Measuring AC Voltages from the Guitar Signal
Once your DC voltages are in order, if your kit is still not working properly, you can measure AC
voltages along the signal path to troubleshoot further.
You will need a volt meter that can measure the small signal AC voltages that electric guitars put
out. The output signal from your guitar will likely be less than 1 V.
First, measure the output signal directly from your guitar. You can do this by plugging your guitar
cable into the guitar and leaving the other end of the cable disconnected. Connect your meter
across the disconnected ¼" plug's "tip" and "sleeve" sections. Make sure your guitar's volume and
tone controls are turned up and strum a chord. When you strum, you should see the AC voltage
reading on the meter quickly rise to some maximum value and then fall back to 0 VAC when you
stop strumming and the strings come to a rest.
Sleeve
Tip
Sleeve
Terminal
(Ground)
Tip
Terminal
(Output)
Tip
Spring
¼” (Mono) Plug
¼” Jack
Once you are able to measure the output signal from your guitar directly, plug the guitar into the
input jack of your kit and use the AC test points to measure the guitar signal along the signal path.
Start with test point one and move along in order. You should be looking to identify the last test point
where the signal seems normal and the first test point where the signal seems unusual or where it is
no longer even present.
The AC voltages on the layout drawing and schematic are numbered 1 through 11 and were
measured while strumming an open E chord on a strat switched to the neck pickup only position. All
test points (except test point 5) were measured with respect to ground.
AC signal voltage levels may
vary dramatically from one instrument to another depending on the electronics and how hard you
strum.
1
2
3
4
*5
6
7
Test Point
8
9
10
11
Measurement
0.16 VAC
0.17 VAC
0.10 VAC
0.62 VAC
23.0 VAC
0.48 VAC
0.01 VAC
0.70 VAC
0.07 VAC
0.13 VAC
0.13 VAC
The 10KL dwell pot was set to “12:00” = 5kΩ (wiper to ground).
The 500KL reverb pot was set to “9:00” = 60kΩ (wiper to ground).
*Test point 5 was measured from TR2's blue wire to red wire.