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PostPosted: 21 Jun 2011, 19:59 
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Gio wrote:
Geek wrote:
Careful - there are more Blue Velvet counterfeits than you can shake a stick at and the only way to tell is to take 'em apart :-\ (If you have a source for real ones under $30, I'd be happy to know!!!)

I should be careful with the "Blue Velvet" terminology. These are the Blue conductive plastic Alps pots that I am talking about: http://www.partsconnexion.com/controls_pot_alps.html (note that pCx is located in Canada). The Alps pots are original as far as I can tell. If someone has a link or photo that shows the fake post, please post. I've only tried the 50k and 100K pots, $17.95. I've made about 6 purchases with pCx over the past few years with no problems.

Thanks!

I keep forgetting about pCx.

That looks like a real one too:


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PostPosted: 22 Jun 2011, 20:29 
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Suncalc wrote:
talking about "conductive plastic" here. Not nearly as precise as cermet but they have a long "cycle lifetime" and much lower noise than carbon (either basic composition or hot molded).

Yes, the longer life and lower noise is what sold me on them. So far they have been great and I would say they are worth the higher cost.

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PostPosted: 23 Jun 2011, 09:13 
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I've had good luck with the PEC carbon pots. (carbon wiper as well) They are around $30.


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PostPosted: 23 Jun 2011, 12:02 
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Location: Bulgaria - EU
I use carbon pot 2 - 10 kohm - RFT Germany.

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PostPosted: 23 Jun 2011, 15:26 
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Hi,
Suncalc wrote:
talking about "conductive plastic" here. Not nearly as precise as cermet but they have a long "cycle lifetime" and much lower noise than carbon (either basic composition or hot molded).

This is somewhat O.T.

If we can afford to spend more, attentuators with LN resistors of 1% or lower discrepance should be a better choice. Gone for ever contact noise of the wiper. We can even build a pair if we get the right step selectors.

c-J

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PostPosted: 23 Jun 2011, 16:16 
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CJ wrote:
If we can afford to spend more, attentuators with LN resistors of 1% or lower discrepance should be a better choice. Gone for ever contact noise of the wiper.


Um, aren't these built using rotary selector switches, which use contacts and a contact wiper, like what used to be found in the channel selector circuits of the old television sets before someone invented "electronic" tuning?

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PostPosted: 23 Jun 2011, 17:00 
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Attenuators are great, but again depend on a mechanical component that's far more finicky than a wiper - the rotary switch.

By the time you fetch yourself a 30 position, gold contact sealed rotary, you're in the triple digits (20 positions are a LOT cheaper, but also don't cut it at least for my tastes).

An interesting attenuator was one used by Jadis - a R-2R using digitally selected relays. Noisy as a newsroom in the Walter Cronkite era, but worked well :D

Cheers!

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PostPosted: 24 Jun 2011, 09:49 
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HI.
Geek wrote:
Attenuators are great, ...but a 30 position, gold contact sealed rotary, you're in the triple digits (20 positions are a LOT cheaper

Nada. A 2 pole 24 steps only asks for USD16.50 plus postage.

For a 100KR, 24x1% metal film resistors of 4.2KR 1% metal firms only cost few bucks. So it not that much costier than a real Alps 27 series pot. Huge saving vs an magnetic volume control & is much much more linear & distortionless.

An attenuator is a major league ballgame compared to AAA like a pot. PLus we can configurate different resistor arrangement to get the best result. IMO, it's a super pot!

c-J

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PostPosted: 24 Jun 2011, 11:59 
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CJ wrote:
..... is much much more linear ......


It has the benefit of being "programmable", so you can make it as linear as you like, or not at all. Otherwise, I don't consider it any better than an old fashioned - high quality - VR. It is certainly more bulky than a VR. Plus, I prefer the smooth transition across the range of a VR over the "channel-selector" feel that a stepped attenuator possesses. But hey, if you like the feel of changing volume levels like an old TV set channel selector, go for it! I'll stick with that smooth movement of a high quality VR. :D

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PostPosted: 24 Jun 2011, 15:43 
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I have always used NOS potentiometers from the closest and cheapest electronics store, though I have an ALPS potentiometer lying around somewhere.
However there are some stuff I want to test and that is:
- the optial volume control. I have all parts (building from scratch from LDRs and LEDs)
- inductve volume control. Got a transformer but with only 13 steps.
- switched resistor ladder. Got a 4-gang 25-step switch. I can even make a it a T- or P-attenuator or maybe an atteuator with loudness ...

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