14.02.2016

Power amplifier packaging

Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors. 1Hz - 2MHz XR2206 Function Generator produces high quality sine, square and triangle waveforms of high-stability and accuracy. Having the ability to control various appliances inside or outside of your house wirelessly is a huge convenience, and can make your life much easier and fun. A high-efficiency output transformer allows the BA-5000 to deliver full rated output at loads of 8, 4 or 2 ohms for 2-channel ultra-stable operation; a full 600 watts in mono. OCL power amplifier circuit 150 W as shown below using a power transistor type 2N3055 and MJ2955 of its physical form as a poultice. Component L, Ra, Rb and C on the output power amplifier OCL 150W can be waived if the speaker wires are used to short.
OCL type power amplifier circuit as shown above will cause a voltage spike at the output terminal is turned on, causing the sound of pounding on the loud speaker that can damage the speaker when it goes on and on each pad is turned on, the beat of the speaker may be prevented by installing a series of speaker protectors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors.
The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored. It is a very useful bench test equipment for testing and finding out the frequency of various devices with unknown frequency such as oscillators, radio receivers, transmitters, function generators, crystals, etc. BA1404 HI-FI Stereo FM Transmitter broadcasts high quality stereo signal in 88MHz - 108MHz FM band. It is an irreplaceable tool for troubleshooting and repairing electronic equipment by determining performance and health of electrolytic capacitors. 8-DIP machined IC socket allows to swap OPA2134 with many other dual opamp chips such as OPA2132, OPA2227, OPA2228, dual OPA132, OPA627, etc. It's breadboard compatible so it can be plugged into a breadboard for quick prototyping, and it has VCC & GND power pins available on both sides of PCB.
The output transformer also functions as a bandpass filter cutting subsonic signals to protect speaker cones.
All files are provided under strict licence and reproduction without prior permission or for financial gain is strictly prohibited.If you have additional documentation please consider donating a copy to our free archive. To purchase BA-5000 spares or accessories, please contact the company via their website or visit an authorised retailer. PCB for the circuit power amplifier OCL 150W can be purchased at electronics stores with multiple brands. Power transistor can be replaced with others such as transistors complement TIP3055 and TIP2955, so it can more easily in the installation of cooling power transistor for the 150 W amplifier OCL. Power amplifier circuit above is still not equipped with a power supply circuit and tone control circuit. It can be connected to any type of stereo audio source such as iPod, Computer, Laptop, CD Player, Walkman, Television, Satellite Receiver, Tape Deck or other stereo system to transmit stereo sound with excellent clarity throughout your home, office, yard or camp ground. Unlike other ESR Meters that only measure ESR value this one measures capacitor's ESR value as well as its capacitance all at the same time. Headphone amplifier is small enough to fit in Altoids tin box, and thanks to low power consumption may be supplied from a single 9V battery. It's small, power efficient, yet customizable through onboard 2 x 7 perfboard that can be used for connecting various sensors and connectors.
You can control lights, fans, AC system, computer, printer, amplifier, robots, garage door, security systems, motor-driven curtains, motorized window blinds, door locks, sprinklers, motorized projection screens and anything else you can think of. OCL 150W power amplifier requires a DC voltage of ± 25 Volt symmetric to ± 42 Volt, which can be made with symmetrical power supply in the previous article. I initially used KT77 tubes as I was familiar with the sound and it would be a good starting point. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings.
Arduino Prototype uses all standard through-hole components for easy construction, two of which are hidden underneath IC socket. For maximum results a series of audio output power amplifier OCL 150W transfomer 5A is minimal use in its power supply. USB IO Board is self-powered by USB port and can provide up to 500mA for electronic projects.


Board features 28-PIN DIP IC socket, user replaceable ATmega328 microcontroller flashed with Arduino bootloader, 16MHz crystal resonator and a reset switch. Series and a list of components to make a 150 W power amplifier OCL can be seen in the following figure. While I was quite happy with my previous tube amplifier projects, I felt there was room to improve (here comes the journey again). Arduino sketches are uploaded through any USB-Serial adapter connected to 6-PIN ICSP female header. Board is supplied by 2-5V voltage and may be powered by a battery such as Lithium Ion cell, two AA cells, external power supply or USB power adapter.
I suspect the reason is related to thermal problems and the use of common (joint) cathode bias. So I tend to like smooth response, lots of detail, wide soundstage and full spectrum of sound.
The circuit allows for adjustment of the bias (the 25 ohm variable resistor) but the EH tubes do not stay in sync. One or the other tube (not predictable which one) will start to conduct more than its fair share of the current.
I have since then acquired a set of new production Gold Lion KT88 tubes and they behave perfectly.
If you are not familiar with tube equipment or are not experienced with high voltages, perhaps this is not a suitable project. This is a pair of mono blocks amplifiers - each with its own power supply. In some ways this is more complex and costly and in some ways cheaper, easier and has advantages.
But the transformers are less expensive than the one needed for a single chassis stereo amplifier. To date I have not been informed of any failures in either application, but I don't feel comfortable with the 37 volt rating of the standard parts in the KT88 application.
It makes sense, but measurements to date have not confirmed it as the level was already quite low.
The power supply uses a Edcor 180-0-180 transformer with a full wave bridge across the full winding.
Unfortunately the voltage rating of the contacts is 120 VAC (breakdown voltage rating is 500 volts when new - whatever that means). So I use the contacts to activate a 12 volt relay that actually does the work of connecting the AC (360 v) to the rectifiers. Then follows either NO or NC, for Normally Open or Normally Closed for the internal contacts. Using the thermal relay is probably a sign of madness and the job could be done simpler with a transistor and a few passive parts, but it sure is cool. I use a generic, inexpensive 12 volt, 3 amp SMPS to power heaters as it is cheap, very compact and provides clean well regulated power. The windings on the Edcor power transformer are 6 volts and would be satisfactory for group "A" tubes.
Generally, it is a bit easier (and cheaper) to get the required power at 12 volts at 2 amps than at 6 volts and 4 amps.
Wiring was point to point and I used some terminal (aka turret boards) boards for connections. The more sensitive circuitry is placed as far from the power transformer and noise sources as possible. A significant feature is the use of a ground buss (seen as a large bare copper wire in the photos). This has worked well in the past projects for minimizing hum, noise and the possibility of ground loops. I discovered some time ago that it is easy to exceed the heater to cathode voltage ratings of the driver tube when you use a SRPP design. If you use a SMPS it needs to have the output isolated from the input and not in any way referenced to the ground.
When properly connected, the current is equal to 1.25 divided by the value of the resistor in ohms. The CCS needs to be heat sinked as it has to handle up to 8 watts of dissipation (when using KT88 at 180ma - less for other tubes and currents).


Now for some magic, if you use a fixed 10 ohm resistor in the CCS for a basic setting it will result in close to 62 mA per tube.
If you have a 22 ohm resistor connected in parallel to it with a simple SPST switch you can bump up the current to 90 mA per tube.
Also, I have posted some suggestions for a tube amplifier wiring color code that you can use during construction. Testing and Operation Before actual listening to the amp it is important to verify that heater and B+ supplies are operational. There should be 12 VDC between the heater pins on the 12SL7 socket and B+ around 475 at the filter capacitors.
The 240 voltage point will be high (close to the 475 reading) as there is no load on the circuitry.
The filters will be fully charged at this point so be careful not to contact any part of the circuitry. Watch for problems (tube plates glowing red, sparks, smoke, noises and other fun things that indicate bad news). If the tubes won't balance then there is probably either a wiring error or a tube that is out of tolerance. It is not necessary to have matched tubes, but if the price is right then it makes them closer and easier to balance.
I have found that not all companies balance tubes the same way and sometimes "matched" sets don't work as well as randomly selected ones.
For what it is worth, I have had good luck with JJ tubes and not so good experience with EH KT88 tubes. Not all tubes work well in all circuits and the EH KT88 tubes may be just fine in other designs. The Gold Lion KT88 tubes worked fine, so it is not a basic property of the KT88 tube design itself. One area that always seems to cause problems is the phase of the feedback loop. It also takes care of any possibility that something will excite the output transformer resonances at around 60 kHz.
With an 8 ohm resistive load the response measured from 8 Hz (the lowest I can generate) to 19 kHz (at -1 dB).
The Gold Lion KT88 tubes were up +0.5 dB at 10 Hz while the JJ KT77 tubes were flat at that frequency. Distortion was 0.14% or less at one Watt (see later comment) throughout the whole frequency range. For group "A" tubes output before distortion was seen on the oscilloscope was 15 Watts depending on the specific tubes used. With group "B" tubes the corresponding output was 24 Watts and around 30 with noticeable distortion.
For those of you who are graphically inclined, I included a spectrum analyzer shot of a 1000 Hz sine wave and a few square wave images. I only included square wave response images as the sine wave ones were perfect copies of the input signal at all frequencies.
The initial results were below the 0.15 % range and until I can clear up the noise problem I don't want to make any additional claims.
They looked a lot like the ones at one Watt. This is as I have noted on several occasions a difficult to address topic. Imaging is excellent, very stable centering, separation is limited only by the other equipment (they are mono blocks after all), detail is excellent, and the sound has that quality of warmth that you would expect from a tube amp.
My personal feeling is that the JJ KT77 tubes have the most refined sound while the JJ 6L6GC and the Gold Lion KT88 tubes have the best bass. The KT88 tubes are of course louder. After Thoughts I always have ideas after the project is done and working. I used mid to upper grade parts and I estimate it was about $150US per channel for the parts.



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