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OMAK JEWEL ONE and JEWEL THREE
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OMAK JEWEL ONE and JEWEL THREE
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OMAK JEWEL ONE and JEWEL THREE

 

These amplifiers use high-current EL509 power pentodes. Such valves are rarely found in power amps, but their outstanding performance is revealed since 1970s. The huge emission current of EL509 is enough even for the OTL amplifiers. We indeed use the output transformers. The configuration of output stage and properly chosen mode of operation provide the low distortion over a wide range of loads. The output stage utilises a distributed load push-pull configuration. A small part of primary winding of the output transformer is connected to the cathodes of power tubes. A little amount of local negative feedback is thus introduced to the output stage. This circuit is known since 1940s and its combination with powerful valves like EL509 and low-loss transformer gives remarkable results. The spectrum of harmonic distortion consists of pure second harmonic for almost all dynamic range. The third harmonic appears approximately at -6B in respect to clipping. This behaviour is similar to that of triode SE amps, but there is a difference: the output power continues to increase up to 2 Ohm load, and at the same time the full output is achieved at 20Hz and even lower. The high frequency limit is determined not by the output transformer, but the driver circuit. The next feature of these amps is a behaviour of output impedance: it is almost constant even well above 20kHz, and the amplifier can safely drive even the capacitative loads like electrostatic speakers.
OMAK JEWEL ONE is a stereo amplifier. It exists in two versions(Mk.1 and Mk.2). These versions differ mostly by the output transformers, the Mk.2 amp has slightly lower output power, but the class A region of operation is much extended. The amount of negative feedback is also reduced. JEWEL ONE is assembled in aluminium alloy case, features the huge power supply and a special wiring technology where a pcb is used only as an array of wiring points thus providing a fixed topology; the poin to point wiring is carried out by the component leads and high-quality PTFE-insulated copper wire. Because the output valves operate with fixed bias, there is a need to monitor a quescent current. OMAK JEWEL ONE comes with a comparator circuit which allows one to detect the lower threshold of bias current of all four power valves simultaneously. When the bias current of any tube falls below the lower limit, the respective green LED illuminates. The practice indicates that after an initial period of approximately 200 hours the bias become highly stable and requires no adjustment. The expected lifetime of EL509 valves in OMAK amplifiers is certainly over 5000 hrs. In fact we observe a number of our amps operating more than 6 years on the same valves and without adjustments.
OMAK JEWEL THREE is a monoblock built in the same casing that JEWEL ONE. It utilizes two pairs of EL509 valves and larger output and mains transformers. The full output into 8 Ohms is achieved in pure class A. When the load is lower than 8Ohms the amplifier still delivers a sufiicient power within class A limits so transfer to class AB operation takes place only at signal peaks. JEWEL THREE can safely drive even 1 Ohm load.The output current is more than 20A which is enough for most speakers including very current-hungry ones. The high load capability is associated with soft clipping and superb linearity. The output power is far enough even for low-sensitivity speakers usually requiring the large solid-state amplifiers.

SPECIFICATIONS

  Mk.I Mk.II
Power, THD < 1%, 20 Hz - 20 kHz    
8 Ohms
2 x 50 W 2 x 40 W
4 Ohms
2 x 80 W 2 x 60 W
2 Ohms
2 x 140 W 2 x 90 W
Class A Power (8 Ohm, 20 Hz - 20 kHz) 2 x 12 W 2 x 20 W
THD at low level, Vout = 2.3 Vrms, 20 Hz - 20 kHz < 0.1 % < 0.1 %
Overall negative feedback at 8 Ohm 9 dB 6 dB
Voltage gain 32 dB 30 dB
Input impedance 50 kOhm, unbalanced 50 kOhm, unbalanced
Output noise, unweighted < 1 mV < 1 mV
Output current 14 А 18 А
Power bandwidth (0-3dB) 16-80000 Гц 16-100000 Гц
Output impedance, 20 Hz - 20 kHz <0.8 Ом <0.8 Ом
Sensitivity 0.6 В RMS 0.6 В RMS
Power consumption: at idle; 230 Ватт 230 Ватт
at full output 600 Ватт 600 Ватт
Mains requirement 220 – 230 V 50Hz 220 – 230 V 50Hz
Dimensions, mm 483 х 455 х 191 483 х 455 х 191
Weight 30 kg 30 kg

 

OMAK JEWEL THREE

Power, THD < 1%, 20 Hz - 20 kHz  
8 Ohms 60 W
4 Ohms 100 W
2 Ohms 160 W
1 Ohm 200 W
Class A Power (8 Ohm, 20 Hz - 20 kHz),at 8 Оhm load 60 W
at 4 Ohm load 40 W
THD at low level, Vout = 2.3 Vrms, 20 Hz - 20 kHz < 0.1 %
Overall negative feedback at 8 Ohm 4 dB
Voltage gain 30 dB
Входное сопротивление, kOhm 50 , unbalanced
Output noise, unweighted < 0.5 mV
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