OTL Headphone Amp project.

[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]

Update:


Seeing as I'm really in the mood for doing some diy scratch-build Tube amp projects this year, the diy scratch-build OTL Headphone amp is officially scheduled for 2023, well, it'll give me something "constructive" to do with my time anyway, besides, it'll fun.

You know what? getting back into doing some diy builds this year again, has made me re-discover why I got into electronics in the first place, it's because it's a whole lot of fun to go through the process of getting together all the parts for your build projects, and put them all together into a finished working electronic device, you get a huge sense of achievement out of it knowing you built it yourself, you also learn far more by doing practical things, rather than sitting in a classroom, well that's how I seem to learn best anyway.

[DrNomis_44]

Here's a link to one interesting OTL Headphone amp design article, it looks really simple and easy to build, just notice how simple the circuit is compared to a solid-state design of similar performance capability:

https://headwizememorial.wordpress.c...ic-headphones/

[DrNomis_44]

Update:


I think I have finally found the OTL Headphone amp circuit I want to build, this particular design uses a set of three 6N1P twin triodes and it looks like it can drive load impedances down to about 64 Ohms, some of the other designs I was considering building aren't happy with driving low impedance loads as low as that, here's a link to the webpage:

https://headwizememorial.wordpress.c...one-amplifier/


This one looks like a relatively easy one to build and I think Evatco stock both the 6N1P tube and the Hammond 269AX power transformer.

Turns out I was right, Evatco do stock the 6N1P tube:

https://www.evatco.com.au/audio-tube...es/6n1p-tubes/

Evatco don't seem to have the Hammond 269AX power transformer in stock, but, Mouser Electronics do seem to stock it, so I'll have to order it online from there.

https://au.mouser.com/ProductDetail/...NOOQQymA%3D%3D


I just found the perfect application/use for my diy scratch-build 6N1P OTL Headphone amp build, currently I'm using a pair of wireless headphones with my new Blaupunkt HDTV, while the wireless headphones works with it, it has a nasty habit of the rechargeable battery going flat at annoying times, I can't use a pair of wired headphones with the Blaupunkt because there's no headphone out socket, but, it does have stereo RCA Audio Line-Outs on the back, all I would need to do is connect up my 6N1P OTL Headphone amp to the stereo RCA line outs and plug in a pair of headphones.

[DrNomis_44]

One of my makerspace students is building one of these

http://www.parasitstudio.se/stripboa...p-punch-amp-v2

That looks like a really cool first diy project for all those wanting to get into amp-building, cheers for posting that.

[DrNomis_44]

Update:

Been making some steady progress on my OTL Headphone amp build, I've elected to go with this design:

https://headwizememorial.wordpress.c...aIUo0sN21SxpNE

I looked on the Evatco website and as it turns out, they do stock 6N1P Twin Triode Valves, they may also stock the Hammond 269AX Power Transformer as well.

I'm going to be mounting all the components, minus the main power supply filter caps, on tagboards, so, I'm now in the process of designing suitable layouts for the tagboards, I'll need to make three of them, one for the power supply, and two others for the left and right channels, this is going to be a fun build.

I've made a hand-drawn copy of the full schematic and will post a scan of it later on......stay tuned!!

[DrNomis_44]

Update:


As promised, here are scans of the full schematics for my 6N1P OTL Headphone Amplifier build I'm currently working on:



Full schematic of the power supply:

[DrNomis_44]

Update:


I just ordered three new Svetlana 6N1P tubes online from Evatco, for my 6N1P OTL Headphone amp build, Evatco don't stock the Hammond 269AX Power Transformer I need, but fortunately Mouser Electronics do have it in stock, so I'll order it online from Mouser Electronics, they may also stock all the resistors and caps that I'll need too, so I'm going to do some browsing on their website and see what I can find.

Jaycar stock this big diecast aluminium box which I will be using as the chassis for my OTL Headphone build, it's a little bigger in size than the one used in the original build article:




Here's a link to the original build article:

https://headwizememorial.wordpress.c...one-amplifier/


Oops....I just found out that the Hammond 269AX power transformer only has a 115/125V AC primary winding, so I'm going to have to go looking for a similar specced transformer with a 240V AC primary.

Evatco do have a Hammond 369AX power transformer in stock that looks like it'll do the job, it has a 250V CT @ 115mA secondary winding, a 6.3V CT @ 2A Heater winding and a 240V AC primary, so I'll order one of them instead.

[Simon Barden]

I’m wondering why you don’t just get a 240v to 6.3V transformer (if such a thing exists) and just use straight 240V instead of 250V for the secondary side. More efficient and you only drop the secondary voltage by 10V/4%.

[Simon Barden]

You could even use a simple 6.3V DC power supply for the valve heaters for reduced hum rather than the transformer, rectifier and capacitor combo. Plenty of adjustable output voltage DC power supplies available.