My friend is planning to make a tube headphone amp as his first tube project, so what would be a good starting point? He was considering this, but it doesn't seem to have global negative feedback, and isn't IRF510 a switching MOSFET?
NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier
Anyways, what kind of project would you recommend? He already has ECC82s from guitar amp stuff, so it would be a bonus if he can use those. Also, preferrably no output transformers..
NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier
Anyways, what kind of project would you recommend? He already has ECC82s from guitar amp stuff, so it would be a bonus if he can use those. Also, preferrably no output transformers..
I am using HD800 as a sample (which impedance is 300 ohm)
HD800’s maximum long lasting input power is 500mW. To reach that output (of 500mW), your amplifier needed to deliver 35 Vpp (peak to peak voltage) for HD800! That means you needed an amplifier with at least ±18V working voltage (or a single DC voltage above 36V). Unfortunately, this is a common problem with high impedance headphones
HD800’s maximum long lasting input power is 500mW. To reach that output (of 500mW), your amplifier needed to deliver 35 Vpp (peak to peak voltage) for HD800! That means you needed an amplifier with at least ±18V working voltage (or a single DC voltage above 36V). Unfortunately, this is a common problem with high impedance headphones
Merlin Blencoe wrote a good article about tubes at low plate voltages. The 12au7 can perform quite well at 12 volts if setup properly!
http://www.valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf
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If you have the budget a transformer coupled D3A is easy to build and works well. I also built an amp based on the Wheatfield HA2 which is good.
http://www.pmillett.com/Wheatfield/manual.pdf
I have been looking for a well designed tube headphone amplifier design and I have not found one I liked. It seems like everything I find is either an adaptation of a preamp or amp that is converted to headphone use or something trying to use the tube as an effect.
If you find something that is really worth building please let us know.
If you find something that is really worth building please let us know.
Try one of the Aikido circuits for High Impedance Phones
I've had very good success with the Aikido amp configured for HPA use.
Aikido Noval Stereo PCB & Kit
It may not be the latest "in" thing but it's a good solid performer for high impedance HPA's.
Cheers, Steve
I've had very good success with the Aikido amp configured for HPA use.
Aikido Noval Stereo PCB & Kit
It may not be the latest "in" thing but it's a good solid performer for high impedance HPA's.
Cheers, Steve
https://www.dropbox.com/s/jtbllax0vj52aix/circuit2.jpg
This circuit (shows one channel only) comes from many comprehensive tests. The input stage has a triode single-ended structure with constant current load, which provides good linearity and enough amplification gain. The constant current source is formed by a low noise, 1.7V red LED and Q5 transistor. A blue LED is series connected in order to light up the bottom of the tube. The output of this single-end stage is directly coupled to the Q6 transistor base, an emitter follower stage, then directly connected to the PowerMOS Q2. This provides enough driving capability to headphones. By using direct coupling, we not only reduced our cost, but also eliminate quality issues (for example: leakage current, ESL, ESR, etc.) from coupling capacitors.
This circuit (shows one channel only) comes from many comprehensive tests. The input stage has a triode single-ended structure with constant current load, which provides good linearity and enough amplification gain. The constant current source is formed by a low noise, 1.7V red LED and Q5 transistor. A blue LED is series connected in order to light up the bottom of the tube. The output of this single-end stage is directly coupled to the Q6 transistor base, an emitter follower stage, then directly connected to the PowerMOS Q2. This provides enough driving capability to headphones. By using direct coupling, we not only reduced our cost, but also eliminate quality issues (for example: leakage current, ESL, ESR, etc.) from coupling capacitors.
The Aikido, as push pull and with some feedback wired in, should also work nicely for 32 Ohm cans.
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As already pointed out, the 12AU7 works perfectly well at low voltage. There is already a raft of headphone amplifiers based on the approach you linked and you can buy them off of eBay (and Parts Express) for not a lot of $ - they are ripe for some DIY 'tweaking' too. They have been well received by many people.
Bravo Audio V2 Headphone Amplifier Class A 12AU7 Tube Valve Hybrid AMP Preamp | eBay
Bravo Audio V1 Review - The Little Headphone Amp That Could
The stock Aikido pcb has no feedback, but for DIYers should be no Problem to wire some in. See attachment. Zout falls to ~4.5 Ohm, which should be plenty good for 32 Ohm phones.
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Check out my improved tube headphones design:
http://www.diyaudio.com/forums/tubes-valves/191632-improved-tube-headphones-amp.html
I still have one PCB left. You are welcome to it for the cost of shipping.
Cheers
Ian
http://www.diyaudio.com/forums/tubes-valves/191632-improved-tube-headphones-amp.html
I still have one PCB left. You are welcome to it for the cost of shipping.
Cheers
Ian
Thanks for the offer, I'll ask my friend if he is interested.
However, I was thinking about a design without output transformer. Would it be feasible to use two small pentodes, such as EL95 or EF95 as a push-pull output stage?
I would have thought that would be rather difficult. Pentodes have very high plate resistances which makes them unsuitable for transformer-less output stages.
Cheers
Ian
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