The amplifier is probably the single most important composite circuit element in electronics. Certainly such familiar devices as radios and music systems would be impossible without amplifiers. The very large majority of amplifiers these days are solid state, that is, they use transistors. While there are many types of transistors, the first mass-produced transistors were BJTs, or bipolar junction transistors, and understanding transistor amplifiers, for most people, begins with these.
The transistor has three terminals and can be arranged in three basic amplifier configurations, the common emitter, common base (or grounded base) and common collector or emitter follower amplifiers.
Common base amplifiers are not commonly employed at lower frequencies as, amongst other reasons, they have a low input impedance, although they can be found in amplifiers for e.g. moving coil microphones. They are sometimes employed as current buffers, having a current gain of 1,...
Keantoken C multiplyer
Here is the output impedance using the 2SC4793/A1837 pair. This rivals some of the best electrolytics I have measured. It would be hard to improve on this using anything but film caps.
post1259, latest version
Q2 & J6 should be fed from the supply rails, not from the measurement rails.
What voltage (Vdg) is across the BF862 when they are set to 2 to 4mA?
I think you should be using a low Vpinch off for some of these locations, particularly J5 and maybe J6.
Here is the SCH of this Board that you see above.
I didn't buy any part yet, but I'm waiting for the board quote.
In fact I'm looking for chassis and cases for my amp. I'm very demanding with the case, especially for a project with this price.
I'm designing a KT-88 Ultralinear amplifier using the idea of Satoru Kobayashi 2002.
The pre amplifiers is a solid state using a TL-72 with gain 10 and the second stage i have the superb DRV134 Burr-brown (Low distortion: 0.0005% @ 1KHz) which is a differential output amplifier.
Following comes the 6N1P svetlana and the EI 12BH7AEG direct coupled and the last stage with KT-88.
The most important part is that it's all in one, I mean, all in one board. I integrated the high voltage power supply regulator and the low voltage for the op-amps in the board eliminating wires around.
I've been working in this board for more than 3 months and creating BOM, calculation an so one. So far the project is around U$ 1266,00 including all parts, not board, and transformers plus the tubes.
Attached you can see the print-screen of the board. I didn't send to production yet, and i plan to go slowly in this project due the cost mostly...
Posted 15th August 2010 at 01:50 PM byalexcp (My DIY projects)
Updated 15th August 2010 at 04:18 PM byalexcp
This handy instrument is a version of the design published in Australian Silicon Chip (a subscription is required to view the details of the article). It is based on a dsPIC33 microcontroller, has TOSLINK and S/PDIF digital outputs (44.1k, 48k and 96k sample rates) and a stereo analog output. Output frequency, phase, attenuation, and other parameters are set by the keyboard. It produces sine, square, triangle, and sawtooth waves and has a variety of modes. It can be powered by an external DC source or a battery. The article claims low distortion for sinewave (less than .06%) and even lower with a good external DAC, but I did not have a chance to verify that just yet. Highly recommended.
Posted 15th August 2010 at 11:05 AM byalexcp (My DIY projects)
Updated 18th August 2010 at 08:24 PM byalexcp
One of the more interesting projects for me was building a tweaked clone of Creek 4330. It was designed for Creek by diyAudio member x-pro; the schematic is available on his web site. The tweak was the topic of x-pro's paper and was discussed in this forum. Last year, this design generated enough interest on one of Russian DIY forums for a group buy of PCBs and some components. I used a PCB from that group buy, a compact chassis from modushop, and a K4700 speaker protection kit from Velleman. Today it is this amp that I use most often for music, and I am very pleased with its sound. Thank you x-pro for sharing the design!
On first power-on the amp oscillated at 12 MHz when connected to headphones. The oscillation was inaudible but clearly visible on a scope. A quick look at head-fi.org showed that PPA instability is not a new problem. I reduced the value of R11 (see PPA's schematic), which eliminated the oscillation and improved the sound. I replaced the recommended OPA627 with LME49710.
PPA is positioned as a high-end DIY headphone amp, and it is in this project that I felt how subjective "high-end" is. PPA is a nice amp, but a true high-end device like Musical Fidelity X-CANv8 simply blows it away.
Posted 12th August 2010 at 07:57 PM byalexcp (My DIY projects)
Updated 15th August 2010 at 11:09 AM byalexcp
ezDAC lacked a USB input, so I leveraged my newly acquired SMD soldering skills building BantamDAC from a kit. While PCM270x-based USB DACs are rather common, BantamDAC is a compact (1" x 2"), neat version.