ADAU 1701 Miniz - No audio output?

Hello,

The problem here might be impedance matching. The ADAU1701's ADC inputs are designed to take in a low-impedance signal source such as an MP3 player's output, or the headphone/speaker output of a computer. A guitar, on the other hand, is a high-impedance signal source with a fairly low signal level. In order to properly condition the signal, you would need a DI box or a preamp, or something along those lines.

A good first step for debugging might be to forget about the guitar for the time being and simply try to use a normal signal source (like your phone's headphone output, an MP3 player, or the audio output from your computer), and then follow the tutorial again.

Thank you Brett!

That was the problem. I didn't think about impedance matching. I used an ipod and designed the equalizer schematic. It worked just fine.

So I could use a DI unit like this -( http://www.musiciansfriend.com/pro-audio/live-wire-spdi-passive-direct-box-with-attenuation-pad ) and connect a 1/4'' cable from guitar to the DI unit, and a 1/4'' to 1/8'' cable from the DI output into the DSP board?

Yes, that should do the trick. But note that this box doesn't have a 1/4" cable output. It's a balanced XLR output. I'm pretty sure there is no impedance change between the 1/4" input and 1/4" output - it's just a direct connection.

Something like this might be a better solution for you, since it has a single-ended 1/4" output. http://www.motu.com/products/guitar/zbox

Actually, the Z-box page doesn't have any details about the output impedance. This might not really solve the problem. It's possible that you might have to build your own preamp.

It turns out that your easiest option might be to use one of your existing guitar pedals set to bypass mode, and make sure the bypass is not true bypass. You want a buffered output to convert to low impedance.

One last note... I've heard that almost all BOSS pedals have buffered outputs. That should do the trick. Put a BOSS pedal (or other pedal with buffered output) between your guitar and the evaluation board. You can just put the pedal in bypass mode, and it will effectively act like an impedance converter.

Thanks again Brett.

With that DI unit, I could just use an XLR to 1/8'' cable from the DI into the DSP, right?

I actually don't have any pedals. I like to keep it simple and just my amp. But I have been meaning to get a Boss tuner pedal. So I could just use the Bypass output on a TU 2 and then I'm good to go?

Thanks for the help, and I'll let you know how it turns out and if I need any more help

Yes, you could use an XLR to 1/8" cable, but the caveat is that the signal coming from the XLR output is differential, whereas the ADAU1701 ADCs are single-ended. So, you can have the non-inverting signal go into one ADC, and have the inverting signal go into the other ADC, and you can subtract them inside the SigmaDSP to create a mono single-ended signal.

I know this is an old thread, but I have a suggestion. You could try using a JFET-input op amp... I would recommend a specific one, but it's not from Analog Devices! Set it up in a non-inverting buffer configuration with the input signal from the guitar going through an AC-coupling capacitor to the non-inverting input. You'll want a pull-down to ground on the non-inverting input of the op-amp to set the impedance - 1 Megaohm should be good. That will give you a nice impedance converter and you can feed the output of the op amp directly to the voltage-to-current conversion resistor on the ADAU1701's ADC input.

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Thank you,
EZ Admin