[1553] Little Angel Chorus – NYE

Date: March 19th, 2014 | Comments : [1] | Categories: DIY.

Little Angel chorus prototype

Over the holidays just a couple of months past, I laid out a pcb for the Little Angel Chorus. After building it, I found that a few changes were needed to get the most out of it with my rig.

I made an number of mods to the circuit, which I have called the New Year’s Edition to differentiate it from previous versions, since the changes are significant.

The first change, which I incorporated into the prototype pcb, was to use a different startup circuit. I selected a J112 jfet transistor (which is still available in through-hole versions) and used it to set the delay time by way of its ON resistance. A differentiator (R-C) connected to the gate of the fet will pulse briefly when power is applied, and that will pinch off the channel (making it high resistance) long enough for the PT2399 oscillator to start. I’ve only tried it with three different PT2399 chips but it seems to work well enough.

I also eliminated the resistor on the non-inverting input of the first opamp, and connected the pin directly to the bias voltage.

Little Angel chorus gut shot

There were a couple of minor problems that I encountered when I started playing the circuit. The LFO made a mild thump as it cycled, and there was not enough depth to the chorus sound. I found myself leaving the Depth control at the max setting.

After a number of attempts to silence the LFO, I finally decided to change the bias resistors (100k and 47k) to 220k for both. This makes the LFO wave more symmetrical and it got rid of the thump. To increase the depth, I decreased the value of the resistor in series with the bias pin of the PT2399 from 33k to 2.2k. This proved to be too low, and I would suggest a starting value of 10k, though I left the 2.2k in my prototype since it did not cause any problem except to reduce the usable range of the Depth control, and I did not want to disassemble the pedal yet again. A few other part values were changed as well, for what I found be minor improvements. Nothing critical.

After making these mods, I found the chorus effect more prominent and the sound was improved (at least with my guitars and amp). The PT2399 is not the best chip for chorus pedals as the delay time is just too long, and there is some variability in the specific delay characteristics from chip to chip, but decent performance can be squeezed out of it if you are willing to tweak the circuit.

Little Angel, New Year’s Edition Schematic



One Response to “Little Angel Chorus – NYE”

[765429] admin Says: 2:52 am, December 21st, 2015


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