On the left is the passive preamp, sitting on top of Mr Ew’s excellent Rapsberry Pi – AD1865 DAC. On the right is Anna! An All Russian Push Pull amplifier.

The passive preamp is a restacked Intact Audio autoformer. By itself, Dave Slagle’s autoformer is already excellent, but restacked for more inductance to fit your system, that’s what a proper DIYer should do!

Note below, wired with Elma switches. I bought these years ago, back then could only afford the 12 steps… These switches are fantastic! The touch, the feel… it’s like Leica camera, you’ll understand if you are of particular vintage…

Here’s internals of Anna. It’s a heavy 2 chassis affair, done mainly because I want to hide the ugly power transformer and chokes inside. And also I don’t want anyone to accuse me of building a “lightweight” amp. Count the number of irons please…

Here’s a close-up of signal wiring. The iron arrangement… went through so many iterations before arriving at this arrangement. Mainly to minimize induced hum… Once it hums, it’s no fun… Resolving hum is just as fun as a root canal…

What is Anna? At first glance, looks like the Simple EL84 concept but instead of using differential long tailed pair as phase splitter, using iron here.

Driver stage is a plate choke loaded 6E5P. My previous experience with 6E5P wasn’t that good. Must have done something right this time… Circuitry wise, nothing special here, other than the 5 Schottkies at the cathode.

Next, it drives a center tapped choke. Yes, it’s an audio choke with its mid point tapped out. As this center tap is grounded, driving one end of the choke will induce an inverted signal at the other end. In other words… a phase splitter! It works very well here and I have no idea why we rarely see such design. So simple and elegant!

After that is our favorite SV83 in triode mode in Push pull fashion. All for a grand 4000 miliwats… Again, nothing special here…

So the magic is in the phase splitter. Push pull can be done right if you get the phase splitter right. None of that “push pull” veil here.

I would add that if you look at the music signal, every stage it sees lots of inductance.

From DAC output, it goes to an autoformer (an inductor with very high inductance ~200H)… Then to the 6E5P (high inductance on its plate 100H)… then driving another high inductance phase splitter choke (easily >100H)… then SV83… Output transformer (PP output transformers easily have >100H)…

Hmm… every stage it sees >100 Henries… Any idea what does it do?

Sorry, I’m not smart enough to tel you what it does. So I’ll just tell you what I hear here.

This is the most dynamic amplifier I have ever built. It’s only 4W but the dynamics, transients is striking. This raises a new bar to the word – realism.

Enuff said.

The post Anna – Push Pull done Right appeared first on diyparadise.

Welcome to the Ultra Compact Club where our perception of Push Pull amps were ruined by this article. However, instead of building this little amp ala Melvin Leibowitz, we proceeded further by tweaking the circuitry to loftier heights via the usage of constant current source, hence it’s no longer the Compact amp but — Ultra Compact.

I admit, I’m guilty of "corrupting" the fine folks here with my Simple EL84 articles but I assure you I’m not the only Evil one here.

Ferry Prasetyo, Jakarta, Indonesia uses this little amp to drive his Infinity behemoths.

Waily, Singapore, is an EVIL diyer. Read about his other works here.

CY Liew, Malaysia, needs a tube cage to protect his sons from those smoking hot EL84s. Or is it protecting his tubes from his son?

The guys above use basically the same circuit — Simple EL84.

Here we have "puff"s Double Compact. puff is based in Denmark. "I like the version with diffential amp in the input stage best, (The Double Compact) which I tried because of the idea: `If it sounds good at the output, why not try it at the input also?’ The sound is better and I have the possibility to use balanced wiring when I build a preamp instead of using CD direct in."

Then we have keto (US) who proved not only the Compact circuitry is usable with DHT tubes, but how about Direct Coupling? At time of writing, this devil of a guy is still tweaking his circuit. Hey ya keto, remember to send me your latest and greatest!

From Germany, we have Helmut Tripphahn who wrote:

Hi Yeo,

I built one stereo channel in conformity with your Simple EL84 amplifier circuit and tested it today. It works unobjectionably, although I’m not using the output transformer and the power supply you recommended. B+ is at only 280V, Ik is at 43 mA per tube (using a matched pair of STANDARD BRAND tubes I even didn’t need to install the trimpot and 15 ohm resistor). Hence the total constant current is at 86 mA.

The bass sounded very clean, but there seemed to be a lack of heights at first. After I’ve replaced the driver tube (one of my "test" tubes for experiments) with an new-old-stock Siemens EL84, the mid-range and trebles sound excellent, too.

Unfortunately the Easter holidays are coming to an end. But I’ve decided to complete the amp as soon as my daily work will allow me to. After several rather disappointing experiences I made with conventional ECC83/ECC82 phase splitter circuits (paraphase, long-tailed pair, cross-coupled cathode followers) I am convinced that the "like-drive-like" approach is the perfect solution for me.

Long before, I’ve read an article in an old German magazine where a self-regulating EL84/EL84 output stage/phase splitter circuit was described, however, I thought that such a strange "inexpensive" circuit wouldn’t be worth of trialing. So it was your publication that lead me to the step in the right direction (in addition, I like your unconventional writing style).
Thank you very much!

Kind regards,
Helmut

This pretty one’s called Norah! By Sylvain FAUVEAUX.

Description of the amp :
– Modified power supply
– All caps are MKP SCR (a.k.a. Solen, France) and mica’s except two Silmic II for the two preamp stages
– 6x6PI14PI-EB tubes
– Lazy man current source
– "ESO Magnetic" (France) power tranny and choke
– Audax TU-101 (France) output trannies
– Remote volume control (Selectronic kit)
Making the chassis was a real pain in the ass (you know what i mean …)!!! But it worth the effort! (I’m planning to built a SimpleEL34 this time! ) I want to give her the name of Norah if you agree. Because the first CD (beautifully recorded) I played through this amp was Norah Jones "Come away with me" : completly delighting!! Her voice is so attractive through this little amp! That’s why!

Thanks guys for all the excellent work!

If you have built any variation of the Compact amp, send me a BIG note!
If you haven’t… tsk, tsk, tsk…

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