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Trim Pots (for Cals and Levels) on an old MX5050

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Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Mon Jul 03, 2017 1:19 am

Hi all, first post here, though I’ve been searching and referencing the info in the forum for years. I’ve made the broccoli soup from here many times! Also a frequent read for all curiosities I’ve had about analog recording.

So… I’ve got an Otari MX5050, and was told by the technician that serviced it that it is the 2SH MkII model (one of 'em that can do 2- or 4-track playback). In great shape all around, and seems to be working fine in all regards. Good clean heads, new pinch roller and brake drums, cleaned switches and pots, clean bill of health recently, etc etc…

The problem I’m having is not being able to find the correct manual for this particular model, and as such, I’m scratching my head a bit figuring out the calibration procedure with the trim pots that are present (or how they are labelled, really). Hoping you folks have either encountered and worked on one of these models, or can help decipher the functions and guide me down a proper set-up procedure. I need to learn how to do this properly, of course… and it was just generally set up for UD-35 tape, and I’ve got some ATR and Pyral I’d like to try. I’m not totally mechanically averse, and so I’m trying to dive in and learn more about the medium by having and working on my own machine.

On the front are screw-cap-hidden pots for BIAS/CAL (bias, easy), HI/LO REC EQ (which should refer to the tape speeds by “HI” and “LO” I believe), and SRL/CAL (setting the output level for the SRL switch mode). Think I’ve got the gist of these ones.

However, around back is another set of trims that differ a bit from the later MX5050 models (manual for which I’m stuck referencing at this point).

Back here we have a REP EQ, SEL/REP LEVEL, REC LEVEL, and REC CAL… as well as an OSC CAL for the little 1k tone button on the front.

My confusion is in which exactly to be adjusting here during calibration steps for playback and record. If anyone can help walk me through a calibration on this guy, it would be greatly appreciated! I have the proper MRL tape, and fresh reels to record onto. And I promise I wouldn’t be asking here if I hadn’t dug around the web a lot already trying to sort this particular situation out. Thanks a ton in advance…
Last edited by Ferdinand Ulrich on Sun Jul 23, 2017 11:47 am, edited 1 time in total.
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Tue Jul 11, 2017 9:20 pm

An update, fwiw... this is an MX5050 2SHTD model, to be more specific.
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby tmoneygetpaid on Wed Jul 12, 2017 11:42 am

SRL/ CAL is presumably your playback/ repro level. SEL/REP level is your sel/ rep head level ("sync" in Studer parlance). Is there a SRL or "repro" EQ trim anywhere? That's the one that seems to be missing.

Our typical alignment procedure is:

CLEAN HEADS!
Mount MRL calibration tape to do:
Playback azimuth and sel rep/ sync azimuth;
Playback level and sel rep level;
playback EQ and sel rep EQ;

Unmount MRL and mount up blank tape to do:
Record bias/ overbias;
Record level;
Record EQ

If there's only one low freq EQ adjustment for repro/ playback level, then we do this last. Steve recently explained this is held for last because typically the record low frequency is not adjustable, so you have to compensate for it with playback low EQ once your playback and record are fully calibrated.

This is what we do on a session-by-session basis. If you are setting that machine up for the first time, you should also do a broader calibration of any mechanicals you can do (tensions, zenith, whatever); then inputs and outputs; then VUs; then oscillator level. Then move onto the azimuth and these electronic adjustments.

You should also fully re-calibrate the machine if you go between quarter-track and half-track. I assume your machine can go between quarter-track and half-track, right, not half-track and 4-track? (Quarter-track is two pairs of tracks/ stereo tracks going in each direction rather than 4 tracks meant to be played back simultaneously in one direction.)
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Wed Jul 12, 2017 9:31 pm

tmoneygetpaid wrote:SRL/ CAL is presumably your playback/ repro level. SEL/REP level is your sel/ rep head level ("sync" in Studer parlance). Is there a SRL or "repro" EQ trim anywhere? That's the one that seems to be missing.


Yes, there is a REP EQ on back, check...

tmoneygetpaid wrote:You should also fully re-calibrate the machine if you go between quarter-track and half-track. I assume your machine can go between quarter-track and half-track, right, not half-track and 4-track? (Quarter-track is two pairs of tracks/ stereo tracks going in each direction rather than 4 tracks meant to be played back simultaneously in one direction.)


You're right, its a head for quarter track playback (not 4 tracks). Likely that won't come up much in my uses, but good call, if it does... thank you.

Any guess what the REC CAL trim is for? There's clearly marked REC LEVEL and REC EQ trims... what else would this be adjusting? Also there is no EQ for the SEL/REP... (these related, or no)?

And another overall thanks for the rest, much appreciated! Will get at it...
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby tmoneygetpaid on Thu Jul 13, 2017 5:13 pm

They're probably not related. I don't know how the rec cal vs. rec level trims would differ.

Are you sure that's the model of your machine, by the way? Does it say that anywhere on there?
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Thu Jul 13, 2017 11:41 pm

tmoneygetpaid wrote:Are you sure that's the model of your machine, by the way? Does it say that anywhere on there?


Yep, the Otari badge underneath has it as an MX5050 2SHTD (actually with a subscript 2 on the D...?). No "B" after the 5050, though. I searched the model number and only found one guy in France talking about trying to repair one... though it looked to be one version previous.

Technician that did the last work on it also noted it has the output transformer option (guess that's the "T"), and called it a "MkII"... hmm.
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Fri Jul 14, 2017 7:51 pm

OK, after going through the procedure yesterday, the REC CAL only had an impact on the Source (input) level while in Record. So... Is it normal to adjust the level again after doing the record eq? (and that's what these REC CAL trims are for?)

Gonna check the actual VU meters, and then run through this all again...
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Sat Jul 15, 2017 1:34 am

Another question that seems obvious but I'll ask to be sure...

While I have the MRL mounted, I can adjust the azimuth on the record head while playing in SEL/REP (sync), no?
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby tmoneygetpaid on Sat Jul 15, 2017 11:28 am

With the rec cal/ level I'm still unclear on what the difference between level and cal would be.

They should both only impact the level you see on the VUs when recording. Does one vary the level in some other circumstance?

You should just be able to do the overall record level and then do the EQ. You are setting, in essence, the overall record amp level across the frequency spectrum with record level, and then making sure the frequency response is (relatively) linear with that level at high frequencies.

Yes, you can do record head azimuth off the MRL while playing back in SEL/ REP.
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Mon Jul 17, 2017 11:14 pm

Yes you're right... it just adjusts the value going to the meter, there is no change in the output signal level. So yeah not certain of what that "CAL" is doing exactly either...... but the rest of the setup I've got down I think. I set it up for 355 nwb/m on Pyral 911, and it sounds pretty damn good! Noise floor much lower too. Going to try the ATR tape next...

Thanks again for the help! Much needed and appreciated.
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby GaryV on Mon Jan 29, 2018 6:37 pm

Hi,
I noticed that you have a MX 5050 2SHTD. I have the same machine and I am looking for tech data for it. I'm having a problem with my Capstan motor and i was hoping on getting some info on proper voltages. Were you ever able to find a manual? GV
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Re: Trim Pots (for Cals and Levels) on an old MX5050

Postby Ferdinand Ulrich on Sat Feb 10, 2018 3:09 pm

GaryV wrote:Hi,
I noticed that you have a MX 5050 2SHTD. I have the same machine and I am looking for tech data for it. I'm having a problem with my Capstan motor and i was hoping on getting some info on proper voltages. Were you ever able to find a manual? GV


No, never could track down the right one... sorry. I'll update here if I do come across it.
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