Project thread on Gearslutz.com

I started a thread on Gearslutz.com regarding this project HERE:
Good comments and suggestions from other posters. Thank you =)

Replace phono jacks with XLR

The phono jacks on channel 7 and 8 are mounted on washers that cover holes that fits XLR jacks so no modification on the back panel have to be made. I used Neutrik jacks that were available in a store nearby and they fit in the original JAE holes if you tilt them a bit.

Recapping

Well, there isn't really that much to it, just get the old ones out and put in some new ones. C3 and C4 have their polarity markings in the silkscreen backwards. I used a marker and marked the negative side of all caps before I removed them.

I bought SMD 0805 680nF ceramics I intend to use for bypassing all electrolytes. Like this:

I tried it on one cap only for now. When I am finished with the balanced input mod on channel 7/8 I will do one hole board and add the same caps as decoupling on the power rails on the pins on all IC's and make a comparison with the stock boards.

INA217 Piggy-back board

Here is the schematic for the INA217 board. It is very simple and I used the example in the datasheet but omitted coupling caps and DC-servo. I have both bulk electrolytes and ceramics for decoupling on the board close to the pins because I want the chip to get as good supply as possible.

The board trimmed and temporarily secured with gaffer. There, i fixed it! =)
Oh, and don't worry about shorting on the underside of the board, gaffer there too.

Wires connected on solder side, black is common, red V+ and brown V-. Green wires are signals.

Tracing the inputs

I traced the board tonight to figure out how to connect the INA217 board.

RED - IN+
BRN - IN-
ORG - OUT
BLK/YEL - GND


The pads are named after the color of the input transformer wires.
There are some differences between the balanced and unbalanced boards. Some resistors and jumpers have to be fitted/replaced/removed. Resistors that are on the balanced board but not on the unbalanced are:

R3 - 2K2
R4 - 360R
R10 - 16K
R11 - 560R

None of which I had at home of course so no soldering tonight.

Balanced

Unbalanced

Some thoughts before I move on.

When I got this console I had a lot of inspiration and many ideas on extending the features of it, but after having it with me for a while and reading what other users appreciate it for I more and more feel like just keeping it more or less stock. I still going for the recap of channel boards/PSU since I don't think there is anything positive about dried old caps. Features that I would like to have but in that case would be external are HP/LP-filters and phantom power. I would really like sweep on the Hi-shelf though.

I would like to clarify my intentions with the preamp board. Although the INA217 chip is a complete preamp I am not replacing the stock preamp. I just want to use it as a balanced receiver because the boards on channel 7 and 8 don't have input transformers. If I could get the original transformer or knew what to replace them with I would put trannys in there instead. (If the cost was acceptable, two Lundahls would probably cost more than I paid for the console) .

I hope I get time to install the board and test It soon.

I made a INA217 preamp board tonight. Since i don't have the schematics and are working a bit blindfolded I assume 1:1 ratio on the input transformers and start with no amplification on the preamp. I've left space for gain resistor though. I omitted coupling caps on the input because I have abandoned the idea of internal phantom supply due to space constraints.

Not to pretty but the circuit is to simple to motivate a pcb.
Notice the surface mount ceramics on V+ and V-.