Archive for the ‘Audio’ Category

Today marked another milestone; the cross-over for my 4 way active speaker is done. The input is a XLR followed by a very common instrumentation amplifier before entering the real crossover it is buffered and split to the signal detection circuitry. This last bit of circuitry is not mine; I originally designed one with a 2.5v voltage reference and another one with a comparator with build-in reference like a LT6703HV however, Rod Elliott’s idea on Project 38 was very nice; a simple dual op-amp and voltage divider.

As always, comments are welcomed. Schema and Eagle Project files are provided. (Full view for links)

Tonight I spent some time in Google Sketchup to sketch up my speakers. This is my ever lasting project and every bit helps to keep myself motivated ! I’m uncertain about the colors and the finish to use as it will all be MDF but the current render gives a good idea.

The project is a 4 way active system; with 2 subs, lower voice, upper voice and tweeter. I have completed an analog crossover but I’m tempted to replace it with a variant of the DSP board I published earlier. The system will feature the ability to turn on when “detecting audio” or with 12v triggers. An output trigger (also 12v) will be present and independent of the input trigger; it will turn on with the “speaker” so I can power/trigger other equipment.

The two subs will likely be a Class-D amplifier based on a TAS5630 while the voices will be based on a LME49811 ‘chip amp’. I will likely reuse my (modified) JLH Class-A for the tweeter, while overkill.

One thing I’m very uncertain is where to unbalance the signal. I’m currently doing it before the crossover (and therefor before the amplifiers) since it’s my understanding that matching parts is critical and very hard when purchasing small quantities.

It’s been a while but I’m very exited to tell you I’ve finished a small DSP board for a simple headphone amp. The original goal was to have a USB input in 16bit 48kHz and pass thought a DSP to “enhance” the sound before a tube power amplifier. I’ve been going mad trying to find a suitable DSP without committing too many hours; those DSP evaluation kits are not cheap.

That is until I found out about Freescale’s Soundbite which has decent inputs ADCs and output DACs. As a bonus they even have the Eagle files available (YES !)

My board is quite simple, two possible inputs:

• PCM2707: USB to I2S
• CS5346: 6 Single-Ended inputs with built-in PGA and MUX

The output is using a PCM4104: 24Bits with 118dB SNR 4-Channel Audio DAC.

The layout is still in review, a lot of thinking still has to be done, especially on the case and the power amp. However here is the board for your review and the Eagle files; please be aware that I make no guaranties this will work. If you like this you are free to buy me something from my Amazon wish list

Not sure how to finish the layout and even if the layout is optimal

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…

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

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.

Stay Tuned

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 !