JJ 2A3-40 DHT Single ended triode, power amplifier

A place for DIY project discussions.
Forum rules
1. No ad-hominem
2. No spamming or shilling
User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Tue Dec 12, 2017 4:20 pm

For those interested, here is the circuit for the audio:
About as simple as it gets, for a three stage amplifier.
6AU6 voltage amplifier, gain of 25 drives a 6AQ5 miniature power valve, gain of 8, which drives the DHT output stage.
No feedback.
6AU6 input stage is biased with a white LED, which doubles as an "on" indicator, when placed behind a front panel, red Fender jewel lamp lens.
Image
The smoothing filters in the power supply (bottom) are duplicated on the other channel, so what we effectively have is a split power supply, once it divides in two after the rectification and smoothing choke.

Now here's an interesting discovery: on a whim, I decided to see how my NVA P20 passive would sound, feeding the SET power amplifier. All I can say is WOW!
The P20 just "goes" with the valve power amp. The sound was good with my existing switched attenuator, but with the P20, the whole passive/valve setup just hangs together superbly well. All sources have benefitted and the overall presentation and dare I say "musicality" is much better, the P20 digging out the music like a JCB.

Lovely :grin:
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

User avatar
guydarryl
Posts: 988
Joined: Wed Jul 11, 2012 10:43 pm
Location: suffolk

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by guydarryl » Tue Dec 12, 2017 8:14 pm

I love your idea of using the drawer handles as feet - great mind at work (rest of the design just goes straight over my head).
LP12,Ittok,DV10X5,Phono2(twin supply),P50/A40's,LS5,SSC,Rega Ela mk1.
Sony cdp xb930,Alessandro ms1

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Wed Dec 13, 2017 9:05 pm

Drawer handles make great Art Deco barrel feet.

Here is the power supply schematic:
Image

This illustrates nicely, the "split" nature of the supply once the juice leaves the 10H choke.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

eagwok33
Posts: 36
Joined: Wed Nov 01, 2017 9:18 pm
Austria

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by eagwok33 » Sun Dec 17, 2017 2:43 pm

Thank you Steve for sharing your SE tube amp project with schematics here on the forum. The amp looks fantastic! 8-) I'm sure it sounds great, too! :)
As it seems - looking at your schematics - you run the JJ 2A3-40 closer to their max. design parameters for the anode voltage to gain more power from the tube. Have you tried this JJ DHT tube also with the normal 2A3 parameters according to the RCA specification (250V anode, -45V grid, 60mA)? And if yes, what is the difference in sound to the parameters used in your design?
I love the sound of a SE 2A3 amp. For me the 2A3 is a wonderful tube with a magical sound! :-)

I'm currently using a pair of Emission Labs 2A3-S in my DHT monos, but with mainly the classic 2A3 parameters (260V anode, -45Vgrid, 60ma). The EML tubes sound great with standard specs and are really well made. It's not easy these days to get a really nice pair of original 2A3s (talking about double plates as single plates are anyway crazy expensive and therefore no option for me).

Wonderful project and very nice fit and finish! Congratulations!
Best,
Norbert
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Sun Dec 17, 2017 3:33 pm

Hi Norbert,
Thanks for the positive comments about the amp.
I haven't tried the JJ at the normal 2A3 operating points. I can't compare the two without changing the HV transformer secondary voltage taps. This would also alter the operating points of the input and driver stages, so the comparison would not work.
However the 2A3 40 is a great sounding valve all the same.

I would love to try a pair of EML solid plate 2A3s and I intend doing so next year.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

eagwok33
Posts: 36
Joined: Wed Nov 01, 2017 9:18 pm
Austria

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by eagwok33 » Sun Dec 17, 2017 5:22 pm

Ok, I understand! Thank you for your reply, Steve!

The JJ 2A3 is a great sounding tube and really priced fair for sure. The EML are unforunately more expensive but really made well. A lot of people only regard the original NOS RCAs, Sylvanias, etc. as the real thing but I have to say after trying some NOs pairs and the EML solid plate pair in my amps that the EMLs are at least on par with NOS tubes. In the bass definition department they are better in my opinion.

Worth a try for sure...
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Sun Dec 17, 2017 11:12 pm

Thanks Norbert,
Once I've got hold of some EMLs, in the new year, I'll report how they sound.
I've always liked the 2A3/6B4G family of tubes. As you say, they seem to sound "just right"
NOS prices are stupid, so I'm glad I found the JJ 2A3-40.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Tue Dec 19, 2017 10:52 pm

Image
Final version of power supply uses a hybrid bridge rectifier.
This config gets the most music out of the amplifier. The difference is not subtle.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Tue Jan 09, 2018 8:39 pm

Final version of the PSU my arse :lol:

This is the current version of the amplifier power supply:
Image
The smoothing choke is now in the ground rail and the hybrid rectifier bridge has been modified with backup diodes
in order to protect the power supply caps and mains transformer, should the valve rectifier develop a fault.
The ground scheme is now a star earth, which has significantly lowered the noise floor, resultng in even more music escaping from the loudspeakers.
This amp is now sh*t hot, though I say so myself.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

User avatar
SteveTheShadow
Posts: 926
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: JJ 2A3-40 DHT Single ended triode, power amplifier

Unread post by SteveTheShadow » Tue Jan 09, 2018 8:48 pm

Below is the latest audio cct:
Image
The high voltage value has been lowered, so that "normal" 2A3 valves can be used in the amp, which is now around 3.5W output.
With my speakers at 96dB sensitivity, the low power is not a problem.

It's a great sounding piece of kit, but needs efficient speakers to show its true capabilities.
The voltages on the schematic are around 10% lower than shown, due to the smoothing choke being placed in the negative side of the hybrid bridge rectifier, but I can't be arsed to alter them on the diagram. With a valve amp, it doesn't matter, within reason if the voltages are not quite right, and nobody on here is likely to build it anyway. ;)
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Sealed cabs with Fane 12-250-TC 12" full range drivers. Also, Winslow Burhoe/Roy Allison/Richard Dunn influenced semi-omnidirectional.

Post Reply