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Thread: Tascam 312B Project

  1. #101
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    Quote Originally Posted by sweetbeats View Post
    Inject tone at J405 please with everything else hooked up regular (i.e. all your meters connected where they’re supposed to be connected). Do the L-R meters respond appropriately to a 1kHz -10dBV tone injected at J405?
    Sorry about the delay.....No, neither the right or left respond.

    So, I guess that means the meter L/R Meter PCB is the problem? Those meters I think I would only use when mixing down right?

    The reason I'm asking is I'm getting closer to the month of February which I set aside for writing songs (....weird.... I know.....) . I would like to use the 312 for this, but have a ton of things left to do.... (this soldering thing isn't doing much for building up my callouses ). Since I'm mixing to a DAW, I could probably use the DAW meters anyway right? (please let me know if I'm overlooking anything in this...)

    If the L/R meters aren't critical, I'll get on to figuring how to hook this beast up.... and revisit them again in March.....

    as always..... I am EXTREMELY appreciative of your help!!

    Brad
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  2. #102
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    The L-R meters are only as important as you decide they are to you. They monitor whatever you have selected in the meter source select switchrack to the right of the PGM group section (right above the monitor source select switchrack). Sure you can use the DAW meters but be clear that will only tell you if your input level to the DAW or in-the-box gain staging is too hot (I don’t know anything about the meters in your DAW...what or how they monitor). The M-312 L-R meters help you maximize gain at the respective outputs without clipping (effectively burying the noise floor as much as possible) for whatever summing buss the meters are monitoring post-fade and post insert (where applicable). Do you need them to use the M-312 and make some music. Nah. But you’ll want to use your ears...which one should always do anyway...but be sensitive to distortion/clipping as you maximize gain/minimize noise. Ears should come first...meters are a nice way to corroborate what your ears hear.

    I hope that helps. I think you’ll definitely want to have functioning meters at some point, but there’s no reason you can’t run and drive the console without them.

    If you get curious though, with everything hooked up normal, and while injecting tone at J405, with your DMM set to AC volts can you “see” your test tone at U901 pins 3 or 5? U901 is the 8-pin DIP opamp, the 4558 that drives the meter needles with audio. Pins 3 and 5 are the non-inverting inputs to that opamp...J405 goes to the meter amp PCB audio inputs on pins 1 and 3, and then traces take the signal to those opamp inputs via input coupling caps C901 and C902. If you can see your tone at the opamp inputs that is helpful information for where to go next.

    You may also want to verify ground to the meters. Set your DMM to continuity, clip one probe to the shell of any RCA jack, and with the other probe check for continuity on the ground terminal of each meter...each meter has two terminals (we’re ignoring the lamps here okay?)...one terminal of the L meter will trace back to U901 pin 1 (through a diode, resistor and cap), the other terminal should connect to ground; same for the R meter but tracing back to U901 pin 7. Check and make sure each meter has good continuity to ground at its ground terminal; should be a dead short to ground with your meter clipped to the ground plane outside of the meter amp PCB (like to an RCA jack shell like I suggested).

    If you’ve got good ground continuity, and your test signal is making it to the opamp inputs, and you have already verified power is getting to the opamp, that leaves only a couple other things to check before we determine the opamp needs replacing.

  3. #103
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    I hope that helps. I think you’ll definitely want to have functioning meters at some point, but there’s no reason you can’t run and drive the console without them.

    If you get curious though
    You had to go and add that “if you get curious though “ part.......

    I’ll look at it again tomorrow.... actually, the meter pcb’s are real easy to get to while the board is on the desk.....and I’ll need to take a break from soldering RCA connectors onto snakes.....
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  4. #104
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    Alright..... Here we go.......

    If you get curious though, with everything hooked up normal, and while injecting tone at J405, with your DMM set to AC volts can you “see” your test tone at U901 pins 3 or 5? U901 is the 8-pin DIP opamp, the 4558 that drives the meter needles with audio. Pins 3 and 5 are the non-inverting inputs to that opamp...J405 goes to the meter amp PCB audio inputs on pins 1 and 3, and then traces take the signal to those opamp inputs via input coupling caps C901 and C902. If you can see your tone at the opamp inputs that is helpful information for where to go next.
    Yes.... I can see my test tone with voltage on both pins 3 and 5 of U901.

    You may also want to verify ground to the meters. Set your DMM to continuity, clip one probe to the shell of any RCA jack, and with the other probe check for continuity on the ground terminal of each meter...each meter has two terminals (we’re ignoring the lamps here okay?)...one terminal of the L meter will trace back to U901 pin 1 (through a diode, resistor and cap), the other terminal should connect to ground; same for the R meter but tracing back to U901 pin 7. Check and make sure each meter has good continuity to ground at its ground terminal; should be a dead short to ground with your meter clipped to the ground plane outside of the meter amp PCB (like to an RCA jack shell like I suggested).
    There is continuity between the meter ground and the chassis (RCA shell) ground....

    Before I started that, I was doing this.....

    file-jan-12-4-18-34-pm-jpeg

    I learned a couple of lessons here too..... don't use the cheap chinese RCA jacks (either they are way to fragile, or I am not a gentle man....) and get a vice for doing solder work...... Vice grips aren't the answer (.....although one vice grip working as a stand holding the other vice grip working as the vice was better......)

    While working on this though, I got to thinking about routing my buss inserts to the compressor rather than the individual channel inserts. Right now a mono compressor is all I have.... Good idea or not??? (If you covered that in your video..... I apologize.... I'm going to watch that again tonight).

    Thanks,

    Brad
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

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    Am I recalling correctly you verified power to U901? -15V to pin 4 and +15V to pin 8?

    Regarding the Buss inserts, you can use Buss inserts for dynamics processing, but the real questions are:

    1. What is assigned to the Buss, and
    2. What is your goal or purpose in processing those signals?

    Answer those questions and we’ll continue chewing that piece of fat.

    I often just lay a hand tool with rubber-coated handles on the wire to which I’m soldering the plug to hold it in place. Alternatively I have a suction cup base vise with rubber padded jaws to hold small work without damaging it. The jaws of the vise attach to the suction cup base on a ball joint so the vice head can be positioned pretty much any way I want it.

    ALSO...I use these for cable-mount RCA plugs...chuck-type strain relief...really like ‘em:

    Neutrik Rean NYS373-0 RCA Plug Connector Black Shell

  6. #106
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    Am I recalling correctly you verified power to U901? -15V to pin 4 and +15V to pin 8?
    Yes..... I just checked it again to make sure.....

    Thanks for the soldering tips .....and parts reference.... I never seem to learn about the cheap ones....

    Regarding the Buss inserts, you can use Buss inserts for dynamics processing, but the real questions are:

    1. What is assigned to the Buss, and
    2. What is your goal or purpose in processing those signals?

    Answer those questions and we’ll continue chewing that piece of fat.
    I’m going to get started on that in the morning.... I’d like to run a layout by you (and others...) to see if I’m on the right track. I’ll have to get back to you on this.....

    Brad
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  7. #107
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    Regarding the Buss inserts, you can use Buss inserts for dynamics processing, but the real questions are:
    1. What is assigned to the Buss,
    Since I only have a four track, busses 1-4 would be mainly left for the tape return but available for tracking too. Busses 5-8 would be mainly for the monitor mix.
    2. What is your goal or purpose in processing those signals?
    The goal is to use less cabling mainly... I can assign the channel that I’d like to compress to the PGM channel and use that insert
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

  8. #108
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    Meter amp issue:

    At this point, though there is more poking and prodding you can do, if it was me I’d probably be shot-gunning U901 and dropping in a replacement 4558 opamp. You’ve got power to the opamp and signal at its inputs. There are other passive components between its outputs and respective meter inputs, and one of those components could be bad, but for it to be the same for both sides all of the sudden? That suggests to me the opamp has failed.

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  10. #109
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    Quote Originally Posted by bachelorb View Post
    Since I only have a four track, busses 1-4 would be mainly left for the tape return but available for tracking too. Busses 5-8 would be mainly for the monitor mix.

    The goal is to use less cabling mainly... I can assign the channel that I’d like to compress to the PGM channel and use that insert
    Okay. I think I understand what you are trying to accomplish, but a couple pieces need teased out here.

    You refer to “busses 1-4” and “busses 5-8”. I think you’re talking about the Monitor mixer section. Those aren’t busses. A “buss” in terms of audio mixing is a signal pathway upon which multiple other signal pathways (aka channels or other individual inputs) can hop on board and go to the same place. It is a summing pathway. If I’m correct that your references to “busses 1-4” and “busses 5-8” are the Monitor mixer channels, those are channels, not busses.

    The Monitor mixer is like a mini version of the main part of the mixer with the 12 channel strips. Think of the Monitor mixer as 8 mini channel strips. But they are channels, not summing busses. Why? And who cares about the distinction? It’s important. Each Monitor mixer channel has two possible inputs:

    1. An individual tape return (each Monitor mixer channel numerically corresponds to a tape return jack...Monitor mixer channel 1 can source tape return jack 1, channel 2 jack 2, etc.) -OR-
    2. A PGM buss, post-fade and post-insert...monitor mixer channels 1 & 5 can source PGM 1, channels 2 & 6 source PGM 2, etc.

    But it’s an either/or situation...a Monitor mixer channel can source either the tape jack or the post-fade, post-insert PGM group sum. There’s no summing there. The Monitor mixer channels are not busses, they are channels.

    And then on the output side those Monitor mixer channels have how many places they can go? On the M-312 the Monitor mixer outputs can go up to two places (kind of three) simultaneously: an AUX buss (AUX 3 for channels 1-4, and AUX 4 for channels 5-8), and the L-R main stereo buss (and that’s sort of two places...there’s two channels in that summing buss, but it’s a ganged stereo buss so we consider it one place, but you have control over how much in each L or R buss with the PAN control).

    In a live FOH setup you could use the monitor mixer as combination of effect returns via the tape jacks to the house, and monitor feeds for the stage via the AUX busses (leaving the ON switch unlatched so your feed doesn’t go to the L-R buss and the house), and in recording the monitor mixer is also a powerful tool as you are using it...a combo mix engineer monitor matrix for tape returns and tape sends it however you are using the PGM groups.

    Remember, in the big picture, a mixing console is simply a device that takes multiple inputs, and sums them and/or routes them to one or more outputs. As we drill down from the big picture we see the typical mixing console typically has inputs organized into channel strips, and often also has strips for output summing busses. Your M-312 has primary inputs organized into 12 channel strips, then there’s eight more mini channels (the monitor mixer) that have a mix of primary and secondary inputs, and then there are primary summing outputs organized into six strips: the four PGM groups, the L-R main buss. The MONO buss *is* one of the console’s summing busses and it’s there and can’t be ignored, but there’s no direct access to it from any of the primary inputs (except for the L-R SUB IN jacks), so it is otherwise a secondary summing buss...a sum of a sum.

    So back to your question about using a PGM group insert for your dynamics processor, yes you can do that, just keep in mind that’s a summing buss, and if you send multiple signals to that buss and insert the compressor, you can’t separate that back out later. Usually a compressor is used as an insert effect: the effect is applied 100% and there’s no dry signal (although there’s a hybrid approach with parallel compression...topic for another day...Google it). So if you want to compress your kick drum and bass guitar, and you assign them both to PGM 1 and compress, your kick track and bass track are now married...no divorce possible. I don’t know about you but I set my compressor settings very different for those two types of sources. That just wouldn’t work for me. However, If you are only sending one source to that PGM group and are simply wanting to leave the compressor inserted on that group so you can, at will, assign individual sources to that group and compress without having to hop the compressor from input channel insert to input channel insert, and I think this is what you are talking about and wanting to achieve, then absolutely yes. That is a good use of the PGM group with insert...flexible and convenient control surface fingertip management of signal routing and processing without having to plug and unplug.

  11. #110
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    Quote Originally Posted by sweetbeats View Post
    Meter amp issue:

    At this point, though there is more poking and prodding you can do, if it was me I’d probably be shot-gunning U901 and dropping in a replacement 4558 opamp. You’ve got power to the opamp and signal at its inputs. There are other passive components between its outputs and respective meter inputs, and one of those components could be bad, but for it to be the same for both sides all of the sudden? That suggests to me the opamp has failed.
    Thank you!! I'll be ordering a 4558 next week. I think I have the troubleshooting process down with your help here.... This has been a great learning experience.... Sometime in March, I'm going to be getting on to a Tascam 244 that has some issues..... I promise not to bother you with this one unless I get in really deep!!

    Brad
    Brad Bachelor
    "Marrying an old bachelor is like buying second-hand furniture." - Helen Rowland

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