Capacitor Questions for Ross Clone

[thinkgenius]

I am on my first actual build and after doing my HW online I noticed that keeley and others are using premium "metal film everything" in their ross clones, and well I wanted to jump on that band wagon.  I was on mouser and I am confused on what the voltage rating is for a capacitor... i.e what exactly 630V 0.001 uF 10% mixed film capacitor means.  We are working with 9V, so would something like that work, or is the wrong one (the scematic simply states a 0.01 uF capacitor)?  Secondly for those who use premium parts, can you really hear a difference? 

Thanks

th

[tiges_ tendres]

You should do a search for capacitor types.  There has been a lot of discussion lately about the difference in sound between certain types of caps.   I think the conclusion people came to was that whatever sounded good to you is what you should use.  Lots of old, great amps used cheap ceramics!  Ceramics also tend to be really cheap!

10 % is the tolerance.  That means that the rating of the cap has a 10% +/- swing, meaning that it could be rated higher or lower than the 0.001 uF stated, but only by 10%

As far as voltage goes, dont use caps that are in that 630v range, not because they wont work, but because they take up more space on your circuit board.

You should check http://www.smallbear.com they have a great range of caps in different voltages, all useable in pedal applications.

When I buy my caps, I usually choose between 25 and 50 volt caps.  If I am really stuck, I will use higher voltages

[Mark Hammer]

I'm never really sure that the people who believe they hear a difference actually hear a difference.  That doesn't mean there IS no difference or never will be.  The problem is that when you take a pedal apart, replace some caps, and a few hours pass between when you last tried it out and when you try it out again, are you really doing an A/B comparison, or are you comparing between what you hear now and a fuzzy acoustic memory?  Not to take away from any of the after-market mod people like Bob (Keeley) and Brian (Wampler), but when people get their pedals back a few weeks later, how much of what the customer hears is a contrast between what the pedal was really like, and now, and how much is a contrast between what they remember the pedal as being like and now? 

I don't doubt their (mod people) complete sincerity, and it may well be that there are a number of instances where people are using the pedal in contexts where those component changes can make a difference.  But it can also be that some folks who *think* they hear a big change are more likely to be hearing more of a change than really happened.  That's not Machiavellian manipulativeness on anyone's part, just the nature of human memory and reasoning processes: when people think something is supposed to have changed, and their memory for how it was is even a little bit sketchy, they tend to exaggerate the change they detect.

Obviously, the place where you would be most expected to hear a difference would be with caps in the signal path itself, rather than caps used for addressing power, such as smoothing caps and decoupling caps, and caps used for LFOs aqnd such.  The other place where you would expect to hear a difference would be in "cleaner" contexts.  It's not at all clear me, at least, that what people believe they hear in distortions is a product of changes in the signal quality, independent of bandwidth, or changes in the bandwidth brought on by small changes in the actual capacitance value of the cap.  If the second one is true, then even a cheap crappy cap will work, as long as it has the same capacitance value.

We've had this "do caps matter?" debate more times than I care to engage in (didn't seem to stop me, though  ), so I won't belabour it.  I'll just simply say that you should not haunt yourself with any sense of having used "less" than what you could have, because it may well not even matter in the end in your particular circumstance.

The voltage ratings you see are specs for how high a voltage you can apply and still have the component hold its nominal value.  You can always use caps that have higher voltage ratings than is called for.  That will not affect their ability to function as intended.  On the other hand, higher voltage ratings generally a) result in a bigger package, and b) cost more. Both of these can affect whether you can fit them into the allotted space and whether you can afford to buy all the parts you need.  That being said, if the part is a decent price, and fits the space provided, going over the specified voltage rating is no problem whatsoever.

Note that:

• The same rating is not always used or needed throughout the entire circuit.  So, while you would need to be able to contend with the full supply voltage for, say, the big caps (47uf or more) straddling V+ to ground, caps in series with the audio signal will generally not need to handle much more than a couple of volts, and those caps used for decoupling the Vref source (half the supply voltage) can be rated lower than those handling the full supply voltage.
• It is generally considered good practice to use a cap rated at 50% higher (or the closest standard rating) than the needed rating, for safety's sake.  So, if you are using something that will only run on +9vdc and nothing but, a 16v cap is fine.  If the pedal runs off a 9v battery but you could just as easily and comfortably stick a 12v wallwart into the socket, then maybe 16v is cutting it close and the next rating up (usually 25v) is a smart idea.  Similarly, a 6.3v cap may well be fine for decoupling Vref (normally 4.5vdc), but if there is an outside chance that V+ might end up being 12vdc, instead of 9vdc, then 6.3v is cutting it close and the next rating up from that is preferred.

[tiges_ tendres]

I just finished making a supreaux, from runoffgroove.com and aside from two poly caps near the output I used ceramic and monolithic ceramic for the rest.

I LOVE this pedal, so I'm going to make another and splurge on some poly caps and see if I can hear a difference.  I will report back, although, I have a funny feeling it's not going to be ground breakingly different.  I dont record or play live, so I'm not sure why I would need to hear a difference if I'm already satisfied! 

oh, science, that's right! :}

[thinkgenius]

Wow thanks all!