Table Of Contents
1......The Drive System
Page 3......The Mod
KAB Main 1200
KAB recoginzed the benefit of clean power delivery and introduced the PS-1200,
the first outboard power supply for the 1200.
An outboard power supply
removes all AC power line voltages from inside the turntable and reduces stray
electro magnetic fields from influencing the delicate cartridge signals. By sending a fully
regulated DC voltage into the 1200, the stock internal regulator need only
concentrate on the load of the motor, which is very small. The most noticeable
benefit of external power is quieter backgrounds. 6 years later, expensive
imitations would appear on the market, some actually moving the main regulator
many feet away which did little to improve performance and may have made things
noticeable benefit of external power is quieter backgrounds."
The next thing
we realized when evaluating the power system was an interesting rippling of
internal the DC supply. This was puzzeling at first for it appeared to be 100
Hz in frequency and that had no relationship to US line frequency; so what was
it? Turned out that the strobe
lamp draws a substantial current and in very sharp pulses, 100Hz on 33.33
rpm, and 137Hz on 45 rpm. Sharp pulses are very difficult for even the
best regulator circuit to supress. (Especially if the regulator is moved
several feet from the main motor board.) It became very clear to us that the
simple solution was to find an elegant way to turn the strobe lamp on and off.
So, in 2004 KAB introduced the SX-1200, an inexpensive, easy to install board
that lets you toggle the strobe lamp on and off at will just by holding the
start stop button down for a few seconds.
When the strobe lamp is off, the residual noise
on the power lines drops to vanishingly low levels. And at the end of the day,
that's what it's all about - clean power delivery.
strobe lamp is off, the residual noise on the power lines drops to vanishingly
2007 - A Very Important
In 2007, the US Goverment passed the "Energy
Independance Act". This law turns out to be more of an energy preservation act
and one of the main sections deals with power supply design. Most notably it
puts big restrictions on power supply efficiency and design. It effectively
outlawed the sale of linear wall mount power supplies for sale in the USA. This
gave rise to the wall mount switching power supply. Now, switchers are popular
because the are very efficient with power. When the load is removed, the idle
power of a switcher is very low. This was not the case with linear supplies, so
the switcher takes a marked load off the power grid. In that regard they are a
good thing. And from a consumer point of view they are inexpensive, which is
another good thing. I suppose the downside of the switching power supply is
noise generation. Fact is the AC line is already pretty noisy and ac line
conditioners are quite common. So from our perspective the main issue is noise
riding on the DC output from the switcher. And that is where the
PS1200GX comes in.
perspective the main issue is noise riding on the DC output from the switcher.
And that is where the PS1200GX comes in."
In 2009 KAB introduced the new PS1200GX.
power supply was designed from the ground up to meet the requirements of the
law and exceed the expectations of audiophiles. Powered by a wall mount
switcher, the heart of the PS1200GX is the DC power conditioner. This state of
the art design removes every vestige of noise from the switcher leaving the
output as clean as a battery.
The design uses a basic choke input capacitor
filter featuring 4700uF of low esr capacitance. This is followed by something
unusual. A circuit best described as a noise canceller. Noise can be
represented by a very small current. And it is possible to inject that current
out of phase with the source and when you do it properly, the noise
cancels out and dissapears. The advantage of doing it this way is that you
produce an ultra clean source of DC while dissipating less than 1 watt of power
and dropping only 0.25V from input to output. Try doing that with a linear
regulator! Expect this circuit to be copied and re introduced by a competitor
at 2-5 times the price. For now, KAB is where state of the art resides in
efficient, clean and affordable power delivery for your SL-1200.
The main internal DC regulator of the 1200
converts the unregulated 36V to a clean 20-21VDC. It is a very basic 3
transistor design using a zener diode as a reference. These circuits were very
popular in the 1970's. They have some limitations, but aside from the response
time, as discussed in the SX1200 section, the circuit handles the 1200 motor
But there are several other aspects of this design
that can be improved upon and are worth exploring.
- High drop out voltage
- Not short circuit protected
- Time consuming to troubleshoot
We wanted to deal with these issues while improving overall
performance and creating a way to transfer easily between the stock supply and
an external one. KAB policy is that the stock form should never be altered and
frankly, sometimes you lose external power paks and you should not have to lose
the use of the turntable because of that. So in 2012 KAB introduced the
shouldn't lose the use of your '1200, just because you lost your external power
Were Going In.
is am elegant drop in 20V power supply circuit board that completely replaces
the stock one.
The DC-1200 uses a modern regulator device that features low
drop out, high speed response, very low noise and short circuit protection. In
addition we added a transfer circuit, for automatic transfers between the
internal power supply and our PS1200GX. You can use your own external PS as
well so long as its output is between 23VDC and 36VDC. The external input is
separately fused and polarity protected. Our DC-1200 also features a slow
startup that mimicks the start up waveform of the original power supply. This
new regulator supresses strobe noise 36dB over stock and with the strobe off,
the residual power line noise is less than 1uV a 69dB improvement over stock.
That's dead quiet power delivery for under $300 USD!
I hope you find this information useful as you contemplate the
next step in improving your Technics SL1200 turntable. It has taken many years
to turn popular opinion, but the proof is in the many audiophiles that now
embrace this laboratory grade marvel of mass production. Get started here:
Modding Your Technics 1200.