[ProAudio] Dragon modifications (was FeralA - Recordings released encoded with Dolby A)

Wed Feb 12 12:04:04 EST 2020

Hi, Bill,

That is fascinating!

One very minor nit: the comparator only works on the right channel of 
the currently playing side. It is actually a six-channel-ish play head. 
The left (outer) channels are normal and the right (inner) channels are 
split--series-connected for the audio.

The LVDT is a wonderful solution.

Do you happen to have the displacement of the azimuth adjuster ribbon to 
arc-minutes conversion factor data?

I have made a modification to the Dragon as I find with many problematic 
tapes, the auto system doesn't work as well as one would hope. This 
modification is simple. I cut the wire that is the ungrounded feed to 
the azimuth motor. I run it through a spare pole on the Timer Play/Rec 
switch so that when that switch is in the Rec mode, the auto azimuth is 
defeated and the motor's feed is switched to a pin on the Gizmo 
connector. Since the Gizmo connector has a bipolar power supply, I 
simply extend a 4-pin DIN cable to a small Hammond diecast box with an 
(on)-off-(on) [(on) means momentary] switch with a series resistor. So, 
I can remotely pulse the azimuth motor forward and back while watching 
the stereotool.com azimuth display.

I do find tapes that are outside the range of the electrically adjusted 
azimuth so I manually adjust the azimuth with the electrical version 
centred and then reset the manual adjustment later (or use an MR-1 and 
manually adjust).

The other modification I've thought about for a while (but haven't done) 
is to replace the remote connector (which I'm afraid to use since the 
logic chip could be damaged by static and I hear it's unobtainable) with 
a 5-pin DIN connector and run that to the head preamp outputs before the 
CMOS switches so that audio from both sides of the tape are brought out 
simultaneously from that wonderful Nakamichi play head. My intent here 
would be to use a standard DIN - 4 RCA cable and RCA to TS adapters and 
use the four instrument inputs on my nearby RME Firefaces to provide the 
additional gain and do whatever else is needed in software. But I don't 
have enough call for four track HiFi cassettes. I can use my DATATape 
CMS1000 tape players for court reporting type of stuff (they do 15/32 to 
7.5 in/s), but are not as HiFi as the Dragon.

And, I previously mentioned always using the outboard Dolby 422 when 
needed rather than the inboard decoder so that I can easily adjust the 
playback level into the decoder to calibrate it. Someday, maybe, my 
colleague John Dyson will do a Dolby B/C decoder...I hope.

Cheers,

Richard

On 2020-02-11 10:31 p.m., Bill Whitlock via ProAudio wrote:
> Not wanting to digress too far, but your mention of the Nakamichi 
> Dragon again reminded me of my years at Capitol. Capitol was unique in 
> the cassette and LP business because they were so highly vertically 
> integrated. They manufactured their own tape, molded their own 
> cassette shells (or C-zeros as they were called) - and even their own 
> lacquer master discs. Part of QC for the cassette shell molding 
> operation involved using modified (in my electronic development lab, 
> which was not located in the "tower" BTW) Dragons to measure azimuth 
> accuracy and consistency. The auto-azimuth mechanics was fitted with 
> an LVDT linear transducer which then drove a large zero-center analog 
> meter reading +/- 10 arc-minutes full-scale. The shells were generally 
> excellent except when someone shortened the cool cycle on the 
> injection-molding machines, which caused the shells to warp slightly. 
> And, for those unfamiliar with the Dragon, the azimuth-adjusting 
> mechanism was driven by a closed-loop servo that measured phase 
> difference between signals from the two "sub-heads" on each track. It 
> was a wonderful tool for QC.
>
> We also developed a super-low noise LP player to measure noise floor 
> of lacquer master discs to help with lacquer additive formulation. 
> Another player measured the increase (and once-around variations) in 
> tracking force caused by electret charges on the surface of vinyl 
> records created during the pressing operation. The staff rheologist 
> (plastic expert and formulator) used it to test new "anti-static" 
> vinyl additives.
>
> My 7-year stint at Capitol was fascinating because of their heavy 
> investment in R&D - but, by the nineties, they'd pretty much become 
> just another record label.
>
> Bill Whitlock
> Whitlock Consulting
> Ventura, CA
>
>
> -----Original Message-----
> From: Mike via ProAudio <proaudio at bach.pgm.com>
> To: proaudio <proaudio at bach.pgm.com>
> Sent: Tue, Feb 11, 2020 5:23 pm
> Subject: Re: [ProAudio] FeralA - Recordings released encoded with Dolby A
>
> Just a side note about Dolby cassettes:
>
>
> Corey Bailey Audio Engineering<proaudio at baileyzone.net 
> <mailto:proaudio at baileyzone.net>> wrote:
>
> > IIRC, it was Dolby B. Could have been "C" because, at the time, I used
> > whatever was built into the record deck & was compatible with my car
> > stereo so that I could switch the NR off.
>
> I reviewed a Marantz cassette deck last year, looking for something I
> could recommend to the home-archivists who want to digitize the closet
> full of cassettes of their band's shows from 30 years ago, but who no
> longer have a means to play them and wouldn't spend the bucks on a
> restored Dragon. It has a Noise Reduction switch (for playback only),
> but no B/C switch. I asked their tech support about it, assuming that it
> was Dolby B, and the answer was that it works for either B or C.
>
> I didn't have a good way of testing how good of a job it did on either -
> the best I could do was to compare playback in the Marantz with that of
> my TASCAM 112Mk2, but with several other significant differences between
> playback on the two decks, I couldn't really evaluate the NR decoding.
>
> It turns out that what's in the Marantz (and also in an almost identical
> deck from TASCAM) is that it's not really Dolby, because there are no
> more Dolby decoder chips available, and that's what was used in all the
> cassette decks. This decoder circuit was something that was developed (I
> don't know by who) to approximate the Dolby playback - one size "fits"
> all - though I suppose not Dolby S.
>
> -- 
> For a good time call http://mikeriversaudio.wordpress.com
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-- 
Richard L. Hess                   email: richard at richardhess.com
Aurora, Ontario, Canada           http://www.richardhess.com/
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.

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