Boss - FA-1 Fet Amplifier  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.

Re: BOSS - FA-1

Postby iq01221 » 06 Dec 2011, 04:41

Duckman wrote:C'mon guycapuano! Give it a chance! The DIYLC program it's not hard at all and you'll be satisfied doing it by yourself :horsey:

Actually, it gives it an "extra" point in your build. Word!
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Re: BOSS - FA-1

Postby roseblood11 » 09 Dec 2011, 21:49

Who can explain what C13 and C14 do in the original pedal? Somehow I remember that they are "for stabilization", but what exactly does that mean and what influence does the chosen value of those caps have? Will a pedal that replaces the HA1457's with a 4558 really sound identical?
http://ustomp.com/files/fa1schematic.pdf

btw: just doing a vero layout, because I'm too lazy to etch a pcb...
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Re: BOSS - FA-1

Postby Duckman » 10 Dec 2011, 00:32

C13, C14 are just to prevent some annoying oscillation in the IC as other single OA based circuits like Distortion+ or Rat.
A bigger the cap can roll off some high end, if I'm not wrong.
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Re: BOSS - FA-1

Postby Duckman » 10 Dec 2011, 00:35

"A bigger the cap"??? Geez! :lol:

Sorry, I mean "a bigger cap"
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Re: BOSS - FA-1

Postby roseblood11 » 10 Dec 2011, 02:07

Unverified:
Image

I added R17, as shown in the schematic at buildyourownclone.com. But I guess it would lower the input impedance significantly. Leave it out or use a much higher value...

For this message the author roseblood11 has received thanks: 2
guycapuano (10 Dec 2011, 03:48), joeboo88 (10 Dec 2011, 02:12)
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Re: BOSS - FA-1

Postby guycapuano » 10 Dec 2011, 03:48

Wow thanks Roseblood, I heard a friend of mine was making a break out box for me for Christmas so, when that shows, if this is not verified yet, i will give it a go.

And if a more experienced dude verifies it, then I 'm all over it! :applause:

Thanks bro.
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Re: Boss - FA-1 Fet Amplifier

Postby roseblood11 » 19 Nov 2017, 21:36

Nice. But you used a font in the layout file that isn't embedded. Those, who don't have that font installed, can't read the text

By the way:
My vero board layout is verified!

Image
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Re: Boss - FA-1 Fet Amplifier

Postby kingmafw » 24 Nov 2017, 22:01

Gandalf_90 wrote:I was asked to build the next BOSS FA-1 replica, so I ordered a PCB according to my design. Today I got it! :D


Do you also sell the PCB's or are you just building complete FX?
it is mei sizzen net to dwaen

Johannes Harald Kingma - FWS Pedals - Germany
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Re: Boss - FA-1 Fet Amplifier

Postby A-NY » 16 Jul 2019, 14:05

Hi all,

Adding on to this great thread!

I just built this version ( https://bit.ly/2JLJe4q ) of the FA-1, using the MC1458 op amp and it does not get loud at all.

In fact, it reduce the volume of my amp!

I found a few errors and the article has recently been taken down, so the link is to a cached version on Google. Not sure how long it will be there.

So here is the strip board diagram and parts list (see photos). Can anyone see why this would not be getting loud? Notice that the volume pot is listed as 1MA in the diagram and 1MB in the parts list. Similarly, the tone pots are 50KB in the diagram and 50KA in the parts list. The size given for the vero board and number of jumpers are also wrong. Also, the wiring to the volume pot lugs produced a reverse circuit, where turning the pot clockwise lowered the volume. So I connected lugs 1 and 2 together and made lug 3 the input. I based that on this article ( http://beavisaudio.com/techpages/pots/ ) That's about the limit of my abilities!

Is this just a mess and I should start over or is there some way to fix it and make it rock?

Al in NYC
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Re: Boss - FA-1 Fet Amplifier

Postby A-NY » 05 Aug 2019, 15:55

Update / build report on the Boss FA-1 clean boost clone project from Tone Report by Nicholas Kula...

HI ALL, updating this post to say this circuit works. I reflowed all the solder joints and checked carefully for shorts. That solved the low volume problem. The noise was from a noisy wall wart power supply. I replaced that and now the pedal sounds very clean, with a sweet, rich boost and lots of gain. It will feed back into the pickups when cranked near my amp. While not the easiest build because of the numerous mistakes in the parts list and instructions, it will eventually work out. :applause:
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Re: Boss - FA-1 Fet Amplifier

Postby A-NY » 05 Aug 2019, 16:02

Here's the full ToneReport article. It seems to have disappeared from Google's cache.

The Edge of Your Seat: Build Your own Boss FA-1 FET Amplifier

By Nicholas Kula @tonereport
September 24, 2016
4 Comments


The year was 1984, and Boss was still garnering praise for its relatively new line of compact stompboxes. At this time, Boss hadn’t yet seized the mind of guitarists when the word “pedal” was spoken, but it was close. Pros everywhere were starting to assemble boards full of Boss pedals, because they finally could. By this point, Boss had the foundation of its empire laid down—the company had the sound of the ‘80s firmly in hand with chorus, delay and flanger offerings, while its older roots were firmly underfoot, so to speak. Boss was on top of the world.

When the 1984 Boss product catalog was released, there was a curious entry, and that entry was called the Pocket Series. Intended as a parallel offering to its wildly popular compact pedals, the Pocket Series was meant to be clipped to a belt or pocket seam by using an included plastic hook. Only two effects in this series were ever produced, with only one of them being an effect at all. The latter was a small amp, the MA-1 Mascot Amplifier. The other was the FA-1 FET Amplifier.

The FA-1 was realized at a time when FETs were the big new thing in effect design. Not many pedals before 1984 used them for anything dirt-related (MXR’s Phase [xxx] and Dan Armstrong’s Orange Squeezer are two early pedals with them) and not many pedals intentionally left out a bypass switch. All in all, the FA-1 was a confusing beast, and its own catalog entry admitted, in a roundabout way, that even Boss itself didn’t know the demographic best assisted by its arrival. It was discontinued shortly and the concept of the Pocket Series was promptly slashed and burned.

Of course, an effect with no clear vision is only without a clear vision so long as nobody famous hitches their wagon to it. Well, after a few years, somebody did. His name is The Edge.

Almost overnight, the prices on second-hand FA-1s shot skyward, and this once-confused pedal suddenly commanded huge sums on the secondary market. Aided by its rarity, the prices reached legendary status when the Internet began globally uniting gearheads. The prices have come down a bit, but this is one Boss pedal that’s not getting any less scarce, and it sounds excellent. And guess what? You’re going to build one.

But first, the disclaimer: Neither I, nor Tone Report Weekly bears any responsibility for any kind of personal or property damage that may occur as a result of the instructions provided herein. Legal mumbo-jumbo aside, we ask that readers be familiar with a soldering iron and its accompanying safety procedures before trying anything listed here. Furthermore, if you fire the pedal up and it does not work, it will need troubleshooting. Assuming the components are not damaged, the pedal will work. I built this very unit according to these instructions and it fired up, first shot, so I know the instructions are correct.

Secondly, we’re going to need some parts. The original FA-1s contained some parts that aren’t so easy to find anymore, so we have to make some substitutions. The original op-amp was actually two single HA1457W SIP op-amps and the original FET was a 2SK246, neither of which I’m going to make you scavenge. Here’s the parts list:

Resistors:

1x 470 ohm

1x 4.7k (for the LED)

1x 6.8k

2x 8.2k

2x 10k

1x 15k

1x 22k

2x 33k

1x 100k

2x 470k

1x 3.3m

Capacitors:

2x 5.6nF film (0.0056uF)

1x 10nF film (0.01uF)

2x 33nF film (0.033uF)

1x 47nF film (0.047uF)

1x 470nF film (0.47uF)

3x 10uF electrolytic

1x 100uF electrolytic

Potentiometers:

2x 50kA

1x 1mB

Semiconductors:

1x LM1458 IC (I used MC1458, a modern equivalent. Both will work)

1x J201 FET

Miscellaneous:

1x piece of stripboard (Veroboard) cut and made according to the diagram

1x 8-pin DIP socket

1x transistor socket (optional, buy a strip of SIP sockets and cut to fit)

Wire

Alright, let’s go!

Step 1: Insert all the resistors, bend their leads outward to hold them in place, then flip over the board and solder them in. Clip the leads, but save them.

Step 2: Using the leads from Step 1, create the jumper wires, solder them in and clip off the extra.

Step 3: Place the IC socket and transistor socket (if using) in the board, then place a flat object on top and flip the board over, holding the socket(s) in place. Solder them in.

Step 4: Insert the film capacitors, bend the leads outward, solder and clip.

Step 5: Insert the electrolytic capacitors, bend the leads outward, solder and clip.

Step 6: Insert the semiconductors into their sockets and solder. If not using a transistor socket, bend the leads, solder and clip.

Step 7: Insert all the wires and solder them in. Run the wires to the potentiometers and toggle, then solder those in.

Before you continue, I must advise you to get a multimeter and check continuity (the sound wave setting) across ALL cuts and adjacent rows. Make sure there are no solder bridges across either avenue. Note that in four positions, the multimeter will tell you that adjacent rows are connected, because you connected the adjacent rows with jumpers. However, there should never be continuity across cuts.

Let’s build that enclosure! You will need:

1x enclosure of any size that can accommodate these parts. I use a 1590B for this project. It will need to be drilled for one footswitch, three knobs, one toggle, input and output jacks, DC power and an LED.

1x 3PDT latching footswitch (not momentary)

2x ¼” mono jacks

1x DC power jack

1x LED

1x LED bezel (same size as the LED, obviously)

3x knobs of your choosing

Wire

Step 1: Mount the power, input and output jacks, the switch and the LED.

Step 2: Feed the negative leg of the LED (the shorter one) through its lug on the footswitch, then join lugs 3 and 9 as shown. Solder the LED leg in, and lug 3 of the switch. DO NOT solder lug 9.

Step 3: We will ground the pedal in this step. Connect a wire from lugs 2 and 6 on the footswitch to the DC negative lug (the one unlike the other two), and solder the switch lugs. Then, connect a wire from the DC negative to the sleeve lug on one of the jacks, and solder the negative DC lug. Then, connect a wire from one jack sleeve lug to the other, and solder the first one. DO NOT solder the second sleeve lug.

Step 4: Your potentiometers have tiny metal tabs on them that prevent them from being mounted. Snap those off with pliers, then mount them. Connect the wires from the board to their appropriate spots, including the switch, the power and the LED positive leg. Connect the black ground wire from the circuit board to the unsoldered jack sleeve lug, and solder that.

Step 5: Connect wires from the input and output jack tip lugs to the switch, including the unsoldered lug 9 on the footswitch.

Step 6: You’re done! Crank it up!

So, what does it sound like?

Due to the Baxandall-style EQ, the pedal becomes so much more than a “clean boost,” and that’s a very good thing. The tones coming from this thing are light and airy, jangly and responsive—“preamp” was definitely the right word to use here. Plugging it before any other dirt pedal yields a clarity that simply cannot be equaled by that pedal alone. The Volume control acts as a “non-master” volume such that it reacts differently as you turn it up. Simply put, the FA-1 is a deceptively inspiring box that sounds great on its own or stacked. Here’s a clip of Andy playing it.
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