Inline Volume Control - What Resistance?

[myrmidon]

Hi All,

I would like to mount an inline volume pot somewhere beside the speaker (so that the player can adjust the volume 'on demand'). Can I simply wire this in series with the speaker to form a 'passive' downstream volume control? If yes, what resistance should the pot be?

Furthermore, (unfortunately I don't have any advanced electronics knowledge), what effect would such a pot have on the games? (BEcause the pot would be increasing the resistance on the speaker loop - is this bad for the audio amp?)

Thanks

[WhereEaglesDare]

You need a pot that is designed for this application.  A normal pot will increase the resistance, or impedance, but one designed to be a inline volume control will do what is called impedance matching and will not burn out your speaker output on your game.  A normal one can blow your amplifier.

[BKahuna]

What you need is called an "L-Pad".
http://en.wikipedia.org/wiki/L_pad

[myrmidon]

What you need is called an "L-Pad".
http://en.wikipedia.org/wiki/L_pad

Aah, interesting (had never heard of that). Thanks for the info.

So I don't know what 'load' I would need. For example, would this one work?
http://www.allelectronics.com/make-a-store/item/8MLP/8_OHM_L-PAD,_MONO_15W/-/1.html

[shfifty]

if you are using pc speakers that already have a volume control knob, it may be easier to just replace/relocate that. I'm using logitech 2.1 pc speakers and will just be rewiring the potentiometer up to my mounted one. the original one is is a 10K linear. 

[Smeghead]

Yeah I took apart from speakers and mounted the control board to my cab

[WhereEaglesDare]

Did you use the orginal speakers as well or did you put in some better speakers?

[Zebidee]

I've done this about a dozen time or more.

You don't need an L-pad.

You don't want to take the volume pot off your amplifier.

Just put a new 10k - 50k pot on the line-out from the PC (ie before the amplifier). This approach will minimise your hassles.

Wire it and mount it like this:

http://scarvell.net/wiki/index.php?title=VOLUME_CONTROL_MOUNTING_AND_WIRING

Enjoy!

[WhereEaglesDare]

I use to repair home stereo and what you are saying will work and I believe you, but there is a big chance you could blow the output amplifier on your machine... This is why they make them, goto Lowes and buy a home audio volume control that has impedance matching.

[Zebidee]

I agree that the L-pad would be good where you are putting a pot between the amp & speakers, but I still say that it is overkill for a volume pot on the PC audio line-out (before the amp). Which is why I advise that people do it this (latter) way - because it is easier & simpler.

If you are using PC speakers, they will be designed for this range of variation in their signal input anyway.

[myrmidon]

I am using the original PCB's (not MAME) so am subject to the on-board audio amp, and it is wired directly to the standard 8-ohm cabinet speaker.

Therefore having read though the threads it appears that while an l-pad is a few bucks more expensive than a simple pot, it definitely seem the better way to go (certainly cannot and will not cause any harm to the amp on the PCB).

[Smeghead]

Did you use the orginal speakers as well or did you put in some better speakers?

Cut off the speakers and attached them to my cab speakers.
Good thing is I even have a headphone socket on that board!

[Zebidee]

I've never seen an L-pad in all the original arcade cabs I have pulled apart (which is a lot). They all use a simple volume pot.

However, it can't hurt, esp. between PCB amp & speakers. Most cab makers would have been more concerned about cost than good design (another example of this is how many original cabs have unshielded speakers placed near CRT screens, causing magnetic anomalies).

[BKahuna]

I've done this about a dozen time or more.

You don't need an L-pad.

You don't want to take the volume pot off your amplifier.

Just put a new 10k - 50k pot on the line-out from the PC (ie before the amplifier). This approach will minimise your hassles.

Wire it and mount it like this:

http://scarvell.net/wiki/index.php?title=VOLUME_CONTROL_MOUNTING_AND_WIRING

Enjoy!

Maybe I misread the OP's question, but it sounded like he wanted a passive device to put inline between his speaker and amp? That would be an Lpad.
I agree, your idea is better, if he's using a PC soundcard output, or has access to the line level audio signal elsewhere, but that's not what he asked for, and at the time, he hadn't actually said what he was putting it in.

[Zebidee]

That's true. One can jump to assumptions based on the idea that this forum mostly being used by people making MAME cabs.