- 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.
VALVE PUSH-PULL MONO OUTPUT AMPLIFIER GG-PP30
The key component determining the sound character of an audio system is the power amplifier. While Single-End (SE) amplifiers offer better musicality, the Push-Pull amplifiers usually have more authoritative, powerful and base presence. The Push-Pull amplifiers are also compatible with a greater variety of speakers.
The GG-PP30 philosophy
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 GG-PP30 valve power amplifier was designed for audiophiles who had moderately efficient speaker systems and for less efficient speakers systems if high listening levels were not required.
Substantial attention is given not to the output power, but to the accurate reproduction of the timbre and the sound dynamics.
The output stage implements the legendary to the audiophiles beam power tetrode KT88/6550. The output amplifier design is based on a push-pull circuit with output power of 22W per channel. Used two matched pair KT88 power beam tetrode valves , connected as triodes operating in class A. Each output valve has its own auto-bias. Low global negative feedback is used, which allows very high dynamic range and detail of the sound picture.
A switch, discretely positioned under the bottom cover, can be used to select low global negative feedback of 0-2 or 4 db. Low global 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 output transformer is one of the most critical components in an audiophile amplifier. The superbly made broadband output transformer, by Hammond http://www.hammondmfg.com/clsover.htm is used to enhance the quality of the amplifier. 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.
The input and the driver stages are realized as a balanced circuit with two valves ĹŃŃ82(dual triode). The combination of fixed bias at the input and the automatic bias control of the driver stage contributes to the stable operation of the amplifier even with no specific valve selection.
The DC converter for the anode voltage is realised in a standard way with a valve rectifier GZ34 and a CLC filter. 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-PP30
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.
For different mains /220-230-240/ voltage the primary coil leads of the power supply transformer need to be re-soldered.
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: Class A
Input: RCA × 1
Input impedance: 50 kOhms (DC connected to the first tube grid)
Input / driver stage: Balanced configuration ( two ECC82 )
Input sensitivity: 1.35 V/22W (without feedback)
Gain : 21,5 db (without feedback)
Output stage: two KT88 (triode connection)
Power output: 22 Watts RMS
Output: Speaker Post × 3 (4 / 8 ohms ) or 16 ohm
Damping factor: 1,5 / 8 Ohm - 1 kHz (without feedback) 3 / 8 Ohm - 1 kHz (with cathode feedback)
(+ 0 /- 0,6
Hz÷20 KHz (1W)- (without feedback)
14 Hz÷36 KHz (1W)- (with 4db feedback)
KHz (1W)- (without feedback)
12 Hz÷40 KHz (1W)- (with 4db feedback)
(+0 / -1,0 db)
Signal-to-noise ratio (CCIR 468-2)
unweighted (15Hz-30kHz) 66db rms
weighted 78db rms
Distortion(1kHz): < 1 % at 15 Watts, below 0,20 % at 1 Watt(without feetback) < 1 % at 18 Watts, below 0,15 % at 1 Watt(with 4db feetback)
: 220, 230, 240
(selected when shipped)
Power consumption: 120 watts
Height 176 mm ( 4HE )
Depth 483 mm( 19" )
Net Weight: 13.5 kg
Shipping Weight: 19.5 kg – in a wooden box
Warranty: 3 Yars Parts and Labor. 90 days on vacuum tubes