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The JE Labs/ Angela SE 2A3 amp done my way

Redboy said:
Not this thread. It was Pak's advice:
http://www.audiokarma.org/forums/showthread.php?t=86502&page=2

Sounds good so far.
Click to expand...

Ok, it's a cathode follower thing. I'll take a stab and say the larger dissimilar side of 6EM7 nets a little more drive and grunt. Lower Z out, or whatever....

I'm not really sure if it will net more lower bass response, but I'm only using 25-30 uF 150-200 volt caps for filament/cathode bypass. They are the little square bathtub looking oil caps.

Quiet on Fortes, looks great.......excellent job.

I remember my Sovtek 2A3's sounding sort of thin and weedy when I first got them, so you may wanna give them a 100 hours or so.
 
Mike,
Yes you are right. In this circuit T1 is the voltage amp and T2 is a cathode follower. In the case of the 6EM7, T1 specs out much like a 6SL7.

Nate,

Get a hold of a pair of 6EA7’s and see how they work. Do you have a pair of 6SN7, probably not enough gain but a different flavor. If you don’t let me know and I send a couple of beaters with the 6H9C’s…John
 
Hey John, I've actually got some 6SN7's. NOS Hyvacs, which I think are supposed to be Tungsols. Might have to try them, too.
 
Nice looking amp! I wish my first, an Angela/JE Labs simple 45, looked that good. I have built a few of 2A3 amps over the years and am amazed at how good they can sound with so few parts. Your work under the hood is really good, even for those of us who have built a few...or 10. And you did a very nice job laying out & machining your top plate. Keep up the great work!

I think I have the solution to your lack of bass. I don't see a cap off the cathode of that 1st stage. Maybe I'm just not seeing it, but that's what I have experienced in the past. Rat Shack might even have something to get you by in a pinch if you didn't order any. Larger values probably won't hurt anything since the cathode resistor on the 2A3 will roll off most sub-sonic frequencies-that is, if you're a vinyl spinner.

Man..now I'm wanting to fire up the drill press and soldering iron and build another 2A3 amp-and actually keep it this time!

Tom
 
Hi Tom. There's a 100uf, 25V cap mounted vertically under the resistor coming off each of those cathodes (pin 6). They don't show up well in the pictures, but they're there.

I'm having less of an issue with the bass. Maybe I'm getting used to it, or maybe those RCA 6SL7's are really as bass-shy as jaymanaa says, but I think I'll stop complaining for now. The rest of what I'm hearing is really incredible.
 
Ah...yes I see them now.

Have you tried the other taps on your transformers? That might be the ticket.

Tom
 
For anyone interested in this, here's some more detail about the parts I chose for this project:

The chassis is a sturdy aluminum plate, 12” square, courtesy of member carpinus7 (Thanks again! :thmbsp:). I drilled all the holes myself with a step bit on a drill press. After drilling, I had it and the transformer end bells sandblasted and painted at a local shop.

Because this is such a simple circuit, I felt that I could splurge a little on components without breaking the bank. Here are some highlights:

• James Audio 6112HS output transformers from Euphonia audio. These are upgrades from the recommended Hammond 125ESE’s.
• Hammond power transformer and choke.
• Angela Instruments copper foil PIO signal capacitors. These are supposedly the same as Jensen caps.
• Sprague Atoms throughout. These were reasonably affordable.
• Riken Ohm carbon film resistors throughout, except where higher wattage values meant I used Kiwame carbon films or a generic metal oxide (in the PS).
• Alps Blue Velvet 100K stereo volume pot.
• Stainless steel allen head screws from Ace Hardware. These little critters are expensive!
• Sockets are Azuma gold-plated, and the binding posts are James Audio. Both from Euphonia.
• I used solid core Belden wire for filament wiring, and stranded Kimber for B+ and signal hookup. That’s some really nice stuff to work with!

For tubes, I’ve got Sovtek 2A3 power tubes. The drivers right now are old stock Sylvania 6EM7’s and the rectifier’s an RCA 5V4G. I’ve got a couple of rolling options for drivers, and someday I’d love to find a bunch of NOS 2A3s in a dusty box…
 
Have you tried the 3.5K taps yet?

I use a pair of Scholl 10 watt OPT's with around a 3600, 3800 ohm primary, and the 8 ohm secondary taps.
It's a 3 stage amp, using each section of 6EA7, IT and cap coupled to the output tubes, with the OPT's inverted.

I ran my Sovtek 2A3's last night in my stereo SET amp. No lack or wonderful bass here.....
One thing I noticed is the Sovtek 2A3's sound like crap for about a 1/2 hour or 45 minutes, then they sound great.......The TJ 2.5 volt solid plate 300B's sound great off the bat, and then start to sound dull over a few hours.
The TJ's are getting on the wanked side, but I do like the sound of them....

Those Riken resistors aren't cheap.....I've been thinking about using some of these in a Magnavox SEP 6BQ5 console amplifier with some Mills....
Nice hardware isn't cheap....I feel your pain.
 
I haven't tried the 3.5K taps yet. I'm putting in more listening time so I can better articulate what I like and don't like. I also want to give things more time to settle in.

Yeah, those Rikens were spendy. Again, it was the low parts count that made it possible. Unfortunately, I'll never really be able to fully evaluate whether they're responsible for the sonic signature of the amp, because so many of the other components are new to me as well. But I figured I'd rather experiment with coupling caps than resistors, so I'll start with something purportedly decent in that category.
 
Well, I wired it to the 3.5K taps last night. It really helped with the bass response! I think I can listen to this thing for a while now, if I can just quit swapping driver tubes like a madman.

How long for a new build to "settle in"?
 
How many hours of operation?

I'm sure the amp will settle-in before the Sovtek 2A3's, if it isn't already.
Pick the prefered driver tube, and enjoy......
 
I'm not sure if it's had 24 hours of run time yet. I've had house guests since I finished this thing, and work keeps getting in the way!

My favored driver tube for the moment is a Sylvania 6EM7.

These OPTs have 2.5K and 3.5K taps. I first wired to the 2.5K taps per the schematic, but I think I like the other better. Oh, there's also an "S" tap, which I assume is a screen grid. Whatever that is...
 
More listening time in now, and I've got to say that I'm really liking what I am hearing. Bass response isn't really a concern to me any more. I'm not sure if it's the tubes burning in or that I'm just getting used to the new sound, but things are sweet. It could be that the mids and highs are just so much more detailed now that the bottom end seemed subdued in comparison initially.

I'm finding that even less of my music measures up now. Poor recordings are unlistenable, and average ones are just blah.
 
Congratulations! You did a very nice job on that amp. Truely something to be proud of. What speakers are you driving?
 
Thanks! I'm currently using recapped Klipsch Forte's (original, not II's) and they sound really great. A promising Frankenspeaker project is in the works, though.
 
"Poor recordings are unlistenable, and average ones are just blah"

I experienced the same thing when I ventured into SET amplification. I haven't found a preamp that will "do" either, which has confined me to a CDP with volume pots inline. To be completely honest, I would say that when I listen to the SET/horn system, I do just that (listen to the system, and not so much the music). I'm not suggesting that's what your doing, or that it's even a bad thing. I just wonder sometimes if I'll ever be able to just use it like other systems. There have been a few occasions when I was home alone and able to just relax, close my eyes, and get lost in the "music". I cling to those few times like a golfer hitting the perfect shot. I guess there are only so many recordings out there that will make a grown man cry, and once that has happened, it's hard to settle for less. :D Anyhow, that's what keeps me tweeking, soldering, rearranging heavy speakers, etc. etc. It's just a different deal, Jay

BTW, are you using vinyl at all?
 
Jay, you've nailed it. Those few moments of perfection are worth it, though! The saving grace for me is a second system that plays everything just the way it used to. When I want to listen to some old favorites, especially the Brit pop or punk or New wave stuff, that's the one I use.

No vinyl to speak of, yet. I've got aboout 50 old records that I've picked up along the way, and I have four TT's, the best of which is not worth mentioning. It's probably time to sell all four and invest in a decent table, but I'll need a phono pre and more music and time and money and...

I've been putting it off while I focus on the rest of the system.
 
I don't know if anyone's actually reading this thread anymore, but today I tried something different again...

I vaguely remembered reading something about the transformer wiring in the original designer's write-up of this project. Went back today and dug it up. Here's Joseph Esmilla's comment (from this page) on the James OPTs:

...one can get significant improvement in overall transparency, resolution, dynamics and bass response with the James 6113HS available from Euphonia Audio. I paid approximately $140/pair promptly shipped within the USA, great service. This unit uses higher grade M3 laminations potted in a cylindrical can with Tango ISO/Tamura level of finish. I used the 2.5K primary tap so that the secondary will effectively reflect a 5K load when connecting an 8 ohm load to the 4 ohm tap and 16 ohm load to the 8 ohm tap. This output transformer really excels and can be used in other 2A3 applications at full 60 ma. current. I've tried it already in my prototype chassis using the SE2A3dx circuit and it was not put to shame pitted against the more expensive and beefier Tango U808 and NY15s. This is an unequivocal best buy in my book because of its synergy with this circuit!
Click to expand...
The part in bold was what had me thinking. So I gave it a shot, and wired it as suggested. This is the best sound so far!

The amp I built is Angela Instruments' "new and improved" version of the original that JE is talking about, and that schematic indicates a primary Z of 2.5K ohms. If I understand it correctly, I've now got it wired at an equivalent of 5K ohms. Considering that the schematics are slightly different, does anyone see a problem with this?
 
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