I am happy to present my new, improved parallel single-ended, low power amplifier, featuring again the amazing direct heated pentode  4P1L. Overall, compared with the first built, I can say the sound is similar, just more refined and definitely is offering more joy for the addicted audiophile…

One recommendation is to try to find the perfect speaker match… and this is not an easy task. One will need a high efficiency full range driver speaker that is seen as an easy load by the amplifier.  If you are not listening at high dB levels than can get away even with 92dB speakers ( such as Alpair 12P).

 

Improvements to 2103 Edition

Transformers:

• OT upgraded to Monolith Etude 1 (3300/4-8ohms, 80mA) for better frequency response and better match ( last OT was 3000/8ohms)
• dual secondary OT for 4 and 8 ohms

Resistors

• Coleman regulator for the driver stage current sensing resistor upgraded to Takman “Rex” audio grade carbon film for improved sonic response
•  Cathode resistors for the final stage upgraded to Mills non-magnetic, non-inductive wirewound, audiophile grade for improved sonic response

Capacitors

• first PSU capacitor 47uF/630V Solen Fast upgraded to TC-4 terminal CCT C4-050 50uF/600V for enhanced high frequency filtering performance

Cabinet Enclosure

• upgraded to cherry boards to enhance look
• routed deeper for top plate to eliminate exposure of top plate edge

Mechanical

• repositioned main heatsink and divide it in two modules for improved heat management
• main amplifier top plate upgraded design for improved heat management and esthetics
• created better access to all connections and parts

Description

“Shiny Eyes” Parallel Single Ended tube amplifier is second in the “Shiny Eyes” series. It preserves the look of the series, with cherry stained hardwood cabinets and gold anodized aluminum top plates by Proto Panel. The first amplifier in the series is a push-pull and the third is a headphone amplifier, both featuring the same final tube 4P1L (4П1Л), a direct heated pentode in triode mode. “Shiny Eyes” PSE is my favorite of all. As one can expect, no sound can compare to the sound of a all direct heated tubes, single ended amplifier.

This a low power amplifier ( 2x3W), providing a transparent, gorgeous sound. However, 3W stereo of single ended tube amp will sound much more powerful than a solid state showing the same power specs. This amp, being single-ended must be used in combination with a high sensitivity  (> 96 dB) full range driver speakers in order to reveal its true identity. Breaking in will take at least 100 hours and will reach the highest sonic performance around 500 hours.

It is hard to describe the sound of this amp for those who never listened to a quality single ended tube amplifier. It has a heavenly aura, harmonic subtleties and a timbre that will give instant goose bumps, and you will definitely fall in love with it.

The amplifier consists of two enclosures: one is the power supply (weighting about 55 lbs.) and the other one is the main amp (weighting 32 lbs.). They are connected by two 7 wire 18AWG umbilical cables, that bring power to the main amp.

The power supply unit (PSU) consists of separate transformers for each stage/channel filament supply , one common high voltage transformer and tube rectifiers followed by separate filtration for each channel. In addition, a shunt regulator supplies power to the driver stage tube ( this regulator is located in the main amplifier enclosure). The PSU is running slightly warm (is designed with a good power reserve). The only temperature hot area of the PSU is around the rectifier tubes (they are placed in  the middle and protected by chokes and transformer covers). Some of the subassemblies of the power supply are located in the enclosure of the main amp for technical considerations(they need to be closer to the audio stages). There are four  Rod Coleman filament regulators placed on a large heatsink in the main amp enclosure and also two high voltage shunt regulators for the driver stage placed in the proximity of the driver tube and interstage transformer.

The main amp is designed with one type of tube for both final stage and driver stage. The two stage design was facilitated by a tube ( 4P1L) with a nice amplification factor of 9. The final stage uses parallel tubes in order to provide a decent output power of 3W. The output transformer is a high-end Etude 1 by Monolith Magnetics. The driver stage is designed with a nice headroom of 12dB, high current capability, being able to easily drive the final pair of tubes. The coupling of the driver stage to the final stage is through a interstage transformer a high quality Lundahl. Both stages of this amp are designed in filament bias where a separate power supply delivers power ( in a close loop) to the filament and cathode resistor. In this case and for this particular tube, filament bias is doable ( decent voltage and current levels) allowing a reasonable heat (power ) dissipation by the cathode resistors. The great advantage is that, because of lower values of this cathode resistor there is no need to use a decoupling capacitor. The compromise of having to deal with the heat dissipated is well counterbalanced by the rewarding sound aura delivered by this amplifier.

The amp is running hot in the middle section where many slots are provided to release the heat developed in the filament bias resistors(a total of 62W). Heat is raising by natural convection provided by over 300 holes on the perforated enclosure’s bottom. The amplifier was repeatedly tested for at least 8 continuous hours at time and presented minimal drift. The driver stage tubes are a bit microphonic ( as many direct heated tubes are). This was “tamed” by starved filaments, suspended sockets, rubber grommets and rings. During a warm up time of 5 to 10 minutes (depending on room temperature) the driver might “sing” ( the filament and whole tube is pinging because of transition from low temperatures to high temperatures). After this transitional time the amplifier goes in a very stable harmonic stage.

The amplifier has one set of RCA isolated inputs and a set of speaker outputs. A 1/4″ headphone output is provided also. The volume is controlled independently for each channel.

“Shiny Eyes” PSE is hand wired and extreme care was taken to high quality soldered connections. Most of the wires used are Teflon silver plated. The layout of this amplifier was carefully designed to ensure the shortest audio path, excellent positioned signal ground, pleasant look and mechanically robust.

All “Shiny Eyes” PSE’s components are attached to a gold anodized 3mm aluminum top plate. This plate is attached to the wooden enclosure with four M4 screws. A pair of nice antique bras handles are attached to the top plate on each side and are used to lift and move the amplifier.

This amplifier features the same tube for all audio stages, the Russian direct heated pentode in triode mode: 4P1L(4П1Л). It is an amazingly linear tube in  triode mode. The sound of this tube is similar to the sound of 300B, 2A3 and some would say that is surpassing the famous ones. In addition, a shunt regulator supplies power to the driver stage tube.

Photos taken during building this amp

and some graphs :

Right channel 1Khz 0dB output 4.7Vrms on 8ohms (2.75W), input at 1Vrms. From this point higher order harmonics will start kicking in.

As we can see below at 3W ouput, input 1.05Vrms. Overall Gain 4.7 times or 13.5dB

Frequency sweep (10hZ to 40KHz) resulted in 30Hz @ -1dB. Measured at 2.75 W out.

 

More pictures:

Final Notes:

• If one wants to squeeze this amp to its limits, can move the operating point of the final tubes towards the power limits of the 4P1L ( I tried to push it to the limits and I could operated it beyond 10W(Pa+g2,3) ( I tried it at 10.5W for few hours and didn’t show any signs of “giving up”). There is always a compromise: you want less distortions and even more gorgeous sound than you’ll have to replace tubes more often. It would be interesting to find out how long this amazing pentode will last at different Pa+g2,3.
• There is a limiting factor that comes with a low power amp: need to find the right speaker ( high sensitivity and easy to drive). This is the reason I am working now on a new PSE amp, most likely a quad 4P1L, class A2 to get easily 10W. It will be a quite different design…Stay tuned….