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.
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.
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.
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.
Stacked metal film capacitors (Panasonic ECQ-V type or similar)
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C9: 1.5uF (Wima)
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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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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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?
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
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
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
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.
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
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.
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.
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.
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.