A/D/A Digital Convertors for 500 Series?

[LunchBoxHero]

The cool thing about the lunchbox format, for me, is the potential to have a totally portable top-shelf tracking system in my groovy lunchbox that I can tote around to friend's houses, other studios, or use on portable gigs.

With the advent of headphone amps (http://www.purpleaudio.com/Product/Cans.html), mixing systems (http://www.alternatesoundings.fr/m2m.html), and other innovative solutions for the format, the reality of a self-contained tracking suite in a lunchbox is becoming more of reality every day... except for A/D/A.

Is anyone aware of any developers pondering any digital convertor options for the 500 series?

Could the XLR's not (theoretically) serve as AES ins/outs? Are there power limitations to the format that would create problems for clocking etc or is it ample enough?

james
lunchboxhero

[sonicdefault]

This is a good idea! I guess apogee showed the first converter aimed at portability with the mini, but with all the cards that have come out, surely this is very do-able as they seem to be compact enough. It would seem to me that heat and noise would be the greatest concern.


-SD

[13rian]

hey heroes -


we're actually working on it right now :)

can't say much more.... yet.....

- b

[LunchBoxHero]

hey heroes -


we're actually working on it right now :)

can't say much more.... yet.....

- b

cool :D

and i received my "lunchbag" - very nice, will be adding it to the database under the "accessory" category, the first of its kind!

[Eisen Audio]

Thinking out loud, the primary issues would be:

a) 5V and/or 12V supplies required for the digital section must be derived the +/-16V power supplies. If just one rail, then you've got an unbalanced load on the PSU. No good! If you hang across the two rails, then you're floating. Where's ground? Does digital world care?

b) How to tie in the digital ground without introducing digital noise to the rest of your rack? Careful PCB layout by skilled engineer.

c) Connectors. Yes, XLRs can give you AES/EBU I/O. On a Purple Audio Sweet Ten rack you could have a stereo A/D in one slot by using XLR IN and XLR OUT 1 (with gender converter) for the stereo analog inputs, and XLR OUT 2 for the AES/EBU out. But what about other connector type and other digital formats? Must put them on the front panel. That could either be convenient (in the case of firewire, s/pdif or toslink out to a laptop or something), or lame.

[Kronos147]

Thinking out loud, the primary issues would be:

a) 5V and/or 12V supplies required for the digital section must be derived the +/-16V power supplies. If just one rail, then you've got an unbalanced load on the PSU. No good! If you hang across the two rails, then you're floating. Where's ground? Does digital world care?


Just thinking out loud as well: there is an emergence of Telefunken modules all over eBay. These pre-amps run at 24v, one legged. I asked a couple of tech guys if it would be possible to rebuild the Telefunken x formers and block into a 500 series frame. The tech guys I spoke with suggested converting from the 48v supply. The math is real even. To go to 12v it would be another even step down. Wouldn't that be a good supply for the converter?

[Eisen Audio]

The tech guys I spoke with suggested converting from the 48v supply. The math is real even.
Even math doesn't matter, because resistors come in many different values. What does matter is how much voltage you have to drop, and how much current is flowing. To drop 24V @ the preamp's current draw (e.g. 60mA? I don't know) will generate a lot of heat and waste! This is a problem.

Furthermore, the VPR spec states no more than 5mA per slot should be drawn from the 48V supply. Why? Because it's the phantom power supply. 5mA is all a condenser mic needs, but isn't nearly enough to do anything else.

What makes more sense is to regulate up from one of the 16V rails (which allows 60mA according to the VPR spec) with a DC-DC converter, or to treat both 16V rails as +32VDC and regulate down. Relative to 48V there is less of a voltage difference between +24VDC and either of the aforementioned, and that is much more desirable than easy math. +24VDC 500 series modules such as Shadow Hills, Great River, and Avedis are (correct me if I'm wrong) doing it this way. The potential problems I described in my last post (unbalanced PSU load, or floating ground reference).

[pan60]

Kronos147 you should start a thread on this.
it might be cool for someone to do as a DIY project and show what was done?

[Dan Kennedy]

The prevention of noise from the DC to DC conversion leaking back into the rack was the major development issue in the MP-500NV. Converters are noisy, no matter which way they go, and as Jens suggested, we take the full 32 and convert it to 24. The outputs are easy to make quiet, the input side isn't usually thought of as much of an issue, but in this case we have to live with our neighbors and not mess in the sand, er, lunchbox.

It can be done, it's just not a slap it in there sort of issue.

[Kronos147]

Kronos147 you should start a thread on this.
it might be cool for someone to do as a DIY project and show what was done?

I spoke to the VSI guys and the 24v rail seems like a viable option, but maybe only for VSI lunchboxes, because the current available is higher than the VPR standards. So, not sure if it would make an appropriate thread on this site because it is looking more "boutique-y" than mainstream 500 series.

And I got an e-mail from Jens at Eisen about the DIY kits I just ordered. Jens reminds me that the Telefunken OpAmp footprint is wrong (as well as the voltage). That does not mean it CAN'T be done. That also does not mean I want to do it on my two new kits.

:o

Also Jens states that the transformer footprint is far different and again I would require customizing.

I spoke to one engineer about the possibility of making daughter boards to mount a Telefunken transformer to convert it to a standard footprint. This might be the best solution. You buy a cheap circuit card (sell for what, $15-25) and mount your Telefunken transformer. Next, plug that into your pre that has a standard footprint output transformer.

The problem? I don't know if there is a standard footprint.

If I look at the API 512, it had a free floating (or wired, whatever) transformer in the original 312 cards, where the 512c has hard mounts for the circuit card. I don't think that is a standard, though. I think the Avedis and the Shadow Hills use the same footprint, but don't quote me on that.

The resource on the Eisen audio website (http://www.eisenaudio.com/diy500/tables/opxfmrs/) shows transformers that will mount to the Eisen circuit card, and they are referred to as "size EI625." Is that the standard? Is that the same as Avedis and Shadow Hills?

It merits more research, as far as I am concerned anyway.

[pan60]

a thought at least.

[tubemooley]

5V and/or 12V supplies required for the digital section must be derived the +/-16V power supplies. If just one rail, then you've got an unbalanced load on the PSU. No good! (((This is not true. Many, many, many electronic systems, audio or not audio, run fine with unbalanced loads.

If you hang across the two rails, then you're floating. Where's ground? Does digital world care? (((Again, untrue. If you connect to one of the rails, you're only floating until you establish a ground. And without a ground, you do not have a power supply. You have a relatively useless voltage potential sitting there. With respect to "Does digital world care?"...... Yes, yes, yes, the digital world does care. Without a solid ground reference, most digital circuits won't operate as expected. They may operate. But not in a way which you want. When mixing analog and digital circuits in the same box, you need to maintain separate analog and digital grounds which only actually connect at one point, usually at the power supply. Or you build completely separate power supplies for the analog and the digital circuitry. DW.)))