Modding the SAKUA AV200

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Modding the SAKUA AV200

Postby tony » Fri Dec 31, 2010 7:42 pm

hi,

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

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for the money mahirap pintasan itong amp na to.....i got curious to find out what makes this amp tick.....
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Re: Modding the SAKUA AV200

Postby tony » Fri Dec 31, 2010 7:50 pm

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..... :D :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:

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Re: Modding the SAKUA AV200

Postby tony » Fri Dec 31, 2010 7:55 pm

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

board before the mods:
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after the mods:
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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:
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Re: Modding the SAKUA AV200

Postby tony » Fri Dec 31, 2010 8:00 pm

with the rectifer tubes out of the way, other mods were done:
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the input board was not spared, the sub-woofer output low-pass filters used ceramic caps, these were replaced with mylars,
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Re: Modding the SAKUA AV200

Postby tony » Fri Dec 31, 2010 8:04 pm

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.....

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Re: Modding the SAKUA AV200

Postby tony » Sat Jan 01, 2011 3:11 pm

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?

another version of this amp is selling for 3000 at pinoydvd.....http://www.pinoydvd.com/index.php/topic,123275.0.html
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Re: Modding the SAKUA AV200

Postby tony » Tue Jan 04, 2011 11:01 am

hi,

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" :lol:

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.....

kudos to the china boys for coming up with such cunning and daring designs..... :clap:
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Re: Modding the SAKUA AV200

Postby brainf » Thu Jan 27, 2011 11:49 am

Too funny Tony! :rofl:

Very good read and a warning for everyone to be "buyer beware"
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Re: Modding the SAKUA AV200

Postby tony » Thu Jan 27, 2011 12:38 pm

brainf wrote:Too funny Tony! :rofl:

Very good read and a warning for everyone to be "buyer beware"


glad you liked it......i got an email from a briton from another forum thanking me for my oosts..... :D

the sakura amp is a good amp for any begginer to learn from, low cost and lot's pf possibilities........

as i type this, my son is playing with the guitar amp i built for him using one of the 5Z4 rectifier tubes......thank you Sakura amp....... :lol:
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Re: Modding the SAKUA AV200

Postby manu1417 » Tue Oct 29, 2013 12:47 pm

Hi sir Tony,

Is this same with SAKURA AV-200T ?
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Re: Modding the SAKUA AV200

Postby tony » Tue Oct 29, 2013 4:51 pm

manu1417 wrote:Hi sir Tony,

Is this same with SAKURA AV-200T ?


yes....
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Re: Modding the SAKUA AV200

Postby rufed » Sat Jan 11, 2014 6:40 am

Hi SirTony,

I am bringing my Sakura AV200 to Canada where wall outlets are 110v. How can I change the circuit so I can plug it to
a 110v wall outlet. Thank you for being so helpful.

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Re: Modding the SAKUA AV200

Postby tony » Sat Jan 11, 2014 7:29 am

you will need to replace the power traffo so that the primary of that traffo can be wired for 110 volts.
that means a power traffo with split primaries each rated for 110 volts...
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Re: Modding the SAKUA AV200

Postby rufed » Sat Jan 11, 2014 9:18 am

Thank you for your quick reply. With my minimal knowledge and experience in electronics, I will certainly do what master llike you suggests. Thank you, again.
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Re: Modding the SAKUA AV200

Postby tony » Sun Jan 12, 2014 4:01 pm

i am happy to report that the other china 5Z4 rectifier was used in my prototype 6SN7.6H8c line amp
and that the china tube held its own against american tubes....

so who says china tubes are junk? 8)
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Re: Modding the SAKUA AV200

Postby tony » Tue Jan 28, 2014 7:17 pm

Service Bulletin:

1. this unit had a hairline crack on the board, very hard to see
with naked eye...

2. in order to avoid cathode poisoning, the two sections
of the triode buffers must be paralleled with jumpers,
in the picture, you will see that pin 1 and 6 are already
connected via pcb traces, so that two wire jumpers are
needed to complete the paralleling mod...

the 6N2 tubes are replaced with Japanese 6r-rh2 FUTABA triodes
which are better suited to lower voltages than the 6N2...
the 6N2 makes a nice gain stage in a phono stage....

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Re: Modding the SAKUA AV200

Postby tony » Fri Feb 07, 2014 11:56 am

just a heads up to those who purchased this amp.
this amp has a built in speaker delay relay...3 sec to about 6 secs...
the purpose of this relay is to avoid annoying turn on thumps...

if you purchased a unit that shows this type of symptoms,
return it to the seller to have it repaired for free
if you are still under a 1 year warranty period...
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Re: Modding the SAKUA AV200

Postby tony » Sun Aug 31, 2014 11:06 am

Sakura with phono stage....
this version of the sakura is latest one i think,
no speaker delay relay but then no turn-on thumps,
a big improvement by the Chinese... ;)
the power amp section has 3 boards mounted vertically
a departure from the early models...surface mount
components are used in these boards...it can only mean that
they are making this amps by the thousands.... :D

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Re: Modding the SAKUA AV200

Postby paugie » Mon Oct 20, 2014 5:15 pm

Tanong lang po Sir Tony, ilang watts po ang power consumption ng amp with and without the mod. i.e. I assume the mod consumes less electricity.
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Re: Modding the SAKUA AV200

Postby tony » Mon Oct 20, 2014 7:35 pm

paugie wrote:Tanong lang po Sir Tony, ilang watts po ang power consumption ng amp with and without the mod. i.e. I assume the mod consumes less electricity.


tbh. i haven't measured but i would estimate it at about 20+watts, if you mean modding it with a phono stage, nothing to worry about as the phono stage adds about 1 watt consumption....
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