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Personal announcement

Posted 26th March 2013 at 06:24 PM by dvb projekt
Updated 26th March 2013 at 06:27 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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Old

Tube-I-zator / TDA1541A recommended modification #2

Posted 24th March 2013 at 03:10 PM by dvb projekt
Updated 28th July 2014 at 11:15 AM by dvb projekt

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Old

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

Posted 21st March 2013 at 06:28 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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Old

Tube-I-zator V2.0 / TDA1541A recommended modification

Posted 20th March 2013 at 11:11 PM by dvb projekt
Updated 28th July 2014 at 11:10 AM by dvb projekt (Resistor type added)

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Old

Active elliptic anti-imaging filter

Posted 20th March 2013 at 04:18 AM by abraxalito
Updated 20th March 2013 at 04:30 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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Old

Marantz SR2285B Receiver : Phono Stage Model Response

Posted 19th March 2013 at 07:02 AM by rjm
Updated 20th March 2013 at 02:54 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, 91 views)
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Old

X-reg voltage stabilizer LTSPICE file

Posted 15th March 2013 at 02:54 AM by rjm
Updated 20th March 2013 at 02:47 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, 134 views)
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Old

What is dynamics?

Posted 5th March 2013 at 03:02 AM by abraxalito
Updated 11th March 2013 at 07:35 AM by abraxalito

Fascinating discussion going on about the nature of 'dynamics' over on this thread : http://www.diyaudio.com/forums/multi...nger-what.html

Pano writes (post 1174):

There is a consistency across several decades and cultures that high efficiency speakers sound more dynamic than low efficiency. That's a common subjective assessment, so we might ask "why?"

I'm not going to chip in on that thread because I have bigger fish to fry, but ISTM they're all barking up the wrong tree. That's because the question itself isn't quite posed correctly even though its a great start. Nobody listens to speakers alone, they're always powered by amplifiers. The answer to dynamics lies in amplifiers, not speakers. Put another way 'Its the electronics, stupid!'.

Higher efficiency speakers tax amplifiers (here meaning their power supplies in the main) much less - so there's no way to do an apples-apples comparison...
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Old

RIAA Equalization Curve

Posted 5th March 2013 at 02:51 AM by rjm
Updated 5th March 2013 at 03:37 AM by rjm

For reference and experimentation.

This excel worksheet will provide you with reference data that you can overlay and compare with the measured/simulated response plots of actual phono stage circuits.
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File Type: zip RIAA Standard Equalization Curve.zip (173.7 KB, 175 views)
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Old

6C33 OTL Fine tuning - BGs, ground and wire dressing

Posted 3rd March 2013 at 03:58 PM by wlowes
Updated 8th December 2014 at 01:39 AM by wlowes (Update - Bulk foil resistors)

The amps continued to run in and proved to be keepers. Well worth doing some final spit and polish. There was a little hum on one amp and some noise / hash on the tweeters of both channels. Nothing major, but certainly audible at 1 foot.
Using AC filament supply for all but the input tube, I figured I should re read the best practices on wire dressing, hum pots, virtual center tap etc.
Looking back there were some spots to improve.
1. tight wire twist on path from bridge rectifier to first caps. Done, no real change.
2. tight twist on b+ supply to input tube plus added BG 3uF 250v cap right at the tube. No change to noise but love the improvement in sound
3. tight wire twist from psu to b+ on all power tubes plus BG 10uF 250v on each power tube. Like the input tube the BG brought an immediate lowering of noise floor that really brought a finishing to the SQ. Quiet background, micro details and just a smooth rich sound. Not colored, just the way it...
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