Pedal problems

[will_raymo2000]

Hi all,

http://hammer.ampage.org/files/Chaos.gif

^^ The above is what I have created on a perfboard. I have even rebuilt it with new components and tried various op amps. All I get at the output (when applying a 1kHz test tone to the input) is a majorly attenuated 1kHz signal with no distortion at all.

The caps I have used are ceramic apart from the three electros which are rated at 50V.

I am powering the op amp with a 9V battery (tried several) and have tried a 9Vdc wall wart also.

Any suggestions?!

Thanks!

[kender]

Hi WIll

in the schematic I don't see the Vref generator, what are you using to make the Vref?

[ACS]

Assuming that vref is the obligatory 9V...

Have a read of the debugging thread - some voltage readings will help out...

[anchovie]

Assuming that vref is the obligatory 9V...

Halt!

Vref is half of the supply voltage, created using two resistors as a voltage divider.

[will_raymo2000]

Assuming that vref is the obligatory 9V...

Halt!

Vref is half of the supply voltage, created using two resistors as a voltage divider.

Forgot to mention that! I have 2 10K resistors set in a potential divider producing 4.25V from a 8.6V Battery.

My testing setup - Computer running 1kHz test tone generator outputting to a Stereo -> 2 mono 1/4" jack.. input into the effects and then I have some oscilloscope software on the computer also to analyse output signal. Also a multimeter to take other readings.

As said earlier supply voltage is 8.5-8.6V. the input voltage (from the PC) is 0.38V. The output is 6.6mV!! the output from the first clipping stage (ie output from the first op amp) is 0.37V as is the other op amp output.

where else would you like me to take readings from?

[anchovie]

All of the IC pins.

[will_raymo2000]

All of the IC pins.

with reference to ground? Will report back in a few minutes

[kender]

normally big problems have "dumb" origins ( i know, been there many times )
have you checked and double checked the opamp pinout?
how is the opamp supply ?
any way, it seems you have a problem and I would suggest triple check the output part of the assembly, after the second clipping stage. ( connections and component values )

[petemoore]

  Degubbing page reads...ughhh...totally worthwhile for this debugging stuff.
  ...Always test for no-short conditions between power rails before applying power.
 Measure the battery voltage with the circuit loading it.
 Connect the battery to the circuit, meausre the battery voltage, if these measurements are about the same fine, if the battery voltage drops a big V drop, you have massive current and hence a debug to find [or a suitable power supply is recommended].
 The potential between the power rails is to what the other voltages compare '%age-voltage-wise', without the loaded battery voltage the other readings are less useful.
 Clip the black DMM lead to ground, use the red DMM probe to touch pin 1 of the first active component, take note of voltage, repeat for all the active pins.
 
 

[will_raymo2000]

Pinouts from the IC the left hand op amp on the schematic -> 0.362V on all pins
Right hand op amp -> 0.332V on all pins

Supply voltage -> 8.33V (the voltage has dropped by 0.3 in the last 20mins  )

EDIT: Measured current draw from battery = 1.3mA

[anchovie]

Obvious problem right there. You should have supply voltage on pin 8 of the opamps and 0V on pin 4.

[will_raymo2000]

I dont think you understood my readings! What i meant was that all the readings on the op amp (ie + & - input and output all read the same value) I have got the supply set up correctly. Pin 8 is 8.33V and pin 4 is 0V.

Thanks

[anchovie]

Ah OK, I was going by you saying "all pins"!

The pins that are connected through  resistors to Vref on the schematic should be measuring half the supply voltage.

[jacobyjd]

it would be best if you followed the actual format for debugging.

[will_raymo2000]

Hope this helps,

Any other readings can be taken if needed.
One thing I have noticed when analysing it is that the gain pot (1M Linear) has absolutely no affect on the output voltage, also has no affect on the frequencies outputted, I have some FFT analysis software on the PC. The tone control does change the harmonics and the intensity of the frequencies however the gain pot does nothing at all!


Cheers

[anchovie]

Are the majority of those readings AC using your scope? DC readings of every single op-amp pin would be most helpful, signal amplitude alone doesn't give a clear idea of what's happening.

[will_raymo2000]

Sorry yep, Meant to put on that image all readings were AC apart from the ones marked. Will read some DC values in a sec

[frokost]

You really should follow the procedure described here. It makes everything easier for everybody.

[will_raymo2000]

You really should follow the procedure described here. It makes everything easier for everybody.

I pretty much have followed that checklist, and apart from posting it in list form I posted the voltages on the schematic.

With regards to DC voltages:-

Op amp 1; + input = 4.04V
- input = 4.23V
Ouput = 4.22

Op amp 2; + input = 4.18V
- input = 4.22V
output = 4.21V

[frokost]

Ah, well, but you see, it's useful for the people trying to help you to know what is right  . That way, we can focus on what we know is wrong instead of what we don't know is right.