ADC input stage, using transformers instead

[Mark Hathaway]

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

[Mark Hathaway]

.

[ThorstenL]

...like this?

http://f3.grp.yahoofs.com/v1/QK-zPjG...0UC%208024.jpg

[apassgear]

Kuei

Your link address seems to have some problems....

[ThorstenL]

Koinichiwa,

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

[Steve Eddy]

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

[Steve Eddy]

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

[ThorstenL]

Koinichiwa,

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

[Steve Eddy]

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.

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

[ThorstenL]

Koinichiwa Steve,

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