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DIY Audio Analyser using CS4398 / CS5381 (CS5361)

Posted 31st August 2015 at 12:50 PM by googlyone

I recently set to work the guts of the audio analyser:
- MiniDSP USB Streamer
- Interface card
- ADC
- DAC

The ADC and DAC were from an old project. the tests I had been able to do on these were done using simple test gear, I knew the distortion was fairly low - but had been unable to really bottom out the level.

I did know the DAC was down in the 0.001-3% level or below.

Imagine my chargin when I fired the system up, got all the bits running and measured something closer to 0.01% distortion at -1dBc!

I was initially convinced that there was something wrong. After cranking the level down to -10dB, the distortion dropped to 0.001%. Further tesing (I ran the DAC at -1dBc and attenuated the output) proved that it was the ADC dominating the measurements.

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Much fiddling led to me concluding that the ADC buffers were the culprit. I would like to blame...
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Old

DIY Audio Analyser using CS4398 / CS5381

Posted 21st August 2015 at 05:16 AM by googlyone

Over the years I have played with measuring - well - just about everything in audio.

distortion measurement has been one of these preoccupations, not the least because it is hard to do, and using commercial gear, expensive.

I have built analogue hear to do this, used mixes of analogue and digital and of late played with using modified commercial sound cards. My efforts on the Sound Blaster x-Fi were interesting but ultimately not rewarding enough for me to leave the mods in there.

I have also been playing with using the A/D and D/A converters from my DSP crossover for this purpose. These are modular and use a common I/O plug with power MLCK, SCLK, LRCLK and Data (alone with I2S for the CS4398 and sometimes a digital volume control).

--- notwithstanding the fact that in previous tests I have shown the digital volume control is the MAJOR source of distortion - I will plug ahead with this, and likely leave that out of the test...
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Old

Improving A/D perfromance of Sound Balster X-fi Music (SB1240) - and a Puzzle!!!

Posted 29th March 2015 at 12:51 PM by googlyone

I have been playing with measuring distortion of signal sources and amplifiers a bit over the last year or two.

I am serious enough to spend some time and thought on this, but not serious enough to sink significant cash into application specific test equipment.

I have a couple of USB Sound Blaster X-fi Music (SB1240) sound cards I use for measurements. The original intent of these was for speaker test and general music. I am pressing these into use for more serious measurement.

The ADC in these is the Cirrus Logic CS5361, which is a pretty good ADC. The DAC is the AKM4396, which is a decent DAC.

When making measurements I hit a problem. The raw performance of the CS5361 is specced to be -99dBc guaranteed an -105dBc typical for THD+N. I couldn't get this.

A few things quickly went onto my list of things to try:
-1- Switching - the sound card has a lot of this - how was it implemented?
-2- Op amps...
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Old

Richard Allan Three Way - Rebuild

Posted 27th January 2015 at 02:07 AM by googlyone
Updated 26th January 2015 at 08:02 AM by googlyone

I recently picked up a pair of, I guess, 1970's Richard Allan three way speakers. The line-up are RA drivers with which I am not familiar. Bass, LP10B, midrange LP5B and tweeters - long dead and replaced with mismatched dome tweeters.

Richard Allan was reasonably popular in Australia in the 70's and 80's, and did some pretty good gear. I was interested to see how these went, but did need to do something about the tweeters.

On pulling the drivers out, I noted a few things:
- The LP10B is a 10 inch bextrene cone woofer, using a 1.5" voicecoil rather than the HP10B's 2" coil. It is also very much an "acoustic suspension" driver - read on.

- The LP5B is very much like a 5" version of the KEF B110 - as used in the LS3A. I read somewhere that Richard Allan made a version of the LS3A under license, but that might be an "internet fact".

- The crossover was made by KRIX, a local speaker manufacturer...
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Old

Richard Allan 3 Way Rebuild - So What Do They Look Like?

Posted 26th January 2015 at 08:39 AM by googlyone

The Engineer in me led to plots and graphs, but no pics of the speakers!!!

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With a neat old badge...

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The bass driver is a classic Richard Allan unit, you can tell them a mile away by the red (sometimes blue and black) felt:

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The midrange has a fair bit of the B110 about it's looks, though it is smaller and behaves quite differently. This thing is very much a product of it's era (1970's):

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The surround on the midrange is stated as PVC in some literature I found. I kind of believe this, though it has been coated with something sticky. It is not sticky on the back.

The cabinets were in moderately good condition. There were some coffee stains on the top of one, and water stains on the side of the other. In the end I sanded and revarnished them.

The timber...
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Old

MJL21194 Transisors: Real, Second Source and Fake

Posted 6th December 2014 at 04:10 AM by googlyone

Over the last couple of decades I have built an awful lot of power electronics stuff, especially power amplifiers.

So I have bought and used a commensurately large number of power electronic devices.

As a young hobbyist this started with salvaging bits from refuse - especially in the late 70's and early 80's larger power devices were far from cheap. This generally worked really well, as I never did really trust what I pulled out of refuse gear, and I tested stuff that I used. (also not the least as data on power devices came from "equivelant devices" books such as the "Towers guide" and if you were really lucky you found a datasheet somewhere (on paper!). no intenet....

Why the digression?

Oddly with the advent of the internet and subsequently things like EBAY:
- I could get all sorts of things that you just could not buy locally in small quantities.
- Unscrupulous buggers out there started...
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Old

Integration and test of CS4398 / PIC based Direct Digital Synthesiser

Posted 2nd November 2014 at 04:03 AM by googlyone
Updated 2nd November 2014 at 09:48 AM by googlyone

About 6 months ago I finished off a CS4398 (DAC) and PIC32MX450 (microcontroller) based direct Digital Synthesiser.

I recently packaged this into an instrument case, and added a power supply cum interface card that allows this to all neatly plug together. As a final chapter to the development of this synth, I have tried to measure the harmonics it generates and to use it to test an example amplifier.

What does it look like? Not super fancy, but neat enough and laid out pretty reasonably I think:

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The larger home made board at the back is a power supply - well five of them in fact - to allow clear isolation between a number of digital and analogue rails.

The square board on the base of the case is the PIC board. This runs the human machine interface and more importantly does all the calculation of the waveforms. You can generate any waveform you want, provided it is repetitive and can be...
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Old

Repair of a vintage driver (Richard Allan)

Posted 6th October 2014 at 10:30 AM by googlyone

Over the last 6 or so months I have built a nice little sub plus satellite system that comprises:
- The "Ikea Salad Bowl Speakers", with some really nice vifa premium line drivers in them, making these 1980's vintage
- A Richard Allan subwoofer, in which I used a 1970's (I guess) HP12B driver, in a complex cubical enclosure with a corner cut off for the driver, and
- A ridiculously complex amplifier built to drive this lot, with DSP, multiple channels, optimised even to the point of addressing the fact the HP12B is 16 Ohms, and running bridged for that output.

So imagine my reaction when last night I settled back and ran the system up "properly" for maybe the second or third time, and CRACK!!!

My initial thought was that I had over "excursioned" the sub, and the voice coil was hitting the magnet backplate. I dug into the amplifier and programmed a subsonic filter, as you do, and settled back in again. CRACK!...
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Old

Retro Amp - final product

Posted 26th August 2014 at 01:18 PM by googlyone

I finally got the retro am finished. At least to the point of all the parts set to work, the case built and assembled and wired up.

The photos really don't show just how orange it is, nor does he slant in the case "pop out" as much as it does in real life.

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Yes, I did the "writing" on the front panel by hand with a paintbrush.... I came close to getting the thing CNC milled, but concluded that the hand painted approach would be (a) fun, (b) a new challenge, and (c) more in line with a retro amp

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The amplifier has:
- A digitiser on its input.

- DSP implementing crossover and...
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Old

DIY Weller WSP80 / WP80 Soldering Station

Posted 24th August 2014 at 08:58 AM by googlyone

I have been using a pretty crappy "Dick Smith" soldering iron for - well too damn long. I have always been meaning to get a decent iron. Given the fact that it worked, and I have been using it for close on 30 years (if not more) resulted in me investing my time and money in other things.

I recently bought two WSP80 Weller soldering irons off ebay at a killer price.

These ate just the "pencil" part of the soldering iron, and need the power supply / controller. Which are not cheap.

Looking on the net there are a number of schematics of various weller power supply / controllers. But various bits and pieces were not quire right for the WPS80 that I had.

As a start I am using this...
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This is evidently extremely analogue. Which is quick and easy to design and build, and analogue just warms the cockles of my heart.

The final product is like this......
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