very small noob question project 88

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hey guys, i was going through project 88 rod elliott's website.

given my limited knowledge of electronics, i am unable to understand the parts used in the bridge and volume control.
for reference, see this schematic
An externally hosted image should be here but it was not working when we last tested it.

i see, VR1(1 st potentiometer) is used to control volume, slider type (potentiometer) but for the balance part, two linear potentiometers are used?

i mean, i have never seen such use of TWO potentiometers for balance controls. do i have my understanding right of the wiring(See the attachments)? or am i wrong somewhere?

Please help!
Sid
 

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  • p88-f3.gif
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The wiper is the arrow on the schematic diagram of a potentiometer. Typically the middle terminal is the wiper, but I've removed some pots from radios that were different. You determine which is the wiper on your actual potentiometer by connecting with clip leads a meter to it. The two terminals that don't change in value when you move it, are the track ends. And typically the end terminals give the resistance that the pot is described by in the sales listing. The terminal which goes up and down in resistance compared to either end terminal, is the wiper.
So, assuming your linear potentiometers pictured are normal, your picture is correct.
The reason they don't use log pots on balance controls is that only huge manufactures running gigantic production runs, could buy pots with the fast moving end on one side of one pot, and the fast end on the other side of the other pot. If they did buy them that way, some stock carrier would probably put them in the wrong bins of the assembly station or something to mess it all up.
 
The wiper is the arrow on the schematic diagram of a potentiometer. Typically the middle terminal is the wiper, but I've removed some pots from radios that were different. You determine which is the wiper on your actual potentiometer by connecting with clip leads a meter to it. The two terminals that don't change in value when you move it, are the track ends. And typically the end terminals give the resistance that the pot is described by in the sales listing. The terminal which goes up and down in resistance compared to either end terminal, is the wiper.
So, assuming your linear potentiometers pictured are normal, your picture is correct.
The reason they don't use log pots on balance controls is that only huge manufactures running gigantic production runs, could buy pots with the fast moving end on one side of one pot, and the fast end on the other side of the other pot. If they did buy them that way, some stock carrier would probably put them in the wrong bins of the assembly station or something to mess it all up.

Got it! thanks :) so in that case, there are 3 potentiometers, one 10k for volume, two for balance. very funny indeed(well, lots of suprises to come the diy route as compared to commercial route)
any idea what that dotted line signifies? :\
Thanks :)
 
Got it! thanks :) so in that case, there are 3 potentiometers, one 10k for volume, two for balance. very funny indeed(well, lots of suprises to come the diy route as compared to commercial route)
any idea what that dotted line signifies? :\
Thanks :)

Seems to be some misunderstanding here.
The single 10K is the Balance control and the dual gang 100K is the Volume control.

The balance control works with R5L and R5R, see fig 2. on Rod's project page http://sound.westhost.com/project88.htm

All the pots are linear. The Volume pot works with R6L and R6R (see fig 4)
to make an approximate log law with better channel tracking than the averege Log pot.

It's all explained quite well in the project page text.
 
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