MXR - Micro Chorus

mictester · Post by **mictester** » 15 Aug 2010, 23:39

Renegadrian wrote:Seems quite a few are eagerly waiting for it...

Sorry about that. I've had to redraw it and should have it finished later. I've had my HDD system fail. The back up also failed - turns out it was a power supply fault - it's creamed three 1Tb hard drives (set up as RAID), a video card (a good one, too) and a network card.

The motherboard appears to be OK, though, so the processors (two of them on this board) and all the RAM survived.

I'll try to do some hard drive forensics later, just in case there's anything else that I hadn't backed up! I normally have an incremental back up that runs at 4 am each day (I'm paranoid that way!), but this layout wasn't included in the back up because I'd forgotten to set the back up file attribute
when I created it.... Sloppiness on my part!

Renegadrian · Post by **Renegadrian** » 16 Aug 2010, 00:57

You don't have to excuse, man! We appreciate your words about sharing the layout and we patiently wait!
As for the PC, surely you had a bad day, hadn't you?! It happens!

Cheers!

hewie · Post by **hewie** » 16 Aug 2010, 17:05

No worries, take your time. Your computer issues are the priority.

In the meantime, I'll attempt another vero layout. If successful, I'll post mine. Keep in mind, my layouts are rather sloppy

DimebuGG · Post by **DimebuGG** » 18 Aug 2010, 04:54

Here ya go...

jbgron · Post by **jbgron** » 18 Aug 2010, 04:55

Thanks Dime!

mistral · Post by **mistral** » 18 Aug 2010, 17:52

thanks

sinner · Post by **sinner** » 18 Aug 2010, 18:29

Smart layout DimebuGG

Thank you Sir! And big thanks to Chris for schemo

Fender3D · Post by **Fender3D** » 18 Aug 2010, 18:56

I made a little mistake when reversing the pedal:

the resistor between IC1's pins 1 and 2 should be 27k and not 2k7.
I couldn't believe this thread would have gone this far...

theehman · Post by **theehman** » 18 Aug 2010, 19:00

I don't suppose this new board will fit into an old MXR Micro-Chorus housing? I have 3 w/ bad SAD512Ds.

Stompin_Tom · Post by **Stompin_Tom** » 23 Aug 2010, 01:24

Awesome. I wonder how this version will compare to the vintage... I used to have (and love) that little yellow box.

I'd still love to see the vero if there's any chance.

mictester · Post by **mictester** » 23 Aug 2010, 05:50

Stompin_Tom wrote:Awesome. I wonder how this version will compare to the vintage... I used to have (and love) that little yellow box.

I'd still love to see the vero if there's any chance.

I'm back up and running. I'll find the relevant files, and post them in the next few days.

Post by **GodSaveMetal** » 13 Oct 2010, 23:48

If any PHOTO of this modified pedal I´ve seekeing this cause I have the MN3007 in my country!!!!! please let me know it is the correct schem, layout and PCB of it!!! is it any actualitation??? please let me know!!!!!

Fender3D · Post by **Fender3D** » 14 Oct 2010, 21:57

Fender3D wrote:I made a little mistake when reversing the pedal:
the resistor between IC1's pins 1 and 2 should be 27k and not 2k7.
I couldn't believe this thread would have gone this far...

mictester · Post by **mictester** » 15 Oct 2010, 05:43

Fender3D wrote:
Fender3D wrote:I made a little mistake when reversing the pedal:
the resistor between IC1's pins 1 and 2 should be 27k and not 2k7.
I couldn't believe this thread would have gone this far...

That resistor just sets the input gain. I found with the MN3007 that 10k was best because you get (roughly) unity gain through the thing, and you don't overdrive the BBD.

There is a significant improvement you can make - increase the supply voltage up to 12 or 15 Volts (don't go higher) to the BBD and oscillator. The distortion reduces. You could do this with an ICL7660S and a 78L15.

The other option would be to use the MN3207, and run it from a 5V regulator. You'd also have to reduce the supply to the multivibrator oscillator to give 5V drive to the clock pins of the BBD.

Post by **GodSaveMetal** » 15 Oct 2010, 12:32

mictester wrote:
Fender3D wrote:
Fender3D wrote:I made a little mistake when reversing the pedal:
the resistor between IC1's pins 1 and 2 should be 27k and not 2k7.
I couldn't believe this thread would have gone this far...
That resistor just sets the input gain. I found with the MN3007 that 10k was best because you get (roughly) unity gain through the thing, and you don't overdrive the BBD.

There is a significant improvement you can make - increase the supply voltage up to 12 or 15 Volts (don't go higher) to the BBD and oscillator. The distortion reduces. You could do this with an ICL7660S and a 78L15.

The other option would be to use the MN3207, and run it from a 5V regulator. You'd also have to reduce the supply to the multivibrator oscillator to give 5V drive to the clock pins of the BBD.

Yeah Brother can you please make a variation of this pedal with your modifications whit the MN3207 BBD???? and perhaps a layout and a PCB??? it will be fantastic!!!! thank a lot!!!!

Fender3D · Post by **Fender3D** » 16 Oct 2010, 16:47

mictester wrote:That resistor just sets the input gain. I found with the MN3007 that 10k was best because you get (roughly) unity gain through the thing, and you don't overdrive the BBD.

Yeah, but remember the filter created with the 10n cap.
The first op amp enhances high frequencies by 27k/2k7/10n gain cell, this enhance is then compensated by the 270//270K/27k/1n gain cell of the second op amp.

Whenever you change the RRC ratio you should compensate with an equal RRRC ratio to achieve a linear freq. response

mictester · Post by **mictester** » 17 Oct 2010, 01:17

Fender3D wrote:
mictester wrote:That resistor just sets the input gain. I found with the MN3007 that 10k was best because you get (roughly) unity gain through the thing, and you don't overdrive the BBD.
Yeah, but remember the filter created with the 10n cap.
The first op amp enhances high frequencies by 27k/2k7/10n gain cell, this enhance is then compensated by the 270//270K/27k/1n gain cell of the second op amp.

Whenever you change the RRC ratio you should compensate with an equal RRRC ratio to achieve a linear freq. response

You're entirely right, but I found it didn't make much difference. This chorus has a serious "jangle" factor!

theehman · Post by **theehman** » 16 Jan 2011, 21:04

Has anyone verified that these new boards will fit in vintage Micro-Chorus pedals? I'd like to replace the boards in 3 units I have with bad SAD512Ds.

jbgron · Post by **jbgron** » 18 Jan 2011, 06:50

I just built Dime's layout and it doesn't work, the signal just passes straight through unaffected. I've tweaked the trimpots and audio probed to no avail. Has anyone successfully built Dime's layout?

Dirk_Hendrik · Post by **Dirk_Hendrik** » 19 Jan 2011, 07:14

2 comments on Mictesters MN adaption;
1) VGG, pin 4 is supposed to VDD+1. Add a diode and filter with a filter cap to ground lift this voltage instead of connecting it to ground straight away.
2) In the current application the supply voltage for the BBD and the BBD bias is the same as the overall supply voltage. This means that when this voltage rises or lowers suddenly your BBD output signal can start to distort or fall away since the bias voltage changes as well. Add a resistor and a 8v2 zener and be on the safe side.

MXR - Micro Chorus [schematic]