OTL Headphone Amp project.

[Marcel]

Bon Voyage my friend on your transformer-less tube journey.... It is a fairly obscure path but at least it is a path that a few others have ventured before...

In the back blocks of my memory I do remember seeing only the one time in a Melbourne meeting of interested individuals a stereo DC coupled transformer-less tube hifi amp. It was in the early '70's as I entered my teenage years, and it was an event that had all who witnessed it in an absolute tizzy... although at the time I didn't see/hear what the fuss was about and frankly I was just a little disappointed as I considered the audio source and loudspeakers were not truly up to the task ...

Since that day I have heard fully DC coupled systems and have been incredibly impressed, and by all reports that I've encountered on transformer-less tube amps they are equally incredibly impressive devices to hear...

Good luck... keep us informed... and postcard to us plenty of pictures...

[DrNomis_44]

Bon Voyage my friend on your transformer-less tube journey.... It is a fairly obscure path but at least it is a path that a few others have ventured before...

In the back blocks of my memory I do remember seeing only the one time in a Melbourne meeting of interested individuals a stereo DC coupled transformer-less tube hifi amp. It was in the early '70's as I entered my teenage years, and it was an event that had all who witnessed it in an absolute tizzy... although at the time I didn't see/hear what the fuss was about and frankly I was just a little disappointed as I considered the audio source and loudspeakers were not truly up to the task ...

Since that day I have heard fully DC coupled systems and have been incredibly impressed, and by all reports that I've encountered on transformer-less tube amps they are equally incredibly impressive devices to hear...

Good luck... keep us informed... and postcard to us plenty of pictures...

Cheers, I happen to enjoy a challenge, and this build project should be a good one.

[DrNomis_44]

Bon Voyage my friend on your transformer-less tube journey.... It is a fairly obscure path but at least it is a path that a few others have ventured before...

In the back blocks of my memory I do remember seeing only the one time in a Melbourne meeting of interested individuals a stereo DC coupled transformer-less tube hifi amp. It was in the early '70's as I entered my teenage years, and it was an event that had all who witnessed it in an absolute tizzy... although at the time I didn't see/hear what the fuss was about and frankly I was just a little disappointed as I considered the audio source and loudspeakers were not truly up to the task ...

Since that day I have heard fully DC coupled systems and have been incredibly impressed, and by all reports that I've encountered on transformer-less tube amps they are equally incredibly impressive devices to hear...

Good luck... keep us informed... and postcard to us plenty of pictures...

I just recently finished building the amplifier, and I have to say that it has exceeded my expectations, it is a real joy to listen to, at first, I wasn't sure if it was able to drive my new pair of Audio Technica ATH-M50x headphones without generating too much distortion, mainly even harmonics, but, I was very pleasantly surprised, not only was it able to drive my Audio Technicas plenty loud enough, the sound was crystal clear, my Audio Technicas are rated at 38 Ohms, my understanding is that some OTL headphone amp designs have trouble driving low impedance headphones lower than about 100 Ohms, apparently not this particular design I chose, it seems perfectly happy with 38 Ohms.

I tried connecting the line outs of my studio pc to the amp, sounded great, also tried connecting it to the headphone out socket of my new Asus gaming laptop, it also sounds great, with nothing connected to the amp itself, it is practically dead-quiet even at full volume settings, the heater supply is 6.3V DC which is floated above ground via a .22uF/630V cap, so as not to exceed the heater/cathode voltage, I put a 220k/2W metal oxide resistor on the output of the +HT supply to ground to stop the caps from over-voltaging with no load on the +HT supply, seems to work a treat, I'm getting about +306V DC or so from it under load, pins 3 and 6 of V2 and V3 are sitting at about +160V, roughly about half the full +HT voltage, I checked a few other voltages with my multimeter, and as far as I can tell, everything looks normal.