# Circuit Help.



## mgboy (Jan 17, 2007)

I'm seemingly having a hard time figuring out how I would wire this variable BSC (eq) up, in line with my amp and what-not. 

I've got a 10k pot, 10k resistor, and my 0.022 Kimber cap, but realized I'm not entirely sure how to make it work. 










Is the diagram, and while I think I can wire that up, I'm finding it hard to think (tonight) of how I'm going to run it through (in) RCA audio cables. 

Would the red go in to leg 3, out leg 2, with the black going past (through?) the cap, which would be connected to the resistor, which would be connected to leg 1, correct? Or do I have everything mixed up?


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## Anthony (Oct 5, 2006)

I'm not sure what you asking: 

Edit: I looked at it all again and the main confusion is that you refer to legs by number and your diagram has no such markings.

For signal level, the shield or outer contact is ground and the pin is signal.

You would need a matched pair for both speakers (assuming a LR and that they needed the same BSC based on room position).

Edit:
It looks like signal would come in top left leg and the shield/ground would be the bottom. 

I hope that clears things up a bit (as I understood the question at least).

Good luck.


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## mgboy (Jan 17, 2007)

I was using this link - here as a reference for pots as this is the first/second time using them.

This variable BSC is for use in between a preamp and power amp, so I thought I could use it through ( in? ) RCA cables, going from a preamp to power amp. That's what I gathered from this page. If I'm mistaken, then I'll just stop here because it's a 'waste' of money. 

And just for clarification, I'm using a 22nF cap, not a 27nF cap as called for by the equation on the aforementioned BSC page. 

The legs were in reference to the outer, middle and outer pins. I hope I've explained this a bit better.


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## mgboy (Jan 17, 2007)

mgboy said:


> I was using this link - here as a reference for pots as this is the first/second time using them.
> 
> This variable BSC is for use in between a preamp and power amp, so I thought I could use it through ( in? ) RCA cables, going from a preamp to power amp. That's what I gathered from this page. If I'm mistaken, then I'll just stop here because it's a 'waste' of money.
> 
> ...


It seems that I didn't explain it much better, or I'm not doing something right..


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## Anthony (Oct 5, 2006)

Your assumption that this is a signal circuit are correct. It's a passive signal circuit, so it eats headroom in your overall amplification chain -- however, it is still more efficient to do it this way than at the speaker.

Okay, onto the circuit: Ground for both would be the shield conductor or black wire on a twisted pair RCA cable. Red in from the preamp to the pot body, red to the power amp from the wiper arm in the pot.

The outer middle and outer pins on the pot are usually the in, wiper, and out of the potentiometer. IIRC, 1 is the in, 2 is the wiper, and 3 is the out. 1 to wiper + 3 to wiper usually sum to the same resistance. However some pots are different, so someone with more experience on these should chime in.

the position of the wiper sets the resistance from 1 to 2 and the remainder of the pot creates a resistance from 2 to 3. So for a linear pot, it wouldn't matter if you have 1 and 3 reversed. However, some volume pots are logarithmic and I have no idea which end is which then.

I probably added more questions than answers, but I hope this helps some.


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## Anthony (Oct 5, 2006)

Ah, found something on the Westhost site:
http://sound.westhost.com/pots.htm

1 is ground, 2 is wiper, and 3 is source. Good diagram lower on the page with a view to ID 1,2, and 3.

Hope this helps.


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## mgboy (Jan 17, 2007)

Anthony said:


> Ah, found something on the Westhost site:
> http://sound.westhost.com/pots.htm
> 
> 1 is ground, 2 is wiper, and 3 is source. Good diagram lower on the page with a view to ID 1,2, and 3.
> ...


Heh, I posted a link to that page in my second post, but I was only really looking at the pictures. =P

I'm just not sure how to set up the diagram I posted. Red to the in, then red out to the amp, and the resistor and capacitor from the "lower" arm going to the black wire? ( ground ) 

I just want to make sure I'm seeing this right.


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## Anthony (Oct 5, 2006)

3 is red in.
2 is red out.
1 is R1 then C1 then a node for both blacks / shield for both in and out.

I saw the page you referenced in your second post when I originally read it but forgot. So I got to have a eureka! moment today  DoH!

Let us know how it turns out.


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## Anthony (Oct 5, 2006)

Also, if you are using twisted pair RCA's, you may want to verify that red is indeed the pin (use a multimeter with a continuity tester to verify -- most have this feature, they beep when your are touching both leads to the same wire).

I'm 90+% sure red is pin and black is ground, but I've been wrong before


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## mgboy (Jan 17, 2007)

Anthony said:


> 3 is red in.
> 2 is red out.
> 1 is R1 then C1 then a node for both blacks / shield for both in and out.
> 
> ...


Haha, alright thanks for the final explanation.

I will let you know how the final project turns out. I've had this speaker build on hold for months but just bought all of the stuff and am now waiting for free time to get the wood cut and routed, then will put the crossovers together, and finish up the speakers for good. I was using this "active" bsc (if you will) to have something adjustable as I move things around in my room a lot and the speakers are never the same distance from the wall. =P And I can use this for multiple sets of speakers, I just have to keep the baffle size the same - roughly 9.5 inches wide.


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