Remotes for Otari MX-5050 MKIII 8 track

[ofajen]

If you decide to use dbx units,what I've experienced from recently acquiring dbx units for mine,is that you have to watch what you do on certain gear.
The dbx150X units require that you have a TRS connector on the output-but the Ring isn't connected when going to an unbalanced Otari.The other wire from a 2-wire w/shield cable should go to Shield.The TRS connector is used in the dbx unit so no signal from Pin 2 touches Ground.If there is no wire hooked up to that terminal,then the signal will just sit safely there on that pin,without harming the dbx unit.
If you just used a TS cable,then Pin 2 signal would be touching Ground,because there's no Ring section on a TS cable.

Thanks! I'm not much of a fan of noise reduction and don't plan to use it on this machine. I like a little bit of hiss... it lets me know how loud to turn the music up! I don't mind a bit of consistent hiss in the background, but what I don't like is having the hiss change with the music.

You have to check carefully for each piece of gear, but most transformered balanced outputs should have the minus leg tied to ground, while most electronically balanced outputs of the cheap variety where they just run through an extra inverting op amp should be left floating, as you point out regarding the dbx 150s. I don't think I have any gear with the fancy electronically balanced outputs that sense the output wiring and adjust.

Cheers,

Otto

 

[ofajen]

Turns out the channel 2 level issue was not on the playback side. When calibrating playback, I didn't need to do anything on the frequency response and I just needed to turn the gain down 1 dB on channel 3. It's got a nice big playback bump of at least 2 dB in the 60 Hz vicinity, but the overall response (input to output) was a bit closer, so I didn't have the urge to turn the low end eq down. The high end is doing well, with very little deviation up to 16K, maybe 1 dB down at 20K, and it even appears to meet the spec of being no more than 2 dB down at 25K.

On the record side, things are looking good, with the one oddity that I can't get channel 2's record level to match the input level. If it shows 0VU on input, the lowest I can get the output level is +2 VU. So I'll have to go a little easy setting the levels into channel 2. Other than that, it's ready to go and just waiting for me to wire up a couple of snakes.

Cheers,

Otto

 

[FALKEN]

Otto,

as far as the snakes go it depends on what you want.... being a +4 machine on an unbalanced line it will easily overload some equipment. I did pseudo-balanced going out I believe (going in there would be no point since its unbalanced). It probably isn't necessary because my cables are only about 12 feet at most. What I WISH I had done was open up the machine and re-wire the inputs and outputs instead of re-wiring the cables. Then I wouldn't need to have a separate snake laying around thats only used with this machine..... and if you are REALLY into it, you could mod the inputs and outputs to be balanced, probably by swapping out the chips in there with some all-in-ones.

As far as the levels setup, It sounds like you may be doin it wrong. I know you have been doing this decades longer than I, but your channel 2 problem does seem odd. I know on my machine my tape is hot so I set the reference to +3, also I found that biasing a full +4db sounded best...and also remember that you are dealing with +4 unbalanced (though there are switches to go to -10 I believe). And one other thing, your input knobs might be getting in the way, there is a button to bypass those.

 

[ofajen]

Otto,

as far as the snakes go it depends on what you want.... being a +4 machine on an unbalanced line it will easily overload some equipment. I did pseudo-balanced going out I believe (going in there would be no point since its unbalanced). It probably isn't necessary because my cables are only about 12 feet at most. What I WISH I had done was open up the machine and re-wire the inputs and outputs instead of re-wiring the cables. Then I wouldn't need to have a separate snake laying around thats only used with this machine..... and if you are REALLY into it, you could mod the inputs and outputs to be balanced, probably by swapping out the chips in there with some all-in-ones.

As far as the levels setup, It sounds like you may be doin it wrong. I know you have been doing this decades longer than I, but your channel 2 problem does seem odd. I know on my machine my tape is hot so I set the reference to +3, also I found that biasing a full +4db sounded best...and also remember that you are dealing with +4 unbalanced (though there are switches to go to -10 I believe). And one other thing, your input knobs might be getting in the way, there is a button to bypass those.

Re: snakes - seems like you could also just use standard TRS-XLR snakes run into a TRS patchbay and then just connect in at the bay from other gear with TS plugs and that would tie the minus input to the shield on the Otari, just at the bay, not the input/output connector. Wouldn't that work, too?

Re: calibration - I'm just looking at levels on the meter, so the output switches shouldn't matter, since they are dealt with downstream from the signal going to the meter. I'm using the SRL inputs, either with my HP oscillator or the internal one, and the result is the same.

I didn't tweak the bias, so there may be an issue there just on channel 2. The good news is that it is constant across the audio band, so it's just a 2 dB record level offset from input metering to actual output level. The playback side is calibrated perfectly, so I can see the level on the tape by monitoring playback. I'm not going to worry too much about it at this point.

Cheers,

Otto

 

[FALKEN]

Re: snakes - seems like you could also just use standard TRS-XLR snakes run into a TRS patchbay and then just connect in at the bay from other gear with TS plugs and that would tie the minus input to the shield on the Otari, just at the bay, not the input/output connector. Wouldn't that work, too?

I think so....I have used that trick...occasionally in the patch bay two pieces don't like each other and so you patch with a TS cable to correct the problem. But don't forget to rewire the otari side. their hot leg is our cold leg.

as far as the channel switch, (I dont have the machine in front of me), each channel has an input knob and a pushbutton switch to bypass it. This could be your issue on channel 2. I always bypass the input knobs when setting bias, well really almost always.

 

[Gary C.]

Is it best to use the manual input levels when recording,or is it best to engage the button on each meter and let it record at "standard" level-whatever that is?

 

[FALKEN]

Is it best to use the manual input levels when recording,or is it best to engage the button on each meter and let it record at "standard" level-whatever that is?

I try to do the latter when possible.....

 

[ofajen]

I think so....I have used that trick...occasionally in the patch bay two pieces don't like each other and so you patch with a TS cable to correct the problem. But don't forget to rewire the otari side. their hot leg is our cold leg.

Well, since mostly I've used 3M and Ampex machines, I'm used to the old pin 3 hot world, so the Otari doesn't seem strange to me. However, I have mostly cables that are newer and from the "fuck you, it's pin 2" European power grab era we live in. I used to have 8 channel snakes for the M-56 that were wired pin 3 hot. I did that by replacing the cheap Hosa plastic TRS connectors with nice Switchcraft metal plugs and switching the polarity at the same time. Now I only have one left and I cut all the XLRs off to make mike cables, or other XLR TRS cables. I do see a fair number of loose XLRs, so I think I have nearly enough parts.

OK, now here is where I'm really puzzled. When I read the MKIII schematic, it shows pin 2 tied to pin 1 going to the line output jack (i.e. in the internal wiring at the output jack) and continuity testing confirms that pin 2 and pin 1 are tied together on input and output jacks.

Soooo, why all the noise about wiring up special cables, when they've already tied 1 and 2 together in the machine? I should be able to plug TRS-XLR cables in and patch them to the bay and I will get unbalanced connections no matter what I use (assuming the TRS-XLR cables put T and pin 3 together!) It doesn't make sense to me why Otari insists that the input and output plugs also tie pins 1 and 2, when it's done internally, too!

Cheers,

Otto

 

[ofajen]

Is it best to use the manual input levels when recording,or is it best to engage the button on each meter and let it record at "standard" level-whatever that is?

The input SRL can be adjusted by a trimmer on the back. The default is +4 dBu for 0 VU reading on input.

My preference is to use the SRL setting, just for the sake of simplicity.

However, the exception is if I am using an input source that is better off operating with a lower level. If I use the preamps in my little Mackie, I set the record gain at least 6 db higher, so that -2 dBu (or maybe less if the peaks are big) gives 0 VU reading. That keeps the output levels on the Mackie a little bit away from their maximum level. I have all the input gains on this Otari adjusted to that -2 dBu level, so I can dial it up just by switching off of SRL.

Cheers,

Otto

 

[FALKEN]

Soooo, why all the noise about wiring up special cables, when they've already tied 1 and 2 together in the machine?

Oh Interesting, I did not realize this!

You would be even better off inserting a resistor there to match the impedance of the output, then you would have pseudo-balanced outputs !

 

[ofajen]

On the record side, things are looking good, with the one oddity that I can't get channel 2's record level to match the input level. If it shows 0VU on input, the lowest I can get the output level is +2 VU. So I'll have to go a little easy setting the levels into channel 2.

It seems this is an issue with the REC CAL trimmer pot (VR204) on the channel 2 card. The control basically does nothing and the level coming through is always pretty much full on. Looking at the diagram, my first suspicion is that it is not tied to ground and so it doesn't attenuate the incoming signal much. It's only a 5K trimmer and is connected to ground through a resistor, which I have a hard time reading the value on in the schematic (22K or 2.2K). Anyway, I plan to pull the board again and do a quick check in that vicinity and see if I can correct that.

Other than that, the electronics are doing pretty well. I can keep overall response flat at 16K and about -1 at 20K with a broad, smooth rise of less than a half dB in the 5-15K region. On the low end, I have about a 2dB dip at 120 and a 2 dB rise at 60 Hz, with response falling off sharply below 40 Hz, just as it should.

I do seem to have an issue with the new pinch roller. I think the pinch roller tension may be too high, as something there (pinch roller, tape, capstan) is making a bit of a squealing sound in that vicinity in play mode at 15 ips (though not at 7.5 ips), which I can alleviate by pushing the pinch roller away from the capstan a bit (pressure on the little lid covering the pinch roller). Supposed to be about 6 lbs. I suspect the new pinch roller is bigger and results in too much pressure at the current setting for the solenoid.

Oh, and regarding the cabling, it seems to work fine to use balanced connections that tie pins 1 and 2 at the bay. Now I just need to wire up a whole bunch more of them.

Cheers,

Otto

 

[FALKEN]

sounds awesome man, what are you using for a mixer?

 

[ofajen]

sounds awesome man, what are you using for a mixer?

Be it ever so humble, I use my old Mackie CR-1604. The original version... I got it new in about 1994. I also have the OTTO-1604 automation unit to automate faders and mutes, but I don't have it in the mixer right now.

The mixer has a very clean, accurate sound as long as you keep input and output levels away from the peak levels. The eq is pretty limited, just three fixed bands. The bass and treble are quite handy for a lot of basic eq needs. I also have an Aphex 109 parametric eq for when I need more control. It can be four band mono or two band stereo, which is handy.

Cheers,

Otto

 

[ofajen]

I do seem to have an issue with the new pinch roller. I think the pinch roller tension may be too high, as something there (pinch roller, tape, capstan) is making a bit of a squealing sound in that vicinity in play mode at 15 ips (though not at 7.5 ips), which I can alleviate by pushing the pinch roller away from the capstan a bit (pressure on the little lid covering the pinch roller). Supposed to be about 6 lbs. I suspect the new pinch roller is bigger and results in too much pressure at the current setting for the solenoid.

The pinch roller pressure was too high. It was a surprising amount of work to actually get all the stuff off the machine and out of the way and the control card loose and find the right size of wrench and a surprising PITA to actually get in there and get the locking nut loose from the adjustment nut for the pinch roller pressure.

A bit of experimentation and now it seems to be about right: about midway between too little (tape stops in play mode) and too much (squealing parts). So, it runs quietly now. I did this just by trial and error, since I'm not expecting the 10 lb. spring scale until tomorrow at the earliest. I can check for accuracy when it arrives, but for now, it's at least close to OK.

Cheers,

Otto

 

[ofajen]

Well, the cheap spring scales came today from Arbor Scientific and they all work just fine. They sell them (and a lot of other stuff) to school science programs.

The Otari actually seems happiest with the pinch roller pressure lower than spec'ed in the manual. About 4 pounds seems better than 6. At 6, the tape squeals on the new urethane pinch roller, while at 3-4 it sounds nice and quiet and still pulls the tape nicely. I wonder if the urethane rollers cause more tape noise than rubber ones?

Anyway, I'm glad to have the panels back on the recorder and now it's time to wire up two snakes and get to recording.

Cheers,

Otto

 

[ofajen]

now it's time to wire up two snakes and get to recording.

I finally stopped putting off this wiring job. Now the Otari is plugged into the patch bay. When I first started monitoring off the tape and just running the thing in record mode to erase the remaining few minutes of test tones, I was hearing intermittent scratchiness coming off the playback on a couple of channels. I couldn't tell if it was actually signal on the tape or noise in the playback circuit. Anyway, after a while it settled down and the machine recorded quietly.

I recorded a brief bass track and drum track. It sounds great! I don't think the background hiss will be a problem, which was something I wasn't sure of. The Otari is quieter than the Teac 4-track and at most only a tiny bit noisier than my 1" machine was.

Interestingly, I happened to check the Jack Endino page on recorders:

http://www.endino.com/graphs/

and he does have an overall response graph for an Otari MX-5050 MKIII 8 track like this at 15ips and the response is just about the same as mine (2 dB hump at 60 and 2 dB dip at 120) except that my high end response is flatter and more accurate because it's properly biased, not underbiased. I find it encouraging that the response is so similar, because that gives me further evidence that there are no serious issues with the heads or the electronics on my machine.

Cheers,

Otto

 

[ofajen]

By way of update, I finally found a reasonable deal on a CB-116 auto-locator remote for my Otari 8-track. It seems to work perfectly on its own, without the full-function remote, which was a question I had back when I first got the machine, but had cleared up since in a conversation with Brian Roth.

The one quirk is that when it starts up the locate point lamp for location 5 is already lit, as if a locate point has been set, though the locate point is at 0.

It handles the tape more nicely than without the locator, since the machine's return to zero function is just to slam on the brakes as it passes 0, while the locator brakes when it's 30 seconds away and then carefully shuttles at a modest speed to its destination.

Since I'm pretty much always recording and playing at the same time, this remote will be very handy!

Cheers,

Otto

 

[ofajen]

I had some free time today, so I swapped out a channel electronics card on the Otari 8-track and then did playback and record calibration for that channel. The old card recorded and played, but I couldn't quite get proper calibration of input and record levels. The replacement card does a better job of setting the record level at 0 VU.

I also learned not to reinstall the back cover while the unit is on, because I blew out the internal fuse on the VU meter lamps. Had to learn where the fuses are, what size and value they are and then managed to locate replacements at Radio Shack. Live and learn!

Otto

 

[ofajen]

I should have a copy of the manual for the CB-116 auto-locator within a week or so, but I was wondering if anyone here knows the procedure for calibrating the auto-locator? It has a calibration button, but how to actually use it is not obvious to me.

Thanks,

Otto

 

[dotneck335]

I am searching for a manual for the Otari CB-116 Locator. Does anyone have a copy? I have some Otari-specific items to trade as compenastion