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.

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Matching the current is critical to sonics here. If you could find matched tubes, great. But over time, even matched tubes will age and most probably, they won’t be matched anymore. Therefore it’s critical to have some adjustment on the tube currents.

There you have it! By varying the pot, we could adjust until both tubes are conducting the same current. Well, as close as you can get. Without too much effort, I managed to get one channel within 1mA while the other channel was within 5mA. If you have trouble getting the tubes to “behave”, sub the 15 ohm with 20 ohm.

After all the improvement, complicating a simple amp, I brought it over to YH’s place. YH uses Harbeth 82dB, 6 ohm speakers. Room size is 16′ x 24′. To say the Simple EL84 faces a daunting task… is an understatement. Well, what can I say? This 10W little bugger drives the Harbeths very well! Except for some complex passages and musical passages where it clipped, the Simple EL84 is a winner. We played a Consonance (Opera Audio) M99 integrated in this same system a week ago. Let me tell you this: the Simple EL84 CREAMED the M99! There’s simply more life in this little bugger. Bass control is simply excellent… for a tube amp.

The EL84 naturally has a sweet sound so the usage of neutral ECC99 and Auricaps help it excel. Sweet front end tubes and caps might give you diabetes! But if you like it, then what do I know? Experiment and tell me what you like!

Hey, if you are longing for a tube amp, but can’t afford one. Here’s your ticket.
If the Simple EL84 can drive the 82dB Harbeths with aplomb, it should be able to drive most commercial made speakers. 88dB? No problem! Unless your listening room is many many times bigger than YH’s.

After the Simple EL84 survived the Harbeth test, brought it to test with other speakers as well. Tried it with 85dB Musical Technology speakers, and 91dB Monitor Audio bookshelves. Again, the Simple EL84 proved itself equal (and even surpassing) some of the much more expensive gears over there. I luv this baby!

Let’s face it, comparing to single ended amps, reveals a not so easy-going midrange and treble but if you favour better bass control and dynamics, you know which I prefer. : ) Single ended amps need very efficient speakers, which are mostly HUGE and COFFIN-LIKE in appearance. Here’s another alternative for you, courtesy of DIY Paradise.

Options? Lots of! You could build all NOS line-up. 5687 driving 8BQ5s. You could build all new tubes line-up. JJ ECC99 driving JJ EL84. Or you could mix and match. There’s certainly more but this will have to do for now.

Before I wrap up, here’s what you need to build the Simple EL84.
Output trans, 8kohm primary impedance. 10W is fine. (New Hammond stock will have this little critter.)
Power trans. 240-0-240V @400mA, 4-0-4V @6A (for 8BQ5), 3.15-0-3.15V @3A (for 5687 or ECC99).
The 23kohm plate load resistor consumes ~2W. Use 5W or higher.
The cathode 390ohm, you could use a 1/2W.
Ditto with 220kohm grid leak. 1/8W is fine as well.
500ohm pot can be 1/2W or more. Ditto with 1.2ohm current sense and 15ohm current adjust.
The LM317 on YHLMCCS (highly recommended) is best fitted with TO-220 heatsink. Run it at 70mA if you think 80mA is too hot. (It is, to a certain extent.)

Lastly, TOOBS! NOS 8BQ5 @RM20 each for a limited time. JJ EL84 matched quad @RM140. JJ ECC99 @RM45. NOS 5687 @RM40. See price list.

Continuing the journey… Variation of the Same Theme

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Okay, sonics wise leaves a lot to be desired, but this is where the actual fun begins.

Began by soldering cathode bypass caps for the ECC99. 470uF/10V should be good enough but as usual, play with this value. I haven’t spent time optimizing it yet. Now gain is higher and you don’t have to crank up the pot like before. But I thought without the cap it sounded clearer. Anyway, let it run in first.

Next, wired in 1.2ohm resistors to every cathode of EL84 to check their current. Need to know how “matched” these tubes are. Well, what did I see?

My goodness! Matching is way way way off! One guy conducts 30mA, the other 50mA so cumulatively they measure 80mA but this is not right. We want each guy to be conducting 40mA, within a few mAs.

So, swapped around a few tubes until they match pretty well. If you are lazy and don’t want to buy so many tubes, you should insist on matched tubes. This will make your life much easier. Alternatively, hang on first. A network to adjust current should be out soon. After I got my mix pretty well, fired it up and…

Sonics is sooooooo much better this time. Even had non-audiophile housemate jump at the improvement! Clarity is improved. Veil is thinner (is there such a description?) but there’s still room for improvement.

YH’s Lazy Man Constant Current Source
YH has suggested to me many times to swap the cathode resistor for a constant current source. But with me being LAZY, I abhor the process of finding suitable transistors (to conduct 80mA in this case) and all the works. Anyway, YH then showed me a pretty easy scheme! So easy you should knock yourself on your head if you don’t try it!

After implementing the YHLMCCS, and verifying the current and voltages are okay (it works like a charm!), fired it up and… Non-audiophile housemate jumped higher this time! Veil is gone. Clarity is good. More amazingly, the BASS. Wham bang boom! Superb bass definition! Many DIYers have commented on how constant current source change their sound and better bass definition is certainly one of them. But hearing it myself is enlightening!

Sonics wise, this is something I could live with. But got to make it easier for DIYers to construct this amp. Proceed to the Update.

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Okay, actually building this integrated amp is a piece of cake. But I took so longggggg…

Chassis
I was determined to make a nice amp as my previous attempts all have a “frankensteinian flair”. So I took extra trouble to get the chassis done up really nice. Got hold of a nice piece of 1mm aluminium chassis. 1mm sounds too thin right? But it’s holding up almost 20kg of iron pretty well right now. Anyway, took me 1 day to drill all the holes I need. 1 day to paint and… an eternity for it to dry!

I used hammertone paint here. Was told that “they’ll dry within an hour”. Really? Okay. Applied first coat (diluted with thinner of course) and left it under the sun to dry. An hour later, was happily applying second coat when I noticed the previous coat was “moving”! Dang! Needless to say, third coat was many hours later. Still not fully dried. Got fed up. Became desperate. Left chassis under the sun. Left it in the car parked under the sun… I thought this should be okay right? But as I grabbed the chassis, I left my fingerprints everywhere! Grrrrr!

Wiring
Seriously, watching paint dry has never been this interesting. Okay, enough talk about the chassis. Made me mad! Wiring is straight forward. Was determined to do it nicely this time as well, but my attention span only lasted a few solder joints. After that was sloppy, sloppy, sloppy job again… Now you know me. But when I rebuilt the power supply circuitry (to kill hum) I rebuilt the signal circuitry as well, using tagboards. Everything looks neater now, but this is relative.

Testing
Testing is easy. Just make sure all voltages are pretty close to that on schematics and you are fine. Sometimes you get a big difference and it could be either your incoming VAC or your heater voltage being out of whack. So check your incoming VAC and heater voltages as well.
Does the power supply circuitry look different? Does the 1.1uF cap bother you? Without the 1.1uF, the ripple on the power supply is about 40mV. With this cap, it went down to single digits. You can read more about it here.

First build
My first build gave me bleeding highs. My ears bled when I hear the highs. Even violins are horrible. What’s wrong? Guru YH suggested the phase splitting isn’t up to mark. Basic electronics tell you that you can improve the phase splitter performance quite easily… but that is another article…

Anyway, as I attempted to kill whatever hum that I was still having, I rebuilt the power supply AND rebuilt the signal circuitry. The layout looks cleaner now. Fired it up and… the highs are okay! Whatever I did wrong previously, I must have done it right this time.

Listening
Critical listening revealed several flaws. The sound is veiled, muddied. The highs are okay but the bass is quite rolled off. Also, you need to crank your volume pot quite high… Hmm…

Complicating the Simple EL84.

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So you need help building your preamp/amp and have no one to turn to? Or is your Significant Other pestering you to build those Ultra Cool stuffs at diyparadise but you don’t even know which end of the soldering iron to hold?

Have no fret! ‘Cause help is here! The PowerPoint files below (with PDF versions as well) has not only helped many a DIYer cooked up their own version of Ultra Cool Audio, they have been extremely educational too. Not to mention just downright entertaining clicking them slide by slide….

Best part is, the info below is free for you to download! The schematics, layout and even wiring diagram are all given FREE! No expensive E-books nonsense! This sure beats some of my competitors asking you $$ to purchase their lousy manuals. And stupid meaningless instructions like “connect point A to point B”. : )

As I spent some hours to build all this, I’ll appreciate your token of appreciation. And also, a note informing me what would you like to see more from diyparadise.

PPT PDF How to build the Simple 5687 preamp

PPT PDF How to build the Simple EL84 amp

PPT PDF How to build the 5842 Grounded Grid Tube Gain Stage

Thanks to all those Really Cool DIYERS for the PDF conversion!

Recommended enclosure plans for Merrill DCA4 and DCA5.5 drivers. Enclosure design courtesy of our resident speaker guru, Gabriel. These are simpler designs, great for DIYers. The horn poses a challenge though… Watch out for more interesting designs in future!

DCA4 Wide Baffle

DCA4 Transmission Line

DCA5.5 Transmission Line

DCA5.5 Double Horn

DCA5.5 Tuned Box

Merrill DCA4 and DCA5.5 driver and TC025 specifications.

Merrill DCA4, DCA5.5 and TC025 specs

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Simple EL84 poweramp/integrated

I’m a simpleton when it comes to names.

The simple preamp using 5687 was named “Simple 5687”.

Now that we have a poweramp/integrated using EL84, it’s going to be called… “Simple EL84”.

I’m going to divert from conventions here. MY conventions.

This amp is push pull, not single ended. I like single ended better but it gets freaking expensive if you need more power. Push pulls, being more efficient, can do a hell lot more power. Besides, not everyone would want huge, coffin-like high sensitivity speakers in their living room right?

Also, using capacitor input power supply here, not choke input.

Using solid state diodes! (shrugs!) No tube rectifier here.

Musicians look at music scores and spend hours talking about it. DIYer wannabes spend hours looking at a circuit and days talking about it.

But this amp is more than your conventional push pull amps. You see, conventional push pull amps consist of at least 3 stages. Driver, phase splitter and power stages. This bugger here, has only 2 stages. Phase splitter and power stages are combined. The idea isn’t new (what else is under the sun?) and you can read about here… .

Notice some novelty here?

First of all, only one coupling cap per channel! Push pulls usually require a lot more! At least 4 pieces. 6 pieces are common too. Real pain if you want to upgrade all of them to Jensen paper in oils… But as there’s only 2 caps here, you can afford to splurge!

What else? No feedback! Usually push pull amps use feedback but none here. Actually there is some local feedback as there’s no cathode bypass caps but there’s definitely no global feedback here.

And? Simplicity! Looking at the schematics, it looks just “one tube extra” compared to 2-stages single ended designs. Very easy heh?

Lastly. If you believe all the audio diatribe about evil electrolytic caps. Look at the circuit again. No electrolytics in the signal path! (actually there is in the power supply but give me some leeway okay?)

The driver stage is sooooo simple that you can’t afford to take out any part! It’s simple as it is. Since the EL84 in this configuration needs less than 15V to swing to full power, if your source signal leve is 2V, this means you only need a gain of < 8x to drive it to full power. Gain of 8? You don’t need

expensive 12AX7 (gain of 100)

slightly cheaper but still damn expensive 12AU7. (gain of 40+)

move over, 6SN7, 6SL7…
In fact, you could use almost any tube! The design above shows JJ’s ECC99 as I have never used this tube but have heard lots of good things about it.

WAIT A MINUTE!

I have already built the Simple 5687 preamp. If you said that any tube can drive the EL84 to full power, can I just use it?

Of course! And this is the beauty of this design! If you have already built the Simple 5687, all you need to build for the power amp is this!

Or you could combine the 5687 driver stage and the EL84 power stage to make your own integrated amp. Cool huh? Life is so much fun when we have so many choices! You could build this with all modern tubes! JJ ECC99 driving JJ EL84. Or all NOS tubes! NOS 5687 driving NOS EL84.

But NOS EL84 aren’t cheap…

This is where DIY Paradise comes to your rescue again! EL84 is also known as 6BQ5. WE DON’T HAVE TO USE 6BQ5. We could use the 8V version, which is 8BQ5! (As I write this, some folks are going to curse me. The price of 8BQ5 is going up! Thanks to fellows like me…)The only difference being this guy needs 8V heaters as opposed to 6BQ5’s 6V heater. If you are going to DIY this amp, you have the flexibility of customizing your power transformer. So you could specify 8V heaters. No problem at all. Non-DIYers are tied by the available heater taps on their amps… DO NOT BE HANDICAPPED, fellow DIYers. Break free!

Does it end here? Not yet!

The circuit above is wired for ultra linear configuration. (~10W)

If you tie g2 to B+, you have pentode configuration. (~15W)

If you tie g2 to plate, you have triode configuration. (~5W)

In other words, once you built this amp, you can really really really anal, and wire a switch to switch between different modes. How’s this for 3 kind of sound in one package?

Oh well, and so I built the above amp with JJ ECC99 and NOS 8BQ5. Proceed to “Building the Simple EL84”.

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Variations of the Same Theme

I’m forever plagued by indigestion problems. Irritable Bowel Syndrome. Yeah, it’s a fancy name that doesn’t do any good to me. Nevertheless, despite the frequent trips to the loo, and the discomfort experienced, there’s always a good thing to it. Inspiration has always struck during this time of solitude where you have no one else but YOU, where all you have is just 4 walls. I mean, how often do you have the chance to sit down quietly and THINK? How often can your inner voice be heard? It is precisely this sort of solitude “moment with oneself”, that our inner voice can be heard. And thus inspiration struck.

Alright, alright. I exaggerate. But these are variations of the same theme – the Simple EL84.

When I first built the Simple EL84, and optimized the circuitry, I was using GE 8BQ5. After all this is done, I switched to Russian equilvalent – 6Pi14-EB. This is supposedly E84L and is supposedly more rugged. Well, the construction looks so to me! A few weeks later, switched to matched quad JJ EL84. Along the way, I maintained the same driver throughout – JJ’s ECC99. [Err… If you are considering/building the Simple EL84, you may want to back off the secondary of your power trans from 240-0-240V to 230-0-230V (or even 220V) as I noticed some times our incoming VAC can easily go above 240V. When this happens, we could have a B+ of 320V. The EL84 DOESN’T like that. I’m sure you won’t like 320VDC on you either.]

I’m hard pressed to describe down to the minutiae the sonic differences between the different versions of EL84. All sound very good! The only thing that stuck in my mind was that the Rusky version is more dark sounding and the JJ’s take a long time to run in. Does the GE sound better? I can’t remember! Never mind, all in all, I love the EL84! (And I still have RCA, Sylvania and Amperex 8BQ5s to play with…)

OK, what else can you do to up the ante? To raise the sonic bar? We could play around with caps, resistors blah blah blah but it’s going to be an expensive and most probably, not very rewarding process. I mean, let’s go for the max bang for the buck! Let’s go for the jugular! And not tiny, minute incremental progress. And this calls for… circuit changes.

First off, by just changing some wirings, we could reconfigure the output from ultra linear operation to triode mode. This is very easy. I would suggest you wire the ultra linear tap from your output trans to pin 8. Pin 8 is internally unconnected inside the EL84 so we could just “borrow” this pin. Then wire a 100 ohm (47 ohm is just as fine) pin 9 (grid2). This is where it gets interesting.

If you wire the other end of the resistor to pin 8 (thereby connecting the ultra linear tap), you get ultra-linear operation.

If you wire the other end to pin 7 (plate), you get triode operation.

Yup! It’s this easy! But with triode mode, you lose half the power. If you can get by with 5 sweet luving watts, you should go triode! I know it’s only 3dB but if your speakers need all the power it needs, 3dB is a lot… Try and see whether you speaker can work well with ~5W.

If you don’t want to lose power, we could play around with the driving circuitry. We could change the driver tube.

The main reason I built my Simple EL84 with 2 driver tubes is so that I could experiment with different drivers. The ECC99 has proven itself to be an excellent driver. Highly recommended. Other choices are 5687, 5842… But let’s do something totally different.

Let’s use EL84 to drive EL84s. Yes, folks. Let’s pay a visit to cool audio artisan from the Land of the Rising Sun – Sakuma San.

Now, Sakuma San is a cool dude. His amp philosophy is very simple. Like drive like. If you like the sound of a 300B, then use 300B to drive it! Why stick a 12AX7 in front and ruin the 300B sound? Sound philosophy eh? Also, Sakuma San is a strong advocate of transformer coupling. Now, this tightwad here (yours truly) has experimented with the Sakuma philosophy before, via the “Not Quite Sakuma Darling”. “Not quite Sakuma” as I used caps instead of transformer coupling. Well, the sonics is something totally different from what I have listened to so far. I hear a very transparent tone. Very very transparent. In addition, a wide wide soundstage! This was quite a revelation to me. Unfortunately, I found the lack of bass lacking and went back to more conventional (read: boring) circuits. You can definitely tell a green horn there.

OK. I will like to think I’m wiser today. (yeah right). So I took out the ECC99 from my Simple EL84. Rewired it for EL84. Since I wanted a quick listen, I didn’t optimize the circuitry and used the existing 18kohm plate resistor, 390ohm cathode resistor etc. Oh yeah, wired in a 100ohm resistor between plate and grid2 for triode connection. It’s a coincidence that triode-configured EL84 has roughly same specs as ECC99, namely mu of 20 and plate resistance of ~2kohm.

This is Sakuma San’s implementation (in 1982!), with phono-stage. For Sakuma San’s complete work, refer here.

As you can see, Sakuma San uses a 30H choke on the EL84 plate and runs it at 27mA! This is hot! This is almost the same power as my Darling amp! This kind of beefy driver can drive almost ANY tube out there. In comparison, I’m only running at a measly 10mA… As it’s pretty obvious from the circuit, the transformer coupling and output stage is pretty different from the Simple EL84.

Okay, enough talk, but how does it sound with the 10mA EL84 driver? Well, not that different from an ECC99. Namely open sounding, very clear and very transparent. But. But. But. It’s more natural as well, and has better imaging. As Good Ears was at my place, he commented that the EL84-EL84 “portrayed the singer’s mouth better”. I love this amp!

While Sakuma-inspired gained naturalness in the sound, triode configured output gain realism. I was quite shocked to hear what triode mode sounds like. Imaging and focus is bettered as well. With EL84 as driver and output EL84 configured for triode mode, MAMA MIA! This is a FANTASTIC combination that has knocked me off my audio socks!

Well? What else have I tried? I changed the plate load to 10kohm for a `hotter’ drive at ~15mA. Look at the blue line below. The curves look more evenly spaced. But I don’t like the sound. It has more guts, more balls but at the expense of naturalness. No, no. Can’t do. (I also tried to grow a beard ala Sakuma San. No. Can’t do either.)

The red line and dot shows what I’m doing right now. The blue one looks more linear at 15mA and is gutsier. Maybe you’ll like it. I don’t.

Later, I wired in a 30H choke for plate load. Now this baby runs hot! With B+ of 310V, the EL84 plate is now at 290V. Cathode sits at ~11V, very similar to Sakuma San’s version, with 28mA running through! I lost some naturalness again but images seem to be better fleshed out. Vocals are thicker and you lose some details along the way…

What else can you try? Surely there’s more right? You could try to regulate the screen grid. Hold it at a constant voltage instead of swinging with the music. RC from the B+ will do. Or gas regulators like 0D3 (for 150V). I’ll try this o-n-e d-a-y……

OK. What’s the point of doing all this? Just to illustrate to you there’s no “perfect amp”. Every circuit you try, no matter how reputedly good sounding it is, it’s still subjective to different pairs of ears. Everyone listens differently, every amp is built differently. Plus choice of components, circuit layout, interfacing with CDP/speakers etc. You can now see that “designing an ultimate amp on paper” is just talk. Build it up first and then tweak to suit your taste. I know it takes more work but once you are done, you know this is YOUR ultimate amp, rather than some sad case’s.

After all this fun, I settled on the 18k plate load EL84 drive EL84 as it’s the most natural sounding of the variations above. Some of the combinations are more fun, more hi-fi and impresses the audiophile in you but since I play my system almost 10 hours a day, naturalness is what I want. Your mileage, of course, should vary!

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