Delay sectionThis is the right hand print you see in the gutshots. This print contains four PT2399 ic's and four quad JFET input opamps
Each delay section is based on the rebote 2.5 except that I dropped all filtering at first and made them allpass stages.
You can see this in the image below. I decided that the delay sections should be in series, to enable individual delay time control.
The other option would be parallel. This would be less noisy, but gives you a shorter max delay time. Now the max delay time is the sum of the max delay times of four stages. Plus it ise easy to get the four quick equally spaced repeats by just setting all head time pots to the minimum.
This turned out to be too noisy, so I added the (rebote) MFB filter at the output of each stage. (in the red square)
You can see them in the pic. They are the four small perfboards hovering over the print
If you look at the rebote 2.5 pdf from tonepad you can see a schematic of the opamp section of the pt2399.
I'm speaking of the filtering after the delay-out node. So the image above is just an indication.
The direct_out line is connected to the input of each subsequent stage. Except of course the first stage taking its input from the clean/feedback mixer.
In the last stage direct_out is not used.
For each delay section there is a buffered output for both playback and feedback. These outputs are fed to the MAX395 analog switch IC and from there to the mixer circuitry
The feedback is mixed in at the input of the first delay stage after some filtering and level control.
The playback signals are mixed and filtered, then fed into a SM2166 set up as a downward expander only (it can compress too, but I set the ratio to 1:1).
This is to surpress all noise when there is no delayed sound present.
I have tried companding around the delay stages too, but that did not improve things much.
The noise I heard sounds more like white noise then high hissing. So any suggestions in this area are welcome.
The left hand print has all signal mixing. The small print stuck to the side is the (sine)modulation LFO (modulating only the first delay stage, interesting options possible here)
The large perf board inside has the arduino on it and a CD4015 SIPO shift register for the LED's. Plus it contains the button detection circuitry (simple voltage divider )
That's it for now. A bit of a messy walkthrough, but I hope it makes sense.
I will start making an improved version. Especially focusing on the delay stages and the power supply. As you can see I have voltage dividers for each delay stage as wel as a 78L05 for each delay stage. I should be able to use the 5V regulated as a Vref there and only use one 78L05 for two PT2399's
This will reduce current consumption a bit ( currently around 160mA !! ).
