Before going to the shunt-volume control, let's take a look the latest amplifier built. I should open up all the amplifier case to make sure the cables are reachable to work on. The power cables from rectifier is the first things I tidy up using cable ties. Then the transformer input cable as well.
The grounding point is move closer to the amplifier circuit. The thermistor for ground separation between audio ground and power ground is placed near the amplifier board.
The output speakers cable which previously is lying around is now hide under the amplifier board. This speaker output cables are in line with power supply cables.
The next step is tidy up the cable on AC input.
Then this is the modification I attempt in the input circuit. The shunt-volume control will be using here by a resistor before pass through directly to the amplifier line input board. Different with common divider volume control, the potentiometer will do the job once the knob are turn, thus the wiper inside the potentiometer will determine the resistor on each divider between input to amplifier and amplifier to ground. Here is the circuit diagram for shunt volume control. I got the image bellow from searching online and this image is courtesy of the owner of the websites as well.
This resistor is very important in shunt-volume control because this is the only signal path pass through the amplifier line input. The potentiometer only act as shunt system from amplifier input to the ground and determine the loudness. Choosing cheap potentiometer for this shunt volume control is very risky. The not reliable potentiometer cause the wiper contact inside the potentiometer is loose on some time of usage and this cause the signal jumping into a very loud signal pass through the amplifier directly. This condition may cause damage to the speakers. I am using ALPS blue in this purpose and I guess this is a good quality potentiometer.
This shunt-volume control impedance is also different with common volume control. The shunt-volume control impedance is count between resistor input plus the half of the potentiometer impedance. In my case, I am using 15 K ohm resistor and 20 K ohm potentiometer. The amplifier impedance using shunt-volume control now is between 15 K ohm up to 25 K ohm.
The interesting fact that the famous Ongaku Audionote amplifier also using this similar shunt-volume control on their amplifier circuit.
Based on the schematic above, I only attach the input and output pin together on each channel at the potentiometer PCB. Then the input pin is directly solder to input cable from RCA after the resistor.
After all steps finished, you should check and make sure there is no fail on the circuit or the potentiometer. With the volume control position on closed or on very minimum, using ohm meter and attach in both RCA input and ground. The reading in the potentiometer should same as the series resistor. In this case is 15 K ohm. Then start rising up the volume control, the resistance will gradually increase up to maximum half from potentiometer impedance. If it is all correct then this shunt-volume control is ready to use.
That is how I modify from common-volume control to this shunt-volume control. The next things to do is solder all cables to the panel terminal.
This is the final internal layout. This is what I call neat and tidy amplifier built.
Anyway, this Avel Transformer company is still the best quality transformer producer. As same quality as the popular Talema transformer. Sadly I heard this company is already shut down last year, but they great products are still their legacy among the audio manufacture.
Finishing up all the amplifier accessories and it is ready to sing.
Testing the amplifier with this new shunt-volume, there is almost no different in the volume level shift between using the common volume control or the shunt-volume control. The sliders movement affect the gradually increase volume is more quick in this shunt-volume control, but both feeling are still smooth. The first very noticeably sound different after modify to this shunt-volume control is the dynamic of the music. It feels more direct and fuller. Quite dry in my opinion, but let's see how the sound quality improve from next long period of listening session. More information about the series resistor I am using in this shunt-volume control here is carbon type resistor from Takman. It is quite cheap, less US$1 each. Perhaps changing to highest quality such as Tantalum resistor will improve the sound quality as well.
Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.
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