Boss - BD-2 Blues Driver 1995  [schematic]

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

question-

does the discrete opamp located in the BD-2 have the same shitty decay as the complete circuit? i've been thinking of messing with it lately but won't bother if it doesn't sound natural.
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Post by WhiteKeyHole »

solder_station wrote:Ignoring C34 and C35, its a more transparent overdrive, and way more natural note fade than both the usual Keeley BD-2* and the various Monte Allums BD-2 mods. Didnt bother with Q9 and Q12, and fixed R51 at 22k. Cheers.

* doesnt Keeley also do a BD-2 with germanium transistors at Q9 and 12, maybe this mod is quite similar?
I don't think Keeley does the germanium transistor modification. Glad it worked out for you.
RnFR wrote:question-

does the discrete opamp located in the BD-2 have the same shitty decay as the complete circuit? i've been thinking of messing with it lately but won't bother if it doesn't sound natural.
If hit hard enough, kind of. Still, I quite like it as slightly dirty boost. It has an interesting character, at least with my equipment.

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Post by new_anuzzerone »

Hi,
I´ve just recieved my 3rd BD-2. I´m going to install the Tweed-Mod (Wampler). It´ll take some time (missing parts...), but I´ll give a report.....hopefully :horsey:

regards

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Post by floris »

Because of all the posts complaining about the bad decay in this pedal and such, is it still interesting to build one for a "bluesy crunch" overdrive or should I just leave it and go for a ROG Umble as modman preferred in post 1?
https://www.freestompboxes.org/viewtopic ... 062#p13246
http://www.runoffgroove.com/umble.html

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shooto
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Post by shooto »

I did the Keeley Phat mod for the BD and now it has a feedback "whistle" when the gain is cranked (from 3 o'clock on)...that isn't normal is it?

also, anyone have the Allums changes?

thanks!

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Post by solder_station »

No thats not quite normal, wouldnt bother with the Allums changes if you've already done the Keeley mod, just try swapping oiut the clipping diodes, certainly dont bother with the opamp.

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Post by shooto »

so, anyone have an idea what might make it do that? (whistle/squeal feedback) when gain is at 3 oclock and above?

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Post by shooto »

should I look for a cold solder?

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Post by clubsprint »

One of the posts suggested searching the archives for a post by Jay Doyle as he give a good description of the workings of this pedal. Searching back it looks like Jay self destructed but I was wondering if anyone still had his BD-2 post?

Thanks
Mark
Xenu will prevail.

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Post by MoonWatcher »

marlow wrote:I am forever on the quest to find the biggest most open sounding low gain overdrive with plenty of volume on tap. I hate it when the gain floor is too high for my uses.
floris wrote:Because of all the posts complaining about the bad decay in this pedal and such, is it still interesting to build one for a "bluesy crunch" overdrive
The low gain/bluesy crunch thing is very doable with the BD-2.

The op amp decay thing is a result of just too much gain and typically too much bass as well, IME. Gain reduction throughout nixes it, and really warms up the pedal. You can end up losing a bit of the cutting trebles that a stock BD-2 is so capable of, but I don't mind the tradeoff, personally.

...The discrete op amps also can sound really nice with some gain reduction and fiddling around with the compensation, particularly on the first one.

Lastly, the "fixed tone stack" can really transform the pedal as well, if you take some time to rework it.

I like to start with the gain reduction, via R31 and R34 (first and second op amps). I've gone as high as 10K for both, but admit that it will lead to a serious gain reduction, and make the pedal very mild. It also typically necessitates other circuit changes to try and recoup a bit of the signal. Possibly 4.7K for both as a starting point might be good. Obviously be aware that C22 and C24 will have to be changed to keep the HP filtering the same, unless you want to change it.

...When you start to really reduce the gain, you will have to address D7 - D10 at some point, typically. Lower gain usually benefits from a larger clipping threshold. Since it's a taste thing, I can't really offer specifics, other than to try for a bit less clipping at those diodes.

I've found that playing with the external compensation on the discrete op amps can work wonders, as well. The most effect can be achieved at R32 and R25, and a little goes a long way. Even a switch from 2.2K up to 3.3K s/b noticeable. I'd only fiddle with one at a time, and I wouldn't alter them by much.

The stock fixed Fender tone stack really wrecks things in this pedal, IMO. It isn't even an accurate simulation. For that, you really need voltage dividers, like pots set at some point partway thru their travel. Have a gander at the schematic for the Fender Champion 600 amp for some ideas. I actually like to mostly nix the tone stack altogether and just replace it with some simpler filtering circuitry, but you could obviously just tweak the stock components for a more subtle effect. Since these tweaks are pretty well documented, I won't bother rehashing them.

...After reducing the gain, you may find that the pedal sounds a bit lifeless, because too much signal is getting attenuated at the tail end. An easy fix is to decrease R26. You can also try removing C19 as well, or altering it's value for less effect (try smaller). You can also remove the input clamps (D1 and D3) as well if the gain reduction is significant. And you can then increase R9 to recover some of it. The cool thing about this is now you can have the op amp contribute a touch of clipping on it's own that doesn't sound like that fizzy crap. Try replacing R9 with a 50K trimmer. I also like to remove C8 as well. And you could also experiment with disabling the gyrator as well.

The BD-2 is a bit tricky because there are 3 amps in it, and it's a balancing act when you redistribute the gain, interstage attenuation, and interstage EQ. I also like fiddling with increaing C23 and C25 to mellow things out just a touch more as a finishing touch, but only after the above are done.

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Post by floris »

Good to hear that the "shitty decay" problem can be solved by reducing the gain.
For a gain reduction mod, see my post here:
https://www.freestompboxes.org/viewtopic ... 277#p87613
floris wrote:For a minimal gain when the gain pot is fully closed, I would put a wire over R29 (22k between Q11 pin 2 and VR1A) and another wire over R27 (33k between Q13 pin 2 and VR1B) thus bypassing them.

The gain is set in the two stages by the ratio of the feedback resistors:
http://en.wikipedia.org/wiki/Operationa ... _amplifier

Forgetting about C22 and C24, the gain can be calculated as follows:

Gain stage 1 = 1 + ( R29 + VR1A / R31 )
Min gain = 1 + ( 22k + 0k / 1.5k ) = 15
Max gain = 1 + ( 22k + 250k / 1.5k ) = 265

Gain stage 2 = 1 + ( R27 + VR1B / R34 )
Min gain = 1 + ( 33k + 0k / 2.2k ) = 15
Max gain = 1 + ( 33k + 250k / 2.2k ) = 147

Total min gain = 15 * 15 = 225

If you bypass R29 (22k) and R27 (33k) the minimal gain of each stage becomes 1.
Even better:
First only bypass R29 and see how you like it. If not good enough then (also) bypass R27.

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Post by clubsprint »

So would increasing VR1 from 250k to say, 470k, increase the maximum gain?

floris wrote:Good to hear that the "shitty decay" problem can be solved by reducing the gain.
For a gain reduction mod, see my post here:
https://www.freestompboxes.org/viewtopic ... 277#p87613
floris wrote:For a minimal gain when the gain pot is fully closed, I would put a wire over R29 (22k between Q11 pin 2 and VR1A) and another wire over R27 (33k between Q13 pin 2 and VR1B) thus bypassing them.

The gain is set in the two stages by the ratio of the feedback resistors:
http://en.wikipedia.org/wiki/Operationa ... _amplifier

Forgetting about C22 and C24, the gain can be calculated as follows:

Gain stage 1 = 1 + ( R29 + VR1A / R31 )
Min gain = 1 + ( 22k + 0k / 1.5k ) = 15
Max gain = 1 + ( 22k + 250k / 1.5k ) = 265

Gain stage 2 = 1 + ( R27 + VR1B / R34 )
Min gain = 1 + ( 33k + 0k / 2.2k ) = 15
Max gain = 1 + ( 33k + 250k / 2.2k ) = 147

Total min gain = 15 * 15 = 225

If you bypass R29 (22k) and R27 (33k) the minimal gain of each stage becomes 1.
Even better:
First only bypass R29 and see how you like it. If not good enough then (also) bypass R27.
Xenu will prevail.

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Post by floris »

clubsprint wrote:So would increasing VR1 from 250k to say, 470k, increase the maximum gain?
Yep.

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Post by modman »

I received this message today.

Please, let me be clear on this.

Freestompboxes is not against anyone, but it continues a tradition I didn't start but that seeks to provide FREE and LEGAL information for building your own stompboxes. There has been, is and will be a growing mass of info online, more than was ever committed to paper. And this has been so since the beginning of the post-"Boss-is-ok" 80s - vintage stompbox hype came with the digital age.

At first newsgroups became platforms of info exchange, much cheaper to send pics and text, and were free. But the info available is in somewhat of a mess and components hard to find, so some commercial enterprises grew on that. Also the boutique business thrived on the availability of schematics on the web. But in fact I have nothing against a $1500 gooped Tubescreamer or Rat, if you're so stupid to buy one the joke is on you.

I think the only thing that really make me a bit wound up is people selling information online, they found on the internet.



However, if there are documents posted that Monte Allums owns the copyright to, I will remove them. Copyright is copyright.

But I need clear pointers, a link to a specific post.
T-Von wrote:Hi, Modman, my name is Monte Allums. You can find my website here:

http://www.montealums.com/index.html

In this thread:

https://www.freestompboxes.org/viewtopic.php?f=11&t=1062

Members are posting my Copyrighted work and offering to give instructions to others. I would appreciate you removing these posts and asking the members to honor my Copyright. Selling mods are how feed my family. I put long hours of research and instruction creation into my work. It is neither legal nor ethical for others to offer my work for free and post them on the net. Any help you can offer me here would be greatly appreciated.

Thanx,

Monte Allums
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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culturejam
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Post by culturejam »

modman wrote:But I need clear pointers, a link to a specific post.
I just read this thread, and I think I found what might run afoul of copyright law:
https://www.freestompboxes.org/viewtopic ... =40#p76138

I can't tell, however, if that's from the Allums mod instructions document, or copy/pasted from somewhere else. There is no attribution given for the text.

And there was someone offering to give the Allums PDF for free here:
https://www.freestompboxes.org/viewtopic ... =20#p74072

Not sure what we can do about that, however.

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Post by new_anuzzerone »

I just read this thread, and I think I found what might run afoul of copyright law:
viewtopic.php?f=11&t=1062&start=40#p76138
You´re referring to my post. If I screwed anyones copyrights, plz remove my post....I don´t want to spoil the party here....but:

There´s enough pics out there, showing the modded pcb / detailed pcb. Monte is showing us the quality parts, which he uses (sing along: Isn´t it ironic, don´t you think....). You don´t have to be "Lassie" to figure out, how it works (I´m not Lassie, so I bought the mods...)

To MonteAllums:
What about a personal message to me?

http://www.cartoonstock.com/newscartoon ... cn842l.jpg

regards

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Post by sinner »

I'm not going to bash anybody (I promise I'm doing this last time), but please Monte, fix the bullshit about 2N3440 germanium mod in your sd-1gt mod as it sucks big time. All we have a families we need to care about, but it's not an excuse for bullshiting people... I'm refering to this https://www.freestompboxes.org/viewtopic.php?f=11&t=3341

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Post by T-Von »

sinner wrote:I'm not going to bash anybody (I promise I'm doing this last time), but please Monte, fix the bullshit about 2N3440 germanium mod in your sd-1gt mod as it sucks big time. All we have a families we need to care about, but it's not an excuse for bullshiting people... I'm refering to this https://www.freestompboxes.org/viewtopic.php?f=11&t=3341
Point taken, that was an early error on my part in the mod. I have since changed it. My new instructions are correct as is the ad at my site. Not trying to knowingly BS anyone. Also, there was a comment on the nut tool I sell. I also tell people on the ad it's a welders tool. Most of the comments I get thank me for repurposing it but I understand why some would object.

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Post by sinner »

Hi T-Von, your explanation is fair enough, but don't you think update note about this mistake would be a professional move? I can't find any updated info in my mail box :roll:

Cheers
Pawel

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Post by T-Von »

sinner wrote:Hi T-Von, your explanation is fair enough, but don't you think update note about this mistake would be a professional move? I can't find any updated info in my mail box :roll:

Cheers
Pawel
You bet, shoot me an e-mail at tvon@monteallums.com and I will send you the updated instructions. I will need proof of purchase, either the e-mail address you used to buy them or a Paypal transaction number.

Thanx,

Monte

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