sound of 45 v. 205d v. 2a3 v. 300b for headphones

[dsavitsk]

I am looking into building a headphone amp based upon jack elliano's ultrapath design. (here's a link to a schematic http://www.electra-print.com/ultrapath.html ) I am considering one of the above tubes and thought I'd ellicit people's impressions about the relative merits of each. Yes, I know ths is probably over the top, but since the Cary 300SEI is the only headphone amp that has ever really done it for me, I think this may be the right way to go. Any thoughts or other candidates?

-d

[arnoldc]

each of those tubes has a different character, so it will be difficult to answer what *you* will like.

As for me, I made a simple 2A3 headphone amp, that doubles as a power amp and I like it. However, I can't lug it along, so I end up with my CMoy most of the time.

In the near future, I'd like to build a 12B4 head amp, so I can bring it to the office...

Cheers!

[astouffer]

Any one of those tubes will output over a watt and blow the headphones off your head. Maybe look into parafeed for the output transformer. How does the Cary amp drive headphones?

[dsavitsk]

Originally posted by arnoldc
each of those tubes has a different character, so it will be difficult to answer what *you* will like.

I guess this is really the question here. I am looking for vague descriptions of the character of these tubes to help decide which to design around. I have 300b based power amps, so I have a sense of what those are like, but I am not familiar with the others. What I am looking for is something full and lush and warm.

Originally posted by arnoldc
As for me, I made a simple 2A3 headphone amp, that doubles as a power amp and I like it.

I'd be curious to see more of your design.

Originally posted by astouffer
Any one of those tubes will output over a watt and blow the headphones off your head. Maybe look into parafeed for the output transformer. How does the Cary amp drive headphones?

Everytime I think I am starting to understand something about this stuff, I am invariably knocked down a few pegs. My understanding, however, was that so long as the voltage is where it should be, that the phones would control how much current is drawn. I know that lots of other headphone amps can put out a watt or two, yet people still seem to use them for headphones, but perhaps there is just a step here that I don't understand. As for the Cary, I guess I don't really know how they do it. I assumed there would be an appropriate tap to the ouput transformers, but maybe not? Maybe they just use a resistor divider?

[Tweeker]

The other variable here is the headphones, impedance on these can be anywhere from 24 to 300 ohms. If using an output transformer (which youd have to for conventional SE), lower impedance headphones will be louder.

[dsavitsk]

I should have been specific. 32 ohms (Grado RS-1)

[arnoldc]

dsavitsk, i won't be able to describe it based on a headphone amp, but as an amp

205 - never got to own one

2A3 - for me is general purpose, from classical to heavy metal which is my music preference, can be fast and furious;
45 - for me this is more suited for vocals, i.e. astrud gilberto;

i made a quick and dirty 2A3 head amp for my Philips SBC HP-890 can which is 32 ohms, and while i draw it up a gain, let me just describe it to you...

PSU is using 1N5408 - 470uF - 5H choke - 470uF to put out around 300V B+ for the 2A3 and 150R - 47uF going to the 12AX7.

driver is a simple textbook 12AX7 (i need gain!! i need small tube!!) Rk=1K, plate R = 220K, cap coupled via Auricap 0.22uF to 2A3 with Rk=880R, OPT is custom-wound with 16 ohm tap, and this is where I get the headphone output. When the headphone is engaged, it is paralleled with a 15R resistor (because I'm lazy!)

the 2A3 filaments are DC but the 12AX7 is not.

though not perfect and may have many faults (choice of driver, use of normal OPT, etc), it sounds good enough to me.

ps.

there's an ALPS blue in front, and i use Sovtek 2A3 (my RCA 2A3 is on my main 2A3 amp)

[tubelab.com]

I have built a lot of amps, and I have used all of these tubes except the 205-D (you can't get those cheap). I can't tell you what to build but I can offer some suggestions. Each of these tubes do indeed have their own character, and you should choose the one that suits your tastes. The character of each tube through headphones will be similar to the character of each tube through speakers. If you choose a tube based on the sound through speakers, use the same speakers to audition each tube. Since any of these tubes has enough power to "blow the headphoned off of your head", don't let power be a factor in your choice. My choice of these would be the 45, but that is just my preference.

Most amps use a resistor divider to drive the headphones. The reasons for this are many. The non obvious one is the fact that headphones couple directly to your head therefore they are real efficient compared to speakers. This sensitivity lets you hear all of the detail in the music AND all of the flaws in the amp. If there is any hum or microphony in the amp (inaudible with speakers) it would be loud if the phones were connected directly to the amp. The resistive divider reduces the sensitivity by about 10db.

With that thought in mind, the amp must be designed to eliminate as much hum as possible. In most cases this means DC heaters.

Full, lush and warm, that kind of describes the 2A3.

[dsavitsk]

Thanks for all the suggestions.

I am thinking that I nmight try 45's as it seems that with a little lookng and a little luck one can find them for not too much money. If I like them, I'll buy some fancier ones later.

That said, I am thinking that to start I might pick up a pair of the hammond 125xSE output transformers. They are about $65 per pair and have a 32ohm secondary tap to boot. If this experiment works, I can upgrade the iron and the tubes later. So, can anyone tell me whether I want the A, B, C, D, or E version of the transformer?

[arnoldc]

E (125ESE)

That's what I used for my prototypes, and if you upgrade later you can still use them for more prototypes