[wdahm519]

Title pretty much sums up what I'm looking to do.  I just finished up my EHHA Rev A build and I'm already itching to start a new project.  In this case however, I'd like to find a project for a headphone amp using 2A3 or 45 style tubes (SET) -- or a 300B amp.
 
I've done a good amount of searching but nothing has really popped up. These are pretty popular as super hi-fi amps but buying them costs a lot of money.  I'd much prefer to build something myself.
 
Any ideas?

 

[wdahm519]

Anyone?

 

[dsavitsk]

There is nothing really different about building a 45 amp for headphones or for speakers. You probably will want a quieter power supply, but frankly any speaker that can be driven by a 45 is so efficient that it needs a pretty quiet power supply to begin with. Still, a regulator is your friend here. Same goes for the filament supplies. So, pick your favorite schematic -- I think Tubelab.com's TubelabSE is probably a pretty good place to start, and it comes with a PCB.

That said, your contention that this is the way to make a super hi-fi amp is probably incorrect. Yes, the 45 is a linear tube. However, the compromises you must make in the design for headphones will undo that linearity. For instance, at least for a single feed amp, the output transformer will need to be sized for the tube, which will make it large, which necessarily reduces its fidelity. You do much better with a 6H30, 6C45, 5687, etc. and a smaller OPT with less of a gap. Or, go parafeed. In either case, while you can use an off the shelf OPT with a resistor in parallel to the secondaries, something custom made for a headphone load will work much better.

 

[FrankCooter]

I've probably built over a dozen DHT based headphone amps. Like Doug says, they're no short cut to a "super hi-fi" sound, but properly implemented, can produce a rich, lush, warm, but accurate presentation that is very appealing and hard to find elsewhere. Currently I'm running a two stage amp based on a CCS loaded type 56 directly coupled to a triode-connected type 46. The 46 drives a 7k:32 Electra- Print output transformer. The cathode of the 46 sits on a CCS bypassed with a 70uf PIO cap. Filament power is supplied by individual current regulators. B+ is supplied by dual-mono tube voltage regulators fed from an LCLC filter. Rectifiers are low noise Schottky diodes. This is the amp I brought to the recent NorCal meet and used to drive Purrin's LCD-3.  For me at least, this is about as far as I can take this technology. All this comes at a price. Be prepared to spend $700+ for parts for a similar amp.
 
If this sort of thing interests you and you want to see more, do a Google image search for FrankCooter.  I'm always happy to share my designs and provide assistance for DIY projects.  Fell free to PM me if you're serious about building a DHT amp.

 

[wdahm519]

 
Quote:

I've probably built over a dozen DHT based headphone amps. Like Doug says, they're no short cut to a "super hi-fi" sound, but properly implemented, can produce a rich, lush, warm, but accurate presentation that is very appealing and hard to find elsewhere. Currently I'm running a two stage amp based on a CCS loaded type 56 directly coupled to a triode-connected type 46. The 46 drives a 7k:32 Electra- Print output transformer. The cathode of the 46 sits on a CCS bypassed with a 70uf PIO cap. Filament power is supplied by individual current regulators. B+ is supplied by dual-mono tube voltage regulators fed from an LCLC filter. Rectifiers are low noise Schottky diodes. This is the amp I brought to the recent NorCal meet and used to drive Purrin's LCD-3.  For me at least, this is about as far as I can take this technology. All this comes at a price. Be prepared to spend $700+ for parts for a similar amp.
 
If this sort of thing interests you and you want to see more, do a Google image search for FrankCooter.  I'm always happy to share my designs and provide assistance for DIY projects.  Fell free to PM me if you're serious about building a DHT amp.

 
$700 is no issue for me.  I will PM you for further details as this is pretty much exactly what I'm looking for.

 

[c12mech]

Frank, look for a PM from me also.  I've been looking for something like this for a while.  Your amps look amazing and from what I read sound as good as they look.

 

[macm75]

You will have to go two stage given the low mu of a 45 or 2A3.  I built a single tube 171a (keep this tube in mind too - globes are cheaper than 45) HP amp and it was fine for low night time listening - you will not rock the phones out with this.  A single tube 45 with step up input transformer can get you there - maybe not much more $$ than two112a/01a/56/26/27/37/etc NOS input tubes and individual filament supplies for them.  If using these types of input tubes, as Frank does, go direct coupled given you will only need ~150 more volts higher B+ than what you would normally need for a cap coupled 45 or 2a3 and you free yourself of an ugly cap (my goal is to always get rid of these any way possible).
BTW, Doug's suggestions gets you there in one stage.  His Electric Ave design is fantastic (at least I love it).

 

[WesternE]

I like the SET-OPT for efficient headphones. But your thread title suggests you are looking for power . For example the 45 it may be easy to build a 1 or 2W speaker amp but when dealing with inefficient headphones like the new orthos it just seems impossible, you have to swing so much voltage at the plate that distortion is high. On the opposite end of the spectrum when dealing with efficient headphones for a 45/2A3 I highly recomend coleman DC regulators for the filament (or the tent labs), another tube to look at is the 4p1L with its 8x gain 1200rp and excellent linearity. But bang for the buck high efficient phones don't dismiss the 5842/6c45p/triodeconnected D3A/c3g. When you really look at the curves and work out the power you don't gain much volume by going to expense of a 45 DHT setup. You want a black-black background and it is much easier/cheaper to do with the little high gm idht's. It is complete myth that an SET is high distortion (with high efficient phones), with an spud set (original 12 yo Andrea Ciuffoli design but perfected further since) there is practically no audible amp distortion at normal listening levels with Grados. The sound is pure and amazing with a spud set, literally no caps in the signal path. But these designs are best matched with high efficiency phones. The other variable is high impedance phones, to match the impedance means a high DCR secondary (possibly poor damping?), here I would look close at the small preamp nickle core parafeed designs. I am very tempted to try a high power 2A3 or 6S4S SET for hifiman orthos, I have recently fell in love with the sound of the hifi-man orthos. But their inefficiency means they need as much voltage swing as a 10W SET speaker amp, 200V swing across the primary. Thats a lot of signal and distortion. I hope to come to a means to design an SET for these new headphones, maybe an EL34, or an expensive dangerous HV GM70 or big buck transformers for a 300B, the light bulb just hasn't lit above my head yet. So my recommendation for what its worth is decide on what headphone you love and want to design around. let us know what headphones you are liking the most and we should start the ball rolling.

 

[mtoc]

Any upadtes yet? Just took a look at the eddie curremt 4 45 headphone amp's price and wet my pants.