Need help measuring the output of my bass.

[Bill Mountain]

OK fine people.  I need some help with something that should be easy but I seem to be missing something.

I play a very awesome G&L bass that wife bought me as a surprise when our son was born because she saw how much trouble it was keeping my other basses (which were well worn vintage basses) in good working order.  I decided at that moment that this would be my forever bass.  The bass is an SB-1 which is Leo Fender's last attempt to perfect the P-Bass and it really is a killer instrument.  If you don't know, Leo created a whole line of super high output passive pickups for these bass guitars.  It was never a problem when I played clean in my blues/stoner rock band but now that I'm in a metal band, I'm down tuning and playing with distortion 99% of the time and this has been causing some issues with effects.

My bass basically turns any dirt box into a fuzz pedal because it pushes the front end so hard!  I have been tweaking effects to lower the gain but this basically makes it useless for other basses (I have a cheap practice bass I keep as a backup).  Up until recently I have been just assuming that my bass's output was double or triple what I'm used to but I realized that I need to get some solid measurements that I can use when building circuits that can handle this bass.

Now here's the part where I'm having trouble.  I have tried to measure the output voltage with my multimeter and it doesn't seem very high (somewhere 100mV).  I assumed it would be closer to 300mV because I can clip some diodes and buffers without any gain!  I tested it by just plugging my bass into a jack mounted on a breadboard and then measured the AC coming out while I played.  Is there a more accurate way to do it using a multimeter?  Are volts even a relevant measurement?  Should I be looking at something else as the culprit?  I do pay a lot of attention to high pass filtering because I know this bass pushes some serious low end (especially when using flats) but I try not to get too extreme because it starts to effect the tone if HPF's are too aggressive.

I have considered buying different pickups but at this point that would just be admitting defeat (but it is an option).

Thoughts???!!!!

[teemuk]

The output from a stringed instrument like guitar or bass has an envelope with very, very large transient in the beginning then a very drastic attenuation followed by more gradual attenuation as the string vibration decays. Secondly, the output is not sine wave but a composition of several harmonics that keep shifting in amplitude, resulting into more like a triangular wave with rounded edge, a wave that also continuously changes its shape in accordance to magnitude of string's vibration. So, even your picking technique will have a great impact on what the pickup is outputting.

All this will fool a basic voltmeter that is configured to measure RMS value of a sinusoidal wave like there's no tomorrow. You really need to get something that measures peak values (which alone is a huge compromise), perhaps try rectifying and filtering the output signal to measure some sort of average value in DC setting (which again is a compromise), or better yet, get an oscilloscope.

If you have a signal generator with known output and a good soundcard you can record signal from the signal generator, see what corresponds to, say, 1V signal (or something) and then record the bass direct and use the same scale to determine the bass' output amplitude. This will likely provide the most accurate presentation of the varying signal levels the pickup generates. I wouldn't be surprised if the transient peaks swing to 5 volts or so, then notes quickly decay to 700 - 500 mV, followed by somewhat more gradual decay to lower signal magnitudes. A multimeter will likely just show all this as a 100mV RMS signal because it simply can't keep up with what you're feeding into it.

[Bill Mountain]

Teemuk I love your book!  I just wish it didn't go over my head!

Anyways, these are great answers.  I thought about looking for some sort of oscilloscope software but then I was worried about signal degradation in my laptop's sound card.

I do like the idea of comparing signals.  I think I need to man up and get/build a signal generator.  Or see if some free DAW's have them built in.

My only idea to level the playing field would be to attenuate at the beginning and then put in a boost knob.  Maybe even an input peak LED like on some amps.  This would help in gain staging but would increase noise.

But would attenuating and boosting solve the problem?  Are there other interactions between my bass and the effect outside of output volume that I should consider?  I'm not looking for any strange effect related to input impedance but can attenuation and then slight boosting (if necessary) replicate the "girth" of my bass?  Will it add "girth" to weaker output basses?

I know these are big (and maybe unanswerable) questions but it's what goes on in my head and I figure someone else has pondered this stuff as well.

[Bill Mountain]

Ok.  I just figured out what I need to do.

I need to establish a max input voltage for the circuit to function as desired and then design around that.

Then I put a simple booster/attenuator at the beginning of the circuit with an LED to ground after it and mount the LED on the outside of the enclosure.  Then, if the "indicator" clips/flashes then I know my signal is too hot.  I could always attenuate a little after the LED if its forward voltage is higher than I want (because most LED's would allow up to around 2.4V).

Adversely, if I wanted to I could purposely clip the "indicator" for some extra distortion.

What would be a good max input voltage?

[Bill Mountain]

Ok.  I just figured out what I need to do.

I need to establish a max input voltage for the circuit to function as desired and then design around that.

Then I put a simple booster/attenuator at the beginning of the circuit with an LED to ground after it and mount the LED on the outside of the enclosure.  Then, if the "indicator" clips/flashes then I know my signal is too hot.  I could always attenuate a little after the LED if its forward voltage is higher than I want (because most LED's would allow up to around 2.4V).

Adversely, if I wanted to I could purposely clip the "indicator" for some extra distortion.

What would be a good max input voltage?

Or I could split my signal and send one side to the booster/attenuator and rectify the other side to go the an LED incicator.  Then I could filter each side independently to get the desired results.

Hmm.  Looks like I'll be breadboarding tonight!

[artifus]

most of the threads i've read concerning bass fx mention split and blend, preserving the low end on the clean split and distorting/effecting the upper portion of the signal. good luck on your endeavour, be sure to post your results.

[Bill Mountain]

most of the threads i've read concerning bass fx mention split and blend, preserving the low end on the clean split and distorting/effecting the upper portion of the signal. good luck on your endeavour, be sure to post your results.

That is a valued technique but I'm trying to move away from the "add a blender to make it a bass pedal" mindset.  It doesn't always sound good and feels like a compromise most of the time.

[Bill Mountain]

Ok.  I just figured out what I need to do.

I need to establish a max input voltage for the circuit to function as desired and then design around that.

Then I put a simple booster/attenuator at the beginning of the circuit with an LED to ground after it and mount the LED on the outside of the enclosure.  Then, if the "indicator" clips/flashes then I know my signal is too hot.  I could always attenuate a little after the LED if its forward voltage is higher than I want (because most LED's would allow up to around 2.4V).

Adversely, if I wanted to I could purposely clip the "indicator" for some extra distortion.

What would be a good max input voltage?

Or I could split my signal and send one side to the booster/attenuator and rectify the other side to go the an LED incicator.  Then I could filter each side independently to get the desired results.

Hmm.  Looks like I'll be breadboarding tonight!

Edit.  I just realized I need to split my signal after the booster/attenuator for this to work.  Would I need to isolate the audio signal from the rectifier for the indicator or would it be fine if I just tapped it before the rectifier?

[artifus]

hearing is a compromise, meaning human perception... as subjective as that may be there's only so much you can do below 100hz or so that will be noticed as an effect. i can't help you with measuring your bass output but physics and human perception are pretty fixed at this point in our evolution.

*i wish that made more sense. night all*

[Bill Mountain]

hearing is a compromise, meaning human perception... as subjective as that may be there's only so much you can do below 100hz or so that will be noticed as an effect. i can't help you with measuring your bass output but physics and human perception are pretty fixed at this point in our evolution.

Agreed.

[Bill Mountain]

Rectifying may be too much trouble.  I could split and boost seperatley then have a stereo gain pot the adjusts the volume to the indicator and the circuit.

I'm thinking this might be the way to go because I'm not quite sure how to rectify an audio signal without special chips.  I have a 555 but I was hoping to avoid this idea getting too complicated but that may actually be the way to go.

[artifus]

whoa! over thinking things a little aren't we? i may have completely misunderstood this thread but i thought you were simply trying to attenuate the output of your bass? assuming the volume pot is not doing it for you for whatever reason could you just not put a volume pot/voltage divider/resistor or two ahead of your input? or have i missed the point entirely?

[Bill Mountain]

whoa! over thinking things a little aren't we? i may have completely misunderstood this thread but i thought you were simply trying to attenuate the output of your bass? assuming the volume pot is not doing it for you for whatever reason could you just not put a volume pot/voltage divider/resistor or two ahead of your input? or have i missed the point entirely?

The volume control on my bass changes the tone too much so I prefer to run it full bore.

This thread has evolved.  It went from thinking about the best way to attenuate to being able to get a visible representation of how hot my signal is.

I'm spit balling here and throwing out everything that comes to me to see what sticks.  Sometimes I do that in my head and sometimes I do it on the web.

[Gus]

What might help is a buffer with maybe a 470k to 1meg input resistance after the bass.
An JFET input opamp buffer, 470k, 1 meg input with a fixed voltage divider or volume control at the output.
This will give you the passive bass controls, cable, input resistance interaction, so you don't have the tone change with the turned down volume on the bass.  The volume control after then reduces the output of the bass.
You need to make sure you don't clip the buffer.