Matt Renaud writes:
It’s time for a little confession: I don’t always spend as much time on my power supply designs as I should. Sometimes I get excited about my latest circuit and after looking for just the right tubes, output transformers, coupling caps, and low noise resistors, the power supply design becomes almost an after thought. Sometimes things turn out ok and there are no problems. Other times I end up with bad voltages, unacceptable power supply sag, channel crosstalk, or worst of all, a hum that I just can’t seem to eliminate. It’s at these times that I always wish I had taken a little more time to get it right.
The truth is, there is no reason to suffer power supply set backs like this. The design of basic tube power supplies is actually very straight forward. And, if we rely on the excellent work of those who’ve come before us (O. H. Schade, N. H. Roberts, D. L Waidelich, H. J. Reich), we don’t even need to tackle any advanced math or taxing mental gyrations to arrive at some truly excellent power supply designs.
Power Supply Design for Vacuum Tube Amplifiers - [Link]
This is so cool, and it has enormous potential — think nanotransponders for the Internet of Things (or sub-dermal radios). From nanotechweb: [via]
The first graphene device capable of significant voltage amplification (more than 10 dB) has been fabricated by researchers in Italy. The result confirms that the “wonder material” could compete head-on with silicon as the material of choice in electronics and is not simply limited to niche, low-voltage gain, high-frequency applications as currently thought.
The voltage amplifier (a device capable of amplifying small alternating voltage signals) is the main building block in analogue electronics. Thanks to its unique electrical and mechanical properties, graphene (a sheet of carbon atoms arranged in a honeycomb-like lattice just one atom thick) should be ideal for use in a host of technological devices – such as high-speed transistors – and in photonics. However, many scientists believe that it cannot compete with silicon in applications requiring voltage amplification, like analogue amplifiers and digital logic gates.
Even though it is their first graphene amplifier, it already shows “remarkable performance”, according to Sordan and colleagues – with a flat frequency response well exceeding the audio range (>20 kHz) and a very low total harmonic distortion (<1%).
Using Graphene to Build Nanoamplifiers - [Link]
I’ve finally gotten around to assembling a breakout board for the Skyworks SKY65116 UHF amplifier. It’s really amazing how the state of the art in RF ICs has advanced. They can still be on the expensive side ($6 at digikey), but still relatively cheap when you consider the cost of all the support parts that it takes to build an amplifier from a RF transistor. This particular amplifier has a 50 ohm input and output, and 35dB of gain. It works from 390Mhz to 500Mhz, which means its perfect for the 70cm ham band. The breakout board is stupid simple, copied directly from the evaluation board schematic in the datasheet, but I’ll include schematic and design files anyway.
SKY65116 Amplifier - [Link]
I made this portable speaker in the summer. It mixes the stereo input into a mono signal, which is then amplified. It’s powered by a six pack of AA batteries. The batteries are held in an external battery pack, so they are easy to change on the fly, without the need of a screwdriver.
Portable speaker for MP3 player - [Link]
Gilberd headphone amplifier. Riad writes – [via]
I listen to music on headphones a lot at work, and my source is almost always a CD/DVD-A/SACD player (Denon DVD-2910). Since it doesn’t have a headphone driver, I need something to power my various cans (1, 2, 3). In the past, I designed a tube-based headphone amp but frankly while it’s nice for nostalgia’s sake I’m not interested in “tube sound” (a.k.a. “a lot of even-harmonic distortion”), so why go to the trouble and expense? Let’s get more modern, cheaper, and a lot higher performance. (The name Gilberd is after William Gilberd, an early figure in electrical engineering.)
Gilberd headphone amplifier - [Link]
While LM386 is very popular among hobbyists, it provides the limited output power of only 1 Watt, and for stereo application, two LM386 ICs are required. This project is about making a 5 Watt stereo audio amplifier using the UTC TEA2025 IC chip.
TEA2025: An stereo Audio Amplifier IC - [Link]
This single-Ended (SE) 6550 design is based on a minimonitor constructed by Lars Ohlsson of ElektroAkustik & Music.
The single-ended amplifier circuit uses a 6550 high power tetrode vacuum tube in the output stage. A 12DW7 or 7247 is used to drive the output stage. The 12DW7 / 7247 is a dual section triode, the first section has a gain factor of 20 and the second section a gain of 100. You can think of it as one-half of a 12AX7 and one-half of a 12AU7 in the same envelope. New production JJ ECC832 tubes are a suitable replacement for the 12DW7 and 7247 which are no longer in production. C2 and C3 should be good quality film capacitors. The cathode bypass capacitors C1 and C4 will also have some impact on the sound and good quality low ESR capacitors are suggested.
Single-Ended (SE) 6550 Tube Amplifier Schematic - [Link]
schazamp shared the Schamplifier:
I am working on my own version of the Squelette mini chip amp, as presented in Make Magazine #23. My ambitions for this project are relatively unbounded, but knowing the trouble I have with follow-through, I am trying to start small and get a working stereo amp with a single input and potentiometer volume control in an enclosure, and I can leave the integrated WiFi radio, IR remote control interface, smart phone remote control interface, integrated digital tone and volume controls, blinkenlights, and mind-control interface projects for later on.
Schamplifier mini chip amp - [Link]
This project described a stereo audio amplifier using two LM386 ICs and a PIC microcontroller to control the volume of the two output speakers. The project uses a DS1868 digital potentiometer that creates a voltage divider network at the input stage of LM386 to control the fraction of signal fed to the amplifier. The potentiometer wiper position is varied digitally by the microcontroller based on the user inputs.
Digital volume control for a stereo audio amplifier – [Link]
NBitWonder built a class-D amplifier. [via]
Class-D amplifier is a highly efficient amplifier that operates its output devices as switches instead of as variable resistors. We posted a highly experimental version of this project last November, and it met with a surprising amount of positive feedback from the DIY community. Therefore, we developed it as a formal project
Class D amplifier assembled – [Link]