All I know about the BOSS DF-2
Ok, so I know a few things about this little orange brick. I’ll try and write it all down here, using a few subheadings to organise it all.
The Basics
The DF-2 was a pedal manufactured by BOSS from 1984 to 1994. It was made in Japan until 1989 when it switched to being made in Taiwan.
It was a distortion pedal closely related to the DS-1, but quite different sounding and feeling - key differences being less angular and more dynamic.
The main selling point was if you held down the footswitch, an oscillator would be tracked to your guitar’s signal to synthesize feedback. It wouldn’t follow any note you played afterwards, just the one you were playing when you held in the footswitch. It’s a cheesy feature, but good for making noise and weird sounds.
One of the things it’s most well known for is not being loud enough, the distortion signal was often quiter than your clean bypass signal. It also runs on 12V ACA adaptor up until a change in 1991 when it was changed to 9V PSA.
The Lawsuit
One of the other well known things about the DF-2 was the Dimarzio lawsuit over the name. The original BOSS name in 1984 was “Super Distortion & Feedbacker.” Dimarzio thought that was an infringement on their ownership of the name “Super Distortion,” which was used for a model of their pickups. BOSS responded by changing the name to “Super Feedbacker & Distortion,” in January 1985 - simply flipping the two nouns around. Dimarzio thought that was ok, I think it’s all a bit silly.
Electronical Bits
This are the bits that make this least sense when I attempt to explain them. Bear with me.
9V
The DF-2 ran on the BOSS ACA Adaptor - a 12V power supply. However it could be used with a 9V battery - which seems weird.
What actually happens inside is a diode and a small resistor connects the negative terminal of the AC adaptor to ground - to step the voltage down to 9V from the 12V power supply. The battery ground was left alone.
The result of it being done this way means that when daisy chaining power with other PSA adapter pedals using a 9V adaptor, the DF-2 circuit would find the easiest path to ground which was in the other pedals - meaning a 9V adaptor could be used.
It also means that you can bypass these two components in any ACA boss pedal and convert it for 9V use. There is a great website here that points out which diode and resistor to bypass on pretty much every ACA BOSS pedal. It also has a quick guide on how to do it, although you don’t have to remove the components like it says - you can just install jumpers or even just solder them together when the connectings are close enough together like on the DF-2.
Volume
The DF-2 is widely regarded as not being loud enough. It’s your parent’s favourite pedal. The reasons for this are mainly that the distortion circuit is a hard clipping opamp setup with silicon diodes, which is then fed into a big muff style tone stack - which ends up cutting a decent amount of volume. There is also no makeup gain stage afterwards either like an actual big muff or a klon or anything similar, so you get what you get in regards to volume.
Differences to the DS-1
Keep in mind that there was only really 1 circuit version of the DF-2 (scroll down about to find the one exception), whereas there have been a few for the DS-1 - this just goes over real basic stuff. The similarities are definitely there in the topology; buffered bypass and JFET switching (as per BOSS), a very hot transistor booster fed into an opamp gain stage with a pair of silicon hard clipping diodes. Then it’s into a big muff style tone stack and a passive volume control. Sprinkle in a couple more buffers here and there - and that’s it. However, if you have ever played them side by side you’ll know they’re very different.
The most immediate difference is the sound. The DS-1 uses different filter values in the tone stack and in the opamp stage than the DF-2, resulting in the more aggressive and sharp sound the DS-1 is known for. Also in the DS-1, clipping diodes and filters are fed to Vbias (4.5V) instead of ground. This usually gives a sharper curve if you were to look at the graphs of clipping and filter cutoff respectively - and also results in a more angular sound.
Gain amounts are slightly different, although not by much. The DS-1 also has less control over the amount of distortion usually. The opamp gain is set by a big resistor (around 100k) and a potentiometer (usually also around 100k) in the feedback loop. The DF-2 just has a 1k resistor, but a 250k pot. I think this contributes to the DS-1 being a bit less touch sensitive, as you’re always dealing with at least the 100k resistor’s worth of gain. The transistor boost is identical in both.
The DF-2 has an extra buffer squeezed in between the tone stack and volume control which isn’t usually present in the DS-1. The DS-1 in some iterations has a buffer between the transistor stage and the opamp gain stage, the DF-2 never had this.
The switching circuit itself is also a bit different in the DF-2 to allow the hold for feedbacker function, more on that a bit further down.
The circuit change, and the mythical “louder” DF-2
In the same year as the name change (1985), the DF-2 had a small circuit change clearly marked on the schematic as happening at serial number 513600. That’s about February. There are a few pre circuit change “Super Feedbacker & Distortion” DF-2s (I had one to help develop the hum along) but most of them are “Super Distortion & Feedbacker” pedals.
These pre circuit change pedals are often regarded as louder and better - but in reality it’s a tiny change. The volume pot changed from 10k to 20k (no difference to output volume) and there was a small series resistor between the tone stack and the volume control which changed from 4.7k to 10k. Most of the time it’s barely noticable, as both circuits are still quieter than most guitar’s standard outputs. If you play a really low output single coil guitar it might be enough to tide you over, but anything more than that and you’re stuck with the same problem.
Swervedriver/Siren Sound
A capacitor connected to ground controls the the vibrato of the synthesised feedback note, in an attempt to get it to sound more like proper feedback. It works well - but on a few pedals the solder joint on the capacitor was cold/would get broken, resulting in wild vibrato. This video from FX Doctor shows this off pretty nicely. This is usually known as the Swervedriver mod, as Adam Franklin from Swervedriver has a DF-2 with this fault and it can be heard in their music. It’s also one of the most popular DF-2 mods, as it’s very easy to do (just break one one capacitor leg). FX Doctor and myself (+ others in the past) offer this mod on a switch, so you’re not bound to one sound.
Switching Circuit
The switching circuit in the DF-2 is slightly different to most BOSS pedals. If you don’t know how BOSS buffer switching works, I highly recommend giving this article a look.
However in the DF-2, circuitry was needed to make the hold for feedbacker function work. If you look at a DF-2 schematic it’s all on the bottom left. Instead of using transistors like most BOSS pedals, it uses an IC containing multiple NOR gates to do the switching. There is still a flip flop using two of the NOR gates to feed the two sets of FET switches, but there is some other stuff tacked on there. I’m going to be completely honest and say that I don’t fully understand how the hold function works, but just tracing some of the lines through the schematic it triggers a couple of things including the envelope generator to let the oscillator sound through, another IC containing NAND gates presumably to control the PLL chip, and some other stuff.
If anyone could fully explain the hold switching in the DF-2 to me, I’ll be forever greatful.
Thank you mainly to all the people who have scanned in and uploaded the original DF-2 schematic to the interweb (if you simply look up “DF-2 Schematic” there are multiple people on multiple sites who have done this. Without this I would have spent months tracing the HUGE circuitboard on the DF-2). Also thanks to the boss serial number decoder, Boss Area, and electrosmash - for teaching me about circuits and mainly the DS-1 so I could compare it to the DF-2. But also in general, electrosmash rules.
