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.

Since we have prepared for the move, we have packed and moved some smaller items. My system has been dismantled and I even lent my amps to my friend as he tries them out.

We were supposed to move house last July but just a week before moving in, something happened and we couldn’t move house. Fast forward today, we are still in the same place.. and it seems like we are still 6 months away from ready to move in.

Anyway, life has to go on and I got the itch again.

As I have these cute little 955 acorn tubes, I just want to build something with it. So why not build a headphone amplifier? If 2 tubes are cool to look at, how about 4? How about a push pull headphone amplifier? I don’t think these are popular out there?

So I asked my friend Mr Ew to cast his magic again. He promptly wound me a permalloy 10k : 32 push pull output transformer. It comes in such a little package, I could hide them under the chassis, leaving only the tubes peeking out.

If you recall, the last amplifier I built was the 6688 headphone amplifier. It was a 2-chassis construction, with power supply in a separate chassis, connected via an umbilical cable. So why not reuse this? Since the B+ is about right too?

Since I built push pull amplifier with the Ultra Compact concept before this, why not try something different? So this time I used an input transformer as a phase splitter – Sowter 3575 ( 1:1 ct).

The construction is pretty clean this time as I managed to isolate the grounds at the input side. The input “ground” side of the Sowter is tied to its shield, and not connected to the “ground” side at the output, as shown in above schematic. Obviously, if you build such an amplifier and it hums like hell, you may need to connect both “ground” sides together.

Okay, okay, how’s the sound?

Oh my, none of that “vagueness” or “fog” of a push pull amplifier. From what I know, that could be attributed to that horrible phase splitting circuitry used.

This fell’s very quiet, very detailed, very musical.

It has none of those irritating features that drives one to stop listening

It has those attributes that make you want to listen more.

Guess what I’m saying is, I don’t hear much of the sins of omission nor addition. If this makes sense…

I’m listening via Spotify these days and even with such “non-audiophile enough resolution”, I’m perfectly happy. Yeah, it could be because of my discrete monica, or it could be that this amplifier isn’t adding hash/rubbish/junk.

We audiophiles sometimes can be quite a pain in the ass, and want to nitpick on just about anything.

If “Spotify -> discrete monica -> 955 push pull headphone amplifier -> headphones” can make one happy and concentrate on the music, what more can one ask for?

The post 955 acorn tube headphone amplifier appeared first on diyparadise.

How to Convert your PP amp to Triode mode

Ever wonder why idiots like me rave about Pentode Push Pull amps in Triode mode? Don’t you hate idiots like me as your amp is only wired for Ultra Linear (or *gasp* Pentode mode) and Triode mode now becomes the sweet tasty Forbidden Fruit everyone raves about but you can’t taste?

Oscar Wilde said the only way to get rid of temptation is to yield to it. And if you know which end to hold the soldering iron, read on.

Shown here is a Jadis Orchestra amp.

Close up for you near-sighted folks.

OK. See the yellow and orange wires? The yellow ones are wired to pins 3 of EL34 while the orange ones are wired to pins 4.

Pin 3 is the anode while pin 4 is grid2.

The yellow wires go to the ends of the output trans so the orange wires is most likely (and it is in this case) the Ultra Linear taps.
Thus our amp here is wired in Ultra Linear mode.

 

To convert to triode mode is a piece of cake. Just wire a resistor between anode and grid2 pins, meaning between pins 3 and 4. Leave out the ultra linear tap on the output trans. See below.

 

 

That’s all it takes! Easy huh? Most common values of this resistor is 47ohm or 100ohm. Either one will work fine. Leak/Mullard claims one is better than the other, but you can’t go wrong with either. Although 1/2W is usable, go for 1W or higher.

A DIYer did the above to his Jadis and these are his exact words.

Hi yeo, fire up the jadis yesterday and wow yes there is a major difference. On the penthode the sound was a bit forward and fatter but on the triode the forwardness is pulled back and the mid/hi is more sparkle and more open leaving more space between the different instruments. Bass was not as heavy as penthode but more in control. Overall 1st listening is good but not to say that in ultralinear is bad just difference in characteristic. In triode mode it is more refine but in penthode you get the sunday live jazz lounge ambience with big chesty vocal( can be a bit fat) with a lot of air in the vocal range but the instrucments is a bit gluey.

Personally I find that triode mode has more realism but please bear in mind one very important point. Going from UL to Triode mode, you lose about half the power. If you have 40W in UL, now you have 20W in Triode. Not a problem for my 97dB sensitive speakers but if your speakers aren’t efficient enough and need all that juice, then for sure your experience with Triode mode won’t be positive.

That’s all for now!

 

diyparadise.com

 

The post How to Convert your PP amp to Triode mode appeared first on diyparadise.

]]>