HiFi-Do E-mail Newsletter

Howdy, this is Ito from the service department. I've got some opinions and suggestions from beloved readers. I'm so fortunate to have such readers who read my writing I come up with in less time every week and give me some suggestions. So if you have any suggestion, opinion, question or whatever, please feel free to email me. It is my wish to learn from you all since I am still learning. Besides suggestions for the topic for mail magazine are very welcomed. Anyway I would like to explain about the waveform measurement continued from the last time and write about the cleaning of the volume etc. which was requested from one of beloved readers of our mail magazine.
Here is a picture showing the waveforms. If you have no idea what I am talking about, please read my writing from the last issue on Sep 30. I am going to use AU-D707F this time, though I used AU-D607F EXTRA the pre main amp last time. Please don't say "Sansui again!". But yes it is, I use Sansui this time again. Now please look at the waveforms. I turned up the volume on the oscillator with -40dB of attenuator the CR oscillator. And the pre main amp received and amplified the output which is displayed on the oscilloscope through the 8Ω load pseudo-resistance as waveforms. The vertical amplification of the oscilloscope is set to 5mV/DIV. And you see the flat square waveforms in the state that the tone volume base is raised up to MAX. you can see the square waveforms become like the "/ \|" if the low range increases. On the other hand, if you turn down the volume, they become like "\| /".
	Here is another picture. For this state, I turned down the TREMBLE which is a tone volume and turned up the base to MAX from the state of square waveforms. In short, I loosened high region and raised low region. This is pseudo-RIAA curves. I named it so without anybody's permission. The output from PHONO shows square waveforms like this.
The actual phono waveforms are like this. Why do we have to output in this kind of waveform? Well I would like to talk about it some other time.
I explained about the waveforms simply followed by the last time issue. Did I make my points clear to you? Anyway I would like to get to the volume cleaning. But first I will explain about volume. The volume is a so-called variable resistor to change the volume or sound quality by changing the value of resistance. In other words, turning or sliding the knob on the volume changes the value of resistance. The change is depending on the volume though there are roughly A, B and C curves when relating it to its rotation angle. (There are about 11 types of curves as standard.) The A curve changes less at the beginning of the rotation angle but changes a lot in the latter half. The B curve changes linearly and changes just for the amount the volume is turned. The C curve changes drastically when the volume is turned only a little bit at the beginning.

You need to disassemble the product to clean the volume. I removed a front panel of the product for cleaning. I would not reveal the product name. In order to remove the front panel, I removed a nut attached on the volume with a needle-nose plier. Actually I know a better tool to recommend than the needle-nose plier though. Let me continue the work carefully so as not to damage the front panel. But how come the nut on the balance volume is being removed? Why? Oh well, don't worry about it and let's go on to the next step.

This is a main volume I just removed. The main circuit board is attached on. There are 4 terminals since the loudness will be added. The normal volume has 3 legs of GND, OUT and HOT from the left leg though, you may find it difficult to notice. Here is a leg attached for the loudness. When you turn down the volume, GND and OUT stick to each other. So you can test the continuity when putting the tester on. And the resistance shows infinity because OUT and HOT are separated from each other. When the volume is raised to maximum, OUT and HOT stick to each other, the resistance shows 0Ω, then GND and OUT show infinity.
Please take a look at this picture. You can see a hole opened horizontally long on the top surface of the volume. Pour contact point recovery agent into that hole. Please refer to my first mail magazine writing for what you need. Be careful to spray the minimal amount but not to put too much since it may deteriorate the volume contrary. Then wipe it off clean and turn the volume round and round. This should remove the noise. It's so easy, isn't it!? However there is some volume with no port for contact point recovery agent. In that case, you just have to exchange it or disassemble it.
That's all for this time. If you have any suggestion or opinion, please do not hesitate to send me an email. Well then, see you next time.

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