Bass guitar output level

[Nevillet]

Hi all,

I am repairing a bass guitar amp and need a test signal to drive it.

Can anyone tell me what that would be in mV or μV?

Many thanks.

[redwire]

Re: Bass guitar output level

I use a line-level music source such as a CD player, with attenuator to feed guitar amps when testing.
About 50mV RMS tried with 1MEG output impedance to confirm the front-end is working. They (input stage op-amp) frequently get zapped by ESD.
The freq. response is of course way off but you can hear distortion, tone control action, a buzzing rattling speaker etc.

[Nevillet]

Re: Bass guitar output level

Many thanks for that.
Would a simple resistor type network work as an attenuator in this case?

I remember that the maunfacturer Rane used to have some very usefull schematics for this kind of thing but I can't see them anymore..
https://www.ranecommercial.com/legacy/library.html

[redwire]

Re: Bass guitar output level

It's just a simple voltage divider with two resistors. You can also mix the CD player's output to mono with a third resistor. For one channel I'll use a 20k+1k to GND to drop 1VRMS down to guitar levels say 50mV. But this forms a low impedance, unlike a guitar. So it will not flush out problems at the input jack such as a leaky or damaged part that loads down the guitar, giving a complaint of low volume.

For that, a 20MEG+1MEG to GND can work, and the high impedance makes cable capacitance shunt HF response and things a bit noisier, so it will not sound as good. I'll do the test once to just confirm the guitar amp's input impedance is high. Or use a guitar that has no electronics- no pre-amp or pedals as these have low-Z output.

You can use sine-waves from a sig gen too but music reveals problems sooner.