No Drive Blues Driver

[joshuav]

I recently modded my Boss Bd-2 to Keeley specs according to:

"Boss BD-2 Blues Driver Mods

This is not all-inclusive in what can be done to the Blues Driver. It is meant to give an idea of where the tone can be improved or changed. All of the changes are subtle but when packaged together offer a nice improvement.

D3 Change this 1SS133 to a different (1N4002) diode for asymmetrical clipping. This adds second order harmonics. This adds to the tube type sound. I like the sound of this change.

D7 D8 D9 and D10 Change 2 of of these diodes from 1SS133 to a single 1N4002. More second order harmonic distortion. Although the change is slight, I like it. We actually take out one of the two pairs and replace it with a single 1N4001.

C1, C7, C6, C12, C13, and C15 Change this electrolytic capacitor to a 10uF Non-polarized caps. Non-polarized caps sound better . I like these anywhere there is signal coupling at this high a value.--- tantalums

C14 Increase input coupling capacitor value to 0.1uF for increased bass response from your guitar.

C100 Here is where we can affect the tone control. I prefer a little more lower-midrange and bass frequencies through the tone section. You can increase the lower frequencies by increasing the capacitor value to 0.033uF. Install a switch to add a 0.068uF cap in parallel with this value for the Phat Mode!

Most of the ceramic caps are changed to Expensive Silver Mica (available through Small Bear Electronics www.smallbearelec.com or www.mouser.com or www.digiley.com). This is what makes our mod sound so good. A noticeable reduction in noise. An increase in the smoothness and no harshness left. This type of upgrade is not found in anyone's mods. The best sound is right here."

After the mods, the gain adjustment never gets it into the "dirty" territory I hear in many of the sound clips.  It does, however, produce a rather LARGE increase in volume.  Also, when hit pretty hard with another overdrive pedal (set clean), it gets a good deal of the dirt back. 

I have checked the clipping diodes, which all appear to be ok (voltage drops as measured by multi-meter).  I have also checked thoroughly for solder bridges, etc. and found none.  I haven't yet checked voltages for any of the FETs, but can do so if it would help everyone help me.  Any ideas on where I should begin (actually continue) my debugging based upon my symptoms?

Thanks in advance for the help

[R.G.]

First - changing capacitor types will not change noise in the sense of hiss. Capacitors do not generate noise, except trivally in the small resistances of their leads.

Second - the differences in harshness or smoothness of sound through different capacitor types is vastly overrated in the popular press. It may be possible, just barely, to hear differences between matched-value caps of different types on high resolution audio equipment in good listening conditions if your ears are good. By far the biggest effect you get from swapping caps is that the new caps have a different value of capacitance due to manufacturing tolerances, and therefore they affect the frequency response and phase response, which is easy to hear.

Changing all caps over 220pf and under 2.2uF to polyester (Mylar) film capacitors gets you at least 95% of the goodness of any possible capacitor upgrade, even in circuit positions where the capacitors MIGHT have some audible effect. In many cases, capacitors of up to 22uF in aluminum electrolytic are made much larger than they have to be to get the frequency turnover where the aluminum cap MIGHT have some audible effect way outside the audio range. In those cases, you can replace the aluminum cap with a 1uF to 2.2uF mylar cap with just as good an effect.

Non polarized electrolytic caps (NP types) are electrolytic caps, and replacing polarized electro with same-value non-polarized electros will not change the sound of the device at all. When a NP cap is put in a circuit where it's always polarized by the existing voltage, any nonpolar effects are lost.

Changing the clipping diodes will definitely affect the clipping and distortion sound.

But more importantly, if you replaced caps with matching nomimal capacitor values, it did not change the gain of the pedal. So you may have made some soldering mistake or accidental damage to the board in ... um... upgrading it.

To help you out, we'll need the voltages on the active device pins and any other changes you did to the board. See "Debugging: What to do when it doesn't work."

[Semperfidoe]

I had a similar problem but I'd made an error with the value of C22 which Id also changed. (which was identified with RG's help)

Ive done all the same mods you have plus some. I remember testing after just doing those mods you've listed before I embarked on the additional mods. It worked fine. Therefore I guess its an error either in a component you've changed or your soldering.

I would assume from the components listed that the error lies in the clipping stage (ie the D3,7,8,9,10). Simply because in other mods ive done such as MT2 and DS1 ive built in a 3 way switch. Taking out a couple of the N series diodes (ie 1n4002 or 1n4001) or switching them to LEds has the effect you've mentioned - reduced gain and significant volume boost. Are they soldered cleanly? Silly question probably but are the diodes alighned correctly (ie the stripe on the facing the direction of the arrow on the PCB etc)

Hence i'd look there first, but someone with more experience may suggest a better alternative, its just my observations.

Hope it helps