Author Archives: remco

Setting the output voltage on a flyback switched-mode power supply

Yes, I am still alive. Sort of. 🙂

This should involve only about 3 people in the world, but hey, I should blog more even if the relevance is negligible. If this helps 1 person, I’m glad.

Not recently at all I bought a bunch of Yokogawa A1D03B supplies from Pollin (originally meant for HP printers). The idea was that they are nice to supply small / medium amplifiers for active loudspeakers. The output is 31.6V but I needed about 24V.

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So, the cat’s out the bag

I had this project saved for later publication, but the first delivery seems to have succeeded quite well. Analog guru Duke Aguiar, who sells the LPT interface cable to the Audio Precision APIB bus (with a USB solution in the works!), has received and favourably tested my recreation of the AES17 compatible 20 kHz brick-wall measurement filter for Audio Precison System One/Two.

Before I knew what hit me there was already a review post up at DIYaudio!

The performance is stellar, like the original AP and much less costly

[source]

Brick-wall 20 kHz lowpass filter compatible with Audio Precision System One/Two

Now available for order – webshop here!

SACDenhancer revisited – part I

About four and a half thousand years ago, I designed (SA)CD player output stages with vacuum tubes and at some point came up with a transistor version, called the SACDenhancer.

Original version, ca. 2003 AD

In double blind tests this was a big preference over the built-in opamp solution. It spawned off a plethora of discrete output stages from various manufacturers and modification shops that were all the rage in the day. I had some pretty good spectrum analyzer but never could find definitive measurable differences between the standard output stage and this one.

Fast forward 15 years and I’m still getting requests for this design, so I had a PCB made. Both fabrication and measurement capabilities have moved quite a bit forward in the meantime.

Reboot, ca. 2016 AD. How nice you can now get solder mask in ‘UltrAnalog’ colour palette from China.

This version follows the original schematic but adds a second output stage for fully differential processing. As such the schematic stays ridiculously simple – just a long-tailed input stage and emitter follower output. Couldn’t be simpler (I tried. Believe me. It wasn’t good).

Basic performance

Test conditions unless otherwise specified – 1V rms differential, 997 Hz input, AES17 measurement filter, unweighted

THD+N : -99 +/- 0.5 dB

Best THD : 109 dB @ 0.7Vrms input

SNR: 100 +/- 2 dB

Frequency response linearity: +/- 0.02 dB, 20 Hz – 20 kHz

Gain linearity: +/- 0.025 dB

THD+N vs. Freq

THD vs Level

Crosstalk

Intermodulation, 1k sine 1:1 with swept sine from 60 kHz to 6 kHz

Good news – the performance indicators are all green: no defects. This is pretty much as well-behaved as you might expect from a discrete design. But while it clearly says there’s nothing wrong with how this will sound, it does not prove it will sound better than an opamp either.

Balls to the wall

So let’s pit this thing against an opamp stage and see what happens. In the left corner, representing the heavyweight class, the Analog Devices OPA275. The challenging contestant, some ridiculous discrete design from some dude in 2003 thinking they know better. All that and more, in part 2…

Outage

Just a quick mention about recent outage. It appears the site was taken over by a spotty teenager in his basement running CMS brute force scripts…

If that was you: hey contact me, I’ll send you some breadboards, tubes, transistors and an old oscilloscope. Go teach yourself electronics, one day you may find you have a nice job. I might even be the one to give it to you 🙂

Much to my chagrin, I can now add PHP to my skill set. I could have lived a long happy life not knowing a thing about PHP and just program in solder instead. If you do spot broken links or things not working, contact me.

Some recent comments (which were actually really nice and constructive) were unfortunately lost. Obviously I’ve tightened security and will make backups more frequently, but couldn’t avoid this. I have been really positively surprised about the level and the tone of comments on itsonlyaudio.com – such an enormous contrast to ultranalog.com back in the day! Please keep commenting!

One page I was in the process of writing was also lost, I’ll have to write it again, until then I’ll just leave you with a nice visual preview.

More soon…

Writing 24LCxxx EEPROMs with PICkit3

Since it took me about 8 hours to fetch all the information together and get it running, maybe this post will be useful for other loonies like me who think this is a good idea 🙂

You see, the Microchip PICkit3 seems like a steal – a cheap, full featured PIC programmer that can also write EEPROMs!

Well, they weren’t lying. Then again, it’s not exactly the truth either. Continue reading

Arduino software control for WM8804/WM8805

WM8804 application board (eBay) modified to output CLKOUT pin (yellow-black wire)

Recently I needed a special type of I2S signal, namely a 4 signal set of DATA, BCLK, FCLK and also an MCLK of 49.152 MHz.

Many modern DACs, DSPs and digital power amplifiers need this high clock frequency. And of course you would want this signal to be synchronous to the Frame Clock such that the converter has a fixed number of MCLK per FCLK cycles so as to minimize jitter.

Many S/PDIF receivers implement a fixed clocking in hardware mode which limits your options and flexibility, so it is worth exploring software control. It is really not so hard. Continue reading

Measuring USB devices with an Audio Precision System One or Two

There is one thing the older Audio Precision System One and Twos don’t have which can be quite annoying: they don’t have USB host functionality. And given that all the processing and clocking happens inside the unit, the control software can’t reroute the digital signal generator to a USB output.

Tenor T7022, an often-encountered USB receiver. Does it do bit correct feed-through?

Of course you can use a PC to feed the USB sound card and measure the output with the AP, but then you don’t have the generator signal to do e.g. sweeps or automation. The best of course would be to somehow get to a full loop starting at the AP signal generator back to the analyzer. After quite a lot of tinkering, I managed to do just that.

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And now, for some music

Surely, you can’t have missed that Linn are giving away a bunch of 24 bit tracks at the end of the year?

Last year, I had to log in every day and still managed to miss a few days, luckily some buddies helped out and we got the collection complete.

This year, they’ve been extra generous and left the whole collection up for grabs until January 6th. So in thanking them I’ll happily plug the Linn site for all my readers (yes, both of you).

Linn Records – 24 bits of Christmas

As the year draws to a close and we prepare for many changes in 2015, I’ll plug in the same wm8741 that Linn use in the Klimax and enjoy the recordings. I’m not a big classic fan, but some of the recordings in this collection are absolutely breathtaking. Well either that or I’m getting older.

Enjoy and see you in 2015, which is shaping up to be a pretty exciting year!