-17-0-+17 VDC power supply

[Yairisan]

My first post on this forum.

I am breaking the mic pre's of a Soundcraft 6000 analog console into half-rack modules, enabling me to install, say, 4 channels in a 2U box for mobile recording.

Each module retains the Mic pre and EQ sections, and there is space for a DI (Line level) 1/4" jack at the bottom front, so the half-rack format of each module follows the lines of a typical Mic Pre, with EQ (switchable in/out) also for EQ'ing while tracking/going into the recorder. The recorder is an Alesis HD24.

Everything works fine - the Pre, the DI input and EQ - which I have been testing using the original power supply unit of the Soundcraft 6000, but need now to make a dual -17/+17 power supply of my own to fit into the back of the rack of pres.

Each module uses 5 TLO7272CP chips, so need to acquire:

1. A -17 - 0- +17VDC power supply schematic (can't find ANYTHING for this on the Internet).

2. With the above specs, what mA capacity I need.

Is it just a matter of adding up the total mA rating of the TLO's (x5), and basing the calculated PSU rating on the total no. of modules used?

Sorry, this is long, but wanted to explain in detail.

Sincerely all,
Robin.

 

[dr pepper]

The circuit would probably work fine on a standard + and - 15v supply, if you got a linear supply with 78 series regs you could put a couple of diodes in series with the gnd terminal, that'd give you 16.8v.

 

[Yairisan]

The circuit would probably work fine on a standard + and - 15v supply, if you got a linear supply with 78 series regs you could put a couple of diodes in series with the gnd terminal, that'd give you 16.8v.

Thanks for the reply!

I've seen a few 15 -0 - 15 supply schematics, but figured the reason for 17 volts was to eek out the last drop of headroom from the op-amps. I'm sure a 0.2V discrepancy isn't going to make any difference if I can arrive at 16.8V. That's reassuring.

I can't envisage how the diodes would be configured relative to earth, but I will do another Web search and see what comes up based on your description.

Thanks, Dr.Pepper!

---------- Post added at 15:24 ---------- Previous post was at 15:15 ----------

The circuit would probably work fine on a standard + and - 15v supply, if you got a linear supply with 78 series regs you could put a couple of diodes in series with the gnd terminal, that'd give you 16.8v.

This kind of circuit, with a different regulator (7815 or 7818) for example? (Ludicrously long URL):

Google Image Result for http://www.eleccircuit.com/wp-content/uploads/2008/03/8v-8v-dual-linear-regulators-by-78l08-and-79l08.thumbnail.png

 

[dr pepper]

If you connect 2 diodes in series from a 7815 ground terminal to actual ground then they will lift the ground terminal of the 7815 up by 2 * 0.6v or 1.2v, therefore incresing the output by 1.2v.

 

[pranam77]

You may use 7815 for posetive regulation where as 7915 for negetive regulation with suggesions given by "dr pepper" for increasing the voltage or for bieng precise you may use LM317 and LM337 for posetive and negetive regulation with variability.
Cheers

 

[Yairisan]

Thanks very much for the details and useful replies, guys. I see the point about the diodes, and will give that implementation a go. Also came across a dual rail supply that was variable up to 20V, which looks like a viable option also.

Cheers again.
Robin.

 

[dr pepper]

If absolute fidelity is your aim, which I suspect it is for recording then try to get hold of a dual tracking supply, not absolutely necessary however should one rail go lower distortion might result, '072's are fairly good in that respect though.

 

[Yairisan]

If absolute fidelity is your aim, which I suspect it is for recording then try to get hold of a dual tracking supply, not absolutely necessary however should one rail go lower distortion might result, '072's are fairly good in that respect though.

Yes, certainly, fidelity is a requirement, since the mic pre/EQ sections are decent, and the reason I'm salvaging them before trashing the rest of the desk. With only 5 socketed ICs on each board, I was also considering playing with alternatives in the future. Plenty of documentation exists on the Net pertaining to that. But suitable power supplies, no...well, not tat I've been able to dig up.

I have the power supply schematics for the 6000, but it would be overkill for this project, since the original PSU is designed to supply the entire 24:16:2 desk, and now I'm just powering probably 12 mic pres/EQ's...