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Boss CE-300 Mods
Old 1st January 2010
  #1
Boss CE-300 Mods



Boss CE-300 gain mod (for keyboards)

- this mod lets you use CE-300 for synths (original design was for guitar impedance / levels)


Intro
This unit represents the classic Roland chorus sound in some way similar to Dimension series, yet little bit different in modulation. It is still true analog based design with BBDs. The problem however is the signal level and input impedance. This effect expects a low signal source (guitar) at the input and an amp (gain unit) at the output. In typical synth studio the setup is however a little bit different, or somehow reverse so to say. Because we want a unit to accept the full level signal of the synth (to maximize s/n ratio) and then add little or no amplification at the output (unity gain). If you connect a synth with max output gain to the CE-300, you'll soon overload the input stage, while output will be quite silent forcing you to add gain (and noise) at the console. This mod solves both of these issues and converts CE-300 into a keyboard signal-level unit.


Modification
First thing we want to do is to reduce the input impedance. This will reduce the noise as well. Here is the schematic which shows a R2 1Mohm resistor defining the input impedance for the op amp. Replace it with 10k metalfilm resistor. A better look at the schematic reveals a high pass RC filter made with R2 and C1. To retain the properties of the input filter we need to replace the C1 as well. A value of 4.7uF is adequate. Since you will most likely use the electrolytic cap you need to pay attention to polarity of the cap. Since the signal goes from input to the op amp you should orient positive side of capacitor to the input and negative to the op amp. This finishes the impedance modification.



Next thing is the input gain which is defined by the R3 resistor across the op amp (and the input resistor R4) that takes signal into the op amp. On default unit, this gain is too strong, thus you'll too easy overload the unit and lose precious dynamic range. By reducing R4 to 10k we are letting more current hit the op amp. And by reducing the R3, we are reducing the gain. Replace both resistors with metalfilm 10k.



Now it's time to take care of the output stage. Default gain is little bit weak for average console. We will increase the gain by increasing values of resistors R105 and R106 from 47k to 200k. Use metalfilm resistors. Replace C72 and C73 (both 47p) with a 10pF. They are located in parallel to R105 and R106 (which you will be replacing, so it's easy to locate them). The reason for this is to preserve the output frequency response curve as original. Without this the unit might sound a bit darker (at 10kHz you might already be loosing 1dB, reaching -3dB loss at around 18kHz).

This completes our modifications. Try CE-300 without the mod and then with the mod. Totally different unit. More dynamic range, way less noise. Here are the pictures that should help you locate points where these components are located.


C1, R2, R3, R4


R105, R106

This article is a part of Service and modifications thread.

Please visit here for more: https://www.gearslutz.com/board/elec...ns-thread.html

Text / images copyright Don Solaris 12.20.2009.
Old 23rd December 2014
  #2
Lives for gear
 
Lorenzop's Avatar
 

Thanks for sharing but u wonder:

Why not use a line-to-hiZ reamp device at input if using synths, and plug the output either in a good instrument DI or even in a good really high (10megaohm) impedance DI as used often for piezos?
Old 23rd April 2015
  #3
Gear Head
Did this mod yesterday.
Holy cow!
This thing is a beast now.
Pure bliss with my SH-101 and Jazzmaster.
Thanks for sharing!
Old 25th February 2016
  #4
Gear Maniac
 

Quote:
Originally Posted by trondl View Post
Did this mod yesterday.
Holy cow!
This thing is a beast now.
Pure bliss with my SH-101 and Jazzmaster.
Thanks for sharing!
Excuse my ignorance here...but once the unit is modded for keys can it still be used for guitar?
Old 25th February 2016
  #5
Quote:
Originally Posted by Lorenzop View Post
Thanks for sharing but u wonder:

Why not use a line-to-hiZ reamp device at input if using synths, and plug the output either in a good instrument DI or even in a good really high (10megaohm) impedance DI as used often for piezos?
Maybe cause it equals stepping with your right shoe on the bench, to tie the left shoe.
Old 29th February 2016
  #6
Gear Maniac
 

Quote:
Originally Posted by trondl View Post
Did this mod yesterday.
Holy cow!
This thing is a beast now.
Pure bliss with my SH-101 and Jazzmaster.
Thanks for sharing!
You say you're using the modded unit with your Jazzmaster. So can I correctly infer that the Boss is still suited for guitar as well as keys after the mod?
Old 13th August 2016
  #7
Hi guys!
@ Don : I stumbled across this thread
electro-music.com :: View topic - Restoring/Modding Boss CE-300
where it is mentioned that on the LFO some clipping is happening. I've not enough knowledge to value what's described there, so here I'm asking you: would you recommend doing the mods mentioned in the above thread as well? Or is this "LFO clipping" thing not happening on each unit, but eventually could be due to some defective components in specific units?

Thanks in advance,
F.
Old 18th September 2016
  #8
Lives for gear
 
DesolationBlvd's Avatar
Bumping for a rave review of this mod.

I've had a CE-300 for quite a while. Somehow, it was noisier than my CE-5 and the internal chorus units on my Juno-60 and Alpha Juno, and was overdriving on pretty quiet signals, so I set it aside.

I finally got around to buying the components today.

on my part: I didn't realize the bottom opened up. I took the whole unit apart last night before I realized that.
on the previous owner's part: Apparently, C1 had an even higher value - and the fuse was replaced by a braided cable wrapped around the fuse terminals. Good thing I caught that before I started the project.

The actual soldering was easy enough. In fact, the pickup swap I did two weekends ago was more effort on my part.

Now, it's clearer than the Junos' internal chorus units.
Old 18th September 2016
  #9
Thanks for your input... I'll be doing the mod in two weeks...
F.
Old 10th April 2017
  #10
I highly recommend using a non-polarized cap on C1. I did this mod years ago with an electrolytic in C1 and I just upgraded it to a Wima polycarbonate cap--the fidelity is vastly superior. It's such an excellent mod!
Old 10th April 2017
  #11
Lives for gear
 

I would prefer to bypass the EQ as it's always on.
Old 10th April 2017
  #12
Lives for gear
 
ionian's Avatar
Quote:
Originally Posted by trondl View Post
Did this mod yesterday.
Holy cow!
This thing is a beast now.
Pure bliss with my SH-101 and Jazzmaster.
Thanks for sharing!

Quote:
Originally Posted by lpedrum View Post
You say you're using the modded unit with your Jazzmaster. So can I correctly infer that the Boss is still suited for guitar as well as keys after the mod?
Bumping for the answer to this - it still works well with guitar after the mod?

@ trondl - still playing your jazzmaster through it?
Old 11th April 2017
  #13
Gear Head
@ trondl - still playing your jazzmaster through it?[/QUOTE]

When I tested it yes. Now it's connected through a patchbay, usually on an fx bus.
Still makes me smile how nice this box is!
Old 22nd July 2017
  #14
Here for the gear
 

This mod sounds like it would be perfect. The Chorus on my MKS50 just died and I've been looking for a way to bring it back to life. Unfortunately Photobucket is blocking all of your photos. Is their any chance they still exist somewhere. Thanks!
Old 22nd July 2017
  #15
Lives for gear
 
ionian's Avatar
Quote:
Originally Posted by oddlefty View Post
Unfortunately Photobucket is blocking all of your photos. Is their any chance they still exist somewhere. Thanks!
Yeah, this is something new Photobucket did recently. They blocked all hotlinking and then tell you it's $399 to get a Photobucket account that's hotlinkable. Madness.

I actually just cancelled my photobucket account because of this have and two other friends who did as well. Meanwhile, I have a ton of posts that are now "broken" lol... Including a review of the Elysia Museq which had a ton of photos but since you can't edit posts after a period of time, I can't replace them with links from a new site.
Old 24th July 2017
  #16
Here for the gear
 

$399, that's really reaching! Hopefully these still exist somewhere. Thanks!
Old 24th July 2017
  #17
Good thing is you can download photos one by one from photobucket. Then simply upload them into imgur. Which is what i will do tomorrow.
Old 25th July 2017
  #18
Here for the gear
 

Thank you, Don. I tried to locate your Photobucket account to see if I could track them down, but the URL encoding made it difficult to decipher, and searching your name didn't yield an account. It is much appreciated. Can't wait to try this.
Old 26th July 2017
  #19
Old 26th July 2017
  #20
Here for the gear
 

Don - Thanks so much. Let's hope my soldering skills don't butcher this. Looking forward to hearing the results.
Old 26th July 2017
  #21
Here for the gear
 

Any recommendations on brands for the resistors and the cap? Does it matter much? There seems to be a wide variety of pricing for things that look somewhat similar to me. Thanks!
Old 26th July 2017
  #22
Quote:
Originally Posted by oddlefty View Post
Any recommendations on brands for the resistors and the cap?
Yes. Do not use Chinese caps.

ELNA and Panasonic are pretty much standard in high end audio.
Old 26th July 2017
  #23
Here for the gear
 

They had TDK and Vishi Dale, Stackpole, and Yageo. I will look elsewhere to find some ELNA and Panasonic. Thanks again.
Old 7th August 2017
  #24
Gear Maniac
 
gerby derb's Avatar
 

How noisy is the chorus itself after this modification? I bought one and had it modified and the unit has become very noisy, most notably on the low bass notes. The more I turn up the level and tone knobs the louder the noise gets when notes are played. Unfortunately, the chorus sounds best at those levels. I have a JX-3p and the chorus on that is slightly noisy, but less than half compared to this. The CE-300 only has noise when notes are being played, could this be something else wrong with unit other than the modification? If someone could chime in I would greatly appreciate it.
Old 7th August 2017
  #25
Vishay Dale is also good IME
nice mod!
Old 8th August 2017
  #26
Quote:
Originally Posted by Reptil View Post
Vishay Dale is also good IME
nice mod!
I will eventually try adding a VEGA$ mode. That will make it way way better!
Old 29th August 2017
  #27
Lives for gear
 
cake100's Avatar
 

Would like to do this.
But going to Mouser there is a myriad of choices and I have no idea what to buy. The filters confuse this newbie.
If someone could assist it would be really appreciated.
For R2: 10k metalfilm resistor Panasonic 10 kOhms Resistors there are 2 options:
http://www.mouser.tw/Panasonic/Passi...sistor&FS=True

For C1: Looking at the Wima as recommended above (polycarbonate cap - Non polarized) there are 3 pages of options:
http://www.mouser.tw/Passive-Compone...d=wima&FS=True

For R3 and R4: Meta film 10k - Panasonic there are 4 options:
http://www.mouser.tw/Panasonic/Passi...lm+10k&FS=True

R105 and R 106: Vishay 200k Meta film resistors. Vishay has axial. Panasonic does not seem to have axial.
http://www.mouser.tw/Vishay/Passive-...a+film&FS=True

And for C72 and C73: Vishay 10pF:
http://www.mouser.tw/Passive-Compone...vishay&FS=True

And I may well be off the mark with these links.
In that case, if anyone buys the parts online, please post the links here.

Again any help would be much appreciated.
Old 17th October 2017
  #28
Lives for gear
 
Chevron's Avatar
 

Huge thanks, the mod has really brought the unit in to the realm of usability in the studio! The effect is so organic and lush
Old 1st February 2018
  #29
Here for the gear
 

Did you ever find the all of the right caps and resistors? Getting ready to do the same mod and need to start procuring everything.
Old 2nd February 2018
  #30
Lives for gear
 
Chevron's Avatar
 

Quote:
Originally Posted by dotwprod View Post
Did you ever find the all of the right caps and resistors? Getting ready to do the same mod and need to start procuring everything.
Yeh super easy they are all very common components... The mod really does make it more usable with line levels, in stock form there is no issue with the unit itself as it was designed to work primarily with guitar impedances and level.
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