let's discuss caps

[hippietim]

I know, I know - the topic has been beaten to death.

Having said that, I'm going to start another one anyhow [img]/images/graemlins/smile.gif[/img]

I've been reading a good bit about different caps on a number of forums. I am naturally skeptical about magic caps - most of the talk sounds like a bunch of nonsense.

However, there is some reason to believe this stuff matters. It seems to me that there are quite a number of things that are variable that would matter besides just the value:<ul type="square">[*]microphonics[*]rate of discharge - attack perhaps?[*]liquid filled caps can dry out which presumably alters things[/list]
There are more than a few folks I respect that have gone the distance with high dollar foil caps and such in their Historic Les Pauls. Some of these guys are pretty methodical - taking measurements and comparing the curves, noting attack velocity curves, etc. In fact, after doing a lot of reading and comparisons I think I'm going to try some Jensen caps in my '59 Historic. Should be interesting...

I'd be curious to see some similar results from some Fender style guitars. Nothing fancy, just some reasonably methodical testing and/or past experience would be very cool. I put an orange drop cap in a parts Tele I built and the guitar sounds great but it's not like I compared it to a different cap to begin with so I'd have a hard time saying how much the cap mattered - I'd just heard good stuff about them and it was like 75 cents. Unfortunately, I'm not really setup to do much in the way of measurements.

[ripley156]

Re: let\'s discuss caps

[img]/images/graemlins/confused.gif[/img]

Yeow!

My favorite color for a guitar is fiesta red.

Any question more complicated than that and a thread is way over my head! I hope that some folks chime-in that know what you are talking about! [img]/images/graemlins/tongue.gif[/img]

Dan

[Twisteramps]

Re: let\'s discuss caps

One mod I'd consider is to take a small area off the 'track' on a pot - so that you can turn the tone control to 'full off' and it doesn't load down your guitar at all. Regarding caps... If you really wanted to hear a difference, move the volume pot off the guitar (push it down, leave it wired) and temporarily put a switch in it's place. Wire two different capacitors to the tone circuit, so you could switch between the two.

Sure, it's going to sound a little different since there's going to be a switch and a little extra wiring, but it will be the 'same' difference between the caps, if that makes sense. one cap that sounds warmer than the other will still sound warmer when you pull the switch and extra wire, etc.

You may also want to experiment with different value volume pots and value of capacitors too.

Pete

[Budman68]

Re: let\'s discuss caps

<font color="aqua">The only cap "trick" I bother with is the one you wire in so when you turn the volume down, it doesn't get muddy, it stays clean but just less "drive".

I'm definitely sure you can hear the differences as I had experimented with all kinds of electronics years ago, but they are so subtle TO ME, I don't bother anymore. Besides, I suck and it's not like I play out.... [img]/images/graemlins/laugh.gif[/img] </font>

[pebber]

Re: let\'s discuss caps

when you look at an electric guitar from the point of electronics, it's really simple:


The pickup acts like an AC source, where the coil itself can be described electrically as an ideal inductance L (whch is the most important quantity,depending on the number of windings, the magnetic material in the coil, and the geometry of the coil) in series with an Ohmic resistance R, and parallel to both a winding capacity C.


Each pickup &quot;sound&quot; is identified by the resonant frequency and height of the resonant peak (or overtones in the range around the resonant frequency are amplified,overtones above the resonant frequency are progressively reduced, and the fundamentalvibration and the overtones far below the resonant frequency are reproduced
without alteration).


The external load consists of resistance (the volume and tone potentiometer in the guitar, and any resistance to ground at the amplifier input) and (cable)capacitance. The pickup + load forms a so-called second-order low-pass filter.


One way to change the guitar's sound is changing the external load:


standard tone controls lower the resonant frequency if u connect a capacitor in parallel with the pickup (usually through a variable resistor to give some control over how much the capacitor affects the pickup), and extending this idea further like seen on some guitars by a rotary switch that connects different capacitors across the pickup.</p>


Personally, I do believe &quot;magical&quot; caps (like like metal-film or polypropylene) have a sort of influence on the sound, but this is because</p>
<ul>[*]their low value tolerance [*]their temperature stability[*]their 'low-noise' ratio[/list]


all compared to the common electrolytic and general purpose ceramic capacitors, but this should not be overrated.


Even if these variations maybe clear in an experimental setup, it all depends on someone's hearing condition to benefit from them.


I do have a measurement setup where I can examine pups with or without external loads, so if anyone cares, I'll draw it one time and beam it up.</p>

[hippietim]

Re: let\'s discuss caps

I'm primarily interested in tools/ideas that enable me to hear the difference - me staring at an oscilloscope ain't gonna happen. So I like Pete's idea of a switch to compare caps. I'd want the volume and tone controls pretty accessible so I think i'd just hook up a dangling switch. Would that just need a SPDT switch?

Pebber, let's see your diagram and please explain what it does.

[pebber]

Re: let\'s discuss caps

okay, the 1st schematic shows the standard (passive) tone/volume control :

(click for detail)

the smaller the TONE pot resistance, the more high frequencies of the guitar signal are shorted to ground and as such do not reach the output jack (I think the most of us leave the TONE pot fully on)
what you easily can do, like shown in the 2nd schematic, is to add 2 or more capacitors which you can &quot;dial-in&quot; discrete:
<ul>[*]if your TONE control is a pot with a 1-pole switch, you can switch to 2 different caps[*]for more choices, use a rotary switch (which are commercially available)[/list]this basically shifts the pup resonant frequency.

if u take this further, you can easily make a test device capable of simulating tone (and measuring the sound characteristic) :

</p>
<ul>[*] take a sine wave generator (with constant voltage vin)[*] connect this generator to a test-pup[*] place the polepieces of this test-pup on the polepieces of the guitar-pup[*]sweep in the audio range [20Hz.. 20kHz][*]measure the output voltage vout for the different frequencies with a voltmeter (or attach a load like a speaker to it)[/list]and you'll get the transfer characteristic.

If you built everything in one housing (a sine wave generator, a frequency counter, a voltmeter and added 2 switches for both different R and C), u can simulate whatever u want, both with a pup in or out of a guitar.
(or if you have a lot of electronic tools like me, you don't have to bother building anything)

[YetAnotherOne]

Re: let\'s discuss caps

That's a great suggestion but it leaves an awful lot of variables in the experimental setup and it doesn't really get down into the nitty-gritty of differences in the transient response due to materials/construction which is something it seems Tim is interested in. To get there reliably and perform actual meaningful measurements of the transient response it's probably going to take a bit more equipment than Tim has on hand and a bit more work to zero out the variables.


Here's an alternative suggestion:


1. Compare oranges to oranges because if you’re going to compare secondary effects you must begin with components having precisely the same primary characteristic. Thus you’ll want to be absolutely certain that you're comparing capacitors of precisely the same capacitance because if you aren't doing so the first-order effect of the RC filter / tone circuit’s response to differing capacitances is almost certain to drown out most/all of the smaller differences arising from the construction & materials and you’ll never know what’s actually responsible for what you hear / see during the tests.

2. As #1 implies, you’re going to have to find a way to accurately test capacitance. The components aren't precise enough to just go by the alleged values, manual matching will be required. Pay close attention to the accuracy of your method because without precisely matched parts any tests you run will be moot. This is left as an exercise for the reader.

3. Buy a couple of those spendy audio caps in a value that you can also get in other materials (ceramic, mica, etc.).

4. Buy a bunch of the cheaper caps with the same alleged capacitance rating as the spendy audio caps.

5. Measure the capacitance of your caps until you find precise matches for the spendy ones among the lot of cheap ones. Personally I’d want the capacitances to differ by no more than a total of 0.1% over the set that is to be compared though another order of magnitude in accuracy of matching would be even better. YMMV.

6. Consider the tone circuit: it’s really nothing more than a simple RC filter fed by an AC source. Rather than introducing lots of variability by soldering things into a guitar and playing it for A/B comparisons why not just remove the tone pot & build the RC circuit on a $5 breadboard (more than sufficient for audio applications) using the tone pot and plugging in each new capacitor to be tested?

7. You’re going to need a source but this too must be identical for each test. The suggestion above of a swept sinusoid is a good one but why not just use the guitar you’re going to install the spendy audio caps in and go straight from the volume pot to the output jack? That’s going to allow you approximate & test/measure the sound of that guitar with each type of cap as you pass the no-tone-circuit output through an external tone circuit and that’s what you actually want to do, no?

8. Of course the problem is that none of us can hit a string precisely the same way two times in a row, much less many, so you’re going to need to record some test phrases with the guitar in #7 above. I’d do short clips 1 each (at least) for a couple of cleans, a couple of overdrives, and a couple of heavily distorted sounds as those tones are all going to have very different harmonics which will sound different when passed through your tone circuit. Be sure to do lead clips, rhythm clips, harmonics, etc.

9. Once you’ve recorded your base clips, play them back through your breadboarded tone circuit and record each result at the highest bitrate available (raw data only, no compression). Swap caps & repeat until you run out of caps.

10. At this point you should be able to chuck the data into a plotting package and graph the waveforms overlaying the results for each identical clip with different types of caps in the tone circuit to see differences in the waveforms (transients).

11. Run each of your results through an FFT and overlay the results for each source clip through the differing caps to see spectral differences.

12. If you have any questions, call Ian. [img]/images/graemlins/laugh.gif[/img]
13. Post results (& MP3s so we can hear the difference for ourselves). [img]/images/graemlins/popcorn.gif[/img]

Someone's going to complain that a breadboarded circuit isn't up to audiophile snuff but for your purposes that's not really an issue (besides, soldering a small cap's leads is probably going to change the primary characteristic of the part and throw all of your careful measurements off thereby ruining the whole test). The game here is to zero out as many differences as possible and allow you to test what you really want to test: whether or not differnt types of capacitors having the same capacitance value produce diffeent tones when used in a guitar's tone circuit. Step #2 will be the most difficult part of this process. [img]/images/graemlins/grin.gif[/img]

[hippietim]

Re: let\'s discuss caps

so what you're saying is I have idea what I'm doing [img]/images/graemlins/laugh.gif[/img] [img]/images/graemlins/laugh.gif[/img] [img]/images/graemlins/laugh.gif[/img]

[YetAnotherOne]

Re: let\'s discuss caps

Naaa what I'm really saying is, "No matter how you attack this, doing it in such a way as to get valid results is going to be a seriously time-consuming pain-in-the-ass but I, too, would like to know about these 'magic tone caps' so it would be really great if you'd just go ahead and burn your time slogging through this then forward me the results. TIA!" I mean I really don't want to spend the extra $0.25 to buy a good cap if I don't have to. [img]/images/graemlins/laugh.gif[/img]

[BLOOD SPLATTER]

Re: let\'s discuss caps

I like caps,I use them at the beginning of sentences or when I'm MAD or when I'm doing my ALZ impression!!

[Twisteramps]

Re: let\'s discuss caps

The only reason I mentioned moving the volume control was so you could (with washers) temporarily mount the switch where the volume hole is. And yeah, you'd just be wiring up a SPDT switch. I don't see how the cap is going to make a huge difference in your guitar tone though unless you roll the tone down, or if it's hooked to a volume control to keep from losing highs as you turn down, turning down the volume.

Then again, us guitarists are kinda nuts about little tone tweaks [img]/images/graemlins/smile.gif[/img] I think you ought to try experimenting with different value volume pots too... that might change your tone more than anything. Probably have a 500k in that guitar, try a 1M and a 250k for grins. [img]/images/graemlins/smile.gif[/img]

Pete