SSL 9000 - 1U - 6 channel Pre-Amp

hi guys,

To finish my studio I want to build a 1U 6 channel SSL 9k pre amp.
I would like this all contained in a 1U box, psu as well.
I wanted to use these Russian step pots as I have quite a few, they have 11 stages and are 3 deck.
I only need 2 deck and wanted to know how to configure them with resistors to achieve Reverse log 2.2k stepped attenuator.

Is this possible please.

Thanks in advance.

Regards

Spence.

Here is some resources I have found on stepped attenuators

http://www.audiokarma.org/forums/showthread.php?t=345644

http://www.dhtrob.com/projecten/stapp_schakelaar3_en.php

Hi guys,

How about this?

Regards

Spence.

The scheme you have is linear, not reverse log.  There are calculators on this forum that will give you the correct values.
Best,
Bruno2000

Hi Bruno,

Yeah I realise now I have done linear,  how about this then?

Revised
position - ohms - resistor

1 - 43% - 1000R
2 - 69% - 680R
3 - 80% - 330R
4 - 88% - 200R
5 - 92% - 100R
6 - 95% - 68R
7 - 96% - 33R
8 - 97% - 15R
9 - 98% - 33R
10 - 100% - 57R

total = 2500R

4 pots wired up and have 2 x 2.2k reverse log, now onto making some pcbs.

Regards

Spence.

Hi,

have made 4 x the main pcbs and power pcbs today.
drilling them tomorrow.
already got a few balancing boards that i can use.

Spence.

hi,

If all pans out now should be able to get 6 channels in a 1U rack, gonna be tight but i think i can do it!!!
stacking pcbs seems to work quite well just have to make sure ive got some low spacers for the bottom.
Also going to postpone the idea of switched pots as the ones ive got i think are not make before break, i will test this first.
by using normal reverse log pots this will give me more space.

Spence.

Hi Spence,


have you seen mine - It is from 2004.
I modified the layout slightly because of the 2 HU restiction and to include a phase switch relais and phantom resistors.

Front

PCAs prior to the installation

hi chefducuisine,

yes i have seen your very fine work, mine is not comparable  to your excellent work.
Question, do you have the balancing boards all made within your pcbs? as i see an extra IC on each board?
Also i spy a relay? ?
regards

spence.

Yes - the balancer is on the board.
The Relais is for phase reversal.

getting there now, still waiting on 4 x 2.2K pots and got to make another 2 balancing boards and 2 more channels.
Channels are double stacked and i will be feeding out cable to XLR connectors rather than chassis mount XLR.
Sorry about the rubbish quality of the photo!!!.

regards

Spence.

Hi Chefducuisine ;-)

Very nice unit.
Can you give us the reference of the case?
Thanks,

Cheers,
Pascal

this Case is from

Schroff
Inpac Series
Part no.: 10828-072

Hi,

Thanks ;-)

Hi all,

4 channels tested and no major smoke yet, getting signal through first unit need to check other 3 pcbs.
Going to make other pcbs tomorrow and start to finish this.

Spence.

Hi all,

All six channels made with 3 balancing board, just gotta wire it up tomorrow and test the other two channels then connect up input and output xlr's.

Spence.

Hi,

Psu pcb keeps shutting down, must be the regulators all overheating?
I would have thought that the SSL 9K psu would be able to handle 6 pcbs and 3 balancing boards? i don't have the 48v connected yet and the only other thing is an LED off the 18v for power light.
I am using a 2 x 18v 30va toroidal transformer.

6 x SSL 9k current 60mA = 360mA
3 x Line balancing boards current 20mA = 60mA
6 x 48v current 10mA = 60mA
Led current = 10mA

total current = 490mA

i think this TXF is good for up to 1.660mA (30 / 18 = 1.66A)

other than put some heat sinks on the regulators i'm scratching my head on this.

regards

spence.

HI,

put some heat sinks on the regulators and all good now, plugged it all in and only 2 channels working!!
need to fault find but on the home run now. the two channels that work sound amazing though.

regards

Spence.