Phase 90 add 4 stages troubleshooting

[Luke51411]

I'm trying to add 4 stages to a phase 90 on marks layout at tagboard effects http://tagboardeffects.blogspot.com/2014/06/mxr-phase-90-4-8-stage.html the main board is working but when I hook up the daughter board I only get a siren type sound when striking a string and no sound at all when not touching anything.
Here is a pic of my build

Here is a schematic for a phase 90 the extra stages are just duplicating the original stages. http://www.electrosmash.com/images/tech/phase-90/mxr-phase-90-script-logo-schematic-parts.png
Voltages on the daughter board seemed good 9v at pin 8 on both ICs and 0 at 4. Half supply at the rest. The fets had similar voltages to the working main board JFETS. Anything obvious wrong here that I'm missing? I've checked continuity on the tracks and cuts and it all seems good.

[Mark Hammer]

Are those SMD FETs on chunks of vero?

Try breaking/lifting the feedback path and see what happens.

[Luke51411]

Yeah they are smd 5457s on fab bed adapter boards someone shared on oshpark. It's a bit labor intensive but a good way to get cheap high quality JFETS. The board has the script mod switch I tried in bot positions. Isn't that the feedback path?

[Mark Hammer]

The phase shift stages are supposed to be unity gain.  Trouble is that when you have more stages, you may end up with some of those stages having a bit of gain (e.g. 1.05x), and since that gain is multiplicative, you can end up with the feedback path creating oscillation; especially if there is no way to dial it back.

A stock  P90 should not have enough feedback to risk oscillation, even with a bit of gain.  But there is always the risk that your wiring has produced that risk.

[Luke51411]

Hmm ok, what controls the gain? What can I do to tame oscillation? Shouldn't I still be getting a normal signal but with a bunch of noise if that were the case? It sounds sort of gated.

[Mark Hammer]

Many companies use a trimpot in the feedback loop to limit regeneration below the point of oscillation.  If you're getting a gated sound, though, I'm guessing what I described is not your problem.

[Luke51411]

It is dead silent until you pluck a string and it's immediately full blast siren not remotely guitar like and no ramp up either, and once it starts it doesn't stop.

[Luke51411]

I guess I should breadboard the input, output, and lfo and Hooke up the daughter board like stock and see what it does then.

[R.G.]

It is dead silent until you pluck a string and it's immediately full blast siren not remotely guitar like and no ramp up either, and once it starts it doesn't stop.

I think you may have two different problems. "Dead silent until you pluck a string" might be a misbiasing that holds something in a nonlinear region of operation. The scream may well be from the feedback issues mentioned earlier as well.