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Old 11th March 2009, 09:00 PM   #1
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Default faulty TKD potentiometers (video link)???

Anyone else has experimented this phenomena with a TKD 2CP-2511 10KOhms dual log taper pot?


http://www.youtube.com/watch?v=j398xiUt-Ko

This is the second one that I received, first one that I returned was doing the same.

Notice that reading is almost the same between 8 o'clock to 3 o'clock (3.5K to 4.5K) which means no gain. During that time also, resistance go a bit up and down.

Channel accuracy is within max 5% tolerance, total pot accuracy is within 10% (9.06 and 9.13KOhms).

Since I got 2 bad ones yet, I'm very hesitant to order and install these in my preamp.

Thanks for your comments,
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Old 12th March 2009, 03:07 AM   #2
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Thought this could also help out. Here are the readings done with my digital multimeter, notice the swing between 8 and 3 o'clock:

o'clock ch 1 (KΩ) ch 2 (KΩ)
Min 0.00 0.01
7 2.12 1.99
8 3.91 3.48
9 3.93 3.48
10 4.02 3.55
11 3.97 3.43
Noon 4.39 3.93
1 4.79 4.37
2 4.20 3.98
3 5.09 5.01
4 5.86 5.86
5 8.02 7.85
Max 9.06 9.13
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Old 12th March 2009, 04:32 PM   #3
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Here's a picture of what I'm experiencing.

Thanks.
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File Type: gif 2cp-2511 10k dual log taper.gif (3.6 KB, 218 views)
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Old 14th March 2009, 09:32 AM   #4
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To whom this may interest...LOL, I have received the present circuit topology from the manufacturer yesterday explaining me a bit the difference between their 2 Taper types: TKD and JIS. Also included, the respectual techsheet identifying these 2 as being the ''LOG'' and ''A'' curves in the graphic.



My first impresion looking at these tapers compare to what I was measuring is that it had nothing in common. I was going to return the pot as being faulty again from what I was seing. But out of curiosity, I decided to try the pot anyway with alligator clips to see how it resulted on the knob and output. To my great surprise, once the pot loaded in the preamp circuit and flicking the switch to on it worked as expected and gradually as contrary to my measurements??? Any explanations?

Also, is there someone here who can explain me how I should've tested the unit outside the circuit? Since the 2CP-2511 is a ladder type volume control, could it be the 6 shunt resistors who faulted my readings. Are thes the ones responsible for the slight up/down measured values between 8 and 3 O'clock?

Note, i'm not shure also, if I'm correct TKD KO-ON Denpa seem to explain that the ladder type (ex: 2CP-2511 mine) is not a potentiometer but rather a volume control. I'm not very knowledged here? What were they trying to explain me?

Any help would be appreciated. I Hope at least, my present experience will help someone on the web someday even if I'm the only one in this thread...lol.

BTW, all this because I've wanted to replace my 10K ALPS Blue velvet with the new TKD. In my preamp, the TKD is miles better. Tonal balance haven't changed except, I have a bit more bass and slightly fatter. Sound is less mechanical, grain is gone in highs, way more fluid and natural in the mids. Well to tell you the truth, it's really not the same preamp anymore, it's sounds very, very good compared to the ALPS.TKD CP-2500 series techsheet

Thanks.
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File Type: pdf circuit.pdf (15.2 KB, 74 views)
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Old 15th March 2009, 12:18 PM   #5
MRupp is offline MRupp  Germany
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Just measured a CP2500 and got the same results, then checked the WEB pages of a local supplier in Germany (Thel) because I remember having read s.th. about this. Result? The supplier actually states on his web page that you can not measure the CP2500 with an ohm meter (and cannot wire it as a variable resistance like with a normal pot).

Note that a voltage divider is usually loaded (between pin 1 and C) with a source of much lower impedance. If you connect a resistor to a normal pot (say alps) and measure the resistance you now get similar "funny" results. The input of the next stage sees both halves of the divider in parallel (one half actually shorted by the source impedance) and this is usually a quarter of the nominal resistance or less.

If you happen to have a signal generator (600 Ohms) and a 2 channel scope you could hook this up to the pot and see if you can attenuate the signal with the desired curve.
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Old 15th March 2009, 06:24 PM   #6
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Mr Rupp,

Thank you for your valuable input and for testing a unit. I'm happy that you well confirm that the volume control could not be measured the way I proceeded.

Guy
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Old 15th March 2009, 10:37 PM   #7
MRupp is offline MRupp  Germany
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You're most welcome and thank you for your listening impressions. If I did not procrastinate building my preamp I could probably confirm the sound differences as well but it may be a few more months.
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Old 15th March 2009, 10:51 PM   #8
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Sir, for me, i felt not just like upgrading a part but more like as if I had a new preamp, that's how good we felt when I've first tested it. This week I'll be soldering it in.

Install it as fast as you can!!!

Sincerely,
Guy
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