Yaqin MC-10L - Electricity in volume knob - diyAudio
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Old 16th April 2011, 12:54 PM   #1
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Default Yaqin MC-10L - Electricity in volume knob

Hi All,

I have been reading a lot on this forum - Trully amazing!

1 year ago I bough second hand a Yamaha HTR-5840 followed by a pair of Wharfedale Pacific PI-10. 2 month ago the Yamaha died and it is the best think that happened to me. I replaced it with a Yaqin MC-10L that I brought back from China (2300HKD incl shipping :-) )

While the sound is fantastic, I have a few issues with the quality of the parts.
1. Numerous websites mention that the MC-10L is 23kg, but mine is more like 17kg. I don't understand how this is possible...
2. The RCA plugs are of poor quality. One came off when I disconnected my cable. The gold color is not clear, looking kind of dirty.
3. After staying on for 10 hours (I am burning it in), there was electricity in the volume knob. When I touch it, it is not like an electrical shock, but I can clearly feel the electricity going into my hand.

I am planning to replace all the RCA plugs with good ones. Anything in particular I should be carefull with? Any advise on brand / model?

Would anyone have an idea why there os electricity in the volume knob? Also when I turn it, the resistance is not uniform troughout (it requires more strenght to go from 0 to 33% than from 33% to 66%). Would changing the potentionmeter solve all my problems? If so, does anyone have the parameter of the potentiometer (to make sure I buy the right one)? Cound someone recomment brand / model (is TOCO from Japan good?)

Thanks a lot,
Serge
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Old 16th April 2011, 02:09 PM   #2
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If the volume pot has a metal knob, you are feeling a tingle because you have a mildly 'hot' chassis! This is probably caused by something on the primary side of the power transformer (or the tranny itself) leaking AC line current to chassis. This is a potentially fatal situation! Especially if your power cord does not have a safety ground (green wire).

Take this unit to a competent TV/audio tech immediately!
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Old 16th April 2011, 02:31 PM   #3
mikje is offline mikje  United States
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The feeling you get in the volume knob might be caused by the hot and return of your main power being reversed. The old 120VAC plugs that weren't polarized, one spade wider than the other, would often cause this type of "tingling" on metal parts of whatever they powered. Flipping the plug over so the spades went in the other slot usually fixed the tingling problem.
As mentioned, if you're not knowledgeable about the mains power, take it to a knowledgeable technician.
Mike
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Old 16th April 2011, 02:58 PM   #4
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Thanks guys!

Audiocarp:
Are you saying that a cable that is located between the power plug and the transformator is touching the case? and that this would be the cause? Why can't I fix myself? If I bring it to someone it will cost the same as a new one.
By "hot" chasis, do you mean warm?
How do I find out if my power has a green wire? Do I need to open the cable?

Mikje:
What is the hot? and what is the return?
My amp is 220V.
By "spades", do you mean the metalic pins that are at the end of the power cable and that goes into the amp? If so, this connection is not symetrical, so it can only be plugged in one direction.
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Old 16th April 2011, 03:20 PM   #5
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Default By your questions it is clear that you can't fix this yourself.

By your questions it is clear that you can't fix this yourself. Take the unit to a qualified technician to have the power cable replaced.

Electrical wiring in Hong Kong - Wikipedia, the free encyclopedia

BS 1363 is the mainstream wiring system in Hong Kong. In old buildings, the BS 546 system is also common.

Due to its proximity to mainland China, electrical products from there are quite common in Hong Kong. Many Hong Kongers and mainland Chinese immigrants purchase electrical products in mainland China and use them in Hong Kong. Even if an item of equipment meets the safety requirements inside mainland China, there are plug and socket compatibility problems when using them in Hong Kong.

Before the enforcement of the Electrical Products (Safety) Regulation, many types of plugs could be found in Hong Kong. Using this old equipment sometimes leads to plug and socket mating problems. Nowadays, virtually all plugs fitted in equipment sold in Hong Kong are BS 1363 compatible.

Many overseas citizens who bring equipment in from their home countries do not use the British wiring system. Citizens from the United Kingdom and countries that use British wiring systems normally do not encounter plug-and-socket issues in Hong Kong.
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Old 16th April 2011, 03:41 PM   #6
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Sergedc, it's probably not a bare contact or wire touching the case, but, something more subtle, like electrical leakage from the power transformer or the power switch. If Hong Kong's wiring is like Japan's, you have no third wire in the power cable grounding the case to an actual earth ground, so, this could get really nasty if you touch the volume control and happen to also touch something else which is grounded, like plumbing.

The third wire would come out at the end of your power plug as a third contact.

Well, if the cost of the amp is as much as getting it fixed, then, your the obvious choice is to open the window, and toss it out! (;o))
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Old 16th April 2011, 04:14 PM   #7
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This is so obviously the kind of thread where photos of the equipment are almost essential. Also, others have assumed your residence is Hong Kong. The only clue I see is the reference to HK currency.
I appears to me that you have very little knowledge of electronics which is a problem.
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Old 16th April 2011, 09:22 PM   #8
Hi_Q is offline Hi_Q  England
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I had this exact issue with my MC-10L which was delivered to me without an Earth connection being made on the mains input connector. In the early days this was normal for these amps as the manufacturers felt that connecting an Earth might cause hum loop problems. My Yaqin became tingly not through a leak from the mains input or even the transformer. It was caused by external equipment being non earthed as it was supposed to be Class 2 double insulated equipment and which I often scorn about due to the fact that metal output connectors are provided. The offending piece of kit was a cable TV box with audio output, this being fed with 2-core cable but had a hot chassis due to its inbuilt switched mode power supply input filters. The hot chassis eventually led to a failure of the audio inputs to a PC sound card. I decided to fit an earth connection to the MC-10L, just a short link of wire required from the vacant Earth pin of the mains input connector to the amps chassis. I had no hum loop problem except a very small in obtrusive one when the PC is connected, probably due to the PC being powered on a distant power outlet. I made a request to Yaqin that they should earth all of their amplifiers as these were indeed Class 1 equipment and was the proper thing to do. You may have an early un-earthed model. Regarding the action of the volume control, it may be your source impedance that is upsetting its action. There is no coupling capacitor and everything you connect will be in parallel with a 20k ohm pot and yes, I sometimes think that is perhaps a little low for a valve amplifier, though I have not had any problems with it. Disconnect all inputs to the amplifier and check if the tingling is still there? Hopefully it will have gone and by connecting each input in turn you will find the real culprit. With regard to the quality of the RCA jacks, I have not had any issue but with the wiring I have, unacceptable crosstalk. So I use a remote switch box though re-wiring of the amp might help.
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Old 16th April 2011, 11:18 PM   #9
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Hi-Q: The hot chassis on the cable box may have been due to improper (or nonexistent!) earthing of the outdoor coaxial cable sheath feeding your box. In the US, this is required for safety, but, isn't always well-done (for various reasons).
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Old 17th April 2011, 07:50 AM   #10
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All, thanks a lot for the input.
I live in Singapore. I am away until wednesday. I will then open the chassis and check what is happening.
The only RCA input connected to the amp is a Creative X-fi USB.
1. I will try to remove the X-fi USB and see if the problem persist.
2. I will check on the earth connection of the power plug. I understand it should be touching the chassis. If it is not, do I just solder it on the chassis?

Hi-Q, I am currently reading you DOC on the MC-10L, great work.
I have an electricity measuring tool, how do I check how much electricity is in the chassis? I will put one leg of the tool on the chassis, but where do I put the second one (any metalic piece not connected to electricity?)?

Yes I don't know much about eletricity, although I had one class on it in uni, but I am very decided about learning and I will not give up (or through the amp by the windows).

Any good link with safety recommendation before I open the chassis? I obviously would prefer not to die :-P

Serge
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