Tube headphone amp designs?

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ambience exists

ambience exists

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Joined 2008
#1
Howdy folks,

I am looking for a simple design for a tube headphone amp for use with some Grado's. I am a bit overwhelmed by the designs I am finding online, does anyone know of a proven design that would be very DIYable with proven results? Say, something with an EL34? I would be down for a triode/pentode switch and definitely something without OT's. I would be willing to give up tube rec in the interest of cost (college student) Single ended would be ideal. If anyone has done something similar, I would be very interested. I also have a stash of 6L6's is I could do anything with those worth listening to...

Thanks!
 
#2
EL34's and 6L6's are absolutely too powerful for headphones.

I've had excellent results with the Bijou which can be gotten in kit or PCB board only form.

Headwize has a nice collection of projects.

Since headphones don't need a lot of juice, little preamp tubes are sufficient for providing power for the job. At least in most cases.
 
#3
Hi!

I assume your grado's have about 32 ohms impedance (like most Grado's I have seen...) This is a really low impedance for tubes, even 'power tubes' as the EL34.

You state that you don't want an output transformer, which I assume is due to the costs associated with such a device? One alternative would be to use a mains toroid... I am thinking about something along the lines of the headphone amp made by member dsavitsk...

http://www.ecp.cc/less-pressivo-plus-plus.html

One could substitute the autoformer at the output for a small toroidal (also in parafeed mode), something like 2x115V and 2x9V/ Put all windings in series, obtaining one 248V winding, tapped at 18V. Connect the Grado's across this winding, and the autoformer action will convert the 32 ohms impedance to a more tube friendly 5k (approximately). Load the tube with a CCS or resistor, select a nice coupling cap and a potentiometer at the input and it should sound nice.
 
#4
Sounds pretty good, I like the looks of really simple circuits. I am still on the search for a very pure circuit with minimal components. Could I essentially also just build one of the tube preamp circuits I am finding and just tie the output to my phones?
 
#5
whitelabrat said:
EL34's and 6L6's are absolutely too powerful for headphones.
Click to expand...

This is simply not true. They are capable of more power than you want, but you don't have to use it. They would not be my first choice in tubes, but they will work fine.

As for designs, to my ear, Grados sound best with a low Zout and high damping factor. There are basically four ways to accomplish this -- output transformers, a solid state output stage, brute force (lots of tubes in parallel), or negative feedback. That list is in decreasing order of preference.

Additionally, you likely don't need any gain. Instead, all you need to do is attenuate and provide current. For details on some measurements of this, see http://www.ecp.cc/less-pressivo-plus-plus.html
 
#6
ErikdeBest,

I would actually spend the money for an OT if it would make my circuit simpler, but I really like the looks of the amp in the link. I have built tube amps but have not gotten into CCS or more advances parafeed style designs yet. I would really like to optimize this circuit for the Grado's too, and yes, you are right about the impedance.
 
#8
ambience exists said:
Sounds pretty good, I like the looks of really simple circuits. I am still on the search for a very pure circuit with minimal components. Could I essentially also just build one of the tube preamp circuits I am finding and just tie the output to my phones?
Click to expand...

It depends on the design, but the answer is likely no.

For what it's worth, a basic mosfet source follower will be hard to beat for sound quality and it will cost a ton less than a tube amp with similar driving ability. Here's an example of how to do it: http://www.headwize.com/projects/szeke1_prj.htm

It won't light up like a tube, but maybe you could use Nelson Pass' trick and use a light bulb as the load.
 
#9
ambience exists said:
dsavitsk ,

do you know of a good circuit using OT's? What tube would you use?
Click to expand...


6H30, 6N6p, 5687, 12B4 could all be decent choices depending on power/gain options.

Here is one example of how to do it: http://www.ecp.cc/less-pressivo-build.html

As Erik says, some of the small power toroids can make really good and inexpensive parafeed transformers. For single feed, Edcor makes some good and cheap options that can work. For what it's worth, I am agnostic as to whether single feed or parafeed is a "better" technology -- both have advantages and disadvantages.
 
#10
Wow man,

That circuit looks real simple, I bet it could be built really pure. I guess sometimes I think about the high voltage and transformers and whatnot associated with tubes and just want to do a nice SS project. I have never done one before though, any advice?
 
#11
I've been playing with this design lately which has shown a lit of promise: http://www.diyaudio.com/forums/showthread.php?s=&threadid=141865

Ignore the DAC part, and just look at the output stage. It is basically two differential source followers. Since they are at the same voltage, there is no DC through the OPT which is 150+150:150+150 and can be used as a step up for a little gain, or not. I got some from Cinemag OPTs that are 50% nickel for $18 each. The 80% nickel are about $30. The output is balanced but can be single ended by tying one side of each transformer to ground.

If your source is single ended, you'll need a phase splitter. There are tons of ways to do this, but a cathodyne might be a neat option for a unity gain hybrid headphone driver. I am actually working on this and I'll post a schematic later.
 
#14
dsavitsk said:


This is simply not true. They are capable of more power than you want, but you don't have to use it. They would not be my first choice in tubes, but they will work fine.

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Click to expand...

Mia Culpa, dsavitsk is correct. Thanks for calling me out. Stax electret headphones require the use of a power amplifier to drive them. A 30w amplifier using 6L6's or EL34's would be a fine choice in that case. Other electrostatic headphones may do well with a tuned down big power tube. It would certainly be a first for me to see a output transformer less EL34 headphone amp. 😱
 
#15
Hello. I'm going to build this http://headwize.com/projects/showfile.php?file=strain1_prj.htm headphone amp. schematic is simple and i like when ps is allso very simple. It is Kurt Strain desing and i ordered all parts today. all parts costs abaut 200€ here in finland. I think it's not too bad. I'm gonna use it with my grado sr-80 headphones. I will tell you more when i get the parts and when amp is constructed and ready for measurements and listening.
 
#17
One more: http://wavebourn.com/forum/viewtopic.php?p=20859#p20859

but there is a mistake on the drawing:

R2 should be 1.2 KOhm, R3 should be 100 Ohm, in such case an idle current will be about 66.6 mA.
Power dissipated on R2 will be 5.33 W.
I would take 4 resistors 4.7K 2W each in parallel to avoid usage of wirewound resistors capable to dissipate 6W and more (they have an inductance that we don't need).
 
#18
Speaking of 6N6P's...
try this one, adapted from a schematic by H. Ahammer to avoid the pricey E288CC of the original.
 

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#19
You said simple? Can I blow my horn? 😀

If you want a simple one, I made one from a spud amp that I turned into a headphone amp.

It drives my Grado SR80i, Audio Technica ATH AD700, and AKG 240 Studio quite nicely from a Harman Kardon HD750 HDCD player.

An externally hosted image should be here but it was not working when we last tested it.


The original schematic is show below

AK-100schema.jpg


I have since replaced the cathode resistor and capacitor with a Yellow LED.

Other planned changes include regulated filament supply and MOSFET-regulated HV supply.

Cheers 😀
 
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