Researching a parafeed tube head-amp - transformers

[SomekPoland]

Friends,

Can you please recommend me transformers for a parafeed headphone amplifier? I'm aiming at around 3-4W output power. Load impedance between 32 and 300 Ohm (but more on the 32 Ohm side, as I like planar headphones).

Thank you!

 

[Windcrest77]

I don't understand why the need for that many watts for phones. Sowter and Lundahl have costly headphone output transformers. I've been waiting to try these $20 Edcor 32/300 ohm line level transformers I picked up as parafeed for headphones. I use 300 ohm phones. You'd need an anode choke too.

https://edcorusa.com/collections/ma...nced-or-unbalanced-line-matching-transformers

 

[artosalo]

I agree.
Usually headphones is driven with some milliwatts.

 

[DontHertzMe]

+1. Very, very few headphones need anywhere near that much power. Unfortunately, manufacturers have been touting crazy high power outputs as a way to differentiate themselves. Unless you have some of the low-sensitivity HiFiMans, <1W is all you need.

For example, the Sennheiser HD650 need a paltry 12mW to reach 110dB.

Spend some time with the calculator here: https://www.headphonesty.com/headphone-power-calculator/

 

[SomekPoland]

I have the HiFiMan HE6SE, and they require lots of power to sing. HiFiMan states min. 2W, but from my experience, 3-4 is a good sweet spot.

I appreciate you guys telling me about the power, but that is a requirement for me.

Sowter 8665 doesn't have the power handling I need at only 2,5W @ 50Hz. Lundahl doesn't have a parafeed HP transformers.

The Edcor mentioned by @Windcrest77 might be a great solution for most applications if the sound quality is there.

 

[wrenchone]

I used a ungapped version of a Transcendar transformer designed for headphone duty in one of my headphone amp projects. That transformer is probably now unavailable. I'll have to go back and listen to the design again to see how it fared sonically. I used a 13DR7 with current source loading on the small triode of the pair as an input gain stage, with LED cathode biasing on the big output triode. I used some Wima 10uF MKPs for output coupling. I may try subbing some Russki 10uF paper/oil caps to see if there's a sonic difference.

The project is described here:
https://www.diyaudio.com/community/threads/se-vt-headphone-amplifier.339328/

I tried both a parafeed and conventional single-ended approach with a gapped XFMR.

 

[rdf]

3-4 is a good sweet spot.

HIFIMAN specs the HE6se V2 at 50 ohms. Four watts into 50 ohms is ~14 volts rms or 40 volts peak to peak. HIFIMAN's sensitivity spec doesn't reference an input level (volts? watts into 8? into 50?) so you may be better off choosing an OPT based on voltage instead of power.

 

[wrenchone]

I picked my output XFMR based on turns ratio. Right now, I have gapped and ungapped versions of Transcendar's headphone XFMR option, and some Electra-Prints generated as the result of a contentious back-and-forth with Jack. I've also used some small toroidal 60Hz transformers as parafeed outputs, though the roll-off was fairly severe due to the stray capacitance. Edcor has some ungapped line duty transformers I might try. I have driven AKG 240s and some 30 Ohm Grado cans. I'm looking for a reasonably inexpensive headphone that will be a little more subjectively nicer than the Grados. In contrast to the Grados, that sit on top of my ears and mash them with the stiff headband, I'd like something that surrounds them instead. One of the options I'll try if I get the time is to mod some Yamaha orthodynamic phones with extra felt pads for damping, as described on several web sites.

 

[SomekPoland]

HIFIMAN specs the HE6se V2 at 50 ohms. Four watts into 50 ohms is ~14 volts rms or 40 volts peak to peak. HIFIMAN's sensitivity spec doesn't reference an input level (volts? watts into 8? into 50?) so you may be better off choosing an OPT based on voltage instead of power.

Funnily enough, it's actually 64 Ohms.
Very good suggestion, cheers. My problem is that I don't know too many good transformer manufacturers that make stuff like this.

 

[wrenchone]

Here is another option for parafeed - you would want to use choke loading or some sort of current source loading for the 12AQ5 final. This design uses feedback to simulate triode characteristics for the 12AQ5 output tube. Details are here:
https://www.diyaudio.com/community/threads/12aq5-partial-feedback-hp-amp.347143/

 

[dukua]

I have the HiFiMan HE6SE, and they require lots of power to sing.

I'm using 2A3 parafeed monoblocks to drive HE6SE, OPT is amorphous LL2774. Have also bunch of 10W parafeed Trancendars for headphones manufactured by Gery to my specs in 2020.
While Transcendar is high quality and very respectable parafeed OPT for headphones undoubtfully, amorphous zero-gapped Lundahl sounds like no transformer at all - 100% transparent.

 

[mwiebe]

If it is really parallel feed transformers you are looking for then they would be ungapped.

Carnhill VTB 2291 parallel feed 10K/600 or 150 ohms
<http://www.audiomaintenance.com/downloads/carnhill_design_guide.pdf>

Magnequest B7s fit the bill but these are no longer made.

Radio Shack 32-1031B, a 70V 10W line transformer had nickel core as was very nice for the money. Edcor in the US used to make all nickel 10K/600 5W with no gap and I assume other transformer makers could do the same. Impedance matching on the output at low power levels is not critical.

Here is the Carnhill VTB 2291 stuffed into a 185mm by 115mm box. Series feed solutions are more compact.
Matt

 

[dukua]

Looks like Radio Shack used an unusual marketing approach for the 32-1031B model (made in China).
While other transformer manufacturers (from UTC to Jensen & Cinemag) everywhere proudly screams about their nickel models, Radio Shack did not put a word on the packaging: