Search for Chinese gems continues...
From shit to gold in 1/2 hour
Nov 24 2007.
This amplifier , known elsewhere as SPARK, looks like nothing special.
It is a no nonsense design, without golden ornaments, without marble,
no granite in sight either. No pierced clit. Just a nice stereo
It is relatively small, quite well made, and the metalwork is excellent. Fit and finish is up to US standards.
It is a circa 50 WPC push pull with KT88 tubes as power, and typical
combination of 6N8 as drivers and 6N9 as input. Electrically it is a
ultralinear pentode class B pushpull, a cousin of Manley/VTL range, a
grand-son (grand-bastard?) of Williamson.
Upon inspection under the hood we can admire one of the best amplifier "guts" that I have seen so far.
It looks absolutely fantastic.
First - all is point to point - no PCB, so we can mod easily anything we wish.
Second - all parts are very good quality (alps pot and switch, brand name caps, and so on.)
All assembly is super neat and super well organized.
The more I look , the more I like what I see.
But how does it sound?
Obviously, now I am going to criticize it so on the background of this
I will look better like a guru who turns this miserable amp into a
So lets start:
the amp sounds absolutely horrible. It is so loud, that at 9 o'cloch it
is in full power and clipping. The treble are grainy, closed in, dirty
and spitty. Bass is boosted like there is a 12 dB uplift. Even the
brothers in the Bronx would probably complain that it has too much bass
and an ugly one as well. One-note kind of overblown boom boom boom.
I could listen to half a song and I had to throw the towel.
"On the workbench or out of the window" - the choice is yours I mumbled
and I prayed that I will be able to find the critical area of this amps
First - unlike the KT88 Music Angel - this amp has no triode-pentode switch. It is a permanent pentode.
Bingo thought I, lets make it permanent triode. (I wanted to avoid the
switch because I had many amps like this and I would NEVER consider
listening in pentode even for a minute. Triode is the only way to go.
This mod already gets us 50 % there - everything explodes - opens up,
there is space, there is air, the bass starts to play music again.
Still too loud tough.
The triode conversion takes 4 minutes - we cut off the orange wire
leading from output transformers ultralinear taps to the octal sockets
of power tubes. We isolate the cut cable because there is 425V on them.
Then, the tube leg where the orange wire used to be, must be connected
to the anode - white wire coming from the same output transformer by
means of a 1/4 Watt 100 Ohm resistor. (+-30%)
After that, we adjust the bias current to a conservative 27 mA. (which
means 270 mV on the 10 Ohm cathode resistor.) The blue pots are super -
user - friendly !!!
Next point is the input tubes - we get rid of the 6N9 (6SL7GT) and we
put in that place the same tubes as drivers - 6N8 (6SN7GT). That
reduces the amplification factor by 5 x, makes bass civillised and
treble super-pure. The input circuit (paralell triode, anode follower)
can remain the same, as well as all resistor values. Shall you really need more amplification - keep the 6N9.
Next, I increased the input triode supply cap from 22uF/450 V to a much
bigger 100 or even 220uF / 400 V (there is only 200 V there).
This mod gets us 90 % to Nirvana alrerady.
Last change, remaining 10 % is to connect the pot DIRECTLY to
first (input) tube grid and to eliminate unnecessary series resistor
and one paralell shunt resistot. These two go OUT.
Now the amp behaves like Conrad-Johnson, I kid you not. In my opinion
it is not as good as Music Angel KT88, but it is close. That means it
is a damned good amplifier, with all the beauty of tubes, it is well
made, the amp and tubes are reliable and I can't imagine a better
starting point into High-End than this little sucker.
It probably costs also more than MA. Anyway, if you have such baby -
the mods cost the value of 4 resistors and two tubes. I recommend
chinese 6N8P or russian 6H8C. You may go as far as the NOS red-base for
400 bucks a quad. ;-) but really - the chinese metalbase is very
Highly recommended !!
Premium capacitors, not expected at all in this price point !!!
Red arrows show the components to be changed: a pair of input resistors per channel (just after the pot and before first tube)
and a power capacitor to be increased - the black one - 22uF / 450 V
was replaced by 100 uF / 400 V - the big black can on photo below.
You can see the triode mode conversion resistors - in each power tube
base there is one small brown resistor - 100 Ohm from anode to controll
grid. (the one standing high up)
I think on this drawing I forgot to add a capacitor just between the
first tube and second tube (grid) - there MUST be an MKP of 220nF/400V.
Again - the triode conversion close -up. The yellow wire is removed and insulated.
The speaker transformer outout wires: the red is input power supply
center tap, the yellow are ultralinear winding taps (to be cut off and
insulated) and the white ones are anode of power tube.