Another Amek Tac Scorpion overhaul!

[Eliani]

Still waiting to finish this little project, but I've got the boards, now just got to find some missing parts. This is a very basic setup, straight out of the THAT Corp. parts information sheet...

 

[bluezplaya]

Has anyone had issues with their meters? I know it's a common problem with the Scorpion consoles and mine are screwed up. The PFL meter is constantly lit and pegged; all 10 LEDs. The L meter works and the R meter works but with only half the LEDs. Group channel 7 meter stays lit constantly but with every other LED on. I've tried to follow the wiring back to the master module to find any shorts, have swapped some TL072s around. I also checked voltages at the Vregs on the meter boards and the voltages were consistent. Does anyone have any insight in to fixing these? I at least need to get the PFL meter working.

 

[Eliani]

I managed to sneak in a THAT1512 pre-amp into on of my S1000 Channels last night!!

And of course it worked exactly how I expected it would work, not as I hoped! Luckily it was an easy fix.
I remembered reading that the THAT1512's gain resistor had a minimum, so I added a 5 Ohm resistor in front of the 10k rev log pot and it was fixed... I did not account for DC-offset in this design, so I'll have to figure that out for a later revision. But for now in Rev002 I will be adding room for that 5 Ohm (should give me 0 to 60dB gain) and a cap behind the potentiometer to avoid changes in the output DC-offset with gain.

 

[Eliani]

So I've got around 50 of these That1512 MicPre boards laying around in my workshop. As there is a small issue of the "minimimum-gain" resistor not being onboard, I thought I would sell them cheap and get a new batch rolling! How about 1$/1€ each?

 

[critterkllr]

I have this strange issue that started popping up. Occasionally channels will start crackling, then get really bad to the point where it overpowers everything. I've had it happen to 5 channels so far over the past couple months. Each time I had to swap out the gar2520 for a different one. Then, the opamp continues to crackle if used in different channels.

Is this something that could be related to the design of the preamp? Perhaps it happens when the console is being power on?

 

[Eliani]

I have this strange issue that started popping up. Occasionally channels will start crackling, then get really bad to the point where it overpowers everything. I've had it happen to 5 channels so far over the past couple months. Each time I had to swap out the gar2520 for a different one. Then, the opamp continues to crackle if used in different channels.

Is this something that could be related to the design of the preamp? Perhaps it happens when the console is being power on?

Did you remove phantompower resistors?
Might be starving the opamps with to many preamps in your console? I have not had this issue with 24 line receivers in place... Did you revise your PSU?

 

[critterkllr]

I did remove the phantom resistors. I also have a much beefier custom psu. I think it's 12 or 14 amps?

One thing I didn't consider. The console is in a garage and it's winter time. The temperature fluctuations might be adding extra stress on some of the pin solder joints. I guess the first step is to see if I can figure out exactly what's wrong with these opamps.

 

[bluezplaya]

Eli, what's the latest development on the inductor EQs? I am modding my channels one at a time by yanking electro caps and jumpering, opamp swaps, and adding opamp bypass caps. I'm holding off on the EQ opamps though until I can see if adding inductor EQs will be a viable option. I'm also interested in adding a transformer balanced Neve output, using Carnhills and a pair of BA283's. I'm sure the wiring would be similar to the API ACA wiring right?

I've done some listening this week with my S3300 subgroup strips (I have 8 of them) and without recapping (yet) and just swapping U2 from a TL072 to an LME 49860, I can hear a NICE difference in detail. Smoother highs, more clarity and distinction in instruments like piano.

Adam

 

[Eliani]

Hi Adam,

There's no real progress to report as I've had little time to work on any project lately.
The schematics are in place, and have been tested, just need to fit it to a board, and look for insertion points on the main board.

 

[bluezplaya]

I just bought a multi-effects unit and I'm trying to patch it through my Scorpion. I've got 32 channels, 2 aux channels, and 8 subgroups.  I'm wondering what the best way is to do this. I was thinking of using one or two of the subgroups as the master fader for the effects, and assigning those channels to the groups is a no brainer, but how would I get individual levels of effects for each track? Or should I go through aux channel? And if so, would that take away a headphone mix?

I have the Scorp manual, but it's so convoluted in some areas and I learn better from a 'do this, do that' scenario.

 

[Eliani]

I just bought a multi-effects unit and I'm trying to patch it through my Scorpion. I've got 32 channels, 2 aux channels, and 8 subgroups.  I'm wondering what the best way is to do this. I was thinking of using one or two of the subgroups as the master fader for the effects, and assigning those channels to the groups is a no brainer, but how would I get individual levels of effects for each track? Or should I go through aux channel? And if so, would that take away a headphone mix?

I have the Scorp manual, but it's so convoluted in some areas and I learn better from a 'do this, do that' scenario.

In General auxes are preferably used to send signal to fx devices.. There's no other way to individualy set send levels.

 

[bluezplaya]

I just plugged it up through Aux 1 and all is well, but I'm wondering how I can patch individual headphone mixes for tracking.

 

[Eliani]

I just plugged it up through Aux 1 and all is well, but I'm wondering how I can patch individual headphone mixes for tracking.

Auxes are used for both Fx and individual monitoring sends... Make an easy to reach patch panel where you can quickly move from one to the other so you don't need to have to get out of your chair! You don't need fx while recording...

 

[Eliani]

I have this strange issue that started popping up. Occasionally channels will start crackling, then get really bad to the point where it overpowers everything. I've had it happen to 5 channels so far over the past couple months. Each time I had to swap out the gar2520 for a different one. Then, the opamp continues to crackle if used in different channels.

Is this something that could be related to the design of the preamp? Perhaps it happens when the console is being power on?

Did you have any more issues with your opamps? Did you manage to fix your opamps?

 

[critterkllr]

I have this strange issue that started popping up. Occasionally channels will start crackling, then get really bad to the point where it overpowers everything. I've had it happen to 5 channels so far over the past couple months. Each time I had to swap out the gar2520 for a different one. Then, the opamp continues to crackle if used in different channels.

Is this something that could be related to the design of the preamp? Perhaps it happens when the console is being power on?

Did you have any more issues with your opamps? Did you manage to fix your opamps?

I think it has something to do with the weather. Since it's been pretty warm out, it hasn't done it anymore. I had these problems with multiple opamps right up until the weather change. After that, I haven't had a single one crackle. Must be one of the perks of having a studio in a garage

 

[Eliani]

I'm glad!, but sorry you have five casualties... But if I recall correctly your great at soldering more DOA's...  ;D

 

[critterkllr]

I'm glad!, but sorry you have five casualties... But if I recall correctly your great at soldering more DOA's...  ;D

Haha, I've soldered more DOAs than I ever care to. For some reason, they all work now, so no need to solder any more. I hope!

 

[Eliani]

So I still get a lot of questions about if it is possible to trim my differential line receiver, or if there's a gain-pot. And somehow I'm confused. The original API2520 balanced transformerless  amplifier circuit states Rf in the feedback loop to be 100k for 20dB gain  with this calculation: Gain A=Rf/Rs you get gain of 10 equal to 20dB

But I was let to believe that all resistors should match as close as possible for better CMRR, or is this for Rs only?  So I should be able to use a 100k trimmer in place of Rf (100k) and set gain between  0 and 20dB... or am I wrong?

Anyway, the most asked question is if this is a mic-preamp replacement...
So I thought maybe it's time too fix this. Here's a Lundahl 1528 balanced API2520 based preamp PCB for the TAC Scorpion S1000/S1100 and possibly S1001/S1101 channelstrips!! Largely based on the original API 2520 documentation and later to be found closely related to the API 312 microphone preamplifier...

I even incorporated the Differential receiver, so the PCB could be used for both... but not at the same time, for now!

 

[bluezplaya]

Looks great! Where would the Lundahl be mounted? What if you designed a full on 312 mic pre board that would mount a cinemag or EA2622?

 

[Eliani]

Bluezplaya,

The EA2622 or Cinemag would be a tight fit.
The 1528 is very low profile.