Author Topic: PT2399 breaks when I play guitar loud  (Read 640 times)

BluffChill

PT2399 breaks when I play guitar loud
« on: December 30, 2017, 05:05:51 PM »
I've built a PT2399 delay based somewhat on the Crap-Fi delay, omitting the transistor input and a few other non-essential parts. It's noisy and hissy and that's how I wanted it. It works really nicely, but my one problem is that when I play guitar loud, really hit the strings, it makes one noisy, fuzzy repeat and then stops altogether until I unplug the battery and plug it back in again. Anyone know of a fix for this?

Plexi

Re: PT2399 breaks when I play guitar loud
« Reply #1 on: December 30, 2017, 05:36:41 PM »
The cause is that you omit the input buffer.
Any schematic?
To you, buffered bypass sucks tone.
To me, it sucks my balls.

BluffChill

Re: PT2399 breaks when I play guitar loud
« Reply #2 on: December 30, 2017, 05:41:09 PM »
Yes, here:




Scruffie

Re: PT2399 breaks when I play guitar loud
« Reply #3 on: December 30, 2017, 06:55:20 PM »
Can you take some voltages and post the full schematic? That kind of behaviour can happen when there's misbiasing though so it might be worth checking the V.Ref cap in the mean time.

R.G.

Re: PT2399 breaks when I play guitar loud
« Reply #4 on: December 31, 2017, 12:12:58 AM »
I'd start with schottky diodes from the junction of C9 and C10 to power and ground. This (probably) prevents the signal from hauling the in/out nodes outside the power supply and causing SCR latchup of the CMOS logic, as would fit the described symptoms.

Probably.
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

ElectricDruid

Re: PT2399 breaks when I play guitar loud
« Reply #5 on: December 31, 2017, 06:39:38 AM »
+1 agree with RG.

Was going to suggest a basic 1N4148 diode clipper to ground to prevent the input signal from going outside the limited input range of the PT2399 (it's running on 5V, remember, and it's not a rail-to-rail device either).
Depending on what the PT2399 can cope with (and I can't remember off the top of my head) a pair of back-to-back diodes to ground might do it (For roughly 1.3Vpp), or it might stand series pairs of diodes (for roughly 2.6Vpp).

HTH,
Tom

anotherjim

Re: PT2399 breaks when I play guitar loud
« Reply #6 on: December 31, 2017, 08:14:39 AM »

I'm with RG too.
Above is what I'd do.
U1 +pin is pin 16 of the PT2399.
RS is R6 in your circuit.
V+ is the +5v supply for the PT2399 pin1
V- is the 0v supply of the PT2399, pins3 & 4. If pins 3 & 4 are not connected together on your board - do so.
"So lets stay within the limit of sureness: lets consider the fuses you have available and lets see what you have to do to light them up..." Farfisa Partner 15 drum machine manual.

davidh

Re: PT2399 breaks when I play guitar loud
« Reply #7 on: December 31, 2017, 08:26:00 AM »
Got the same problem. A green LED from PT2399 pin7 to ground fixed it. Found this idea in the Hamlet delay schematic...

BluffChill

Re: PT2399 breaks when I play guitar loud
« Reply #8 on: January 02, 2018, 10:16:39 AM »
Thanks all for your suggestions, but it turns out the battery was dying, and that's all it was! It works a dream with a full battery.
Made a bit of a mess of this PCB but I'll be sure to post when I have the whole thing totally perfect. God bless OSH Park and their 3-board prototype run...