Drums Volume is almost non-existent

Hello friends,

I’ve just taken my Anushri out of storage. I assembled it long ago and everything was perfect then, but in testing it now, the drums volume is extremely low on its own. I’ve tested this both out of the main out and the drums out and the volume is very low in both cases.
Any ideas on where I should be looking to discover the issue? I do have a multimeter I can use to test too.

Thanks for your assistance!

Do you have a large signal on either sides of C2? at the junction of R5 and C4?

A multimeter is not the right tool - an oscilloscope, or connecting the signal to an amp, is a better way of checking the audio path.

I also have an oscilloscope available, but I do not think I have a way of connecting directly to an amp. I will find my osc test leads and see what kind of reading I get.

Here’s the reading I got. I have to admit, I’m not savvy when it comes to using this Osc. I mainly use it to watch cool waveforms from the modular system :slight_smile:

The channel is set to 1v divisions, so is this considered a strong signal?

Ugh, sorry, I was testing C4. Let me go test the correct points.

Okay, I’m seeing 24v at both sides of C2 and the junction of R5 and C4

Grounded, I get nada… no signal

Looks like the ground of your scope is not connected to anything :slight_smile:

I’m a total amateur. Totally forgot to attach my probe clip to ground.

I’ve got the ground clip of my probe connected to a post I have soldered into the open GROUND contact points near the voltage regulators. When the clip is attached and I test those points, I’ve got no signal. Remove the clip and I get those 24v readings. My oscilloscope is plugged into a grounded outlet.

Am I failing miserably at this, or is there a malfunction somewhere that is not my brain :slight_smile:

It’s normal to get weird readings when the oscilloscope ground clip is not attached to anything.

But it’s not normal that you get no signal from the point I’ve mentioned - while you can still hear faint drums.

Okay, so I checked again and the signal was so low, that I didn’t notice it. I cranked up the volts division and I can see signal now. So it is there, but its’ very very low at all 3 test points.

What about the signal at pin 5 of the ATMega?

Same signal strength as the other points, very low, Just about 0.8V p-p

Bad ATMega?

What is the shape of the signal you observe on the pin 5 of the ATMega?

Looks like an audio waveform in sync with the drums beats


Based on this image from the DIY Resources page, point 16 in the image, which is what I understand as pin 5, is where that wavefrom I recorded is from with the sequencer running.

That’s the right pin, but it’s not normal that you don’t see a PWM square signal - unless your oscilloscope has a very shitty bandwidth.

I don’t think it’s a defective MCU - there might be another build issue, but I don’t really know which one.

It’s a 20mhz oscilloscope, so I expect I would see a 39khz pulse. I don’t see anything on pin 5 unless I have the sequencer running

Okay, I see a pulse, but I have to crank the sensitivity so high (10mv) to see it.

Sounds like that pin is connected to ground with a very low resistance (almost shorted). You could try to measure the resistance from this pin to ground. If there is a short, you can open up the board file in eagle, highligh the corresponding track with the “view” tool and see to which solder joints it goes. Then you have a rough idea where you could find the soldering error.