Has this ever been done?
Is it a good/bad idea?
Are there any DIY designs available for an intermediate level DIY'er? (we used to use the term "advanced beginner" in ski school, LOL)
Don't ask me why, but I keep thinking about this and looking. But, because the search terms are a little too generic I haven't found anything significant either way.
Is it a good/bad idea?
Are there any DIY designs available for an intermediate level DIY'er? (we used to use the term "advanced beginner" in ski school, LOL)
Don't ask me why, but I keep thinking about this and looking. But, because the search terms are a little too generic I haven't found anything significant either way.
6L6 is obviously overkill as headphone amplifier, but it is still a interesting choice that I also was contemplating because it is cheap, easily available, and there is a large selection of brands to try. To keep things as simple and cheap as possible, I would build this as "spud" amplifier. A standard single ended output stage with 5.5k or 6k output transformer. Input directly feeds the 6L6 grid trough a coupling cap, with 100K grid leak resistor and 1k grid stop resistor. The line-level input from the preamp should be enough to drive a standard headphone to ear splitting volume and maybe more. The 1954 STC datasheet lists a "low power" class-A configuration: 6L6 triode connected, 250V plate voltage. 6K load, and 500 ohm cathode autobias resistor to set 40mA anode current (-20V at the grid). Output power should be 40mW with 0.5% 2nd harmonic distortion when input signal amplitude is 2V. The only unusual component is the output transformer with 32 ohm (or more) output impedence taps, but I believe that a standard 5W 5.5k/8 ohm transformer would work just as well with a 32 ohm headphone; maybe I will add a small resistor in parallel to the headphone. Plate dissipation is 10W only: a small EL84 power transformer would be enough, and the chassis may also be small due to the lack of preamp tubes and the low power transformers. This is only a speculation based on a old datasheet diagram, but I will probably try it with a 32 ohm headphone soon.
So, apparently Ampsandsound is making "The Forge" tube headphone amp that uses KT88/EL34/6L6GC output tubes.
https://www.headphones.com/communit...-ampsandsound-and-headphonescom-collaboration
I guess that means it's doable. Now my interest is piqued even more. There has to be a good sussed out design out there somewhere.
https://www.headphones.com/communit...-ampsandsound-and-headphonescom-collaboration
I guess that means it's doable. Now my interest is piqued even more. There has to be a good sussed out design out there somewhere.
This is my 6L6 headphone amplifier.
The circuit is trivial, and the build is easy. The transformers are cheap parts from Aliexpress. The output transformers are sold by many sellers on that marketplace, and also fitted on the cheapest 6P1P and 6V6 tube amplifier kits. They are advertised 5k to 4-8 ohms 5-8W 40mA primary current. They are actually more like 3W parts. The primary winding resistence is pretty high, 330 ohm, but the inductance is also high and they have a nice shield. I've found them good enough for this headphone amplifier: full audio bandwith is there at headphone level power. Hammond and Edcor sell comparable or better versions. The power transformer I used is bigger than needed but I wanted to keep it cool, because it is wound with little separation between primary and secundary windings. The winding looks like a vintage transformer from the '60: it is funny what they sell on that marketplace. The required current is 3A on the 6,3V filament supply and 60-70mA on the high voltage supply. The hardwood enclosoure is a Zeller #25305 also sold by Amazon EU. A metal enclousure would be better, but wood can be used because power consumption is low and little heat is produced. I tried several 6L6 and EL34 tubes and I like EL34 most, but this is a subjective preference. Wildly unmatched tubes can't be used because the sound level will be unbalanced between channels. The circuit is trivial and should also accept 6V6 and basically anything by changing the cathode resistor and the socket wiring as required. I only tried a few headphones. The sound level is just ok with the Hifiman Sundara (magnetic planar), Sennheiser HD590 and Beyerdynamic DT990 pro 250 ohm. If I connect the amplifier directly to the source (nominal 2V) the volume knob needs to be near the maximum; if I connect to my preamplifier (4V) the volume is turned in a more normal way. It is not enough for Beyerdynamic DT990 600 ohm, while a very sensitive "DJ monitor" closed headphone with extremely enfatized bass range is louder than I like, but there is also an almost imperceptible faint hum in the background at idle - not even a issue with the kind of music this headphone is meant to be used.
The audio quality is good. I am still evaluating it, but there are no obvious flaws and it compares well with other headphones amplifiers I've built previously. This came as a surprise because the circuit is extremely simple, transformer set and tubes are pretty cheap, and the tubes are forced to work outside the normal range. I was anticipating unbearable background noise and insufficient gain, but it has not been the case in practice. Sometimes the simplest things are the ones that works.
The circuit is trivial, and the build is easy. The transformers are cheap parts from Aliexpress. The output transformers are sold by many sellers on that marketplace, and also fitted on the cheapest 6P1P and 6V6 tube amplifier kits. They are advertised 5k to 4-8 ohms 5-8W 40mA primary current. They are actually more like 3W parts. The primary winding resistence is pretty high, 330 ohm, but the inductance is also high and they have a nice shield. I've found them good enough for this headphone amplifier: full audio bandwith is there at headphone level power. Hammond and Edcor sell comparable or better versions. The power transformer I used is bigger than needed but I wanted to keep it cool, because it is wound with little separation between primary and secundary windings. The winding looks like a vintage transformer from the '60: it is funny what they sell on that marketplace. The required current is 3A on the 6,3V filament supply and 60-70mA on the high voltage supply. The hardwood enclosoure is a Zeller #25305 also sold by Amazon EU. A metal enclousure would be better, but wood can be used because power consumption is low and little heat is produced. I tried several 6L6 and EL34 tubes and I like EL34 most, but this is a subjective preference. Wildly unmatched tubes can't be used because the sound level will be unbalanced between channels. The circuit is trivial and should also accept 6V6 and basically anything by changing the cathode resistor and the socket wiring as required. I only tried a few headphones. The sound level is just ok with the Hifiman Sundara (magnetic planar), Sennheiser HD590 and Beyerdynamic DT990 pro 250 ohm. If I connect the amplifier directly to the source (nominal 2V) the volume knob needs to be near the maximum; if I connect to my preamplifier (4V) the volume is turned in a more normal way. It is not enough for Beyerdynamic DT990 600 ohm, while a very sensitive "DJ monitor" closed headphone with extremely enfatized bass range is louder than I like, but there is also an almost imperceptible faint hum in the background at idle - not even a issue with the kind of music this headphone is meant to be used.
The audio quality is good. I am still evaluating it, but there are no obvious flaws and it compares well with other headphones amplifiers I've built previously. This came as a surprise because the circuit is extremely simple, transformer set and tubes are pretty cheap, and the tubes are forced to work outside the normal range. I was anticipating unbearable background noise and insufficient gain, but it has not been the case in practice. Sometimes the simplest things are the ones that works.
