I wanted to start working with my ESP8266 and needed a 3.3V regulator to get enough current. I had ordered some 1117 regulators, but went looking through what I had laying about, and "created" this simple circuit.
It is not very efficient, and would benefit from a Darlington in place of Q1, but it gets the job done with enough current for the ESP8266. If the output voltage is just a tad to large, try replacing D1 with a Schottky type.
Adding a 10uF capacitor from 5V to ground is a good idea.
I have some PIC18F4550s lying around, and I want to play with the USB features of this chip, therefore I made this breakout board. It contains enough components to get the PICMicro running, and nothing more, all the pins are routed to pin-headers to use with an experimenter board.
- ICSP connector (In-Circuit Serial Programming, AKA PicKit 2 & 3)
- USB-B Connector
- 20Mhz clock crystal
Eagle files: PIC18F4550 USB ICSP breakout board
The transistors in the current mirror, and differential amplifier will benefit from having thermal contact, to keep the temperature difference as small as possible, thereby minimising the DC output offset. I have taken the best picture I could, of this coupling for one channel, in my amplifier.
I have gathered together the schematics for the non oversampling TDA1545 DAC. Mind that I am only responsible for the shunt regulators, the microcontroller, and the input selector. The digital input circuitry was developed after reading some post from Jocko Homo on the diyhifi.org forum. The TDA1545 circuit is mostly from the Philips data sheet. The I/V stage is from rbroer on DIYAudio.
At some point in time I have made the following block diagram, and from memory it seems correct.
From the top here is the input selector board, the micro controller for the relays are on a second board, as per the block diagram.
After the relays, comes the SPDIF buffer/amplifier circuit based on Jocko Homo's. The CS8412 converts the SPDIF signal into the correct I2S format, I2S data goes both to the DAC board, and the micro controller board. The micro controller signal is buffered by one of the 7404 inverters, in the hopes that any noise from the micro controller, will be isolated.
The shunt regulators, are duplicates of the similar valued ones in the shunt regulator schematic, you do not need to build these twice!
Here is the DAC circuit.
Everything is in the puzzling Philips data sheet. The relay shuts off the data, while the micro controller scan through the inputs.
Here comes the shunt regulators
The one at the bottom is the one for the DAC, and the one that is not
duplicated on the input selector board.
Here comes the I/V from rbroer, which is fed from the unregulated DC supply.
And the micro controller schematic.
I have redesigned the PCB layout's without saving the ones I used in the working DAC. Therefore they have not been tested, and I would rather not publish them, and have them blow up in some poor persons face.
The above mess is the first prototype of a transconductance amplifier like the First Watt F2. It came to life after numerous SPICE simulations and chewing through OTA datasheets, Pass papers, and forum posts on DIYAudio.
In short it seems that some full range drivers will benefit from being driven by a transconductance amplifier. A transconductance amplifier is a voltage to current converter with amplification. Our standard power amplifiers, are mostly voltage amplifiers, and will vary the voltage to the load, according to the input voltage. A transconductance amplifier will vary the current to the load, according to the input voltage. For a purely resistive load, this makes no difference as I=U/R, but a loudspeaker is not a purely resistive load. It is actually the current through the voice coil, that controls the force of the generated magnetic field, not the voltage. Because of this, a variable current source seems the most sensible way to drive a speaker. There is a catch though, since most amplifiers, are voltage amplifiers, most n-way speakers have their crossover designed for voltage drive, and will behave wrong, when driven by current. Nelson Pass has written a paper on how to design filters for transconductance amplifiers instead, I have not studied this very hard, since I am building this for full range drivers.
Nelson Pass had designed both his First Watt F1 & F2 as transconductance amplifiers, since I have a bag of IRF640 N-channel MOSFET's. I ended up modifying the F2 (First Watt F2 schematic), to use only N-channel MOSFET's and added a simple regulator, from Nelson Pass ZEN series.
The resulting sound, was good. Despite the two fans needed to keep the amp from burning a hole in the table, that it was lying on (class A, silver, custom made mains cord, 300B, nuclear reactor in the kitchen, mumble mumble). Despite the crude boxes the SEAS drivers had to put up with. Despite the insane amount of distortion, compared to most amplifiers. I have not tested this, but believe I can hear a change to the better, when driven with this amplifier. I have not yet tried correcting the speaker response as per Mr. Pass papers. I have simply decided that it sounded so well I want to finish it, and play with it some more along the way.
The beast has been tamed. It sounds good too, although my headphones are cheap Sennheisers. The headamp is enclosed in a Hammond enclosure, using the aluminium casing as heat sink, it gets hot. It makes for a nice way to keep the coffee warm by placing the cup on top of the amplifier.
Q6, Q8, Q15, and Q17 are the output transistors, and needs heat sinks, I have not calculated the exact size needed, but the bigger the better. I use the aluminium chassis of a Hammond 1455N2202 with the transistors mounted on the bottom, and it gets warmer than I like. Never test the amp without proper heat sinking in place, as the output section will most certainly release the precious blue smoke.
Power supplyI have used a 2X12V toroid, a rectifier bridge, and 4700uf on each supply rail. Each channel draws about 200mA.
GroundingSome attention is advised when wiring the ground, my first ground layout resulted in a nasty saw-ish 50Hz hum from the amplifier. I now connect the separate grounds from the input RCA connectors to their respective ground pads, next to the input pads. The power ground are connected to a star ground between the 4700uf power supply capacitors, as well as the ground wire from the headphone jack.
I have just finished testing a prototyping board I have designed for the PIC18F2550, that I will be using in a project I am doing for a friend. The board is designed to interface with the PICKit 2, programmer/debugger, has an on board 5 Volt regulator, and pads for a serial port through the MAX232 line driver/receiver. This is not rocket science, just a nice PIC18F2550 to breadboard converter.
Cadsoft Eagle project files: uc-proto.zip
Generated on 2018-05-03 01:14:21.909763