-   GeekZone (
-   -   Bypassing the SSM2015 mic pre chip in a TAC Scorpion II (

Drzayuss 18th June 2005 05:25 PM

Bypassing the SSM2015 mic pre chip in a TAC Scorpion II
I recently asked a tech about the biggest sonic shortcomming of the TAC Scorpion II . . . this is what I was told:

The SSM2015 mic pre chip in the inputs. You mix through this part so it's a bottleneck. An extensive mod to replace this chip with a line in opamp is possible, or the high speed mic pre card will do the trick for both line and mic in's.

How is this done? How "extensive" is it? Do the line only strips (s1201 stereo input modules) in the console also suffer from this short coming?

Also, thanks for everyone's help regarding the blown capacitors in my mix bus . . . I replaced the opamps with LT1358s, cut out all the electrolytic polarized caps . . . and it works like a charm.

Thanks again,


Nutmeg II. 21st June 2005 07:29 PM

How about the zero $ option?
You could use the insert returns to inject the signal into the console.
This should bypass the complet input amp section. kfhkh

Drzayuss 22nd June 2005 08:11 AM

I actually thought of this . . . but would I need a transformer to properly unbalance the signal to go in the insert? Also . . . would this bypass the EQ section of each channel strip?

Jim Williams 22nd June 2005 03:53 PM

Yes it would, inserts are post EQ. Fudging in a opamp line stage is possible, with some clever trace cutting. It may be easier to set the insert pre-EQ, less trace cutting and wirewrapping. This is not for the faint of heart, get help if you have any doubts about it.

Glad you like the 1358 master tricks, here's another: Change R-56 and R-57 to 22.1k ohms. This sets the fader to unity so you push it to the top. This lowers d.c. offset, noise and distortion and allows full fader travel for fade outs. It also makes setting the levels easy, just shove it back to the top after a fade.

Jim Williams
Audio Upgrades

Drzayuss 22nd June 2005 05:12 PM

Jim . . .
Thanks for the tip! As far as using the inserts to bypass the mic/line amp chips, would I need input transformers, and if so . . . what would be a good one to use? Also . . . in my chasis I have 12 s1001 strips (mic/line) and 4 s1201 (stereo line input only) . . . the shematics for the s1201 modules don't show an ssm2015 chip in the circuit . . . am I correct in assuming that these strips don't suffer from the same sonic shortcommings (as the s1001) due to their lack of the ssm2015 bottleneck (thus, no point in attempting to mod)?

Thanks Again,


Jim Williams 23rd June 2005 03:15 PM

You wouldn't need transformers as most all balanced outputs can be run into unbalanced inputs as long as you know the circuit feeding them. They will either require grounding pin 3 or floating it, consult the manuals for the source gear. If you want transformers, I would use Jensen JT-11's at around $70 each. Fitting them in there would be tough as the modules have little room.

The stereo modules and the groups both have cleaner line in designs. Shove a great opamp in there and you will be happy.

Jim Williams
Audio Upgrades

Drzayuss 24th June 2005 07:03 AM

Would LT1358s work well here too? How many LT1358s could I get into the console without stretching the limitations of my power supply? I have yet to see any other opamp used in my console other than an TL072 . . . typically accompanied by coupling caps. If I were to replace all these TL072s with LT1358s, could I then cut out all the polarized electrolytics?

Also . . . would using the Jensen input transformers sound better than floating or grounding pin 3?

Jim Williams 2nd July 2005 06:13 PM

The LT chips should work well there. Add a few .1 uf mono ceramic caps from the + and - rails to ground. Check for dc with a meter, if you see under a few millivolts just jumper the caps.
TL072's draw 1.8 ma, the LT's draw 2.3 ma, pretty close. If you do the entire console and the power supply isn't a really big one, consider going to a Power One outboard linear supply.
All transformers have a sound. Whether you like it is subjective.

Jim Williams
Audio Upgrades