[Jerm111]

Hi Everyone,

This is the first build thread I've done on Head-Fi, thought I'd give it a try.

I'm building a 'Papa Rusa' HPA which is a design published by Wauwatosa Tube Factory. I have already built an OTL amp but was looking for something that would work with all different impedance headphones.

I haven't seen many other builds using this design, I'd be interested in hearing if you have tried it.

The design uses the Russian 6S45 tube in para-feed configuration with CCS regulation. It also features a switchable Hi/Lo Z output. The schematic is below.

Started off with these two nice bits of walnut, initial milling exposes the beautiful grain.

I cut the miters on my table saw then used my DIY CNC router to machine some pocket details.

Four sides ready to glue up.

Managed to preserve the grain match around the front and sides of the chassis

Planing the faces smooth after glue-up using a block plane.

Moxon vise is the ideal clamping method for a workpiece like this. (Please excuse my messy workshop, at this point I was in the middle of renovating my basement and the garage was a total mess.)

I water-jet cut the sub-plate and top-plate.

Countersinking all the sub-plate holes.

All of the holes would be covered up by the top plate. I really like this approach as it allows you to make as many mounting holes in the sub-plate as you need to hold components without compromising on the aesthetics.

I machine these transformers covers from billet aluminium.

Mockup, starting to think about potential colour schemes.

Glueing in some corner braces, these perform double duty to strengthen the mitres and also provide a surface for the sub-plate to rest on.

After a couple coats of Osmo Poly-X the grain really pops.

Sub-plate painted in matte enamel.

Thinking about the internal layout. A custom machined regulator heatsink/mount can be seen in the middle.

I also like to include a DAC (Khadas Tone Board) in my HPAs, I find it's very convenient to plug directly into my computer as the majority of my headphone listening is done at my desk at work.

A bunch of brackets, water-jet cut and folded 1.4 mm stainless steel

This is the PSU wiring which I tried hard to keep tucked away in the far corner to avoid noise issues.

Overall view of where I am up to with the wiring, all of the PSU and tube wiring is done.

Next up will be inputs, coupling caps, OTX and headphone jack.

I machined this custom knob an a 5-axis mill. This shows the part band-sawn off the waste material.

Mounted on a mandrel on the manual lathe where a faced the front surface and hand-shaped a nice round on the edge.

I think the shape suits the case nicely. Everything will look a bit more cohesive after I paint the transformer covers, top-plate and knob.

On previous builds I have anodised these components but it is a fussy process and can be tricky to get consistent results, not to mention the cost outlay. I've been thinking about trying Cerakote or DuraCoat in the future but for this one I think I will probably fall back to the good old spray paint.

I'll leave it here for now and I'll post again after I have made some progress.

In the meantime, please let me know what you think. I'm a real amateur when it comes to the electronics side of things, so I am happy for some feedback/suggestions!

This project is helping me learn the basics of tube theory and I am building my way up to building a Single-ended 2A3 stereo amp, perhaps a 2A3 or 45 HPA??

I'd love to build a 2A3 HPA with a capable headphone output but it seems difficult to get output transformers that suit both speakers and headphone. I've seen that it is possible to use a resistor arrangement get a headphone output but is this a compromise?

Cheers,
Jeremy

 

[msing539]

Beautiful... ok, I'll take one.

 

[kevin gilmore]

the insulators you are using for the 10m45s are not sufficient and will punch thru. you need the ceramic insulators and the appropriate sleeve for the screw.

 

[Jerm111]

the insulators you are using for the 10m45s are not sufficient and will punch thru. you need the ceramic insulators and the appropriate sleeve for the screw.

That’s interesting, are you sure?

The kit I am using (see below) has a screw insulating washer and the insulating film is “Thermasil III” material, according to the data sheet it has a “dialectic breakdown voltage” of 26,300 volts/mm. I assume this is relating to the thickness which is 0.15 mm. This should result in being able to withstand 3,945 volts? Am I interpreting this correctly? I’m happy to swap it out with something more suitable if I need to.

 

[kevin gilmore]

there are published pictures of the first diy-t2 with it arcing around the insulator to the screw. At 600v which is more than the 400v you are using.
easy to change later if necessary.

 

[Jerm111]

there are published pictures of the first diy-t2 with it arcing around the insulator to the screw. At 600v which is more than the 400v you are using.
easy to change later if necessary.

That's interesting, I will keep it in mind.

Yeah I'm actually significantly less than 400V as well.

 

[Jerm111]

I spent many hours over the last couple of days troubleshooting a minor hum problem, it's dead quiet now and sounding great!

I still have a few aesthetic things to finish off, painting the knob and top-plate etc.

See photos below, these were taken prior to fixing the hum. I ended up changing the grounding a little bit and using shielded cable all the way up to the grid resistors.

 

[Derivative]

I am totally lost when it comes to the technical side of this build, but can I commend your choice to keep the grain match around the chassis - it looks fantastic and gives it a very professional look. well done!

 

[carlman14]

Dang, that's some really satisfying-looking wiring! Way cleaner than I bother making my wiring haha. Congrats and nice build!

 

[Jerm111]

I am totally lost when it comes to the technical side of this build, but can I commend your choice to keep the grain match around the chassis - it looks fantastic and gives it a very professional look. well done!

Thanks! Yeah I really like that feature as well, I think it's really worth the trouble

 

[Jerm111]

Dang, that's some really satisfying-looking wiring! Way cleaner than I bother making my wiring haha. Congrats and nice build!

Thanks, yeah I really enjoy trying to make the wiring really clean.

 

[tomb]

Outstanding casework and build! The circuit is also a close resemblance to Dsavitsk's ECP Audio L-2. I would strongly recommend that with that much work put in, you change out those Edcors for a pair of Cinemags or amorphous core Lundahls.

 

[Jerm111]

Outstanding casework and build! The circuit is also a close resemblance to Dsavitsk's ECP Audio L-2. I would strongly recommend that with that much work put in, you change out those Edcors for a pair of Cinemags or amorphous core Lundahls.

Thank you!

Do you think upgraded OTXs would make a big difference? Where is the best place to source Cinemags or Lunahls, I could be tempted if I can fit them into my enclosure and they aren't too pricey. I am located in New Zealand, shipping can be prohibitive.

Where can I find the schematic for the ECP L-2? I've had a quick search but couldn't find much on that amp, I've found the Torpedo T series amps which you are building, they seem to be of a similar vein. I actually remember coming across the Torpedo project during my research for the Papa Rusa, I might need to dig a bit deeper into some of the build threads.

 

[tomb]

Thank you!

Do you think upgraded OTXs would make a big difference? Where is the best place to source Cinemags or Lunahls, I could be tempted if I can fit them into my enclosure and they aren't too pricey. I am located in New Zealand, shipping can be prohibitive.

Where can I find the schematic for the ECP L-2? I've had a quick search but couldn't find much on that amp, I've found the Torpedo T series amps which you are building, they seem to be of a similar vein. I actually remember coming across the Torpedo project during my research for the Papa Rusa, I might need to dig a bit deeper into some of the build threads.

Absolutely, upgraded output transformers will make a huge difference. The Edcors are OK, but IMHO - you don't want "OK" with your superlative build. Lundahl amorphous cores can be large and very expensive. They work through exclusive dealerships worldwide, but are based in Sweden. This is a link to their distributors page: https://www.lundahltransformers.com/distributors/. IMHO, there is nothing better than their amorphous core, it just depends on whether they're affordable for you - or will fit.

The Cinemags are still significantly better than Edcors. They are the nickel-core type and you will still hear the difference immediately; it's not even close. Their transformers are only slightly larger than Edcors, at least with the PCB-based versions we used, and I think we're still talking the same relative headphone output loads and a 10K input impedance. Unless I'm missing something, that should work in your design. If memory serves, they're only about twice as expensive as Edcors and considering that Edcors are very, very inexpensive anyway, that's still not very much for a Cinemag. The Cinemag part # we used on the T3 is CM-15615PC.

Just an FYI, but a steel Lundahl (non-amorphous core) may still sound better than a nickel-core Cinemag. The Cinemag may sound more dynamic while the Lundahl is laid back in comparison, but It's a close difference. The amorphous core Lundahls win out, though, with exquisite detail second to none. As stated, the Edcors are not even in the same league with these choices, even the simple steel Lundahls.

I have a schematic for the L-2, but there are parts of it and the power supply that I believe Dsavitsk (ECP Audio) may consider IP (Intellectual Property), so I don't think I can share it. However, most parafeeds are very similar with regard to the actual tube circuit. Use the same tubes and the IXYS CCS, then you essentially have the same circuit.

 

[Jerm111]

Absolutely, upgraded output transformers will make a huge difference. The Edcors are OK, but IMHO - you don't want "OK" with your superlative build. Lundahl amorphous cores can be large and very expensive. They work through exclusive dealerships worldwide, but are based in Sweden. This is a link to their distributors page: https://www.lundahltransformers.com/distributors/. IMHO, there is nothing better than their amorphous core, it just depends on whether they're affordable for you - or will fit.

The Cinemags are still significantly better than Edcors. They are the nickel-core type and you will still hear the difference immediately; it's not even close. Their transformers are only slightly larger than Edcors, at least with the PCB-based versions we used, and I think we're still talking the same relative headphone output loads and a 10K input impedance. Unless I'm missing something, that should work in your design. If memory serves, they're only about twice as expensive as Edcors and considering that Edcors are very, very inexpensive anyway, that's still not very much for a Cinemag. The Cinemag part # we used on the T3 is CM-15615PC.

Just an FYI, but a steel Lundahl (non-amorphous core) may still sound better than a nickel-core Cinemag. The Cinemag may sound more dynamic while the Lundahl is laid back in comparison, but It's a close difference. The amorphous core Lundahls win out, though, with exquisite detail second to none. As stated, the Edcors are not even in the same league with these choices, even the simple steel Lundahls.

I have a schematic for the L-2, but there are parts of it and the power supply that I believe Dsavitsk (ECP Audio) may consider IP (Intellectual Property), so I don't think I can share it. However, most parafeeds are very similar with regard to the actual tube circuit. Use the same tubes and the IXYS CCS, then you essentially have the same circuit.

Thanks for the info, very interesting.

I'd love to try some Lundhahls.. I have been looking at their website and they only seem to list 3 headphone specific models, none with an input impedance of 10k and suitable secondaries. I think I could try and work it out with respect to turns ratio but I'm not sure how close they would be, I also have limited knowledge in this field so aren't that confident. The Papa Rusa design specifies "The various (secondary tap) configurations allow for about an 8k load with 32 ohms, a 20k load with 300 ohms, and everywhere in between with other headphones.". I also noticed that the way they have secondaries set up I'm not sure how easy it would be to have switchable secondary taps, do you have to just wire it for one specific impedance?

That leaves the Cinemags, I see that the CM-15615PC is a custom order, maybe I could just order these? Are there any published specs with info on secondary taps etc?

Please forgive all my novice questions, this is really the first tube amp I've built from a schematic by myself.