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Cmoy: What makes Panasonic EVJ/ ALPS so appealing for audio amps ? Why can't I use a panel mount...

post #1 of 30
9/19/10 at 4:00pm
Thread Starter 

Hello,

 

I am new to this forum, so hello!

 

I am trying to put together a Cmoy. Everything seems pretty straight forward but something that is really bugging me is the potentiometer that will be controlling the volume. I've heard a lot of buzz about the Panasonic EVJ pots. However, that would mean I'd have to order from someplace other than Mouser, because they don't stock it. This translates into more boxes and more shipping charges that I wish I didn't have to pay for. Maybe I will be proved wrong, but for now.

I am uncertain as to what makes a good potentiometer. I've researched but I'm still not seeing why the EVJs are so highly praised. (Them and the ALPS). So, does anyone have any potentiometer buying tips? These are just some questions I came up with


1.) Any brand in particular that is good?

2.) Panasonic EVJs have 5 terminals/leads while it seems most others only have 3...What does this mean?

3.) What material is best? Cermet or Conductive Plastic or something else?


Here are two I've been considering. Are they valid for this application?

http://www.mouser.com/ProductDetail/Bourns/91A1A-B24-D15L/?qs=sGAEpiMZZMtxdMMi52izypLiU99JhMSfgm/C64w7MfY%3d

http://www.mouser.com/ProductDetail/Bourns/51CAD-E24-F15L/?qs=sGAEpiMZZMtxdMMi52izyl5EHWC5efBypctZFZ3QC4Y%3d



These seem very legitimate to me but I don't know anything more than you do regarding potentiometers.

Thank you very much


Edited by TheLaw - 9/19/10 at 4:18pm
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post #2 of 30
9/19/10 at 5:18pm

You need a stereo or "dual gang" pot.

The ones you referenced are single gang pots.

You would need two for stereo.

You can get Alps pots at Mouser and Panasonic at Digikey.

A big bonus with the Alps pot is it includes a switch for power.

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post #3 of 30
9/19/10 at 7:24pm

if you have a radio shack near you, they carry one as well. it's one of the alternatives in the bom tangent has on his site for the cmoy.

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post #4 of 30
9/19/10 at 9:59pm

Why not just order the 10K Alps RK097 from Mouser?

The # for the model with the built in switch is 688-RK0971221Z05

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post #5 of 30
9/20/10 at 1:51am
Quote:
Originally Posted by TheLaw View Post

I'm still not seeing why the EVJs are so highly praised. (Them and the ALPS).

 

A large part of the answer is "they're available."

 

After you eliminate from the readily available stock of parts those that are unsuitable, you're not left with a lot of choices.  There's no especially good reason this should be so, it just is.  The Panasonic EVJ and ALPS RK09 series, in particular, are merely average quality.  The RK27 is well above average, but not beyond its competitors ability to match.

 

I've got other pots here that'll stand toe-to-toe with all of those mentioned.  You don't hear about them as much because they're harder to get, so fewer people have tried them, and consequently there are fewer posts mentioning them.  Simple as that.

 

Quote:

Any brand in particular that is good?

 

No general-purpose pot maker makes uniformly excellent parts.  Every one of the general manufacturers -- including ALPS and Panasonic -- make pots with a wide range of quality and suitability.  Don't buy on brand alone.

 

 

Quote:

Panasonic EVJs have 5 terminals/leads

 

Nope, there are 6.  Two neighboring pins are grounds and some pics show a single wire going to both, with solder bridging the pins together.  That may be where you got your count from.

 

 

Quote:

while it seems most others only have 3...What does this mean?

 

A simple potentiometer has 3 pins: the two fixed end-points and the variable wiper.  A dual-gang pot -- typically for stereo, but not always -- has two sets of 3 pins.

 

Watch my How a Potentiometer Works video for a more detailed explanation.

 

You may also find my article Notes on Audio Attenuators helpful.

 

 

Quote:
What material is best? Cermet or Conductive Plastic or something else?

 

No doubt there is a "correct" answer to the question, but since the pots you're going to be able to choose among won't give you a choice of materials, it's hard to see how knowing that answer can be of more than academic interest.  You might care if you're selecting trim pots or something else with more available variety.

 

 

 

 

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post #6 of 30
9/20/10 at 2:56am


 

Quote:
Originally Posted by TheLaw View Post

I am uncertain as to what makes a good potentiometer. I've researched but I'm still not seeing why the EVJs are so highly praised.


Just to chime in with my limited knowledge and findings on this one...

 

In the CMoy application, a good potentiometer would be one that is well matched between the two channels/gangs. There are lots of statistics like voltage rating etc that do not matter as you will not exceed them. As tangent says, the EVJ seems popular in builds but the reality is that it is a standard potentiometer. It's funny that a few components gain huge popularity due to availability alone. Gaining a 'quality' status along the way.

 

If you used an EVJ, you will not be disappointed but I think it would be fair to say that even if you used a stereo pot from a factors in town (Radioshack in the US?!), you would still have a fine CMoy.

 

I have found this with the ALPS RK09 - I have used the ALPS RK09 series for years - a fine pot but at the low end of the volume (first 10% maybe) there is usually a noticeable imbalance. That said, fine pot, nice and clean, good action. If you get the switched one, it feels very nice and gives a sleek pro look to your build (no switch - I like that)

 

If you have time on your hands, check out eBay as well, there is a bargain to be had sometimes.

 

Whatever you do, as long as you keep your build tidy and stick to the circuit, you will have a CMoy that you can tweak to your liking. Good luck and enjoy!!

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post #7 of 30
9/20/10 at 2:54pm
Thread Starter 

I don't know how I completely missed the fact that I would need dual gang for stereo. Silly me. Thank you for clearing that up. All of you have been very helpful. Thanks to those particularly with the detailed responses.

 

One question however...

 

If I am going to be hooking this up to my iPod with a volume control, is there any reason to even use a pot? Can I make it even louder than the max iPod volume using a pot?

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post #8 of 30
9/20/10 at 2:59pm

Pots are attenuators..they can only make the signal passing through smaller.  At "max", they simply do not attenuate.  However, the CMoy amp will be providing gain, so yes, the combination will go louder than the iPod alone.  Think of the pot as counteracting the gain.

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post #9 of 30
9/20/10 at 3:47pm
Thread Starter 

Thanks Tangent. By the way, best Cmoy guide ever. Maybe you should finish the op-amp list? Regardless,

 

I'm not too good with all of the technical audio jargon. I know what the words mean but its hard for me to put two and two together.

 

So here's my understanding of what you said:

 

Potentiometers are resistors, therefore they can only resist current/signal and not really make it larger. When they are fully turned or maxed out, they allow all of the current/signal to pass through with no resistance. 

 

I got confused after that.

 

My theory is that if I just don't run it without a pot I can still get the Cmoy's provided gain regardless of whether or not it has a pot. I reckon it should sound better without a pot too...could be wrong.

 

I don't quite understand what you mean by the pot counteracting the gain and re: gain. Am I missing something? If there is volume control from the source (iPod), is there a real reason to include volume control on the amp? Say I kept the audio output from the iPod maxed out and then only adjusted via Cmoy, would I get better sound?

 

Sorry.

 

Thanks.


Edited by TheLaw - 9/20/10 at 3:50pm
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post #10 of 30
9/20/10 at 4:00pm
Thread Starter 
Quote:
Originally Posted by MrTom View Post


 


Just to chime in with my limited knowledge and findings on this one...

 

....Whatever you do, as long as you keep your build tidy and stick to the circuit, you will have a CMoy that you can tweak to your liking. Good luck and enjoy!!


Thanks.Yeah I have plenty of time on my hands. I'd MUCH rather have a quality unit than a slipshod unit with parts from Radio Shack. Not that Radio Shack is bad but I'd prefer to use Nichicon and Wima caps compared to ShenzengCon and ChinatenCap. :p  It's not like the price is that much different. Maybe $0.50-1.00 each. Really not too big of a jump.

 

It's not very complicated at all and there are tons of guides so I am in good shape but yeah...we'll see.

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post #11 of 30
9/20/10 at 5:44pm

the pot basically acts as a voltage splitter for the signal that's coming into the gain stage. larger signal amplitude = louder; twisting the knob on the pot will change the amount that it attenuates the signal. it is not strictly necessary, and if you are not planning on changing the volume on the cmoy ever it is perfectly feasible to skip it.

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post #12 of 30
9/20/10 at 7:31pm
Thread Starter 

So my question is: Why would anyone have a separate volume control on the CMoy Amp if 95% of CMoy users will most likely be using it in an application where you can easily change the volume directly from the source?

 

What benefits, if any, does having a pot directly on the amp have? I mean, if you think about it, or atleast in my opinion, I'd just crank the volume up on my iPod and not necessarily the Cmoy because, why do that when I can control everything from one device?

 

So here's one thing I've been wondering. A scenario:

 

1.) iPod connected to headphones without Cmoy Amp. Volume is Maxed out on the iPod

 

2.) iPod connected to headphones via Cmoy Amp (one that does not use a pot). Volume is Maxed out on the iPod.

 

 

Now, 2.) should be louder just by nature, right? Even though I don't have a knob/pot, it will still be louder and/or distort less or whatever, right?

 

Am I right?

 

Thanks for all the responses.

 

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post #13 of 30
9/20/10 at 7:48pm

If you are using a LOD on the iPod you will have no volume control from the ipod, so you'll need one on the cmoy to prevent your ears starting to bleed :-)

 

cheers

FRED

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post #14 of 30
9/20/10 at 7:54pm

The trade-off is noise.

 

The volume pot attenuates noise from the source and provides a low

impedance path for noise at op amp inputs. To minimize noise you always

want your sources to be at high levels and the volume is controlled at the

last component.

You most certainly can design the amp with no volume control, I have several

examples in my design thread, but you might not always want to use the amp

with a device that has it's own volume.

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post #15 of 30
9/21/10 at 2:52pm
Quote:
Originally Posted by TheLaw View Post

Why would anyone have a separate volume control on the CMoy Amp if 95% of CMoy users will most likely be using it in an application where you can easily change the volume directly from the source?

 


 

Knobs are nice.

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