Boss GE-7 Mods

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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mildew
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Post by mildew »

My ge-7 is the most recent revision, and i suspect that the cap numbering has changed since the mods described on the first page of this thread. Ive currently only got a blurry .jpg of the circuit for my ge-7, but for instance "change c23 to a 270pf silver mica" seems not to match my ge7 where c23 is not in the signal path, its part of the switching circuit.

heres my blurry .jpg ..
GE-72schem.jpg

Can anyone post the .pdf of the circuit diagram for the revision 2 ge7? (also posted this in requests)

The cap changes i was intending to make were c13, c23, C18,C25, C29, C30,C21, C22, C32 as per the mods on the first page. Can anybody confirm what the equivalent cap numbers are on the revision 2 board?


thanks,

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phatt
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Post by phatt »

Hi mildew,
It matters little as it seems there is little difference between schematics.
I'd First change the first stage to a *Follower* and leave the De-emphisis filter in place for now.

Work in stages until you find the balance,, if you change it all at once you have no way to know which mods worked,, some may even make it worse. work in small steps.

As to all the pretty coloured extra mods I'd leave them as last resort.
Understand this simple reality; Quite often noise issues are due to poor design NOT the quality or performance of Active components. In most cases using exotic chips achieves little.

If folks spent as much time learning RC maths you will come to realize how daffed this Mod with fancy parts game is. :slap:
I have more tone control from crap cheap gear than some of the big name pedal boards.
Why ? because I paid close attention to grounding and just where to bump up the gain.
Do it in the wrong place and noise will drive you mad. :evil: :evil: :evil:
My bet is this circuit is noisy because it has too much gain in the wrong place and if I had time to spare I could bread board test it to prove that but I would rather play my guitar :mrgreen:
Phil.

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mildew
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Post by mildew »

Mods all finished, pedal now far less hissy and removing the output emphasis has taken the blanket off the sound. Turned out the cap numbers in the first page of thread were already correct for the new version of the pedal for c18,c30,c25,c29 and c21, c22, c32.

What got me confused was the references to jumpering r1, and caps c13 and c23. As far as i can tell the new versions of the pedal are already intended to run from a normal 9v supply so have no r1 resistor to drop the current from the boss "9v" supply that actually outputs 12v.

And i just cant understand the mods to c13 and c23. In both the old and new circuit, c13 controls the frequency of the lowest eq band, when i tried a .1uf the band stopped working. c23 is a shunt to ground in the old circuit, and part of the switching system on the new circuit, so i cant see why the tonal benefits of a silver mica would be any use in those positions.

Im an eternal beginner at this stuff tho so its quite likely im wrong:)

thanks phatt for the info on removing the emphasis and converting the first stage to follower, and heres the link to the .pdf of the new circuit that lolbou kindly provided...

https://www.freestompboxes.org/download/ ... p?id=28630

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Post by phatt »

So I take it that you changed the first stage into a follower? :scratch:
Hey great news ,, you got it to work better :thumbsup
Phil.

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Post by lolbou »

I've done a full remake of the unit and adapted the vintage PCB to match the recent schematic and to use low noise DIP8 opamps. I've redrawn a vintage sliders pot PCB too, since I wanted to use ribbon cable, but if you don't mind a little spagethi, the PCB can be used with a recent stock unit.

Result is a complete no-hiss when compared to a stock one at exact same settings.

During the process, I've found an excel sheet (by Dirk Hendrik) showing the corner frequencies and quality factor.

I've tweaked it to get a lower value for C10 (and lower size) while keeping the same corner frequency and getting equal or better Q factor.

Here's what I got : R20 = 430R, R19 = 91k, C10 = 1µF, C13 = 68nF (modern schematic numbering). It gives a corner frequency of 98Hz with Q=3.7 (was 96Hz and 3.36).

Same goes for the 1600Hz band. Corner and quality were 1549Hz and 3.11 (the lowest value of all). Tweaking R11 to 270R and R3 to 100k gives 1551Hz and Q=3.8 which is more consistent with the average 3.77 of the unit.

Note : the Ibanez Q value is definitely lower (average Q is 1.5).

Just my two cents on this.
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did concombre
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Post by did concombre »

hi and thanks,
this is what I am looking for. Do you know how it works? I was wondering if changing only the caps values would be enough to lower the impacted frequencies or if I have to change the resistors too. I don't know what has an impact on what i.e. freq or Q
thanks a lot
did

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Keedo
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Post by Keedo »

blackbunny wrote: 16 Jun 2011, 10:47
mortad wrote:1- Is this Mod focused on runnig the GE7 ONLY with 12v or there is posibility about choosing 9 or 12v?
You can still use 9vDC, if you reduce the voltage drop across R1 and D1. Use a 47 ohm 1/4 watt resistor for R1, and try and get a Schottky diode for D1, such as a 1N60P or a 1N5817/5818/5819.
You can also simply solder a link across D1, but the circuit won't have as much protection from accidental reverse-polarity of supply voltage.
mortad wrote:2- In the case that I want to run my modded GE7 with 9v, Which OTHER components should I change, and which values should the replacements have for running it without problems with 9 v?


The power supply modification outlined above should be all that is necessary to run the pedal from a 9vDC power supply.
The pedal (modified with high performance op amps) may draw too much current to work from a 9v battery though.
I know it has been forever and a day since this thread was started but I’m trying to mod my GE-7 Taiwan V2 (2004 I think) and I am confused about this power supply section mod. I’m using NE5532AP chips and plan to replace IC3 with an OPA2134. I plan to run it with a regulated 9V power supply after the mod but it would be nice if I could run it at a bit higher like 12 Volts. For my version, do I need to do this power section mod or ? R1 and D1 are shown in the picture below of my board. Any help would be greatly appreciated.

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Post by clintrubber »

Got an old GE-7 in today, the type still using the ACA adaptor.

Needs some work, as was announced - but surprisingly the freq-sliders don't have any freq-selective effect.

Looking inside, no messing around or after-fab soldering as it seems.... but I found the gyrator-opamps all three being the TI NE555P type ?!? Timer-ICs, not the dual opamp. Wow !

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Post by guiddruid »

Getting clipping on my GE-7 when hitting the strings hard, even when in bypass. Suspect the output from my Black Winter pickup is a little high & is clipping in the emphasis circuit, IC5.
Will try it on 18v to see if that helps, but will mod appropriately first.

Have already replaced all the tantalum caps in the gyrators with metal film - which happened to be 250v rated, so they will be OK.
IC1,2 & 3 already replaced with RC4559 - will be fine with 18v
IC4 & 5 are stock. Will be fine with 18v.

Just need to replace C17 & C18 with higher voltage rating. Will use some 25v I have lying around.

Whilst in there, I will disable the pre-emphasis - shouldn't be needed now, with the lower noise RC4559 opamps - and that should also give more headroom for high-frequency transients. Had a look at this thread to see if there was any guidance & it was not very clear.

One of the suggestions included increasing C20. Looking at the circuit, this doesn't seem right. That would move the knee of the 10x emphasis boost to a lower frequency. Would only be noticed if you compared with & without the pedal on your board, as it will always be enabled.

I think the changes should be: remove C20 (or R28) & C27 (or R36)
R33 isn't needed & could be replaced with a link, but it doesn't look like that will change much/anything.

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Post by guiddruid »

Removing R28 & R36 possibly slightly reduced the clipping - or at least made it sound less harsh.
Running on 18v improved the clipping greatly.
Checking with the pedal removed from the signal chain I was actually getting clipping on the clean channel of my amp. Dropping the pickup down by 1 turn of the screws fixed that.

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Post by gvego »

lolbou wrote: 26 Oct 2016, 13:30 I've done a full remake of the unit and adapted the vintage PCB to match the recent schematic and to use low noise DIP8 opamps. I've redrawn a vintage sliders pot PCB too, since I wanted to use ribbon cable, but if you don't mind a little spagethi, the PCB can be used with a recent stock unit.
Would you be willing to help a civil engineer with some soldering skills to mod recently acquired vintage GE-7 by sharing your list of replacements? Thank you :)

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Post by lolbou »

Damn, I can't remember exactly... ICs have been upgraded to low noise dual opamps. I've changed some caps in the filtering section.

Again, I went the hardest way, and made the PCB for vintage units. Since the sliders board of the modern ones is different, i've redrawn it as well, unsoldered the sliders and place them back on the new PCB.

I can't remember why I went this route, but I guess i expected it to be a one shot and it must have seemed easier to me to draw based on the older wiring (it's all hand drawn with Inkscape).

Here are the files for the sliders and main PCBs, as well as the layout and my file for gyrator frequencies. Hope this helps!
Attachments
GE-7 - Sliders PCB - vintage.pdf
(124.1 KiB) Downloaded 99 times
GE-7 - vintage - layout.pdf
(48.26 KiB) Downloaded 93 times
GE-7 - vintage PCB.pdf
(1.09 MiB) Downloaded 88 times
Gyrator EQ Frequencies.ods
(21.88 KiB) Downloaded 82 times
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Motter
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Post by Motter »

I'm thinking about modding my GE-7 to add a clipping stage and make it essentially an overdrive with super control over the frequency response.

Has anyone done this before? Any ideas on where to add a pair of clipping diodes? I've also thought about inserting a little transistor circuit (maybe an Electra distortion) right around where R27 is.
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boss-ge7-equalizer-schematic.png

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Post by x-tn »

Motter wrote: 22 Nov 2022, 18:49 I'm thinking about modding my GE-7 to add a clipping stage and make it essentially an overdrive with super control over the frequency response.

Has anyone done this before? Any ideas on where to add a pair of clipping diodes? I've also thought about inserting a little transistor circuit (maybe an Electra distortion) right around where R27 is.

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Post by Motter »

That's perfect. Glad to see someone else has had this idea. Thanks!

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