Another Neutron

[nosamiam]

Looking over the past posts, I'm wondering what possessed me to build this box.  But I did.    So... any brave soul willing to lend some knowledge toward helping me get it working right?  Right now, it is very overdriven (it's an interesting bass fuzz, but it's got waaay to high of a parts count to recommend it to someone else), and the sweep doesn't really do much.  After the note has sustained for a loooooong time, the sweep seems to kick in.  Right now, for consistency's sake, I have a 560ohm resistor as Rx as per R.G.'s recommendation.  I tried a 10K, then a 20K and finally a 100K pot as Rx and got varying degrees of fartiness.  Sometimes it's a lot, sometimes it's a little.

I've triple checked all of my cap orientations and values, resistor values, looked for (and found some) broken traces.  Basically everything I could think of.  It's a PCB.  Here's the "What to do if" list.

1.What does it do, not do, and sound like?

2.Name of the circuit = Neutron

3.Source of the circuit (URL of schematic or project) = http://www.generalguitargadgets.com/diagrams/neutron_filter.pdf

4.Any modifications to the circuit? Y. I am doing an AC powered version of it mounted in a 1U rackmount enclosure.  It has no battery option and gets its juice from the Regulated Power Supply project at GGG: http://www.generalguitargadgets.com/pdf/ggg_reg_power_supply.pdf.  It puts out +9V and is built on a separate PCB inside the enclosure.  I connected the +9V to the Bat (+) pad and the power ground to the Bat (-) pad.  Conversion to bipolar 9v takes place as per project specs using the 7660 power converter (Mouser part #570-ICL7660CPA).

I have bypassed the transistor/resistor switching portion of the circuit (in the lower left of the board) by jumpering from the emitter pad to the collector pad.  The input jack is 2-conductor.

5.Any parts substitutions? If yes, list them.

For the 150k log 'Peak' pot, I used a 250k log pot with a 470k resistor in parallel. Worked out to 150K very nicely. For the 1M reverse log 'Gain' pot, I'm simply using a 1M linear for now.  (Does anyone know a source for a 1M reverse log?)

I opted for the H11F3 optoisolators setup. But I subbed them for a pair of H11F1's, which were locally available.  Same exact specs according to the datasheet.  I can't figure out what the difference is, if any.

6.Positive ground to negative ground conversion? N

7. Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => N/A.  But with unit plugged in to AC, voltage at power supply output = 8.96

Voltage at the circuit board end of the red battery lead = 8.96
Voltage at the circuit board end of the black battery lead = 0

IC1
P1 = 0 (but it wasn't zero when I first powered it up. It counted down to zero and then stopped there)
P2 = 0
P3 = 0
P4 = -8.59
P5 = 0
P6 = 0
P7 = 0
P8 = 8.96
 
IC2
P1 = 0.01
P2 = 0
P3 = 0
P4 = -8.58
P5 = 0
P6 = 0 (did the same thing as IC1:P1)
P7 = 0.17
P8 = 8.96

IC3
P1 = 0
P2 = 0
P3 = 0
P4 = -8.59
P5 = 0
P6 = 0
P7 = 0.13
P8 = 8.96

IC4
P1 = 0
P2 = 4.48
P3 = 0
P4 = -4.29
P5 = -8.59
P6 = 3.44
P7 = 2.06
P8 = 8.97

u100
P1 = 8.36
P2 = 7.58
P3 = 7.58
P4 = -7.24
P5 = 0
P6 = 0

u101
P1 = 7.58
P2 = 6.77
P3 = 6.77
P4 = behaves like the other weird voltages above
P5 = same as above
P6 = same as above

D1
A (anode, the non-band end) = 0
K (cathode, the banded end) = 0.13

D2
A = 0.12
K = 0.95

Anybody got any ideas?

[nosamiam]

Bump?

[nosamiam]

Don't sweat it, y'all. I found another post where R.G. was helping someone else with similar probs.  I'll go through what he told them and see if I can't figure it out.

[Bernardduur]

I build the version off Viva Analog (here and I love it

[R.G.]

it is very overdriven (it's an interesting bass fuzz, but it's got waaay to high of a parts count to recommend it to someone else), and the sweep doesn't really do much.  After the note has sustained for a loooooong time, the sweep seems to kick in.  Right now, for consistency's sake, I have a 560ohm resistor as Rx as per R.G.'s recommendation.  I tried a 10K, then a 20K and finally a 100K pot as Rx and got varying degrees of fartiness.  Sometimes it's a lot, sometimes it's a little.

You have the misfortune to have one of those problems that's not obvious from the DC voltages - at least it's not obviousl to me yet  The DC voltages don't look grossly incorrect.

Just as a curousity, what happens to the DC voltages on U3a and U3B when you flip the up/down switch.

The symptom that it's distorting seems to say that there's something with too high a gain in the audio path portion of the circuit, not the sweep sidechain, perhaps due to a wrong compnent value. Taking that at face value, too high a gain, along with bass fartiness and the filter only moving when the signal decays a lot, one guess would be that the input gain pot is too small a value, or somehow connected so it cannot cause gain change in U1a. If it were, the gain would always be maxed out, distorting the signal at U1a's output.

It's also possible that R3 is the wrong value, bigger than 120K, or that some other component that does not affect DC bias is not the correct value. From here, the first order of business is to check the resistor values. R7 is also a suspect, but so are other parts.

All of the preceeding puresumes that the PCB is correct, of course. Did you etch your own, or is this from GGG?

[nosamiam]

Thanks for the help R.G.  I'll look closer tonight or tomorrow when I get some time.  Something else I've been doing to debug is that I've built an output jack with alligator clips on it that I can use to take the output from any point in the signal chain.  I'll see if I can find out where it's going el distorto.