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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Jul 2017, 5:44 pm | #21 |
Hexode
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
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Re: Pot wiring. Pot questions.
Connecting a log pot 'backwards' does not give anti-log, that was a mistake I made before I realised the truth. In any case if that were the case then there would be no need for special anti-log pots!
Also, logarithmic pots, with moulded (carbon, cermet, whatever) tracks, are made up from just two linear sections rather than a smooth log taper which is very difficult to produce. It is possible to hear the effect on the volume and hence most serious audio designers will use the 'modified pot' arrangement with linear parts to obtain a much more realistic logarithmic change of resistance/volume. Placing a resistor across the wiper and 'top' end of the pot synthesises a log taper and a resistor across wiper to 'bottom end' of the pot synthesises an anti-log taper, the only disadvantage of this arrangement is that the impedance presented by the pot to the driver stage will vary as the pot is turned, this will give an even more interesting characteristic to the volume control if it follows a high impedance (i.e. valve anode) signal source. http://sound.whsites.net/project01.htm That page also contains a very novel stereo balance control which solves all the problems of having to use special pots or tolerate poor balance adjustment. |
20th Jul 2017, 6:43 pm | #22 | |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,983
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Re: Pot wiring. Pot questions.
Quote:
http://www.alps.com/prod/info/E/PDF/...eter/TAPER.PDF Craig |
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22nd Jul 2017, 6:59 am | #23 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,662
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Re: Pot wiring. Pot questions.
Ah, see the thread has burst back to life. I guess whether a pot is truely logarythmic is academic as most amplifiers are rarely turned up past the transition.
RF Burn brought up a point I've also been mulling over. We have a valve voltage gain stage with a pot to vary the signal seen on the control grid. My practice is to put a grid resistor on as well as the pot, I usually use a 1M. Obviously with the pot in parallel the input Z is going to change. So what is best practice and while were at it and what value pot? I've read a 1M pot favoured by vintage amp/radio builders is too high and that 10 - 100k is better.... A.
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23rd Jul 2017, 1:25 pm | #24 |
Hexode
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
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Re: Pot wiring. Pot questions.
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