The Tone God's Payback v1.1 Looper - ISD1616 beeping

[molwam]

Hello everyone, I'm new here and I'm pretty desperate 

I breadboarded Tonegod's Payback v1.1 Looper (http://tech.thetonegod.com/payback_v11/payback_v11.html). I got it to work, it is able to loop and record but there is a "popping" sound everytime the loop starts and ends. If I turn down the sample rate, the "popping" turns into a short high pitched "beep". I'm using a ISD1616B as the main chip. I used seperate grounds for the audio and digital part to cut down noise, as recommended in the datasheet (http://cdn-reichelt.de/documents/datenblatt/A200/ISD1600B.pdf). For 5v power supply I used a TL7805 with two 47uf and two 100nf filter caps. I also decoupled vcca, vccd and vccp as shown in the schematic. I'm a little bit confused which ground to use for vssa, but switching between grounds didn't make a difference regarding this problem.

I switched the ISD for a spare new one I had laying around, but the behaviour is the same. Then I tossed out the control logic to narrow down the suspects but everytime I record a loop "maually" and play it back there is still this beep. Enlarging filter and decoupling caps didn't help either. I think this problem might be related to the chip powering down after the loop and the starting up again, but I'm pretty clueless how to avoid that.

Has anyone of you guy experienced the same thing I do? Is this behaviour of the chip normal or am I doing something wrong? Any help would be greatly appreciated 

-Ben

[anotherjim]

The pin numbers for the 4093 are, I think, wrong. Have you used the connection in this drawing?

And the CD4093 is...

What is the unused 4093 gate doing? Are it's inputs grounded to stop it making noise?

[molwam]

Thats true, the pin numbers are wrong. (Sadly) I've already noticed this and connected the right pins from the beginning. For now I have completly removed the control logic altogether with the CD4093 but the popping is still there when I start the loop manually.

I've also temporary disconnected the audio input from Mic+ and disconnected Mic- and recorded a loop (of silence obviously). Even with this setup there was the beep audible so I think the problem must be somewhere around the recorder chip. I'll try to temorary ground Mic+/Mic- to see if I get the same results with this setup.

But anyways, thanks for trying to help 

[molwam]

I grounded Mic+ and Mic- and still got the same results. So I'm sure, the recorder chip doesn't record this sound but produces it itself. And I'm still not able to get rid of it, but since it's relatively quiet when I turn down tone and playback volume and raise the record level I think I'll stick with it. The only thing that annoys me a little bit is the short pause between loops. But I don't think there is a way to avoid that. And hey, it's a lofi-looper anyway 

I had the problem that whenever I turned up record level past 10 o'clock the playback immediatly stoped. Same thing if I played some heavier chords. It turned out I had to adjust r11 to the limiting LED D2. In case someone else runs into this problem

-Ben

[GraemeR]

I know this is an old thread but hell....you never know.
Did anyone manage to fix the thump in the loop on the payback?

[anotherjim]

All these voice recorder chips gap/glitch when looped in my experience. Looping is not what they were made for.

[ElectricDruid]

All these voice recorder chips gap/glitch when looped in my experience. Looping is not what they were made for.

+1 sounds reasonable to me. Anyone who was *designing* a chip for this would add a short crossfade of perhaps 10-50msecs where the loop goes around to hide the join. These chips don't do that since that's not what they were intended for, and consequently there is an inevitable "tik" when the loop point is hit.

[GraemeR]

Hey, thanks so much guys. I suspected as much. Ive tried a few things. On the Payback, noticing that the led from pin 4 of the 4093 goes bright during the moment the chip is down (where the thump is) I thought about a vactrol setup that sends the audio to ground for that moment........ doesn't seem to work. I'll dream on.
Anyone know of any other chips out there with similiar characteristics that do loop without hiccup. The isd1820 is way too lofi for my tastes btw.
thanks in advance

[anotherjim]

The loop noise may be less dramatic if used last in an amps fx loop. Having lots of preamp (or other pedals) voltage gain after the looper is sure to magnify the bump.
The best DIY approach I'm afraid is a microprocessor with external RAM chips. Even for a coding guru, it's not simple since it has to work out the crossfade of loop points to avoid the bump as Tom outlined and this works best if there's a little audio data before and after the loop points so it doesn't go silent.

One thing I've thought of but haven't tried is the memo chip may have an EOT (end of tape!) digital output (may be used for a LED drive) and you might calm the bump if this drives a mute circuit on the audio output. It happens at the same time as the playback stops, but the ear is sometimes easily fooled if we do things fast and smooth.

[GraemeR]

hmm. will look into the EOT idea.
thanks again for the input. Its appreciated.