Hainbach's NAGATRON with a Nagra 4.2

Hi there.

So if you’ve seen Hainbach’s latest video, he uses a Nagra IV S equipped with a CV input to control playback speed to make a mellotron-like performance using tape loops.

He mentions in the video that with a Nagra 4.2, there is a space where a similar CV speed jack would go but it is left empty and perhaps could be tapped into with modding. I happen to own a 4.2 and indeed the space is there (it’s just a hole with no jack that’s filled with a little stopgap), but what modification would help me in installing a CV jack using this hole?

Alternatively, the Nagra 4.2 has an input jack for a a speed varier which requires a Tuchel 6 pin input. Here are the pin designations:

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If I make an adapter that only goes to pin 2 and 4 (ground and tape speed) and then the other side goes to an input jack for CV, would this work similarly?

That pinout only says there’s a signal input, but doesn’t say anything about what signal levels it expects.

This manual mentions a speed control device that plugs into the ACC port. It’s a box with two potentiometers (see below), and a guess is that they’re used to dial in a voltage between −10 V (pin 6) and ground (pin 2) but a few minutes on the Internet didn’t bring up any schematics, just people who’d be happy to sell you a scan they made of someone else’s documentation…

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Thanks fredrik for your response!

I did see that device (the QSV-2, I believe) in the manual. I emailed someone at Nagra on an off chance that they might be able to get the schematic for me. I do believe Hainbach says the IV S was taking -5V to 7V, but I suppose I shouldn’t assume the same range for the 4.2

Do those pay sites actually work? If I’m desperate enough I might shell out a few bucks.

The connector only has −10 V, so not clear where they would get 7 V from. I guess you could try connecting the speed correction input to ground or −10 V through a resistor to limit current and see if that does something.

As for people selling documentation, I’m not convinced they offer anything that’s not in the PDFs I found via Google (none of which had detailed schematics), but don’t know enough about the Nagra 2nd hand market to make any qualified guesses.

Ok, I googled for schematics and service manuals etc earlier, but now I googled for “Nagra 4.2” and turns out Nagra has a product page with manuals, including a 90-page service manual with assorted schematics.

https://www.nagraaudio.com/product/nagra-4-2/

Here’s the speed control input:

The control voltage is fed into a differential amplifier, and the input test point (TP3) says the pin is held at −4.93 V with nothing connected, so the −10…0 V guess seems reasonable (it seems the internals use positive ground, which explains the odd voltages).

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The IV-S circuitry is identical:

From the service manual here: Nagra IV-S - Nagra

Brilliant. Thanks a ton, fredrik. I think I have enough information to experiment a little now. Will report back!

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Oh yes, i am curious how it works.

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Hi) was wondering if you got this to work?
I put positive and negative voltage between 2 and 4 but only made the machine go fast with no variable speed. Hopefully you cracked the code!

Hey there,

Unfortunately when I went to start playing around with it, I realized there was an issue (completely unrelated) with my playback and rewind so I ended uo taking it to a shop. And now I’m out of the country until July at least. Such a bummer since I was really looking forward to taking it with me and including it in my rig, but patience is a virtue I suppose.

hi there,
sorry for the bump after this long time
i found this post on google after i also saw Hainbach video…

and i was wondering if you managed to get it to work in the end?
i’m kinda curious if its possible to make a diy time variable for the nagra 4.2,
instead of spending hundreds of dollars for the real one.

also, if there is anyone here who happen to have the time variable for the nagra 4.2 and can share some photos of the pcb board from the inside, it could help to try to better understand it (or maybe even to reverse engineer it :slightly_smiling_face:)

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Would be excellent to get a Varispeed to the Nagra.

I’ve also seen the schematic for the 4.2, however for the Nagra III (which I repaired) there was rather a L/C network, trim was done via a trim coil (not a potentiometer).

Here are some pictures for a “Time Varier”. Again, it looks like some fixed capacitors, next to a rotary switch, and then a variable capacitor (for the “fine” I guess).

Either way, a schematic for a working Nagra 4.2 varispeed would be greatly appreciated!

Nagra speed varier QSV IV

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