Boss - GE-7B Bass Equalizer 1988 extreme hi-fi upgrade

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Snaxster
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Post by Snaxster »

Project background

Hi, everyone. This is my first post at freestompboxes.org. :) Since I am indebted to site members who posted about BOSS GE-7 mods, I registered here to post about my vintage BOSS GE-7B mods. My thanks to all whose posts helped me.

Recently I sought a 1988 MIJ BOSS GE-7B Bass Equalizer for audio upgrades, to use with bass guitar. The cheap one I found was a bit beaten up, but it worked.

Researching this project, I saw that for the cost of an upgrade kit, I could upgrade almost all the GE-7B's electronics instead. Sensibly, the kits upgrade only critical parts. But I decided to work from scratch, learn more, and maybe get a better result for the same money.

My pedal probably was not cheap by this sub-forum's standard. But my decision tree was simple: I wanted a bass-specific model, MIA or MIJ, not cosmetically trashed, and upgradable by me. Even if I dropped the MIA/MIJ part, I think most of the current cheap ones use surface mount circuits that I cannot upgrade. As long as I am seeing what I think are equal or lesser pedals selling for the same or more, I believe I did well (and I am, so I do!)

photo: With only most of the modifications done, the GE-7B is already sounding much better than stock. Read below to see how the project went.

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My background

New to electronics and soldering, I am learning and having some success with projects. Soon I will make pedals from DIY layouts.

I seriously collect and listen to vintage vacuum tubes. After years in playing, synthesis and production, I spent years away. Now I play bass and tweak processors just for fun.

Project references

Prepping for the GE-7B upgrades, I used various references. They included Qatbyte's 'summary of mods' post in this forum, and other of the later posts in that thread (page 4 and page 5).

Several of blackbunny's posts there were very helpful. But my one experience of a stock MIJ GE-7B was other than their note that "The GE7B circuit is not too noisy anyway": with the stock pedal, boosting most bands and/or the master level revealed a high noise floor. Would a new GE-7B do that? I don't know, but my stock 24-year-old one did.

photo: In this photo of the PCB in otherwise stock form, the two jumpers replacing the power diode and resistor are in the lower right corner, just above where the yellow cable terminates.

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The Boss GE-7B Bass Equalizer pedal schematic diagram page at hobby-hour.com was mostly a good source. But its schematic said R10 is 3.9K, which I found was wrong for my GE-7B: After upgrading many parts that worked perfectly, I did more, including changing R10 to that value. This killed audio pass-through and left only hum. Luckily when debugging this, R10 was the second change I regressed and that fixed it. So use that webpage, but note that the stock value of R10 may be 2.7k 5% for your GE-7B, as it was in my 1988 example.

photo: About half of the capacitors are upgraded, the ICs are replaced with sockets awaiting upgraded ICs, and the jumpers that were in place of the stock power diode and resistor are now replaced with upgraded parts.

Image

Mods done

Stacked metal film capacitors (Panasonic ECQ-V type or similar)

Code: Select all

C1:  .068uF
C2:  .068uF
C4:  .15uF
C5:  .22uF
C6:  .012uF
C7:  .47uF
C8:  .047uF
C9:  1.5uF (Wima)
C10: 2.2uF
C11: 1uF
C12: .01uF
C13: .1uF
C19: 1uF
C22: .047uF
C23: .047uF
C24: .047uF
C25: 1uF
C26: .047uF
C27: .022uF
Silver mica capacitors

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C21: 47pF (Cornell Dubilier)
C28: 470pF (Cornell Dubilier) 
C29: 470pF (Cornell Dubilier)
C30: 220pF (generic)
C31: 220pF (generic)
R26: 270pF in parallel (Cornell Dubilier)
Low ESR electrolytic capacitors

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C16: 10uF (Nippon KY type 50V)
C17: 100uF (Panasonic FM type 50V)
C18: 47uF (Panasonic FC type 50V)
1/2 watt metal film resistors (Vishay Dale)

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R1:  47R
R14: 1K
R24: 3.3K
R25: 3.3K
R26: 10K
R27: 10K
R30: 10K
R33: 4.7K
Diodes, ICs, sockets

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D1: 1N5817 (Vishay)

IC1, IC2, IC3: DIP socket with OPA2134PA (TI Burr Brown)

IC4: DIP socket with NE5532AP (TI)
Mods to be done

For some reason, I omitted buying a few caps. So I will upgrade them soon.

Stacked metal film capacitors

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C3:  .0033uF
C14: .022uF
C15: .0056uF
Also, I wondered if I should replace the power diode with a different type better suited for an external 12V power supply (would that include 1N914, which I happen to own now?)

blackbunny wrote, "IMO, the modified GE-7's should be run from a regulated 12-18vdc supply for lowest noise and improved headroom."

I would like that, but is it safe to power these pedals with an external 18V supply? :)

photo: Fully reassembled after the first pass of upgrading, the GE-7B awaits the moment of truth: did I break it or make it sound better?

Image

Mistakes and repairs

For similar pedals, in future I will get smaller resistors if possible. Though I fitted the ones I got, they dwarfed the originals, and their leads were too thick for the PCB holes. Eventually I saw I could narrow then re-tin the leads' ends. But at first I used posts made of thinner clipped leads. (I later learned these are "vector pins" or "vector binding pins" generically.)

photos: ribbon cable repair prep

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The ribbon cable between the two PCBs is fragile! I learned the hard way that unless real care is taken, the soldered wires in the ribbon cable will break. Maybe after 24 years those wires are brittle. And the design probably assumed that repairs would be rare, so the cable would not have to take much stress.

When I saw that I broke the cable, I decided not to despair or replace the cable. I repaired the cable instead:
  • 1. prepped the main PCB by clearing the solder, wire, and adhesive left by the ribbon cable

    2. prepped the broken end of the ribbon cable by exposing the tips of its wires

    3. soldered to the main PCB short lengths of lead clippings, then trimmed them to equal length for use as vector pins

    4. soldered each vector pin to the corresponding ribbon cable wire

    5. wrapped the exposed new connections in one length of electrical tape.
The result is much stronger than stock, I think. Though I could have insulated each new connection individually, they should never touch in the pedal's normal use. Someday I may improve the insulation.

photos: ribbon cable repaired, front and rear

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Power supply, empirical

When I first got the GE-7B, before buying the parts for upgrading it, I modified it for use with an external 9V power supply. I used the jumpers method, replacing the power diode and resistor (D1 and R1 in my GE-7B) with jumpers.

photo: most mods done, internals reassembled

Image

Powered with 9V externally, first with this mod and later with a 47R resistor in R1 and a 1N5817 diode in D1, the GE-7B worked correctly and behaved thus:
  • With an unregulated 9V 500mA adapter, and with its audio output connected directly to an amp, it hummed slightly. The hum was very noticeable when lower bands were boosted.

    With a Voodoo Lab ISO-5 regulated 9V output shared with another pedal via a ground isolated splitter cable, and with its audio connections in series with other pedals, it did not hum at all.
Powered with 12V externally, with the new resistor in R1 and diode in D1, the GE-7B worked correctly and behaved thus:
  • With a Voodoo Lab ISO-5 regulated 12V output, and with its audio connections in series with other pedals, it did not hum at all.
photo: Years ago, someone drilled the base plate and added large screws in deep set collars, probably for theft prevention. A later owner tried drilling out the screws, and I finished the job.

Image

Audio quality, subjective

The stock GE-7B sounded okay. Functional and kind of boxy and dull. The extremely upgraded GE-7B, however, sounds very good indeed.

Since I did most of the mods at once, I can only guess how each upgraded part improved the audio. Also, because I assume that parts in an audio circuit may work together to affect audio systemically, the matrix of possible test paths (with and without each part upgraded), whose traversal could (only possibly) indicate what's affecting what, is enormous and beyond my patience to try testing, I didn't try. :)

Now upgraded, the GE-7B is far from high-end studio quality. But for a pedal it sounds excellent. Basically musical-sounding, it transmits dynamics and most tonality faithfully.

Though my first tests suggest that ideally it would sound more open, I think the pedal now sounds altogether more natural and dynamic than it did stock, and that (as with so many audio devices) only by careful operation of the settings can the best sounds be found for each situation.

photo: more mods done, new resistors

Image

For a test harness, I repeatedly alternated between the Audere Classic 4-band preamp in my 4-string bass guitar and the upgraded GE-7B. With various pickup selection, playing styles and sound shaping goals, I tried to get the same tone with both devices. Some outcomes were surprising!

The Audere Classic had only its four bands to the GE-7B's seven. But the Audere's connection to the pickups is very different from the GE-7B's, giving it a great advantage. And it is a more modern circuit by over 20 years. So this test really was just a harness, an excuse to exercise the upgraded GE-7B with some real world task, not a competitive comparison.

Presumably thanks to the 271pF capacitor added in parallel with R26, the GE-7B's high frequency response was extended beyond stock. When its highest band (4kHz) was boosted even moderately, the tone was more like a shelved EQ. It revealed articulate sibilance and "air". Not harsh, this response floated in and around the rest of the spectrum in a natural-sounding representation of the source. Really nice, and it gave the Audere Classic a run for its money with this trait!

photo: In this photo, the added silver mica cap is near the left of the circuit board, oxblood colored, marked 271J03, attached to the tilting resistor just behind it in R26.

Image

In midrange definition and dynamics, and for overall naturalness, the Audere Classic handily beat the upgraded GE-7B. It sounded "alive" and urgent by comparison. This was interesting to me, since I normally find the Audere preamp to be unforgivingly neutral: it doesn't sound cold, but neither does it leave its mark.

However, in an earlier test of the upgraded GE-7B, I used it in my pedal setup as a utility equalizer for an overdrive loop. In that role it was very strong, letting me dial in thickness and bottom with pretty detailed control, while retaining the overdrive's signature resonances and dynamics. The net sound was alive and singing. Excellent.

Conclusion, subjective

Improving the vintage BOSS GE-7B Bass Equalizer with an extreme parts upgrade was well worth it. 25 years ago, bass guitarists had far fewer options for sound shaping, and the GE-7B was a rare, powerful solution. In improved form, if less rare, it is powerful today.

What is it for? What any bass equalizer pedal is for: each player can decide what. For me, the utility role seems strongest. Not for my basic or overall sound but for one loop, like the overdrive I mentioned.

This was a good beginner's project, a good confidence builder. I paid dues and had to learn to fix what I broke, but I got the good result. Well known to all makers is that the satisfaction of crafting or improving something oneself cannot be bought.

photo: Stock parts after the first pass of upgrading. They don't look like much, but for me it was a lot of work replacing them. I plan to use all the leftover stock GE-7B parts in a DIY pedal someday, just for the vibe.

Image

I owned BOSS pedals the first time around, before they were vintage. Back then I had mixed feelings about BOSS (e.g., the digital delay was a little marvel, but the flanger was cold if convenient.) Now I have a different perspective and some nostalgia. But sentiment for history alone can't make me like an instrument. So I think I actually like the extremely upgraded GE-7B Bass Equalizer, and I recommend trying one.

Best,

Snaxster

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Post by uncleboko »

Fascinating read and wonderfully clear photos :D

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Post by blackbunny »

Welcome to the pirate crew, Snaxter. I enjoyed the detailed description and images. You must surely be a frontrunner for an award for the most comprehensive overhaul of a Boss pedal ever!
Snaxster wrote:Also, I wondered if I should replace the power diode with a different type better suited for an external 12V power supply (would that include 1N914, which I happen to own now?)
You have several choices for the V+ series diode if you're running the pedal from a well-regulated 12-18VDC power supply.
While the 1N5817-8-9 Schottky diodes result in a low forward voltage drop, the 1N4001-7 series will give better reverse polarity protection due to their 1 amp current rating.
1N914 or 1N4148 are small signal diodes with much smaller current ratings, so they would be more likely to fail and short out in the event of incorrect polarity of the V+ supply.
Snaxster wrote:Powered with 12V externally, with the new resistor in R1 and diode in D1, the GE-7B worked correctly and behaved thus:
With a Voodoo Lab ISO-5 regulated 12V output, and with its audio connections in series with other pedals, it did not hum at all.
Good! Exactly as it should be.
Snaxster wrote:blackbunny wrote, "IMO, the modified GE-7's should be run from a regulated 12-18VDC supply for lowest noise and improved headroom."
I would like that, but is it safe to power these pedals with an external 18V supply? :)
Yes. The op amps are rated at 36VDC (or +- 18VDC) max power supply, and you have fitted electro capacitors with a voltage rating of 25VDC or more. The film capacitors will be rated for at least 50VDC, so 18VDC is no problem at all. In fact, the OPA2134's will sound noticeably better at the higher voltage when using big boosts on the faders.

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Post by ~arph »

Nice work! where did you get those awesome resistors btw? (the big ones with the color bands)
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Post by FiveseveN »

It's a very thorough and nice writeup, without question. But am I the only one who's uncomfortable with the conclusions?
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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Post by Snaxster »

uncleboko wrote:Fascinating read and wonderfully clear photos :D
Thank you, uncleboko! I tried to make both good. :)

Only I wished I could find the edit button for my post, since I wasn't "[seeking] a 1988 MIJ BOSS GE-7B". I would have taken any year of MIJ production. ;)

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Post by Snaxster »

blackbunny wrote:Welcome to the pirate crew, Snaxter. I enjoyed the detailed description and images. You must surely be a frontrunner for an award for the most comprehensive overhaul of a Boss pedal ever!
Hello, blackbunny, and thank you! I wondered if you would comment in my thread. Again, I thank you for your previous posts.

As for the award, I'm just happy I didn't cripple my GE-7B. That's my award. :D
blackbunny wrote:You have several choices for the V+ series diode if you're running the pedal from a well-regulated 12-18VDC power supply.

While the 1N5817-8-9 Schottky diodes result in a low forward voltage drop, the 1N4001-7 series will give better reverse polarity protection due to their 1 amp current rating.

1N914 or 1N4148 are small signal diodes with much smaller current ratings, so they would be more likely to fail and short out in the event of incorrect polarity of the V+ supply.
Thanks for taking the time to explain this (I'll be thanking you a lot in this reply.) I read and read about diodes, but apprehension of electronics comes slowly to me. 1N400x it will be!
blackbunny wrote:
Snaxster wrote:blackbunny wrote, "IMO, the modified GE-7's should be run from a regulated 12-18VDC supply for lowest noise and improved headroom."

I would like that, but is it safe to power these pedals with an external 18V supply? :)
Yes. The op amps are rated at 36VDC (or +- 18VDC) max power supply, and you have fitted electro capacitors with a voltage rating of 25VDC or more. The film capacitors will be rated for at least 50VDC, so 18VDC is no problem at all. In fact, the OPA2134's will sound noticeably better at the higher voltage when using big boosts on the faders.
THAT is what I was looking for. Thank you!!

I keep hearing that the better op-amps are power hungry; that to get from them the performance you want and paid for, you have give them more power. But as I venture into DIY audio, with a special interest in high headroom applications, I feel nervous about circuits using charge pumps or >9V external power supplies.

You're alright, blackbunny. I appreciate your help, and I'm glad you enjoyed my documentation!

Best,

Snaxster

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Post by Snaxster »

~arph wrote:Nice work! where did you get those awesome resistors btw? (the big ones with the color bands)
Hello, and thank you! I got all those resistors from Mouser:

Code: Select all

MOUSER PART NO.      RESISTOR DESCRIPTION

RL20S470GB14         1/2watt 47ohms 2%
RL20S103GB14         1/2watt 10Kohms 2%
RL20S472GB14         1/2watt 4.7Kohms 2%
CMF603K3000FHBF      1/2watt 3.3Kohms 1%
RN65D1001FB14        1/2watt 1Kohms 1%

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Post by Snaxster »

FiveseveN wrote:It's a very thorough and nice writeup, without question.
Hello, FiveseveN, and thanks for saying so!
FiveseveN wrote:But am I the only one who's uncomfortable with the conclusions?
Well I did say my conclusion was subjective. It was only my opinion. :) What about it, particularly, made you uncomfortable?

Thanks,

Snaxster

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Post by FiveseveN »

There's nothing wrong with subjectivity but I'm afraid you're confusing it with vagueness:
If I were trying to be diplomatic I'd say your conclusions are unintentionally obscure, which stems from your admited limited knowledge in the field.
If I were my usual dismissive self I'd say you were covering superficial correlations with the equally gratuitous droning "audiophile" drivel I've grown so, so, SO tired of.
What in the name of Jesus Jean-Baptiste Emanuel Christ does "functional, boxy and dull, alive and urgent, strong, thick, detailed control, singing" etc. mean?! And why do they constitute an improvement in function? And why should we care?

You seem pretty level-headed and methodical so I hope you can sort out what's relevant and apply it in your future endeavours.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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Post by Snaxster »

FiveseveN wrote:There's nothing wrong with subjectivity but I'm afraid you're confusing it with vagueness:
If I were trying to be diplomatic I'd say your conclusions are unintentionally obscure, which stems from your admited limited knowledge in the field.
If I were my usual dismissive self I'd say you were covering superficial correlations with the equally gratuitous droning "audiophile" drivel I've grown so, so, SO tired of.
What in the name of Jesus Jean-Baptiste Emanuel Christ does "functional, boxy and dull, alive and urgent, strong, thick, detailed control, singing" etc. mean?! And why do they constitute an improvement in function? And why should we care?

You seem pretty level-headed and methodical so I hope you can sort out what's relevant and apply it in your future endeavours.
Thanks for keeping it real, FiveseveN. And for being so presumptuous! You know significantly nothing of my experience, and so are unqualified to gauge the extent of my knowledge of "the field" (speaking of vagueness).

Anyway, I took the bait of your initial passive-aggressive contrarian comment, so I deserve what I get. Now to unearth my copies of the old post modernist critical theory writings I ever had, so I can finish decoding your self-indulgent reply!

Best,

Snaxster

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Post by Snaxster »

Regarding recent comments in this thread, anyone interested in the language of music and sound (that is, how we talk about them to try to describe them) may like to read this: Scents and Sensibility

It was written by Brian Eno and published in Details Magazine in 1992. I am a musician of many years and a perfume collector of some years, and I think that Eno nailed the matter in that piece, 20 years ago.

Best,

Snaxster

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Post by FiveseveN »

My background

New to electronics and soldering, I am learning and having some success with projects. Soon I will make pedals from DIY layouts.
Is that not what you said?! There is nothing postmodern about my appeal to critical thinking, just good ol' scientific realism. To construct a theory we need both a strong correlation and a model that explains it. You have neither.
Just to be clear, the theory here would be that the modifications you made imply the effects you (try to) describe.
I don't have a problem with you attributing subjective properties to this mod but with the fact that they are fictitious.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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Post by Snaxster »

There is one part of the documentation I forgot at first: noise. It is important. :)

Noise, empirical

After the upgrades, my GE-7B was far less noisy than stock.

I think that switching was much more audible before the upgrades, but I was not careful enough to note this well.

After the upgrades, though, I repeatedly tested switching the pedal without audio passed through it: it made no sound being engaged, but made a very soft and short "pah..." sound being disengaged. Very soft, but there.

Noise, subjective

Upgraded, even idling with high bands boosted, the GE-7B's noise floor is more than acceptable for use live; and it should be low enough for use in recording, especially in the context of a typical pedalboard setup.

Stock, the GE-7B simply was too noisy for me to get much utility from it. For me, with respect to noise floor alone, the upgrades reclaimed the pedal.

Best,

Snaxster

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Post by Pruttelherrie »

Snaxster wrote:Thanks for keeping it real, FiveseveN. And for being so presumptuous! You know significantly nothing of my experience, and so are unqualified to gauge the extent of my knowledge of "the field" (speaking of vagueness).

Anyway, I took the bait of your initial passive-aggressive contrarian comment, so I deserve what I get. Now to unearth my copies of the old post modernist critical theory writings I ever had, so I can finish decoding your self-indulgent reply!
...


*WHAT* ?!?!?

...

I have to agree, your report reads like one of those audiophile reviews, and your writing style reminds me of reviews like these yet not as amusing.

Good photos though. :thumbsup

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Post by Seiche »

i dunno, for that amount of work involved, you could've just built an "extreme hi-fi" clone and do a true a/b test. I mean good on you for being satisfied with the result, but why not take that extra day for acquiring the right size of resistor and properly replacing the ribbon cable?

to be honest, some areas of the pcb look like they could lead to possible failure and problems in the future (those components that were tacked on from the top).

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Post by stompthis »

nice work! :thumbsup
...although it occurs to me that if you are replacing all the parts yourself then the only thing left that is made in japan may be the sticker! :P
(unless you happen to be located in japan) :hmmm:

i am considering modding mine to reduce the underlying white noise to within reasonable limits and found this post an interesting read.

if you ever feel like redoing the ribbon cable you might find ide hard drive cable an easy substitution.

cheers :)

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