Boss CE-2 Clones - impedance mod for keyboards

[mkraus1]

Hey everyone,

In this thread I found here, a user was wishing to modify the input circuitry of his Boss CE-1 to be more suitable for his guitar. The CE-1 has a low input impedance that was designed for keyboards, but he noticed his guitar tone was negatively impacted as a result.

On the complete opposite end of the spectrum, I'm a keyboard player wishing to build one of the Boss CE-2 clone kits for my Wurlitzer 200A. But in my reading, including this ElectroSmash analysis of the CE-2, the CE-2 was designed to be more suitable for guitar impedance.

I'd like to know if there's a way to modify a CE-2 (clone) circuit to more closely match the impedance of my Wurlitzer? In the above thread, someone suggested changing the stock pot and feedback resistors to different values. I'm a relatively new student of electronics and especially the theory of component values and the like, so this is all a bit mystifying to me. I just want to avoid building my CE-2 clone and finding I have very little range or noticeable effect. I'm looking at kits from either BYOC or Mad Bean Pedals (PCB clones). I feel this will be simple arithmetic for an experienced tech, so I hope this question makes sense and am excited to learn!

Having said all that, if there's going to be no noticeable issue, it'd be great to know that as well! I'm still learning the theory behind impedances, forgive my novice skills!

Regards,

Matt

[Enzo]

Why not build the kit and FIND OUT if you have an issue or not. If you do, then you can chase down some mods, but if not, no extra energy spent.

After the great success of the bulky Chorus Ensemble CE-1 issued in 1976, which was based on the Roland Jazz Chorus JC-120 Amplifier integrated chorus effect, Boss decided to revise and release a similar sounding effect but in a compact size modifying the circuitry. The CE-2 builds on the legacy of the CE-1 with reduced features: mono output instead of stereo, no vibrato mode, no integrated power supply, no level and no intensity controls.

The CE-1 was designed more to be a multi instrument effect, with a 50K low input impedance suitable for keyboards. The CE-2 has higher input impedance and boosted mid frequencies, both arrangements very suitable for electric guitars

Seems to me your concerns are misplaced.

[mkraus1]

Uhh, well, that's certainly one way to look at it. But I prefer to understand WHY I'm doing the things that I'm doing, trial and error isn't always the best way to do something. I'm also not able to throw money at it and take a chance that it'll work, so this is why I'm doing my research ahead of time. As I mentioned, I'm a novice student of the electronics world so I was simply wondering if there might be some considerations I should make before I drop money on a kit to find out that it is not suited for my instrument at all.

So anyway, I'll see if anyone else has some thoughts but thank you for your advice

[g1]

So you want to use it for keyboard?
I'm sure the changes from the CE-1 to CE-2 (regarding input Z and mid-bump) could be reversed.
But for anyone here to be able to tell you how to do it will require both schematics. Can you post them?

[mkraus1]

Thanks g1:

Boss CE-1 Schematic

Boss CE-2 Schematic

So in my rudimentary understanding, impedance matching is a result of your source (keyboard) impedance and matching to the input impedance of the pedal, effectively a voltage divider. The magic number I gotta find is the output impedance of my Wurlitzer which I plan to track down tonight, and then I would think it should be just a matter of trying to find a different value for R1 in the CE-2 circuit? I'm not sure if that's what is referred to as the 'feedback resistor', as was talked about in the first thread I linked up above.

As much as I'd love to take Enzo's advice and just build the thing and test it, I have nothing to compare it to, and I know for a fact I will not track down a CE-1 where I live. I built a clone of a Phase 90 pedal and, while it sounded fine, I had a heck of a time dialling in the trim pot to a specific place where the pedal actually had range. I was fortunate to actually test it compared to a real Phase 90 and they sounded like two completely different pedals. Again, this particular pedal had been 'optimized' for high Z input, so this is the source of my hesitation to jump out and buy/build the CE-2 clone.

[Jazz P Bass]

Here is the Boss CE-2 Service manual.

Take note that the specified input impedance is 470K.

[mkraus1]

Thanks man! Much appreciated.

[Enzo]

My underlying point was more that it really won't matter much. These are guitar amp and instrument amps, not lab equipment. We can make a case on paper about impedances and such, and yet the guitars we use have all manner of impedances, yet they all work into most amps seamlessly. Same with keyboards. I don;t recall ever plugging a keyboard into an amp and have it just conk out. Some amps sound better than others for the purpose, but I can say that about comparing amps with guitar too.

Your CE2 schematic looks funny to me. WHy would they connect the minus end of the power supply to the input when nothing is plugged in? Try this, it looks more accurate:
http://bmamps.com/Schematics/Boss/Bo...ice_Manual.pdf


Ultimately you don't need to compare it to a CE1, you just need it to work well. My suggestion to build it meant the stock CE2 will probably work fine just as is, and if not, then you can go ahead and change the input circuit as needed.