Could this tube be used for a headphone-amp?

[Mikael Abdellah]

Mi first tube-project was supposed to be the Headwize 6N1P OTL Headphoneamp, but I couldn't get it to work properly. When I tried it with my AKG 240 Monitor, the gain was WAY too high and there was quite a lot of humm, so I just put it aside for a while. But since I hade allready bought the headphones I, still need a good amp to drive them. I don't wanna build an OTL amp. I wan't a simple yet good sounding single ended amp, preferably with just triodes. Then I saw the 6AS7. Would that be a nice output-tube for a small 2-channel amp? I guess it won't have any trouble driving my 600ohm phones OTL, but I wan't a transformer.

http://www.svetlana.com/docs/products/glass/6AS7.html

This has nothing to do with this thread but I thought it could be useful. I've found the frame-page for svetlana.com, so that you can browse the site: http://www.svetlana.com/docs/tubeframe.html

[Colt45]

yeah, ive seen designs for it before

half a 6AS7/6080 in cathode-follower, transformerless, per channel.

never tried it though.


If you want a tranny, why not use a better tube for the job then? you don't need so much damn current when you have an OPT.

Not to mention that a 6AS7 in SE will give enough power to melt your headphones several times over, and that the impedance ratio would need to be about 2:1 to match a 6AS7 to your 600 ohm headphones, so you'll have to wind the OPT yourself i guess...

blah, just overkill. use some little double triode or something instead.

you've already got those 6N1P's, you could use those fine with a little teeny opt.. parafeed or something.

im going to sleep.

[Morse]

Hi Mikael;

As far as your 6N1P amp is concerned, did you try the "optimized" Morgan Jones circuit with NFB? I built the same amp (with 6922's instead of 6N1P's so I had to drop the operating point accordingly) and encountered excessive gain at first, too. After I added the NFB loop, the gain dropped to about 6 or so and it's very useable with either my Senn 570's or Senn 600's.

As far as hum is concerned, did you try using DC on the heaters? I had the same hum problems 'til I switched to DC and floated my heaters' up about 12V.

Good luck with all your projects!!
Morse

[Mikael Abdellah]

Originally posted by Morse
Hi Mikael;

As far as your 6N1P amp is concerned, did you try the "optimized" Morgan Jones circuit with NFB? I built the same amp (with 6922's instead of 6N1P's so I had to drop the operating point accordingly) and encountered excessive gain at first, too. After I added the NFB loop, the gain dropped to about 6 or so and it's very useable with either my Senn 570's or Senn 600's.

As far as hum is concerned, did you try using DC on the heaters? I had the same hum problems 'til I switched to DC and floated my heaters' up about 12V.

Good luck with all your projects!!
Morse

I haven't tried NFB but I don't think that's my problem. At least not all of it. Since I have quite a large PS-cap (2200uF) I tried do disconnect the mains-transformer and only ran the amp on my big cap and AC-heating. Dead-silent... I couldn't detect any humm anywhere what-so-ever. This might have to do with cathode-to-heater potential. But I doubt DC-heating would take care of all my problem. I'm not sure I like OTL-amps. I like the galvanic (?) separation I get from at transformer, as well as the transformation of the total signal. If I have a few mV of humm at the output, it will almost be completely erased in the transformer.

I reckon I'll get 1W output from a 6AS7, more than enough to fry most headphones.

[fdegrove]

Hi,

The obvious advantage the 6AS7G has over the 6N1P is power and current drive.

It can drive any kind of headphones with aplomb, I like its' sound too, and it can drive capacitive cable with no problem.

Moreover you can transformer couple it instead of using a cap at the output and still retain all the advantages mentioned above.

Just promise me not to spread the word on your dislike for OTLs for you probably disliked the coupling cap in the SE design, not the OTL.

Cheers,


P.S. OTLs are for real men.

[zobsky]

why are output transformers preferred to capacitors for this application?


thanks

[fdegrove]

Hi,

why are output transformers preferred to capacitors for this application?

Are they?

I wouldn't favour one over the other in general...although I'd love to get rid of both of them...

If I had a headphone amp only driving headphones I'd say let's go for the cap coupling (not all will agree).

Now if that little bugger had to drive both headphones and a set of highly effecient speakers, I go for the xformer...see?

And if it were to be for my own use there'd be neither...go figure.

Cheers,