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FM tuner for Jitter analysis

Posted 29th March 2013 at 03:34 PM by 1audio

A few quick notes on using a tuner for digital audio clock jitter analysis (before I forget the details). Someone here (I have forgotten who) suggested an FM tuner for monitoring jitter. After a little research and experimentation I went pretty deep into figuring this out.

First the internal clocks on ADC's and DAC's have strong harmonics into the FM band. Second, FM tuners are very sensitive to modulation to carriers. modulation and jitter are closely related. The other advantage of this is that the jitter/phase noise is multiplied by the ratio of the actual carrier and the harmonic you are looking at. E.g. a 22.5792 MHz clock becomes 90.3168 MHz with the noise amplified by a factor of 4.

This is very simplified but covers the essentials-You need a really low noise FM tuner. Sound good is not an issue. The Yamaha TX-930 and TX-950 are possibly the lowest noise tuners ever made. They can be had for around $100 on eBay. What I did was to take the output directly...
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Old

Red Baron 3.3V I2S attenuator modification

Posted 29th March 2013 at 01:15 PM by dvb projekt

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Red Baron free running DEM oscillator modification

Posted 29th March 2013 at 12:02 PM by dvb projekt

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Personal announcement

Posted 26th March 2013 at 05:24 PM by dvb projekt
Updated 26th March 2013 at 05:27 PM by dvb projekt

Well my friends it is time again to say thanks to all of you, who like and ordered my pcbs.

Because i am no developer of electronic circuits but have the knowledge to design pcbs,
i wanted to give something back to the community.

Since i started with my 1st pcb, the Optical-Volume-Control on 15th October 2009,
a small donation from every sold pcb goes to diyaudio.com

Today i am proud to say that your cumulated donation achieve

$ 3104

Keep on having fun with my pcbs and best regards

Oliver
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Tube-I-zator / TDA1541A recommended modification #2

Posted 24th March 2013 at 02:10 PM by dvb projekt
Updated 24th March 2013 at 02:19 PM by dvb projekt

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Old

I didn't even know this site offered blogs...

Posted 21st March 2013 at 05:28 AM by Midnightmayhem

I did not know that you could do this until just now so bear with me. I intend to make this a main outlet for the cool stuff I build.
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Tube-I-zator / TDA1541A recommended modification

Posted 20th March 2013 at 10:11 PM by dvb projekt
Updated 24th March 2013 at 02:18 PM by dvb projekt (Resistor type added)

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Old

Active elliptic anti-imaging filter

Posted 20th March 2013 at 03:18 AM by abraxalito
Updated 20th March 2013 at 03:30 AM by abraxalito (Added FR)

Passive filters rock for SQ, no doubt about it but I'm still curious how good sounding an active DAC I/V post filter might be. So I've figured out an almost equivalent FR active version of my 7th order LC elliptic filter. This active elliptic has been designed using LTSpice's FilterCad program giving the pole/zero positions, then the Williams handbook of filter design helped me translate those numbers into a working circuit. Its using what Williams calls the VCVS 2nd order section based on a twin-T network to realize the zeroes.

My first attempt at an active elliptic filter was using gyrators but that proved very hard (practically impossible) to get stable with CFB opamps due to their HF gain peaking. VFB opamps I ruled out at the start for inadequate SQ - its not hard to make gyrators stable with them. Hence this approach which promises to work with CFBs though I'd guess I'll probably need to add series Rs between the stages in practice. Nothing built yet but thought I'd...
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Marantz SR2285B Receiver : Phono Stage Model Response

Posted 19th March 2013 at 06:02 AM by rjm
Updated 20th March 2013 at 01:54 AM by rjm

Mid-range 1970's stereo receiver.

I was curious to find out a) what the phono circuit was, and b) how tight the RIAA response might have been.

The answer is "four transistors" and "pretty damn good", respectively.

We are impressed. These Japanese engineers knew a thing or two. I would like to see some of these old circuits resurrected as discrete phono stages with modern components to see just what they are capable of.
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File Type: zip Marantz LTSPICE.zip (1.5 KB, 75 views)
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X-reg voltage stabilizer LTSPICE file

Posted 15th March 2013 at 01:54 AM by rjm
Updated 20th March 2013 at 01:47 AM by rjm

I did up the X-reg circuit in LTSpice.

Results shown below, together with the LTSpice .asc file you can use to play around with this yourself.

First attached image shows FFT for the rectified DC (green), reference voltage (red) and X-reg output (blue) for the designed-for 10 mA output (top) and a more punishing 100 mA (bottom).

Second image shows an LTSpice screengrab for the LT1086 with bypassed adj pin under comparable loading. Input voltage in blue, output in green. This is a reasonable approximation of a "good" IC regulator.

Last image shows a plot of the exported LTSpice FFT data for the X-reg and the LT1086-12V (Cin 1000uF, Cout 100uF) both at nominal currents of 10 mA. The LT1086-12V is a reasonable substitute for a generic LM7812, i.e. a "bad" IC regulator.

A typical op amp will have sufficient PSRR to mop of the residual noise from the bypassed LT1086. The fixed LT1086-12V, on the...
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File Type: zip xreg 01.zip (1.9 KB, 103 views)
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