more 2399 weirdness...in a rebote

[pinkjimiphoton]

hey guys,
last nite at rehearsal, i was running my cheezy little rebote delay at the end of my signal chain like usual, and running it
on a 9v battery.

at the end of one of the songs, something was going CRAZY,...not the usual "ocean" from having like, 5 fuzzes on at once. like a horrible shrieking i've NEVER heard before.

using the process of elimination, i finally figured out it was the rebote. i turned it off...noise stopped.

turned it back on, and there it was again. so i unplugged the input jack, and replugged...noise stopped..

but now, the delay trails all started to ascend...the pitch bent upwards!

this worked for a couple seconds before it went shrieky again, but i was thinking since most likely this was cuz the battery
was dead, some of the more astute noise makers here may be able to exploit this weirdness to their nefarious needs.

i'm thinking a "sag" control may actually be usefull to add to some 2399 circuits, so you can dial in the point where it starts doing this..
it's a cool sound, and VERY tape-echo like...seemed to be less noisy (on the repeats) than at 9v, too...

so, if you're bored, and wanna mess around with something to make pure noise, check it out!!

i have a feeling there may be more to it than what i've found so far, but hey, in for a $....

[garcho]

until the 9V dips below 5V, there's no difference, is there?

[pinkjimiphoton]

no idea garcho, i imagine it must have been low enough to mess with the regulator or something?

[timd]

Jimi - was this weirdness 100% confirmed to a dead/dying battery? I'm very curious about this...

[garcho]

Tested the PT2399 datasheet echo with voltage sag tonight. Not much happens below 5V. It cuts out really quick, and before it does, all that happens is the delay time shifts down, which makes sense.

[pinkjimiphoton]

i messed with this yesterday before the gig.... the battery was dead, (according to the "tongue" test)

as soon as  i plugged in a power supply, the led got bright and the thing gained volume...which was the other issue with the battery.

i think maybe it was from browning out the regulator, the 7805, more than browning the pt2399 itself.

i got the OPPOSITE of garcho...each repeat was raising in pitch, and then would go into a horrible lockedup screeching noise.

what i'm thinking is the regulator probably keeps functioning til it hits between 6-7 volts, and then starts malfunctioning, but i'm not sure.

garcho, did you try browning it out directly, or were you regulating it? try it with the rebote circuit maybe, and brown the whole circuit out.

i bet when ya find just the right voltage, it will start doing what mine did.....and when it drops below, locks up.

i WASN'T using an alkaline battery, just a cheap radio shack carbon one...they have some "memory" and will soak up free electrons from  *?* but seem to recharge slightly when the load is removed..

so i'm wondering if that has something to do with it. after G leaves for work, i'll see if i can brown out my other 2399 delay the same way. it was really cool,

i wonder if you could use an lfo or something to modulate the 5v supply slightly up and down to make it wobble in pitch on the echo returns?

all i know is it was weird as hell, and when locked up turning the delay time pot would raise/lower the pitch of the screech, although nowhere near as dramatically as you'd think.

i'll see if i can make it happen later, and if i can, try and get a clip of it.

[timd]

I hope you can figure it out. It would be cool to have a build dedicated to making that effect. I wonder if the lower voltages screw with the regulator. I remember reading somewhere that the regulator has to be (please correct me if I'm wrong) over 3 volts lower than the voltage pumped in it. So, I wonder with voltages lower than 8 if that could confuse some types of regulators.

The only thing I would be worried about is the regulator failing and smoking the pt2399.

[pinkjimiphoton]

my money is definitely on the regulator more than the 99.

they both were kinda warm when i had it apart yesterday.

[Earthscum]

I have had some strangeness with my LA v.1 regarding dying batteries. The original chip from Smallbear had no issues. The LFO would just quit working.
With the Mammoth chip, which got swapped into a couple circuits before, it starts acting up similar to what you describe. It's always on a battery that is on it's way out.
This makes me wonder about using something like current regulation rather than voltage.

[pinkjimiphoton]

yeah, always with the dieing battery sounds right.

if i get to it, i'll go out and try and grab my pedal board out of the trunk of my car and see if i can see where the battery is sitting at.

after it was plugged in a little while yesterday, it started doing it  again, tho no bizzarre locked up oscillation.

[garcho]

Who knows what I'm screwing up?!     But when I tried it, the delay time and therefore pitch, would lower, until on the verge of crappin' out all together, it would fart out two or three sickly, garbled repeats and then die. I had a 9V wall wart going into a 50k trim, going into a 1N4001 going into the regulator. I could try again without the diode, but aren't they only a 0.6V drop?

[Earthscum]

So, you're running 50k trim 9V+ to ground, wiper to diode to regulator? 

Or 9V -> Diode -> 50k -> (wiper) Regulator? I would try dropping the voltage down to about 6V before the regulator, 5-6 diodes, or a couple LED's to take up that 3 V or so. Then put a trimmer between the 6V and the regulator to sag it from there. I would suspect the circuit to start acting up around 6V, about when the regulator starts to wonder WTF.

[pinkjimiphoton]

me too. sorry, been trying to get some stuff done on my live rig that needed fixing up, didn't get a chance to pull the pedal board yet.

also, i suspect it may be from the "sag" of the battery...when the attack from the guitar fades, the voltage rises i'd assume, making the delays seem to speed up maybe?

[Earthscum]

Sag = tank cap (power filter cap) being drained faster than the regulator can supply the current. Remember that the regulator is going to do all it can to put out 5V. I was thinking this afternoon that something like a 1k trimmer after the regulator should "sag" it. But what I was thinking above was basically starving the regulator, in case it has something to do with the interaction.

[pinkjimiphoton]

i would put it BEFORE the regulator... i think the fact the regulator doesn't have enough to work with may be making the effect happen like that.

[bluebunny]

what i'm thinking is the regulator probably keeps functioning til it hits between 6-7 volts, and then starts malfunctioning, but i'm not sure.

Yeah - I recall reading (here, most likely!) that these regulators need an extra volt or two to do their stuff.  So I guess yours may well have been misbehaving if your battery dipped too far...

[pinkjimiphoton]

yeah, it would seem to mess with the power supply, it would have to be before the reg.

using a cheap battery probably has something to do with it too, as the "recovery" time of a carbon and an alkaline battery are completely different.
alkalines seems to stay pretty consistent, but carbon zinc batts seem to vary under load when they're weak.

[pinkjimiphoton]

here ya go, battery was DEAD...under 4volts!!!

i read off the voltages per pin on the 2399 as i go.... you can clearly hear the echoes bend up AND down... i have a feeling some savage hacker is gonna start messing with a
trimmer on the input to the regulator and find some real weirdness...

anyways, stupid pedal trick, rebote weirdness. have fun.

[bluebunny]

Great vid, Jimi!  Very trippy.  Yeah, make this into a feature - control the "sag" from a treadle.  Perhaps combine with Rob's sustainer and do theremin impersonations!

[pinkjimiphoton]

it is a completely inadvertant effect...it's useless but cool .

i wonder if you could add modulation effects to a pt2399 delay by modulating the 5 v supply to it?

i'm too newb to understand much about this stuff.