+4/Bal to -10/Unbal & vice-versa - conversion options...?

[miroslav]

So with my recently acquired MX-80 and my TASCAM M-3500...there's a mismatch in their ref levels.
While the MX-80 can be dialed down, I want to run it at +4/Bal.

OK...I have some Fostex line converters, but only 16 channels worth...I also have the balancing kit for the TASCAM board...but it's only for the 8 group outs and 16 Tape returns...the MX-80 is 24 channels.

Going to the MX-80 is not an issue. I don't even track through the M-3500, so all my outboard pres are +4/Bal along with the majority of my racked comps/EQs. It's coming out of the MX-80 that I'm looking to maintain the +4/Bal or at least have 24 channels of line conversion for going to the M-3500.
Yes...I know the board is designed so you can just pad the preamp inputs (which are Bal)...and use them instead of the -10/Unbal line inpouts...but then I'm running all the tracks through the 3500 preamps on mixdown...which may sound good, but I would like to have the ability to go to the line inputs.
Now I don't see much of an issue with just turning down the Line gain on all the board's channels, and not even bothering with a line level conversion...but, I'm still wanting to find the best-case setup if possible...or is that it?

I know Aphex makes some 8-channel boxes which are the same as their 2-channel +4/-10 conversion boxes (I have one of those). I've seen the ATI 2-channel boxes which are similar to the Aphex.
There's the Ebtech stuff, but I'm not that warm-n-fuzzy about the Ebtech options...and I would then just find another 8-channel Fostex line converter box instead, and that would give me 24 channels of line conversion...though the Fostex boxes, while they can be used, I was told once by the Fostex tech that they weren't really meant to be generic line converters, but were meant for some specific Fostex gear....though I don't quite know what he was trying to say with that remark.

Anway...I was wondering if there were any other line converter options besides what I'm already aware of...and that don't cost some insane prices (the ATI 2-channel boxes list for around $500-$600 new, though can be had for under $100 used).
When I was down at the Sonicraft Lab in NJ a couple of months back to pick up that spare Fostex G-16...I saw that he was using 3-4 of the Aphex 8-channel units, and he said they weren't super-high end, but were quite good and did the job well. I think they sell for about $300 new if I'm not mistaken.

So if anyone knows of other options.......?

 

[RRuskin]

Running the 24 track through the board's mic pre's won't do anything good for the signal. I'd simply go straight from the machine to the line ins. Your biggest worry will be whether or not the console has enough headroom to accept the +4 signal from your 24 track. If it does, no problem. If it doesn't, lower the sync & playback outs at the machine. The machine won't care and the board will breathe a lot easier. BTW - the signal is even cleaner if the machine is brought back into the each board input's "receive" jack.

 

[The Ghost of FM]

Do the Mic pre inputs on the M3500 offer up some kind of flaky frequency response or unacceptable noise or distortion when padded down to line level?

Is the MX-80 putting out a pristine hiss free signal that these things would be noticed?

I believe the answer is no to both of those questions.

So I'd try them first before going some other route which may not be any cleaner or transparent.

Cheers!

 

[miroslav]

Thanks for the suggestions Rick.

Here's the thing...the Receive (I'm assuming you are talking about the Insert Send/Receive)...is in-between the channel EQ and fader, so if I want to use the EQ, that won't work.

Also, the TASCAM manual does state that the Mic inputs can be used for line-level sources up to +4dBm if the PAD is engaged and the MIC TRIM controls are set to minimum. I've heard of folks doing this, but I've never tried it with my board, so I'm not sure how it sounds since it does pass through the preamp section...but apparently it can take the +4dBm nominal level.

AFA turning down the sync/PB level on the MX-80...yeah, that is an option. I think just using the single switch on the Audio Control PCB, let me go from +4dBm to -8dBm on either all Input or all Outputs or both. I also think the reference levels can even be adjusted on the MX-80 to some other values according to the manual (must be just a pot on the PCB).
Yes, this may be the easiest and certainly most inexpensive way to go. I was initially thinking about leaving the MX-80 at +4 because I am not always going to go out to my console with it, as I also will be doing dumps to DAW, and my DAW converters can take +4....so that's why I was looking for line converters for the console hook-up.

I think what was making me pause at just going with the lower output level at the MX-80 was the fact that the snake from the console to the patchbay is 30' long...so I thought keeping the output at the hotter level and fully balanced would be better...???....but I think you're right, and it should be OK.
I may just try it with an SOP of switching the Audio Control PCB output level on the MX-80 to -8dBm when going straight to the console, and back to +4 when going to my A/D converters....though the converters take +4 or -10.

Thanks for kicking the ideas around some, I think that may work out...unless anyone has other suggestions...?

 

[miroslav]

Do the Mic pre inputs on the M3500 offer up some kind of flaky frequency response or unacceptable noise or distortion when padded down to line level?

Is the MX-80 putting out a pristine hiss free signal that these things would be noticed?

I believe the answer is no to both of those questions.

So I'd try them first before going some other route which may not be any cleaner or transparent.

Cheers!

Yes...I do plan on trying out the 3-4 options I already have at my disposal...but I was just thinking ahead in the event I still wanted/needed some kind of level conversion solution besides what I already have.

In kicking these ideas around with you guys...it does help reaffirm/confirm some things. You know, sometimes the answer is right there in front of you...but you end up second-guessing yourself into thinking it needs to be more complicated to be better!

 

[RRuskin]

Do the Mic pre inputs on the M3500 offer up some kind of flaky frequency response or unacceptable noise or distortion when padded down to line level?

Is the MX-80 putting out a pristine hiss free signal that these things would be noticed?

I believe the answer is no to both of those questions.

So I'd try them first before going some other route which may not be any cleaner or transparent.

Cheers!

Frequency response is probably ok. Transient response probably not. That has been the weak point in every TASCAM -10 board ever built. Pushing drums through those TASCAM front ends has always been a less than pleasant experience.

 

[The Ghost of FM]

Yes...I do plan on trying out the 3-4 options I already have at my disposal...but I was just thinking ahead in the event I still wanted/needed some kind of level conversion solution besides what I already have.

In kicking these ideas around with you guys...it does help reaffirm/confirm some things. You know, sometimes the answer is right there in front of you...but you end up second-guessing yourself into thinking it needs to be more complicated to be better!

I used to own the M312B series mixer from TASCAM and used the balanced Mic ins as line level ins for my Yamaha REV500 returns and found them to be very clean and natural sounding. I would hope the higher end M3500 series pres were no worse.

Cheers!

 

[RRuskin]

Thanks for the suggestions Rick.

Here's the thing...the Receive (I'm assuming you are talking about the Insert Send/Receive)...is in-between the channel EQ and fader, so if I want to use the EQ, that won't work.


Also, the TASCAM manual does state that the Mic inputs can be used for line-level sources up to +4dBm if the PAD is engaged and the MIC TRIM controls are set to minimum. I've heard of folks doing this, but I've never tried it with my board, so I'm not sure how it sounds since it does pass through the preamp section...but apparently it can take the +4dBm nominal level.



AFA turning down the sync/PB level on the MX-80...yeah, that is an option. I think just using the single switch on the Audio Control PCB, let me go from +4dBm to -8dBm on either all Input or all Outputs or both. I also think the reference levels can even be adjusted on the MX-80 to some other values according to the manual (must be just a pot on the PCB).
Yes, this may be the easiest and certainly most inexpensive way to go. I was initially thinking about leaving the MX-80 at +4 because I am not always going to go out to my console with it, as I also will be doing dumps to DAW, and my DAW converters can take +4....so that's why I was looking for line converters for the console hook-up.

I think what was making me pause at just going with the lower output level at the MX-80 was the fact that the snake from the console to the patchbay is 30' long...so I thought keeping the output at the hotter level and fully balanced would be better...???....but I think you're right, and it should be OK.
I may just try it with an SOP of switching the Audio Control PCB output level on the MX-80 to -8dBm when going straight to the console, and back to +4 when going to my A/D converters....though the converters take +4 or -10.


Thanks for kicking the ideas around some, I think that may work out...unless anyone has other suggestions...?

The receives on older TASCAM Boards would bring the signal in before the eq, which is why I suggested it. You could mod the inputs to do this if you like the way coming into the receives sounds.

I know using the preamps as line ins can be done but it will degrade the signal. Been there, done that.

+4 is hotter but not necessarily better. If you have good low capacitance wire and you don't have RF, AC, or EMI problems, I would not bother.

 

[briank]

The Ebtech Line Level Shifters work fine, they're basic, well built passive units and do the job fine. I did keep a couple small ones around when I ran an M3700 that I used for some things. I considered them the best option of the bad bunch all around when I ran that rig, not sure your reasons for dismissing them but that's my 2 centavos.

The Tascam rack mount level shifters were/are too expensive to even consider.

Personally I'd be looking for deals on the Ebtech 8 channel units. They turn up used pretty often, sometimes for stellar deals and other times not, just keep an eye out.

 

[sweetbeats]

30' snake raises my antennae.

Rule of thumb is to keep unbalanced runs to 25' or less is it not? 30' probably would be fine depending on your environment. It wouldn't work at my place with the radio station down the street.

My vote is to use the unbalanced tape returns on the board and adjust the output at the machine if necessary. That's what it was designed for. That will be the cleanest, cheapest and most operationally sensible option imo because of the tape return sourcing/routing features on the board.

 

[miroslav]

The Ebtech Line Level Shifters work fine...not sure your reasons for dismissing them but that's my 2 centavos.

I don't think they are "bad" units...but they seem to only have one set of I/O, though they claim that they work in either direction +4 to -10 and -10 to +4.
The Aphex, ATI and even my Fostex units have a double set of I/O...one set for +4 to -10 and another for the other way, plus the Ebtech are passive, and seems like on the pro side (and I don't mean that any using the Ebtech is not )...they all go for the active, servo-balancing line converters....at least from what I've seen.

 

[miroslav]

My vote is to use the unbalanced tape returns on the board and adjust the output at the machine if necessary.

Yeah...though there's only 16 tape returns on the 3500...and I need 24.

I think the 30' snake will be OK...I have pretty clean power, no existing AC noise or grounding issues...and my area is free of any transmissions or high-voltage lines or anything that could be an issue.

I will be trying out the various options...so nothing is definite yet, which is why I was looking for some additional ideas and input from the group.

 

[trancedental]

You can make up some H & / or T Pad attentuators to change interface levels on your equipment, if you can wire up cables it's not much harder just a few resistors & heatshrink needed Uneeda Audio - Build your own attenuator pads or search for H / T pads to find out what resistors you will need, there's calculators online for various levels.

 

[SteveM]

I did not find a huge difference in signal or sound going straight from an Ampex 440 to an M35 compared to using a 4 channel Tascam LA 40. So I guess it all depends on how much head room your mixer has. I'd try without.

 

[RRuskin]

Yeah...though there's only 16 tape returns on the 3500...and I need 24.

I think the 30' snake will be OK...I have pretty clean power, no existing AC noise or grounding issues...and my area is free of any transmissions or high-voltage lines or anything that could be an issue.

I will be trying out the various options...so nothing is definite yet, which is why I was looking for some additional ideas and input from the group.

There is no reason not to use the 16 tape returns for machine tracks 1-16 and use line ins 17-24 for the rest of the machine's outputs. It's probably the most convenient & flexible way to to go.

 

[miroslav]

There is no reason not to use the 16 tape returns for machine tracks 1-16 and use line ins 17-24 for the rest of the machine's outputs. It's probably the most convenient & flexible way to to go.

Mmmm...I'm not seeing the benefit of using the 16 Tape Returns and 8 Line inputs instead of just using all 24 Line inputs...?
I mean, yeah, I can Flip the Tape Returns...but why not just use all Line Inputs and not bother with the combination of the two...?

OK...I can see using the Tape Returns would make sense IF I was tracking through the console and then needed the Tape Returns for Cue/PB...but I don't track through it, so the Line Input is serving the purpose for both tracking Cue....and PB at mixdown. This is the way I've used it for years....and the only time I've used the Tape Returns is when I needed a few more channels at mixdown.

Maybe I'm not understanding your meaning...?

Are you maybe thinking about me using the 16 Tape Returns w/Balancing Kit installed at +4dBm...and the last 8 channels on the Line Inputs at -10...?
Hmmmmmm.....
I don't have the Balancing Kit installed (not a big deal to put it in) mainly because up to now I had no reel need for it, since my 16-track ran at -10, so again, I just always used the Line Inputs, but now with the MX-80, I'm having to reevaluate my options, but lots of good options and food for thought....thanks!

 

[RRuskin]

Mmmm...I'm not seeing the benefit of using the 16 Tape Returns and 8 Line inputs instead of just using all 24 Line inputs...?
I mean, yeah, I can Flip the Tape Returns...but why not just use all Line Inputs and not bother with the combination of the two...?

OK...I can see using the Tape Returns would make sense IF I was tracking through the console and then needed the Tape Returns for Cue/PB...but I don't track through it, so the Line Input is serving the purpose for both tracking Cue....and PB at mixdown. This is the way I've used it for years....and the only time I've used the Tape Returns is when I needed a few more channels at mixdown.

Maybe I'm not understanding your meaning...?

Are you maybe thinking about me using the 16 Tape Returns w/Balancing Kit installed at +4dBm...and the last 8 channels on the Line Inputs at -10...?
Hmmmmmm.....
I don't have the Balancing Kit installed (not a big deal to put it in) mainly because up to now I had no reel need for it, since my 16-track ran at -10, so again, I just always used the Line Inputs, but now with the MX-80, I'm having to reevaluate my options, but lots of good options and food for thought....thanks!

You're making this a bigger deal than it really is. I suggested using the tape returns so you could still have as many line ins available to you for other things should you want or need them. In your position, I would look at the board's block diagram and determine and use the shortest signal path that still gives access to the eq and aux sections.

 

[miroslav]

You're making this a bigger deal than it really is. I suggested using the tape returns so you could still have as many line ins available to you for other things should you want or need them. In your position, I would look at the board's block diagram and determine and use the shortest signal path that still gives access to the eq and aux sections.

Oh...OK....I thought maybe it was some other reason you were suggesting the Tape Ins.

Yup, like I said earlier, sometimes the answer is right there, and it's usually the simplest one...but we start second-guessing ourselves in the hopes of finding a better one.

Thanks again for the suggestions!

 

[miroslav]

So I've been doing some recording with my MX-80, just trying to find the sweet spots...and on the input side, I'm going with the +4 dBm level. All of my outboard preamps (and outboard processing that I might use during tracking) are running at +4 dBm Balanced...so no issues there.

Now, on the output from the MX-80, going to my TASCAM M3500...I am using the consoles Line inputs, which are -10 dBV Unbalanced. OK...the MX-80 was pretty hot with it's +4 dBm output level, so I simply dialed back the Line input trims to a comfortable level.

Tonight I decided to try a different approach, and I simply flipped the output of the MX-80 from High to Low, which took the +4dBm down to -8 dBm (which is basically the same as -10dBV, and what my console Line inputs are).

The tracks I had recorded with the +4 dBm at the inputs played back about the same in both cases --- with MX-80 output set at High +4dBm output and console Line inputs dialed back....or the MX-80 set a Low -8dBm output and the console Line inputs turned up to where they normally are when I run -10dBV signals into them.

OK...so now I'm a bit on the fence which way to go. I guess my biggest concern is if running the MX-80 at +4dBm output is safe (and better or worse) even with the Line inputs trimmed down on the console...or drop down the MX-80 and turn up the Line inputs to their "normal" position.


The Line inputs specs say they can take up to +20dBV, with 25 dB of headroom...so +20dBV is +22.2dBm.
The peak meter on the MX-80 has been calibrated for +12dBm...so I'm still looking at 10dBm of "wiggle" room...and on top of that the Line inputs of the console have an additional 25 dB headroom.
I thinking I should be fine (and better off) letting the MX-80 run at +4dBm output into the Line inputs of the console and just trim them down.
I'm leaning toward this rather than lowering the output on the MX-80 to match the console because my logic tells me that my signal gain structure is better if the Line trims are lower rather than higher where they would normally be for -10 dBV input.

Someone...please slap me now and tell me it's OK to go that way, so I can move on from this.
I just need one confirmation so I can rest easy that I am not hitting the console too hard even though the Line trims are down. I just don't want to stress the console electronics as it is an older board and I don't need any drama with it.

And oh...the 30' length of the MX-80 snake doesn't appear to be a problem with the console unbalancing the signal coming from the deck. I'm not hearing any noise getting into the signal path...but I could/may decide to shorten the snake once I decide which spot the MX-80 will occupy permanently.

(If all that gives you a headache reading it...you know how I feel).

 

[Track Rat]

Your M-3500 only has 16 tape returns? Mine has 24. Oh well. I've been running +4 into the tape returns on mine for years and no problem. I've tried all the inputs as tape returns for the same reasons as you're concerned about and settled on unbalancing the outputs of mu HD24 and going in on the RCAs. Just unbalancing drops tghe level by about 6dB. I don't clip the board and I can use the Line Ins on the M-3500 as AUX returns (24 of them on faders).