Tone cap question: NOS or polyester?

[Delmont]

My Strat has a polyester tone cap on the middle pot. It looks like a brown Chicklet. A friend has offered me an NOS cap to replace it.

 

How much of a difference would a good NOS cap make? Is it worth the trouble of opening up the guitar and swapping it out?

 

And if I'm opening the thing up, anyway, I might put in a new volume pot - the one I have is a little finicky. Any recommendations for a good brand?

 

Thanks!

 

Del

www.thefullertons.net

( •)—:::

[DeepEnd]

AFAIK, "NOS" just means "New Old Stock." The capacitor your friend has is probably ceramic. I've read that some ceramics can sound "grainy," whatever the heck that means (http://www.regiscoyne.com/tech/cap_resistor_types/). In any event, I'm of the opinion personally that a cap is a cap, unless you need something with tight tolerances or high voltage handling. As for pots, CTS are supposed to be very good and frankly, pots are cheap so it doesn't make sense to skimp. I have a stray 500K Audio WD brand pot lying around that I'll send you if you want it.

[Delmont]

Hi, Deep! Thanks for the offer. I'll probably be getting a 250k pot, and they're not expensive. It's just a matter of deciding which one.

 

Del

[Delmont]

PS - Yeah, I know what NOS means. I buy NOS tubes sometimes. For some reason.

[Mr.Grumpy]

For tone cap applications, there is NO difference you can hear. Spend your money on other things. The poly "chiclet" caps are stable and consistent.

[WRGKMC]

Caps can sound different depending on their Q factor. Q stands for Quality. As a specification, its how sharply a cap cuts off the frequency.

 

A low Q cap when seen on a frequency graph will have a long slope beginning at zero and slowly rising up to maximum frequency. The total cut off may begin at say 3K, gradually taper down to 1K where it stops cutting frequencies.

 

A High Q cap will have a very sharp cutoff, like a mountain cliff. It may be good for rolling off to say 3K then drop off to nothing so frequencies below 3K are not attenuated.

 

Caps of the same value can begin to cut off at the same frequency but the differences you hear can be how gradually they cut frequencies below that point.

 

 

Allot of guitarists like Orange drop caps because they do have a higher Q then other caps. They cut at the treble frequency and leave allot of the mids intact.

 

NOS caps may be good or bad. The problem with many is the electrolyte dries out and they either get weak and can even short out.

 

Many of your cheaper caps can have between 10~20% tolerance. When they get old they can drift way out of specs and be well over 50%.

Best thing you can do is just try them and see if you like how they sound.

 

I definitely wouldn't pay more then $1 for any cap however. There's a bunch of unscrupulous people selling snake oil out there trying to convince people old caps have some kind of magic mojo. The fact is caps go bad like batteries when they aren't being used.

 

Would you play mega bucks for antique batteries? Of course not.

 

When you take amps in for repair the first thing you look for are spent capacitors. Amps over 10 years old often have at least the power caps replaced. Over 25, all your non electrolytic should be suspects for replacement. Non electrolytic last allot longer then Electrolytic, but their values can and do drift. This can cause losses in frequencies and attenuate signal strength as well as a whole bunch of other symptoms.

 

There are some really high quality caps. Your glass ones are the best I've ever heard. I have thousands of caps in my repair cabs. Many are NOS I got when repair shops shut down and instead of throwing them out companies gave them to me. The Brown Green and Orange drops are all decent caps for guitar work. There are plenty of others too. The wax/oil caps can melt and leak. If they work that's fine. Just realize the values on them can be way off and you'll either need to test them with a meter or use your ears.

 

A quick test can be done without soldering them in. Just unscrew the cap on a guitar cord and touch the cap to the hot and ground wires. This will be the same as soldering the cap in and rolling the tone completely off. This will give you and idea of the maximum tone roll off and cut off. If its not too severe, the pot will do the rest.

 

I used to mess with caps as a kid experimenting allot. I don't think there isn't anything I haven't tried with them. I'm pretty much like Mr. Grumpy is however. A caps a cap. So long as it works and isn't too muddy, or too weak, move on and find something better to waste your time on. Noone ion that audience is going to hear the differences between one type or another. Most of the sound shaping done by guitarists is done on their pedal boards.

 

I don't even put Tone controls in m,y guitars any more. The less there is to load down the pickup signal the better. I have tone controls on my amp, all my drive pedals have tone controls, I even run an EQ pedal with a full set of frequency adjustments. Why would I need another redundant tool to do the same thing.

 

I do have tone controls in my stock guitars. I occasionally use the one on my Tele when I have new strings which are really bright. I may have my rig set for a darker guitar and when I plug the Tele in, its too bright. Instead of re-tweaking my rig I just roll the tone off 1/2 way. It doesn't sound as good as re-tweaking the setup however.

 

I never use them on my Gibson's. Gibson's use darker sounding woods and if anything they usually need a treble boost, not a treble cut.

 

I do use pickups to vary my tone however. I've been known to swap out the two tones on a Strat for three volume knobs. When you attenuate the pickup it also tends to get a little darker which is all I ever need in most cases. If they get too dark then using a treble bleed cap can retain the treble loss as you turn down.

[DeepEnd]

^ Not sure I buy that. The experts say Q factor pretty much doesn't matter at anything below the RF range (http://www.capacitorguide.com/q-factor/), above 3KHz and normally well above, as opposed to the frequencies a guitar produces. The fundamental of the E on the 1st string at the 24th fret is 1318.51Hz. The same note bent up 2 semitones is 1479.98Hz. That's pretty much the highest note a guitar will produce under normal circumstances. Sure, there are harmonics that extend above 3KHz but for the most part a guitar doesn't produce anything in the RF range. Plus, the rate of rolloff is determined by the way the circuit is wired (http://www.bcae1.com/xoorder.htm). I've never heard of a cap that stops cutting off at a certain frequency either; it's supposed to keep going to infinity, cutting more and more as the curve continues.

[WRGKMC]

Q is an efficiency rating similar to SPL as an efficiency rating in speakers. As a rating, its often ignored in audio circuits because we aren't worried about caps exploding in low frequency audio circuits. Q is an indirect factor in an LRC audio circuit however.

 

You need to ask yourself, What makes a high Q cap different from a low Q cap.

In order to work efficiency a cap needs to have a low amounts of leakage across the dielectric, In other words low DC resistance and low inductance. To get those you need to have quality materials. Film Polyester, Teflon, polypropylene, polystyrene, etc. Are your highest Q caps and recommended for audio. Teflon is supposed to be the best but unless you work for NASA its unlikely you can get your hands on them or afford them. They don't take to soldering heat well either.

 

Efficiency isn't necessarily something you want in audio. Some people want a blurred audio image in order to tame a pickups output. A Leakey dielectric using older materials may be the character someone wants. We're dealing with peoples ears and their opinions on what sounds good and what doesn't. My point was, am extremely efficient cap with high Q materials is going to cut off sharply compared to a lower efficient cap. This is often the case.

 

If you want to understand how this does work in real life you have to get out there where the rubber meets the road and do some of your own lab work. Since you're reading this post on the internet you already have a powerful tool for testing. All the computer needs is a sound card and a few programs installed and you can test the theory.

 

Something you can do is download a good Frequency analyzer. You can then your computer sound card to test your circuits. Most sound cards will easily handle 20~20Khz. For an audio analyzer Voxengo span should work.http://www.voxengo.com/product/span/ Its free but it must run within a daw program. There are several free daw programs as well that run VST plugins.

 

Next you'll need a Frequency generator. There are several you can Google up. you can also just download recorded Pink and White noise files and just play them back with your media player. Then you use say the Left output of your sound card output as a signal generator and the Right input as your frequency analyzer. You set the output to feed the test tones through cap filter circuits and use the input back to the computer to view what's being making it through the circuit.

 

Span is a dual channel analyzer so you can even view the signal leaving the computer and compare it to what's coming back after it passes through the filter circuit.

 

The effects of different caps can easily be viewed using free plugins.

 

Heres a pro level audio test program which contains both a signal generator and analyzer. Its designed to be run on a normal windows sound card. Its used for tuning rooms and fixing room acoustics but I think it can be used as a signal tracer too. https://www.trueaudio.com/rta_faq1.htm

 

Testing actual results is much better then relying solely on theory to come to conclusions. I haven't had to crack a book in 40 years yet I know how to do allot of this stuff because I do it for a living.

 

Or you can just go low tech use your ears which is the simplest method of all. Buy several tone caps of the same value from different manufacturers and you will hear slight differences in how the midrange is preserved.

[isaac42]

Q is the ratio between the reactance of the component, in this case a capacitor, and its resistance. As we're talking guitars here, and using these caps in series with resistors (potentiometers), I doubt the internal resistance of a cap (usually expressed as effective series resistance, or ESR) will have much effect in a guitar tone circuit.

 

I've read at least one article that claims that ceramic caps have the highest distortion among caps tested for that article. I can see that being a problem in active tone generating circuits, but again, I doubt that it would make much difference in a guitar tone circuit where all it's doing is shunting highs to ground and making a resonant circuit with the pickup coil(s). I think that in most cases, maybe all, the thing that makes audible differences is the value of the cap. Other factors might make a difference to people with better ears than I have (years of playing rock and roll have taken their toll), but I doubt it, and I'm sure they wouldn't make a difference to me.

 

But hey, what do I know? I'm just a bass player.

[isaac42]

For anyone who wants to get more technical, here's a three page article about capacitors. Note that most of the effects that cause a cap to depart from the ideal are negligible in the audio frequency range, though some can be a factor for high fidelity speaker crossover networks.

 

http://www.murata.com/en-us/products/emiconfun/capacitor/2013/02/14/en-20130214-p1

 

Here's an article about capacitor distortion.

 

http://stephan.win31.de/capdist.htm

[isaac42]

My guess is that, to the extent that NOS caps sound different, it's that their capacitance value has drifted, and that if you substituted a modern cap with the same value - actual value, not nominal value - it would sound the same.

[AJ6stringsting]

I've replaced some caps in a 2007 Epiphone LPC copy, which inspired me to rewire the whole guitar and get new pots.

I put in some Orange Drop caps and the tone improved 100%.

Caps do make a difference.

[isaac42]

No one said they don't make a difference. The discussion was about why they do.