Designing PSU for Nagra recorder.

Hello, I've been lurking around this forum for some time, finally decided to register.

I have Nagra 4.2 lying around. The thing is, I don't have a PSU and it runs on 12 D-type cells, it would cost over 120 euro to buy them (I refuse to buy alkaline batteries, only rechargeables) + a charger.

Even though building my own PSU probably won't be any cheaper, at least it would increase the value of the recorder and it's in the DIY spirit. 

It has "external PSU" 6-pin input:
Manual says:
The connections are as follows :
pin 1 battery negative
pin 2 chassis (positive)
pin 3 pilot playback output
pin 4 speed correction signal input
pin 5 negative external supply
pin 6 -10 stabilized output.

??? not sure what I should do with it...

Well, I know that the "pilot playback" is a 50 Hz signal, coming from the tape (it's a reference for playback speed).
Speed correction signal input is probably the signal, that is created by reading the "pilot" and then it increases or decreases the speed of the motor.
So for instance, if "pilot" coming from the tape is 49 Hz, speed correction signal from PSU would increase the speed of the motor.

As you can see, it's not just a typical PSU... and if I would just ignore these 2, then you would probably have no speed correction whatsoever.

It would be of course so much easier, if I could find the schematics for the ANT-3 (the PSU from Nagra)

There are of course other option: making a PSU that connects directly to the battery terminals, kinda amateur solution.
Or stacking a lot of AA batteries (I have a lot of them), and somehow connecting them to the recorder.


So what suggestions do you have? Am I way over my head?

Power supplies are good simple circuits to get started with.

Making a battery replacement is the easiest first step, since you just need to hit the ballpark battery voltage and it will regulate that voltage for use.

After success with this you can try for the more sophisticated approach but crawl before you walk and walk before you run...

JR

Get pin-out details, very preferably a schematic.

The pilot and speed pins are not used in the power supply. They simply pass-through to another box where the camera-sync is handled. This minimizes the number of connectors on this very teeny recorder.

I wonder if there is ANY demand now for Nagras for film-making. The few people still spooling film in this digi-video age probably LIKE non-sync sound too. It is still a lovely tape recorder and an incredible jewel of technology, but will probably never see a pilot tone again.

I am in exactly the same boat with my Nagra IVS.... here's the thing, the Nagras have very very flexible voltage torlerances, anywhere from 12-30V. I believe the spec PSU is 24V @ 900ma. I have my nagra running off a 15V A 200ma cordless battery charger, it runs fine, I can check the voltages on the modulometer and it's just within tolerance, but runs great.... pretty much any no-switching half decent wall wart will work, or you could build your own PSU... or if you have a 24v psu for other gear you could run a tap off that. You just need to buy the tuchel connector, and hook up the positive and negative and ignore all the stablized out stuff... basically just replace the batteries. Just make sure the positive goes to ground (pin 5) and the negative goes to Pin 2... JLM Audio sell good 24V kits, probably a bit overkill though...

If you're rich, you could just buy one of these:

http://www.trewaudio.com/store/product.php?productid=463&cat=58&page=1

But seriously... nothing fancy here, it'd be a pretty simple build if you can't find something lying around...

I love these nagras, they are seriously fantastic little recorders...

Thank you guys for the replies, they have been very helpful.
Yes, they are really good (if not the best) analog field recorders. I've worked with SoundDevices 702/744t - Nagra just sounds more interesting (probably has something to do with analog tape compression/saturation, transformer based preamps). Btw, Hollywood professionals still used them today, for recording really loud/dynamic sounds, like explosions and gunshots.
744t of course beats it in the area of noise levels and flexibility, but I can still find some uses for 4.2, and it's just so cool to own one ;D

It's good to know that it won't disintegrate, if voltages are not 100% correct 

So all I really need to do, is get a regular 24v PSU and change the connector, sounds much easier than I've expected.
But I'll try to build my own, to gain a better understanding of how power supplies work.

Post up what you do with schems! building a new PSU for my nagra has been on my list for a while... so if you get it happening I'd love to see it!

http://www.nagraaudio.com/pro/index.php

In the support section there are manuals and schematics for every Nagra. I'm also in a need for a PSU for my Nagra III, running on batteries for now.

3-pin Line-cord
Sturdy box
Ground screw
1A fuse and holder
DPST power switch
power transformer, 12VAC 1A secondary
Full Wave Bridge rectifier, 100V 3A (or higher)
2,200uFd 25V electrolytic capacitor (1,000u will work)
1A fuse and holder
DIN plug to fit

Note that the old Nagra is wired positive ground!!

For your safety, the box and PT core must be bonded to wall-outlet Earth/Ground pin.

Both the Wall-cord and the Nagra-side should be fused against mistakes and shorts. Have spare fuses.

Leave the 18V DC output floating. (Neither side to wall-ground.)

The + side goes to Nagra pin 2.
The - side goes to Nagra pin 5.
The wall-ground/earth should banana-plug into Nagra GROUND jack.

This can safely supply 0.6A of 15V-18V DC power. The Nagra 4.2 needs only 0.3A to rewind, less in other modes.

Thank you PRR! Looks simple enough.