Tascam 48 Calibration clarification

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Not sure I’m interpreting this passage right, but the piece about using the pins on the balanced outputs seems to contradict itself.

It says be sure to use either 1 and 2 or 2 and 3 for measurements when using the balanced outputs, but then says when using the unbalanced outputs be sure not to short the circuit and use 1 and 2 or 2 and 3. The unbalanced RCA connections don’t even have 3 “pins” right? The wording has me confused.
 

sweetbeats

Reel deep thoughts...
What page/section of the manual are you referencing? I want to read the section for any context.
 

sweetbeats

Reel deep thoughts...
Is this the same as in your manual?

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It makes sense to me. If it is different then maybe my manual is a revised/corrected version. Read what’s in my manual above and if it is the same as yours or it still doesn’t make sense let me know and we’ll walk through it and get it cleared up.
 
Yep, that's what mine says. I think the only thing that confuses me is the wording here: "As a complimentary amplifier is used for balanced output... ...when using the unbalance outputs for checks and measurement." Their use of "unbalance" there after talking about taking measurements with 3 pins is what I don't get.

While you're here, could I ask you another question? I want to make sure I am maximizing the relationship between my mixer and the 48. My Tascam M208 mixer has a nominal output at the group XLR (unbalanced) outs of 0dBu, while the Tascam 48 has a nominal output of +4dBm at the XLR (balanced) outs (but they specify the XLR connection there is 600 Ohms, and that 0dBm = 0.775v = 0dBu). So assuming I calibrate the VU meters to read 0 VU when each device is outputting its respective nominal level, there will always be a discrepancy between the VU meters on each machine. That is, 0 VU on the mixer will not equal 0 VU on the 48 if I'm understanding this all correctly.

I suppose my hang up is that I want to be able to drive the signals on both devices hot enough to gain some positive benefits, but due to the 48 being calibrated 4dBu hotter than the mixer I'm worried by the time I get suitably hot signals out of the mixer I will find the tape machine is receiving them at much too high a level (past the point of any positive saturation, etc.).

Perhaps this will not be the case and I will find 0VU on my mixer to drive the tape just perfectly. Alternatively, in a pinch I will simply reference the levels on the 48 and hit the tape where I like without worrying about driving the mixer much. I don't have this all set up at the moment, this has just been rattling around in my brain for a few days now.

Thank you as always. I'm very grateful for your help.

Si
 

sweetbeats

Reel deep thoughts...
Yep, that's what mine says. I think the only thing that confuses me is the wording here: "As a complimentary amplifier is used for balanced output... ...when using the unbalance outputs for checks and measurement." Their use of "unbalance" there after talking about taking measurements with 3 pins is what I don't get.



Yeah it’s worded really weird. Here’s what they are trying to tell you...if you are trying to measure the output level at the XLR jacks, you either have to have a meter with a balanced input (not common...only found on more expensive audio test sets and equipment), and in that case if you want the test tone level at the output to equal +4dBm, you adjust the level so your balanced meter reads 1.23V AC RMS. Okay. Fine. But what if you’re like me and most of us and you only have an unbalanced meter with which to measure the output? When you connect your unbalanced meter to the complimentary balance amplifier output (via XLR pins 1 & 2 or pins 1 & 3), you are unbalancing the balance amp, and furthermore you are only measuring one side of the balance amp output. That +4dBm is achieved via signal on two conductors...pins 2 & 3 of the XLR jack. If you’re only measuring one leg of that complimentary pair, then when the output is at +4dBm, your unbalanced meter is going to read 6dB lower. -6dB is a halving of the signal level, so the correct measurement with an unbalanced meter at the XLR output is not 1.23V, but 0.615V (1.23V divided by 2). Does that help? Furthermore, best practice is to “load” the output...IOW to have the output you are measuring connected to an input. How do you do that? ‘Y’ cable. That way you can have the output connected to an input, but also still have access to the output vid the second arm of the ‘Y’.



While you're here, could I ask you another question? I want to make sure I am maximizing the relationship between my mixer and the 48. My Tascam M208 mixer has a nominal output at the group XLR (unbalanced) outs of 0dBu, while the Tascam 48 has a nominal output of +4dBm at the XLR (balanced) outs (but they specify the XLR connection there is 600 Ohms, and that 0dBm = 0.775v = 0dBu). So assuming I calibrate the VU meters to read 0 VU when each device is outputting its respective nominal level, there will always be a discrepancy between the VU meters on each machine. That is, 0 VU on the mixer will not equal 0 VU on the 48 if I'm understanding this all correctly.



How can I say this...don’t get hung up on there being a “mismatch”. Both the 48 and the M-200 series consoles’ internal nominal operating level is -10dBv okay? And understand that by “nominal” we mean some number that is in the middle of a range. 0dBu nominal outputs are typically going to have no problem driving +4dBu nominal inputs and vice versa, and when you are calibrating the meters on either the tape machine or the console, if you think about the instructions, the procedure, the meters are being calibrated to the device’s internal nominal operating level anyway. That’s why, for instance, on the tape machine you are being instructed to calibrate to different voltages depending on which outputs you are referencing (i.e. 0.3V for the unbalanced RCA jacks, 1.23V for the XLRs, or as we discuss above 0.615V if you are using an unbalanced level meter...) So the meters are actually calibrated to a common standard between the two machines, and even if it wasn’t common that wouldn’t matter, because what you really care about is that the meters inform you about the device they’re mounted to. So feel free to calibrate the meters of each device per the instructions for that device, and feel free to drive your tape machine inputs using the 0dBu outs on the console, but honestly why even mess with the balanced I/O? In case you didn’t know, the balance amp section on the 48 branches in and out of the unbalanced I/O, so by using the balanced I/O, unless you actually need to use it (i.e. you are interfacing a console that must interface hi level balanced I/O, which your console does not), or you have long cable runs (like greater than 25-30’) and are actually having issues with environmental noise interference, by using the balanced I/O when you don’t need it you are adding noise and distortion to your signal chain. Also, I suspect it is true for the 48 as well, but my 58 actually has significantly better HF spec when using the unbalanced I/O as compared to the balanced I/O. They included this detail in the manual for the 58. I see they redacted that set of specifications when they wrote the 48 manual.



I suppose my hang up is that I want to be able to drive the signals on both devices hot enough to gain some positive benefits, but due to the 48 being calibrated 4dBu hotter than the mixer I'm worried by the time I get suitably hot signals out of the mixer I will find the tape machine is receiving them at much too high a level (past the point of any positive saturation, etc.).



Refer to my above comments about nominal levels, etc., and to summarize, unless you tell me your mixer and tape machine are 50’ apart, or you live down the street from an AM radio station, if it was me I’d 100% skip the balanced I/O and go for the lower noise, lower distortion and higher bandwidth unbalanced interconnect. You’ll lose nothing in terms of drive and gain in all the above elements as well as simplifying the interconnect. Now here’s the other thing...people seem to fixate on this idea that to get “that tape sound” you have to use super high output tape and bury the meters. No. What you will get on your setup if you do that, depending on how you calibrate your 48 (more below), is likely some degree of line amplifier clipping (which on this type of gear is not typically desired), and little if any actual sought after third order harmonic tape saturation distortion. And furthermore if you are using any dbx noise reduction you’ll freak the crap out of those electronics and cause pumping and tracking errors. Now, I’m completely convinced that there is a whole echelon of tape enthusiasts that believe their line amp clipping dbx pumping artifacts are tape sat. But these are not the droids you’re looking for. If you are actually seeking tape saturation, then just calibrate your machine so the signal hitting the tape is marginally hotter. You don’t have to do this by shoving it down the tape machines inputs from the console outputs. Yes you want to maximize your signal level so it is as far away from the noise floor of your equipment as possible, but not to the point of clipping the console and tape machine line amps. When you set the record and playback levels on the tape machine during calibration, you are adjusting trimmers that set internally how hot the nominal level of signal is that goes to tape. Teac specified this nominal level on a 48 to be 250nWb/m @ 1kHz using “+6” tape. A nanoweber is a measure of magnetic energy. The higher the number, the hotter the nominal signal level. And the “+6” designator simply means the tape formulation will take 6 more dB of signal before eliciting 3% harmonic distortion than the original Ampex standard operating level. That’s right...the higher the number, the harder it is to saturate the tape. It also means you can hit the tape harder without distorting, and that means cleaner signal to tape and more sonic distance from the tape noise floor. See? There are all these things in play with a tape machine and tape formulations. I always advice first to set the machine up as designed, which is, in your case, calibrate to 0VU = 250nWb/m using +6 class tape. Interconnect using the -10dBv I/O on both the console and the tape machine and see what you think. Then experiment during tracking and start pushing the levels to tape during tracking. Rather than 0VU averages shoot for +3. Remember those are averaging meters, so your peaks are well past +3VU. Now if you want more saturation you can either calibrate for a hotter signal to tape during tracking (meaning during your record level calibration try increasing the record level trimmers so that your signal to tape is at +3VU, and then when you do your playback level cal you’ll turn down the playback level trimmers so that the hotter signal on tape is at 0VU level at the output jacks...see the point here is so that you can play around with having signal that is at 0VU averages at the tape machine inputs actually hitting the tape at +3 level, and then when you are playing back it reproduces at 0VU...input = output as far as volume level consistency, but what actually hit the tape was at 355nWb/m vs 250nWb/m. You’ve effectively increased the the level of signal to tape without impacting the headroom reserve if your input and output line amps, and for ease of visual reference everything still lines up to 0VU across the system. The other way to approach this is to set the machine up at 250nWb/m, but use a +3 class tape. In doing so you take the signal level intended for the higher threshold +6 tape and you lower the saturation threshold by using a +3 tape. Or you can combine these two approaches for even more saturation potential without potentially overloading your line amps. It can be a powerful tool to understand you have multiple gain stages in your system with independent trim controls so you can isolate *where* you want to push. And if it is to distort the tape, then you can isolate driving that stage, and/or experiment with different classes of tape.
 
Sweetbeats, you are the man. I did not know that about the 48's balanced amp, and I do not need to use the balanced I/Os but always hear how balanced is cleaner, quieter, etc. I'll take your advice and roll with the unbalanced connections.

I've got a test tape and have things calibrated as specified but hadn't considered throwing those specs (regarding how hot the tape gets recorded to) out the window and experimenting to find what I like best.

Thank you sir.
 

sweetbeats

Reel deep thoughts...
You’re welcome!

Balanced connections are totally the way to go if it’s all you’ve got, or if you have a problem with noise. You bet balanced us generally quieter if there is a noise problem. That’s why it was invented in the first place (in the telephone industry)...it wasn’t because the sound quality was “better”, but it abated the noise interference across 1000s of miles of telephone wire. So use it if you need it, but in your particular case, it’s an add-on fed by the unbalanced outs (or on the input side the balanced ins just feed the unbalanced circuitry), which is often the case. It’s fine...relatively typical...but if you don’t *need* then try skipping it.

And yes that is one of the really great and fun things about tape is the latitude to experiment to suit your goals and taste. You can even go wild and if you have consistent tracking profiles calibrate individual tracks differently...pushing levels internally on tracks that you want lots of saturation and leaving tracks you want for less saturation calibrated for a lower level to tape. You can mess with bias levels too...a whole ‘nuther topic.
 

wkrbee

Member
The 48 uses a separate circuit for the balanced out puts- powered by it's own fused power supply. Don't short 1 and 2 or 1 and three to run unbalanced. You short the output transistor to ground- fuse blows or you take out the transistor.
 
Calibration was always done using the RCA jacks, we only check to see if the XLR connection work other than that they are a waste of time. They are not going to be cleaner as they derive their source signal from the unbalanced circuits in the deck and then add amplification and more circuit to the path. Since when does adding more circuits to a audio path make it cleaner. Yes if you are running a cable 100 feet to a stage that is needed as it operates on the CMR idea but that would be the only case. In a studio where the deck is on the same floor within 20 feet of the console why make things more complicated by using balanced? Also know as I have been checking that different mute relays are used for balanced and unbalanced so one can work and the other not. Each card has these relays and I have changed a lot of relays in the past years.
Additional if you are the preventative type- the Audio cards have the Marcon caps on the power rails. I found some on the schematic called C031 and C032 and these are 100uFd at 16V but they are connected to 20 Volt supplies. These may be the two large caps next to each other over the two relays side. These have been known to short and when the shorted one was found as the other ones were tested they check all over the place resistance wise- to be safe I changed them to better grade caps.
 
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