Roland DD6 effects pedal

at

Boss

flow

Would you adam and eve it? I seem to have made a peak limited (grey?) white noise generator. I wanted to see if the DAC was still working as there is 5V on the supply and the datasheet recommends 3.6V and absolute maximum of 4.6V. I cut data-in line, pin 4, of AK4352VT, from the main Boss chip and connected , via 1K, to pin 9 , data out, of the ADC AV5353VT. Maximum allowed on the ADC is 6V supply and of course absolutely no technical data of any sort on the www for the DD6 so anything I can establish is new territory.

Feeding sine in, the ADC o/p datastream varies on frequency. No data into the DAC then nothing out. Connect datastream and there is 2V peak limited white noise on the analogue output. Varying sine input or even disconnecting makes no observable difference to the noise output. Scope shows no obvious periodicity 100Hz to 100KHz, and sounds like white noise. Other select lines are still connected but what , in principal, is occuring ? Presumably the DAC is still working, both channel o/ps have this "white" noise.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Sounds like something's wrong on the input side of the ADC. Have you tried using a scope to follow a signal from the input socket to the ADC?

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  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
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I did introduce the sine at the 1/4 inch inputs , and op-amps between but scoping the ADC inputs , they are fine. Curiously my first job in electronics was constructing a psedo-random sequence generator, filtered down, to produce peak limited "white noise". For RF transmission line testing , so requiring MECL logic , rather than for audio. No longer have access to a spectrum analyser, but would like pass it through one. There are (scope measured) 50K, 400K, 11M clock and other pulse trains and not determined whether they are as should be , at the moment just an interesting curiosity. It is stable , invariant to ps voltage change from

4.3V to 5V. Not grey noise or any other "coloured" noises that I can find reference to. The pk to pk maximum is 1/2 the power rail voltage of 5V, so no nasty short duration peaky spikes of real noise that cause their own problems over transmission lines IIRC.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Are you still seeing the sine wave at a pin on the ADC? I ask because the symptoms you describe sound like something in the ADC input chain is losing the signal & supplying noise instead.

I doubt that that would help you. I think that a scope is all you need, based on the symptoms you're describing.

Do you have any data on the correct Vcc for the chips?

Maybe I'm wrong, but it really looks to me like you're getting noise at the ADC input, & your tweak is merely coupling it to the output.

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------

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The serendipitous noise generator works whether there is a signal or not at the input of the ADC. I just started out feeding a sine in. The supply to the DAC may just be wrong. I've no info from Boss but except for the opamps the main chippery has a regulated 5V including the ADC and DAC. According to the datasheets this is fine for the ADC but recommended 2V to 3.6V for the DAC and maker's maximum stated as 4.6V for the DAC. I cannot find info on the regulator but it functions properly giving 5V but of course it maybe wrong and jumped from 3.5V to 5V but my hunch is 5V is the intended voltage and some variant of DAC used by Boss.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

N_Cook wrote: [...]

That's why I think something's gone bad on the input side of the ADC. Scoping out the input signal path should identify your noise source.

That sounds reasonable.

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------