External switched capacitor integrator (clear saa7323 datasheet needed) - diyAudio
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Old 7th May 2006, 01:54 PM   #1
ash_dac is offline ash_dac  United Kingdom
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Default External switched capacitor integrator (clear saa7323 datasheet needed)

Hi,

As per suggestions on this forum I have moved the internal integrator after the switched capacitor network off the saa7323 chip (in my QED Digit).

I could not read the datasheet value of the integrating capacitor but I put a 1000pf for testing.

I could hear the music but it was very quiet and the bass passages seemed to cause a crackling sound probably due to the incorrect integrator capcitor value. Certainly if I increase the integrator value the crackling sound changes.

Does anyone have the saa7322_3 datasheet that is readable or should I leave the capacitor out completely ?

http://www.docethifi.com/saa7322-7323.pdf In this version the capacitor value isn't readable!
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Old 7th May 2006, 02:41 PM   #2
Netlist is offline Netlist  Belgium
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Not having a digital head, where should I find that cap in the pdf?
Pin name/number?

/Hugo
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Old 7th May 2006, 04:23 PM   #3
ash_dac is offline ash_dac  United Kingdom
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Default It works.....I actually built something

Quote:
Originally posted by Netlist
Not having a digital head, where should I find that cap in the pdf?
Pin name/number?

/Hugo
Hugo,

It's figure 10 on page page 16.

I have been working at it all afternoon while listening to the end of the Premiership football season.

I managed to get the external circuit working.

1. I had the left and right vref's muddled which was causing some distortion. The vref's are 2.5V.

2. I removed the op amp powersupply completely but left the bypass cap in place. I measured about 1.4V across the op amp +/- inputs.

3. Removed 1000pf caps

soundstage has improved I think.
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Old 7th May 2006, 05:47 PM   #4
Netlist is offline Netlist  Belgium
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Euh...well..I still don't know what cap you are talking about but if you fixed it, that's fine.

/Hugo
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Old 7th May 2006, 06:25 PM   #5
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My datasheet ist'n very clear as well, but could barely see that capacitor parallel to feedback resistor is 86pF and capacitor from inverting input to Vref is 500pF... see image.
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Old 7th May 2006, 07:52 PM   #6
ash_dac is offline ash_dac  United Kingdom
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Quote:
Originally posted by aparatusonitus
My datasheet ist'n very clear as well, but could barely see that capacitor parallel to feedback resistor is 86pF and capacitor from inverting input to Vref is 500pF... see image.
Thank you for this.

I currently don't have the decoupling to vref on the board. I may add it
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Old 7th May 2006, 11:21 PM   #7
ash_dac is offline ash_dac  United Kingdom
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Thumbs up Never do audio work with a hangover.....

Hi,

Just realised that the internal integrator op amps were still connected up!

I've desoldered the connection, and rewired the external op amp vdd pin.

It works (properly) now. If no power is amplied to the external circuit I have no sound so I'm confident the internal integrator has been bi-passed.
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