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Bob Cordell's Power amplifier book
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Old 22nd October 2019, 02:59 AM   #9721
anatech is offline anatech  Canada
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Bob Cordell's Power amplifier book
Hi Alan,
Oops! You're absolutely right about that. Thanks.

Hi astx,
As for signals up around 350,000Hz, it doesn't take much of a stray capacitance at higher impedance's to reduce the level way down. Were you using a X10 probe when looking at the output, or was is connected directly to the 1 Mohm input? If you were simply directly connected, that level might be a lot higher than you think it is.

-Chris
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Old 22nd October 2019, 05:07 AM   #9722
keantoken is offline keantoken  United States
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On Mouser today I spied new P channel Jfet:

InterFET SMD/SMT P-Channel JFETs JFET | Mouser

Datasheet says June 2019.
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Old 22nd October 2019, 09:22 AM   #9723
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by mjona View Post
I got the third article - in this Kusunoki speculated that "8x oversampling/digital filter can only cut-off frequencies between 22.05kHz and 330kHz. Everything beyond 330kHz is all coming through untouched, meaning the degree is determined by how " the equipment "reacts to the ingredients beyond 330kHz.''

.
It is apparent from the spectrum analyzer that above a certain freq, the 'stuff' comes thru again untouched.


THx-RNMarsh

Last edited by RNMarsh; 22nd October 2019 at 09:26 AM.
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Old 22nd October 2019, 01:00 PM   #9724
astx is offline astx  Austria
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Default DAC output HF filtering

Quote:
Originally Posted by anatech View Post
...
As for signals up around 350,000Hz, it doesn't take much of a stray capacitance at higher impedance's to reduce the level way down. Were you using a X10 probe when looking at the output, or was is connected directly to the 1 Mohm input? If you were simply directly connected, that level might be a lot higher than you think it is.

-Chris
Dear Chris,

the output of the pcm5122 DAC is low ohmic and followed by a simple output filter (470R resistor and 2.2nF). See datasheet excerpt.
A standard oscilloscope probe (200MHz, 1X set) was connected from the output filter RCA side to the 1MOhm input of the spectrum analyzer.
(so the "stray" capacitance of the cables adds to the 2.2nF)
Amplifier input impedance is about 40kOhm. I think we can trust the measured levels.

BR, Toni
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File Type: png pcm5122_output_filter.png (88.0 KB, 310 views)
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Old 22nd October 2019, 05:40 PM   #9725
anatech is offline anatech  Canada
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Hi Toni,
That's a lot better than what I thought it was going to be. Your output impedance is therefore going to be about 500 ohms or so. Not too bad.

Being the careful tech I am, just for yourself, you should measure the output voltage at some of the higher frequencies to prove to yourself that it's flat. I've had some nasty surprises in the past when equipment performs differently than the specs would suggest. It never hurts to actually check and make certain the claims are true.

So, how do you like the sound of that one?

-Chris
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Old 22nd October 2019, 08:33 PM   #9726
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by RNMarsh View Post
It is apparent from the spectrum analyzer that above a certain freq, the 'stuff' comes thru again untouched.


THx-RNMarsh
There was a radical approach to the 'stuff' that appeared in The Audio Amateur 3/94 issue by Kalman Rubinson - "Passive Filters For Digital Audio" using coils for a DAC project.

Due to the cost of a DAC and shielding issues in a CD player this didn't get to fly with me however I have kept all of my vinyl and CD collections and have some interest in getting rid of the 'stuff'.

The approach Kalman adopted was neither for a Butterworth nor a Bessel pattern but something in between.

The graphs in the article represented SPICE simulations with Miller, Renco and Toko coils. The main illustration used Miller 9250 coils and I have shown the form of this in a dummy .asc file

Some references were Analogue Devices Application Note AN-327; Burr-Brown Application AB-026A; Ultra-Analogue Devices Application Note AP-02
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File Type: asc Rubinson DAC analogue filter.asc (1.2 KB, 14 views)
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Old 22nd October 2019, 08:56 PM   #9727
mjona is offline mjona  New Zealand
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The network in my post should feed into a buffer stage. I omitted to save that in the .asc file before posting it.
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Old 22nd October 2019, 09:17 PM   #9728
astx is offline astx  Austria
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Quote:
Originally Posted by anatech View Post
...
So, how do you like the sound of that one?
...
... beside the datasheet values about THD+N I think this combo "raspberry + pcm5122" (e.g. hifiberry, justboom ...) offers an outstanding performance for the low price.
I'm using it as "party machine" where the master volume level is controlled by a rotary switch and the software volume as well as the player can be controlled remote using MPDroid or M.A.L.P. accessing the mpd server on the raspberry. An nginx web server delivers "folder.jpg" files to the 2 different clients.

BR, Toni
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Last edited by astx; 22nd October 2019 at 09:23 PM.
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Old 24th October 2019, 04:41 PM   #9729
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
Doug Self, for one, has measured increases in distortion when HF gets into amp circuitry via power supply route.

Other sims show marked affects.

Just sayin' ...
THx-RNMarsh



And oscillators too.
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Old 24th October 2019, 05:41 PM   #9730
shadders is offline shadders  United Kingdom
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Originally Posted by rsavas View Post
see p370, 16.7 Resistor Distortion
Hi rsavas,
Apologies for the late reply - thanks for pointer. The changes should not be too bad for any input bias currents if i use low value resistors (comparatively), and if both resistors have the same ppm temp coeff, it should be somewhat mitigated.

Regards,
Shadders.
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