Noisy output
Posted: Wed Oct 29, 2008 7:34 am
Hi,
I built a homemade version of the circuit from the data sheet and the tonepad website. I used surface mount the resistors and decoupling caps. Caps in the audio path are WIMA through-hole types, as are the JFETs, crystal, and 3.3V linear regulator (500mA version). The power input is 9VDC.
The basic function of moving the ADC input to DAC output seems to work beautifully.On internal program 5-"Test", a guitar or tone generator produces a nice crisp output. The Tremolo (internal program 2) sounds fantastic (nice rounded beats).
The problems start when I turn up the Reverb mix in any of the internal programs. The signal comes through more distorted than reverb-y and the output starts sounding like popcorn. As I turn it up more, the the clip LED eventually turns on (without turning up the input volume). I back down the input signal, but that doesn't cause any changes (other than a lower signal, which eventually turns off the clip LED, but keeps the popcorn).
On a high speed oscilloscope (100MHz), with the Reverb Mix turned down, the output matches the input. As I turn up the Reverb Mix and start hearing the popcorn effect, I see transients and glitches that coincide with the popcorn.
Aside from the surface mount parts, my circuit board design differs from the tonepad design in that I added a ground fill under the FV-1. I also noticed that the tonepad layout forgot the 100 ohm resistor between 3.3V and REFP. Is there anything else I'm missing?
I have a DIP socket for an external I2C EEPROM, but haven't tried an external program yet.
Thanks for any help,
...Gary
I built a homemade version of the circuit from the data sheet and the tonepad website. I used surface mount the resistors and decoupling caps. Caps in the audio path are WIMA through-hole types, as are the JFETs, crystal, and 3.3V linear regulator (500mA version). The power input is 9VDC.
The basic function of moving the ADC input to DAC output seems to work beautifully.On internal program 5-"Test", a guitar or tone generator produces a nice crisp output. The Tremolo (internal program 2) sounds fantastic (nice rounded beats).
The problems start when I turn up the Reverb mix in any of the internal programs. The signal comes through more distorted than reverb-y and the output starts sounding like popcorn. As I turn it up more, the the clip LED eventually turns on (without turning up the input volume). I back down the input signal, but that doesn't cause any changes (other than a lower signal, which eventually turns off the clip LED, but keeps the popcorn).
On a high speed oscilloscope (100MHz), with the Reverb Mix turned down, the output matches the input. As I turn up the Reverb Mix and start hearing the popcorn effect, I see transients and glitches that coincide with the popcorn.
Aside from the surface mount parts, my circuit board design differs from the tonepad design in that I added a ground fill under the FV-1. I also noticed that the tonepad layout forgot the 100 ohm resistor between 3.3V and REFP. Is there anything else I'm missing?
I have a DIP socket for an external I2C EEPROM, but haven't tried an external program yet.
Thanks for any help,
...Gary