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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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Old

Multi Channel Amplifier with DSP Crossover - Retro styling

Posted 13th July 2014 at 02:26 AM by googlyone

What sort of amplifier do you build to go with a funky retro subwoofer and "Ikea Salad Bowl" speakers?

How do you reconcile this with the fact that you have a "metric shitload" of DSP stuff laying around?

I have run into this problem, and concluded that I need to mash these into something that is not new and higher tech than old style.

This has resulted in me trying to train smash "new and old" into what I am hoping will be a retro styled, but thoroughly high tech-on-the-inside amplifier. (Stopping short of going class - D which I hold aesthetic objections against).

So lets get started with the basics. The amplifier will not be square - it will be a parallelogram...

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And to follow up with my (albeit young) recollections of the 1970's, it CANNOT be black.

This amplifier needs to be the most acid driven shade of orange that I can find....
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Old

Cubist Subwoofer to go with Ikea bowl Speakers - just looks wrong!

Posted 1st June 2014 at 12:20 PM by googlyone
Updated 1st June 2014 at 12:24 PM by googlyone

A while back I built some Ikea bowl speakers using Vifa bassmids and tweeters. The performance came out very good indeed, but when you are dealing with a 5 odd inch driver, there will never be masses of bass.

A subwoofer was always on the cards.

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Given the spherical speakers perched on the retro "rocket like" stands, I initially thought of doing a spherical subwoofer - but in the end concluded that while I could do this, I was looking at using fibreglass on a "fit-ball", placement in the room was looking to be a challenge.

So I chose to do the absolute opposite - and came up with an off the wall approach to a conventional sub.

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The idea was to move the implementation of a conventional sub well away from the "box with a driver stuck on the front".

I find it fascinating that...
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Old

Simple DSP Crossover implemented using PIC32MX450

Posted 17th March 2014 at 10:49 AM by googlyone
Updated 17th March 2014 at 10:58 AM by googlyone (incomplete)

It must be close to 12 months ago that I saw the PIC32MX450. I was convinced that a chip that included two I2S audio interfaces, and ran at 100MHz implementing 32bit arithmetic in pretty snappy time would surely be able to do some fun audio stuff.

I started with getting a board designed, and porting the code that I use to control my Analog Devices audio DSP. Then I generated the code to implement a direct digital synthesiser. These worked fine.

Over the last couple of weeks I have completed the "core code" for a digital crossover all implemented in the PIC32 itself.

The basic implementation is:
- An analogue to digital converter
- The PIC
- A digital to analogue converter
(Oh and an interface PCB done on veroboard to route the MCLK and power to the A/D and D/As. I am kind of tempted to re-spin the PIC32 board to do this for me...)

The PIC drives the I2S interface as master, generating...
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Old

Code for dual channel DDS...

Posted 25th January 2014 at 01:37 PM by googlyone
Updated 26th January 2014 at 05:34 AM by googlyone (Incomplete)

I was asked if I would share the code for the audio DDS I was playing with.

It is here...

Ver0.1.zip

I think this is all the files you need.

To show just how lazy I am, the main function is the file titled "dig_cross.c" - as that was the main function I edited as the base of this code. There is also a file "ad1940.c" which contains a bunch of the SPI stuff. This is yet another illustration of my bone idle-ness - as this module is probably a decade old. It is used, but has nothing to do with an AD1940 IC....

No apologies

There is a bunch of comments in this, but some general overview comments are:
- About 95% of the source code is about:
- Running the user interface
- Generating the display (rather utilitarian implementation)
- Reading from the EEPROM, and doing limit checks on data
- Writing to EEPROM

...
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Old

Low Distortion DDS based dual channel audio synthesiser

Posted 24th December 2013 at 01:40 AM by googlyone

Well now I am on holidays over XMAS I got the time to really put in a solid chunk of time on the DDS based synthesiser.

Previous blog entries describe the PIC32MX based core to this. The thing works like a charm...

To get decent precision on the sinewave I have implemented an interpolation on a high precision Sinewave lookup table.
- The DDS references into a 12 bit "long", 24 bit "amplitude" precision sinewave LUT.
- Of itself this gives mediocre spurs, which in a DDS are heavily dependent on the frequency, but seem to result in 85-90dBc spurs. There is a fair hash of these without treatment.
- By adding a linear interpolation between samples in the Sinewave Lookup table, the spurs come out as shown below...

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- The interpolation is actually quite simple in concept:
- The top 12 bits of the DDS Phase Accumulator looks up the "Sine Sample"
...
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Old

PIC32MX450F256 as DDS core driving CS4398 DAC

Posted 18th December 2013 at 09:35 AM by googlyone
Updated 18th December 2013 at 09:38 AM by googlyone

Over the last couple of months I have been playing with a PIC32MX450F256H as the DDS core, and using one of the many DAC boards I built for my DSP based crossover as the D/A element.

It has taken a while to get up and running - mainly due to me actually having commitments other than a hobby... (Bugger)

That said, getting this thing up and running also required me to get my head around the microchip XC32 compiler, and the configuration bits in the PIC32MX.

On the compiler, the most serious issue is the schemozzle they call documentation. I imagine if all you wanted to do was simple I/O and stuff you might be OK. As soon as you want to dig into the more detailed registers, the high level library documentation is borderline useless, and spread over a number of directories and the Microchip website. Very frustrating.

The other challenges I had were:
- To set up the PIC I2S interface such that there was no jitter on the LRCLK...
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Old

PIC Microcontroller as a potential DSP / DDS Element

Posted 3rd November 2013 at 02:29 AM by googlyone
Updated 3rd November 2013 at 02:31 AM by googlyone

I noted that the new PIC32 series micro controllers include I2S along with the SPI interface. Well at least a few in the range do. This got me to thinking:
- A 32 bit micro using a fairly efficient RISC architecture
- With I2S in and out
- That runs at 80MHz.

I chose the PIC32MX450F256H.

Surely to god I can do something fun with this. But what?

Ultimately I will try chucking some IIR filters in here to see how they go (there is heaps of processing time available). But in the first instance I want to do a DDS. Reason being that I have more active crossovers than I have speakers (and that is saying something! - ask my long suffering wife!).

One thing that I have been on the look out for is a decent DDS synthesister for audio band that has really low distortion. My current Audio synthesiser uses the AD9952 DDS chip. OK, this runs at 400MHz, but it does use a 14bit DAC, and can be run right down into the...
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Old

More on Doping Speakers

Posted 25th May 2013 at 10:25 AM by googlyone

I got a question or two on doping of speaker surrounds.

Here is the thing: If you buy an OEM cone kit it will either come with a pre-doped surround, or be provided with the doping material and instructions.

I have reconed a lot of drivers and until recently either used OEM kits or kits from providers who have looked after this for me.

A good example of a provider that gave doping compound was BEYMA. The instructions etc for this were idiot proof, and the material nicely packed in the kit.

To apply this I used a stiff "cleaning brush" as you would but from your local hardware store - a steel handle about 100mm (4") long crimped onto stiff bristles. Worked a treat.

The beyma doping material looked and smelt for the world like really thick PVA glue. The difference was that when dry it did not go that hard, and remained almost but not quite tacky.

The before shot is:
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