Otari MX505 calibration help

H

Hi_Flyer

New member
so I got my TEAC test tape, and I got a Radio Shack multi meter... I want to try to get this deck set up before I record some stuff next Saturday. I have to go through the manual again, but the last time I looked at it the calibration process, it sorta left me scratching my head.

I gues the biggest question is what exactly do I do with the multimeter? Like, how do I hook it up to the deck?

Any general advice or can anybody point to a comprehensive guide on the topic?
 
Do you have the MKII or MKIII, or other?

There are so many models… some have balanced connectors and some don’t.

With XLR connectors you can almost manage by just holding the probes on the pins (red lead to pin 3 and black lead to pin 1 & 2 for Otari), but that can be a pain. It’s handier in the long run to buy or make a special cable with two banana connectors on one end to interface with the multi-meter and an XLR connecter on the other end.

Once you’ve got tools together the first step is to verify that a 1k test tone entering the input at a given voltage is showing the same voltage at the output. The voltage for the MX5050 should be specified in the manual. Some models are switchable between +4 dBm (1.23 volts) and -10 dBv (0.316 volts).

I'll dig up my old calibration links and post them later.


:)
 
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Here are a few useful links to study. As with anything there is a learning curve and you may get headaches during the research phase until things start to make sense. There’s a whole ‘lota info here, but building a foundation is very important before you start tweaking trimmers and whatnot. Take your time and be sure first. ;)

http://www.churchsoundcheck.com/tra.html
http://home.swipnet.se/herbalifeinfo/Audio/engRULL2.htm
http://www.digitalprosound.com/Htm/TechStuff/2000/Sept/AnalogPt2-1.htm
http://www9.dw-world.de/rtc/infotheque/magn_recording/magrec.html
http://web.archive.org/web/20031212.../MarApr1996/StudioMaintenace/90+Mar-Apr96.htm
http://www.larryseyer.com/align.php
http://www.analoguerules.com/basicalign.html
http://www.bilver.com./tape.html
http://www.barryrudolph.com/greg/align.html
http://www.johnvestman.com/alignment.htm

Hope that helps. :)
 
OK, so much for that. test tape is sticky shed, it wouldn't even come clean off the reel. I guess I can try baking it in the oven tomorrow...
 
so correct me if I'm wrong here... basically, once you get the heads physically aligned, you start to adjust the repro electronics. You play back the test tones and adjust the repro EQ so that your hi freq test tone (10k or 12.5k?) reads O on the VUs, right? and you do the same with the other test tones as well...

THEN, you adjust the record EQ, in my case, I can do it with the built in O-scope on the Otari.

am i getting warmer? do I even need the multi meter or can I simply use the meters? I'm a little confused about that...

I have no idea how measure +4dBm with this multimeter anyway... this is some complicated stuff.

EDIT: nevermind, re-read Beck' spost... 1.23 volts..
 
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any more help here?? slowly figuring this out... I know I need to measure AC voltage with the multimeter, so what is the equivalent to +4dBm in AC voltage on this multimeter?? uh thats not in the manual...

and more weirdness... I was able to get all of the test tones to play back about 0VU, except track #4 & 6, on those tracks the hi frequencies fall off very quickly at about 4K. why would this happen?

EDIT: re-read Beck's post, got the 1.23 V = +4 dBu

monitoring from the repro head is different than the sync head. sync head is flatter. does this mean I have a problem with the repro head? seems possible since track 4 & 6 are in the middle? am I making sense or way off base?
 
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What is the model number of the test tape that seems to have sticky-shed? Yeah, you'll have to get a working test tape first. You shouldn't bake it in a conventional oven. You'll need a convection oven or a food dehydrator.

The tracks that are down at 4kHz could be due to running sticky-shed tape. You have to really clean the tape path after bad tape has been dragged across it.

I don’t have the MX5050-8 manual, but the Otari manuals I’ve seen for the 2-tracks aren’t very clear in the calibration section.
 
Its a TEAC YTT 1144 test tape, bought as NOS on ebay.

yep I think it was the middle tracks on the tape that were not dried out all the way through. I dehydrated the tapes for a couple hours, probably not long enough though, only long enough for the outside tracks to dry out but not all the way to the middle. There was some gunk built up on the middle of the repro head (not so much on the sync head, which explains the difference in freq response maybe?)

The tape is baking again (I'll leave it overnight this time), hopefully its not ruined and I can still get the EQ close enough for rock'n roll on those middle tracks... Tape path is very clean now.

also I'm confused on the output calibration now... I followed the instructions to get playback at 0 dB on the VU meters, but now, when I run the built in oscillator at 0dB on input, it jumps up to +4 dB (at 1K) when I switch to monitor from the repro head (with a brand new SM911 tape and clean tape path, by the way) So does that mean the input level is 4dB too hot and I have to turn the trim pot down? I believe the guy that sold me this thing had it calibrated for hotter tape than the 456 (+9), is that why there is such a dramatic difference?

things slowly become clearer... what a pain though! thanks again Beck!
 
just when you think you have something figured out, more questions come up... from one of the Becks' links:

Example:
Say you want an Operating Level of '+5' on tape,
and only have a +3 level test tape.
Since 0 VU (your reference level on the RECORDER'S VU METERS)
should equal +5 level, you would see -2 on the VU meter
when a tape 2 db lower is played back.


so now i'm wondering if I have to compensate for the SM911 tape, which is +6 tape. How do I know if the reference tape is the same output? it only gives a reference fluxivity value.
 
That’s something I was preparing to address in a longer post, since you talked about level differences in a previous post.

You don’t have to compensate for the SM911, but rather the difference between the test tape and the recommended flux level of the machine. In your case, the MX5050 should be set at 320 nWb/m (+5) and the TEAC test tape is 250 nWb/m (+3). So when you set the repro level you set it so the VU meters are 2 dB down from zero. Alternately you can set the machine at a higher or lower flux, but it’s probably best to follow factory spec when starting out. Flux and output are the same thing when your talking about +3, +6, etc. TEAC used Ampex 456 on the YTT-1144, which is a +6 tape, but the tones are recorded at 250 nWb/m (+3).

Also, if the test tape was not fully restored from its sticky-shed state (perhaps not baked long enough and/or hot enough) it may play at a lower level than specified. Sticky-shed lifts the tape away from the heads like any major oxide build up would. The result is lower levels and muffled high end. On the later improved version YTT-1144-2 they used different tapes, including AGFA, 3M and 456 with the improved binder. All the older YTT-1144 will have sticky-shed... sooner or later, but the YTT-1144-2 won't.

I’m curious as to what the VU meters were reading when you first ran the test tape before you adjusted any level trimmers.
 
Beck said:
T So when you set the repro level you set it so the VU meters are 2 dB down from zero.
Click to expand...

OK, makes sense. but if I do this, then it won't be seeing +4dBm at the line output playing back a test tone. but thats OK, because once I compensate, if i DO play a tone at thats actually at 320 nwb/m it will read zero on the VU which will equal +4 dBm at the line output, right?

I don't even remember where the VUs were when I started, I think this guy had this thing set up for hotter tape.

as for damaged test tape, all I hope for is that it gets me close. I left it all night in the food dehydrator. it played much better last nite compared to the nite before, and it was only in there for two hours or so. I'm thinking eight more hours should have about done it.
 
having a weird problem with track #2... On all the other channels, I got the same VU reading monitoring test tones from input and from the repro head. so what is going in is pretty much the same as what is coming out. There are some weird bumps down low, 63Hz is up around 2dB and 125 is down about 1dB, but I checked the frequency curves for different decks here: http://www.endino.com/graphs/ and it looks like that is just the way the deck is...

Anyway, back to track #2. Can't get that one line. no matter what I do, its just playing back way hot, and there is some audible distortion or harmonics or something. Either this channel is just WAY out of wack, or something is wrong with it. I think the SRL and the input trim pots need adjusted or something...

Tomorrow I'm going to try to bias.
 
If you set the line level and calibrated the VU meters first, all you have to worry about is what the meters indicate. Some calibration procedures will say the test tape needs to show 0VU at a certain voltage from the output, but it’s redundant if you’ve already calibrated the meters. It’s really a double check in case you missed something in a previous step.

The only thing you can do if the meter and output voltage don’t agree while playing the test tape is to go back to the previous line level/meter calibration steps using the 1kHz test tone from the oscillator.

You’ll be able to verify this later after the record calibration step using the blank SM911. When you record a 1kHz tone @ 0VU it will play back @ 0VU and your output will read 1.23 volts for +4 dBm line level.

If the instructions for the 8-track are anything like the MX5050 half-track, it is a bit confusing. The order is screwy. It’s easiest to follow the order below once mechanical adjustments are made:

1. Line level input/output matching, including zeroing meters.
2. Reproduce level adjustment - playing 1kHz tone on test tape, reference VU meters
3. Reproduce equalization
4. Record bias level
5. Record level using SM911 or tape you'll be using most
6. Record equalization

Your track-2 problem could be bias related or a relay problem, which is fairly common with the MX5050... or something else. It's not likely the head if all other tracks/channels seem ok.

:)
 
Beck said:
The only thing you can do if the meter and output voltage don’t agree while playing the test tape is to go back to the previous line level/meter calibration steps using the 1kHz test tone from the oscillator.
Click to expand...

no, everything seemed alright *playing* the test tape. the bass was a little funky, but I am assuming that is the head bump(?). I was able to measure the output on the XLR outs, and they were pretty close to 1.23 volts at 1KHz, so I think I am alright.


You’ll be able to verify this later after the record calibration step using the blank SM911. When you record a 1kHz tone @ 0VU it will play back @ 0VU and your output will read 1.23 volts for +4 dBm line level.
Click to expand...

right. did this last nite, thats where I ran into the problem on track #2. got all the other channels even. didn't verify that the output at 1.23 volts, but assumed its good. I'll test tonite to make sure.

If the instructions for the 8-track are anything like the MX5050 half-track, it is a bit confusing. The order is screwy. It’s easiest to follow the order below once mechanical adjustments are made:

1. Line level input/output matching, including zeroing meters.
2. Reproduce level adjustment - playing 1kHz tone on test tape, reference VU meters
3. Reproduce equalization
4. Record bias level
5. Record level using SM911 or tape you'll be using most
6. Record equalization
Click to expand...

yep, the manual was very confusing. I'll try your order tonite, picking up with bias adjustment. I skipped it last nite, so I guess I'll have to double check the record level/EQ after I get the bias set.

Your track-2 problem could be bias related or a relay problem, which is fairly common with the MX5050... or something else. It's not likely the head if all other tracks/channels seem ok.
Click to expand...

didn't think it was the head, definitely seemed like it was strictly related to the recording circuit. any ideas for a fix? a relay huh? it might be useable as-is since I can get it sorta close. I guess I could use it for a tom track or something not really "essential". this weird distortion might even be kinda cool...

thanks again
 
Do the bias adjustment first and see if track 2 is better... then go from there. It could be a number of things but relays are always suspect with Otari and they cause problems you wouldn't intuitively associate with a bad relay.

So on the other tracks you had about 1.23 volts at the output running the test tape with the VU at -2?
 
are the relays the little line input and line output level switches? if so, yep, I think they are starting to go bad. are they hard to fix? do I have to replace the entire channel card?

ch2 is so weird. when I play a tone on input at -10, it plays back at like 0.
 
did a little research on the relay issue on the MX5050s... yeah, this sounds like it might be a problem on this deck. besides #2, some of the other channels have some weird stuff going on too, little intermittent problems. I can hear some weird upper harmonic distortion tones fading in and out while I monitor playback of a test tone off the repro head, almost like a scratchy pot sound. still not sure if its causing the channel#2 weirdness though... but the machine sat unused for a long time, and I think it has a dust contamination problem.

so can I clean these relays or do i have to replace them? do I need to solder them? I gathered that the "cheap" relays were soldered to the channel cards, but I'm guessing this isn't the case with the Otari? is it worth trying to get at them with some Deoxit? Guess I gotta pull the channel cards to get at this eh??
 
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