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Old 3rd May 2003, 10:17 AM   #1
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Default ADC input stage, using transformers instead

Hello everyone,

I'd like to remove the input stage from a crystal semiconductors cs5361 analog to digital converter evaluation board and use transformers instead.

the current/recommended stage is here:
http://www2.freepichosting.com/Images/34475/7.jpg

they used ne5532 opamps on the eval board, and a pathetic clock circuit, just 2 caps and a crystal. eeeeeeew.

I've got some jensen transformers i'd like to use instead for the input stage.

Has anyone got any experience with transformers on the front of ADC's, and or recommendations for this particular one.


Thanks,


Mark
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Old 3rd May 2003, 10:23 AM   #2
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Default the "vcom" is connection to the internal quiscent reference voltage of the adc chip

.
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Old 3rd May 2003, 12:58 PM   #3
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Are you looking for something.....

...like this?

Click the image to open in full size.http://f3.grp.yahoofs.com/v1/QK-zPjG...0UC%208024.jpg
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Old 3rd May 2003, 04:18 PM   #4
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Kuei

Your link address seems to have some problems....
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Old 3rd May 2003, 04:26 PM   #5
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by apassgear
Kuei

Your link address seems to have some problems....
It's fine from here, so no idea why it ain't working for you. Try instead:

http://groups.yahoo.com/group/Thunde...ts/Ultracurve/

The file is called:

The Ironimous Solution for Behringer UC 8024.jpg

Sayonara
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Old 3rd May 2003, 04:57 PM   #6
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Default Re: ADC input stage, using transformers instead

Quote:
Originally posted by Mark Hathaway
I've got some jensen transformers i'd like to use instead for the input stage.
What Jensens do you have, specifically?

se
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Old 3rd May 2003, 05:09 PM   #7
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Quote:
Originally posted by Kuei Yang Wang
The file is called:

The Ironimous Solution for Behringer UC 8024.jpg
In the schematic, you've written "Vin full scale appx +15 dbu (7.07V)."

How did you get +15 dBu out of 7.07 volts? 7.07 volts should be +19.2 dBu by my calculation.

Is 7.07 volts a peak value rather than an RMS value? That would bring it down to about 16.2 dBu.

se
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Old 3rd May 2003, 05:29 PM   #8
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by Steve Eddy


In the schematic, you've written "Vin full scale appx +15 dbu (7.07V)."

How did you get +15 dBu out of 7.07 volts? 7.07 volts should be +19.2 dBu by my calculation.

Is 7.07 volts a peak value rather than an RMS value? That would bring it down to about 16.2 dBu.

se
The +15dbu are of course a type. You are right, it's +19dbu.

It works like this:

Vin for ADC full scale = 4V P-P for the CS5394 which is used in the Behringer EQ.

The transformer is 5:1 stepdown thus for full scale you need 4V * 5 = 20V P-P. Now 20V P-P = 7.07V RMS. And 7.07V RMS is appx. +19dbu.

Sayonara
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Old 3rd May 2003, 05:53 PM   #9
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Quote:
Originally posted by Kuei Yang Wang
The +15dbu are of course a type. You are right, it's +19dbu.
Ah, ok. Thanks.

Wasn't trying to be hypercritical or anything. Been working on a transformer-based power amp and have had dBu on the brain lately so that one just jumped off the screen at me.

Quote:
It works like this:

Vin for ADC full scale = 4V P-P for the CS5394 which is used in the Behringer EQ.

The transformer is 5:1 stepdown thus for full scale you need 4V * 5 = 20V P-P. Now 20V P-P = 7.07V RMS. And 7.07V RMS is appx. +19dbu.
Ah, ok. So the Behringer's being used between a preamp and power amp? Can't think of any source components beside that wacky DI/O that will give you an output on the order of 7 volts.

se
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Old 3rd May 2003, 06:42 PM   #10
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa Steve,

Quote:
Originally posted by Steve Eddy


Ah, ok. So the Behringer's being used between a preamp and power amp? Can't think of any source components beside that wacky DI/O that will give you an output on the order of 7 volts.

Well, it's simply that the "ironimous" approach was meant to be a 1:1 replacement for the Behringers analogue stage. As so much other Pro gear it is set to >+20db for full scale. This improves S/N Ratio and gives good headroom. And it makes sure the ADC's delta-sigma modulator is driven from a really low impedance. With the usual 200...5000 Ohm source impedance of anything preceeding the Digital EQ unit the drive impedance to the ADC is below around 25 Ohm under such conditions (this is important).

BTW, the 5361 the input voltage differs slightly, but I feel a stepdown transformer remains required to avoid impedance issues. Alternatively a very large capacitor is required across the ADC input (2.7nF) which would make the input a very difficult load.

Sayonara
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