hooking up otari mx5050 mkiii with tascam m520

IronWine

Member
Hello fellows!
I had the chance to grab the OTARI MX5050 MKIII-4 earlier this week. i paid 500$ for it and got 2 tape reels too, not too bad.
It plays and record well on all tracks. heads feels pretty neat. cant wait to work the first project on it!

I will be glad to get some info from your guys regarding two issues:

1) the otari is known to feature 7.5 and 15 speeds. Tho it felt a bit slow to me. I tried to look up videos of the machine but it's hard to tell.
the guy couldn't tell if it had been modded thru the years. Can someone advice me on a method to check if the machine i got truly operates at 15ips? is it even possible to mod it?

2) I am wishing to hook it up with a TASCAM M512 console. I have come to know from reading here and there about the "pin 3 thing" with the Otari' but also that it is unbalanced in's and out's (attached from the manual). also, it is +4dbm .

One the tascam side:
M520 is pin3 hot - But It is a true differential output with both pin3 and pin2 driven.
The tascam features balanced transformerless +4 or +8 dbm outputs , but tape returns are unbalanced RCA .

Can anyone advice what's the best way for hooking the tape and the mixer?

thanks!
 

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1) thread up a known 2500’ reel of tape. Press PLAY and start a stopwatch at the same time. At 15ips the tape should run out after about 33 minutes and 20 seconds.

2) So, both the Tascam and Otari are pin 3 hot, unless somebody has modified either unit. So that is helpful. The 1/2” 8-track version of your machine has switchable input and output levels. Does yours have that? Does the manual talk about it? What options do you have for cabling? If it was me I’d be soldering up an 8 channel snake using balanced multi conductor cable, RCA plugs on one end (Rean makes some nice affordable chuck-type strain-relief RCA cable-mount plugs) and on the other end channel 1-4 on male XLRs and channel 5-8 on female XLRs. On the RCA end I’d wire the low signal and ground conductors to the outer cinch part of the RCA plug, and the high signal conductor to the pin. On the XLR end I’d just wire high signal to pin 3, low signal to pin 2, and ground to pin 1. I’d set the input and output level switches to the low level setting, and I’d connect the tape machine inputs to PGM group 1-4 RCA outputs, and the tape machine outputs to TAPE IN 1-4 RCA jacks.

If you have a bunch of XLR to XLR cables and you want to just do a quick and dirty test to make sure things are working, you could use PGM groups 1-4, patch their output RCA jacks to BALANCE AMP IN RCA jacks 1-4, and then connect the BALANCE AMP OUT XLR jacks 1-4 to the tape machine inputs 1-4. Then connect the tape machine output jacks 1-4 to 4 mic input jacks. Set the level switches (both input and output) on the tape machine to the high level (+4dBm) position, and make sure you switch the PAD in on each of the mic inputs. This will pad the input level down so you can essentially use the mic input as a +4dBm line input.
 
1) thread up a known 2500’ reel of tape. Press PLAY and start a stopwatch at the same time. At 15ips the tape should run out after about 33 minutes and 20 seconds.

2) So, both the Tascam and Otari are pin 3 hot, unless somebody has modified either unit. So that is helpful. The 1/2” 8-track version of your machine has switchable input and output levels. Does yours have that? Does the manual talk about it? What options do you have for cabling? If it was me I’d be soldering up an 8 channel snake using balanced multi conductor cable, RCA plugs on one end (Rean makes some nice affordable chuck-type strain-relief RCA cable-mount plugs) and on the other end channel 1-4 on male XLRs and channel 5-8 on female XLRs. On the RCA end I’d wire the low signal and ground conductors to the outer cinch part of the RCA plug, and the high signal conductor to the pin. On the XLR end I’d just wire high signal to pin 3, low signal to pin 2, and ground to pin 1. I’d set the input and output level switches to the low level setting, and I’d connect the tape machine inputs to PGM group 1-4 RCA outputs, and the tape machine outputs to TAPE IN 1-4 RCA jacks.

If you have a bunch of XLR to XLR cables and you want to just do a quick and dirty test to make sure things are working, you could use PGM groups 1-4, patch their output RCA jacks to BALANCE AMP IN RCA jacks 1-4, and then connect the BALANCE AMP OUT XLR jacks 1-4 to the tape machine inputs 1-4. Then connect the tape machine output jacks 1-4 to 4 mic input jacks. Set the level switches (both input and output) on the tape machine to the high level (+4dBm) position, and make sure you switch the PAD in on each of the mic inputs. This will pad the input level down so you can essentially use the mic input as a +4dBm line input.



Thanks Sweetbeats for your informal reply!

Regarding the actual cabling - i have a bunch of quality RCA's, XLR's and VAN DAMME wiring 2-conductor cable, so as far as the materials required i have it all. i am more concerned about the right level-matching etc. man, the 1980'! you had to know stuff back then!

About the right hot pin wiring, from what i am learning - going into the the otari it won't matter as it is unbalanced in, going out the otari i will need to wire pin 3 hot to rca signal pin. easy.

You motivated me to look into it deeply - i easily opened up the upper panel on the OTARI ,there i found the adjusting panel. as you can see, and from the manual:
the LINE INPUTS are switchable between "Minimum -6 or -18 dBm,unbalanced 50 kohm"
and the LINE OUTPUTS are switchable between +4dbm or -8dbm .


so if the Tascam offers +4 or +8 outputs, and the OTARI is either -6 or -18 , what is the right combination?

and on the other way same question, knowing that the tape in's on the M512 are -10dbm..?(correct me if i am wrong).
 

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You need to tell me what outputs you are using on the Tascam. That will determine where you set the level switches for the inputs on the Otari. If you have the ability to make up RCA —> XLR cables for your console outputs to tape machine inputs, there is no reason to use the BALANCE AMP section of the console. The only reason to use that BALANCE AMP is if the inputs you are feeding with your console outputs are balanced, and high nominal level (such as +4dBm). The Otari is unbalanced, and has switchable input level sensitivity. So avoid all the extra balancing and level boosting/attenuating circuitry and just use the RCA PGM BUSS output jacks on the Tascam, they are -10dBv nominal level, and set the Otari input level switches to the -18dBm minimum setting.

The TAPE in jacks on the Tascam are not -10dBm, the are -10dBv, but that roughly corresponds to the -8dBm output level setting on the Otari.
 
You need to tell me what outputs you are using on the Tascam. That will determine where you set the level switches for the inputs on the Otari. If you have the ability to make up RCA —> XLR cables for your console outputs to tape machine inputs, there is no reason to use the BALANCE AMP section of the console. The only reason to use that BALANCE AMP is if the inputs you are feeding with your console outputs are balanced, and high nominal level (such as +4dBm). The Otari is unbalanced, and has switchable input level sensitivity. So avoid all the extra balancing and level boosting/attenuating circuitry and just use the RCA PGM BUSS output jacks on the Tascam, they are -10dBv nominal level, and set the Otari input level switches to the -18dBm minimum setting.

The TAPE in jacks on the Tascam are not -10dBm, the are -10dBv, but that roughly corresponds to the -8dBm output level setting on the Otari.

that makes absolute sense. i will go with the rca to xlr snake.
thanks for your time.
 
You bet!

Post back if you have any issues. Otari is saying to tie or “jumper” the pin 2 conductor to ground at the XLR at the tape machine, but I would do that at the console, at the RCA end. Hope that makes sense.
 
You bet!

Post back if you have any issues. Otari is saying to tie or “jumper” the pin 2 conductor to ground at the XLR at the tape machine, but I would do that at the console, at the RCA end. Hope that makes sense.

so at the tascam side - cable sleeve to ground, conductor 2 also to ground ,conductor 1 to signal.
at the otari side - sleeve to ground, conductor 2 not connected , conductor 1 to pin 3.

that's what you mean?

btw and i guess it had to do something with what you are saying - my tascam has no grounding. never had issues with it, but maybe it's time to dig into it.
 
so at the tascam side - cable sleeve to ground, conductor 2 also to ground ,conductor 1 to signal.
at the otari side - sleeve to ground, conductor 2 not connected , conductor 1 to pin 3.

that's what you mean?

btw and i guess it had to do something with what you are saying - my tascam has no grounding. never had issues with it, but maybe it's time to dig into it.

RCA end, just as you wrote above:
Cable sleeve —> RCA plug ground
Conductor 2 —> RCA plug ground
Conductor 1 —> RCA plug pin

XLR end:
Cable sleeve —> XLR pin1
Conductor 2 —> XLR pin2
Conductor 1 —> XLR pin3

What do you mean your Tascam has no grounding? Do you mean the power plug is just a two-prong plug? No ground prong?
 
RCA end, just as you wrote above:
Cable sleeve —> RCA plug ground
Conductor 2 —> RCA plug ground
Conductor 1 —> RCA plug pin

XLR end:
Cable sleeve —> XLR pin1
Conductor 2 —> XLR pin2
Conductor 1 —> XLR pin3

What do you mean your Tascam has no grounding? Do you mean the power plug is just a two-prong plug? No ground prong?

Alright!

Yup. only 2 prongs. i have some outboard gear and cassette multitrack tapes, and also hybrid setup to PC, it's all connected and i never had noise problems..but maybe it's time to do something about it.

does it have to do something with the way i will choose to wire the cables?


I have learned that the best way is to ground only the mixer and keep all the rest "floating", grounded thru the mixer, is it true to your knowledge?
 
The m520 power supply does only have a two prong plug. But the case has a ground similar to turntables.
I have mine grounded to the metal racks as well as to the power box.
 
The m520 power supply does only have a two prong plug. But the case has a ground similar to turntables.
I have mine grounded to the metal racks as well as to the power box.



iv'e got the title wrong.. i am using the m512. it has internal power supply
 
Ok, then you’d have to ground the chassis. :)

All that goes out from the mixer is 2 conductors electricity cable.
Not sure tho if the grounding should be connected to the circuit grounding of the power supply PCB?
Or connecting grounding to the chassis would have same results?
 
All grounds internally should end up at the chassis.

On the m520, yes, the power supply is a separate unit, but still the ground is on the chassis. Just like on older two prong stereo receivers and turntables, there’s always a chassis ground.

So I’m just speculating, and I’m sure if I’m wrong, sweetbeats will let me know I’m full of it,..... but I’m pretty confident of what I’m saying. ;)

Just loosening a screw on the chassis and using a spade lug to attach a ground should do the trick. Quick, easy, and if it cuts your hum you’re golden. If not, your hum is from something else.
 
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Yup. only 2 prongs. i have some outboard gear and cassette multitrack tapes, and also hybrid setup to PC, it's all connected and i never had noise problems..but maybe it's time to do something about it.

I would say in the sense that you’ve never had an issue with noise problems then no don’t start fixing something that isn’t broken. More below.

does it have to do something with the way i will choose to wire the cables?

No it really doesn’t. Even if you find you have “noise problems” (and there are a couple different categories of noise problems...more below), you’re not likely to wire the cables differently, unless you find you are having to make sweeping changes to the grounding of multiple devices to address a problem. That’s the key...I wouldn’t go down the rabbit hole at all unless you are having “noise” issues. Assuming your M-512 is hub if your studio, if you are having noise issues with the cables to/from the tape machine, I would start by disconnecting the wires from pins 1 & 2 of the XLRs at the tape machine. But ONLY if you are have issues you otherwise can’t resolve.

I have learned that the best way is to ground only the mixer and keep all the rest "floating", grounded thru the mixer, is it true to your knowledge?

I can’t generally agree with that methodology. And we need to define what you mean by “ground” the mixer. Do you mean connecting the chassis of the mixer to the building ground (through a 3-prong grounded power cable, and this is also assuming the grounded power outlet actually has the ground conductor wired back to the service panel and the ground buss is actually appropriately bonded to a ground rod that is in...the ground)? If that’s what you mean, understand the 3-prong power cable does not directly *necessarily* have anything to do with your audio signal ground...it *may*, but it depends on the problem present, your equipment specifics, etc.

When we talk about grounding in electronic audio equipment, there two camps to address: the safety ground, and the audio signal 0 volt or “ground” reference (as well as any other systems within a particular piece of gear, like logic circuitry, lamps, etc). The ground prong is a “safety ground.” It is there to protect you in the event there is a failure in the device, building wiring or electrical service involving the neutral leg of the AC power source. Without the safety ground the hot leg of the electrical service is then going to try to resolve this failure through you and any physical continuity you have to physical earth. With a safety ground in place, that becomes the pathway to resolving the neutral leg failure. So the fact your console does not have a 3-prong power cable, just means it does not have a safety ground bonding the chassis to literal earth. So there’s the safety consideration, but also the potential for unwanted noise (60 or 120Hz hum typically) if you have multiple devices with no common earth reference, or in the absence of earth reference no common bonding of each chassis’ ground reference to each other. The best way I know to eradicate this problem is to, if possible, have all devices plug into a single circuit (be on one breaker), and for each device to have its chassis bonded to the ground conductor of that circuit either through a 3-prong plug (and for the ground conductor of that plug to be positively bonded to the device’s chassis as close as possible or to the entry point of the cable into the chassis), or for a device with a 2-prong plug to have its chassis bonded to the building ground (through a separate cable bonded to the device’s chassis and then terminate at building ground...this is preferred), or if that is not possible for the device’s chassis to be bonded to the chassis of another device that *does* have a proper bond to building ground through a 3-prong plug. The goal is for each device to have a path to ground (for safety), and for each device to have only one path to that ground. This avoids loops and differentials that increase the risk of line service hum.

So now that we’ve addressed safety and common chassis earth reference for each device, we have to go next to the complicated part; how each device’s internal ground scheme is designed. If all devices’ ground scheme topology was the same, we’d be done. But there’s no standard. There or some common practices, but if you have multiple devices from multiple manufacturers and multiple eras, you are highly likely to find differences, and/or bad designs. So then if you have problems with noise at this level (usually manifesting as higher than spec noise floor or RF noise induced into the audio path), to fix the problem you have to pull out the schematics and open up each device to find out how they did it and modify things so there is some commonality between all your devices, and possibly fix bad designs. I had to do this with my Soundtracs MX series console I used to have. And guess what? There remains controversy around what is the “right” way or what is the best practice implementation for signal grounding. It is a topic of ongoing debate. My practice is to ensure that the shield/signal ground/“pin1” of each audio input/output jack is bonded to the chassis as close as possible to where the jack is located, that the 0 volt or “ground” reference for each audio power rail is bonded to the chassis as close as possible to the output of the power supply, that all metal parts of the chassis are positively bonded to each other, and that the signal ground plane of each active audio circuit (whether it’s on a PCB or point-to-point wired, or something in between) connects to the chassis at only one point for each circuit or board.

So...

You see...

It is not simple. So I recommend, leaving it alone unless you are having problems.

I was without knowledge in this area when I owned an M-520...but I never had problems either. I had gained knowledge when I had an M-512, but didn’t look closely at any of this. I *have* looked closely at this with my early 80s Tascam prototype console (the Tascam “M-__”), which was a prototype for the M-50/M-500 series, and I’m using a modified PS-520 to power it. Part of the modifications to the power supply include changes to the ground scheme. I also revised the bonding between the power supply chassis and console frame, as well as the bonding of all the supply rail 0 volt references to the console frame. These changes would all likely carry over in some way to the M-520. I’m not sure about the M-512, but some of these issues would be essentially irrelevant to the M-512 since it has an onboard power supply. In my prototype console there are some minor improvements I could make to the individual grounding circuits in the console to maybe improve RF rejection, but it’s not been an issue where I’m living, so I’ve left it alone for now. The Soundtracs MX was a different story, as I was living a block away from the highest power AM radio station in my state at the time, and the Soundtracs ground scheme on all points needed significant help.
 
Wow that's a mighty complicated subject! thanks for all the information sweetbeats. i think i understand must of it but my knowledge of electricity is pretty lacking so i temd to go with the "if it ain't broken don't fix it" mantra.

I might do it just for the safety reasons you have mentioned which are important of course. I live in a shared house, and it's 130 years old! i can confirm that the grounding is proper from the last electrician visit last month tho.
So - basically connecting ground to the chassis and making the cable into a 3-prong cable. can't harm so much innit?


I'm on it as far as the cabling , should be done with the snake in a day or two.
 
Yes that’s correct...you could remove the existing two-wire power cable and replace with a two-wire with ground cable...3-prong plug, solder the hot and neutral up just like the factory two-wire cable was soldered, and then bond the ground conductor up to the chassis as close as you can to where the cable comes into the console. Ideally you would put a spade or screw lug connector on the end of the ground wire, and then use a machine screw and nut to fasten the connector to a bare metal spot on the chassis, and put a star lock washer in between the connector and the chassis for bite.

And I apologize for vomiting grounding all over the thread in my last post but it really is a complex subject, and best to hook things up and see if there is a problem and if there is then systematically working through steps to rectify the problem.
 
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