Mic pre based on Angela A10 Module

Hi all

A buddy of mine wants me to design a plug in module for his
old 70s tangent bar board that he can just drop in his frame
to use for tracking in his project studio.

Here is a rough schmo (It still need a few revisions yet
like a dropping resistor for led as an example but you get the idea.):

BIG PICTURE

Working on cutting down the size of this .gif with out losing to much detail.


This guy is a lot like the amek 2500.  I will be using BC560 transistors instead
of the ZTX214 or BC415 like the orginal Angela.

Here is the rough PCB layout for my buddys tangent:



I am thinking of designing a basic general purpose A10 mic pre card
without the tangent spec. details if there is interest.

GARY

gar381 said:

Hi all

A buddy of mine wants me to design a plug in module for his
old 70s tangent bar board that he can just drop in his frame
to use for tracking in his project studio
. . . . .
GARY

Click to expand...

One error:
Q9 & Q10 have their collectors and emitters swapped!

I'm concerned about the quality of DC voltage with such a simple design. You'll have a lot of 50 Hz ripple to filter out. I reckon you should have either additional filtering (1000 uF) or regulators.

Three improvements:
Add electrolytic caps between V+ and bases of Q9 & Q10 to filter out noise in the current gens. Even better replace D5/D6 with one single green LED. If you do so, you will have to increase
R10 & R11 to 470R.
Add current balancing resistors in the emitters of all 8 input Q's (10-20 ohms)
Get rid of the electrolytics  between collectors and negative input of opamps, delete R19&R20. If you do so, you need to bias the non inv inputs of U1A & U1B, with a resistor coming from V+.

I reckon that some DC offset will be present at the output, even if you match the DC path around the negative and positive inputs of U1A & U1B. So I suggest you install a DC blocking cap at the output (with resistor to ground).

abbey

Thank you very much for your input.
You have some good ideas!

Just double and triple checked my Angela manual
and a real A10 module from my desk for the orintation of Q9 & Q10.
They seem to be correct in my schemo.  Its a little confusing as the silk screen
on the A10 module is set up for ZTX214 transistors but Amek used BC415
transistors in my desk and are fliped to the silk screen.  The pinout of the BC415 is
backwards to the ZTX214. (e-c flip)

Any other ideas are VERY welcome.

GARY