what output transformer for a 6sa7 Headphone Amp

[colin.hepburn2]

Hi All
Well I’m considering anther Headphone Amp I have a circuit in mind but its OTL which I am not to keen on it uses a 6SN7 the output valve is the 6as7 I want to use a gapped output TX but not sure what I m looking for to match the 6sa7 valve it has to drive Headphone from 32 up to 300 ohms
On the other hand I am secretly thinking of the mother of all headphone amps a 2A3
I may just do this so I am assuming the output TX will be 2.5k or 3k for the 2A3

 

[picklgreen]

The mother of all headphone amps is a 2A3? Your kidding right?

 

[cotdt]

The mother of all headphone amps would be a EL84.

 

[picklgreen]

I guess you have never listened to a Cary 300SEI than...the mother of all headphone amps is a single ended 300B! EL84? what amp would this be?

 

[Voodoochile]

Apparently it takes more than one mother.

They all sound like fun projects to me.

 

[colin.hepburn2]

Quote:

Originally Posted by picklgreen /img/forum/go_quote.gif The mother of all headphone amps is a 2A3? Your kidding right?

Well it would be a bit different and may we’ll sound good too but which output transformer to use I haven’t seen a 2.5k or 3k with sec windings for Headphones I still want to no which is a good matched output single ended TX for the 6AS7 tube for headphones as I have a set of these to try out
You help is welcome
Thanks
Colin

 

[AndrewFischer]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif The mother of all headphone amps would be a EL84.

EL84 isn't even a Triode. They were used mostly in lower priced hi-fi amps and receivers.

But I've heard some really good sounding EL84 amps. My favs used triode connected EL84s in push pull parallel.

As for the OP, Sowter make several headphone output transformers with taps for both 32Ω and 300Ω headphones. I've seen schematics using the 8665 but I've lost the link.

 

[cotdt]

Quote:

Originally Posted by AndrewFischer /img/forum/go_quote.gif EL84 isn't even a Triode. They were used mostly in lower priced hi-fi amps and receivers. But I've heard some really good sounding EL84 amps. My favs used triode connected EL84s in push pull parallel. As for the OP, Sowter make several headphone output transformers with taps for both 32Ω and 300Ω headphones. I've seen schematics using the 8665 but I've lost the link.

but as you mentioned the EL84 can be configured in triode mode, so it can be a triode too. and it sounds very nice, the good ones anyway.

 

[AndrewFischer]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif but as you mentioned the EL84 can be configured in triode mode, so it can be a triode too. and it sounds very nice, the good ones anyway.

The first bit about not a triode was a little sarcastic. I'm not a member of the "it has to be a singled-ended directly heated triode" club.

I've seen the EL84 trashed more than once. I think it is because that tube saw a lot of use in mid-grade consumer gear that just doesn't sound good. Didn't then, didn't now.

Anyone who discounts the EL84 out of hand should give a serious listen to a Manley Stingray.

 

[colin.hepburn2]

Hi All
Well I’m considering anther Headphone Amp I have a circuit in mind but its OTL which I am not to keen on it uses a 6SN7 the output valve is the 6as7 I want to use a gapped output TX but not sure what I m looking for to match the 6sa7 valve it has to drive Headphone from 32 up to 300 ohms Heres the Schematic for the 6AS7 H Amp

 

[colin.hepburn2]

.

 

[AndrewFischer]

Transformer choice depends on where you set your load line and how much current is flowing through the tube. If you stick with 50mA you could try the Sowter 8976. £127.75 each. Ouch. You could cut down the current and go to one of the smaller ones, but then why use a 6080 tube?

I've mostly seen the 6080 used OTL, mostly because it can stand up to the abuse. If you are switching to a transformer coupled amp, you could change to something like a EL84 and use a less expensive transformer.

You could also use the 16Ω tap on a Hammond and then multiply the input Z by 2. That would work for 32Ω headphones but not for Sennheisers. But you don't need an output transformer for 300Ω

Does this amp absolutely have to work with both high and low Z headphones?

 

[colin.hepburn2]

Hi Andrew
Thanks for your reply
Does this amp have to work with both high and low Z headphones well no but I wanted to open up the range of useably headphone at the moment I only have the senn HD650s I could build to otl but I’m not happy with that It seems unsafe to me
Thanks
Colin

 

[AndrewFischer]

It is as safe as your output caps

The output impedance of a 6AS7G is something like 300Ω. I don't remember if that is for a single triode or for both sections in parallel. Anyway that's really low for a tube. Low enough that they work well in all sorts of OTL circuits.

To select a transformer, you can use the 4*Rp rule. That's about 1200Ω. Higher is ok, with the penalty of reduced power. For headphones, I'd guess a primary in the 2k to 3K range would be good. As far as I know only Sowter have an off the shelf transformer with the specs you are looking for. Current exchange rates make that transformer very expensive in USD. If you poke around you may find something else that will work.

The 6AS7G is notoriously hard to drive. The amplification factor is really low. 2?? anyway, make sure that 6SN7 is putting out enough swing.

 

[colin.hepburn2]

Hi Andrew
Thanks again for the info on the output TXs the sowter are bit price so unless I can find some else I will Go OTL the Schematic I posted is not my design the original is on headwize it uses a (6922/6DJ8/ECC88) http://headwize.com/projects/waarde1_prj.htm

This amp bares an uncanny resemblance to the Woo3and the darkvoive on ebay
I have so far only built the Mapletre Mad + which is modd up plus my WD PhonoII
So still learning this tube stuff
So all help is welcome
I was considering this as the front end of the 6AS7 may have some psu voltage to sort out though
Your thoughts please...