I guess this is what it’s called “life happens”.

Also, there is another reason for this. As your system progresses, you eventually reach a point where it’s harder to get significant improvement. I’m not so interested in “lateral forays”, more interested in “vertical improvements”, if you get what I mean.

So in other words, no improvement, no news from me.

That said, I built this amp some time in July 2015 but I had problems with it. She sings but worse than the toad in me. I spent lots of time checking before I start to suspect it is the output transformers when I then packed her up and sent to my friend to debug and rewound the output transformer.

True enough, it’s the output transformers. Unfortunately the core can’t be re-utilized, hence it’s now a C core instead. I know, the looks isn’t that coherent anymore but looking at the bright side, my wizard friend wound up an awesome pair of output trans.

With new pipes, she sang fine as a lady but… not very exciting. Yeah, I’m a greedy bastard! Is this another case of “lateral foray”?

Ahem, This is where you earn your spurs!

Buoyed by my success with Schottkies in the Wet Dream project, I had the Schottkies installed and…

Boom! Crash! Bang! OMG!!!

Through the roof Expletive Factor!

What a huge improvement!

But then why am I surprised? I was thrilled before by what this little sand device could do, so the improvement wasn’t unexpected. What’s unexpected is it is as though she went from a lithe slim lady to a kick ass MMA fighter with a bod to match.

THE BASS. THE IMPACT. THE DYNAMICS. THE PRESENCE.

When these 3 attributes improve, everything else improved by a quantum leap.

As any experienced amp builder will tell you, the biggest bang for the buck is at the front stage. So opting for the Schottkies at the 5965 cathodes make perfect sense.

I then told my friend Tim about this new girl who caught my heart, and as I was describing the sound to her, particularly the kick ass bass and gut wrenching dynamics, Tim said, “Hey, sounds like a Gina to me.”

And so Gina she is.  

All is good so far but a new problem presents itself. My favourite 5965 tube is a GE 5 star. An absolutely rock solid tube but in current iteration of Gina, the sound is now a bit too forceful and tends to be harsh at peaks.

Yeah, I like foreplay, girl, but you are too rough! Foreplay doesn’t mean a broken finger or a sprained ankle, OK? One of these days, I may end up with a torn ligament for God’s sake…

That said, Gina is back to being a lady when Telefunken 5965s are used. But what good is an amp if she only sings with rare premium tubes?

Ahem… back to what I had in mind. My original vision of Gina uses TV damper diodes to provide slow turn on and I kinda like the brightness of TV damper diodes besides the other tubes.

“Slow turn on + Foreplay = Win Win”

But the TV damper diode was taken out when I was debugging the amp when it was distorting badly.

Now that the culprit’s been identified and replaced, it’s now time to put this fella back to work.

I’m using 6AX4 here as it’s an octal tube so if I hate it, I could easily mod for other octal tube type rectifiers. The slow turn on is a bonus.

And now we have a new Gina! No more of that harshness at peaks. No more of that “I will only behave if you give me Telefunken” attitude. The heft and dynamics seemed to have reduced a little, but I’m okay with this. After all, this is the MOST dynamic sound I’m getting out of my pair of horns right now. Chew on that!

Okay, about the schematic.

Gina can be built at a budget. And I mean it.

The stars

5965s, SV83s and 6AX4s are plentiful and still cheap. Before Gina, my favourite little pentode is the EL84. After dating Gina, SV83 is my true love. There is no contest here.

The SV83 or 6P15P is operated in a triode mode. The cathode RC combo and the triode mode connection are options for mods in future. But for now, Gina is very good to me.

Don’t be fooled by the looks of the 5965. Though touted as an 12AV7 equivalent, some folks have used it in circuits calling for 12AT7 etc. From my time with this tube (since the days of the Darling amp), I find this tube to be way better than the other 12A*7 brethrens.

6AX4 is such a nice approachable fella. Big glass, uses the common octal sockets, dirt cheap, low voltage drop (~10V with Gina), pretty bright and slow turn on of about 15 seconds… What more not to like of this fella?

Power supply

Nothing special here but nowadays I stay away from electrolytics in the supply. I know the SV83 cathode electrolytic capacitor still influences the sound, so this may go one of these days but the usage of plastic caps in the power supply is recommended here. Hey, plastic works wonders on some girls right?

I didn’t specify grid stopper resistor value nor power transformer secondaries. These need to be adjusted for what you have in hand. You may not need any grid stopper resistor. My Gina needs them, as without them, there was some oscillation. Since this is a choke input supply, if you need to bump up the B+ a little, a small cap just before the first power supply choke will do.

Most amp builders will zoom in on the coupling capacitor here and tell you that you need to use boutique part here. That’s fine if that’s your preference but my Gina uses a USD2 Russian teflon capacitor. And I don’t feel inadequate in any way. And I have used various boutique caps before. But if you feel inadequate, by all means…

Gina above gives a glorious 2.3W to your speakers. Very efficient since she’s only flowing ~32mA. I recall I built a similar amp with a big honking pentode in octal sockets and even with the much higher current, it was only good for 1.5W. And not very good sound to boot.
There you have it.

Gina oh Gina!

She doesn’t need Telefunkens to shine.

So I could reserve this special tube for the special occasion.

Like when the real Gina comes knocking on my door.

Err, kicking it down is more like it. I’ll get the handcuffs ready…

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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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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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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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