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Volume Control Question

amos

amos

Hey,

I'm installing a stereo into an older car, and I have a question.

The stereo is a 2 channel, and I'm using 4 speakers, wired parallel. The rears are much louder than the fronts, and of course since it's a 2 channel radio there's no front/rear fader control.

What I'd like to do is put a volume control inline with the rears, to attenuate the rears so that the fronts can be heard. Choosing which one to get, and wiring it, is a bit over my head.

Would a 100k stereo volume control be the right one to use? Radio Shack Model 271-1732 is one i've found. But I'm thinking that might be the type control that would be used in a circuit before amplification. What should I use?

And, the radio shack control (it's 2 mono units ganged together) has 4 terminals per channel. I was expecting 3, and I thought I understood that. What's the right way to wire it? The fourth terminal is apart from the other three.

The way I have it now, I have the commons on terminal A (left), signal input on terminal B (center) and signal output on terminal C (right). It does work, but there's almost no control, going from full on to full off very quickly.

Should I have gotten something like radio shack model # 40-987?

Any advice is very much appreciated!!

amos
<P ID="signature">______________
</P>
 
> The stereo is a 2 channel, and I'm using 4 speakers, wired
> parallel. The rears are much louder than the fronts, and of
> course since it's a 2 channel radio there's no front/rear
> fader control.

Very common. Make sure the impedance matches the unit...parallel resistors are a pain in the neck. 8 ohm rear and 8 ohm front means it's now 4 ohms...likewise, 4 ohms plus 4 ohms means 2 ohms. Most amps are not 2 ohms stable.

I bring this up because your best bet is to place a fixed resistor in series for the rear amps rather than a pot...but make sure you take that into account when calculating your total resistance per channel.<P ID="signature">______________
</P>
 
> > The stereo is a 2 channel, and I'm using 4 speakers, wired
>
> > parallel. The rears are much louder than the fronts, and
> of
> > course since it's a 2 channel radio there's no front/rear
> > fader control.
>
> Very common. Make sure the impedance matches the
> unit...parallel resistors are a pain in the neck. 8 ohm
> rear and 8 ohm front means it's now 4 ohms...likewise, 4
> ohms plus 4 ohms means 2 ohms. Most amps are not 2 ohms
> stable.
>
> I bring this up because your best bet is to place a fixed
> resistor in series for the rear amps rather than a pot...but
> make sure you take that into account when calculating your
> total resistance per channel.
>

The easiest best solution is to build a fixed value L-Pad or buy one
(they are not expensive) for each channel. Diagram and explanation:

http://www.bcae1.com/lpad.htm<P ID="signature">______________
Electricity is really just organized lightning.
~George Carlin</P>
 
thanks, andy and sam for your help...

i remember L-Pads from working with engineers back when i was in radio. i also remember T-Pads, but i can't quite remember the difference. i'm thinking an L-Pad is for an unbalanced line, and a T-Pad is necessary for a balanced line. is this right?

the problem with a fixed L-Pad is i don't know the amount of attenuation i need. i just want to turn the level down so that the front speakers can be heard. :eek:) so i'll go with an adjustable one. i guess radioshack doesn't have what i need.. any ideas for a source? i'd rather it not be a big "wall mount" type. my plan is to hide it way up above the passenger's feet, as i'll not need to adjust it once it's set. so just something i can mount in a switch plate and attach up high on the firewall where it will be unseen is what i want.

also, i can't find info about my amp's 2 ohm stability, but i suspect i shouldn't run these speakers in parellel. i can't find the resistance for the speakers listed, and i don't have a voltohm meter with me, but i think the fronts (4" blaupunkt) are 4 ohm, and i'm not sure about the rears, (6x9 pioneer), they may be 4 ohm too. so, in series, the load should be ok on the amp, but not in parellel, right?

the stereo is a mitsubishi mx-4, it's peak power is 25w at 4 ohms for the 2 amped channels.

thanks again
amos

> > > The stereo is a 2 channel, and I'm using 4 speakers,
> wired
> >
> > > parallel. The rears are much louder than the fronts,
> and
> > of
> > > course since it's a 2 channel radio there's no
> front/rear
> > > fader control.
> >
> > Very common. Make sure the impedance matches the
> > unit...parallel resistors are a pain in the neck. 8 ohm
> > rear and 8 ohm front means it's now 4 ohms...likewise, 4
> > ohms plus 4 ohms means 2 ohms. Most amps are not 2 ohms
> > stable.
> >
> > I bring this up because your best bet is to place a fixed
> > resistor in series for the rear amps rather than a
> pot...but
> > make sure you take that into account when calculating your
>
> > total resistance per channel.
> >
>
> The easiest best solution is to build a fixed value L-Pad or
> buy one
> (they are not expensive) for each channel. Diagram and
> explanation:
>
> http://www.bcae1.com/lpad.htm
>
<P ID="signature">______________
</P>
 
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