J. E. Labs PP 2A3
I'm a new DIYer, and therefore wish to have suggestions from all of you.
Most push-pull designs require either interstage transformers or center taping inductors. To avoid using these 2 components, I wish to build a simple 3-stages 2A3 push-pull, which is shown in J.E. Labs' website as follows:
http://vps.angela.com/catalog/how-to/JE_Labs/PP_2A3/
My questions are as follows:
1. Can anyone please share with me the sound quality of this amplifier?
2. How can I avoid using the coupling cap. in this design? (Any Loftin White push-pull 2A3? )
3. Can I replace the 7k output tran to 2.5k output tran.?
4. Since differential amplifier concept is used to drive the 2A3, will this cancle off the even harmonic which is believed to give better listening effects?
Thank you very much.
I'm a new DIYer, and therefore wish to have suggestions from all of you.
Most push-pull designs require either interstage transformers or center taping inductors. To avoid using these 2 components, I wish to build a simple 3-stages 2A3 push-pull, which is shown in J.E. Labs' website as follows:
http://vps.angela.com/catalog/how-to/JE_Labs/PP_2A3/
My questions are as follows:
1. Can anyone please share with me the sound quality of this amplifier?
2. How can I avoid using the coupling cap. in this design? (Any Loftin White push-pull 2A3? )
3. Can I replace the 7k output tran to 2.5k output tran.?
4. Since differential amplifier concept is used to drive the 2A3, will this cancle off the even harmonic which is believed to give better listening effects?
Thank you very much.
1. Can anyone please share with me the sound quality of this amplifier?
It should sound very good. You could build it with 6J5GT types rather than 6SN7 which would give you the possibility of trying out a lot of good sounding tubes like the 7199 and 6P5GT
2. How can I avoid using the coupling cap. in this design? (Any Loftin White push-pull 2A3? )
Use a transformer in push-pull for the second stage. Like a Lundahl LL1660
3. Can I replace the 7k output tran to 2.5k output tran.?
It's a bit low. 5K is possible.
4. Since differential amplifier concept is used to drive the 2A3, will this cancle off the even harmonic which is believed to give better listening effects?
I don't know if that would be significant. The other thing you can do is use a differential pair for the first stage with a constant current sink under it, so you could use balanced signal in if you wanted to. You would then just ground the second grid for SE input.
It should sound very good. You could build it with 6J5GT types rather than 6SN7 which would give you the possibility of trying out a lot of good sounding tubes like the 7199 and 6P5GT
2. How can I avoid using the coupling cap. in this design? (Any Loftin White push-pull 2A3? )
Use a transformer in push-pull for the second stage. Like a Lundahl LL1660
3. Can I replace the 7k output tran to 2.5k output tran.?
It's a bit low. 5K is possible.
4. Since differential amplifier concept is used to drive the 2A3, will this cancle off the even harmonic which is believed to give better listening effects?
I don't know if that would be significant. The other thing you can do is use a differential pair for the first stage with a constant current sink under it, so you could use balanced signal in if you wanted to. You would then just ground the second grid for SE input.
Hi Andy,
Thanks for the suggestions. I found a similar design shown in the following link:
http://www2u.biglobe.ne.jp/~tossie/F2A3PP-E.html
The designer use 6A6 instead of 6J5 or 7199. It's hard to get 6J5 in Singapore though.
Is there any direct coupling push-pull 2A3 withoud using inter-stage transformer or center-tapping inductor?
I've build a direct coupling 6C45 single stage SE amplifier, and when I use it to push my FE206, it simple gives me an unbelivable natural souding effect. I think it's the coupling capacitor which introduces extra time delays and distort the purity of the sound.
Thanks for the suggestions. I found a similar design shown in the following link:
http://www2u.biglobe.ne.jp/~tossie/F2A3PP-E.html
The designer use 6A6 instead of 6J5 or 7199. It's hard to get 6J5 in Singapore though.
Is there any direct coupling push-pull 2A3 withoud using inter-stage transformer or center-tapping inductor?
I've build a direct coupling 6C45 single stage SE amplifier, and when I use it to push my FE206, it simple gives me an unbelivable natural souding effect. I think it's the coupling capacitor which introduces extra time delays and distort the purity of the sound.
khooyang said:
Forget about a dc coupled PP amp. Keeping unbalanced dc out of the output transformer primary won't be trivial.
Why do you want to avoid an interstage transformer? IME no phase splitter sounds as good as a transformer. And using a 6S45P or similar driver you only need two stages.
I use a LL1660 18mA which is certainly a compromise and the results are still exceptional.
The circuit is somewhere on this forum. As chance will have it i just ended up rebuilding it to fit in a reasonable single case. The lovely 83 rectifiers are now history 
Nothing exciting circuit-wise. I use an ultrapath cap similar to Lynn Olson's amps and in this latest iteration tried to explore the low impedance PS route. PS arrangement for the 6S45P is still not finalised. With the current minimal filtering it has great dynamics but lots of hum. I might try a regulator tube as increasing either capacitance or inductance doesn't sound too good.
I also used a snubber to load the secondaries of the 1660 and greatly reduced the ringing.
Although i could draw the circuit immediately i would prefer first to find a good-sounding solution for the driver PS with minimal hum.
Nothing exciting circuit-wise. I use an ultrapath cap similar to Lynn Olson's amps and in this latest iteration tried to explore the low impedance PS route. PS arrangement for the 6S45P is still not finalised. With the current minimal filtering it has great dynamics but lots of hum. I might try a regulator tube as increasing either capacitance or inductance doesn't sound too good.
I also used a snubber to load the secondaries of the 1660 and greatly reduced the ringing.
Although i could draw the circuit immediately i would prefer first to find a good-sounding solution for the driver PS with minimal hum.
Attachments
Yeap, why don't just try out the simple RLC tube rectifier PS design? To me, the simpler and straight forward the PS design, the better the sound quality. I will normally parallel the Elec. cap. with the normal AC cap. (Solen as seen in ur circuit) to give fast and dynamic performance. Please comment if I'm wrong.
Khooyang
I've had it pretty much as you suggest. First with 5U4G, later with 83 and at present with Cree diodes. It is incredibly heavy as is. No tube rectification this time.
As already mentioned i decided to pursue a low impedance PS. Power transformer secondary for the output tubes is just 2.8ohm; choke is 16ohm. First cap is indeed a Solen followed by a Cerafine.
Driver PS (separate winding) is similar but choke input. Any additional filtering either by introducing resistors or an extra choke/cap doesn't do much good for the dynamics so most probably i'll try a CCS into a shunt tube regulator. I don't anticipate it to be easy.
I've had it pretty much as you suggest. First with 5U4G, later with 83 and at present with Cree diodes. It is incredibly heavy as is. No tube rectification this time.
As already mentioned i decided to pursue a low impedance PS. Power transformer secondary for the output tubes is just 2.8ohm; choke is 16ohm. First cap is indeed a Solen followed by a Cerafine.
Driver PS (separate winding) is similar but choke input. Any additional filtering either by introducing resistors or an extra choke/cap doesn't do much good for the dynamics so most probably i'll try a CCS into a shunt tube regulator. I don't anticipate it to be easy.
I have done a PX25 PP and a 842VHD (300B on steroids) PPP with interstage transformers running in class A. They both sound very good! I can’t see any reason why 2A3 shouldn’t sound great in PP...
Schematic PX25 PP (with cathode feedback):
Jan E Veiset
Schematic PX25 PP (with cathode feedback):
An externally hosted image should be here but it was not working when we last tested it.
Jan E Veiset
Where did you get a output transformer with cathode feedback windings? It is difficult to convince winders to make them.
Rgs, JLH
You'd want the plate choke to have enough inductance to give you a good low f3 in the bass. If you're using 6SN7 or 6J5GT, that would need to be quite a high inductance, as you can expect plate resistance of those tubes to be about 9k to 10k ohms.
There's a thread here where I asked how to figure the L needed for a given tube's rp.
-=|=-
Here's that thread about inductance for center-tapped choke in plates of an LTP:
http://www.diyaudio.com/forums/tube...l-plate-load-choke-how-figure-inductance.html
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I have PP2a3 "Amity" amps driving my ME2 satellites crossed at 80Hz. They sound great, but with all lundahl iron they cost fortune too
Subs are driven by big A** Adcom Amp.
Only problem I had was faint hum and I solved it by adding hum nulling circuit from Lynn's "Karna" Amp. Basically I wound extra secondary on filament transformer giving me around 2.5V rms floating voltage and using it to compensate for hum. Now the amp is DEAD quiet. Moral of the story is that if you build PP amp with interstage transformer, add hum compensating circuitry.
Subs are driven by big A** Adcom Amp.
Only problem I had was faint hum and I solved it by adding hum nulling circuit from Lynn's "Karna" Amp. Basically I wound extra secondary on filament transformer giving me around 2.5V rms floating voltage and using it to compensate for hum. Now the amp is DEAD quiet. Moral of the story is that if you build PP amp with interstage transformer, add hum compensating circuitry.
Hook it up to a pair of Bozak 302's and I think you will be very happy with the bass. The scott 222 is a great amplifier.
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