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Old 27th November 2006, 11:56 PM   #1
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Question Need some help with potentiometer.

Looks like I have to replace potentiometer in my Reylon SET amplifier. Original pot used there was ALPS RH2701 50kAx2 stepped attenuator . Any suggestions where could I find one or better of what higher quality pot could I use instead? Thanks
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Old 28th November 2006, 12:55 AM   #2
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There is a seller in Taiwan on eBay that sells very nice stepped attenuators made from Vishay resistors. ($55) They are stereo and available in various resistances including 10, 50, 100 & 250K. I own one and it's very nicely made. Seller ID is kyc111 (no affiliation) His email is in the pix.

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Old 28th November 2006, 03:45 AM   #3
kmtang is offline kmtang  Canada
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I bought two of this kind of ladder type potentiometer from Taiwan. Very unfortunately that I found they suffered from coupling through internal stray capacitance.

The high frequency can coupled to the output.

I fed a 10kHz square wave to the input and I could see a very sharp spike and the rising and falling edges when the volume is at low level.

If you want to buy this kind of economical ones, you should buy the series resistor type which would have less stray capacitance problem.

Watch out!!!!

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Old 28th November 2006, 06:47 AM   #4
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Thanks a lot HollowState. Couldn't find seller you mentioned but found another one, item # 290053710138 but it's 100k. While on Ebay I spotted some ALPS pots 50k but 621G and 527G not RH2701.Does anyone know what's the difference? Also I couldn't find RH2701 on ALPS web site. Does it mean it's discontinued?
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Old 28th November 2006, 03:41 PM   #5
alfiax is offline alfiax  United States
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Alps apparently never made a stepped attenuator in the 2701 'Blue Velvet' form factor; the step attenuator you have is likely a Chinese-manufactured counterfeit. All Alps volume controls in this series are in fact potentiometers. That's not to say it's bad; the channel matching on these attenuators is supposed to be excellent, and in fact better than the real Alps pots. However, the quality of construction is not as good as the real thing. You could replace this control with a real blue velvet pot, or with a higher end stepped attenuator like the one mentioned below or a DACT control, or with a high-end similar pot like the Noble conductive plastic types.
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Old 28th November 2006, 11:23 PM   #6
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Thanks Alfiax, would that explain why I cant find RH2701 in ALPS current products lineup? Along this lines, what's the differences between 621G, RH2701 and AK2701 present on their web site? Could I use any of them instead as long it's 50k and type A?
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Old 29th November 2006, 04:55 AM   #7
alfiax is offline alfiax  United States
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Can't speak to the differences between those lines, but the standard dual audio blue Alps pot in my experience is the RK27112.

AMB and Tangent both sell these for reasonable prices, as do a number of other online retailers. You might find a slightly better deal on eBay; search for the colloquial names "Alps blue" or "blue velvet." Just beware of Chinese knockoffs; the stepped attenuators are not actually too bad but there are supposedly lower-quality conventional parts out there as well in counterfeit Alps cases .

If you really want to 'upgrade' you could go to a higher quality step attenuator or a Noble or TKD brand pot; I think Parts Connexion sells those. I haven't actually seen evidence that the channel matching is any better on the Noble or TKD parts, but the Noble pots I have seen are built like tanks- full metal case construction in a blue velvet compatible pinout.
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