Somewhat nebulous, YMMV. From THE BOSS BOOK, an interview with Yasuyuki Yamada of the Roland Corporation Development Department: 'We decided on the name Blues Driver first, and then started on development.
Boss BD2 Schematic. The BD2 is called the 'Blues Driver' since it is designed for use by jazz guitarists. It provides a light overdrive sound similar to that of the.
We were after a new crunch-like distortion. If you distort using the amp and turn the guitar volume down, you can get a clean sound.
This was the idea, and the BD-2 was the first effect that allowed you to control the distortion using the volume control on the guitar. It has the same feel as the analog version of amp simulation. The circuit is completely different from circuits up until then because it represented a completely different dirrection.
'In the case of distortion and over drive, in general, when you turn down the guitar volume it effects the filters in the circuit, and the sound gets a little muddy -this is a weakness of distortion and over drive. On the other hand, when you increase the volume, you get a great sound. With the BD-2 and the BOSS COSM amp modeling, you get a crunch-like sound from the amp distortion even when you turn the guitar volume down.' Despite the fact that the text above comes directly from Boss (the source/designer of the BD-2) I kind of take issue with the 'crunch' characterization of the Blues Driver. Maybe that refers to the sound at higher Gain settings, but the author kind of glides over how nice of a lighter natural breakup you get from the pedal at low Gain, IMO it's 2nd best feature. Thankfully it does mention guitar volume cleanup, which this pedal does, like no other OD I have ever used- some folks claim cleanup ( you get this all the time on demos, where pedal X claims 'cleanup' but it's just volume reduction, the distortion is still there.) I can take my stock BD-2, put the Tone at 11:00 the other two controls at NOON, and just leave it ON for great cleandirty tone from the guitar; it's a great OD.
I dial enough amp volume (clean Fender) so that I get enough rhythm volume with guitar volume 1/2 the way UP, an then turn it up for OD. Dynamic indeed!
Boss Bd 2 Mods
Click to expand.This may have been a big deal back when Boss rolled out the BD-2 years ago, but cleanup sans distortion isn't such a big deal to achieve any longer (IMO) - even with older Boss pedals! Case in point - I can alter the DS-1 to give it stellar cleanup. In some of my experiments, the cleanup was 'too good,' at least for a so-so player like myself (revealed too much of my ham-fisted clinks when playing). I'd still argue that Boss' marketing missed the mark, and the 'crunch term' is further proof of that. The circuit complexity with the BD-2 is not necessary for 'warm boost with just a touch of hair.' Even the OD-3 is overly complex if that's all you want. What separates the OD-2/BD-2/OD-3 apart from almost every other OD pedal out there (that I am familiar with) is the use of something called a 'differential amplifier' - an op amp is a 'scaled up and perfected' version of a differential, in many respects.
But it's sort of a problem WRT a guitarist's uses. The amplitude gain is typically very large, and the op amp doesn't 'impart any of the good stuff' to the overdriven sound in most cases.A differential amplifier uses a 'back to back' arrangement of two transistors - one gets the 'inverting input,' and the other gets the standard 'non-inverting input,' just like an op amp. There is also a PNP bipolar transistor to 'tie things together.'
I realize that's getting a bit tech'ish, but the reason I bring it up is why go to all that trouble with such a complex circuit? Because when the differentials clip, they do so asymmetrically. This is due to the amplitude limitations of the positive and negative regions of the signal not being able to 'properly reflect each other.' .And using jFET's means that you have a good input impedance as well.
Using unsorted jFET's in a class A configuration isn't a typically feasible option with a mass produced pedal. The circuitry has to be bolstered to get the singular transistor to 'autobias,' or the transistors have to be sorted and measured so that they will correctly bias up with a 'hardwired' circuit, or there has to be a provision (trimpot) for measuring and setting bias.The 'answer' is to either use something like the Orman minibooster as a modular piece of the OD circuit, or something like the differential works well, but with MORE circuit complexity. Hence the BSIABII using the minibooster building block. IDK if you recall a thread from many years ago where folks were snipping the 'last two' diodes out of the OD-3 for 'better performance,' but one of the side effects was the buzzy/fizzy thing that the BD-2 does when you breach a certain point of gain.
Gee, I wonder why? I'd argue that the 'normal' mode on the OD-2 followed by the cheap clean boost of your choice would probably give even more flexible performance than the BD-2. What would actually be COOL would be the OD-2 going into a Seymour Duncan Pickup Booster, since it uses a bipolar differential.
Sorry for the verbose/tech-speak stuff. I LOVE that Boss has used the differential circuit as they have. Prior to them, the only fairly common/popular application of the differential that I'm personally aware of is a bipolar arrangement in an old fuzz pedal - a buzzy one. Drawing a blank as to which one, but it's spaghetti western city. Click to expand.Yeah, it's literally just on the cusp. I would love to take the time to strip the BD-2 down and 'perfect it' (from scratch) for the specific application that is so popular - very low gain for that very slight breakup.
The BD-2 has TWO of those 'differential' amp stages I was referring to, and they are controlled simultaneously by a 'dual ganged' pot.I really think that just a single differential with some tone shaping, and then fed into a simple boost - even a SHO would probably work to keep the parts count super low - would be exactly what a lot of the 'slight breakup' crowd seems to crave. I have no doubt that it would have an advantage over the BD-2, because that would be the absolute intended design - when compromises are eliminated, there always seems to be benefits. But even a very stripped down BD-2 (I'd have to make this thing from scratch) would still be a pretty involved endeavor. For that reason, I've always been grateful that Boss has supplied great raw materials to work with. I should actually try and hunt down a few OD-2's, and just find the 'perfect boost' to run after one. This may have been a big deal back when Boss rolled out the BD-2 years ago, but cleanup sans distortion isn't such a big deal to achieve any longer (IMO) - even with older Boss pedals! Case in point - I can alter the DS-1 to give it stellar cleanup.
In some of my experiments, the cleanup was 'too good,' at least for a so-so player like myself (revealed too much of my ham-fisted clinks when playing). I'd still argue that Boss' marketing missed the mark, and the 'crunch term' is further proof of that. The circuit complexity with the BD-2 is not necessary for 'warm boost with just a touch of hair.'
Even the OD-3 is overly complex if that's all you want. What separates the OD-2/BD-2/OD-3 apart from almost every other OD pedal out there (that I am familiar with) is the use of something called a 'differential amplifier' - an op amp is a 'scaled up and perfected' version of a differential, in many respects. But it's sort of a problem WRT a guitarist's uses. The amplitude gain is typically very large, and the op amp doesn't 'impart any of the good stuff' to the overdriven sound in most cases.A differential amplifier uses a 'back to back' arrangement of two transistors - one gets the 'inverting input,' and the other gets the standard 'non-inverting input,' just like an op amp. There is also a PNP bipolar transistor to 'tie things together.'
I realize that's getting a bit tech'ish, but the reason I bring it up is why go to all that trouble with such a complex circuit? Because when the differentials clip, they do so asymmetrically. Berlitz english course. This is due to the amplitude limitations of the positive and negative regions of the signal not being able to 'properly reflect each other.'
Boss Bd-2 Blues Driver - Monte Allums Mod
.And using jFET's means that you have a good input impedance as well. Using unsorted jFET's in a class A configuration isn't a typically feasible option with a mass produced pedal. The circuitry has to be bolstered to get the singular transistor to 'autobias,' or the transistors have to be sorted and measured so that they will correctly bias up with a 'hardwired' circuit, or there has to be a provision (trimpot) for measuring and setting bias.The 'answer' is to either use something like the Orman minibooster as a modular piece of the OD circuit, or something like the differential works well, but with MORE circuit complexity. Hence the BSIABII using the minibooster building block. IDK if you recall a thread from many years ago where folks were snipping the 'last two' diodes out of the OD-3 for 'better performance,' but one of the side effects was the buzzy/fizzy thing that the BD-2 does when you breach a certain point of gain.
Gee, I wonder why? I'd argue that the 'normal' mode on the OD-2 followed by the cheap clean boost of your choice would probably give even more flexible performance than the BD-2.
What would actually be COOL would be the OD-2 going into a Seymour Duncan Pickup Booster, since it uses a bipolar differential. Sorry for the verbose/tech-speak stuff.
I LOVE that Boss has used the differential circuit as they have. Prior to them, the only fairly common/popular application of the differential that I'm personally aware of is a bipolar arrangement in an old fuzz pedal - a buzzy one. Drawing a blank as to which one, but it's spaghetti western city.