The tube headphone amplifier in figure 1 is a high current mu follower, with a 12AU7 cathode follower driven by a 6CG7. Both sections of each tube are paralleled to minimize noise. It's a zero global feedback, OTL design of pretty high quality. I use it and like it for Grado, Sennheiser, and Sony headphones. The maximum gain is about 25 dB with the 6CG7, so it pays to watch the attenuator level. This design can be used as a line preamp as well.
Click here to download the full size of the above Circuit.
Click here to download the full size of the above Image.
The power output depends a lot on headphone impedance. The circuit has significant output impedance (something like 500 ohms) which some headphones don't mind, some do. It will put out around 20 mA peak current. The output impedance is pretty much constant and independent of load, but any tube changes will greatly affect it. It runs off a 330V supply, which necessitated changing R2 to 5.6K ohms, 2W. The 6VDC filament supply is regulated with 7806 regulators. All instructions, including a chassis drilling guide and parts layout, can be found at http://home.online.no/~wsaa/otl/otl.html.
7/16/99: Revised volume control in figure 1.
1/14/00: Jason Portman writes:
The OTL is now fully tweaked and working beautifully. In fact after the conversion to DC heaters it was MUCH MORE STABLE! I have been experimenting with 3 different front end tubes. The 6CG7, 6FQ7 and my favorite, the Svetlana 6N1P. The GE 6CG7's with "white" logo seen second best in terms of level and sound quality. The 6N1P's are really much better though; they are much less muddy than the 6CG7's, have better low end, better imaging and much more transparent. Also an added benefit of their 300ma heaters is they glow quit nicely!
7/15/00: Eduard Orvisky built this headphone amplifier using ideas from Kurt Strain's and Eric Barbour's designs. It uses two 6SN7s in the mu follower (compared to Eric Barbour's circuit, R4 is reduced to 2K, 2W) and solid state and...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: