Eli-Audio.com Diff.Rev00x OST

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Eliani

Well-known member
Joined
May 27, 2011
Messages
244
Location
Belgium
This thread is the official build and support thread for the AMEK/TAC Scorpion I S1000/S1100 and Scorpion II S1001/1101 API 2520 style differential line receiver mod. The Diff.Rev004 is currently (2015/07/16) the latest revision for this little mod. We designed this PCB with help from this incredible forum! Thanks to Mitsos, Gary and a few more for getting me this far!!

Fair Warning!
To install the Diff_Rev00x sub-pcb on your channel-strip you'll need to remove some components from the main board! Removing these components should be done with the utmost care not to damage solder-pads and/or traces! Remember, these consoles we're build half way through the 80's and they came at a budget-price so everything about this console (maybe except the mega-heavy frame) was not built to last for ages! A de-soldering station would be the best option to remove these components from the board!

BOM:
  • C1/C2 - 47uF/25V
  • C3 - 10p/50V
  • R1/R2 - 10R.25/1%
  • R3/R4/R5 - 10k.25/1%
  • Rf - 10k.25/1% (unless you need CMRR calibration, Rf could be 9.1k with a multi-turn trim pot around 2k)

STEP 1: Buy an assembled PCB or build your Diff.Rev00x Kit.
There's only a few components needed for the differential input board as most of them are already on your DOA (Discrete Operational Amplifier). So look at this picture to sort out where to put what. If you're not familiar with CMRR calibration testing don't bother installing a multi-turn trim pot, just extend Rf towards the pots wiper pad. (Yes I thought about this when designing the PCB!) When using 0.1% or matched 1% resistors CMRR (Common Mode Rejection Ratio) will be excellent!

Do not install the header pins to the PCB just yet, as it's far less troublesome to line up the sub-pcb with the main pcb!

Only thing to watch out for is the electrolytic cap polarity, they will go out with a bang if you get it wrong!!

STEP 2: remove these parts from the main-pcb. (red circles represent the sub-connections)

1b9442_6e7b48ec56f54c7898238269c2ca97c2~mv2.jpg


STEP 3: as I said before I prefer to slide the header pins in the main-board first before soldering them to the Diff.Rev00x board. Make sure the holes are clear of any solder residue because you might push the soldering pad away from the board, ending up messing about to get a clean connection! For the Diff.Rev00x boards only seven connections out of nine are needed! There are no pins at the C4 or R16 main board connections.

1b9442_cde7ce29c79441d7babd3e09ccac6d7b~mv2.jpg


EDIT:
- To protect your line-source outputs remove R1 and R2 phantom power resitors on the channel-strip PCB!!
- If you want to use both XLR and TRS Line-input connections as a line-source, you'll need to remove and replace R6 and R7 10k resistors with a wire bridge and remove R8 altogether.


API%202520%20Differential.PNG
 

Attachments

  • DIff.Rev004.JPG
    DIff.Rev004.JPG
    65.1 KB · Views: 90
If we're using the line input connections on the console, should R6, R7, or R8 be changed? Do these play a role in padding the signal down to mic level?
 
critterkllr,

For true unity gain you should use the XLR connection, the TRS (Jack) connector is the original line-input which is padded down by R6, R7 and R8 in a U-pad attenuation configuration . You could however remove R6, R7 and R8 and bridge R6 and R7 (leave the shunt disconnected! = R8) to remove the pad altogether and have both XLR and TRS connectors available for true differential unity input!

EDIT: I added this information to the first post!
 
Great. I already have a bunch of TRS Dsubs, so taking care of the resistors is much easier! Bonus is I won't need to worry about the 48v.
 
I still recommend removing the phantom power resistors, it's not like you're going to use them anymore...  8)
 
Hey critterklr,

That's great news! That means a lot more people can use the Diff.Rev00x boards to mod their consoles!! Now I can add this to the top post!
 
Iprovlek,

With a bit of clever wiring this can be done! There's enough space between the 200B channelstrips, and the voltages should work too!! A great adition to the 200B is a 2-Aca-Bo by ClassicAPI!
 
critterklr,

If you've got balanced to balanced transformer I would just put them in a transformer box, so you can stick them wherever you want, but a better option would be to add 2-aca-Bo PCB's to the groups and choose your colour through routing!!
 
The rest of the channels are built and ready to be installed. I can't tell you how happy I am to not be building any more 2520s for a while.
 

Attachments

  • image.jpg
    image.jpg
    1.9 MB · Views: 124
critterklr,

Wow! good for you, I've got 16 more to go, oh and some more for a little Group test...
 
Hi Jitter,

let's have a look at those "not standard" PCB's, how about you show us a picture of your Scorpion PCB.

Yves.
 
i just want to make sure I have this right: with this mod, I would not be able to use the S1000/S1100 input module as a mic preamp, correct?
 
realstrange said:
i just want to make sure I have this right: with this mod, I would not be able to use the S1000/S1100 input module as a mic preamp, correct?

That is correct! The mic-preamp is replaced with a balanced line level receiver circuit based on the 2520 opamp...
 
Eliani said:
That is correct! The mic-preamp is replaced with a balanced line level receiver circuit based on the 2520 opamp...

Ok, thought as much. Now, next question is can this be used on the S3300 buss line inputs? I use those a lot for DAW summing, instead of the input channels, leaving me with recording inputs. Would that be doable? 
 
Should be doable, I could whip up a universal PCB containing the circuit 8 times so you could place it on the consoles bottom plate and wire the channels in by hand...
 
Hi Tony,

There's no Gain in a differential (balanced) line-level receiver. RF is a 0.1% matched 10KOhm resistor for optimal CMRR.

Your order has bveen processed and will be shipped out on Monday!

Eli.
 
Back
Top