The all DHT SET Headphone Amp

[regal]

This is for dynamics, not an average listening level, its called headroom. I think speaker guys have about the same target's. Many target 115, but this I don't think is needed for an SET.

Better explanation here:NwAvGuy: More Power?

[12B4A]

That is a clearly written and empirically supported piece of writing meant to advance a subjective viewpoint of how much loudness an amplifier/headphone system should be able to attain. It is based upon using a corner condition in the sub-genre of audiophile recordings of classical music. I can't say that I would use this as a design goal for my purposes but I now have a better idea of what have been the unspoken assumptions that you've been working under and I respect that as we all have different goals.

[regal]

Originally Posted by 12B4A

That is a clearly written and empirically supported piece of writing meant to advance a subjective viewpoint of how much loudness an amplifier/headphone system should be able to attain. It is based upon using a corner condition in the sub-genre of audiophile recordings of classical music. I can't say that I would use this as a design goal for my purposes but I now have a better idea of what have been the unspoken assumptions that you've been working under and I respect that as we all have different goals.

Yea I have a large collection of raw (un mastered/uncompressed music) with huge dynamics compared to commercial stuff. With the spreadsheet one can change the headroom goal to meet your indicidual goals (that's the nice thing about aspreadsheet), just trying to help people understand the relationhip between what is asked of the output tube/transformer and actual headphone sensitivity/impedances, in no way is the spreadsheet "static", its a tool.

[mogliaa]

All,
Firstly many thanks to Vegard for sending the 307a sample for tracing. I had very little time today for this and hopefully can do further testing next week. Initially in my view 307a is better to be used with Schade feedback and is not that great in triode mode. Also created a SPICE model which haven't tested so would be great if someone can play with it and report any issues.
307a DHT in triode and Schade feedback | Bartola Valves
Hope this helps!
Cheers,
Ale

[iko]

Ale, thanks for taking the time and doing this! Much appreciated!

[merlin el mago]

@moglia
Many thanks Ale to post 307a curves.

@Iko
YHPM

[regal]

Originally Posted by mogliaa

All,
Initially in my view 307a is better to be used with Schade feedback and is not that great in triode mode. [/url]
Hope this helps!
Cheers,
Ale

Thankyou, this rules this one out, I guess this is much worse linearity than even a modern eastern 300B.

[regal]

Just an update, since Ale ruled out my 307a's I found a pair of RCA 2A3's for $80. Now the DAC is done (ecept designing a case) and I can focus more of the DHT head-amp. I am looking forward to an amp with more power than my little WE417 can provide.

I settled on a transformer its 5k/8+8+8+8. This is a great combination, very versatile and efficient, it has a newer type C core but I am going with this mainly for the expertise in winding (interleave, low DCR, etc.)

On the front will be a cinemag input transformer to give a 4Vrms from the balanced DAC outputs.

Simple single input/driver : a Phillips E182CC. which is basically a super select 5687. Just a single CCS common cathode for each channel from each section. I like this tube because it has a high enough Cg to use the full 4Vrms input. Then coupling capacitor, fixed bias for the 2A3. I just like oil caps so the pragmatisst can shoot me for ordering AmpOhm copper in oil's, they have worked nicely for me in the past.

Power supply is going to be a SSHV2 per channel feeding only the output tubes. I am over sizing the transformer (Edcore) so if I want to upgrade to the 40W 2A3's (basically 2.5V 300b's) it will be easier. Of course coleman regs for the output tubes. The nice thing about the SSHV I you can have a high prefilter B+ and stimy down the voltage with a big resistor without affecting the sound (the first stage of the SSHV is a CCS.)

It will be a 2 chassis build with umbilical cord. I am looking for a chassis that is big enough that I can switch to 841 DHT's should a pair ever find my way. I strongly considered a pair of the 4p1l's with a 1:2 IT but 4 SSHV's and the heat sinking required would be very difficult.

The nice thing about the E182CC is it is a linear tube that really simplifies the build, gain is 24 (much higher than a 5687 or 6n6p), but has a distortion profile that matches the DHT output well enough for good harmonic cancellation which I find to be the real reason for needing a DHT driver when I was number crutching. The new 841 model Ale posted simulates amazing, but these tubes are impossible to find right now.

That's it in a nutshell, pretty simple except the coleman and SSHV regulators and the output transformers, but I hope others are building and if you do share your experience. I would be happy to post schematics but its basic enough I think anyone can figure it out. Key is low noise and flexibility.

[Abszero]

Regal,
I played recently with Rod's regulators and they are wonderful. Eas to build and to adjust. Just make sure you have a decent size heatsink. I used a flatback standard finned Al heatsink size 100x75x40mm for a regulator that feeds 1.3A and it stays warm to touch. When I used a heatsink 1/2 of the size above it got very hot. Also it is important to make sure you design the raw power supply to fit your needs. I used a 75w 2x9V at 4A to feed two of Rod's regulators on 4.2V/1.3A filaments.
Hope this helps.

[regal]

Originally Posted by Abszero

Regal,
I played recently with Rod's regulators and they are wonderful. Eas to build and to adjust. Just make sure you have a decent size heatsink. I used a flatback standard finned Al heatsink size 100x75x40mm for a regulator that feeds 1.3A and it stays warm to touch. When I used a heatsink 1/2 of the size above it got very hot. Also it is important to make sure you design the raw power supply to fit your needs. I used a 75w 2x9V at 4A to feed two of Rod's regulators on 4.2V/1.3A filaments.
Hope this helps.

Thanks for the tip, I'm going to try a common mode choke for the raw supply along with the capacitors , unfortunately it will have to be in the power chassis and share umbilical cord. Did you use a separate raw supply for each tube ? Hopefully can find a domestic dual bobbin transfo supplier like he uses in England.