Pickup output

galmar · Post by **galmar** » 17 Mar 2013, 21:13

Hello people,

I wonder if there is anyone that has ever used an oscilloscope to measure the exact output of sinlge coil pickups in a stratocaster. I am planning on doing this when I grab one, but so far I had no chance.

I am interested in the peak value of the waveform. And I mean peak - coming out of a heavily abused string, low or high, to be really sure about the real margins of the voltages we get.

Thanks in advance!

teleK · Post by **teleK** » 18 Mar 2013, 00:42

about 600mv peak, take 100-200 as an average, and then somewhere around 10mv is a relatively quiet signal. but you do have to keep in mind, the peak is only at a very short time at the beginning of the note

deltafred · Post by **deltafred** » 18 Mar 2013, 09:29

galmar wrote: I wonder if there is anyone that has ever used an oscilloscope to measure the exact output of sinlge coil pickups in a stratocaster.

Just about everybody that owns a scope and a guitar has probably looked at the output of a pickup.

"Measure the exact output" is probably not the quite right phrase to use as there are so many variables, string height, pickup turns, magnet strength, how hard you pick the string, how accurate you scope is calibrated.

galmar · Post by **galmar** » 18 Mar 2013, 10:31

Well, of course, saying "exact", I mean anything more accurate than just measuring an rms value with a voltmeter.

Of course all these parameters you mention are important, but I was just seeking for a good average approximation. Sorry if I did not make that clear.

I assume you mean 600mV amplitude, but not peak to peak.

phatt · Post by **phatt** » 18 Mar 2013, 14:12

What are you hoping to achieve that has not already been noted by folk with the qualification to understand what they are observing?

It is all very much load dependent,, meaning the Z of the input has a massive effect on the result as noted here;
http://www.ozvalveamps.org/pickups.htm

Be aware that a very high Z input will probably give bigger swing but can make the reso point a little harder to control.
Phil.

galmar · Post by **galmar** » 18 Mar 2013, 22:24

phatt wrote:What are you hoping to achieve that has not already been noted by folk with the qualification to understand what they are observing?

Well, just trying to calculate some gain stages to ensure I have no nasty clipping.

Thanks for the answer, by the way.

teleK · Post by **teleK** » 19 Mar 2013, 14:16

Ah. Well that's a slightly different question.
And you're going to need to define "nasty" clipping. Does that mean you don't like clipping in general, or you just want to avoid super harsh stuff?
Designing the circuit so it clips at around 2V will probably work for you, although nothing is stopping you from 4V, or more if you have a higher power supply.

MoonWatcher · Post by **MoonWatcher** » 19 Mar 2013, 16:36

galmar wrote:I mean anything more accurate than just measuring an rms value with a voltmeter.

I don't know how valuable your time is, but I honestly would just check out the spec's for a few different DiMarzio pickups that seem to be designed like an original Strat pickup. Since there are so many variables, I'd just use those published spec's as a sort of "nominal best guess."

And then I'd tweak my gain stages based on that info. If it seemed like it was too low or too high, I'd adjust my gain stages appropriately.

Even armed with scope output, waveform output with computers, etc. - I still have had stuff that I didn't tweak properly because I was basing it around what amounted to a snapshot of something that was not a decent nominal representation. That's why I suggest not spending much time with a scope or other tools.

Depending on how we measure things, it's possible to overthink them, or come to the wrong conclusions or theories. Then when we go to implement our tweaks, the results will typically not pan out, because the initial measurements or idea behind how/why to measure were not very helpful.

And don't always rule out the quick/low tech methods. Lots of times they can provide the necessary info that your brain can proceed with.

galmar · Post by **galmar** » 19 Mar 2013, 19:27

teleK: Nasty clipping goes for any opamp clipping, not something I will try to create.

MoonWatcher: I have done this - still, as someone pointed out above, it is not enough since other valuable parameters come into play.
Sorry for the confusion, but all this is meant for a solid state amp I built, not a pedal. And I use quite a bit of gain, if we are to compare the cases. And since I heard something that my ears did not like when using a lot of volume capable of driving the amp, I posted that question. I will lower my gains as you folks mention, I will not depend on a scope. But just out of curiosity, I wanted to get some more info. No ruling out of low methods.

Because, look at the above posts - a member said something about 100mV-200mV. On the net, you find posts about 10mV. Go check a Fender schematic, giving a test voltage of 5mV. Seems like there are quite big differencies between random opinions. Not that this is weird, anyway, I just want to gather information so as to gain experience.

After all, I don't find it nice working on numerous circuits with an input that sometimes is not well-defined. (please note the word in bold

)

apollomusicservice · Post by **apollomusicservice** » 19 Mar 2013, 22:02

Here is simply circuit that can memorize for "long time" peak voltage.
Peak detector circuit can "remember" highest value of input signal and
each time charging C1 will go higher to new peak voltage. Of course
value can be reset by switch S1 to zero. It is suitable as add for DVM.

DrNomis · Post by **DrNomis** » 19 Mar 2013, 22:29

galmar wrote:Hello people,

I wonder if there is anyone that has ever used an oscilloscope to measure the exact output of sinlge coil pickups in a stratocaster. I am planning on doing this when I grab one, but so far I had no chance.

I am interested in the peak value of the waveform. And I mean peak - coming out of a heavily abused string, low or high, to be really sure about the real margins of the voltages we get.

Thanks in advance!

I've actually done it, when I had a look at the signal level coming out of my Mexican Strat (it has three Fender Vintage Noiseless pickups fitted), I had the Volts/Division knob set to 1, and I measured about a volt, note that this was when I plucked the strings hard, the level-reading you get will be determined by a few factors, how hard/soft you pluck the strings, pickup height adjustment, how strong the pickup magnets are, how many pickups you have selected, whether they're in-phase or out-of-phase, how old/new the strings are, where you fret the strings......

Humbucking pickups tend to produce a much higher signal output compared to Single-coil pickups

galmar · Post by **galmar** » 19 Mar 2013, 22:56

Well, thank you all for your replies! Apollo, quite an easy and clever circuit, thanks! I will give it a try. Seems like a nice implementation of a half-wave rectifier with no load.

(I think I would add a 1k resistor between pin 3 of the reset switch and ground, to discharge the cap slowly, and maybe try a slightly better opamp to avoid a voltage divider at the input.)
DrNomis, I find your post quite accurate.

galmar · Post by **galmar** » 20 Mar 2013, 23:13

apollomusicservice wrote:Here is simply circuit that can memorize for "long time" peak voltage.
Peak detector circuit can "remember" highest value of input signal and
each time charging C1 will go higher to new peak voltage. Of course
value can be reset by switch S1 to zero. It is suitable as add for DVM.

Well, I built that circuit, using a germanium diode. It went "well" for a 800 Hz sine wave, stayed at 560mV for some time (but then it dropped to 350mV, without new alteration!) - but when I plugged the guitar, the voltage at the 1u cap wasn't stable!
It read 160mV, then very quickly 35mV, then 20mV and finally went to zero. All these within less than a second.

Any opinions?

apollomusicservice · Post by **apollomusicservice** » 21 Mar 2013, 09:38

For a better measurement results of the guitar level add a buffer between the guitar and first IC, or put some Boss pedal that already
contains an buffer and set the position through. In order to extend the time for readings may increase the value of capacitors to 5u (but it
would be nice to add parallel per 1u and find the optimal value because it increases and charging time for C).
Of course this simply circuit has limitation in frequency performance especially for low signal levels but it can be upgraded for full wave rectification.

MoonWatcher · Post by **MoonWatcher** » 21 Mar 2013, 18:13

I still think this can be kept simple and methodical.

If your pickup is "standard Strat construction" - uses alnico 5 magnets, standard Fender stagger, standard Fender bobbin, standard Fender wire and wind, you can probably grab spec's of similar pickups and come up with a max value for the lot of them.

Let's say the value is 270 mV. If you want no clipping at your first gain stage, design it so that it can take 350mV at its input and reproduce it at its output. If you want some clipping, try dropping it right down to this max value.

The first gain stage will be the most crucial, and the max output pickup is your "worse case scenario."

You should probably replace what you can at the first stage with trimpots, too. If it's higher than unity gain, build a prototype of just this singular stage as if it were a booster or something. After all, if the clipping in isolation sounds bad, adding a 2nd or 3rd stage after it will not un-do what was wrong from the beginning.

If you know your max amplitude gain at the first gain stage, you have your upper limit as a starting point for the second gain stage. The only tricky thing at this point is you may obviously want some stages to be more for altering EQ or something, so determining how much more or less amplitude each one should have might get a little tough. But again, trimmers should help.

Another low tech thing you could try is either a pre-gain trimmer or pot. Set it at max, audition the pedal. If there's nasty clipping, attenuate the signal with the pre-gain control. See if you can find a spot where the the clipping is no longer so bad. It should give you an idea of how much/how little you will have to alter the first gain stage.

Last low tech thing to consider? If you have a lot of bass in any given gain stage, you'll probably want to be more modest with its max gain factor. And you might want to design the stages so that the bass isn't emphasized until a later stage. Just because you cut the bass some early in the signal path doesn't mean that you can't amplify it down the line.

Again, these are just things to help make the tweaking process a little more intuitive and flowing as opposed to trying to do some "static level tests" noting the numbers, and adjusting based on them. You could go nuts with that, with a lot of back-and-forth. I wouldn't rule it out - just try to think of the options is all.

I learned some of this by working on computers. The shop would have lots of diagnostic tools, and I could do nothing but run diagnostics for hours. For something like a machine that was running hot, I stopped using the diagnostics for the first test. I'd simply open the computer up. Oftentimes, the issue was dust in the machine or something with a heatsink. Fan bearings could go bad w/o being noisy, or w/o the fan stopping altogether. There could be a ribbon cable that was blocking the fan. Lots of things like that apply to electronics of all sorts. Precise measurements can sometimes be only that - a precise measurement, with no help to rectifying the issue.