The story I am about to tell you is not fiction, it is pure reality. I want to share it because I hope it can warn other enthusiasts and beginners taking their first steps into the world of tube audio, and above all because I hope to take away a bit of credibility from a breed of characters who dominate this environment, people closed inside the shell of their fanciful world, surrounded by their followers, who most of the time drive away anyone who tries to approach the world of valve amplification and has the misfortune of getting tangled up in their wacky theories.
Chapter 1: Alberto’s Single Ended EL34
It all started with Alberto who, after successfully upgrading the Nuova Elettronica LX1321 amplifier, came across the design of a single ended with the EL34, born from the reworking of a competitor’s kit, which you can view by clicking here (it is the first of the projects shown on the page).
He ordered the transformer set from me, but after a few days he started sending worried messages on WhatsApp (back then the schematics on my site were still visible and not pixelated), because he had spoken with a friend of his who lives in America and is into DIY.
This “expert from overseas,” after taking a look at my design and my schematic, began the usual oracle-of-Hi-Fi litany: “Don’t do it!”, “From that schematic you can’t expect anything special!”, “It will never sound good!”, “It’s all wrong. You must remove the negative feedback, you must put grid stoppers there, that part is no good, you must do this, you must do that…” basically the only thing missing was “and remember to align the tubes with the full moon.”
I did everything I could to reassure Alberto about the soundness of the project and, luckily, he decided to trust me. He built my schematic with my transformers, and the result is reported below, written in his own words.
Alberto’s experience with the SB-LAB project
Below is Alberto’s account, he built the amplifier and describes the experience first hand.
Greetings to those who will have the patience to read this report of mine and to Stefano Bianchini. Having already owned an LX1321 modified on an SB-LAB project, I decided to make one entirely assembled by myself, not on PCB, so point to point and in Class A, above all something within my reach both economically and in terms of assembly difficulty.
I chose the SE EL34 schematic. Fully aware of the quality of Stefano’s transformers, I ordered a set dedicated to that project and downloaded the schematic. I started sourcing all the components, relying entirely on a retailer specialized in tube electronics near my home. Getting them online here and there would have pushed me over budget because of shipping costs. Seeing my inexperience, the shopkeeper immediately tried to foist on me some silver Hi-End solder. Which promptly flew out the window, to return to the classic solder I have used all my life. With the “audiophile” solder the joints remain dull, which drives me crazy, and above all they break on their own.
I got a sheet of bakelite, which I consider necessary, first to insulate from the metal chassis, the voltages involved are not therapeutic, and then to make the whole assembly neater. This way you do not see fastening screws sticking out of the top cover, and while working it is very handy for fixing tie points.
Drilling bakelite is no joke given the smelly and not very healthy dust it generates, I would recommend doing it outdoors. The chosen case is from Hifi2000, decent quality, but not designed to house tube electronics. In fact it cannot support the weight of the transformers on the top cover, and there are ventilation slots that create problems during drilling. If you happen to buy Bianchini’s transformers you will immediately realize that they weigh much more than commercial ones (compared to those used on amps of similar power and often even much higher power).
To solve the cover problem I added a sheet of brass on the top. By making a sandwich with the cover sheet metal and 3 mm bakelite I got a rock solid support base. I cannot stand those amps where, as you insert a tube into the socket, you feel the counterplate give way under your hands. Moreover, brass can easily be engraved by any workshop to create custom labels. But anyway, apart from the mechanical matter, this is only a question of taste, which is strictly personal.
Little by little I got familiar with point to point wiring, I twisted the wires where necessary by putting the pair in the chuck of the screwdriver. I also recommend not throwing away the wire offcuts that remain from the transformers, they are soft, good quality, easy to strip and solder very well. I tried to mount all components with the value easily readable, so that if Stefano, or I myself to recheck the wiring, had to put our hands back in, there would be less swearing. I proceeded in parallel on the two channels, so that with a single oversight I could make the same mistake twice :-)) I also tried, within my abilities, to make the neatest possible assembly. I was helped by the generous size of the chosen case, suitable for a beginner like me at my first point to point build.
On and off, it took me a few months to assemble everything. I am very meticulous and careful with measurements, so before drilling metal I make trials on graph paper and check by laying things out on the case itself so I do not have to do things twice.
I made sure the input and output binding posts were not shorted to the chassis, I connected two dummy loads, verified the voltages, and thanks to these checks I fixed assembly errors. After connecting the oscilloscope and the signal generator, I started to see that everything was working correctly. I attach the waveforms I measured. The first power on was very exciting. After hours and hours of work it emitted its first cries, albeit instrumental ones.
Finally I moved on to listening. It is true that every cockroach is beautiful to its mother, but I immediately found the amp excellent. First of all, ZERO hum, no background noise, and a low range that is just SUPERB, very detailed and controlled. I tested it on several types of speakers, even a friend’s 4 ohm Thiels which are quite a challenge for a small amp. The amp always delivered great detail and silky violins, never screechy. Of course, Beethoven’s Fifth in the densest orchestral passages put it slightly in trouble, losing a touch of detail, but we were soundtracking a 60 square meter room with speakers that in my opinion sometimes drop to 2 ohm, so I will not complain, also because the comparison was against a 100+100 W RMS MOSFET power amp I built and a much more powerful tube OTL owned by my friend.
Anyway, some details and nuances on Hugh Masekela’s “Coal Train” live only came out with the SE-EL34, so much so that my friend, owner of the much vaunted OTL, turned pale given how much money he spent on it. We repeated the test several times with the same track, and still certain nuances only came through with mine. I tested with different music genres and different speakers, and the results were always up to expectations, confirming the instrumental measurements.
In short, today I am fully satisfied with the work done which, although long and tiring, gives incredible satisfaction. Building a tube amp by hand takes time, patience, and skill, so it is not worth jumping on schematics grabbed randomly online, and above all you should not skimp on transformers, which are the heart of the amp. The advantage of Stefano’s schematic is that it is “built” around his transformers, basically ad hoc. I am aware I only did the manual work. He is the architect who designs, calculates, and fine tunes. Even so, it was demanding. I am happy I did it and I do not think it will be the last. The amp is widely approved by me and by everyone who has listened to it so far. Thanks to Stefano and to his transformers and his expertise in advising you in difficult moments.
PS: I am not a friend of Stefano, except professionally. I do not earn anything and I do not get discounts. I am only an electronics enthusiast, a hobbyist builder with many passions that span very different areas. As for sound, I listen a lot, I am open to comparison and very curious, I always question the work I do. They are almost always “open” projects that need to be refined, practically I am almost never at the word “end.” I often go to Hi-Fi shows and demos, and when I see people spending crazy money on things that do not really deserve even a tenth of their price, I stop to reflect. Thank you for the patience to read me to the end.
The photos
Chapter 2: The American friend
A few months after the first article was published, I received a WhatsApp message from Alberto. The famous “American friend,” the one who said “from that schematic you can’t expect anything special”, had come to Italy on vacation. Naturally, as the great expert he believed himself to be, he could not resist the temptation to “have a listen” to that amplifier which, according to him, should not even have turned on.
Well, after five minutes of listening he remained there with the face of someone who has just discovered that the Earth is not flat. Literally petrified, the device not only worked, it also sounded gorgeous, with detail and musicality that his ego was not ready to digest. After a couple of hours, between a grunt and a “well maybe…,” he was forced to admit with the grace of someone swallowing a brick that he had never heard anything sound so good.
“Zero feedback at all costs” guru: 0, SB-LAB: 1.
Chapter 3: Gozer the Destructor
Almost two years after the events described in the previous chapters, I found myself exchanging a few WhatsApp messages with Alberto about the burned transformer of an old little Geloso radio. During the chat, however, a much more interesting story emerged, and a bit tragic, that of his single ended with EL34s.
With the naivety of someone who trusts too much, Alberto had sold his amplifier, perfectly working, quiet and sounding amazing, to a friend. All was well until this friend decided to do the one thing you should never do, take it to be “checked” by a so called technician, the classic character who proclaims himself a tube expert but in reality has the same finesse as a drunk butcher with a soldering iron in his hand.
The result, a disaster foretold. But I will let Alberto tell it in his own words.
I will tell you a strange story titled, THE TWISTED MIND OF THE AUDIOPHILE.
After building the amp there were several listening sessions with friends. One of them, fascinated by the sound, asked me to sell it to him, since I could build another one. Given the friendship and the generous offer, I left the amp with him on trial. After he had listened extensively he decided to keep it and he was very satisfied.
Things went well until someone put it into his head that by replacing all the tubes with very precious NOS ones things would go much, much better. I naively had told the inglorious tale of a defective KT77 that had also burnt a couple of resistors during the first power up tests of this amplifier.
Having to make a substantial investment in tubes, he decided to take the amp to a tube guru he met at a Hi-Fi show and who was recommended by another friend for a general check of the unit. He should not have done it. It was the beginning of a nightmare and the loss of a friendship.
The guru, after seeing everything, pronounced his verdict, they sold you a lemon, with this schematic the amp cannot work, it is normal that the tubes broke, and so on. So he began to make a whole series of circuit changes, but the fundamental one was to remove the feedback, all GOOD amps have no feedback, configure as triode, completely redesign the driver.
The poor guy paid the hefty bill and took the amp back, accusing me of having sold him a BROKEN amp (????) that could never have worked, even though he had happily listened to it until that moment. He showed me a bag of replaced components that were the proof of my FRAUD. Basically the guru left the tube sockets and the volume pot. (SB-LAB NOTE, Alberto had used top notch Mundorf capacitors all purchased from AudioKit in Rome, recommended by AudioKit’s own technicians, and the same for the resistors and other components).
He put in his ultra expensive NOS and started listening. But, the power no longer seemed sufficient, the amplifier had lost energy, it no longer sounded as before, it could not drive the speakers, the low frequencies were flabby and annoying, how come.
I explained what it means to configure an EL34 as a triode, 4 W if you are lucky. Even angrier, he went back to the guru to ask to make the amp “play loud” again. SURE, he replied, I will give you a quote right away for the modification, maybe we will put it in ultralinear to make it work better. More money, of course, I work.
So he came to me with his bag of components, asking with his tail between his legs to restore it to the original configuration, naturally for free. I offered to buy the unit back at half price, we will see if he gets back in touch.
In the world of Hi-Fi, and in particular in the strange world of tubes, every technician is better than the previous one, everyone has the magic recipe to make these strange things called tubes sound good, others are inept. A home built device, even if listened to, compared and appreciated, becomes doubtful if criticized by a GURU, people trust the third party and not the friend, and to conclude, when we talk about PSYCHO ACOUSTICS I think it refers to this kind of people.
“Zero feedback at all costs” guru 0, SB-LAB 2
Chapter 4: Undoing the mess
After the battered amplifier returned home, we were able to examine the work done by this fairground bungler. It was something that left you torn between crying and laughing.
In short, he had modified the voltage divider that lifts the 6SL7 heaters, risking a destructive internal discharge in the tube. He wired the EL34 from pentode to triode and installed a wrong bias resistor, too low, with EL34 bias current close to 200 mA. Then, not understanding the purpose of the series resistor to the rectifier before the first capacitor, he concluded that 220 µF of capacitance was “too much” for the rectifier, so he removed the resistor and replaced the capacitor with a 22 µF one. Too bad that in my circuit that resistor was precisely there to protect the rectifier and allow the use of a larger capacitor. Result, with the output tubes run hard the rectifier ended up blowing badly, and the B+ rail was so hungry for current that the power transformer heated up like a flat iron.
As if that were not enough, he removed the polypropylene capacitors that were in parallel with the electrolytics, because why would you ever want it to sound clean and bright, no, it must sound dark, closed and without detail. Obviously the feedback network was eliminated, and the driver was modified to have less gain. But less on less meant the amp became too sensitive, with the volume reaching the maximum already with the knob at nine o’clock.
Then he added diodes to rectify the driver supply separately. Evidently the cutoff of a single RC cell of 18 k + 47 µF was not enough for him. Or, after reducing the first capacitor to 33 µF, low frequency oscillations appeared.
The assembly was not even better than Alberto’s which, as a first job, is more than forgivable. But he, as a “trade show guru” who had the nerve to declare that the circuit was wrong and could not work, put together a pig’s breakfast like that. Truly shameful.
How did it sound, wonderful, for someone who hates music. The classic “zero feedback” put together by a cellar goat in a fit of enthusiasm, flabby waterbed bass, mushy soup like mids, and highs so dull that not even a tweeter with bronchitis could have done worse.
And to think this individual even had the nerve to say that the 6SL7WGT JAN by Sylvania “were not good,” claiming that the ECC32 (6SL7 equivalents) he had sounded better, obviously only because he had to find a way to inflate the price without effort, or perhaps because the nice “dome” shaped glass of the ECC32 made them seem better. Sure, because, as we all know, if a tube is prettier, it sounds better, right.
Lastly, he even declared that the two output transformers were too close and therefore intermodulated. He took a device that worked beautifully, declared that it did not, and transformed it into a tube toilet. WOW.
Folks, be careful with these characters who justify nothing with verifiable technical arguments, only with peddler chatter. The fact that they appear at various trade shows does not qualify them as good technicians. Now let us look at the restoration. Alberto worked hard, with my help, to rebuild the amplifier, then he sent it to me for final bench verification.
As a reminder, you can find the design of this single ended with EL34s by clicking here.
Measurements
Power: 7 watts RMS per channel
Distortion: THD measured at 1 kHz, 1 watt on resistive load, 0.11%
Passband: 18 Hz / 90 kHz, ?1 dB
Damping factor DF: 5.7
Channel separation: 48.8 dB (so much for those who said the transformers are close and therefore intermodulate).
Harmonic spectrum
Bandwidth on resistive load
Bandwidth on reactive load
Square waves at 100 Hz, 1 kHz, 10 kHz
“Zero feedback at all costs” guru 0, SB-LAB 3
Conclusion
Do not think that stories like this only happen to me. I know several technician and repairer friends scattered around the Italian boot, and all of them, really all of them, regularly run into the same tragicomic episodes. It is a daily battle to make customers understand that they have been filled with nonsense by a fauna of charlatans who keep shooting verdicts with the confidence of someone who has just discovered the Holy Grail of audio, only they put steaming manure inside the Grail.
If you have an amplifier that works well and you like it, do not touch it. There is no need to “improve” it at all costs. If anything, it makes sense to do a targeted, sensible component upgrade and, if you really want to put your hands on a project of mine, ask me. Do not give in to the temptation to have it “reviewed” by some improvised luminary you met at a Hi-Fi show, those characters can ruin in one afternoon what was designed with weeks of measurement, calculation, and common sense.
And above all, do not listen to those who say that “it cannot work” when you have just heard it working with your own ears. That is the sign you have a Hi-Fi Pied Piper in front of you.
Also beware of those who propose “upgrades” for no reason. As in the case of the guru of the moment, who had branded as junk or even a “scam” the set of Mundorf capacitors in Alberto’s amplifier. After changing everything, we do not know with what, he decided to replace the EL34s with NOS, fine so far, but then, stroke of genius, he swapped a pair of NOS 6SL7GT for NOS ECC32 because, he said, “they sound better.” Too bad that ECC32 is simply the European designation for the 6SL7GT, that is, the same tube. It is like saying that an ECC83 sounds better than a 12AX7, only the label changes, but for some people that is enough to feel like a reincarnated sound engineer.