PMHayesEngineer
New member
I am a new poster here on this forum. Let me start by saying thank you to all the previous posters who shared their experience, expertise and insights on the Cepheid Chorus pedal. My grandson (14) bought one as a project. I was somewhat concerned with the notation that the kit was for experienced builders. So before we took off building the pedal I found this forum and read many of the threads. My background is electronic engineering, but I am not a musician nor do I have any experience with guitar pedals, so this was going to be a learning experience for both my grandson and me.
The good news is everything is working, but not without a few bumps. My grandson had never soldered before, so his early attempts in soldering did require some rework. But as he progressed in the build, his skills improved.
We took a progressive approach to testing the pedal. We first started with none of the ICs installed. I have a current limited power supply and by setting the current limit and voltage to their lowest values we were able to check the pedal's power supply without letting the magic smoke out. As a note the pedal works properly with 10 volts and draws 24ma.
Second, the TL022 was installed and the clock was verified as working. So far success. With the clock working the V3102 was installed and again we had success as the 3102 produced the 2 phase clock. The RC4558 was installed and with about 200mv of tone from my function generator on the pedal's input we got about 880mv of signal at pin 1 of the RC4558.
Now on to the V3207, and this is when the problems came up. We saw signal from pin 7 and 8 on the 3207, but nothing on pin 7 of the RC4558. There are two 47K resistors, R34 and R35 that combine the wet and dry signals. On the RC4558 pin 6, where R34 and R35 are summed, there was no signal, but on the other side of the resistors signals were present.
I removed the RC4558 and bent pins 5 and 6 so they would not make contact, and reinstalled it. With pin 5 and 6 not connected, there was a low level signal at the junction of R34 and R35. Upon examining the RC4558, I noticed the part number was engraved on the IC body. A number of YouTube providers, IMSAI Guy, Noel's Retro Lab among others, have all done multiple presentations about fake ICs, and one the the telltales is engraving the part number on the ICs body. I ordered a replacement RC4558 and everything is working properly. I did put the engraved RC4558 on a breadboard to test it and the "B" side is not working.
I did read a number of comments about the setting of the trimmer for the RC4558's Vref. I used my oscilloscope and looked at the output on Pin 1. With Vref set to below 1.9 volts or above 8.5 volts the waveform either clips or the IC stops working. I found between these two values Pin 1 of RC4558 produced a clean output. I set the Vref value to 3.3 volts and everything appears to work properly and sounds excellent.
I have access to an oscilloscope and some other good test equipment. I know for many people the investment in test equipment can become quite prohibitive. IMSAI Guy, a former Hewlett-Packard engineer in their optics division and another YouTuber Adrian Black, Adrian's Digital Basement, have both done reviews on low cost, below $100, oscilloscopes. There are a couple of offerings that look interesting.
Again thanks to all those who shared their experiences with the Cepheid Chorus Pedal as it gave me a good information on any potential problems with the build, possibe solutions, and made this build go very smoothly.
The good news is everything is working, but not without a few bumps. My grandson had never soldered before, so his early attempts in soldering did require some rework. But as he progressed in the build, his skills improved.
We took a progressive approach to testing the pedal. We first started with none of the ICs installed. I have a current limited power supply and by setting the current limit and voltage to their lowest values we were able to check the pedal's power supply without letting the magic smoke out. As a note the pedal works properly with 10 volts and draws 24ma.
Second, the TL022 was installed and the clock was verified as working. So far success. With the clock working the V3102 was installed and again we had success as the 3102 produced the 2 phase clock. The RC4558 was installed and with about 200mv of tone from my function generator on the pedal's input we got about 880mv of signal at pin 1 of the RC4558.
Now on to the V3207, and this is when the problems came up. We saw signal from pin 7 and 8 on the 3207, but nothing on pin 7 of the RC4558. There are two 47K resistors, R34 and R35 that combine the wet and dry signals. On the RC4558 pin 6, where R34 and R35 are summed, there was no signal, but on the other side of the resistors signals were present.
I removed the RC4558 and bent pins 5 and 6 so they would not make contact, and reinstalled it. With pin 5 and 6 not connected, there was a low level signal at the junction of R34 and R35. Upon examining the RC4558, I noticed the part number was engraved on the IC body. A number of YouTube providers, IMSAI Guy, Noel's Retro Lab among others, have all done multiple presentations about fake ICs, and one the the telltales is engraving the part number on the ICs body. I ordered a replacement RC4558 and everything is working properly. I did put the engraved RC4558 on a breadboard to test it and the "B" side is not working.
I did read a number of comments about the setting of the trimmer for the RC4558's Vref. I used my oscilloscope and looked at the output on Pin 1. With Vref set to below 1.9 volts or above 8.5 volts the waveform either clips or the IC stops working. I found between these two values Pin 1 of RC4558 produced a clean output. I set the Vref value to 3.3 volts and everything appears to work properly and sounds excellent.
I have access to an oscilloscope and some other good test equipment. I know for many people the investment in test equipment can become quite prohibitive. IMSAI Guy, a former Hewlett-Packard engineer in their optics division and another YouTuber Adrian Black, Adrian's Digital Basement, have both done reviews on low cost, below $100, oscilloscopes. There are a couple of offerings that look interesting.
Again thanks to all those who shared their experiences with the Cepheid Chorus Pedal as it gave me a good information on any potential problems with the build, possibe solutions, and made this build go very smoothly.
