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Old 28th August 2005, 10:59 AM   #11
ash_dac is offline ash_dac  United Kingdom
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Hi,


I have now studied the service manual (which is top notch btw).

So far I have changed the dac to TDA1541 s1, and I am pleased with improvement.

Just a few questions about what's in the service manual:-

-TDA1541a has the -5V supply set at -6.2V . The manual does say that the input board and dac need the -6.2V supply. Maybe for convenience use -6.2V ?



Kind regards,


Ashley.
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Old 16th September 2005, 03:38 AM   #12
Ruach is offline Ruach  Singapore
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Hi guys,

Is there any way to reduce the effects of the EMI of the Arcam Black Box?

I am not sure that -6.2V is good for the TDA1541A chip in the long run. Datasheet stated that max voltage is -5.5V.

Ash_dac - can you post a picture of the innards of the black box? Thanks.
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Old 16th September 2005, 05:50 AM   #13
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Change the -6.2 V tot -5 V. Arcam and Cambridge ( CD2, CD3 ) used to run the chips on -6.2 V. That's the reason that they sometimes fail .....
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Old 16th September 2005, 11:01 AM   #14
guido is offline guido  Netherlands
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What is the actual value for the -15 supply with this player (before you do anything)
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Old 16th September 2005, 11:34 AM   #15
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If I recall correctly the Black Box 1 ( not a cdplayer ) has -15 V for the -15 V line.
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Old 16th September 2005, 06:25 PM   #16
guido is offline guido  Netherlands
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Just asking because current generator supply is between -15 and -5. So 10 volts. If the -15 would be -16.2 to get that 10V, decreasing the -6.2 to -5 would make the 10V 11.6. Which might just be too much again. But n.a. here.

Wonder if decreasing the -6.2 to -5 means a higher current out = louder output
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Old 17th September 2005, 08:11 AM   #17
ash_dac is offline ash_dac  United Kingdom
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Hi,


Many thanks for the replies.

"The DAC requires 3 supplies to operate correctly, +5V,-6V,-15V" (Black Box Service 1 & 2 D/A Convertor Service Manual, 1991)

The -15V supply is supplied by a 7915 regulator.

The -6.2V supply also supplies the input board. If i'm reading the service manual correctly it's just supplies the NE529 voltage comparator (+5V, and - 6.2V).

In terms of altering the lm337 for -5V supply I used the formula from the datasheet , and calculated that I need to change the R2 resistor to 360. Currently R1=120 ohm, and R2=470 ohm.

Why run at -6.2V when like Ruach says the datasheet shows a -5.5V max?

In terms of EMI reduction I have no info (I would need to read some books!)

Regards,

Ashley.
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Old 17th September 2005, 11:54 AM   #18
guido is offline guido  Netherlands
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Maybe the comperator needs the -6.2 to work and they did not want to make two supplies. As for the max ratings, maybe the unit started life with the non a version which is -6 (or even -7 according to IEC134).

As for the output current. It is variable in the datasheet:

typical -5 -15 = 10v gives 4 mA so divide 10 by 2500

max -5 and min -15 is -6 and -14 is 8V / 2500 = 3.2
min -5 and max -15 is -4.5 and -16 is 11.5 / 2500 = 4.6

So one should find 3.2 and 4.6 as min and max values.
It actually states 3.4 and 4.6, close enough?

So i still suspect a hight output current if you go for -5.
See what happens.
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Old 17th September 2005, 01:11 PM   #19
ash_dac is offline ash_dac  United Kingdom
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Hi Guido,

So in the black box: -6.2 -15 = 8.8 divide by 2500 = 3.52ma

So lower output current (good) but the voltage -6.2V is quite high for that pin input(bad). Is this correct ?

There is a 1K resistor to ground on the dac output listed in the service manual which is confusing me because it seems way too high for tda1541a. Maybe reading the schematic wrong or an error!



Kind regards,


Ashley.
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Old 17th September 2005, 06:26 PM   #20
ash_dac is offline ash_dac  United Kingdom
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Guido,

Apologies I knew something was wrong after reading the tda1541a datasheet with 25mv voltage compliance!

Not sure how to calculate voltage now with this one:-


Regards,


Ashley.
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