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Old 15th July 2003, 11:39 PM   #1
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Default Noob: GC Potentiometers...which? where?

I'm new to the gainClone scene (meaning i'm trying to build my first one), and I was trying to figure out which potentiometer to get for my volume control. Unfortunately, I'm on a tight budget, or I'd buy everything and compare them myselves. What are the differences between stepped attenuators and POTs in sound?

And generally I find stepped-attenuators are not a particularly attractive option since they are so expensive, and I find the notches to be limiting. But if know of a cheap one w/ more than 12 steps, i'd me interested. (i know this has been asked before on the forums)

I've heard good things about the ALPS "blue" POTs, but these are using conductive plastics....I've heard that cermet type is the way to go?? but i really have no idea\experience. Any suggestions welcome.


I am also having trouble figuring out where to get these. I could only find the ALPS POTs at two places:
-Angela Intruments: www.angela.com
-World Audio Design


Notes:
I am making the non-inverted gainClone (positive feedback), so log tapered is preferred. I also want "dual-ganged" attenuation.

Thanks for any replies!
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Old 16th July 2003, 08:16 PM   #2
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those "blue" alps pots are $32 each!!!! how tight is your budget?
i used radioshack 100k stereo pots for about $3 each, and i am very happy with the sound. mine is linear tapered and if you use a linear taper instead of log taper you'll have a lot of volume change in the last 1/4 turn or so. some people hate that but i have no problems with it.

the angela.com site also sells riken resistors. if they don't have a min order charge it might be a good idea to order from them
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Old 16th July 2003, 09:01 PM   #3
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Just for your information
If you got a linear pot of e.g. 100k, just put a 100k resistor in parallel (from input to ground) and then you have an almost linear pot
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Old 16th July 2003, 09:16 PM   #4
ronc is offline ronc  United States
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Default ALPS pots

www.goldmine-elec.com
P/N g6830
Alps pots 50K $1.00 ea.
I run them on my input with 22k resistor (input line) then the alps with the ctr tap going to ground.I found out that it will still make a loop but the pot is less in the input line.
ron
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Old 16th July 2003, 09:35 PM   #5
moamps is offline moamps  Croatia
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Quote:
Originally posted by ACD
Just for your information
If you got a linear pot of e.g. 100k, just put a 100k resistor in parallel (from input to ground) and then you have an almost linear pot




Hi,

IMHO,
(lin pot 100k)+(15k to 22k resistor - slider to gnd)="log" pot 100k

Regards
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Old 17th July 2003, 02:41 PM   #6
zobsky is offline zobsky  India
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speaking of pot wiring, ...any opinions on shunt wiring a pot, ..the following link has more info ==> link

specifically speaking, i'm interested in the "easy shunt mode"
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Old 17th July 2003, 03:57 PM   #7
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Quote:
Originally posted by rocktboy
those "blue" alps pots are $32 each!!!! how tight is your budget?

I bough my Alps Blue for 20 Euros here in Lisbon.
They had the Alps Black for 35 Euros.
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Old 17th July 2003, 04:05 PM   #8
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Red face The gain factor

Quote:
Originally posted by julester

I am making the non-inverted gainClone (positive feedback), so log tapered is preferred. I also want "dual-ganged" attenuation.
The 220K feedback resistor on the inverted GC is absolutely correct for a power amp (feeded by an active pre).
If you are going to make an integrated GC amp, use 300k on the feedback.
The pot will be a log one.

It seams to me that some people are using linear pots because of the low gain with the 220k resistor.
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Old 17th July 2003, 04:39 PM   #9
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Default might be a really stupid question

Carlos,
I'm working on this project with julester and I was confused about your posting regarding the feedback resistor. Currently, we're using the schematic found at

http://www.euronet.nl/~mgw/diy/amps/uk_geenkloon_2.html

which calls for a 20k feedback resistor. The data sheet for the LM3875 also calls for a 20k resistor. Is there a reason you recommend 220k? Also, why do you recommend a 300k if it's an integrated amp? Thanks a lot for your time.


Doovieman
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Old 17th July 2003, 06:25 PM   #10
UrSv is offline UrSv  Sweden
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Carlos & Doovieman:

The pot in the inverting GC should be linear because it is effectively in part in parallell with the 10 K resistor and thus will assume a near log scale anyway. The call for the 220 K is that high for the same reason and since the input resistor is in parallell with part of the pot and will, sometimes, be the input impedance as seen by the pre-amp. Using a 20 k feedback would have meant a 1 K input resistor giving less than 1 K input impedance in worst case. Could have worked with some pre-amps but not all.
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