AMPLIFIER
 
Glow Master Series
KT-88 True Balanced Push-Pull Amplifier
GlowMaster KT-88 receives 5 Global Award
from Hi-Fi World Magazine, UK, February 2008 Issue.


This amplifier is the second generation of our pride GlowMaster Series KT-88 push-pull. We have set new goal to implement the newest true balanced circuit topology from input stage, driving stage and output stage to ensure the absolute purity and authority of signal transmission that is better than any conventional unbalance amplifier. Our true balance circuit is based on new balance amplification principle which we utilize to help cancel harmonic distortion that enable our design to focus on finding the most linear portion of each circuit stage to realise the fullest linearity and minimizing the use of negative feedback.
 
Balance signal transmission principle can be viewed as two separate circuit working in parallel that have signal in opposite phase. Thus any noise and distortion that occur during transmission will be cancelled out at the output stage. Since the distortion of the balance circuit is so low, we are able to utilize new GlowMaster with very small negative feedback. The benefits we found are tremendous. Phase problems usually associated with high feedback circuit dissappear, that's why New GlowMaster KT-88 has true wide bandwidth of 100KHz, -1.25dB with very low harmonic distortion.


Without the new development of SILK P-4200 balanced output transformer, the performance of true balance circuit in New GlowMaster KT-88 can not be fully realised. Other balanced push-pull amplifier can get very distorted waveform at high frequency once drive an unbalance capacitive load. (most loudspeaker has passive crossover network comprised of R/C/L) Even drive a load with very small capacitive value of few pico farad, regular balance output transformer from other companies will display abnormal behavior (this happens to be the case when just connecting an oscilloscope which has only 3pF shunt capacitor at input terminal to see the signal trace). SILK P-4200 Balance output transformer uses our own special balance winding technique to counter this effect so it can handle unbalance capacitive load without any problem and extend the quality of balance circuitry to the extreme.

New power supply transformer (SILK Special layered wound) with +700VA is the main power source to supply all current needed to drive GlowMaster KT-88 a champion of its class. There is special electro-static shield built in the main transformer so this amplifier can be used in environment where high voltage noise would normally cause system instability. Further the main transformer is also feature electro-magnetic shield to suppress any magnetic flux leakage to other sensitive input circuit. Main power supply is separated into high voltage for output tubes and low voltage for input and driving tubes. High voltage power supply has big DC choke with low output impedance to smoothing out the supply ripple and provide very stable voltage. Low voltage is a dedicated regulated supply that has more than 105dB of ripple rejection. Bias adjustment voltage is also regulated to maintain the most stable voltage.

Input and driving circuit use 3 x 6N1P dual triode per channel. This 6N1P tube has gold plated grid winding that offer the best sounding characteristic of any input tube. We have selected each input and driving tube to match with predefine working of our circuit. Output tube is our own hand selected matched quad KT-88.

We announce that the new GlowMaster KT-88 has output power of 65 watt RMS per channel, but the true reserve power (peak instantaneous power) of close to 100 watt/Channel. At clipping (soft clipping) GlowMaster develops 80Watt RMS.

High output power is not alway guarantee that the amplifier has superb diving power. The true specifications that indicate true driving force are output impedance and damping factor. Most KT-88 push-pull amplifier has more than 2 ohm output impedance and damping factor of less than 5 (if most manufactures really provide truth specification). Even if such amp has 150 watt per channel, it will sound flabby and slow when play against new GlowMaster KT-88.

With hundreds of hours of fine tuning, we are able to make the new GlowMaster KT-88's Output impedance of only 0.7 ohm while damping factor is 10.5 or better. This can only mean that new GlowMaster has breaked the limitation of regular vacuum tube design for under 100 watt RMS per channel amplifier.
Its low output impedance and high damping factor means that it can fully control any loudspeaker with precise timing and pace even from low listening level to the highest level.
Its true wide bandwidth means that it can equally render music signal and capture all harmonic overtone of each instrument without bandwidth limitation.
Its ultra low harmonic distortion combine with true wide bandwidth characteristic allow new GlowMaster KT-88 user to hear details and inner details at all listening level.

New GlowMaster KT-88 sounding performance enters new era of true high definition vacuum tube amplifier.

 
Built to withstand the test of time, the massive chassis with beautiful tube cages and gorgeous front acyric plate offer high class look and esthetic. Transformers are housed in separate SILK canister to minimize viberation and noise. This also keeps future services and upgrades very easy task.

So many times output tube in push-pull amplifier can have current drift over time and cause sound degradation while the users have no indication and get use to hear all extra distortion. It only takes as little as 2mA current drift of each tube bank to alter the harmonic spectrum and most tube amp with over 6 months of running time can get as much as +20mA current drift. Imagine how vunerable to hear extra distortion, harh sound and lack of details without the way to monitor the output current of each tube.
New GlowMaster KT-88 features new front LCD display that generates critical information of each KT-88 output tube. Each numeric number shows current level in real time allowing end user to monitor the amplifier whether or not it works at absolute performance.
Front LCD is controlled by a micro controller which can be software upgraded at later time to provide future compatability with new software development.
New GlowMaster KT-88 features high quality parts through out the circuit. Point to point hand wiring is used for all signal path to maximise the signal transmission. We use high quality Amphenol XLR input, Gold plated RCA, Heavy duty gold plated (insulated) binding post, Miyama switch, OFC bus wire, silver solder and best of all, the new SILK P-4200 Balanced output transformer. Power transformer is SILK handwound with special electro-static shield and electro-magnetic shield.
 
Test Report
 
This picture depics the output harmonic spectrum of new GlowMaster KT-88 balanced with 1KHz signal at 1 watt into 8 ohm load. THD is -68dB (0.039%) while this number is one of the best prove number for any tube amp, it is more important that -68dB is almost entirely derived from the second harmonic. Second harmonic is very pleasing to ear at low level; moreover, it is very hard to detect the second harmonic even at high level.
This test shows that in most listening session (where 95% of the music passart is under 1 watt) GlowMaster KT-88 will display the best music integrity while not generating harh sound from high order harmonic distortion.
 
This picture depics the output harmonic spectrum of 10KHz signal at 1 watt into 8 ohm load. GlowMaster shows amazing low distortion figure of -68dB (0.039%) same level for 1KHz. This is not easy to achieve for other amplifier where 1KHz performance may be good, but start to get high distortion at higher frequency. New SILK P-4200 output transformer contributes great deal in this catergory.
 
This picture depics harmonic spectrum of 1KHz signal at 65 watt into 8 ohm load. Amazing low distortion of -56dB (0.15%) is actually obtained. There is no other manufacture that eager to show this except numeric figures in their data sheet table.
 
Frequency characteristic of new GlowMaster KT-88 can be seen in this picture. The response can go down to 1Hz up to 100KHz with -1.25dB only.
 
Frequency response at 65 watt is linear within 0.1dB from 20Hz to 20,000Hz. This is better than most solid state device (which already use tons of negative feedback). The level of accuracy of new GlowMaster KT-88 is only available in reference instument grade, which set a new class of its own.
 
Specification
Product Type:
Stereo Vacuum Tube Power Amplifier
Feature:
Fully balanced circuit (XLR) from input stage to output
Front LCD monitor real time current of each output tube
Input/Driver Tubes:
Matched tripple 6N1P
Output Tubes:
Matched quad KT88
Rectifier :
1.5KV/1500mA Hi-speed Damper Diode
Filter Capacitor:
Audiophile Grade Rubycon
Filter Choke:
Low Loss 2H/500mA
Coupling Capacitors:
Solen Fast Capacitor
Signal Resistors:
Precision Metal film
Output Transformer:
SILK P-4200(Balanced) Precision Handwound Output Transformer
Output Power:
65 watts RMS/CH (THD less than 0.15%)
(measure with 225V AC line voltage)
80 watt RMS/CH (THD less than 1%)
Frequency Response :
1-100,000Hz (-1.25dB) at 1 watt
Frequency Response :
20-20,000Hz (-0.1dB) at rated power
Input Sensitivity:
1.2V for rated power output
Input Impedance:
200K ohm XLR, 100K ohm RCA
Overall Gain:
26.5dB
Damping Factor:
10.5
Output Impedance:
0.7 ohm
THD at 1 Watt:
0.039% or -68dB
THD at 65Watt
0.15% or -56dB
S/N ratio:
better than - 98dB
Size:
(W) 32 x (D) 48 x (H) 24.5 cm.
Weight:
28.5 kg. (62.7lbs)
Shipping Weight:
Approx 32 kg.