TimeLine Micro Lynx audible 9.6KHz capstan frequency

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ethervalve

Well-known member
Joined
Nov 19, 2008
Messages
210
Location
Montreal
Hi all,
I recently got a Micro Lynx unit and built cables per the attached document (using screened twisted pair cable) for linking up my two Otari MX70 decks.
Everything is working well except for a faint but very annoying 9.6kHz tone bleed into my monitor amp (an old McIntosh MC 2120) whenever the capstan is set to 'resolved' (it immediately disappears when the capstan is set to 'wild').  I experimented with putting a 1:1 edcor transformer in the patch bay between the amp and my console and it reduces the tone pretty considerably (-10db or so) but it's still there. The level of the tone is not affected by the monitor volume on my console.
Just wondering if anyone else has encountered this? I bought another system unit for spare parts and I noticed the owner insulated one of the boards from the chassis with duct tape. Maybe grounding issues are common with these?
Thanks in advance for any clues.
 

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Just bumping this to see if anyone might have any clues?
I've had really good success with my Micro Lynx so far (synchronizing 2 Otari machines; also able to use DAW as master with the help of a MOTU Digital Timepiece) except for this annoying high frequency noise when the capstan is set to 'resolved'.
The attached cable assembly shows the capstan frequency output highlighted. Is there any sort of 'brute force' technique anyone could recommend (like running the external capstan frequency on its own shielded cable?)?


 
..I remember we used a 1:1 (audio) line transformer for timecode and tach for our MTR90 and '100.. Some cheap "car-fi isolation" do fine.

Jakob E.
 
Thanks for the insights Doug and Jakob!

In my case, the noise is not affected by the tape speed or whether or not the tach is spinning so I'm thinking it's more the 'capstan clock in' (pin 20) rather than the tachometer. This 9.6khz tone is only present on the pin when when the capstan is 'resolved' and this is the noisy state. Sound reasonable?

I'm just a bit confused about how to hook up a transformer here. To further confuse me, it seems like Timeline uses COM as an abbreviation for both common and command in the cable schematic.
Would something like this be worth trying?
                  1:1 transformer
ML Serv B COM [32]----{||}------- [20] Otari Ext Freq
                  ----{||}---        (capstan clock)
                /            \
                /              \
ML Cmnd COM [36]----------------- [16] Otari Tran GND
                                      (signal ground)




 
Thinking about this some more... Am I right in reading that the Tach and the external capstan frequency are the only connections in use that carry an AC signal?
The rest are just TTL, I think.
If I could figure out which ground to use I think I could use one of those car stereo transformers to isolate both the tach and external capstan clock.
 
Hi Brian,

I've got your replacement output boards in my 16-track MX-70--they work perfectly! Kudos on the great design.

Yeah this issue is a weird one for me. I built my cables on different days and double-checked the work.
I've never come across any Micro Lynx schematics or service manual. The user manual is a bit light on details for a lot of the features too (barely anything on the machine-specific settings--had to do a lot of trial-and-error). 
 
Thanks for the kind remarks.  I've sold more of those than I ever would have imagined.  What got me into making those was a MX-80 24 track that had eleven (!) bad output boards.  All were the latest/last revision, too.

I just double checked, and all I have are a bunch of cable pinouts for various machines.

Bri

 
Thanks for looking Brian!

(BTW I saw a trio of MX70s for sale here in Montreal a couple months ago and they were loaded with the early revision output drivers with the metal case.  So if anyone bought them as-is, hopefully they'll find out about your parts!)

I hacked up one of my cables and discovered a few things
1) the noise disappears when I unhook the external capstan clock (but the synchronizer of course can't work without it)
2) the 'trans ground'*/'signal ground'† and 'ground'*/'power ground'† are separate on the micro lynx end
3) running the external clock and signal ground through a 1:1 transformer doesn't affect the noise but does give me a 'tape out' error.
*Micro Lynx terminology
†Otari terminology
 
That clock line might go into a pulse shaper which then generates harmonics, or might have a low impedance input. Try putting a series resistor in the line. Play with the value to get the largest value the synchroniser will tolerate, and of course see if it lowers the noise.
 
Hey I finally got it working pretty much perfectly!

Thanks for the help Doug, Jakob, and Brian!

The series resistor idea was interesting Doug but my Otari decks ended up being quite picky about the synchronizing voltage signal. 

In the unlikely event that someone else encounters this problem, here's what worked for me:
I ran separate shielded wires from the Micro Lynx external frequency output (called ML Serv B COM for some reason) to Hammond 1:1 signal transformers mounted very close to the tape decks. An excellent local tape machine tech sold me the transformers; he also figured out that a 4.7kKohm resistor across the Hammond's secondary gives a decent square wave in the usable frequency range (about 4khz to 20khz accounting for potenial vari-speed extremes). I was also able to get a bit more attenuation by routing the Micro Lynx cables further from any audio bundles.
Now with both decks set to resolve and the power amp cranked, and the console monitor level at zero, there's the tiniest hint of 9.6KHz detectable with my ear pressed against one of my 4311 tweeters. That's well below the noise floor.
 

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