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clock (bck) buffer SAA7220
clock (bck) buffer SAA7220
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Old 3rd July 2007, 02:25 PM   #1
Jaman is offline Jaman  Netherlands
diyAudio Member
Join Date: Nov 2006
Default clock (bck) buffer SAA7220

Cambridge CD3.

Due to a broken SAA7220 the clock (bck) measures 1,4V on a voltmeter.
I think I've shortcircuit the clockline and thereby broken the SAA7220p/b partially.

I don't have a scope.
I want to repare the player and keep the filter.

Can I place an 74HC08 buffer in the clockline?
(filter -> Buffer -> timingboards & dacs)

I'm asking this because the datasheet says: High Level Input Voltage is 3.15V (Vcc is 4,5V ok, 5V)


Will the buffer work?

The SAA7220 in the CD3 has to feed 6 time-registers and 4 Dac's with Clock. A bit to much I think?

Thank you.
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Old 4th July 2007, 10:34 AM   #2
MidiMaze is offline MidiMaze  Netherlands
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Join Date: Jul 2005
Location: Enschede
Isn't it easier to get a donor cd player for the SA7220? Many philps players from marktplaats will do.
Doe iets goed, of doe het niet.
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Old 4th July 2007, 01:34 PM   #3
Jaman is offline Jaman  Netherlands
diyAudio Member
Join Date: Nov 2006
The 7220 is allready a donor. I accidently shortcircuit the clockline.

all the rest seems to work ok; WS, DATA are a nice 2 V.

First thing I want to do is repair it, then modify it some.

I want to know if a 74HC08 can bring the clock back to 2V so the timing boards work again. now the don't trigger, to low clock.

Another option would be to direct clock, /2, it from the Master-clock. Would that be better? What kind of IC should I use 74HC74 to match the propagation delay of the SAA7220? the slowest I guess: 74HCT74 ??? maybe some extra delay with a buffer?
(At the end of the thread: Difficulty with 1/2clock to TDA1541 they're discussing this, only nobody seems to have measered the prop. delay of the 7220, DATA, WS, BCK)

(I've read the 150+ page thread: The ultimate NOS dac using TDA1541A)
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Old 4th July 2007, 02:09 PM   #4
QSerraTico_Tico is offline QSerraTico_Tico  Europe
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I could sell you a used 7220. Contact me by email.
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Old 7th July 2007, 05:33 PM   #5
Jaman is offline Jaman  Netherlands
diyAudio Member
Join Date: Nov 2006
Thank you but I have a NOS (new old stock) spare one for reserve.
I first want to try fixing the player.

I seems that only the clock output of the SAA7220 is not functioning properly. I read that bypassing of the clock is also better, so I would try this.

Only I don't know wich logic to use, Fast or slower? This to meet the propagation delay of the filter, so that the clock is in sync with the DATA and WS. Maybe use a buffer also?

What is the best option, since I rather not want to test something and then change and test again, etc.
I want to install it so that the player works first.

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