Transformers for valve headphone amps

[fireworks]

What are good sources of transformers for valve headphone amps ?
I'm thinking of a simple single-ended circuit. The headphones I'll be using have 32 ohms impedance.

Alternatively, I might build them myself. What are good sources for the laminated sheets I would need ?

 

[wa2ise]

I was going to suggest using reverb transformers, like these https://www.tubesandmore.com/products/transformers_chokes?filters=Type%3DReverb%20Driver but I don't see any frequency specs.
Or 22921 Fender Reverb Driver Transformer MADE IN USA and they mention use in a headphone amp, but again no mention of the frequency range. Guitar amp transformers are likely more limited than hifi ones...

 

[fireworks]

Thanks I'll take a look.

 

[famousmockingbird]

What valve are you looking to use for finals? This will help narrow down output transformer options due to primary load requirements.

 

[JMFahey]

I'm curious about something.

Building a tube headphone amp, which is way more complex and expensive than going SS with some chipamp, or even an Op Amp (think NE5532), should at least in theory be justified by better quality in some aspect.

But reverb driver transformers are cheap narrow bandwidth, poor quality designs 😱, designed to drive narrow bandwidth, poor audio quality reverb tanks 😱

Am I missing something?

 

[famousmockingbird]

Good design compromise would be use valves for the voltage gain and go SS for the finals to drive the headphones eliminating the need for expensive HiFi iron.

 

[00940]

There's some choice.

Sowter makes special transformers for headphones: see here

Electra-print has experience with winding transformers for headphones, according to your specs.

If you go parafeed, there's a lot more choice... I used cheap little edcor PCW10K-7K/300-32 in a recent build and they're very decent.

 

[madisonjam85]

I ordered a pair of 5k-32 ohm xfmrs from Electra-Print. Haven't done anything with them yet so I can't comment on them. They were about $130 each shipped, and I got them in about 4 weeks.

 

[MrCurwen]

I always use Hammond 125D in parafeed, for both SE and balanced. 10k : 4 ohm.

Works perfect for pretty much any kind of headphones. Also speakers can be driven with the same amp, same output.

 

[famousmockingbird]

I believe the Hammond 125 series frequency response is only 100Hz-15kHz.

 

[fireworks]

What valve are you looking to use for finals? This will help narrow down output transformer options due to primary load requirements.

I'm looking at using 6E5P for finals, maybe even as a unique active element. Nothing is set in stone, yet.
I'm also considering using a cathode repeater as a final stage which would allow me to eliminate the transformer. This would make the circuit cheaper but especially much lighter.

 

[fireworks]

So far I've found Edcor tranformers to be reasonably priced:

https://www.edcorusa.com/gxse5-8-5_5k
https://www.edcorusa.com/xse10-4-8k

Both weigh 1.2 lbs, which means that my headphone amplifier would weigh 2.4 lbs in output transformers alone ! 😱

They are both very oversized for a headphone amplifier: 5 and 10W.

If possible, I would like smaller and lighter ones.

 

[fireworks]

There's some choice.

Sowter makes special transformers for headphones: see here

Electra-print has experience with winding transformers for headphones, according to your specs.

If you go parafeed, there's a lot more choice... I used cheap little edcor PCW10K-7K/300-32 in a recent build and they're very decent.

Edcor PCW10K-7K/300-32 is a good suggestion as it is smaller, cheaper and most importantly only weighs 0.4lbs! 😀
Sowfter seems to be much more expensive, so it's out for the moment.

 

[00940]

I'm looking at using 6E5P for finals, maybe even as a unique active element. Nothing is set in stone, yet.

It works... see this post 😀 Sorry for the shameless promotion.

The little edcor are btw cheap in the US (11$) but quite expensive in Europe (29$ at Don-Audio).

If you use a cathode follower as output, the hammond 119da is used at good effect by Mappletree

 

[MrCurwen]

I believe the Hammond 125 series frequency response is only 100Hz-15kHz.

I wouldn't use them in serial feed for hifi, but in parafeed the frequency response is flat from like 10 Hz all the way up to bat territory.

Also general sound quality of the OT improves drastically in parafeed, since there is no DC.

 

[famousmockingbird]

For you it is not an issue with the parafeed. Just making a point for fireworks that in a standard SE design those transformers are not hifi.

I don't have much experience with parafeed but I have heard you can have low frequency problems if the parafeed capacitor is not chosen with great care.

 

[counter culture]

That FR for the Hammond's is full power. You probably get better than that at headphone power levels.

 

[MrCurwen]

With half of spec max DC frequency response starts usually at something like 25 Hz, then rises rapidly with increasing current.

Anyway why do serial feed in a low power application? It's not like we do tube amps for their overall efficiency? I say always go parafeed for headphones at least.

 

[counter culture]

Anyway why do serial feed in a low power application?

Because it's absolutely conventional, and single-ended, transformer in the plate circuit is in some ways both considered the best performer and the most likely to deliver that characteristic valve sound.

I'm not trying to start an argument here, I'm just pointing out that that topology is considered attractive in some quarters. Parafeed and hybrid are somehow second best, with OTL acceptable if it'll work with your phones.

 

[Vincent77]

I always use Hammond 125D in parafeed, for both SE and balanced. 10k : 4 ohm.

Works perfect for pretty much any kind of headphones. Also speakers can be driven with the same amp, same output.

I confirm: I used the same Hammond transformers in a parafeed D3a amp, and surprisingly, they sound VERY good with my Sennheiser HD650 headphones!
I also drive bookshelf speakers with it.