Digidesign 192 IO "brain dead" analog output circuit

[brianroth]

I hope this is the correct section to post this question...

This one recently bit me in the butt. The audio output circuit in the Digidesign 192 IO analog interface submodule seems to behave like an inexpensive, mid-70's mixing console's "balanced" output stage. There is even a silkscreened "warning" on the module's rear plate that says NOT to ground the "negative" lead of the analog outputs.

To me that implies the output stage is a "brain dead" push-pull stage, with two opamps running 180 degrees out of phase with each other. Sure enough, grounding the "negative" lead results in a 6 dB signal loss compared to running the output into a balanced input. I now wonder if a grounded "negative" will attempt to pump milliamps of (severely distorted) audio current into the ground plane of the studio system, just as did the "brain dead" mixing consoles Of Yore.

In a Perfect World, everything in a studio's patchbay will have balanced inputs, but API hasn't gotten that religion with their 550a and 550b EQ modules. I am certain there are other devices lurking out there with unbalanced input circuits as well.

The much-maligned MCI desks and recorders had "cross-coupled" transformerless stages that avoided this problem back in the 1970's, yet the "modern" Digidesign 192 IO boxes still seem to use a discredited analog output circuit design! That's a nasty thing to discover after paying all the money to Avid.

So, what to do?? Install 32 Jensen transformers in an add-on box to handle four 192 IO analog units in order to make the system fully bullet-proof??? (Hmmm..assume $75 per Jensen xfmr...that's $2400 just for the iron.)

Bri

[djui5]

There's always this route

http://images.enterthegame.com/q4sit...ns/shotgun.jpg

[brianroth]

LOL! While I detest Avid and Digidesign, the fact of the matter is that they control the HUGE portion of the marketplace. IOW, they can sell an interface with a truly defective output stage, and NO ONE complains. "We all have to be compatible with Avid." Hence, love it or be left out.

In a way, it's as if Avid woke up one morning and decided that 75 Ohm terrminations for their video products all had to be changed to....say... 50 Ohm terminations.

Avid/Digidesign seem to be able to command the entire marketplace with NO fallout when they unilaterally decide to screw everyone.

"But, our studio is compatible" with what is obviously a manufacturer who doesn't even vaguely understand what real-world studios face, and Digi's "fix" is to force the owners to modify their facilities to "comply" with their poor analog electronic designs.

Of course, Avid Cares Not, since everyone SHOULD mix inside the box....I have to assume their analog I/O modules are considered with contempt inside of the Avid World View.

I am reminded of the mindset of one of the vidiots at a local TV station who told me that the stations's audio was merely a NUISANCE he had to deal with versus his "precious" video feeds.

OTOH, another friend says "broadcast video without decent audio is merely a security camera feed from the bank's parking lot."

Bri

[HiRaX]

You should repost this on the Digidesign User Conference to make the admins nervous. Maybe you could get us some answers .

[thethrillfactor]

Originally Posted by brianroth

but API hasn't gotten that religion with their 550a and 550b EQ modules. I am certain there are other devices lurking out there with unbalanced input circuits as well.

This part of the reason the API EQ's out of the console sound like bright "bunk" with digital gear(even worse on inserts on an SSL).

Originally Posted by brianroth

So, what to do?? Install 32 Jensen transformers in an add-on box to handle four 192 IO analog units in order to make the system fully bullet-proof??? (Hmmm..assume $75 per Jensen xfmr...that's $2400 just for the iron.)

Bri

Actually what i've done is bought some original trannies from an API console and put those infront of the EQ's to get the sound closer to the console.

[Tibbon]

Brian,

Would have Digi's design been cheaper to implement? Or just poor design?

Would it be prohibitive to modifiy the outputs, asides from using the transformers?

The best alternatives I can think of... would be to just not use the 192's. Getting the Apogee or Mytek (or whoever else makes compatable interface devices) convertors would be sure cheaper than modifying the 192's with transformers, and then it would be done right!

[crna59]

My 192 is the only piece of equipment I've had to actually start sparking and smoke coming out of it!
I do have to hand it to Digi though. I sent it back and got a new unit in 2 days!

Regards,

[Reptil]

Originally Posted by thethrillfactor

This part of the reason the API EQ's out of the console sound like bright "bunk" with digital gear(even worse on inserts on an SSL).

Actually what i've done is bought some original trannies from an API console and put those infront of the EQ's to get the sound closer to the console.

Thrill, which ones did you use, and how did you connect them?
(facing the same problem)

[idylldon]

Originally Posted by brianroth

So, what to do?? Install 32 Jensen transformers in an add-on box to handle four 192 IO analog units in order to make the system fully bullet-proof??? (Hmmm..assume $75 per Jensen xfmr...that's $2400 just for the iron.)
Bri

I've been considering doing this as well to unbalance the outputs of my recorder (Alesis HD24XR) so it doesn't drop the signal 6dB while going into my unbalanced Neotek desk. The price has stopped me, and I haven't really encountered any issues with it yet, but it just seems "right" to do it this way.

How about Cinemag or Edcor transformers? Cinemags seem to be on the level of Jensen, and Edcor has surely received high praise on the Prodigy DIY forum.

Cheers,
--
Don

[RKrizman]

Originally Posted by brianroth

OTOH, another friend says "broadcast video without decent audio is merely a security camera feed from the bank's parking lot."

Bri

The version I heard was:

Audio without video is radio.
Video without audio is surveillance.

[RKrizman]

Originally Posted by Tibbon

Getting the Apogee or Mytek (or whoever else makes compatable interface devices) convertors would be sure cheaper than modifying the 192's with transformers, and then it would be done right!

Never had a problem with Digi, but my Apogee AD-8000 simply will not play nicely with unbalanced gear.

-R

[djui5]

Originally Posted by brianroth

LOL! While I detest Avid and Digidesign, the fact of the matter is that they control the HUGE portion of the marketplace.
Bri

For commercial studios, they ARE the marketplace

So what happens when you just leave the negative lead un-connected when using unbalanced gear? Silly question, I know. I haven't hooked a lot of unbalanced gear to Pro-Tools interfaces.

[danasti]

Originally Posted by brianroth

The much-maligned MCI desks and recorders had "cross-coupled" transformerless stages that avoided this problem back in the 1970's, yet the "modern" Digidesign 192 IO boxes still seem to use a discredited analog output circuit design! That's a nasty thing to discover after paying all the money to Avid.

Hey Brian,

Thanks for pointing that out. Can you comment on other brands of converters such as Mytek, Apogee, Lavry, Lucid, Radar, Lynx, RME regarding their output and compare them to the Digi 192 I/O... With all the people who run PT here (I'm even moving HD into my home setup now and I'm getting a new converter) I think it would be nice to have the other converters compared on this particular issue you bring up.

I use HD and various converters at work everyday but I'm about to make the largest (studio) financial investment of my life and every time I read something like this it freaks me out completely. I wasn't considering the 192 but obviously I immediately think OH CRAP! WHAT about xxxx converter? Is it outdated junk too?

Thanks!
Dan

[brianroth]

Originally Posted by djui5

For commercial studios, they ARE the marketplace

So what happens when you just leave the negative lead un-connected when using unbalanced gear? Silly question, I know. I haven't hooked a lot of unbalanced gear to Pro-Tools interfaces.

You will lose 6 dB of "headroom". IE, the analog output will clip at a point 6 dB lower than with both output "legs" in use.

I had initially thought of making up some "comedy" patch cables with the ring floating on one end until the 6 dB headroom problem occured to me.

Bri

[djui5]

Originally Posted by brianroth

You will lose 6 dB of "headroom". IE, the analog output will clip at a point 6 dB lower than with both output "legs" in use.

I had initially thought of making up some "comedy" patch cables with the ring floating on one end until the 6 dB headroom problem occured to me.

Bri

Thanks for clarifying that Brian, without making fun of me...hahaha.

That does seem to be a problem for sure.

[Bassmec]

Originally Posted by brianroth

I hope this is the correct section to post this question...

This one recently bit me in the butt. The audio output circuit in the Digidesign 192 IO analog interface submodule seems to behave like an inexpensive, mid-70's mixing console's "balanced" output stage. There is even a silkscreened "warning" on the module's rear plate that says NOT to ground the "negative" lead of the analog outputs.

To me that implies the output stage is a "brain dead" push-pull stage, with two opamps running 180 degrees out of phase with each other. Sure enough, grounding the "negative" lead results in a 6 dB signal loss compared to running the output into a balanced input. I now wonder if a grounded "negative" will attempt to pump milliamps of (severely distorted) audio current into the ground plane of the studio system, just as did the "brain dead" mixing consoles Of Yore.

In a Perfect World, everything in a studio's patchbay will have balanced inputs, but API hasn't gotten that religion with their 550a and 550b EQ modules. I am certain there are other devices lurking out there with unbalanced input circuits as well.

The much-maligned MCI desks and recorders had "cross-coupled" transformerless stages that avoided this problem back in the 1970's, yet the "modern" Digidesign 192 IO boxes still seem to use a discredited analog output circuit design! That's a nasty thing to discover after paying all the money to Avid.

So, what to do?? Install 32 Jensen transformers in an add-on box to handle four 192 IO analog units in order to make the system fully bullet-proof??? (Hmmm..assume $75 per Jensen xfmr...that's $2400 just for the iron.)

Bri

Jensen's are not too bad but in a mix with vintage UTC or Sowter's might make for a wider pallet of color's I think you can use saturation variations in transformers to enhance compressive feel so the outcome might well have a more squishy tape feel. Why not have a big box of transformers. after all it would still be cheaper than 32 channels of Tonelux or neve summing.

[N.J.]

Originally Posted by danasti

Hey Brian,

Thanks for pointing that out. Can you comment on other brands of converters such as Mytek, Apogee, Lavry, Lucid, Radar, Lynx, RME regarding their output and compare them to the Digi 192 I/O...
Thanks!
Dan

Hi Dan,
RADAR's analog converters (Classic, Nyquist, S-Nyquist) all have cross coupled outputs. When you ground one of the outputs the other output increases by 6 dB, simulating the operation of a transformer.

[brianroth]

Originally Posted by idylldon

I've been considering doing this as well to unbalance the outputs of my recorder (Alesis HD24XR) so it doesn't drop the signal 6dB while going into my unbalanced Neotek desk. The price has stopped me, and I haven't really encountered any issues with it yet, but it just seems "right" to do it this way.

How about Cinemag or Edcor transformers? Cinemags seem to be on the level of Jensen, and Edcor has surely received high praise on the Prodigy DIY forum.

Cheers,
--
Don

As a temporary quick fix (the studio is starting a large mixing project next week), I'm stuffing six Edcor XSM xfmrs. in a metal box that will sit behind the API lunchbox at my client's studio. The longer range plan is to concoct 24 or 32 channels of "something" that will sit with the Avid 192's. I may end up doing a transformerless solution with the DRV-134 chips or something silimar.

Too bad THATcorp *still* can't seem to get their "OutSmarts" chip out the door:

http://www.thatcorp.com/1600desc.html

Bri

[brianroth]

Originally Posted by Tibbon

Brian,

Would have Digi's design been cheaper to implement? Or just poor design?

Would it be prohibitive to modifiy the outputs, asides from using the transformers?

The best alternatives I can think of... would be to just not use the 192's. Getting the Apogee or Mytek (or whoever else makes compatable interface devices) convertors would be sure cheaper than modifying the 192's with transformers, and then it would be done right!

I'm guessing it is just a poor/ignorant design from someone who has never set foot in a real working studio.

As mentioned in another post, I'm pondering a transformerless solution using DRV or similar chips.

I'm unsure how much 24 or 32 channels of Apogees or Myteks would cost compared to retrofitting the existing 192's.

Bri

[craigmorris74]

I refuse to buy into the who Digidesign Protools game. I have M-Powered, just so I can pull up outside projects recorded on it and then send it to a program that doesn't kill my creative flow. It's totally not neccessary at this time to have the big shitty digidesign dongle.

Craig

PS-Hey Brian, been trying to get in touch about Urei Modulimter. Give me a PM.

[Tibbon]

Has anyone thought of calling Digi and grilling them on how to fix this problem? They do advertise themselves as being the answer for every studio, and able to integrate into everything.

I'd assume their answer will be to sell all outboard, and all consoles, and buy an ICON instead and mix ITB, but maybe there's a chance that you could get someone real onthe phone that might have a good reason that they did this, and maybe, just maybe they would do somethign about it.

[thethrillfactor]

Originally Posted by Tibbon

Has anyone thought of calling Digi and grilling them on how to fix this problem? They do advertise themselves as being the answer for every studio, and able to integrate into everything.

I'd assume their answer will be to sell all outboard, and all consoles, and buy an ICON instead and mix ITB, but maybe there's a chance that you could get someone real onthe phone that might have a good reason that they did this, and maybe, just maybe they would do somethign about it.

Has anyone thought about calling API and asking them why do they sell a module that they never mention has unbalanced inputs even though on the lunchbox its all TRS and TT jacks?

Also why not include the trannies?

Everyone is ready to jump down Digi's throat but the truth of the matter even when it came to interfacing some of the API modules with an SSL it was always a problem.

I know a couple of SSL guys who chucked there API gear because of this.

[audioez]

Originally Posted by thethrillfactor

I know a couple of SSL guys who chucked there API gear because of this.

now you know a neve guy who has as well.

Although I traded my new production api gear for an HD1 PCIe, 192 with 8 AD and 16DA. Best trade ever!

Kept the original 550A's I just leave them hooked up to a pair of 312's, lot's of iron in there!