For those who can, amplifier kits must be the option that tickles the mind and fingers. Tube amps especially. But what are the options actually, I mean those that really are reliable and trustworthy and in constant production. Not that many, I guess. Especially when world-wide online shops are left out.
Anyway, Uraltone, the Finnish importer/dealer for audio components, offers a series of Hi-Fi amplifier kits (incl. phono stages, preamps etc.), in fact has done so for a almost two decades now. Their very first creation was a EL84 Push-Pull amp, and it’s still on the menu, although the original design (Mauri Pännäri) has been later revised and optimized. I’ll come back to the new version further below but now, since it’s the first version that I once had a chance to experiment with, and since the later changes have retained the essence of the original amp, I’ll focus on it first.
Uraltone’s HIFI PP EL84 is an amplifier kit with a simple but well-thought-out circuitry and quality parts. For all its essential parts the circuitry of the HIFI PP EL84 is based on tube amp guru Mauri Pännäri’s Revenge PP EL34 amp reviewed HERE. I think it’s fair to say that the kit is a traditional EL34 design with a set of unique features. Designwise, a prerequisite is its toroidal output transformers, designed byt Pännäri, Johannes Roine and Timo Liusvaara, manufactured by Muuntosähkö Helsinki, and retailed by Uraltone. What the Uraltone team has done to the original design is that they changed the output tube to EL84, and at the input replaced the ECC81’s with the ECC83’s (the amp can be modified to carry the original ECC81 too).
They also made the constant current generator adjustable, and added a cathode capacitor to the output stage. Negative feedback circuit is slightly modified, and a cap added parallel with the feedback resistor. The power supply was rationalized to some extent, some new components were selected, and the layout design changed so that the amp would be more easily implemented, quieter and more durable.
The phase splitter is connected to the output stage with a coupling cap, the only cap on the signal path. For the purpose, Uraltone recommended reasonably priced Icel, Solen Fast, Wima and Dijon caps, or Jupiter Cryo HT. The amp is designed to output approximately 10W @8ohm, with a frequency response 6.2 Hz – 60 kHz (+/-0.5dB, without a low pass filter at 100kHz), and THD at 1W 0.01% (0.3%. 10W).
The amp sports 3 x RCA stereo inputs, and a switch for the Negative Feedback selection between 0 dB, 6 dB or 10 dB. Hobbyists are predicted to like 6 or 10dB best, but I didn’t notice such a big difference betweenk the different settings. As a compromise I ended up using the 6dB point.
The kit is easy to build onto the custom CNC machined chassis provided the hobbyist knows the basics of layout design. Toroidal transformers make a small chassis possible. The principle idea behind the kit has been that it’s suitable for beginners. Basic tools, ability to solder and concentrate are the most important required characteristics. What if a person knows how to solder, but has no prior experience of assembling amplifiers? I’d say that this kit is not insurmountable. What significantly facilitates the assembly is the use of durable turret boards for easy soldering. Power supply components are soldered directly to each other. Instructions are available in Finnish and English, and schematics, layout and bill of materials are multilingual. Plus, email support is available in English free of charge.
I’ve heard and even reviewed at least a half of dozen commercial PP EL84 readymades. It’s pointless to make sweeping generalizations, but the EL84 PP amps do appear to produce a sound typical to them only, and different from DHTs or the EL34/KT88 tube family. They make an excellent choice for headphone amps but also for stereo amp systems in which loudspeakers have been meticulously selected.
I briefly compared the Uraltone PP EL84 Kit to my equally powered DIY PP 6V6 amp driving my 8Ohm/>95dB sensitive horn speaker system. And I must say that the Uraltone HIFI PP EL84 Kit amp managed well in the test. It took a firm grip of the bass notes, and under no condition did it run out of power. The mid-range sounded objective and unmasked, yet possessed a certain musical delicacy. In short, a very likable performance by this little c. 500 euro amplifier kit. Since this PP EL84 kit amplifier does not offer a traditional preamplifier stage, it can be used as a power amplifier as well. I tried and added a tube preamp in front the kit, and the sound quality, without delving in details, bettered still.
VERSION 2.0
The PP EL84 kit is now available as an updated 2.0 version (695 euro) with a new case and mechanical structure. The best features of the old design are maintained with improvements here and there. As a result, the kit should now be even easier to build and look more modern. Which one looks better is a matter of taste, of course.
The circuit is the same as in the predecessor: simple and with only necessary components. The design swears by the sound quality rather than by lowest possible distortion measurements. For the size and output power, the amp delivers about 2 x 10W which is an ideal choice for a pair of EL84 pentodes. The amplifier is designed for 8-16 ohm speakers, but the power transformer can also be connected for 2-4 ohms loads. THD is 0.01% at 1W and 0.3% at 10W with only 10dB feedback. More feedback would have lowered distortion figures but at the cost of input sensitivity making a preamp necessary. A single ECC83 provides good input sensitivity, allowing the entire driver and phase inverter stage to be implemented with a single tube (this amp kit has only 3 tubes per channel!).
The input selector switch relies on a relay selection, making the burdensome wiring unnecessary. As for other components, the best possible reasonably priced parts were opted for. As in the version 1.0, the output transformers – perhaps the most important single part of a tube amplifier – is a high-quality toroidal core transformer designed and manufactured in Finland. As is the powder coater black chassis.
TECHNICAL FEATURES
Tubes: 4 x EL84 and 2 x ECC83
Output Power: 10W @ 8 ohm, with 0.4-0.9V input (0dB-10dB with feedback)
Inputs: 3 x RCA stereo and 1x 3.5mm inputs
Controls: on-off, feedback 0, 6, 10dB, volume, input selector
Very high sound quality
Frequency response min. 6.2Hz-60kHz +/- 0.5dB (without cutting up to 100kHz)
THD 0.01% at 1W, 0.3% at 10W
Feedback selectable with switch: 0, 6 or 10dB (6 – 10dB perhaps the optimal, the sonic effect being very speaker-specific).
External dimensions approx. 360x215x130mm (with tubes and protective housing).
Weight approx. 4.7kg.
Unlimited email support.
The kit comes with a layout picture, schematics, and a bill of materials. A series of pictures of the construction of the amplifier will be published soon in our info section.
