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Old 24th February 2008, 08:39 PM   #1
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Default Introduction from Denmark - interested e.g. in Delta-sigma A/D converter design

Hello DIYs’,

What an inspiring forum this diyaudio - so many angles, views, ideas, opportunities - interesting, interesting...

I have been active with DIY audio since I was about 16 years (am 39 today). I typically have been exploring a purist and sort of minimalistic approach to audio, designing and building components with the aim of achieving the best possible sound. My first builds were based on relatively complex designs but in the later years I have pursued designs based on optimizing simple circuitry with selected components & very stable power-supplies (often based on batteries). In my experience the balance of the sound imprints contributed by the individual components in a design and a benign noise profile of the powersupply makes for maybe 50% of the resulting sound. Also it seems to me that all circuitry have an imprint on the sound and this imprint cannot really be balanced out by e.g. complementary or balanced designs. My experience/opinion, of course.

In my amplifier designs I do without global feedback and my later designs have been single-ended (including the output stage). They have been wide bandwidth, essentially from DC to about 1 MHz. In my view this has resulted in a sound quality characterised by effortlessness, a natural presence, and audibly quite extended at both ends of the audio spectrum.

Just to give you an impression of where I come from, I can say that I have built/modified e.g.:

- A turntable with airborne platter and battery-powered DC motor with a flywheel for increased sonic stability, transparency, dynamics and firm bass.
- Single-ended, battery powered, very few components, bipolar and mosfet based “integrated amplifiers”. Built on balsa wood sheets for low sonic imprint from the “printed circuit board” (I have tried to attach a picture of one of these amplifiers but it seems not to be there?)
- L’audiophile’s “Le Monstre”, le “Pre-pre” (single-stage common-base topology MC Amplifier), and “Le Kaneda” preamplifier.
- One of the sound-wise very successful modifications I have made, has been to replace resistors in loudspeaker crossovers with very thin wire made from pure gold. These resistors are non-inductive, have no insulation, and low power rating. Not very reliable but the sound, in my opinion, is very airy and it tends to – probably not damp – but somehow not provoke the tweeters’ resonances.
- built output stages for PCM D/A converter. Based on ultra-high bandwidth circuitry and without filtering. Stability obtained by placing ferrite beads on the transistor’s pins – something that also improved the sound.
- modified cd-players. Damping and stabilizing the drives and improving power-supplies.
- Magnestat speakers. Early in the 80’ties DIY magnestat speakers had a surge in Denmark and we built a pair about 2m tall with a bass/midrange membrane cut from aluminum foil and then taped. Some work it was :-)
- Airborne tonearm (didn’t work though).

Although I recognize the qualities of analog reproduction chains, e.g. turntables, I have decided to go digital for convenience.

I have some technical insight, yet I am more like the kind of person who (sometimes) easily grasps general concepts but am not very strong in the actual technical calculations. I tweak designs.

Being here at DIYaudio I hope to connect with other people with complementary skills who are interested in designing a multi-channel - but physically designed as individual channels - delta-sigma A/D converter based on discrete components, a low-order delta-sigma modulator (e.g. second order) with an audibly benign noise-shaping profile, and a 256 or 512* 44,1 kHz sample frequency. Data to be stored in a stand-alone storage unit (i.e. not connected to a PC while recording).

Alternatively an FPGA or the like 24 bit A/D converter, at about 352,8/441 kHz, only with an analog 6 dB filter (I know that there is folding of the audio signal but the music power at e.g. 80 kHz is quite low - see e.g. James Boyk’s research on the music power of ultra-sonic frequencies http://www.cco.caltech.edu/~boyk/spectra/spectra.htm and the article “Inaudible High-Frequency Sounds Affect Brain Activity: Hypersonic Effect by Tsutomu Oohashi and more).

For best possible sound quality – e.g. to be used close to microphones or for high quality recording of records or the like.

Looking forward to meeting you in this forum!

Regards,

Jesper
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Old 25th February 2008, 02:33 PM   #2
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