they had to keep track the various types of connections. It would make more sense to me to keep all connections and cables balanced, especially with cables in case I would have to use them for something besides the console. It just means I have to decide which ones to do.

Thanks!

Paul

 

[Michael Tibes]

SSL 4/6k did not have balanced insert sends and a simple one opamp balanced return (even on the mix bus afaik) - and I don't remember anyone complaining about that. I do remember a lot of other complains though ;-) The only practical downside which comes to my mind  is the 6 dB lower headroom on the send. The upside is that there will never be any difficulties feeding unbalanced gear. Just a thought...

Michael

 

[Potato Cakes]

Thanks for continuing to provide the information, everybody!

Today was Day 1. All 24 input channels were pulled with chips, caps, and the necessary section where the Eli-Audio Diff.Rev00x boards are to be installed with the garAM10 opamps I built a couple of months ago. All of that and the installations of those DOA add on cards were completed in about 9 hours. I had a friend assist by pulling the channels and labeling the ribbon connectors as well as removing all of the chips. I was making full use of my recently purchased as Hakko FR301 desoldering tool and I can't recommend it enough. Should have had one of these years ago.

I'm going to try to get as many bypass caps as I can installed tonight and then see how many caps I need to order.

The next items I need to start thinking about are the bus and master sections. I am already planning on doing a CAPI ACA-Bo for the master output, but I am considering doing this for all of the bus sections. This will give me balanced outputs to feed outboard gear for parallel compression and recording stems. I had originally thought about using the bus outs to feed a CAPI Sumbus so that myself or another mixer would have the option of having two different sounding mixing options for different material, but I now I don't know if I'll get a similar sonic benefit of just trying to do all of that in the console. I may be over thinking this and maybe because when it gets late all the ideas start colliding into one in my brain and start considering more and more complicated setup schemes. I'm curious if anyone had added the ACA circuit to the bus channels in addition to the master bus.

Back to the iron I suppose...

Thanks!

Paul

 

[Potato Cakes]

Here's my approach for bypassing the chips. I had found some 0R resistors that were closer to some of the connections, but I didn't know if there was a chance they would ever burnout or fail, so I decided to go to an actual ground connection. I didn't do electrolytics as well as during my reading on bypass caps, the information I came across stated electrolytics weren't needed at each point but just at the main incoming source. I'm not sure if doing this at the channel or at the console power input would satisfy this statement. I also read a Jim Williams post regarding doing bypass caps in a Scorpion upgrade and he only mentioned the ceramic 0.1uF caps.

I also found a number of 10uF caps that someone had used to replace the 100uF on the channels. I don't know if this was done in error or if there was some intent involved with this decision. These will all be 100uF when I order the new caps.

Thanks,

Paul

 

[Potato Cakes]

For the balancing of the various connections, I believe I am going to heed john12Ax7's and Michael's advice and leave them unbalanced. The thing that was hanging me up is the fact that several of the connections have the same signal but with different voltage values in respect to pins 2 and 3. My fear is when this gets connected to a patch bay then passed around to different pieces of gear it will cause all sorts of trouble. What I believe i will do is properly unbalance them and tie pins 3 and 1 (ring and sleeve) together and I shouldn't have to worry about making special cables that can only be used with this console. I will be using an ACA-Bo for the master output.

Another thing that I didn't notice was that the inserts are not switchable. I become so accustomed to having an insert switch on modern gear that I had assumed there was on this desk. This changes/confirms some decisions for me. I will definitely be doing any inserts to the channels directly out of the converters to a processor and then to the channel. Since I've switched everything over to unity gain with the DOA boards it won't matter as there will be no gain control to drive any thing at the desk to get "tones." For the buss channels, I do think I would like some way of utilizing the insert points on at least a handful of them to use for things like compressed drum buss, etc. I think I have a plan...

I have found that after engaging in numerous projects here that this is project is pretty easy and if I did have all of my parts ready I could easily knock this out in a week working at a medium pace. Medium for me at least. As with any project like this I come up with grandiose plans with all of the options available and then whittle them down to what is actually important. I appreciate everyone here helping contribute to this process.

Thanks!

Paul 

 

[iampoor1]

Here's my approach for bypassing the chips. I had found some 0R resistors that were closer to some of the connections, but I didn't know if there was a chance they would ever burnout or fail, so I decided to go to an actual ground connection. I didn't do electrolytics as well as during my reading on bypass caps, the information I came across stated electrolytics weren't needed at each point but just at the main incoming source. I'm not sure if doing this at the channel or at the console power input would satisfy this statement. I also read a Jim Williams post regarding doing bypass caps in a Scorpion upgrade and he only mentioned the ceramic 0.1uF caps.

I also found a number of 10uF caps that someone had used to replace the 100uF on the channels. I don't know if this was done in error or if there was some intent involved with this decision. These will all be 100uF when I order the new caps.

Thanks,

Paul

Probably done in error, or they blew some caps on the channels in the middle of a session and 10uf was the only value they had laying around.  ;D

Channel decoupling would be at the channel input, post any input resistors (Many console have eg: 10 ohmn resistors at the input, I prefer to call them "fuseistors" since they are usually intended to blow if you have a dead short on a single channel).

One other suggestion: Its good practice to make the lead for the additional decoupling caps as short as possible on the opamp side. Get the cap as close as you can to the chip. 

Your work looks great! Keep it up! 

 

[Potato Cakes]

Thanks for the information on the 10ohm resistors I'll look at the schematic and see if that they are utilized that way and add them if they are not.

I was trying to keep the legs as short as possible for the bypass caps, but where the nearest point to the ground plane was and also navigating around the other solder joints this is where I landed without doing some physical alteration to the copper traces. I agree not ideal and I would like them shorter but I think it will be fine and certainly much better than without.

I'm going to start adding up the caps that I am short as well as ICs and hopefully place an order this weekend.

Thanks!

Paul

 

[TonyW]

Hi Paul

We have been chatting about the Cavendish, I didn't know you have a Tac Scorpion, I have one too
Did you ever check-out this mod
https://www.eli-audio.com/blank
I have installed these on 12 of my channels for play-back of protools, made the board sound great!

 

[Potato Cakes]

I am using that same mod for all 24 input channels.

Thanks!

Paul

 

[Potato Cakes]

It was nice out today so I took the empty frame outside and gave it a bath, so to speak. Also inspected the faders and after blowing them out and throughly cleaning the guide rods, the faders seem totally fine mechanically. I'm going to get some fancy fader contact cleaner/lube had go over them one more time. As long as they are providing the necessary resistance and aren't intermittent/scratchy, I may be able to avoid needing new faders, which was going to be about $1200 for 44 of them.

I have some replacement shafts for some of the Omeg pots that are broken off. I didn't know this was a serviceable part, but I'm going to remove one of the broken ones and see how this can be done.

Also, does anyone know where to get replacement potentiometer caps for this that are D-shaft press on?

Thanks!

Paul

 

[Potato Cakes]

Regarding the faders, I got some prices today for TKD faders that would fit in this console. From the distributor for 44 faders it is $31USD plus $105 shipping from Japan, 45-60 day lead time. There was another company that I called who advertises they have them in stock, but they did not and would have to do the same process of ordering direct, however their price was about $58 a piece. I was asked about which console I was this was for and then there was a discussion about how the new faders would make it sound better and that they build replacement PSUs for this as I was told the one for this is inadequate. I mentioned that I had rebuilt it and when I put a fan in there is should be fine, but was told that it was only about 3 amps a leg and still wouldn't be enough. I was gracious and told him that when I get to that point of testing and if there is a problem I would be in touch. What is amazing is if I was doing this project and hadn't spent as much time here learning as I have been I probably would've just believed all of what I was told at face value.

Also, the panel that all of the faders attach to is a long single piece and is very flexible, so one had to be careful when removing it.

Thanks!

Paul

 

[Potato Cakes]

I was able to change out one of the broken shafts, and when I finished I was like, "I should have taken some pics!" I do have some more to do and when I get to those I will do so. It's really easy though. There are four tabs holding the front metal plate in place. You carefully bend those back and the front plate pulls off allowing you to easily remove the broken shaft and replace it with a new one. When you do, make note of where the flatted side is supposed to be compared to the other ones because you can get the orientation reversed and then of course your knob is backwards. The replacement shafts that I have are a little shorter than the ones on the console, but it still works totally fine with the knobs and I can't tell a difference. Of course if the pot itself is completely damaged this exercise is pointless, but I think that with some quality contact cleaner/lube these pots will be more than fine.

Thanks!

Paul

 

[TonyW]

Sorry to butt-in again, does anyone know if the tac bar meter replacements  are available anywhere? there was a place in the UK, but they stopped making them.

 

[Potato Cakes]

I believe this would be a question best asked in the Black Market.

Thanks!

Paul

 

[Tubetec]

I can tell you must love that Scorpion loads , wow thats more like forward engineering redesign than an overhaul  ;D
Scorpion was king of the live desks , it really never got much better , only more digital and less hands on.
Back in the old day you stood a chance of walking into a venue and instantly getting a feel for the board and pa set up , no more ,spit licks to the management who dont know their arse from their elbow overzeallously guard their patch with bluff.
Whoever decided accessing aux/monitor sends virtually via menu  in a combined live foh/monitor engineer setup never mixed a gig in their life ,thats for feckin sure , actually Im not sure the ratio of console designers who also happen to be sound engineers , but the gap between the designers and the users seems to be diverging as technology rolls on .Analog reached a peak a long time ago , dark side of the moon time ago and as I said to the boss today, 'Daithi boy, they dont make em' better anymore only cheaper'.
I settled on an Amek Bc3 a long time ago as my pet ,it did get the full on Colin treatment before being retired by ITV and subsequently aquired  ,so its got years and years on the clock for a hobbiest like me , 3 band swept mid ,balanced +4 all round ,no vca ,every control within arms reach ,job done ,no bllsquit, no compromise ,trouble is all me talented musician  buds are way worse the wear for drink than me .

A comment in Brewery could be in order ,

'always grab a scorpion by the tail '

 

[Potato Cakes]

Not so much I have a love for the console itself but it is the realization of it's potential with how good components are and the accessibility of getting boards and metal work designed that gets me excited. I'm not old enough to have worked on one of these when they were plentiful, but I did start in the business when analog consoles were still regularly toted around on tours. Without turning this into a thread suited for the Brewery, I vividly remember being a complete in the box guy and very skeptical when analog summing units started showing up. It didn't take very long to hear and realize that I was able to get better sounding mixes faster and where each track could have it's own place in the mix and not have to be compromised sonically to fit in a crowded sound scape. That was about 10 years ago and since then all I do is some form of analog summing and in addition to analog outboard processing. Obviously there is the loss of convenience having everything totally recallable and it will require to make notes on what gear was used how and where to allow to be able to recreate sounds. But for creating a recorded product that is consistently more pleasant to listen to and has that "it" or "thing" or whatever that people overtly or secretly want in their albums, there is nothing better than  analog and all of the imperfections that go with it. At least what I have found.

Now back to show...


Thanks!

Paul

 

[Tubetec]

Computers hadnt fully matured enough in my time in pro recording to be of much use , Hd's could barely fit a cd on .
Mastering was done to Dat or 1/4 inch , so all manual cueing etc .
Tascam Da88 was the first digital multitrack recorder we got  ,and I got the chance to location test it in my pals rehearsal room /studio ,  it blew  old tascam 1/2 inch 8 track away for sound quality . Noise was virtually non existant
Im glad to hear someone who started out in computer recording realising the old style hands on approach is hard to beat ,the visual distractions of the modern age of recording are not my thing at all ,the concentration required by  the visual elements subtracts from my abillity to use my ears , I find .