Noisy output

Hardware questions and issues with the FV-1

Moderator: frank

Post Reply
gvidelock
Posts: 5
Joined: Wed Oct 29, 2008 7:10 am
Location: near Boston, MA

Noisy output

Post by gvidelock »

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
frank
Posts: 1244
Joined: Wed Oct 19, 2005 12:26 pm
Contact:

Post by frank »

Hi Gary,

Interesting issue, have not seen it before. Program 2 also has some reverb in it, does it sound clean? How about program 3, the pitch shift program? Also program 4, the pitch-echo, does it sound ok?
Frank Thomson
Experimental Noize
gvidelock
Posts: 5
Joined: Wed Oct 29, 2008 7:10 am
Location: near Boston, MA

Post by gvidelock »

Hi Frank,

All of the programs, except for Tremolo and Test, have the same problem.

A friend of mine just built the 2nd of the 2 PCB's I made and his is working flawlessly, so I'm pretty sure it's my physical build skills (or lack thereof). We used the same components (split an order from Mouser). I need to go through my build tonight with a finer tooth comb.

The only difference between the boards is that he was running his from a 9V battery and I was running mine from a Hotspot AC adapter. I'm going to try the battery tonight also.

...Gary
gvidelock
Posts: 5
Joined: Wed Oct 29, 2008 7:10 am
Location: near Boston, MA

Post by gvidelock »

Well, the 9V battery idea didn't work. And my finer tooth comb did not turn up any opens or shorts.

What I've observed is that on programs 1 and 2, if I turn the mix of the effect (Flanger or Chorus) to off and the Reverb mix to off also, the original signal comes through to the output clean as a bell. I think that tells us that the ADC and DAC are working.

I'm just wondering out loud now...the Tremolo works, sounds nice and clean...does that use the RAM / registers where the coefficients for the other algorithms are stored? Could I have damaged (by heat or electrostatic discharge during handling or installation) some part of the chip that is not used by the Tremolo code?

I hate to blindly order another one chip without some clue, but since the other PCB works with all the same passive components I'm thinking I might just have to.
frank
Posts: 1244
Joined: Wed Oct 19, 2005 12:26 pm
Contact:

Post by frank »

Hmm, it is sounding like the internal ram was damaged. There is protection on the pins internally but the chip is done in 0.35u so it is a small geometry.

The best test to isolate the ram would be a pure delay, if possible program up the EEPROM with a simple delay and see if you hear clicks/pops.
Frank Thomson
Experimental Noize
gvidelock
Posts: 5
Joined: Wed Oct 29, 2008 7:10 am
Location: near Boston, MA

Post by gvidelock »

I loaded the external EEPROM with the OEM suite from the web site. I'm not sure how the echo program compares to a simple delay, but I hear the clicks and pops on all of the programs. I was planning on learning how to code the DSP when it was all working and I could hear the implementation (i.e., I'm not ready to whip up a simple delay because I wouldn't really know if I did it correctly).

Anyway, I ordered a new chip from Small Bear. It should be here next week.

At least the good news is that all of the other circuitry, including the programming of the I2C EEPROM, is working.

Thanks for the advice. I'll post back here after I replace the chip.

...Gary
gvidelock
Posts: 5
Joined: Wed Oct 29, 2008 7:10 am
Location: near Boston, MA

Post by gvidelock »

The chip was the problem. The replacement came today and after some fidgety soldering it's down and working.

The sound is crystal clear. The reverbs, chorus, flanges and delays sound great. External EEPROM is working. Now for some programming fun.

...Gary
Post Reply