- GG Audio Design is a small and very flexible firm for design and manufacturing of audio equipment. The products are made in small series and mostly to individual orders.
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The key component determining the sound character of an audio system is the power amplifier. The ‘valve sound’, particularly that of the Single-Ended (SE) power amplifier always attracts with its blend of warmth, purity and authenticity. The particular charm of its sounding attracts many contemporary fans. The SE valve amplifiers are reverberation from the thirties of the last century, reflected in modern technologies.
Appreciating not just the romantics of the past, but also the contemporary trends in the development of hi-fi technologies, we offer the valve amplifier GG-SE20 with its exceptional qualities to the present day audio fan.
The GG-SE20 philosophy
Our approach is to design amplifiers, which we would be ourselves happy to buy. Substantial attention is given not to the output power, but to the accurate reproduction of the timbre and the sound dynamics.
The amplifier is designed especially for audiophiles, who use high quality speakers with high sensitivity and prefer the superb musicality of the SE amplifiers.
Equal attention needs to be given to absolutely everything – from the circuit design and the materials for the box and the chassis, even down to the temperature of the solder joints.
The circuit design solution is based on the shortest possible signal path, using only two amplifier stages.
The output stage implements the legendary to the audiophiles beam power tetrode KT88/6550. Many manufacturers, in order to achieve ‘high wattage’ use KT88 as a rule in a push-pull circuit, sacrificing the pure sound. Using KT88 in a Single-Ended circuit its true potential is felt instantly, expressed through the detail, transparency, high speed, depth and very broad total palette. The listener detects the ‘correctness’ of the sound, a sure sign of natural, easy musical presentation.
The output stage is designed as a single-ended circuit. The output power of the SE triode amplifiers is not high, particularly when based on a single valve. This is why two selected KT88 power beam tetrode valves are used, connected as triodes operating in class A. Each output valve has its own fixed positive auto-bias, with the anodes connected in a quasi-parallel configuration. There is no common negative feedback, which allows very high dynamic range and detail of the sound picture.
A switch, discretely positioned under the bottom cover, can be used to enable local cathode negative ac feedback, across the output stage. The shallow 2.6db negative feedback contributes to the balancing of a dynamic sound and good dumping factor.
There is no ‘optimal’ position for this in engineering context. While the negative feedback improves the dumping factor and reduces the non-linear distortions, it somewhat degrades the musical picture. In other words there is a little good and a little bad in the negative feedback. Through listening and switching on and off the negative feedback it is possible to reach a preferred subjective presentation of the sound picture for the audio system as a whole. With dynamic loudspeakers the sound without negative feedback will be very transparent.
When loudspeakers with high reactive impedance (e.g. QUAD-ESL63) are used the use of negative feedback helps achieving open and spatial sound.
The 5kg output transformer by Hammond ensures the very even frequency response of the amplifier in the lower range. It is possible to connect speakers with nominal impedance of 4 or 8 Ohm directly to the output terminals of the amplifier, and 16 Ohm speakers by re-soldering the leads of the secondary coil of the output transformer. It is necessary to use loudspeakers with minimum sensitivity of 88db (2.83V, 1m). The recommended value is 90db, while 93db is the ideal choice.
Two valves ECC81 (dual triode) connected in parallel in an SRPP circuit are used as an input/driver stage. The DC converter for the anode voltage is realised in a standard way with a valve rectifier GZ34 and a CLC filter. For different mains /220-230-240/ voltage the primary coil leads of the power supply transformer need to be re-soldered. Other factors contributing to the high sound quality include:
• capacitors by MUNDORF; three types of capacitors are used depending on the application, M-CAP ZN (in the signal paths), MLytic HV and TubeCap in the power supply circuits
• valves by JJ Electronic
• resistors by Allen Bradley, HOLKO, RIKEN
• cables by Van den Hul
Construction specifics of GG-SE20
The two mono units are made in a classic streamlined design and placed next to each other give 19’’ total width.
The front panel is made of a 10mm aluminium plate with a power on/off button and a corresponding LEC indicator. The bottom is a 2mm steel plate, on which the mains transformer, the output transformer and the filter choke are fitted. Suspended on 4 supports, 40mm above the bottom is the chassis, which is made of 2mm aluminium. The valves and the passive components are mounted on it. At the back the heavy-duty output terminals for connecting the speakers are positioned, together with the RCA input, the IEC supply socket, the fuse, connected in the primary coil of the mains transformer and the earth switch (audio-earth decoupling). This switch allows to isolate the audio (signal) earth from the mains preventing the appearance of mains hum in the speakers. This usually happens when two or more components of an audio system are on simultaneously, which leads to potential difference between their different earth connections.
The wiring is handmade point-to-point. The lid of the box is 2mm perforated aluminium. The meticulously worked out wiring technology ensures the shortest signal paths.
The stability of the construction and the use of sound absorbing (deemphasising) materials, ensures the necessary protection of the preamplifier from external sound waves as well as internal vibrations, caused by currents in the electrical circuits. The preamplifier rests on special three point supports by Soundcare (http://www.soundcare.no/). These help to minimise the mechanical-acoustic feedback, which appears in a closed listening environment. The supports are made of special materials selected through long times of listening, tests and measurements.
The result is improved control over the low frequencies and clarity of the musical landscape.
The amplifier connects to the mains with a three-wire power supply cable. The earth wire is connected directly to the earth terminal of the chassis (the box), while the audio (signal) earth connects to the chassis through the decoupling switch (isolate/ground). In ‘isolate’ position the audio and radio frequency signals are connected to the chassis, while the DC is blocked.
The recommended work-in time for achieving perceptive musicality of the output amplifier is 75-100 hours. It is normal during this period for the sound to become more and more dynamic and coherent. The sound will improve perceptibly, transforming from blurred into the desired musicality. As they say patience is the virtue of high quality.
Technical details and performance figures:
Type: Pure Class A
Input: RCA × 1
Input impedance: 100 kOhms (DC connected to the first tube grid)
Input / driver stage: SRPP configuration ( two parallel ECC81 )
1.40 V/14W(with cathode feedback)
db (without feedback)
17.4 db (with cathode feedback)
Parallel single ended, triode
with cathode feedback ( two parallel KT88 )
Power output: 14 Watts RMS
Speaker Post × 3 (4 / 8 ohms ) or 16 ohm
/ 8 Ohm - 1 kHz
4 / 8 Ohm - 1 kHz (with cathode feedback)
(+ 0 /- 1
Hz÷22 KHz (1W)- (without feedback)
6 Hz÷25 KHz (1W)- (with cathode feedback)
Hz÷33 KHz (1W)- (without feedback)
5 Hz÷35 KHz (1W)- (with cathode feedback)
(+0 / -3 db)
Signal-to-noise ratio (CCIR 468-2)
unweighted (15Hz-30kHz) 55db rms
(30Hz-16KHz) 78db rms
weighted 84db rms
Distortion(1kHz): < 3
% at 14
Watts, below 0,45
% at 1 Watt(without
< 3 % at 14 Watts, below 0,15 % at 1 Watt(with feetback)
: 220, 230, 240
(selected when shipped)
Power consumption: 130 watts
Height 176 mm ( 4HE )
Depth 483 mm( 19" )
Net Weight: 15.5 kg
Shipping Weight: 20.5 kg – in a wooden boxWarranty: 3 Yars Parts and Labor. 90 days on vacuum tubes