Modifying the June 60 Chorus...

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LektroiD
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Modifying the June 60 Chorus...

Post by LektroiD » Sun Sep 22, 2019 3:50 pm

I bought a TC June 60 chorus and compared to my Juno. Initially I thought the sound was too dense due to the 1024 stage BBDs in place of the 256 stage BBDs used in the Juno. But on further inspection scoping, etc, it turns out the LFO is WAY too fast.

I have attempted to slow the LFO, but cannot for the life of me find what I need to change... I have found the 2 LFO sources coming from the opamp (TL064), which starts as a square then goes through a series of resistors until it becomes a triangle. I assume there is more to the waveshaping circuit than solely resistors, but reverse engineering an SMD board without a schematic is like wallpapering a hallway through a letterbox. I looked at the Juno 60 schematic, but it doesn't give any indication what regulates the LFO speed. Anyone with a bit of knowledge in these things like to help out and get a working mod to share with the world? Having it the same rate as the original Juno would be great, but variable speed is what I'm really looking for.

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Post by guest » Sun Sep 22, 2019 11:09 pm

do you have a clear shot of the PCB? from looking at the juno 60 schematics, the frequency is switched via a 4066 analog switch.
openmusiclabs.com

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JimY
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Post by JimY » Mon Sep 23, 2019 3:53 am

See..
http://www.florian-anwander.de/roland_s ... em_LFO.jpg
From a very useful site...
http://www.florian-anwander.de/roland_string_choruses/

IC2 pin 8 is the basic triangle LFO wave.
Cap C3 is the basic speed set. Increase to make it all slower.
The 4066 switches amplitude and the speed via resistance changes between IC2 pin2 and pin7.
TR1 switches R6/C2 as a sine filter for the I+II mode.

BTW, I think the I+II speed is 7Hz, not 1Hz. Solina Ensemble vibrato speed is 6Hz

Thanks for confirming that they used the common 1024 stage BBD's!

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