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Old 18th April 2009, 02:35 PM   #1
Gabdx1 is offline Gabdx1  Canada
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Default PCM56K iv resistor value?

Hi, I did my first passive conversion with pcm56k and there is very much audible distortion. It increases with the music volume and decreases when the music is quiet.

I used this setting: I output: 750R i/v
The filter is 18 R in series and 0.1uf in //
There is also a 22uf output cap in case of DC current.

I saw schematics with 1k resistors so I choose 750R , lampizator uses 500R, and some other people use only 50R - 100 R. I might try 375 now.

Peace. Please answer only if you have a pcm56 I output resistor and knows what value is best for output level vs distortion.

For the others I noticed a funny fact: distortion sounds like 5 % - 10 % depending on output level, well with classical its very apparent, piano, midrange etc. BUT when I listen rock or electric guitar or Michel Jackson it's sounding ok disco too.
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Old 18th April 2009, 09:19 PM   #2
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18 ohm + 100 nF ? where did you see that ?

That is more or less the same as if you shunt the Iout directly with 100nF to ground
Can not work.

Analog filter for a single PCM56 per channel, 200 ohm I/V:


Click the image to open in full size.


Or for a 750 ohm I/V:

put 10nF ll to R_I/V.
No series resistor.
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Old 18th April 2009, 11:12 PM   #3
Gabdx1 is offline Gabdx1  Canada
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Quote:
Originally posted by Bernhard
18 ohm + 100 nF ? where did you see that ?

That is more or less the same as if you shunt the Iout directly with 100nF to ground
Can not work.

Hi Bernhard ! Thanks for helping. I have 3 questions concerning your post.

1.
The 18 R + 100nf are to do a first order LP filter... Why it cannot work ???????

This afternoon before I saw your answer I used 375 R for I/v and the distortion was mostly gone.

2.
Do you use the schematic in the picture ?

3. Now my problem is with the BASS, it is cut, what is the possible explanation ??? Is it because the 375 R is too low and cut bass ? I heard that some people say its more bass when the resistor value is higher...
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Old 19th April 2009, 07:10 AM   #4
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Quote:
Originally posted by Gabdx1

Hi Bernhard ! Thanks for helping. I have 3 questions concerning your post.

1.
The 18 R + 100nf are to do a first order LP filter... Why it cannot work ???????

This afternoon before I saw your answer I used 375 R for I/v and the distortion was mostly gone.

2.
Do you use the schematic in the picture ?

3. Now my problem is with the BASS, it is cut, what is the possible explanation ??? Is it because the 375 R is too low and cut bass ? I heard that some people say it�s more bass when the resistor value is higher...
1. 750 ohm ll Z of PCM56 give 455 ohm.
With 18 ohm and 100n you have -15dB @ 20 kHz.
Those values are totally wrong.

2. No, I made that schematic for a forum member, but I use a similar higher order filter.

3. I use 250 ohm per chip and bass is very good.

Are you sure that everything else is ok ?

Did you build a DAC or mod a player ?
Internal opamp disconnected correctly ?
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Old 19th April 2009, 03:06 PM   #5
Gabdx1 is offline Gabdx1  Canada
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Yes, I don't know how to calculate a filter and don't know how to calculate the Z at the output...

I modified a player, I already broke my old Sony by modifying it, and I posted that in another part of forum. This is the dbx5.

Everything is fine, no opamps, no pop or noise.

I try to build a first order LP and set the i/v resistor to good value and I aim for around 1/4 of power of the normal cd player, more is ok.

I think ill try it with 100 R for i/v, but what is the value I should use for the cap and resistor of the filter???

Right now I can't build that complicated filter in picture because I don't have a PCB right now.

Regards
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Old 19th April 2009, 03:27 PM   #6
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You could try 500 ohm for I/V + 13nF parallel.

That should be a good compromise.

Did the player use the internal opamp of the PCM56 ?
All connections removed ?
Pins 9, 10, 10 open / not connected.
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Old 19th April 2009, 07:46 PM   #7
Gabdx1 is offline Gabdx1  Canada
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Yes the player used the internal opamp, I didn't disconnected 9 - 10.

I have a problem :::::::::::::::::::
I tried it on my more sensitive system just with woofer speaker connected: unfortunately there is 3 mV 60Hertz pollution signal at the output of the dac , it is continuous even when the power is off !!!!, I need to disconnect the cd power cord to stop that 60 hertz pollution ...

Thats a huge problem ... Ill try to disconnect pin 9 and 10
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Old 20th April 2009, 12:46 AM   #8
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Quote:
Originally posted by Bernhard

Pins 9, 10, 10 open / not connected.
Sorry, I made a typo:


9, 10, 11 all must be disconnected.

Most important: 9 must be disconnected from 10
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Old 20th April 2009, 12:25 PM   #9
Gabdx1 is offline Gabdx1  Canada
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Ok, I had disconnected pin 11- 13 already

I didn't thought that disconnecting pin 9 - 10 was necessary but I will do it.
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Old 20th April 2009, 06:27 PM   #10
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But you did not disconnect pin 12 ???
Pin 12 is analog ground, pin is 13 Iout.
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