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

Thanks for the response.

Yes, I tried with tape at first with no luck. I am familiar with reel to reel and have a Pioneer rt-701.
I am not sure what the Capstan pulley solenoid is. Is there another name for that part? I have mucked around with all the levers and pulleys to get some response from the capstan with no luck.
The capstan does not respond to anything. Tension arms moved around any nothing. The upper reel motors do respond.
I have downloaded the service manual but find little information on the capstan. What I find strange is that when I spin the capstan by hand it keeps spinning on and on. Absolutely nothing mechanical jamming it.

It is a pity as This one seems to be in much better shape than what I see people working on YouTube.
 
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I serviced pro and semi-pro tape machines for years. This capstan motor is direct drive, no belt. It should spin freely. In fact it looks to be pretty similar to some Tascam models which I serviced under warranty.

Just make sure you have power to the motor for one. Troubleshooting it should be pretty straight forward. There is probably a signal to run,and if you have vari-speed or more than one speed you will have signals for those too. Just check that the motor is getting all the signals it needs before fretting over it.

In the event that the motor isn't running when it should, you may have a problem in the motor assembly. Information may not be readily available but they can be serviced. You just have to be more familiar with servo controlled motors. They all operate in a similar way.

These units blow away consumer machines. Much higher quality and far better tape handling. Your Pioneer hasn't any hope of comparing well against this machine.

-Chris
 
Just opened this thread as it may help me solve a UK based problem!

I have a large collection of 15" NAB copy masters, all boxed with full studio notes.

Many are well known albums, outtakes and a few from US studios alternate mixes etc.

The full set for 'World War II' (Beatles covers by top-artists), Family's Its 6 albums
Frankie Vaughn 'Tower of Strength 4 track 1/2" - only one - totally unique!
etc etc

I am now 81 and wish to dispose of this collection - about 100+ tapes which will
have to be collected from South East Scotland.

Please be aware that the contents of these tapes are Copyright and cannot be used for any commercial purpose whatsoever.

What I would like to do is exchange for analogue equipment.

Please respond by Personal Message.
 
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The motor is a 3 phase BLDC with hall encoders, there are no electronics in the motor. The servo electronics are located on the large PCB in the back of the unit. Confirm that all of the cables are connected and the switches are in the correct position.

Make sure the FIX speed indicator LED is lit on the front panel above the head cover, if not press the button next to the speed control until that LED is lit. At least one of those settings requires an external master clock IIRC and the motor will not run if that option is selected. (You can use Fix or Variable in normal use)

My recommendation is to return the unit, it does not sound like you have the resources to do the actual repairs required which at this point are significant.

I had to do diagnostics and repairs on the servo in my MC-50N because on 15ips it would run occasionally run backwards at very high speed at start up.

It turned out to be a bad pot. I ended up replacing all of them in the control PCB, less some other components I no longer remember.
 

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I sprayed deoxit on all the pots On the boards. But did not workThe. Lard pots because I don’t want to change the settings. As a last attempt I may work the pots back and forth. This is actually easier to work on than the consumer stuff but more complex. thanks for your help.
 
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Hi Guys,

You Know I LOVE You All, so I must update my post (with polemic topics) about my Otari MX5050 mods....

I purchased a non-working 5050IIb years ago and had it working both mechanically and electrically after some studying...I did not like the "stock sound", so I began "major surgery" (warn to the faint of heart here) which included:
  • Bifilar Reisert (current) Balun at AC power entry. I do it with all of my projects.
  • Independent "Charge-Transfer" (from ECdesigns') double regulated power supply (28VDC down to 20 then to 14VDC) with TeddyRegs (small footprint) for the repro amp, which required some cutting to isolate that part of the PCB...watch that the PCB is rather odd and one might miss a link here and there.
  • Replacing the stock ballanced outs (major contributor to heat) with THAT 1646 ballanced modules that I had on hand.
  • Swapping signal coupling caps with Vishay Film (the green ones) 10uf which required some more cutting and drilling, and, you guessed it, some unwanted problems...
  • PCB's copper is thin so expect troubles. There is a guy on Ebay that has 5mm lead spread 10uF Wimas that should more or less work there...
  • Replacing stock opamps with OPA2604 in class A (with Rs) which IMHO sound very natural and "tape-like" ; I tried opa2132 and did not like it.

* I also replaced all JFETs in signal path and FB circuit for 2SK170; mind the pinout sense for the Common-Gate fets arrangement...


* I replaced the Pinch-Roller for a new one: rather expensive But very worthy...

* Latelly, I've been testing an upgrade that our technical brothers say It cannot possibly work: adding Bifilar Reisert (current) Baluns to the dedicated Repro Amp PS, first on the Transformer's Secondaries paths for the PS and then between that PS Caps and the Regulators.
I attach some files to show ferrites with more desirable qualities probably than those that I am using, whose specs are un-known since they come from discarded PC Power Supplies. I also attach a diagram for the current state of the dedicated PS. Please neglect the Balun on the primaries because the Moderators do not like when one messes with that...
This mod is So important that I am now on the final stages of upgrading one of my beloved DAC's PS, both on the digital and on the analog side...Niquist was right, guys, hehe.
I always forget to mention that when I started using Baluns, 15 or 20 years ago, I purchased 3 rings whose specs said they worked even on tens of KHz (30KHz I seem to recall) made form other material than ferrite...amorphous something; I've lost the file....those baluns are still in operation on some of my digital sources...

* On the output XLR, I disconnected the Ground cables and connected Pin1 to chassis.

I won't extend in the audiophile's description of the improvements: suffice to say that the noise floor is significantly lower now, I got rid of hum/buzz which is only faintly audible when I put my head "inside" my big Beyma coaxials (98/105db/W/m sens.), and dynamic contrasts are more marked, which is one of the reasons we listen to tape in the first place.

With all of these mods, which were additive in effect, now the sound is Very satisfying... so my need for an external Tape-Head Amp is posponed....

https://fair-rite.com/43-material-data-sheet/

https://fair-rite.com/77-material-data-sheet/

Best Wishes to All...
M.
 

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Interesting choice of the 2SK170 for the N-channel switching device. Couldn't find its on-resistance. Best N-channel device I could fine for use in my Otari MX-5050 MkIII-8 was a J109-D26Z---on resistance of 12Ω. My Otari also uses P-channel FETS--the best I found there was a 2SJ104V with 40Ω 0n-resistance. Does your machine also use P-channel devices? What did you use there?
I went with period-correct Signetics NE 5534/32s for my opamps. A bit difficult to find, but sonically superior to the TI and On offerings, I believe.
I put Elvee-style LT317/337 regulators in for the audio rails---the transistor feedback to the adjustment pin gives about 30 db improvement in noise and source impedance improvement.
Also put balanced audio circuits right on the XL connectors, with (as you noted) pin 1 going directly to the chassis.
 
Hi guys and thanks for your inputs...better late than never...

I have some Shotgun Amobeads that can be bifilarly-wired to make baluns for low level signal...great little products. I will search the file.

About the FETs, I took out a pair, looked at the specs and forgot about them (probably on a box somewhere) and I have a big bag of 170's bought from a reputable seller two decades ago or so, so I use them a lot. Time ago I did measure some samples and they measured according to what is to be expected...I don't remember the value from memory.
I did compare the "old" opamps, the 2134, a short try of the 4562 but my preference is clearly the 2604. I am still waiting to swap the IC501....
Better VRegs will give even better results. I have some Shuntregs that I would love to try but they would hardly fit-in...

About the "Baluned PS" (sorry to insist) it is quite a remarcable discovery of yours truly, hehe, and now I have competing my OTARI with two of my DACs which are also "baluned" and the results are consistent. Quite astonishing is the fact that, due to improved noise floor and dynamics, the sound presentation is "louder", not-"your-neighbors-Boom-Box" louder but "the-orchestra-just-got-their-pay-check-plus-a-bonus" louder, hehe. The un-modded digital sources sound "harmless" but the modded ones sound "dangerous", truly scarry.

I've been studying some articles and I seem to get how these amazing little things work. Appart the known facts about CMRR and balancing the lines between them, it seems that they also "balance" the currents inside them, meaning they treat the skin effect and probably improve "group delay"; maybe that explains why the system sounds more powerfull, with punchy bass/midbass and drums that "jump" outside. Apart that is the effect on "reactive currents" which I have to study further. See, the filter works both ways: they isolate the unit from the rest of the power grid and also inside between sections....that is what I understand until now...

I attach a pic of the pinch-roller, the DIY tensions arm and of little Baluns, dipped in varnish. Those ring measure +/-17mmOD and 10mmH and they give an L of 10mH (each winding) and a C of 334pF. Given that the N° of turns is less than 100, the AL number is bigger than 1000, for what it is worth. I really have to ask some clever guys like Jimmy Neutron and Wintermute.....
Anyway, now I have to buy rings with different materials and try to source enameled OCC Copper (mono-crystal) to make even better quality units.

Cheers,
M.
 

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Hi guys,

The following mods and pictures are NOT for the faint of heart...

Following with my mods for the Beloved OTARI MX5050 and since the "Baluned Power Supply" produces a beast like dynamics and weight, I decide to use some Bybees (previously used in I2S tasks on several DACs; very low power tasks) to give more elegance and refinement to the beast. I installed First Generation Small Bybees After the Voltage Regulators, TeddyRegs in my case. As expected, perceived frequency extension and detail increased BUT a hardness in sound presented itself, which almost made me give-up. After 10 to 14 days the sound softened again, retaining the "seeing inside the music" effect of these. I asume the First Gen Bybees had to burn-in in this new task. Once used to the new sound presentation I decide to instal bybees direct from the Tape-Head signal, being this one the lowest power in the chain and arguably more prone to 1/f noise. Unfortunatelly I only have one SIlver Slipstream....well, you know me, I cutted in half the unit ending with two Half-Silver Bybees, which are the latest and more refined units, more than enough for the very low current signal. I installed them and was in awe at the effect.........listening to my 4Track Opera Collection (london) is the nearest to a Time-Space Travel....I won't go into the audiophile details because I know you hate them....suffise to say that it is exrtemelly detailed, elegant and refined soundwise.
And guys, don't even bother to criticize my use of the Bybees: IF you don't hear a difference with them or never used them it is NOT MY PROBLEM.....

I attach a picture of Mods (Warning again) and a small video about the tension arm mods. I inform that I purchased a lot of different bearings ( shipped) to test the best and most recommended possible Tension Arm Mod, which experiments I will initiate as soon as the units arrive. This superb OTARI machine deserves the best transport....

Cheers,
M.

PS: Joy-full 12:12 Portal!
PS: there is a little mistake on the pick; it should read "Class A opamp".

 

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