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UA 2192 Converter - PROBLEMS!!! Utility Plugins
Old 8th September 2007
  #1
Gear Head
 

UA 2192 Converter - PROBLEMS!!!

Hello,
I'm new to posting on this forum but have read it for a while.
I apologize in advance because I posted this topic in the LAB too but wanted to share my finding & possibly bring attention to a possible problem with the UA 2192 & the gear its hooked to.

If you own one of these you MAY want to check your unit... Read below why.

Here's what I posted on the LAB:
---------------------------------------------------------
I just bought one of the UA 2192 Converters for my studio & it's causing problems with most of my gear that I plug INTO it! (not as much, if at all out of it)

I first noticed the problems with my mixing board (SOUNDTRACS TOPAZ Project 8) Going from the MAIN L/R out INTO the UA 2192:

I noticed - Switches were POPPING in the master section & the audio sounded dirty & constricted!
When I unplug the UA the popping switches SLOWLY dissapear & the sound of the board opens up :shock:

Sounds like caps charging & DC to me... so I got my scope out & tested the XLR input of the UA 2192:

2 VOLTs of DC - measured from GND to pin 2 or 3
50mv of DC from 2 to 3 (+ to -)


WTF... My board don't like that :mad:

How can ANY device without a transformer OUTPUT be happy with 2 VOLTs of DC coming back into it... & is this normal???
What can/should I do about it?

I found this article
Universal Audio 2192 Master Audio Interface

(READ THE PART BELOW IN BOLD)
Quote:
It starts with the use of a newly design analog portion that doesn’t use capacitors or DV-servo circuits as decoupling devices. They found these where causing phase problems that became very noticeable at higher samplerates. The sound would appear to shift up and down the audio spectrum first giving clear highs with a muddy bass and then shifting again to giving a tight bass with a loss in the high end. Capacitors are normally used to block any DC offset that might be present in the signal. The problem is they are basically operating as high-pass filters with a very noticeable phase distortion at low frequencies. The sound produced is missing the presence and detail that should normally be there. It was solved by removing the capacitors and servos and running the preamp in Class A. The preamp section’s op amp was actually designed by UA and biased (a DC current is applied to the input terminal) to eliminate the cross-over distortion that would occur if the circuit was run in bipolar mode (using a Positive and Negative Voltages). The op amp they designed used minimal component stages and only enough ‘negative feedback’ to insure the op amp remained stable. Because there are no DC blocking capacitors or DC servo components used in the 2192 the output of the op amp is biased using a “digital offset calibration scheme”. This allowed the system to maintain its maximum headroom without the caps or the use of digital high pass filters.
Could they have done this on purpose :?:

So much for "UNIVERSAL" audio :?
Old 8th September 2007
  #2
Gear Head
 

Here's a link for anyone interested.

Prodigy Professional :: View topic - UA 2192 Converter - PROBLEMS!!!

it seems I may not be alone.

Is it possible you guys that own a 2192 could measure the DC of your units (input & output) & post the results?

A simple volt meter will work fine.

Also, listen to your console with & without it plugged in to see if YOU hear anything.

Thanks,
Kevin
Old 8th September 2007
  #3
Lives for gear
 
Martin Kantola's Avatar
 

Kevin,

there is a DC voltage of about 2.3 Volts on the input of my 2192 too (pin 2 or 3 to ground). GUessing it would only be possible problem if your console has DC-coupled or unbalanced output, or something not right. Feeding the converter from an output transformer here, so no problem.

Could you try connecting the output of your console to your 2192 through some other device with balanced inputs and outputs in between?

Or try connecting the XLR pins like this instead:

1 -> (open)
2 -> 2
3 -> 3

Martin
Old 8th September 2007
  #4
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Martin Kantola's Avatar
 

Just had a look at the Prodigy thread... so your console output IS unbalanced. In that case try:

cold (sleeve)-> pin 3
hot (tip) -> pin 2

If this doesn't work, you'll probably need capacitors or a transformer...

Martin
Old 8th September 2007
  #5
Lives for gear
 

If I remember correctly the 2192 doens't like unblced inputs/returns. Try floating pin3. I believe that's what I did when I had my Trident.
Old 8th September 2007
  #6
Gear Head
 

Thanks guys!

Quote:
Quote:
- UA 2192 MANUAL -
"For Un-Balanced operation, Pin 3 can be Grounded"
Well this doesn't work for me.

I'll be talking to UA again on Monday to see what they say & will try what you guys said too.

This sucks... the least they could do, for all that money, is tell people BEFORE they buy it & give options to hook it up & work CORRECTLY.
Old 8th September 2007
  #7
Gear Head
 

Quote:
Originally Posted by kellyd View Post
If I remember correctly the 2192 doens't like unblced inputs/returns. Try floating pin3. I believe that's what I did when I had my Trident.
Does that affect the sound "Quality" or performance at all?
Old 8th September 2007
  #8
Lives for gear
 

Sound quality no. Can't remember if you lose 6db because it's one less leg. Easy to check.
Old 9th September 2007
  #9
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Martin Kantola's Avatar
 

Quote:
Originally Posted by KHStudio View Post
Well this doesn't work for me.
Why not? Have you tried it already? It is basically the same as I suggested.

Once again, not trying to defend UA but their converter will work with most pro gear with balanced outputs. If they wanted to add a capacitor to block the DC they could easily, but it would affect performance a little.

Your console and other gear is packed with capacitors, so don't worry too much about that...

What I would try is:

mixer cold (sleeve) -> A/D pin 3
mixer hot (tip) -> capacitor pack -> A/D pin 2

The capacitor pack could be a 10 uF audio grade polypropylene cap in parallell with a 470 uF 16 Volts electrolytic cap (+ pole facing the A/D).

Martin
Old 9th September 2007
  #10
Gear Maniac
 

So, what does this all mean? My 2192 works great for me. Does this mean you need to use balanced cables? I am not a friggin electronics wizard, so clue me in here.
Old 9th September 2007
  #11
Gear Maniac
 

Bump! After reading the other link to the other forum, it sounds like you are the only one with the problem. Where are all these other people you say are having problems?
Old 9th September 2007
  #12
Gear Head
 

Quote:
Originally Posted by Rick Shepherd View Post
Bump! After reading the other link to the other forum, it sounds like you are the only one with the problem. Where are all these other people you say are having problems?
Just because you don't have a problem now doesn't mean you won't... especially when connecting FROM Un-Balanced gear.

You may not find this info useful but I'm SURE others will.

Sorry... I should have said I MIGHT not be alone.
Also, I never said "ALL or a LOT of people".
Old 9th September 2007
  #13
Gear Head
 

Quote:
Originally Posted by Martin Kantola View Post
Why not? Have you tried it already? It is basically the same as I suggested.

Martin
Yes I tried grounding Pins 1 & 3... it doesn't work - my console doesn't like it.

I think we're on a different page here but I do get what you're saying & understand the fix by adding caps.

It's quite possible my board isn't designed to handle it.
You don't see too many pieces of gear doing this... & when they do, THEY add caps for safety & compatibility.
Old 10th September 2007
  #14
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Martin Kantola's Avatar
 

Quote:
Originally Posted by KHStudio View Post
Yes I tried grounding Pins 1 & 3... it doesn't work - my console doesn't like it.
But your CONSOLE does not even have a pin 3!!! How would that affect your console then??? It's unbalanced, isn't it? Only hot and cold (tip and sleeve)? Or are you maybe unning a cable with TRS (tip-ring-sleeve) plug from your console into an XLR at the A/D? In that case, your console might not be unbalanced as you said after all...

Please consult the manual about what it says on your output connection. (couldn't find the info fast enough on the net)

Quote:
I think we're on a different page here but I do get what you're saying & understand the fix by adding caps.

It's quite possible my board isn't designed to handle it.
You don't see too many pieces of gear doing this... & when they do, THEY add caps for safety & compatibility.
Agree it's a rare situation, but you will make it work in the end, we only need to figure out what's what. Luckily it's not really a safety issue.

Martin
Old 10th September 2007
  #15
Gear Guru
 
u b k's Avatar
 

Quote:
Originally Posted by Martin Kantola View Post
Or are you maybe unning a cable with TRS (tip-ring-sleeve) plug from your console into an XLR at the A/D?

that's what i was wondering, whether the plug going into the console is true 2-conductor unbal or if it's trs. i've gotten burned by that once or twice.


gregoire
del
ubk
.
Old 10th September 2007
  #16
Gear Head
 

Quote:
Originally Posted by u b k View Post
that's what i was wondering, whether the plug going into the console is true 2-conductor unbal or if it's trs. i've gotten burned by that once or twice.


gregoire
del
ubk
.
Martin, Thanks for helping man.

My console automatically grounds pin 3 (for the main & group outs)
With a TRS or not ... it's grounded.

I did try a TS, NO change.

Jacob just posted an interesting comment on this topic at the LAB about the 2 volts of DC hitting other devices output caps (-) Negative side being BAD!
Old 10th September 2007
  #17
Gear Maniac
 

KH Studio - it was my impression that pros used balanced I/Os precisely to avoid problems with stray voltages, which are everywhere. You can hardly avoid them. I wouldn't be surprised if you measured all your gear, you'd find DC voltages present. Using a balun would probably solve the problem right away.
Old 10th September 2007
  #18
Gear Head
 

Quote:
Originally Posted by John Brook View Post
KH Studio - it was my impression that pros used balanced I/Os precisely to avoid problems with stray voltages, which are everywhere. You can hardly avoid them. I wouldn't be surprised if you measured all your gear, you'd find DC voltages present. Using a balun would probably solve the problem right away.
Are you sure about that?

Balancing is for Noise... except for trannys - you get the added benefit of floating each device & some added color... & in this case it would stop the DC from reaching the other device. Some trannys, like the steel core ones I'm about to try, can handle some DC to a certain degree but I'm not sure about 2volts... still MAY need a cap... or a gaped tranny.

I did measure other pieces of gear in my studio & none of them had measurable DC coming out of their INPUTs.

2 Volts DC is a LOT... especially when slamming into another devices output CAP in the WRONG direction (-) side of cap.
Old 10th September 2007
  #19
Lives for gear
 
Martin Kantola's Avatar
 

The DC voltages you normally would find are much smaller than 2 Volts.

Since your console grounds pin 3 from the A/D, you can try disconnecting pin 1 at the A/D end as I wrote, but the DC will probably flow some other ground path unfortunately...

If you use a transformer for your problem it won't see any DC from the A/D because you'll connect it between pins 2 and 3 which have the same voltage.

It's an very unlucky combination with a console that allows DC to enter through it's (unbalanced) outputs and an A/D that actually has DC on it's inputs. Use the pair of caps as I suggested earlier in this thread, that will solve your problem for good.

If the 2192 is used with standard, electronic- or transformer-balanced gear I don't think there will be any problems, so just enjoy the good sound. It's DC-coupled for a reason...

Martin
Old 10th September 2007
  #20
Gear Head
 

Quote:
Originally Posted by Martin Kantola View Post
The DC voltages you normally would find are much smaller than 2 Volts.

Since your console grounds pin 3 from the A/D, you can try disconnecting pin 1 at the A/D end as I wrote, but the DC will probably flow some other ground path unfortunately...

If you use a transformer for your problem it won't see any DC from the A/D because you'll connect it between pins 2 and 3 which have the same voltage.

It's an very unlucky combination with a console that allows DC to enter through it's (unbalanced) outputs and an A/D that actually has DC on it's inputs. Use the pair of caps as I suggested earlier in this thread, that will solve your problem for good.

If the 2192 is used with standard, electronic- or transformer-balanced gear I don't think there will be any problems, so just enjoy the good sound. It's DC-coupled for a reason...

Martin
Points taken. Thank you.

I'm hooking up the trannys right now then going to try some caps.

The only thing you didn't comment on is the fact that most gear has polarized caps @ their output with the (-) Negative side facing the jack (or UA 2192 in this case)

Do you not agree that this can cause those caps to FAIL & or sound BAD when they're hit with this kind of DC voltage on the WRONG side?
Old 10th September 2007
  #21
Gear Head
 

One more thing... I did try disconnecting Pin 1 of the UA & it still found a path... no luck there.
Old 11th September 2007
  #22
Lives for gear
 
Martin Kantola's Avatar
 

Quote:
Originally Posted by KHStudio View Post
The only thing you didn't comment on is the fact that most gear has polarized caps @ their output with the (-) Negative side facing the jack (or UA 2192 in this case)

Do you not agree that this can cause those caps to FAIL & or sound BAD when they're hit with this kind of DC voltage on the WRONG side?
Reverse voltage of this magnitude is not good at all, but we also need to remember that in some cases the output caps of gear are there to stop a larger POSITIVE DC voltage, in which case the +2Volts will still be NEGATIVE in comparison or relative terms. Assuming that the caps are oriented negative facing the output...

And what if the output is capacitorless with a DC servo? I wonder...

Guess one needs to know exactly how the output circuitry is designed to know if it might cause problems or not.

Interesting issue, shows that it's good to have a basic understanding of electronics as soon as you start connecting one piece of gear to another.

I will certainly remember this every time I hook up my 2192!

Martin
Old 11th September 2007
  #23
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Martin Kantola's Avatar
 

Quote:
Originally Posted by KHStudio View Post
One more thing... I did try disconnecting Pin 1 of the UA & it still found a path... no luck there.
Yeah, you might have the D/A of the 2192 connected back to your console for monitoring. or then through an SPDIF connection (AES/EBU works without PIN 1), or then the UA has it's safety ground and signal ground tied together... many possibilities.

The more I think about it UA could have designed the unit in the first place so that any offset voltage is much smaller. Might even modify my own unit if I get hold of schematics at some point...

Martin
Old 11th September 2007
  #24
Gear Head
 

Quote:
in which case the +2Volts will still be NEGATIVE in comparison or relative terms. Assuming that the caps are oriented negative facing the output...
How can it "Still be negative"?

It can't be... unless the + side of the caps are Higher than the UA's +2.34 volts DC going into the negative side... which is what I measured.

I have never seen an op-amp put out over 2 volts of DC offset under normal conditions.

I ran a LOT of tests tonite & most are looking good. I also spoke with Dave Derr from EMPIRICAL LABS & Scott Dorsey - both were pretty shocked & felt this could be problematic with certain gear. They both mentioned transformers & coupling caps but in the case of the FATSO... it has a DC coupled output & the DISTRESSOR has caps... (with the + side facing out... so that helps).

The FATSO pulled the 2.3 volts DC down to about 50mv (pin 2 & 3) Dave told me to test for this & said anything under a few hundred mv should be OK... so this looks good for the FATSO.

I also wired up some trannys so I could test - Patching them in between my console & the UA.... then the FATSO & UA.

I have to be honest... they BOTH sounded GOOD!
The tranny added some flavor (in a cool way) but all in all there was no drastic change for the worst either way.
The tranny WAS blocking all DC too... no popping.

So this makes me feel better. With or without the tranny blocking DC to the board DID NOT seem to HURT the MAIN Output & sound quality.

The ONLY problem I'm left with, that still exist is when the UA is plugged into my consoles master out it still distorts the control room & 2 trk returns. When I put the tranny between the console & UA it sounds NORMAL.

This is very strange because I took the advise of SEVERAL people to put some coupling caps in line between my boards output & the UA input... THIS DID NOT WORK! It DID stop the popping, but STILL ruined the sound of the control room. It MUST be getting into something else OR messing with the GROUND of the board.

I tied pin 3 to GND then put caps between the two pin 2's... with the + of the cap facing the UA.

This one stumps me.
Old 11th September 2007
  #25
Gear Head
 

Quote:
Originally Posted by Martin Kantola View Post
Yeah, you might have the D/A of the 2192 connected back to your console for monitoring.

Martin
I do & tried disconnecting it.

Quote:
Originally Posted by Martin Kantola View Post
or then the UA has it's safety ground and signal ground tied together.
Martin
It MUST be... I think it's finding a past thru the EARTH GND.

Quote:
Originally Posted by Martin Kantola View Post

The more I think about it UA could have designed the unit in the first place so that any offset voltage is much smaller. Might even modify my own unit if I get hold of schematics at some point...

Martin
I don't understand what you mean on this one?
Old 11th September 2007
  #26
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Martin Kantola's Avatar
 

Quote:
Originally Posted by KHStudio View Post
How can it "Still be negative"?

It can't be... unless the + side of the caps are Higher than the UA's +2.34 volts DC going into the negative side... which is what I measured.
Exactly!

Quote:
I have never seen an op-amp put out over 2 volts of DC offset under normal conditions.
If it's a device running on a +24V power supply the output (before the output caps) would probably sit at +12 Volts, 10V higher/more positive than 2V...

Quote:
This is very strange because I took the advise of SEVERAL people to put some coupling caps in line between my boards output & the UA input... THIS DID NOT WORK! It DID stop the popping, but STILL ruined the sound of the control room. It MUST be getting into something else OR messing with the GROUND of the board.
What kind and size of caps did you use? If the popping is gone, so is the DC, but the caps can degrade the sound. Maybe you have some HF problems too, transformers usually take care of that as well.

Instead of directly grounding pin 3 of the 2192 you can try to connect it to pin 1 with another (identical) set of caps. Even if the manual says it should work...

Martin
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