Designing this front-end for my amps has been harder then I planned. Part of the complexity is the time delays I need to add; my woodworking is not bad but it’s not excellent and decided I’d put the speakers front-aligned. This lead to having to delay frequencies so everything sounds right. Now, there’s no way I wanted to do all that in analog so a simple DSP system is in order !
In order to keep the design work to a minimum I decided to use power board from panson_hk on diyaudio; then I only need to make a front-end. This front end shall have DC Servos and DACs so keep the number of PCBs and complexities to a minimum.
All is good until…
Ground Planes or not
Here you can see Channel A has a ground plane and Channel B has a star ground; which is best and any ideas on optimizing the layout ?
Seems I had the tool to create round hole all along…
Almost nice round holes !
Well it started !
Speaker building fun
Well, seems it’s easier said then done. For the last week I’ve been trying to route my data bus (highlighted in the picture) to the FPGA (the left most IC). Considering I’m trying to do it on a two layer board I have no idea how I’ll do it. Feel free to leave a suggestion. Other possibilities include making a daughterboard with the ARM9 and memory. That would “Emulate” a 4 layer PCB and would allow me to reuse the “core” module.
A milestone was reached today, I’ve routed the 18bit address bus to the FPGA, next is the 32bit data bus. Click image for PCB fun.
Up until now I limited my self to text VFDs or LCDs with a common HD44780 interface but yesterday, I stumbled upon this nice PSP-LCD (LQ043T3DX02) for sell on SparkFun. Now I wanted to do graphics ! However you won’t display something on those LCDs with a PIC16F… (Well maybe a dual port memory with a CPLD to do the timings)
As my projects (Blamp and my active speakers) progress, I always find myself in need of a fast core with possibility of lots of expansion and that can be deeply embedded (read: no ports on the board). Here enters my efforts to have a working, dual-layer AT91SAM960 board with 256Mb RAM and a FPGA. oh and yes, it will run Linux.
There comes a time when you just want to build the whole thing. I recently read about a DIYer who built a three way enclosures with Vifa Drivers. For space saving it would be the perfect enclosures to build the amplifier in it. Since Adam McCall got beautiful results I decided not to reinvent the wheel and build from his plans.
But why just one amplifier ?
Active Crossover, Class-A 20w Tweeter Amp, Class-AB 50w Full Midrange Amp, Class D 200w Woofer Amp.
As you may or may not know I’m building an audio/video pre-amplifier/pre-processor. Since this a quite a bit DIY project I decided to make it very modular.
It will accept either SPDI/F coax and optical as input along with the more basic analog inputs. Every input module handle one input and will output an I2S signal over a 5 pin header (4 for I2S and the last bit will be for if audio is present). Every input will then go to a mux board which will simply be relays controlled by the main logic board (possibly by some simple PIC) this board will have only one output and will be I2S. Exception to this will be the SPDI/F inputs; the CS8416 in software mode will be responsible for the mux and the output will then go to the mux board.
The fun stuff will be on the main board; the I2S input will go into a SRC (Sample Rate Conversion) the output will always be at 24-bit 192kHz and will go into a DSP. The SRC will be pulled into bypass if the “audio present” bit is not present – this will allow me to pass raw SPDI/F data and possibly implement AC-3. The main control logic will be a Freescale Coldfire MCF5282 at 80Mhz and will possibly interface with a Freescale DSP56367. The Coldfire will handle the infrared, the VFD display the power (ON/OFF), programming the DSP and monitoring the pre-amp for over-temp and such.
The video will follow the same pattern; Inputs will be converted to digital, will be muxed and then back to analog for the output – however I will not put a DSP in the single path. This project is already complex as it is.
For the power I decided to keep it simple and will use a ATX12v power supply.
Right now, the output PCB is done and I’m designing the main board. Fun stuff !
Features more space and place for bigger heatsinks. I also added a balanced input driver (INA137 at -6dB)
It’s one thing to build and amplifier, it’s another to build a pre-amplifier. I selected a CS4398 [PDF] as DAC; this chip has a differential output for both channels, an I2S input and up to 120dB dynamic range.
What’s nice is that Cirrus Logic made a very well designed evaluation board for this chip, the CS4398. I’ve used the XLR output as a starting point for my own output stage.
The DAC will run at 96kHz with an oversample of 512x. The master clock is just over 49MHz (49.1520MHz). The input (I2S) will be feed from either a DSP or my “Core Module”; I have not yet tested if the ColdFire v2 @ 66MHz will be able to keep up with video & audio. As for the PCB, all the components will be surface mount to minimize space and keep the trace length to a minimum.