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So you think you want to play with tape: An Otari Story
So you think you want to play with tape: An Otari Story
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Old 18th May 2019, 03:47 PM   #21
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
Next step is to install some relatively inexpensive stepped attenuators for input and output level control. They're ordered and should be here in a few weeks.
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Old 18th May 2019, 04:04 PM   #22
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
Default LED Relamp

Here is the relamp circuit I used. Simple, the leds are cheap.

I'm going to evaluate soft white LEDs next. (I'm not rocking the blue ones too much.. LOL)
Attached Images
File Type: jpg Led_relamp.JPG (84.7 KB, 135 views)
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Old 19th May 2019, 12:05 AM   #23
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
I completed some more cap replacements and changed a few things. (Noted in previous post) New photos..

Removed some switches and a few more transistors.

There are a number of shots relating to removal and bypassing of the SEL REP switches (SOS, etc.)
Attached Images
File Type: jpg switch and pot mod.jpg (612.8 KB, 115 views)
File Type: jpg switch mod.jpg (928.8 KB, 118 views)
File Type: jpg switch mod2.jpg (594.0 KB, 115 views)
File Type: jpg tape replay amp + more recap.jpg (681.0 KB, 109 views)
File Type: jpg replay output.jpg (682.4 KB, 38 views)
File Type: jpg Inside view 1.jpg (413.0 KB, 37 views)
File Type: jpg Today's done.jpg (657.7 KB, 44 views)
File Type: jpg today's done2.jpg (702.4 KB, 47 views)
File Type: jpg back together2.jpg (701.8 KB, 44 views)
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Old 19th May 2019, 12:20 AM   #24
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
Default Otari Switch Problems (Panasonic Switches)

The Panasonic ESB-701T was used to switch power in the MX-5050BII series as well as the MKIII. It was not used in later decks, and was probably used in earlier models not familiar to me.

These switches were used to switch AC power where they usually, but not always hold up well. Where they fair less well is in logic level applications - tape speed/reel size/edit where their use was inappropriate as they were not designed for switching low level signals - predictably the contacts oxidize or the goo they applied to the contacts hardens with age and the low operating currents render the switch inoperable.

These switches were discontinued decades ago, new replacements are almost impossible to find and go for stupid money when you do. Purchasing board assemblies that contain them seems to be the best way to get replacements. This is what I did - the tape speed switch on my MKIII was bad, low speed worked, but high speed was at best intermittent and basically did not work.

Here are some pictures of the switch.
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File Type: jpg 20190331_102924.jpg (657.4 KB, 67 views)
File Type: jpg switchboard.JPG (439.2 KB, 59 views)
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Old 19th May 2019, 02:30 AM   #25
anatech is online now anatech  Canada
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So you think you want to play with tape: An Otari Story
Hi Kevin,
You're right. That is a popular old power switch. Power switches are not suitable for switching low currents either. Maybe you can use them to control signal relays? You can use a resistor or light bulb to draw current to make the contacts happier.

I am wishing you luck on this one.

-Chris
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Old 19th May 2019, 03:58 PM   #26
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
Those are good suggestions, but as long as the deck is exercised regularly the switches should continue to function, they made it 35 years and only one has failed in this machine in that time - so while it was an inappropriate choice it hasn't prevented most of these machines from working reliably as long as the switches are exercised.

Otari apparently purchased large quantities of components and continued to use them for years and years until used up. I am not 100% certain but I am pretty sure some of the op-amps were already a few years old when they got into this machine in 1984. Some of the electrolytics had 1980 - 1981 date codes as well.

On op-amps the ones fitted are far from horrible sounding and given the 1970s approach to power supply bypassing (there is no local decoupling anywhere!) and the general design rationalization for lowest cost within the design goals I would be hesitant to advise changing any of the op-amps in this design. (Were anyone inclined the 5532 is pretty forgiving and would provide a small improvement in performance over some of the originals - whether this is audible is anyone's guess.)

I will say the modified and recapped Otari MKIII sounds a lot better than I would have ever expected, particularly considering the generally unpromising condition it arrived in. It's not quite indistinguishable from the source, but it comes a lot closer than the BII with its unmodified audio electronics, and it sounds far better than any of the other decks I've had. The Saki heads undoubtedly contribute as well, will know more when I get the other deck updated and the now spare head stack fitted with refurbished heads.
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Old 19th May 2019, 04:51 PM   #27
anatech is online now anatech  Canada
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So you think you want to play with tape: An Otari Story
Hi Kevin,
What op amps did they use? If they are TL072 or TL082, you will hear a difference. Now, since those are FET input op amps, the best upgrade would be OPA2132 (or single / quad) for two op amp packages. Try on one channel near the center of the tape if you want to really see if there is an improvement. If you're ultra stingy, then just the positions that are low level - like the head amp for example. But anywhere you see a TLO7x or TLO8x, you need to replace them with something better. Those did sound better than the 4558 and similar chips, and if you find any of thoser, install NE5532 or NE5534 replacements.. FET to A FET device, BJT to a BJT device.

Don't forget to set the bias oscillator frequency and the bias traps. Misadjusted traps can allow a lot of energy to pound through to the record amp final stage. It doesn't react well to ultrasonic energy and that can cause distortion. I only mention this as many techs skip this step.

The OPA2132 will most definitely make a difference, especially in the head amp position. Just be glad it isn't a 24 track machine! Anything wrong in the tape path at all and that 2" tape is heading off in its own direction.

-Chris
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Old 19th May 2019, 05:39 PM   #28
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
All Japanese op-amps which are several notches better sounding than the TL072/82 series stuff you referenced. (No fet op-amps in this design)

Low noise JRC2043 in the tape pre-amp and JRC 4560 which are higher performance cousins (faster, more bandwidth, lower noise) of the 4558/4559 you are probably already familiar with. (They are admittedly mediocre by today's standards, but my history with op-amp upgrades has not been positive - some of the older devices sound just fine and replacing them with more modern ones has not resulted in substantial improvements in sound quality, sometimes unfortunately quite the reverse.)

Given the overall design approach I strongly recommend not changing the op-amps, I think given the complexity of the design and the lack of any decoupling at the op-amps this is just begging for trouble. This is a single sided PCB with relatively mediocre board ground - there are a lot of buss bars for power and ground.

Given the way it now sounds I also don't see a lot of reason to make the change. None of the JRC stuff IMHO is bad sounding - past upgrades of devices like dacs and CD players using these parts did not result in the sort of gains in performance I would have expected.

I suspect in a lot of ways this is a pretty studied design and was the result of a lot of evolution with small changes over the years.

Further improvement is likely possible but I will need to look at what's next.

Edit: You might be surprised but I am not a fan of the OPA2132 sound at all, much prefer the newer OPA1641 and 1642 to the old BB devices. It sounds too warm and slow to me.
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Old 19th May 2019, 06:20 PM   #29
kevinkr is offline kevinkr  United States
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So you think you want to play with tape: An Otari Story
For those of you hesitating to participate there are often decks available for short money at electronic flea markets, and hamfests.

A friend of mine recently (just a few weeks ago) acquired two MX-5050 BII series decks at a hamfest for a couple of hundred dollars each. I've not seen them, but I believe they are in a lot better shape than my two freebies were when I got them.

There are often decks offered on eBay that are represented as being in better running condition than typical finds offline. There are some reputable refurbishers selling on eBay as well as private sales. These tend to be a lot more money.

Other sources can be public auctions at radio stations and advertising agencies as well as estate sales. These are a long shot but sometimes machines come out of these for next to nothing. (Mine came from a radio station and advertising agency respectively for next to nothing and were eventually gifted to me by friends looking to free up space at home.)

My plan ultimately for these machines is to use them for casual recording as I see fit, and for playback of commercial studio quality tapes I will start to acquire once I am confident that these machines will play them safely.
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Old 20th May 2019, 11:46 PM   #30
Mr_Zenith is offline Mr_Zenith  United States
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So you think you want to play with tape: An Otari Story
M- m- m- must... r- r- resist... urge!

Received a Revox B77 as a radio station refugee around 1989. Wonderful-sounding deck, and mesmerizing to watch, too. Wound up selling it at a hamfest back in 2007 and regretted it ever since.

Don't have much experience with the Otari decks, but if yours sound anything like my old Revox then you've got some keepers for sure!
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