Well, you learn something every day. I suppose if you don't manage to learn as you go, then you probably stuff things up every day!!!
About 12 months ago I came across some RCF L18/551 eighteen inch subwoofer baskets. I reconed them using aftermarket parts, the process went OK but I was kind of bemused by the untreated cloth surrounds.
I was busy, and had no immediate plans so the drivers were shelved for a rainy day.
The Thielie and Small parameters were "OK" but not exact as OEM. I measured these using the addded mass method, an important fact for later. As an aside, they would do well enough as subs, but their Fs was a bit higher than I would have hoped.
Fast forward to last week, I loaded one into a 220 litre box tuned to 34Hz, and measured the impedance.
Bugger me if the resonance showed one massive peak at pretty much the driver Fs, and a tiny lump out at 80Hz. Huh?
I stumbled on the people making speakers from the Ikea bowls. It kind of inspired me as the speakers were truly different and bizarre, but at the same time something completely different.
So I had to make some.
I fumbled around in the cupboard and came up with three choices of woofers that would do OK in a small enclosure - and after a few measurements and stuff settled on a pair of old Vifa M13SG-09-16 drivers. These were pretty well suited to an enclosure of a bit over 8 litres.
This drove me to the larger bowl, a 28cm one.
This is how they came out...
To fit the driver I simply routed a rebate - and then cut the inside out.
The material of the bowl was quite thin once I had finished routing things - so I cut out a circle of ply and glued it to the inside of the bowl. I had to go out for the evening at that point so I simply...
Posted 20th November 2012 at 11:55 AM bygooglyone Updated 20th November 2012 at 12:02 PM bygooglyone
I have had a few people ask for the CAD files and software for the ADAU1442 DSP. I have tried uploading the whole lot as a series of ZIP files - I hope this works OK.
There are a few things that warrant comment, and if you try to untangle this lot, I am sure a few questions to me. Feel free to ask away...
- The sigmastudio file is simply there to generate the code for the DSP. All the actual values for filters etc are calculated by the microcontroller under user control.
- SigmaStdio generates a bunch of export files, my software uses the *.h files, both to load the DSP code, and also to get the addresses in the ADAU1442 of registers for biquad coefficients etc. The microcontroller code pretty well loads these in straight, but there is a tiny bit of tidying up the sigma generated files first...
- The microcontroller is a PIC18F4560 (from memory) the CAD file has a PIC18F5420 in the schematic - these are pin...
Posted 2nd September 2012 at 08:11 AM bygooglyone Updated 15th September 2012 at 08:10 AM bygooglyone
Wow - it has taken me months to finally get around to packaging up my latest DSP. With work, travel and holidays I have a huge bag of excuses, but I guess the actual reason is that my old DSP using the Analog Devices AD1940 actually works just fine.
The results are I think pretty neat:
The case was made from leftover bits from the last set I built - the sides are simply timber with a groove routed for the top and bottom panels to sit in, and the front and rear panels screw into the timber sides. It makes a change from the multitude of "all metal" cases that litter my workroom and playroom.
The implementation here has one analogue to digital converter and four digital to analogue converter cards.
These can be seen here:
Where the ADC is the first vertically mounted bard on the left with the slightly scruffy IDC cable. The four DACS...
I got to the point with my new audio DSP / crossover that I had no more excuse not to load the remaining PCB's I had manufactured.
I initially only loaded one of them, on the basis that if I had a clanger in the layout I could get a new spin of the boards.
Well the thing is all working and I have updated the DAC board - so the remaining five boards needed loading. I find a bit of PCB manufacture and loading to be quite therapuetic - as my previous blog entries will show.
This weekend I found my limit - loading the SMD's for these five boards - by hand in my toaster oven - took about three hours, then loading all the through hole parts, particularly headers and power supply parts blew away I would guess six more hours. I am over it!!!!
They do look pretty though!
The only part remainig to be loaded on these boards is the ADAU1442 regulstor transistor. Thay will allow me to...
One thing that always used to give me grief at home was loading fine pitch surface mount IC's.
I recently bought a toaster oven having read several people's experience using these to relow SMD's.
I lashed out and bought the el-expensivo fan forced model, as this was in one forum reported to give more even heat. After some playing around I concluded the oven would actually be really very good.
I found that if I did the following (with my oven):
- Turn on and run on 2 bars until temperature = 100C,
- Turn down to one bar, and run for 60 seconds,
- Turn on two bars and continue until the temperature is 210C,
- Turn all bars off, leave fan on and open the door a crack.
The heat continues to increase to about 220, and the profile is really very close to many manufacturers recommended profiles.
I don't use silksceeens, I use a syringe and put a very little...
Just finished set to work of the new DAC for the digitial crossover. This includes a PGA2320 programmable attenuator on the output of the CS4398 DAC.
This replaces the home made PCB thai I was using on the CS4398 output. I went the professionally made board mainly because PCBCART was able to deliver 16 of these to my house for $140, that includes tooling!!! The actual boards were like $3 or 4 each!
The quality of these baords is fine - though I must admit that I am not breaking any new ground in PCB technology here.
The board is only double sided - I thought about adding a seperate ground and power plance - but the routing density is so lot it would be crazy. The whole back side only has a handful of tracks on it - and is a ground plane in itself. The top side even has room for significant ground fill.
All the digital stuff is in between the connector and the DAC, with a few SPI lines up the left hand...
I have never been happy using DACs to implement volume control. I guess largely because of the obvious degradation in resolution at low volume levels.
On my first DSP crossover I used an AD1939 CODEC, which has 24 bit resolution - though obviously lesser precision - and my approach here was to use a mix of steeped attenuator and digitally implemented volume control.
It worked well - though pretty shortly after I built an 8 channel PGA2320 based volume control.
For my new DSP crossover I started with a simple CS4398 in the DAC output. even when I built the first boards I KNEW I would be going back to integrate a programmable attenuator.
Why didn't I just start with it? **** knows.
At lease with the modular approach all I had to do was respin my DAC board to include a PGA2320 along with the CS4398. I already had SPI to the board, sop I can sneakily use these lines for the PGA 2320, as the CS4398 is in hard wired...
Well, it has been a few years since I built my last digital crossover - like six I think.
It is not that I was planning to do this - but a conversation with someone about my seemingly modest choice of the AD1941 DSP chip for my old crossover made me look at what else Analog Devices are offering.
The ADAU1442 is on the surface a very similar chip to the AD1940, but it has a lot more integrated into it, and offers significantly greater capacity.
So I set about designing a new crossover that used this, and also addressed a few of the shortcomings of my original design.
The goals were broadly:
- A modular DSP based crossover
- That provides a standard interface for the ADC
- That provides a standard interface for the DAC
- That includes SPDIF in and out
- That anybody can design digitisers and dacs for - no code level drivers built in, though the interface does ALLOW for SPI control of these
- That is controlled from a simple...