KAB Audiophile Times
Jan 2013 - Power Delivery - Page 3

Table Of Contents
Page 1......The Drive System
Page 2......The Tonearm
Page 3......The Mod Process
Page 4......Power Delivery
KAB Main 1200 Page

  In 2003, 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 even worse.

"The most noticeable benefit of external power is quieter backgrounds."

Strobe Attack
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.

KAB SX1200 Strobe Disabler

  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.

"When the strobe lamp is off, the residual noise on the power lines drops to vanishingly low levels."

2007 - A Very Important Year
  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.

"from our 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.
This new 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 currents satisfactorily.
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 DC-1200.

"You shouldn't lose the use of your '1200, just because you lost your external power source."

Were Going In.
The DC-1200 is am elegant drop in 20V power supply circuit board that completely replaces the stock one. DC1200 Internal Voltage Regulator

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.

If Form Follows Function, So Then Music Follows Precision.
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