So you think you want to play with tape: An Otari Story

Administrator
Joined 2004
Paid Member
A few months ago one of my best friends decided I needed a new audio affliction™ and gave the first of my current two OTARI tape recorders.

Today I am the proud owner of two ancient Otari's;

A 1983 vintage MX-5050BII-2 which arrived here sometime in late January if memory serves.

And in late March I came home from the Montreal hifi show after a detour to the deep woods of NH with a rather challenged example of a 1984 vintage MX-5050MKIII-2 with its cart. This is a bridge style recorder which is a dream to work on by virtue of the cart. I don't recommend buying one without as the form factor is otherwise brutally awkward to deal with.

Neither of these decks were in running condition when I got them..

This then is the story of one fool's mission to save them from the scrap heap.

The machines now both run, record and sound surprisingly decent recording test dubs from a digital source here.

The whole point in the long term is put together a couple of good, and not too expensive machines to play those hideously expensive commercial tapes on.
 

Attachments

  • MX5050BII-2.JPG
    MX5050BII-2.JPG
    755.3 KB · Views: 1,611
  • MX5050MKIII-2.JPG
    MX5050MKIII-2.JPG
    970.7 KB · Views: 1,870
In the 1980's I worked at a studio that had two MX5050s. It was my job to align them, replace heads (we used them a lot), and generally make sure they were meeting spec. I also maintained Ampex 350s, Ampex 440s, and even an old MR70 (huge!).

The 5050s did a great job on location recording, and were a go-to machine for voice-over original recordings (we did a lot of radio spots). I recall they had a switchable playback head, usually used for 1/4 track playback. We used the 440s for in-studio high-quality mastering.

It was a lot of fun working there (while a grad student in EE). Glad to see someone using them. Good job getting them running! I hope you can get tape!

Tom
 
Last edited:
Administrator
Joined 2004
Paid Member
There are a fair number of myths circulating about the Otari decks. My observations should apply generally to models other than the two referenced in the opening post.

Each successive generation has improvements in the electronics.

BII, MKIII, and BIII series machines are similar with the BIII being the most evolved. The BIII is the first series to use improved switches in the transport, they also tend to be somewhat more expensive than the older models.

Surprisingly dead machines are often not too hard to bring back to life if you are patient and can use a scope and do basic trouble-shooting, should that not be the case I recommend you not consider buying a non-functional deck as they are quite complex.

Things to look at are the condition of the heads, guides and pinch roller. Probably a good idea to avoid machines with bad heads - they will be expensive to replace.

Heads that are worn to the depth of 1 mil (the thickness of the tape generally used) or so can generally be relapped at considerable expense by an outfit like JRF.

Replacing the heads on the head block is possible for a skilled diy'er, but doing a good alignment probably isn't.

My BII had some corrosion damage due to the foam pad on the back panel that disintegrated into a corrosive goo. This resulted in an open trace that cause some very odd problems preventing the capstan from engaging.

The MKIII had some bad switches and a capstan motor that liked to seize up.

One of the myths circulating about these machines surrounds the Nichicon capacitors used in these machines not ever needing to be replaced. Otari was extremely conservative and they almost never fail, but that does not mean that they are still doing the job effectively.

After a recap (provided you don't break something in the process) the machine will run and sound better.
 

Attachments

  • done2.JPG
    done2.JPG
    809.5 KB · Views: 666
  • done1.jpg
    done1.jpg
    206.7 KB · Views: 635
  • before.JPG
    before.JPG
    842.6 KB · Views: 1,371
  • Board_r.jpg
    Board_r.jpg
    241 KB · Views: 1,493
  • Resr_view_r.jpg
    Resr_view_r.jpg
    233.6 KB · Views: 1,631
Administrator
Joined 2004
Paid Member
Capstan Motors

Before lubricating the capstan motor bearing you need to remove the bearing dust cap, to do so remove the pinch roller, noting location of all washers as you remove it.

Make sure the well is clean before adding lubricant, any accumulated debris in there due to neglect and lack of service will get washed down into the bearing and likely cause the motor to seize.

Use only the proper lubricant which is Anderol 431 or the Athan branded equivalent. These machines have an oilite bearing.

The capstan motors in these decks are often neglected, but very easy to remove and disassemble. This applies only to the later servo capstan motor decks. I've not worked on an older deck with the AC motor and belt drive.

You need to remove the pinch roller, and may at worst have to remove the head cover, and the rear trim piece if you cannot remove the capstan dust cap. If you can actually remove it you only need to remove the pinch roller.

In a BII you must remove the screws that retain the logic board to the rear frame rails and move it out of the way.

In a MKIII you will need to remove a bunch of screws and carefully remove the front trim and move the logic board out of the way.

There are 4 screws that secure the servo PCB, there is a tie wrap to one of the frame rails that you will need to cut (carefully) and 4 screws that secure the motor to the chassis that you need to remove. The whole assembly then lifts out.

See illustration shamelessly lifted from one of the many scans of Otari service manuals on line.

There are 3 screws that retain the motor to the mounting plate - I remove them and the plate.

There will be a tie wrap or two snug up against the body of the motor, carefully snip this and remove. Failure to remove tie wrap could result in an expensive mistake as you attempt to separate the motor halves.

There are 3 screws that secure the case halves, remove these and pull straight up.

Check that the 3 sensor coils in the top half have remained in place. (If broken Athan can repair) Secure them with a dab of high viscosity superglue on the bottom if necessary. (I took pictures but cannot find them.

Clean the bearing bore in the top half of the housing. Polish the shaft if there is an scoring with very fine sand paper (320 grit) until any sharp edges are removed.

Clean everything!

Apply a small amount of the anderol and reassemble. Add a couple of drops in the well.
Reinstall. Should run quietly and maintain speed.
 

Attachments

  • Capstan motor.JPG
    Capstan motor.JPG
    62.3 KB · Views: 558
  • electronics compartment.JPG
    electronics compartment.JPG
    604 KB · Views: 461
Administrator
Joined 2004
Paid Member
In the 1980's I worked at a studio that had two MX5050s. It was my job to align them, replace heads (we used them a lot), and generally make sure they were meeting spec. I also maintained Ampex 350s, Ampex 440s, and even an old MR70 (huge!).

The 5050s did a great job on location recording, and were a go-to machine for voice-over original recordings (we did a lot of radio spots). I recall they had a switchable playback head, usually used for 1/4 track playback. We used the 440s for in-studio high-quality mastering.

It was a lot of fun working there (while a grad student in EE). Glad to see someone using them. Good job getting them running! I hope you can get tape!

Tom

Thank You!

Tape is actually easy to get from a variety of sources. I use SM900 tape which is essentially the old BASF studio master series stuff now made by RecordingTheMasters - Professional Analog Audio Tapes

This is what I have calibrated my decks to use.

The other source is: ATR Magnetics

Demand seems high enough now to keep tape viable.

I currently own 3 head stacks, and a set of good relapped heads as well. The best stack has new SAKI heads on it now installed in the MKIII.

The next best stack will be relapped sometime in the next year, and I have a third stack with heads that could be relapped but will be replaced. I will send the stack to JRF as I am unlikely to be able to align it properly due to lack of experience and the tools required.

The MKIII is modified, and sounds quite nice, the BII-2 will get the same mods soon. Jumping the gun a bit, but here are a couple of shots of the MKIII. (looks rough, sounds really good)
 

Attachments

  • MKIII-2E.jpg
    MKIII-2E.jpg
    114.4 KB · Views: 542
  • MKIII-2F.jpg
    MKIII-2F.jpg
    126.3 KB · Views: 473
  • MKIII-2C.jpg
    MKIII-2C.jpg
    94.2 KB · Views: 557
  • MKIII-2A.jpg
    MKIII-2A.jpg
    118.5 KB · Views: 515
Administrator
Joined 2004
Paid Member
Hi Kevin,
CHRIP! :)

I think maybe you might want to discuss the tape head amplifier and line level circuit modifications. The electronics are of the early 80's and were not made to be extremely good, just good enough. With our parts today, and some of the circuitry we now use, those machines could be given a real boost in performance. Additionally, if you look at improved turntable EQ amps, they would easily adapt to a tape head application. The very low noise Salas phono preamp would drop the noise floor a lot and may possibly really wake that machine up.

From what I see there, the Otari was similar to some of the Tascam machines in build except no bridge. So electronic improvements to the Otari would also apply to the Tascam and maybe even Revox and Studer. That encompasses pretty much every member who is interested in tape.

Another cool idea for you. Look at the head amps in Nakamichi BX-300 or later machines. Nakamichi made some really low noise circuitry, and ripping off their designs might also be a giant step forward.

-Chris
 
A few months ago one of my best friends decided I needed a new audio affliction™

OMG, those things look scary to work on, large, very complicated, lots and lotsa wires, all sorts of i.c.'s., impossible to align mechanical bits and limited folk who can help. Are you sure your best friend is actually a friend ? :p
 
Administrator
Joined 2004
Paid Member
Hi Gareth,
There are plenty of people out there to help. We were invisible because we worked in studios and radio stations. Places where the public never see.

These machines are easier to work with than consumer grade equipment. They were designed with service in mind for starters with less emphasis on marketing and more on performance. They are more satisfying to work on because the results are better when you're done than consumer equipment. In most cases the equipment is built heavier with fewer short cuts because they had to be able to run to high hours, then be repaired and do it all over again.

Once you hear something recorded live off one of these machines, you will marvel at the impact the music has. Even off a CD, comparing one of these to a cassette deck has a clear winner that is predictable. You would be shocked at how basic the audio electronics are with R-R decks, meanwhile all the stops were pulled out on cassette decks to make them listenable. If you put some effort into the electronics in a good open reel machine, you can attain pretty high levels of performance.

-Chris
 
Administrator
Joined 2004
Paid Member
Hi Gareth,
And, I did! It was a Tascam BR-20. I have probably about 4 ~ 5 open reel machines in here right now for service. I'm probably going to have to buy some new test tapes, but only if it becomes worthwhile. The current MRL tapes are a lot higher in price today than they were back in the day. You haven't lived until you had to buy test tapes for cassettes, 1/4", 1/2" and 1" open reel machines. Every studio normally has their own 2" test tape sets. Oh yes, I did say sets. Then there is the Tentelometer for setting the tape tensions. The nice ones used bearings on the probes. They cost me a fortune as well. For cassette and open reel, there are sets of test tapes at different speeds too.

- Chris
 
Administrator
Joined 2004
Paid Member
The Tascam BR-20T is a pretty sweet little machine that commands similar money to the Otaris we are talking about here, and it's a lot prettier. German Woelke heads add to the mystique given their reputation for quality and durability. They are not quite as rugged as the Otaris and usually need some mechanical refresh, but the parts are available.

I have done a number of modifications to the MKIII-2 which basically removed the selsync/sound on sound option which I will never use. The significant change is removing the switching FETs directly in the head signal path. The same circuitry in the record path is jumpered.
Given the wholesale replacement of caps in the signal path plus the Saki heads it is hard to attribute the improvement just the mods, it's the sum of the changes to date.

In the stock, and tired machine the Saki heads made a very small difference.

Calibrating a deck to tape used for recording is sort of important, these machines can only be calibrated to one formulation at a time, whereas some of the late Studers like the A-810 can be calibrated to 2 different types.
 
Administrator
Joined 2004
Paid Member
Hi Kevin,
Yes, I agree completely. Mine didn't have the time code track.

Studios generally calibrate for each tape. Normally just a touch up is needed if they are using the same brand of tape. So I'm not sure how much a two tape memory buys you at the end of the day. Once you're in that habit, it is difficult to just accept the calibration is correct and continue. I even check when using cassette decks.

On every recorded reel of tape I've looked at, there are cal tones at the beginning for level and azimuth. Maybe even EQ too. Mind you, that's in music studios where a project may bounce around the globe a bit.

I'm trying to think of a situation where a two calibration memory would be helpful. Drawing a blank. Not unless they are setting it up for two formulations so only a touch up is ever needed, that's compared to a more in depth adjustment such as using a different tape brand.

There are other types of upgrades to the parts used, focusing on the signal path that can make a difference for sure. Can you post the reproduce circuit diagram? Let's see what is the first stage in making noise off the tape. You're talking about tiny signals on par with turntable cartridge land. Its a natural to compare those old circuits with SOTA type circuits in use today. At these levels, everything matters.

-Chris
 
I love R2R tapes too. It was also my dream to aquire the Otari mx5050 -BII

Sorry to be off the topic a bit but I can't help but notice are you using Tannoy dual concentric driver with your DIY cabinet on your 1st pix of your system ? Is it a 12'' or 15'' Gold or red monitor ? How do you like the sound of these Tannoy ? I'm on my way to aquired a pair of 12'' Gold monitor sometimes next week. Will probably play around with DIY the cabinet as well. Not sure which style should I go with

Thanks,
Tom
Thank You!

Tape is actually easy to get from a variety of sources. I use SM900 tape which is essentially the old BASF studio master series stuff now made by RecordingTheMasters - Professional Analog Audio Tapes

This is what I have calibrated my decks to use.

The other source is: ATR Magnetics

Demand seems high enough now to keep tape viable.

I currently own 3 head stacks, and a set of good relapped heads as well. The best stack has new SAKI heads on it now installed in the MKIII.

The next best stack will be relapped sometime in the next year, and I have a third stack with heads that could be relapped but will be replaced. I will send the stack to JRF as I am unlikely to be able to align it properly due to lack of experience and the tools required.

The MKIII is modified, and sounds quite nice, the BII-2 will get the same mods soon. Jumping the gun a bit, but here are a couple of shots of the MKIII. (looks rough, sounds really good)
 
Administrator
Joined 2004
Paid Member
Hi Tommy,
I assume you were asking me about my speakers? The system pictures are very out of date. There have never been Tannoys in this system, the bass bins are Onken diy cabinets with 16 inch Iconic 165-8G (AKA Altec 515-8G), mids are JBL 2440 on 2380A horns, and the highs are Fostex T825. Amps are of my own design and there is six channels of amplification, 3 way LR4 (24dB) electronic crossovers (also mine), room EQ is provided by a MiniDSP SHD. Signal interconnects are all balanced from the transformer coupled line stage (again one of mine..lol)

Tape is all on balanced I/O both for play and record.
 

Attachments

  • MKIII-2C.jpg
    MKIII-2C.jpg
    94.2 KB · Views: 523
  • vinyl+tape.jpg
    vinyl+tape.jpg
    188.3 KB · Views: 535
  • amps_little.JPG
    amps_little.JPG
    595.8 KB · Views: 520
  • side view horns 2.JPG
    side view horns 2.JPG
    381.6 KB · Views: 514
  • system_feb_2019.JPG
    system_feb_2019.JPG
    536 KB · Views: 533
  • MKIII-2B.jpg
    MKIII-2B.jpg
    133.1 KB · Views: 289
Administrator
Joined 2004
Paid Member
I love R2R tapes too. It was also my dream to aquire the Otari mx5050 -BII
<snip>

They still show up from time to time for reasonable prices if you look around a bit. A friend of mine scored two BII recently at a hamfest at $200 each. They turned out to be in good running condition - in fact better at the onset than either of the machines I own.
 
Thank you Kevin. I really like your DIY system. You're my inspiration!!

I also have my own DIY Class A Pass amps together with 3 way open baffle speakers assisted with Ripole push/pull subs.

My current R2R machines are Pionner RT-707 to playback 4track and Pioneer RT-1050 for 2 track 15 ips IEC eq. Not quite as nice as Otari Mx5050 BII. Will keep my eyes and ears out for a good deal in the future.

Thanks,
Tom

47463596552_90531b4f21_b.jpg
[

46950796955_ff1922bfd1_k.jpg


Hi Tommy,
I assume you were asking me about my speakers? The system pictures are very out of date. There have never been Tannoys in this system, the bass bins are Onken diy cabinets with 16 inch Iconic 165-8G (AKA Altec 515-8G), mids are JBL 2440 on 2380A horns, and the highs are Fostex T825. Amps are of my own design and there is six channels of amplification, 3 way LR4 (24dB) electronic crossovers (also mine), room EQ is provided by a MiniDSP SHD. Signal interconnects are all balanced from the transformer coupled line stage (again one of mine..lol)

Tape is all on balanced I/O both for play and record.
 
Last edited:
Administrator
Joined 2004
Paid Member
MKIII-2 Audio path mods

Chris asked me to share the mods I have done to date. In addition to the mods shown all of the electrolytics in the audio path plus supply bypass caps at minimum should be replaced. (Including ones not shown in my redlines.)

Basically this removes the SEL REP (sound on sound, etc.) feature. I would recommend removing the switch as well to prevent the possibility of it getting into the wrong position and preventing recording. (I jumpered mine)

The high/low output option can be deleted. I recommend the low option for most applications, if high is desired jumper across C-E Q116/Q216 once removed. (I prefer the high output option.)

These mods are not for the inexperienced, the PCB quality leaves something to be desired and lifted traces are possible if care is not exercised. Things are pretty tight.

Jumper Q105/Q205 outer pins (middle is the gate).

Note C131/C231 can and should be jumpered if Q116/Q216 are removed. (Gain is now fixed in the high output mode.)

The schematics for the MKIII-2 are widely available online.
 

Attachments

  • Audio Schematic_reduced.pdf
    230.6 KB · Views: 201
  • Input Circuit.png
    Input Circuit.png
    420 KB · Views: 297
  • mid-path.png
    mid-path.png
    391.2 KB · Views: 295
  • Output circuit.png
    Output circuit.png
    456.5 KB · Views: 261
  • Record_input.png
    Record_input.png
    658.5 KB · Views: 243
  • record_output.png
    record_output.png
    349.5 KB · Views: 276