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Old 8th September 2014, 08:51 AM   #1
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Default ALPS Potentiometer 100k ... Blue RK27112MC noise ??

Hello everyone,

about a month ago I bought this pot ;ALPS Potentiometer RK27112MC Blue Velvet motorized Pot 10K 50K 100K log o linear | eBay , a few days ago I noticed that turning, both manually and remotely controlled, it emits a noise on both canali.La strange thing is that from position 0 to 9 o'clock is normal no noise, passed 9 o'clock starts to make noise .I changed the cables but nothing to do ... you think it is damaged?
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Old 15th September 2014, 09:12 PM   #2
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Quote:
Originally Posted by mprivitera1 View Post
Hello everyone,

about a month ago I bought this pot ;ALPS Potentiometer RK27112MC Blue Velvet motorized Pot 10K 50K 100K log o linear | eBay , a few days ago I noticed that turning, both manually and remotely controlled, it emits a noise on both canali.La strange thing is that from position 0 to 9 o'clock is normal no noise, passed 9 o'clock starts to make noise .I changed the cables but nothing to do ... you think it is damaged?
Hello mprivitera
First i need to say that there is nothing wrong with the potentiometer, unles you didnt see anything that indicates the potentiometer used before you. If you have any doubt about the seller please kill them because i am also an ebay seller and buyer, most of the seller out of some places in the world do not sell the used parts as indicating they are new even ebay dont let this kind of intentions.

Here is your problem and the solution
Your problem is gronding network , your potentiometer is in wrong grounding path, you need to change potentiometer's grounding , sometimes it helps to connect potentiometer's body to ground ( front metal face ).

99% i am sure that you grounding network cause that problem after 9oclock position. To be sure you can connect potentiometer in reverse position ( swap the side leads by keeping the middle leads constant) in this case at the right end of your potentiometer position your amplifier will be fully silent and start to open towards to left side. The problem stay same but in opposite side positions ( i mean problem starts at the counter 9oclock position).

You need to connect potentiometer to the ground in different points forexample to the rca input's ground or power supply capacitors ground or to ground somewhere on the pcb board.

I hope those info will help
good luck
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Old 15th September 2014, 09:15 PM   #3
jono1 is offline jono1  United States
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If you bought it from China, there is a good chance it is a fake. I have had lots of problems with the counterfeit ones.
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Old 15th September 2014, 09:47 PM   #4
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I don't think Familygate (Germany) deal in fakes. I buy a few similar motorised pots from them periodically without problems but certainly, Chinese traders are often selling copies of ALPS products. However, neither should have a fault like the one described as making noise only when used outside the normal range of operation (7-9 o'clock)

Question: is this noise the same and does it commence at the same position in both channels? If so, I would try another type to check that behaviour, making certain of the correct and recommended grounding of metal work and motor drive circuit, because if it is related only to the physical position in a new product, there will be a serious (wear) problem and you should seek a refund/replacement - outside Ebay if need be.
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Old 16th September 2014, 11:32 AM   #5
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Quote:
Originally Posted by huseying View Post
Hello mprivitera
First i need to say that there is nothing wrong with the potentiometer, unles you didnt see anything that indicates the potentiometer used before you. If you have any doubt about the seller please kill them because i am also an ebay seller and buyer, most of the seller out of some places in the world do not sell the used parts as indicating they are new even ebay dont let this kind of intentions.

Here is your problem and the solution
Your problem is gronding network , your potentiometer is in wrong grounding path, you need to change potentiometer's grounding , sometimes it helps to connect potentiometer's body to ground ( front metal face ).

99% i am sure that you grounding network cause that problem after 9oclock position. To be sure you can connect potentiometer in reverse position ( swap the side leads by keeping the middle leads constant) in this case at the right end of your potentiometer position your amplifier will be fully silent and start to open towards to left side. The problem stay same but in opposite side positions ( i mean problem starts at the counter 9oclock position).

You need to connect potentiometer to the ground in different points forexample to the rca input's ground or power supply capacitors ground or to ground somewhere on the pcb board.

I hope those info will help
good luck
thanks for advice, ...... I feel this change of rotation and test other points gnd
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Old 16th September 2014, 11:40 AM   #6
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Quote:
Originally Posted by Ian Finch View Post
I don't think Familygate (Germany) deal in fakes. I buy a few similar motorised pots from them periodically without problems but certainly, Chinese traders are often selling copies of ALPS products. However, neither should have a fault like the one described as making noise only when used outside the normal range of operation (7-9 o'clock)

Question: is this noise the same and does it commence at the same position in both channels? If so, I would try another type to check that behaviour, making certain of the correct and recommended grounding of metal work and motor drive circuit, because if it is related only to the physical position in a new product, there will be a serious (wear) problem and you should seek a refund/replacement - outside Ebay if need be.
the seller is trustworthy ..... think that the problem is in connecting GND or perhaps the preamplifer .....
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Old 16th September 2014, 03:46 PM   #7
Bare is offline Bare  Canada
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Alps stopped building Blue velvet pots a while back :-)
Fakes/copies don't feature subtle details like fully recessed into the ali casting, philips head screws .
If in doubt... temporarily insert a cheap(er) pot into the circuit to see if there is difference or noise.
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Old 18th January 2015, 07:04 PM   #8
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hello everyone,
I take this old tread to tell you that the potentiometer object works well has no problem. The problem is preamplifier homebuilt "TNT preamble" and I can not fix it...
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Old 18th January 2015, 09:03 PM   #9
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This one? Looks like a pretty simple circuit TBH, should be fixable.

I wouldn't be surprised if it's somewhat noisy though, gain seems to be reasonably normal at ~3.5 (11 dB or so) and the somewhat unfortunate input attenuation setup and highish volume pot value means that the circuit may be presented with rather high source impedance... up to about 35 kOhms worst-case if my estimate is correct.
For the same reason, all the connections to the volume pot and at the inputs should be shielded and the layout of R106-R105-J101 as compact as possible in order to minimize hum pickup. A shielded box may not hurt.

How much power amp gain and what sort of speakers do you have behind it?

The basic circuit should be quite OK subjectively, though with the rather high level of 2nd-order IMD (kinda expected for a single JFET input, though possibly the current-source-less buffer also is at fault) I wouldn't be surprised if it struggled with complex music like metal.

BTW, the power supply design of this amp is a bit silly, taking hours before full output is reached. I am fairly certain that a simple resistor of 100-330 ohms (try 1-5 W) between C503 and C504 - thus establishing 2nd-order filtering - would drop ripple enough to allow for R503 to be reduced in value dramatically (as in 10k-47k, max).

I must say that the quality of DIY designs has improved a fair bit since then...

Last edited by sgrossklass; 18th January 2015 at 09:13 PM.
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Old 19th January 2015, 05:35 AM   #10
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Quote:
Originally Posted by sgrossklass View Post
This one? Looks like a pretty simple circuit TBH, should be fixable.

I wouldn't be surprised if it's somewhat noisy though, gain seems to be reasonably normal at ~3.5 (11 dB or so) and the somewhat unfortunate input attenuation setup and highish volume pot value means that the circuit may be presented with rather high source impedance... up to about 35 kOhms worst-case if my estimate is correct.
For the same reason, all the connections to the volume pot and at the inputs should be shielded and the layout of R106-R105-J101 as compact as possible in order to minimize hum pickup. A shielded box may not hurt.



How much power amp gain and what sort of speakers do you have behind it?

The basic circuit should be quite OK subjectively, though with the rather high level of 2nd-order IMD (kinda expected for a single JFET input, though possibly the current-source-less buffer also is at fault) I wouldn't be surprised if it struggled with complex music like metal.

BTW, the power supply design of this amp is a bit silly, taking hours before full output is reached. I am fairly certain that a simple resistor of 100-330 ohms (try 1-5 W) between C503 and C504 - thus establishing 2nd-order filtering - would drop ripple enough to allow for R503 to be reduced in value dramatically (as in 10k-47k, max).

I must say that the quality of DIY designs has improved a fair bit since then...


hi,
thanks for reply,

it is connected to this amplifier power MOSFET Amplifier IRFP240/IRFP9240 built by me. How to use a source pocorn A410 that mounts inside a DAC ESS Technology Sabre .The speakers are Dynavoice Dynamite8. So you mean I have to put a resistor between C503 and C504, as in parallel? and I have to replace the R503? with a 47K
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