Antidote for a TAC scorpion

[toddjal]

Ok, long story short. Modding my 1985 Tac scorpion. Line stage gets padded down and then goes through a SSM2015 mic pre, not so nice. Since I only use it for mixdown out of the box I want to scrap the mic pres altogether making it line in only (which seems to be a common goal now with old scorpions). yes, I could just use the insert returns but they're post eq and I use the eq. Soooo...

I was wondering if you can see any reason why a little wiring trickery to jump in after the preamp thus making the line input PRE-eq wouldn?t work (after where the SSM2015 used to exist). Tie the ring to ground to unbalance it and it?d seems to be just like using the insert returns as far as I can tell, except for one 10v/100uF electrolytic blocking cap, a 100k resistor to grounda, and a 47ohm resistor after the eq.

-do I need some sort of opamp line stage in there to drive it?
-should the 100k be made a 10k like on the insert return?

Here's the schematic. sorry it's rotated sideways.
http://web.mac.com/toddjal/iWeb/Message ... s%202.html

I'd be eternally gratefull for any advice you may have.

Todd

[Professor]

Well, without trying to dig through the specs, I can say that if you "unbalance" by tying the Ring connection to ground then all you're doing is shorting that phase to ground and not getting any common-mode rejection from the unbalancing. The positive & negative phases of the incoming line must hit an opamp or transformer to accomplish that. Of course, that might not be a huge issue, but if the target is quieter operation, and your environment is RFI/EMI heavy, then it might be.

Even by looking at the schematic, it's hard to tell this, but is there perhaps a way to simply move the insert send/return point to be pre-EQ? Maybe you could even just drop in a switch that would route the insert return to just after the dastardly preamp. In that case, the preamp as both a mic & line input would still exist as a useable feature, and the insert would be more flexible. It would be a mod that increase functionality rather than removing it. Yeah, it would still be an unbalanced connection coming in, but you're going to see that either way unless you add an opamp or transformer per channel.

-Jeremy

[Leopold]

Todd,
Colin from Audio Maintenance is supposed to have a mod availalbe soon for exactly wht your trying to accomplish, not sure what it is or how much $ but maybe you can send him your question and he can give you some guidance?


Good luck,
Eddie

[toddjal]

Thanks guys. Yes the langley mod board is just out and the pics are nice but at 20GBP each and 28 channels it's not gonna happen. That's half the total value of the board. I'm not particularly worried about common mode rejection in my very short cable run but will think about the pre-post idea. Very interesting. Thanks

Todd

[A.David.MacKinnon]

Thanks guys. Yes the langley mod board is just out and the pics are nice but at 20GBP each and 28 channels it's not gonna happen. That's half the total value of the board. I'm not particularly worried about common mode rejection in my very short cable run but will think about the pre-post idea. Very interesting. Thanks

Todd

Do you have a link for this? I'm curious.
We should start a TAC self help group.

[toddjal]

There's a great new TAC/Amek forum at...
http://forum.analogconsole.com/index.php

The specific pic of the new langley line level mod are here...
http://www.audiomaintenance.com/downloa ... ut_mod.jpg

...and can be ordered along with pretty much any replacement parts or caps from Colin at...
www.audiomaintenance.com

Todd
www.toddjal.com

[slenderchap]

We now also make a mic input upgrade to replace the SSM2015 circuit with a "semi discrete" amplifier circuit;

http://www.audiomaintenance.com/acatalo ... ducts.html

(part number AML-16-007)

[There are upgrades for Matchless and BC2 / Classic as well.... Einstein and Magnum will follow shortly]

Colin
www.audiomaintenance.com

[slenderchap]

"Langley" Mic amp upgrade boards are now available for the AMEK Einstein E10 module;

http://www.audiomaintenance.com/acatalo ... ducts.html

Part number AML-16-010

TAC Magnum version should be available in a few days.

Colin
www.audiomaintenance.com

[slenderchap]

"Langley" Mic amp upgrade boards are now available for the TAC Magnum MG1001 module;

http://www.audiomaintenance.com/acatalo ... ducts.html

Part number AML-16-011

[They are also available for the TAC Matchless, TAC Scorpion, AMEK BC2 (Classic, G2520, APC) and AMEK Einstein ]

Colin
www.audiomaintenance.com