Bass preamp (similar to Fender ToneStack pre) - no output

[simon.blanchaert]

Hi all,

i've tried to build this bass preamp explained by Rob Mods ( in the pedal version.

Here's the schematic (also attached): https://16523fc6-ac2c-4fa9-ac46-96b5c75 ... fa8b99.pdf

However, after soldering everything, i don't get an output when I engage the pedal. However, the LED is lighting up (so stomp switch seems to work properly), but don't hear anything (no noise hum, nothing).

When I bypass the pedal, my signal moves through the pedal, so no issues with that.

Does anyone have tips & tricks on how I could start debugging? I have a multimeter and can perform signal testing, but i'm not technical enough to know where to start.

Thanks in advance for someone's help!

Kind regards,

Simon

[stolen]

Hello Simon,

there are a few simple tests you can perform (although we're not quite sure what you mean by signal testing - audio probe? scope? soundcard?). We'll assume you're a beginner; please let us know if we're wrong in that.

The first thing would be to simply check if input and output jack are swapped. We know, it sounds trivial, but we've seen it happen with early builds quite a few times. Just plug your bass and amp into it "inverted" and see if that changes things.

The next thing to check for would be bias voltages. The VREF Node and all OPA pins except for the power supply (pins 4 & should be at around 4.2V - if it's a little bit off, that's perfectly fine, but anything below 2V or above 6.5V would be very worrying. If the OPA is socketed and the test fails, you can repeat it without the OPA plugged in.

If the bias voltages are fine, and you do have a way to scope the signal (such as an audio probe, or just connecting the positive end of C8 to various points in the circuit), we'd recommend you check all inputs and outputs of the amplifying stages to see where signal disappears. That would be Pin 3, 1, 5, 7, in the order of signal flow. However if you don't have equipment to perform this test it's fine too - it will just make it a bit more tedious to find the error source. In that case it would be very helpful to have well-lit high resolution pictures of your board and also the wiring.

Hope this helps,
stolen

[deltafred]

Welcome to FSB.

It is good that you supplied a link to the PDF, not everyone who is asking for help provides a schematic and the layout that they used.

A photo of both sides of your board would be helpful.

I started typing this before stolen posted so I'm going to post it. (I'm not fast at typing.)

1. I would start by checking that you have all the correct cuts and links installed and that there are no solder bridges and that all the joints look good and that you have the correct component values in their respective places, including that you have the IC in the correct way round.

2. With either a battery installed or a power supply plugged into the socket and a jack plugged into the input socket check that you have 9v between the 9v and 0v tracks on the Vero.

If there is nothing there check that there is 9v between the 9v Vero strip and the battery 0v. This checks that the 9v is getting through the power socket. (It is very easy to get the connections wrong, don't ask how I know.)

If that is ok check that there the 0v is getting through the input jack by putting your meter across the battery +ve and the vero 0v strip.

3. If there is 9v reaching the Vero then check that it is on pins 4 (0v) and 8 (+9) of the opamp.

4. Check that there is about half your supply voltage (4.5V) between pins 3 and 4, and 5 and 4 (pin 4 is 0v) on the opamp.

If all those check out then it is starting to look like a faulty component (but as always without the board on my bench it is only a guess).

[Topaz]

Same, not working here either.

Hi all,

i've tried to build this bass preamp explained by Rob Mods ( in the pedal version.

Here's the schematic (also attached): https://16523fc6-ac2c-4fa9-ac46-96b5c75 ... fa8b99.pdf

However, after soldering everything, i don't get an output when I engage the pedal. However, the LED is lighting up (so stomp switch seems to work properly), but don't hear anything (no noise hum, nothing).

When I bypass the pedal, my signal moves through the pedal, so no issues with that.

Does anyone have tips & tricks on how I could start debugging? I have a multimeter and can perform signal testing, but i'm not technical enough to know where to start.

Thanks in advance for someone's help!

Kind regards,

Simon

[Jarno]

Weird way to do noiseless biasing, and that 600k seems a typo to me, shouldn't cause it to not function though.