Modding the SAKUA AV200

[TonyTecson]

hi,

about a year ago i purchased this amp for 3500, it is a hybrid tube amp......

An externally hosted image should be here but it was not working when we last tested it.

for the money, 3500 in philippine peso, it's uite hard to fault this amp.....i got curious then to find out what makes this amp tick.....

 

[TonyTecson]

so what i did was to look under the hood:

what i found was 2 5Z4 rectifier tubes supplying rails of +/- 6 volts using 6 volt zener shunt regs..... :lol:
these rectifers supply an input op amp, 4558.....there are two 4558 opamps, the other one drives 6H23(6DJ8/6922 like) cathode followers, mind you, only one half of each tube was used as cathode followers so then you technically have a spare tube... :lol:

this is the schematic of the 5Z4 tube psu:

 

[TonyTecson]

the mods aimed at removing the rectifier tubes so that these can be more gainfully employed in another project:

board before the mods:

after the mods:

so now one 4558 ic has no rails, what i did was to tap to the existing +/-12 rails for the other 4558 using a 100ohm resistor and 0.22 mylar bypass caps to power the orphaned IC:

 

[TonyTecson]

with the rectifer tubes out of the way, other mods were done:

the input board was not spared, the sub-woofer output low-pass filters used ceramic caps, these were replaced with mylars,

 

[TonyTecson]

so how was the mods?

i must admit that i am happy because now i have spare rectifier tubes, one of which will be used on a guitar amp and the other on a line preamp i am in process of making:

sound wise i noticed a slight improvement, but this amp being an SS amp despite the tubes will perform in accordance to what you feed it with.....

 

[TonyTecson]

final modding will get rid of the 6H23 cathode followers....there are too many coupling capacitors in the signal path.....removing those tube buffers gets rid of 2 capacitors in the signal path.....and 2 high transconductance tubes to boot...

don't get me wrong, this is a very nice amp despite the tubes......and at 3500 who can complain?

i got inquiries as to why i decided to get rid of those 5Z4 rectifier tubes and as always my response was, "because I can"

seriously though, the 4558 ic needs about 3ma or so at idle, with +/-6 volt rails, the 2 5Z4 filaments consumes about 10 watts of power so that it is like doing hard work for nothing....that 20 watts of power can them be used by the power amp and sent to the speakers instead....

on a side note, should you opt to keep the rectifier tubes, it is going to outlive the amp itself, it is in now way stressed out......6 volts at 3mA is way too low even for the 2200ufd/25volt caps used for filtering.....