I found this PT2399 based delay design called Small Time on the Valve Wizard web site. These PT2399 delays can sound really good, and the Small Time has tails, which is a very interesting option. I had to give this a try.
Tails, if you’re not familiar, is the effect where the echoes persist after bypassing the delay. The signal continues to decay over time but new echoes are not created. This has a nice sound if you are turning the delay on or off mid song. To implement tails the delay needs to use a buffered bypass.
PT2399 Delay in a 16 pin DIP
First some thoughts on the PT2399. If you haven’t used this before or wanted more background check out this article. In short I’d describe this as a digital analog hybrid. It’s good for short delays, under 1 second. The times are a little bit longer than most BBD (Bucket Brigade Delays.) For me this is a huge bonus. The chip is a 16 bit DIP, easy to get and cheap! It also doesn’t require a lot of external components.
Making the Small Time PCB
I redrew the schematic from the Valve Wizard site in Eagle and designed a PCB. I wanted this to fit in a 1590B enclosure so I used 1/8 watt resistors everywhere.
I ordered some boards from PCBWay.com. Their prototyping service is very reasonably priced. I got 10 boards for $5! The boards came in about 2 weeks and everything looked great!
I soldered all of the parts to the board. I was all out of 50K pots with legs. But I did have some with long shafts and lugs. I soldered some wire legs and cut the shafts down with some hand tools.
I milled an enclosure on my desktop mill.
Next I put it all in the box and wired it up. The Small Time needs only an SPDT type switch for bypass and the LED. You can use one pole of one of these standard blue 3PDT type switches. I had one of these old Carling DPDT switches in my parts bin so I used that. You can see I’m only using one pole in the picture.
Turns out I didn’t have any PT2399 chips left, except one in a plastic bag dubiously labeled “Bad!” I decided to use this anyway. What could go wrong? 🤔
To be honest, I love Tayda I use their service a lot but, beware some of the things they sell are not the highest quality. In the past I had gotten a few PT2399s from them that didn’t work! I’m sure this was one of these chips.
Testing and debugging
I plugged everything in and the LED was working but nothing else 😕. I put it aside for a few days. I came back and got the multimeter out. Turns out the op-amp was not getting power. I checked the schematic I had drawn. Turns out I had forgotten the power pins for the TL072 🤦.
I ran a couple jumpers to pin 4 and pin 8 of the TL072. Now I had sound. But it was a weird noise wash which sounded like it was affected by the delay. But there was no signal from the input. This is strange because the input signal should go all the through the effect.
I got out the audio probe and I had no signal at the input jack. The jack must be grounded!
The off board wiring for this is a little different from other projects. Turned out I had swapped the input ground and tip. Once I corrected these issues I could hear the guitar signal, delay, and the noise all mixed and delayed.
I also noticed the Time pot was reversed. I added a couple wires to fix this.
At this point it seemed like things were working except for the noise issue. “Bad!” PT2399? 🤔 I pulled a PT2399 from another pedal I knew was working. And, everything is working as it should! 🙌
The last step was to add some knobs and box it up! 🏆 Thanks Valve Wizard! 🙏This is a great project and sounds good!
I got these knobs at Jameco.com. They look good but not exactly like the picture! The black on black look seems to be working. $0.69 each they seem like a good deal. I might have to order some more. This black on black look is looking pretty good!
Would I build this? Definitely! Delay is a great effect that can be used in almost any context. The tails on Small Time give it a little extra je new sais quoi!