"Silver-Carbon" Pot ex Tawan - Photo - & ignore my ugly Pinky!

[KT]

OK, this shows that I haven't done my homework (and maybe that it's late and I'm a little bit lazy), but in the GC design, why is it advantageous to have a lower value pot?

I noticed, for example, that Carlos uses the 10k pot. I think Peter tried the 50k value. Why would the 10k value be preferable, if it is?

I bought some 50k pots, myself. Would these be fine to use in Brian and Peter's non-inverted design?

Would it be different in an inverted circuit?

Thanks for indulging me on this.

Best,
KT

 

[Nuuk]

KT - this may help answer your question! 😉

 

[carlosfm]

I noticed, for example, that Carlos uses the 10k pot.KT

KT, I'm testing the 10k pot on my preamp.
Anyway, on Brian/PD boards you have 22k from input to ground, and there should be no problem in using 10k log there.
You may prefer it over the 50k log if you have "normal" sensitivity speakers (say, up to ~89db).
If you have very sensitive speakers the slight attenuation at the low range of the 22k resistor + 50k pot may be better for you.
Use what you have for now, try it.

 

[KT]

Thanks, Carlos.

If I understand it correctly, the value of the pot along with the 22k shunt resistor affect the response curve of the volume control? The 50k pot will give better control in the lower ranges, then?

I'm not an engineer, but just briefly, how do the pot values affect the input impedence of the amp? Is that something I should keep in mind, or am I just playing around with the volume response curves when I change values, let's say between a 10k and 50k pot?

A little OT, here: has anyone tried the PEC pots in an electric guitar? Must sound very nice.

Thanks,
KT

 

[carlosfm]

Thanks, Carlos.

If I understand it correctly, the value of the pot along with the 22k shunt resistor affect the response curve of the volume control? The 50k pot will give better control in the lower ranges, then?

Yes.
It may be fine, or it may be too much, depending on the sensitivity of your speakers.

I'm not an engineer, but just briefly, how do the pot values affect the input impedence of the amp? Is that something I should keep in mind, or am I just playing around with the volume response curves when I change values, let's say between a 10k and 50k pot?

The pot makes the input impedance of the amp.
10k is fine, 50k is an easy load for the previous stage to drive.
I tend to prefer lower impedance pots (10~25k).

 

[wrenchone]

The thread that rose from the dead.... I just picked up some 50k single unit Alpha 9mm pots from Mouser. They are amazingly tiny, and very smooth and well damped. I'm currently running a pair of Bourns 50k conductive plastic pots in my new preamp with 19k Dale MF law-fake resistors. They sound OK, though there is some channel imbalance. I'm pulling the preamp this weekend to do some other changes, and I'll throw in the Alphas to see if I notice a difference...

 

[Joseph K]

So as to push this thread another bit forward, I've just noticed in the catalog of RS the little, green, 9mm carbon pots, which are Alps. Apart from the name, they seem to be the exact same thing than those Jaycar/ Alpha taiwan pots.. They are of number 249-9137.

What is your opinion, am I right?!

Ciao, george

 

[mrlots2do]

I've just noticed in the catalog of RS the little, green, 9mm carbon pots, which are Alps. Apart from the name, they seem to be the exact same thing than those Jaycar/ Alpha taiwan pots..

They are of number 249-9137.

I went to RadioShack website but they don't list this pot. Can you post a pic. I'm very much interested.

Phil

 

[Joseph K]

Here You are!

 

[Joseph K]

Some more details [compare this with the Jaycar documents]

Elemento resistivo al carbone
Potenza nominale a 70°C 0,05W
Tensione massima 50V~
Tolleranza resistenza ±20%
Errore in serie entro 3dB da -40 a 0dB
Rotazione 300°
Durata rotazionale 15.000 cicli
Temp. di funzionamento da -25°C a +70°C

Dimensioni corpo Largh. 9,5mm; Alt. 11,35mm

Profondità corpo 7,05mm (singola) 9,55mm (doppia)
Boccola di montaggio Æ 7,35mm; Lungh. 7mm (singolo);
Lungh. 10mm (doppio)
Alberino Æ 6mm; Lungh. 13mm (singola);
Lungh. 15mm (doppia)

Maybe it is present only in the Italian catalog?

Ciao, George

 

[mrlots2do]

Maybe it is present only in the Italian catalog?[/B]

I can almost understand those specs, LOL. It doesn't say if they are log pots and at what ohm value.

What do they cost in Italy and how much to send me some in the USA?

Phil

 

[Joseph K]

I hope you were able to decipher the Italian ? As a sum, it seems to me that all the main parameters are equal -
power 50 mW, 50 Vac max voltage, 3db tracking error from -40 to 0 db.. etc.

I think there is a common manufacturer, then there are different re-badging distributors..

Still, I might be wrong, this is why I ask.

Ciao, George

 

[Joseph K]

These are the generic parameters, then You have the choice from
10 k lin /log single / dual up to 100k lin / log single /dual.

The price here is 2.48 EUR / single + VAT; 3.18 EUR / double +VAT.

Not cheap - here, in Europe, RS was never cheap.

Should control the situation with foreign transports. If it would not work out, maybe the UK RS branch could be checked?

 

[mrlots2do]

I just called Radio Shack in USA. They don't have these items listed for USA sales.

 

[motherone]

The RS listed above is not Radioshack.. It's a supplier in the UK/Europe, I believe.

 

[maxw]

The RS listed above is not Radioshack.. It's a supplier in the UK/Europe, I believe.

Yes you are right except RS components is pretty much world wide 😉

 

[taj]

is this the ones?

Are these the ones you're all talking about?

http://www.mouser.com/catalog/622/469.pdf

(upper-left corner, items A &B) I don't see any dual (stereo) versions though.

..TAJ

 

[JandG]

On the Jaycar silver-carbon pots, should I be getting the Linear or LOG taper..? I would be using them for tube preamp vilome controles @ 100k in dual mono or maybe even stereo pot.

 

[taj]

I would think you will be better off with a log (audio) taper. The volume will rise too quickly (the control will be very sensitive at the beginning) if you use a linear pot. Apparently you can fake a log taper by adding a resistor to a linear pot, so that may be an option for you if the appropriate log pot is hard to find.

You might also want to consider getting or making a stepped attenuator. There's a guy in Taiwan (search on eBay) who makes quite satisfactory ones for a great price. He uses Dale resistors and the switches look and act pretty nice. He will make up the proper resistance for you if he doesn't have the correct one for sale already.

..Todd

 

[btran]

I now this thread is old but am searching a volume pot for my 26 tube preamp and I come across this thread. Would anyone confirm the pot below is the one that Joe R. talked about? Thank you all for your help!