| julester |
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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| rocktboy |
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 :cool: |
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| 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:nod: |
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| ronc |
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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| moamps |
| 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:nod: |
:scratch: :scratch:
Hi,
IMHO,
(lin pot 100k)+(15k to 22k resistor - slider to gnd)="log" pot 100k
Regards |
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| zobsky |
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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| carlosfm |
| quote: | Originally posted by rocktboy
those "blue" alps pots are $32 each!!!! how tight is your budget?
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:eek: :bigeyes:
I bough my Alps Blue for 20 Euros here in Lisbon.
They had the Alps Black for 35 Euros. |
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| carlosfm |
| 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.
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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.:devily: :eek: :bawling: |
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| Doovieman |
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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| UrSv |
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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| Doovieman |
So in answer to our original question, what are the differences between a pot and an attenuator (in quality)? What makes the ALPS pot the pot of choice by so many GC designers? Is there actually an audible difference between the ALPS pot and cheapo from radioshack? What makes a good pot a good pot? If there is actually an audible difference between different pots, is there a consensus on pots that are "good"? If so, please elaborate as to costs and locations of purchase. Thanks for your time,
Doovieman |
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| Tor M |
| quote: | Originally posted by moamps
:scratch: :scratch:
Hi,
IMHO,
(lin pot 100k)+(15k to 22k resistor - slider to gnd)="log" pot 100k
Regards |
Hi!:)
(lin pot 50k)+(7k to 11k resistor -slider to gnd)="log" pot 50k?
Or is this more complicated than that?:confused:
Tor M :) |
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| moamps |
| quote: | Originally posted by Tor M
(lin pot 50k)+(7k to 11k resistor -slider to gnd)="log" pot 50k?
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Yes.;)
In inverted GC (Thorsten schematic, I guess) you have typically 50klin pot on input which is loaded with GC input impedance (10k). (You don't need additionaly resistor in this case.)
Regards |
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| Cradle22 |
Hi!
Does anybody know who manufactures this pot called CP-2500
http://www.thel-audioworld.de/bauteile/regler/Potis.htm
(the second one on the page)
Thel says that it's better than any stepped attenuator, and better than all the other pots he sells, with best tolerances.
Anybody heard of this so far?
Maybe would be a new addition of a "high end" part to Peters commercial GC...
Bye,
Arndt |
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| carlosfm |
| quote: | Originally posted by moamps
In inverted GC (Thorsten schematic, I guess) you have typically 50klin pot on input which is loaded with GC input impedance (10k). (You don't need additionaly resistor in this case.)
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Even with a cap in the middle?:dodgy: |
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| moamps |
| quote: | Originally posted by carlosfm
Even with a cap in the middle? |
Why not?:)
For AC signal routing (audio range), impedance of input cap is very small. Zin=sqrt(R1+XC)= ca R1
Regards |
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| Doovieman |
So I'm still trying to figure out the differences between an attenuator and pot. Does anybody actually know or is it all speculation. Is there an audible difference? What makes a "good pot" a good pot? What are the factors that one should look for when purchasing a pot? Is there an audible difference between the pots they sell at radioshack (they cost about $1 a piece) and this famous Alps blue pot that everyone is using? On a separate note, where exactly in the circuit does the pot go? We are using the schematic found at:
http://www.euronet.nl/~mgw/diy/amps/uk_geenkloon_2.html
Does it simply act as a voltage divide on the input? Does it go in parallel to the 22k resistor (which I assume is to prevent oscillation)? Does it go in series to the input? Thanks in advance for your help.
Doovieman |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by julester
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?
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Well, a few things first. Conductive plastic pots have a distinctive sound. You may like what they do, I don't. Secondly, log pots are "dreck". Due to the production process they generally offer poor tracking making well tracking examples the result of a selection process and making them costly, also due to the varying composition of the track to vary the resistance/length the sound is messed up.
The solution would seem a good stepped attenuator, however the series resistor chain types I have encountered are not very good, this includes the DACT. Kondo san once commented on the typchical series resistor chain attenuator by saying it causes "hilarious dummy sound" and I think he is right. If you want a stepped attenuator you MUST use the single series single shunt resistor (S4R) or "true ladder" topology and use really high quality resistors.
There are no commercial optiosn I'd consider good and even doing it yourself with switch and resistors costs a lot of money and takes ages (I have hand build quite a few resistor switched atts before I finally got decent transformers to do the job of the resistors without sonic problems).
So, I'm with Hugh on this. Linear Track carbon Pot or linear track cermet Pot. For a non-inverting Gainclone with a 22k Input resistor I'd recommend a 220k to 470k Pot, for the inverting Gainclone 100k and (yes, I agree Carlos) a 330k Feedback resistor.
However, if you want good realistic sound, NEVER, UNDER ANY CIRCUMSTANCES use Log pots and stay away from plastic track stuff. If you want that classic "High End HiFi" mechanical, artificial sound go for Alps plastic log. If you want natural sound simply use a good transformer attenuator.
Sayonara |
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| jackinnj |
| You don't really need a "pot" with the GC -- since this part of the circuit is "set and forget" -- build the amplifier with a trimmer pot, measure the resistance level on the potentiometer arm to ground that result in the output you need given the source, then substitute a pair of resistors. You should do your volume controlling in the preamp stage. |
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| Variac |
| A lot of people don't use a pre-amp stage, and control volume with the pot on the chip amp |
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| parrychua |
The main problem of most pot is the center lead is just a wiper and it contact may give different resistance value.
Try this and you may get the different. Get two good resiators (helco, vishay, caddock), connect one between the upper lead and the center lead, the other between the center lead and the lower lead. chose the right resistance value. Eg if you have a 50K pot, try 25K to 40K resistance.
I am using a modify series shunt step attenuator. It cost mush less than the ladder attenuator.
Parry |
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| Nuuk |
Well, I built a 12 step shunt type attenuator based on the resistor values that Thorsten recommends and it works fine with my inverted Gainclone.
I don't find the steps too coarse and I can listen as quietly as I want, or as loud as I want.
Cost is about 12UKP depending on what resistors are used.
If people cannot hear the difference between a shunt attenuator and a pot, I am very surprised! You just don't get the extra level of detail with a pot. |
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| parrychua |
I don't build the GC, base on the notes post, it has 10k or 20K input resistance. you can test by using 500K,100K or 50K pot and
you select the best sound (volume and quality) and take note the position of the volume control position. Then you measure the resitance from the upper lead of volume control wrt center lead. Buy two good quality resistor of closer value and soldered it between upper lead and the center lead of the volume control. This effectively lik connect two resistor as voltage diivider with control by pot to a most stable resistance value offer by the static resistance chosen. Now you test again, I belive you will hear the different. This is what I do on my modify series shunt attenuator using Vishay and helco resistor.
Parry |
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| Nuuk |
| quote: | I don't build the GC, base on the notes post, it has 10k or 20K input resistance. you can test by using 500K,100K or 50K pot and
you select the best sound (volume and quality) and take note the position of the volume control position. Then you measure the resitance from the upper lead of volume control wrt center lead. Buy two good quality resistor of closer value and soldered it between upper lead and the center lead of the volume control. This effectively lik connect two resistor as voltage diivider with control by pot to a most stable resistance value offer by the static resistance chosen. Now you test again, I belive you will hear the different. This is what I do on my modify series shunt attenuator using Vishay and helco resistor.
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Sorry, I don't understand. :confused: My shunt attenuator is just a number (12) of voltage dividers, each one consisting of two resistors.
Are you saying that we should replace the resistors in the most used positions with better quality alternatives? |
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