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Author Topic: Head direct out/internal electronics switching  (Read 2599 times)

Offline ironbut

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Head direct out/internal electronics switching
« on: August 17, 2012, 02:08:30 pm »
The question of wiring the heads for direct out (to use with an outboard unit like the Tube Repro) and switchable to the stock electronics comes up every now and then.
I've always tried to discourage this because of the delicate nature of the tiny signal that's produced by a playback head.
There's always the chance of picking up noise and/or signal degradation which might be insignificant with a larger signal but can be clearly audible when the signal is small.

The question has always been "Can I have a switch installed to toggle between direct out and the internal electronics?".
Well, today I read a post form one of the long time participants of Audio Asylum's Tape Trail, Dave Pogue, and it was one of those forehead slapping moments that's usually accompanied by a thought bubble with "Why didn't I think of that?" in it.

Dave has a Otari 5050 which he uses an outboard tape amp with but has had it configured to also use the internal electronics. But instead of having a switch, the Otari has been modified with 2 sets of back panel jacks. One is for the direct connection to the playback heads and the other is the input to the internal electronics.
When he uses his outboard tape amp, a pair of interconnects goes from the direct out to the input of the tape amp (of course).
But when he wants to use the internal electronics, he connects the direct out jacks with a pair of interconnects to the other pair of jacks which restores the original signal path of the Otari.
So, if there is going to be any loss of signal quality, it's going to be when he uses the internal electronics and quite frankly, most stock electronics aren't revealing enough to make this noticeable anyway.
So, with mod, it creates a built in patch for the stock playback electronics.

Doing this modification compared to the "normal" direct out mod shouldn't be a whole lot tougher. The amount of work will depend on if you have a "extra" pair of output jacks. On my Technics, there's a pair of "Throughput" jacks that could easily be changed to the internal electronics input by disconnecting the the stock wiring and attaching the wiring that you disconnect from the playback heads.

Of course, there may be some "hitches" involved that I haven't thought of and I welcome Doc and the other "greater minds" here to tear into this mod, but for folks who may be interested in taking their machines out of the listening room and maybe doings some location recording or something, this would be a great option to have.

steve koto
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Offline xcortes

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Re: Head direct out/internal electronics switching
« Reply #1 on: August 17, 2012, 02:28:01 pm »
For my Nagra IV-s Charles had a great idea. He used the NR jack which has (me thinks) eight pins. I have different plugs, one gets the signal from the 4 track head, another from the two track one, a third one gets the signal from the two track heads and sends it back to its original path thus making the machine electronics operational. Not that they sound good though!
Xavier Cortes

Offline shipsupt

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Re: Head direct out/internal electronics switching
« Reply #2 on: February 03, 2014, 01:05:38 pm »
I am trying something a little different someone might be interested in.

I'm in the process of getting my RS-1506 up to speed to listen to some project tapes.  One of the first things I did was pull the head unit and send it to John French to have some flux heads fitted.  John and I talked about what I planned to do with this deck.  I explained I'd be using it for playback only and mostly (if not always) with external Bottlehead electronics.  We originally planned to keep the erase and recording gear intact even if I didn't plan to use it. We started talking about wiring externally form the front of the tape head or modifying the internal wiring. 

That's when John had a thought... he asked me what I though about having a switch on the front of the playback head to switch form internal to external?  The downside, I'd need to put dummy heads in way of the erase and record heads to have room, but otherwise he thought he cold fit it in there.  That sounded pretty slick to me.  I turned John loose to be creative, and as I understand it at least one brainstorming call was held with Jeff from J-Corder.

You can see what John came up with in these photos.  I am working on routing some internal wiring from the spare pins now in use from the switch to new RCA's I'll mount on the back.  I think it's a really clean set up which meets my individual needs perfectly. 

Cheers,
Chris






« Last Edit: February 03, 2014, 01:09:25 pm by shipsupt »
Chris

Offline docb

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Re: Head direct out/internal electronics switching
« Reply #3 on: February 03, 2014, 03:28:02 pm »
Don't throw that switch with the preamps powered up until you are sure that the voltage differential isn't enough to magnetize the head. Don't ask how I know...
Powering down both repro amps and waiting at least 30 seconds before you throw the switch is the safe way to do it.
Dan "Doc B." Schmalle
President for Life, Bottlehead Corp.
Managing Director - retired, The Tape Project

Offline shipsupt

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Re: Head direct out/internal electronics switching
« Reply #4 on: February 04, 2014, 03:24:48 pm »
Thanks Doc! I love getting tips to avoid wrecking gear!! 

I don't plan to do any crazy A/B testing or anything, in fact I'm likely to set it to external and leave it like that for a LONG time!
Chris