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Boss DE-200 gain mod for use on keyboards
Old 20th September 2012
  #1
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Boss DE-200 gain mod for use on keyboards



Intro
To anyone who wanted to use DE-200 with synths, he most likely encountered two major problems which relate to signal levels and input impedance. Those are: output of the effect unit is very low in the volume while the input would overload at slightest increase of the input knob. The unit can be quite difficult (and frustrating) to operated under these conditions!

Here is why. This effect expects a low signal source such as the guitar at its input. Further more, it expects a guitar amplifier at the output. In typical synth based studio the setup is reversed actually. Because we want a unit to accept the full level signal of the synth (synth set at max volume) to achieve maximal s/n ratio. We also want effect unit to add a little or no amplification at the output (also known as Unity Gain). If you connect a synth with max output gain to the DE-200, you'll soon overload the input stage, while output will be very silent forcing you to add a lot of gain at the console. This mod solves all these issues and converts DE-200 into a keyboard signal-level accepting unit with approximately -10dB level signal at the output (typical for average synth).


Gain Modification
First thing we want to do is to reduce the input impedance and gain. This will reduce the noise as well. Here is the schematic which shows a R10 1Mohm resistor which should be replaced with 10k metalfilm resistor. A better look at the schematic reveals a high pass RC filter made with R10 and C3. To retain the properties of the input filter we need to replace the C3 as well. A value of 4.7uF is adequate. This so far effectively reduces input gain stage from the current +12dB to around +6dB of gain at 10kHz. We will further reduce it across the op amp by changing R2 to 4.7k. At that point we should have input stage set at around +3dB gain which is just fine.



Important: Since you will most likely use the electrolytic cap you need to pay attention to polarity of the cap. Polarity must follow the signal, and as we all know the signal goes from the input jack to the op amp thus you should orient positive side of capacitor to the R1 and negative to the op amp. This finishes the input buffer and impedance modification.

Now we come to the Roland's pre-emphasis part of the machine built around IC 2b where additional gain is built. Pre emphasis is basically a high pass filter with gain defined by R6, R7 and R8 resistors and corner frequency defined by C5. Our goal is to have near 0 dB of gain of the filtered signal and amplify only the non filtered part. We will achieve that by replacing resistor R8 with 110k ohm value. This effectively reduces gain from 19dB to around 13dB at 10kHz. Or globally, we reduced gain of the input stage for a total of 15dB.



Now it's time to take care of the mixer / de-emphasis stage. Default gain is a little bit weak for average console, since it is expected a guitar player will us an amp, rather than line mixer. We will increase the gain replacing R159 with 47k and R158 with 220k ohms. It is necessary to replace C109 as well, since we're working on a low pass filter in here made of R158, R159 and C109 (ignore the C110, it's purpose is something different and unchanged value isn't that critical unless you live right across FM transmitter). Same applies to C7. Both can be left at existing values.

This completes our modifications. Try DE-200 without the mod and then with the mod. Totally different units! More dynamic range, much much less noise. If you want more, please continue to read.




Crazy Ivan modification (addendum for experienced)
While calculating component values for the de-emphasis part i came with one idea to try. How would machine sound if we would have the signal partially pre-emphasized and passed thru. The rest was easy. In fact this is uber-simple yet very effective modification for all of you experimenters and le sonique bizarre aficionados. The best part is that it includes one of the components that you already need to replace during the previous gain modification.



In the image above, points A and B mark the place where existing C109 capacitor is, which you need to replace with 1nF as detailed earlier. However, while replacing it, you can solder just one of its legs, then use a wire and lead it to the switch, which can be placed on the front panel. From the other side of the PCB, in the same place you can solder another capacitor, this time 100pF value and again lead it with a wire to the switch. Then you add another wire, from the center point of the switch and lead it to point B.

There's enough space on the front panel to do the drilling right next to the Power on/off switch. Just measure everything carefully. I strongly advise you to start drilling from the front side, with the plastic panel on. Once you get the small hole done, you can remove the plastic, and use correct width for metal drill so that switch perfectly fits in. The goal of the hole in the plastic is to make it as small as possible yet enough space to move the switch up/down. Please do not place nut on the front plastic. You will make the unit look ugly for no reason. Because there's a metal plate right below the plastic where a nut can be placed and tightened.


Installed and ready to fire...

In the image above you can see the Crazy Ivan ON/OFF switch added right next to the POWER switch. The goal of such modification is to make it non destructive (a click of a switch resets the unit to original sound) and of course to maintain the sleek design of the unit.

What this modification does is that it shifts the de-emphasis curve (low pass) from the 600Hz up to the 6kHz. Result are really exotic and make the unit cut through the mix like a razor. Use carefully though, since harsh delays can irritate the listener after a while. Flanges and Choruses with Crazy Ivan are interesting as well and give some extra edge to the sound!! Unit can be used for processing drum beats as well (feedback set to 0) particularly because the signal path contains some exotic elements like a compression, dynamic expansion and the emphasis. The work detailed in this article can be performed under one hour. This article is a part of Service and modifications thread.

Please visit here for more: https://gearspace.com/board/electron...ns-thread.html

Copyright Don Solaris 09.20.2012.
Old 22nd June 2013
  #2
Here for the gear
 
🎧 5 years
Hello......URGENT ASSISTANCE WILL BE MOST APPRECIATED. I have made the above modifications (not including Crazy Ivans ON?OFF mod) and plugged in my unit to try it. I only use the rear input and mixed output but unfortunately I do not get any echo out of the machine after the modification.

On the front panel I can see the unit is giving echo as the lights flash up and show repeat.

I am wondering if the above modification only works if you use the front input and output, which I haven't tried as yet (I hope not as I always use the rear connections to keep the rack tidy).

Please can anyone shed some light??? As I have now a previously working unit not working :(

Many thanks

Scee

Last edited by Don Solaris; 9th July 2013 at 01:38 PM.. Reason: why quoting whole text???
Old 22nd June 2013
  #3
Lives for gear
 
🎧 5 years
off topic, but im picking my de-200 on monday,
will i need a digital to analog converter if i am to use it as outboard fx for my roland mv 8800?
Old 22nd June 2013
  #4
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Acid Mitch's Avatar
 
🎧 10 years
No.You don't need D/A converters .
Why do you think you would ?
Old 22nd June 2013 | Show parent
  #5
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🎧 5 years
Quote:
Originally Posted by Emperorfari ➑️
Hello......URGENT ASSISTANCE WILL BE MOST APPRECIATED. I have made the above modifications (not including Crazy Ivans ON?OFF mod) and plugged in my unit to try it. I only use the rear input and mixed output but unfortunately I do not get any echo out of the machine after the modification.

On the front panel I can see the unit is giving echo as the lights flash up and show repeat.

I am wondering if the above modification only works if you use the front input and output, which I haven't tried as yet (I hope not as I always use the rear connections to keep the rack tidy).

Please can anyone shed some light??? As I have now a previously working unit not working :(

Many thanks

Scee
Ok tried it with input and outputs turned up maximum. I am getting an echo but its seriously low volume compared to prior modifications.

Are there any mods needed to boost the output? Although I thought this. Was part of the mods already made as above?
Old 22nd June 2013
  #6
Deleted 2ecf148
Guest
does this mod need doing on all boss pro rack gear?
Old 22nd June 2013
  #7
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🎧 5 years
No not as far as I am aware
Old 22nd June 2013
  #8
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fooddude's Avatar
 
🎧 10 years
I did this mod when I got my DE200 a month ago. It works excellent and made the unit totally different in an awesome way - clearer sound and echos, no more distortion, way more dynamic range, just generally higher quality sound and I guess what it's supposed to sound like. And yes, I use the rear inputs and outputs.

Maybe you installed something wrong, or installed the wrong component in the wrong place, or broke a trace on the pcb? I would recheck and resolder the components that were modded. Mine works perfect after the mod.

As for other older Boss units (what about the half rack units? ..the colored knobs/look/design look very similar)..I am unsure since I've never owned many old units.. but there's a possibility. I say this because I had an old SDE-1000 Roland rack (before it broke). And i too noticed it had the very similar problem as the stock DE-200 - way too sensitive on the input gains, always clipping very easily and at the same time the output was low. So, there's a possibility that the majority of vintage early 80s Roland, Boss, Korg, etc racks were built this way similar impedances of guitar pedals.. I'm not 100% positive though. Maybe same thing goes for even older units, that are nice, like the Tape Echos, analog 1010 1005 yamahas, etc...I'm unsure too, since I've never owned those nice old tape echos and analog delays...but if you think about it, if a boss de-200 made in '83 had guitar pedal impedances, then theres a good possibility that older '70s units were the same way... something I've always wondered if they did.
Old 9th July 2013
  #9
Lives for gear
 
🎧 5 years
just got my de-200 in the mail yesterday :D
also ordered a boss bx 400 mixer to go with it for 20 dollars, shouldnt controlling levels thru that work just as good as modding the de-200 itself?

i am a troglodyte and can not mod anything at all
Old 18th August 2014
  #10
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68000's Avatar
 
🎧 5 years
I have just modded a DE200 with this mod. The difference is worlds apart. It opened up the sound. The DE200 sounds somewhat like a Roland SDE-1000 now. It's a bit more difficult to do the DE200 compared to the CE300 as the components are smaller in the DE200.

Regarding the Boss Micro racks; as far as I know they are all line level devices and thus do not need this mod.

The SDE1000 should not need any mod to sound okay. It's made for studio use not guitar input.
Old 28th August 2014
  #11
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Stitch333's Avatar
 
🎧 10 years
Can the 4.7uf be a film cap?
Old 17th June 2016
  #12
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ocoughi's Avatar
 
🎧 5 years
greetings,
i just made the output mod and it's way better than before! input is good for me as is...maybe i'll do it later...
tooks me 15mn to do the mod...
thanks for sharing Don solaris!
peace.
Old 18th June 2018
  #13
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Great mod. The DE-200 is surprisingly low-noise.



Anyone stymied by part selection or where the components are located on the PCB might be helped by this guide:
Boss DE-200 Digital Delay Line Level Mod - R-Massive
Old 2nd February 2019 | Show parent
  #14
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JPogo's Avatar
Quote:
Originally Posted by 68000 ➑️
I have just modded a DE200 with this mod. The difference is worlds apart. It opened up the sound. The DE200 sounds somewhat like a Roland SDE-1000 now. It's a bit more difficult to do the DE200 compared to the CE300 as the components are smaller in the DE200.

Regarding the Boss Micro racks; as far as I know they are all line level devices and thus do not need this mod.

The SDE1000 should not need any mod to sound okay. It's made for studio use not guitar input.
weird -- I just got an SDE-1000, and it has exactly the issue described above -- input must be absolutely minimal or sound distorts. I'm keen to try this mod to see if it improves
Old 18th February 2020
  #15
Here for the gear
I've had a DE-200 for about 20 years and used it heavily. I've just done this mod - I loved the unit before, and time will tell if I preferred it one way or the other, but I am immediately struck by much greater clarity, lower noise, greater dynamic range... it's just responding in a way which is more appropriate to the sounds going into it - so likely a keeper in its current state!
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