spdif input circuit help

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
Elso Kwak

Elso Kwak

Banned
Joined 2001
geocities.com/elsokwak/
300_baud said:
Here's the schematic as promised.. oh yeah i should also add that jocko's circuit is smoother, but more detailed as well when compared to elso's circuit.

Have fun guys ;)

btw, the transformer to get is a newava S22083 transformer, which you can get from digikey
Click to expand...

Hi, Just a minor problem, but I fail to see your circuit terminates the cable with 75 Ohm.
The diodes Jocko keeps complaining about have no sonical impact.
 
M

macboy

Member
Joined 2003
Hi, Just a minor problem, but I fail to see your circuit terminates the cable with 75 Ohm.
Click to expand...
Part of the termination is on the primary side of the transformer, and the rest is on the secondary side. The two 150R resistors give 300R of loading (termination) and this in parallel with the 100R on the primary side gives 75R. Be sure to note the the two logic gates are not really there... this is really a differential output opamp.

(Actually there is a small problem in that the 150R and techinically in parallel with the 1K resistors, for 130R each side, or 260R total. This in parallel with 100R on the primary side gives termination of 72.2R)
 
M

macboy

Member
Joined 2003
If the gain of that op-amp is high enough, the inputs should look like virtual grounds. Haven't built one to confirm the actual value.

And don't you mean it will be 150 ohms in series with 1K divided by the op-amp gain?
Click to expand...
Aha. I had forgotten to switch my brain to differential output mode and made some errors in logic. You are right that if the opamp has high enough gain, then the inputs should become just like virtual grounds and the termination will be accurate. However, it's not a given that this is the case for all frequency components in the S/PDIF signal. The circuit that 300_baud posted doesn't list the opamp used, but it had better have a very high GBP.
 
Jocko Homo

Jocko Homo

RIP
Joined 2002
Yeah, it does.......

Something that National makes, LMH6550 or such. Went to one of their seminars last week, so they get one free plug. AD makes a similar device, should work just as well. The output voltage range of the 2 are a little bit different, but sufficient to drive a '841x RX chip.

Yeah....switching brain modes...........gets harder the older you get.

Jocko
 
3

300_baud

Member
Joined 2004
Another tweak that Jocko recommended to me! For me, it removed the last bit of harshness in my system. I wouldn't say it's 10x better, but there is a slight difference. Besides, it's easy to implement and doesn't cost a whole bunch of money either.

BTW, these three resistors go in front of the zobel network that was shown in jocko's spdif input circuit as shown in a few messages before.

Take care guys,
300_baud
 

Attachments

  • untitled.gif
    untitled.gif
    2.6 KB · Views: 1,255
ble0t

ble0t

Member
Joined 2004
I threw together a layout for this design after finding this thread and I was going to etch when I get the chance. I just wanted to post it and get some feedback to see if anyone saw any glaring mistakes or had any suggestions to improve it. The total size is about 1.25" x 2.25". Thanks!
 

Attachments

  • input.zip
    50 KB · Views: 344
T

Tubist

Member
Joined 2004
I read this with interest and would want to try. However, I do have some questions:

The outputs from the LMH6550 are inverted? If so do I connect pin 4 (Out + ) to the positive input of my SPDIF receiver and pin 5 (Out - ) to the negative input or vice versa?

Thanks in advance :) :)

JS
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom