Noob: GC Potentiometers...which? where?

[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

[Tor M]

Originally posted by moamps






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?

Tor M

[moamps]

Originally posted by Tor M
(lin pot 50k)+(7k to 11k resistor -slider to gnd)="log" pot 50k?

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

[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

[carlosfm]

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.)

Even with a cap in the middle?

[moamps]

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

[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

[ThorstenL]

Konnichiwa,

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?

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

[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.

[Variac]

A lot of people don't use a pre-amp stage, and control volume with the pot on the chip amp