Simple Op Amp Based Booster Pedal

Hey Everyone,

I'm in the process of building a simple booster pedal based on a construction article I found in my book "The Guitar Handbook" by Ralph Denyer.

It was originally a small Op-Amp based preamp that you could build and install in an electric guitar as a switchable clean-boost, but, you can easily mod it to work as a booster pedal, I started this thread because I thought that it may prove useful to other members, here's a pic of the circuit board I made using a small piece of vero/stripboard, I just need to pop into my local Jaycar Electronics store for a couple of TLO71CP Op Amp ICs and then it'll be finished and ready for the next step.

Attachment 45867

That's a great idea! I have read that everyone should have a boost pedal. I have an orange peeler, modified a bit for bass, that has a volume knob and I have been thinking of using it as a boost (I have heard that there are folks who do that). I realize that "I have heard" is not very scientific.

What this makes me wonder if if I should consider something similar to what you are suggesting. My G&L ASAT bass has an onboard boost circuit (identical to the L2000 bass circuit) powered by a 9v battery. I think a lot of folks misunderstand the circuit, and think the bass is active like the Music Man basses. Actually the pickups are passive, and quite hot.

The boost is is operated by a three way micro-switch. The three settings are: Off (or passive); On (which is quite tone-neutral); and treble boost, which is just what it sounds like.

I don't like leaving a battery in my basses (particularly if I am not playing them all the time) so I pretty much play the bass passive. I am not completely sure what Leo Fender had in mind when he added this circuit, but I think the boost was primarily to compensate for long cable runs, effect loops and such. Lately I have been thinking that it might not be a bad idea to make a pedal out of it, so that I'd have some limited boost on top. I have never actually used the treble boost, partly because I generally turn the tweeters off and turn the treble down on my rig...but I can see how it might be useful on really long runs.

There's a link to the circuit on BassesByLeo. This is the wiring diagrams page:
https://www.bassesbyleo.com/gl_bbe_wiring_diagrams.html

I am pretty sure mine is the 1.1 version in the top right corner since the chart is from 1997 and my bass is a '94. and am not really too sure how different the 1.2 and 1.3 circuits sound. What this does not show is the three way dpdt switch. For that you need to look at the "L-2000 wiring diagram from 1998" which is also on the wiring page in the right hand column.

I am curious if there are differences between your op amp and the one that Leo Fender designed for these basses? I like the transparency of the op amp on the ASAT bass, even though it's either "on" "off" or treble boosted, and there is no way of adjusting how much boost you get...

Quote:

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Originally Posted by fender3x

That's a great idea! I have read that everyone should have a boost pedal. I have an orange peeler, modified a bit for bass, that has a volume knob and I have been thinking of using it as a boost (I have heard that there are folks who do that). I realize that "I have heard" is not very scientific.

What this makes me wonder if if I should consider something similar to what you are suggesting. My G&L ASAT bass has an onboard boost circuit (identical to the L2000 bass circuit) powered by a 9v battery. I think a lot of folks misunderstand the circuit, and think the bass is active like the Music Man basses. Actually the pickups are passive, and quite hot.

The boost is is operated by a three way micro-switch. The three settings are: Off (or passive); On (which is quite tone-neutral); and treble boost, which is just what it sounds like.

I don't like leaving a battery in my basses (particularly if I am not playing them all the time) so I pretty much play the bass passive. I am not completely sure what Leo Fender had in mind when he added this circuit, but I think the boost was primarily to compensate for long cable runs, effect loops and such. Lately I have been thinking that it might not be a bad idea to make a pedal out of it, so that I'd have some limited boost on top. I have never actually used the treble boost, partly because I generally turn the tweeters off and turn the treble down on my rig...but I can see how it might be useful on really long runs.

There's a link to the circuit on BassesByLeo. This is the wiring diagrams page:
https://www.bassesbyleo.com/gl_bbe_wiring_diagrams.html

I am pretty sure mine is the 1.1 version in the top right corner since the chart is from 1997 and my bass is a '94. and am not really too sure how different the 1.2 and 1.3 circuits sound. What this does not show is the three way dpdt switch. For that you need to look at the "L-2000 wiring diagram from 1998" which is also on the wiring page in the right hand column.

I am curious if there are differences between your op amp and the one that Leo Fender designed for these basses? I like the transparency of the op amp on the ASAT bass, even though it's either "on" "off" or treble boosted, and there is no way of adjusting how much boost you get...

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Yeah, that's essentially what the booster/preamp circuit I'm building is, it takes the signal from a passive pickup and boosts it up to where the signal is strong enough to overdrive an amplifier more, the original article in the book specifies a 50k multi-turn trimpot to set the boost to a preset level, and then you use a DPDT toggle switch to switch the boost in and out, what I'm doing is to house the little board in a small diecast aluminium box with sockets, a footswitch and etc, but, instead of a 50k multi-turn trimpot, I'm going to use a standard single-gang 24mm 50k linear pot mounted in the case, so you have more control over the amount of boost you get, some guitars might need more boost than others, I made a drawing of the schematic for the Booster that I reverse-engineered from the little circuit board I made, it's a very simple circuit which lends itself to all kinds of mods, which I'll see if I can post tomorrow.

I'll also see if I can create a nice vero layout using a free app called DIY Layout creator, you can create all kinds of board layouts and export them as an image file.

Will be interested to see it!

Will be interested to see it! I think I'd want a true-bypass switch on the pedal. I used to have problems with the one in my G&L when the battery would start to go bad--even when I had it set to passive. Weird sort of cutting out and distorting. I pretty much stopped using it altogether when it did that at a gig...

Quote:

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Originally Posted by fender3x

Will be interested to see it! I think I'd want a true-bypass switch on the pedal. I used to have problems with the one in my G&L when the battery would start to go bad--even when I had it set to passive. Weird sort of cutting out and distorting. I pretty much stopped using it altogether when it did that at a gig...

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Yep, I will be including a proper true-bypass footswitch in the form of a 3-pole double-throw footswitch, when bypassed, the booster is taken completely out of the signal-chain.

Back in the early 80’s this exact project was my first ever pedal build. If I remember correctly, the first edition of the book actually had an error in the circuit, either a cap missing or an incorrect value… too long ago, memory fading.

Good luck with the build.

Update:

As promised, here's the hand-drawn schematic I reverse-engineered from the article in my Guitar Handbook, as you can see, it is a very simple circuit.

Attachment 45869

Update:

I've made some more progress on the booster preamp build, got all the mounting holes in the diecast aluminium case all drilled-out to size, all that's left to do is spraypaint the case with some matt white prime n paint spraypaint, label it with my labelmaker, and then satin clearcoat it, and then it'll be ready for final wiring-up and etc.

A couple of pics of the diecast aluminium case, with all mounting holes drilled out to size:

Attachment 45871

Attachment 45872

Do you plan to use an external power supply with the pedal? One of the things that came with my recent pedal was short chord to allow me to hook up an *external* battery. I noticed that you are keeping the internal battery. Do you intend to use it that way?

Quote:

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Originally Posted by fender3x

Do you plan to use an external power supply with the pedal? One of the things that came with my recent pedal was short chord to allow me to hook up an *external* battery. I noticed that you are keeping the internal battery. Do you intend to use it that way?

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Yep, that's my concept for the booster pedal, basically a simple battery powered op amp based booster pedal, the original design was to have the circuit board mounted inside a guitar's control routing.

Update:

Made some more progress on the booster pedal build, both parts of the diecast aluminium case have been spray-painted with flat white prime n paint spraypaint, just waiting for it to dry so I can do the labelling and satin clear-coating, and then it'll be ready for the final wiring-up and testing.

Update_2:

I gave the two parts of the diecast aluminium case a spray with some satin clear coat after applying the paper labels I made with my Labelmaker, I think it looks pretty good so far, just need to let it dry overnight and then tomorrow I can do all the final wiring-up and testing.

Attachment 45890

I was wondering how you planned to label it. I am slowly working up to doing one for a double footswitch. Thinking of using waterslide decals.

Quote:

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Originally Posted by fender3x

I was wondering how you planned to label it. I am slowly working up to doing one for a double footswitch. Thinking of using waterslide decals.

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I used some white paper labels I made using my Dymo Labelmaker, very useful little device, though they can be a bit expensive.

My Dymo Labelmaker:

Attachment 45891


The finished and working booster pedal:

Attachment 45892

I managed to give my new Booster Preamp pedal a quick test out last night with my Fender USA Stratocaster going into the audio interface of my Studio PC, I had it going through FL Studio's Hardcore plugin which is a virtual pedal board and amp simulator, one thing I did notice is that at the lowest gain setting it still boosted the signal a bit, when you turn up the gain it really comes alive, my Fender USA Stratocaster has a set of three Fender Noiseless Single Coil pickups installed in it, they tend to sound a little weak to my ears, but when put through the new Booster pedal, they definitely sound like they benefit from having their output boosted, but it's a different tone than what I get when I try boosting them with my TS-9 Tube Screamer, the natural sound of the Noiseless pickups seems to come through along with the boosting, I noticed that when I was testing the pedal with my Digital Scope, if I fed in a 1Vpeak 1kHz Sinewave, the output signal was a bit greater than 3Vpeak.

I'm thinking of having a go at designing a Mk II version of this Booster pedal that includes a very simple Op Amp unity-gain input buffer circuit, which will allow the use of standard Dual Op Amp ICs like the NE5532, JRC4558D, TLO72, LF353 and etc, plus maybe some tweaks to boost the output level capability so you get almost 9V peak without clipping.

I tried playing my Fender USA Stratocaster through the preamp booster, into my Marshall amp, wow, the booster pedal really kicks things up a few notches, works great.