Alesis to Tascam M3500 (the +4db/-10db thingy)

Hi Guys,
I posted this on the end of another thread and I'm not sure anyone saw it so I'll have another go!

I'm interfacing an Alesis HD 24 (+4db balanced) with a Tascam M3500.(-10 db unbalanced - I think?) I recently bought the console s/h and have no documention.

As suggested here I have read the Rane notes on balanced/unbalanced etc and I think I understand the concepts therein But I have a couple of questions specific to the M3500. I hope one of you guys experienced with this console may be able to help me.

Firstly - most of the ins/outs are mono 1/4' plugs - except 2 track in, mic ins and stereo outs - I think I read somewhere that these XLRs are not wired pin 2 hot. Can anyone confirm this? BTW when I connect the stereo out 1/4" jacks to my power amp via mono unbalanced leads(guitar leads) I get an earthloop big time. When I connect the XLR stereo outs to my amp with unbalanced mic leads (XLR to mono plug) - the signal is clean???

Is there a viable way to convert 24 channels of in and outs on the console to +4db. One thread mentioned an external box in regard to db's A&H - but is this available or are we talking DIY. I believe I can do the DIY if someone can direct me to a design schematic

I understand (well I think I understand!) that connecting balanced to balanced with an unbalanced lead can attenuate the signal by 6db. But is it possible to incorrectly connect balanced to unbalanced in a way that needlessly attenuates the signal? That is - so far I've used single core shielded cable with a mono plug at the console end to a TRS at the Alesis with the ring and sleeve bridged. With regard to signal level, is there a better way to do this with 2 core cable?

And finally - does it all really matter? It worries me mostly that the 0VU test tone from the console arrives at the Alesis at about -30 dbfs - That same test tone comes back to the console Tape Ins at about +5VU. I can bring it back via the console line ins and trim it - but how do I get it to the alesis hot enough (from the direct outs) with out overdriving the console? Or should there be enough headroom for this not to be a problem?

All of the usual apologies apply for dumb novice questions!!!
Thanks guys
Jeremy H

> a mono plug at the console end to a TRS at the Alesis with the ring and sleeve bridged.

Cut the bridge. Does the signal stay the same?

> 0VU test tone from the console arrives at the Alesis at about -30 dbfs

VU meters do not read transient peaks. The test-tone has no transient peaks; real music does. Music at "zero VU" will have peaks 12dB to 18dB higher than the VU meter zero calibration. Ideally, you trim a zero VU tone for -16 or -18 dB FS. In addition, it sounds like an older TASCAM where zero VU was hi-fi level, -10dBV, which is 12dB lower than +4dBu. Taking 16dB peak allowance and 12dB lower calibration level, 16+12= 28dBfs, about what you see.

The TASCAM will deliver +4dBu, though the mechanical VU meters will slam badly, and high-frequency transients may be smeared (especially on the early Model 8). You could just try re-calibrating the VU meters for 0VU = 1.23V, though it sure would help to have schematics. Or just run the mixer VUs gently tapping +3VU, and accept about 9dB "excess headroom and reduced signal-to-noise".

Where is mixer-noise relative to ADC noise? If you disconnect inputs, work faders and treble controls through their normal range, record, boost, and play back: do you hear analog hiss rise and fall, or do you get constant digital grit? The Alesis ADCs may well have more dynamic range than an old TASCAM, so "under-recording" is not a big problem.

Hi PRR,
thanks very much for the info/advice - I'll try what you have suggested and get back to you.

If I cut the bridge between sleeve and ring on the TRS at the Alesis - do I leave the ring connected or the sleeve? Is it safe to try it either way? Am I right in thinking one may be the Alesis signal ground and the other the Alesis chassis ground?
Thanks again
Jeremy

Hey there,

Building upon the advice PRR gave, the I/O of the HD24 is balanced. As you know this means that the inputs are looking for balanced signals. This also means that the outputs are giving balanced outputs. If the inputs do not receive a balanced input the signal *should* be ~6db lower than usual. However... the output will also be ~6db lower than usual too.

Here's the catch. Ground the inverted input (ring) on the input. if designed like i think it is, then this is a good thing(without getting more technical). Now unground the ring. This is what PRR is wanting you to test.

Don't ground the inverted output(ring), leave it floating. You don't want to have your ICs driving a short in case they aren't designed to deal with that. Then again i don't know how Alesis designed this thing.

:thumb:

Hi Svart,
thanks for the clarification - I see what your getting at. I'll try it and report back
thanks a lot
Jeremy

> do I leave the ring connected or the sleeve? Is it safe to try it either way?

"Safe"? It won't kill you. It may buzzz like a monster bee, so try with your monitors turned down low.

Many "balanced" outputs will deliver a fine unbalanced signal at tip and sleeve. Grounding the ring is correct for old "floating balanced" outputs, and a few active-floated outputs, but on other gear a ground on the Ring is a short on an internal chip. I'm helping another friend with a signal that "goes away" after a minute, and it may be an overheating thing.

The blunt answer is: the -10dBV Tascam stuff was not meant to interface +4dBu gear, because working -10dBV unbalanced is (or was) MUCH cheaper than +4dBu balanced, at no loss of quality in a table-top studio. There were and still are -10/+4 converters: I had a Tascam rack-box with 4 in and 4 out... it wasn't as clean as the mixer. Two of those or four stereo I/O boxes could be costly, or could fall in your lap if you snoop the right closets.

OK: Alesis's dang server finally dribbled-out the HD24 manual. Full-scale input is 6.9VRMS (15dB above +4dBu). Tascam nominal (zero VU) level is 0.316VRMS (2V maximum). A zero-VU tone from the Tascam should read -27dBfs on the Alesis. A music signal running about zero VU should have peaks about -10dBfs on the Alesis.

Alesis claims Signal/Noise is 103dB. 103-27= noise is 76dB below Tascam level. That's just about as good as many of the old popular-price mixers would do, so you may not be hurting much driving the Alesis at Tascam levels. And recall that the Tascam tape recorders, even with dBx noise reduction, didn't really do better than 80dB S/N, yet still made very fine recordings. Now that you got a 103dB S/N recorder, it would be reasonable to work it 10dB below recorder overload level, because you still have 10dB better noise floor.

I just found a picture of the M3500. That's a lot of board. Are you sure it is -10dBV? Tascam clung to -10dBV for a while, but lower chip costs and rising expectations took them to +4dBu interfacing on their bigger boards. In my Googling, I didn't find any mention of interfacing problems. You might just wind it up and see how it sounds, not fret over-much about what the Alesis meters say.

thanks prr - I was't worried about it killing me - I was worried about it killing the Alesis!!
I think you're right and I'll hook in and let my ears be the judge.

I do believe it is -10 db - coz I read it somewhere. And its definately unbalanced - unless its unbalanced +4 db????????

I take your point on the S/N issues - but I was more concerned about using all 24 bits - I believe lower recording levels in the digital world equates to lower resolution as well, not just more noise?

I do realise I am dealing with a fundemental incompatability issue here - Just trying to achieve the optimum for this particular set up.
thanks for your help
Jeremy

Hi Jeremy,

I use almost the same setup M3500 and three Alesis Ai3- AD/DA- Convertors. I connected them this way:
The Alesis - OUTS to the LINE-IN of the mixer. I did'nt need the Line-ins for other things so.. Now I can adjust the Input-Level. Only drawback are: Flip-switch of the mixer doesn't make sense anymore (no problem for me, since I use Cubase for recording and routing). Other drawback is asymmetrical connection. You could also use the MIC-INs with PAD-switch pressed and use it's GAIN-pot for adjustment. Depends on if you need the mixers MIC-amps and how many of them.
I only use outboard pre-amps so I don't have the problems with the -10-out/+4-in.
But there were additional boards available in the old days that made the Line-Ins and the Group-Outs +4dB/symmetrical. LA-something it was called. By looking at the back of the desk you can tell where they should have been installed. they used D-Sub-connectors. Maybe you can get one of these or the schematics.

regards

Chris

Hi Chris,
Thanks for that. I think the add-on was called LA 3500. I've seen them mentioned but i can't find one or a schematic so far.

And you have now explained what the rectangular holes with the plastic covers are for!!

I guess that also means the add-on boards were made by Tascam. I wasn't clear on that. I had thought the LA 3500 was an external adapter made by another company.

You've been a big help. Thanks a lot
Jeremy

Yes,

LA3500 could be. And yes Tscam offered them as an add-on for the M3500 and M3700. To be honest: I have a set of these but haven't installed them yet... Whenever I get hold of a scanner, I will put the PCBs on it and put it online so other people can do copies of it.

I think the schematics are not much different from the symmetrical Master-Out and from - ehhh I think there is a symm. Input as well. Well you can find it in the manual. So if you like you could copy these to get the same boards. You just need eight per board.

Chris

That's great Chris!
I dont have any manuals or schematics - there on back order with Tascam USA.
If you can get to a scanner, I sure would appreciate anything you may be able to email me in this regard.
Specifications or schematics etc - [email protected]
thanks again
Jeremy

Hi Jeremy,

What is the cables lenght between the console and the HDR?

(The Tascam M3500 unbalanced nom.levels (ins and outs) are -10dBV (0.316V), the headroom is +18dBV, the stereo out is balanced, pin "3" is hot, with +4dBm nom. level.)

Regards,
Milan

Thanks for the info moamps!

Yeah the cable length may be an issue. The console is only about 1 metre away from the Alesis, but by the time the cable gets under the desk, across the floor , up the wall and into the back of the recorder - cable length gets to be about 6 metres!

From what I've read - that is enough to degrade an unbalanced signal.

Any suggestions?

thanks,
Jeremy

[quote author="Jeremy H"]
Yeah the cable length may be an issue..... cable length gets to be about 6 metres[/quote]

Hi,

The best solution is using the bal-unbal converters placed close (behind) to the console (like the LA80/81 from Tascam). Also, good results you can get using the transformers (passive converters) placed also close to the console inputs/outputs. Check the Beyer transformer groupbuy here (good and cheap transformers). Anyway, optimum cables setup depends of you needs: do you have patchbays, do you record simultaneoslly all 24 channel from direct outs or you use the group or stereo out to feed the HDR, etc. Like someone already said it's also possible to re-adjust the console to +4dBm nominal level.
I have some the 3500's and the LA80/81 datasheets, I can scan the critical schematic for you.

Regards,
Milan

Hi moamps
good stuff.
yes please for the schematics - [email protected]
wont be using the group outs for tracking - don't record more than about 8 tracks at a time and then individual overdubs - only ever use about 15 to 20 mono tracks - then I use more channels for effects returns etc at mixdown
No patchbay for tracking - maybe insert compression.
use a patchbay on mixdown for reverbs etc

I like the idea of the passive transformers - How do I know what i need for the transformer specs? Do the Beyer ones have respectable sonic quality?

thanks for your help
Jeremy