The tube headphone amp project: design overview

[@a.r.5124]

very interesting to absorb the design thoughts. coincidentally i chose the ll2765 20ma for the darling (first build, yet to be done) that I'm unsure of how it can be wired for multiple output. will you use more than the 300r out?

[@EduardBroekman]

My plan is to use the 32 and 150 ohm output so a 300 ohm headphone creates a ~13K impedance for the tube and for a 55ohm headphone (on 32), it's about 10K. With two 4PDT switches we can switch between the 2 output configurations. However, I noticed the 4P1L quite likes delivering current, so I do need to have a listen to it on the 300ohm output. With using/offering the 32-150 ohm switch, we can support a wide range of headphones (~25-300 ohm): a lot of models from Hifiman, Audeze, Dan Clarke have impedances in the 25-60 ohm range (if I remember them all correctly).

[@jedi-mic]

Maybe try the Vishay metal film resistor probably a better choice! are those wirewound inductor free?

[@EduardBroekman]

Yes, probably best for the grid resistors, but so far never had oscillations with the 4P1L...

[@rickg8015]

Looks sweet.. What operating point are you using for the 4P1L for now?

[@EduardBroekman]

I'll measure it again, but it was about -17V / 19mA

[@raoulselten9480]

HELLO thanks for the video, i'm currently in the process of deep diving into learning about electronics. and videos like these help! how have the Lundahls been for you? i'd like to make an (auto)transformer volume control sometime soon, do you think any Lundahl's could be considered remotely usable for that goal? cheers from Tilburg!

[@EduardBroekman]

Hi Raoul. I have not yet compared Lundahls to vaunted / other premium transformers but compared to budget transformers I heard, I find them well worth the premium in sound quality: they're generally high bandwidth, of extremely consistent quality and have good availability. As for your autoformer question.. I'm not sure exactly what you're thinking of and I can't really comment on modifying them for use as an auto-former.. for single ended connections, it just seems that i-cores are the way to go.

[@raoulselten9480]

@@EduardBroekman oehh you changed your youtube name, nice! okay thanks! hope you have a nice day 😊

[@Nihil1st1347]

I got a broken OTL headphones amp. The proper tube heating fails. It's known as Pharao. Can anybody help me with this? The builder disappeared.

[@EduardBroekman]

If you are safe to work with high voltages when the amp is open, even a multimeter can quickly tell where the power is failing (filament voltage is easily checked), replace fuse, or that the tube is simply bust.. else you'll need to find someone local to you (Location?).