Boss Bass OD; any mods??

[Bernardduur]

Hey all!

I just got this Boss Bass OD from a friend..... and I think it kinda sucks. It cut mids, it sounds nothing like a good OD pedal. So, what can I do to add some more warmth???

Oh, btw, I made a schematic as I couldn't find one

Boss ODB-3 schematic

I'll remove the schematic if someone disagrees with me posting it!

[lowstar]

sorry i haven´t got any mods, but i very mucho appreciate the schem ! i was always curious about it.
thanx ! 
cheers,
lowstar

[Bernardduur]

LOL

Kinda cool to see Boss uses the technique of the OD-2 and OD-3 in this bass version. Shame to say is that it doesn't sound as nice as the OD-3; it is too shrill, too "industrial" and I lose a lot of mids........... I also hate the fact that the clean blend is most of the time lower of volume then the OD part so it is hard to get a good clean vs od tone

I like the bass knob so I would love to use it more!

[Bernardduur]

To answer my own question

One mod

Although I don't know what it does

[petemoore]

  Tryin' to help, I'm not the best TC calculator, some work right there might be a place for mid-scooping or other tone control alterations...perhaps someone will chime in...
  There;s a split just before the first 1/2 of the 5m218al.
  THe bottom side must be the dirty one, with the BTB LED's doing the clipping.
  They sum into the balance, then get the OA to re-bump-up the signal, TC in the FB loop, on to switching some schtuff *then output.
   First thing I see is the smallish 47nf input cap, I'd just swap numbers on the input cap and resistor, use a 47k into a bigger cap of choice value, let more bass input, try that first.
  c23 and r16 alter the gain and voicing and gain on the clean side.
  Not sure what the diode between -/+ inputs of that opamp do, probably conducts and clips the signal maybe compresses the clean a bit?...I'd wait and see what's said, or adjust balance to that side then pull it and see what it does, maybe try a lower threshold there for more effect of whatever that diode does.
  The LED's themselves...you could clip a twisted diode parallel across each or one of the LED's, same polarity, to see if you like the sound of harder clipping there. LED's are relatively high Vt for clipping, not sure that you'd get any clipping at all by adding seriesed diode to one or both...anyway you can diddle with the clipping elements there.
  Near the LED's are a 1k5/10uf and a 1k8/100nf, making the resistances small to none, or increasing the 100nf would cut highs at preclipping and during clipping, this might be a good place to adress the 'shrill' [I imagine the 'shrill is in the clipping section].
  the 330nf parallel to the diodes is a LP filter for the clipping, made bigger would smooth the clipping.
  R43 made bigger would shunt a bit less signal to ground right before the split.
  Also the two 100nf's between the input buffer and first OA could be made larger to let more bass through there.
  Not sure...
  If you start letting alot more bass in whether this will be too much signal for the gains the oa's would be set at.
  I would start with the LP filters, to get rid of the 'shrills', also allow more bass through input R/C by making the R and C larger values...say 47k and 100nf?..I'd keep the input C around 100nf until I had to still get more bass, then open up the next two 100nf caps to say 2x their value before making the input cap larger than the next to down the line.
    the '*LED clipping elements and *330uf cap' alterations is another thing you'll probably want to experiment with.
   If still not enough bass the 100nf's could be made bigger...if you start letting bass open up too much it could begin to sound too loose or flabby.
   I'd start with those anyway, making more bassy will make it seem less 'middy', taming HF's will certainly help trim 'shrillness', you might not feel need to alter tone control, which probably resembles a Boss OD's TC.. in topology anyway, perhaps some applicable mods could be found that way.

[Bernardduur]

Thanks man!

I'll try to experiment with these things!

[George Giblet]

I guess it depends what you want to change!

> Shame to say is that it doesn't sound as nice as the OD-3; it is too shrill, too "industrial" and I lose a lot of mid

The first thing is that ckt has a lot of gain on the overdrive path.  You could try increasing the 1k5k and 1k8 resistors on the gain stages to reduce gain.  If you increase the 1k8 arguably you need to decrease the 100n.

To re-voice the overdrive another option is play with the 100nF cap to ground on the second gain stage.

You can knock out some shrill by placing a cap from the output side of the 3k3 resisistor (following second gain stage) to ground, perhaps start around 22n.

> I also hate the fact that the clean blend is most of the time lower

That's easy to fix simply drop the value of the 820R resistor on the divider following the second gain stage.

> It cut mids, it sounds nothing like a good OD pedal. S

The mid cut is set by the 33n+22u + 2x4.7k circuit following the second gain stage.  (See note below for possible schem errors.)
To reduce the cut an keep the frequency the same try increasing the 33n by some factor then reducing the 22u by the same factor.

You can also revoice the mid cut by increase or decreasing both caps by the same factor.

> One mod
> Although I don't know what it does

It modifies the clean path only.  I'm not sure if the main motivation is to add a small amount of OD to the clean path or to change the character of the clipping of that stage.

BTW: I don't think increasing the input cap will do much.  The 2x100n + 100k is the main cause of any roll-off.  The easy fix is to increase the 100k.
------------------
Regarding the schematic I think there's a few errors.

Obvious:
- Bass and Treble EQ pots should connect to the + input of the EQ opamp
- the emitter and base are reversed on the gyrator transistor.

Speculative:
- The 22uF cap on the bridge-T should be 220n?
- the 1.5k + 820R looks a bit funny, should the 2k2 on the
  discrete opamp collector be rmeoved?
- The drain and source look reversed on the discrete opamps,
  should still work anyway

[Bernardduur]

Thanks man!

I'll check the errors; first some gigging!

[Bernardduur]

You were right; the schematic had errors;

I corrected em!

[George Giblet]

Cool.

Regarding the imbalanced balance control the 47k across the balance pot is going to make the levels biased towards the OD path.  You could add another such resistor to the clean side of the pot.  I wouldn't increase the existing 47k, that would increase the impedance to the EQ which is already too high IMHO.

[Guga Ramone]

Bringing the dead back to life... hehehe

I'm playing a lot with my Boss ODB-3 lately and a problem arose. One of my basses have a really hot output and the pedal, even with the level control on maximum, can't give me unity level. How can I mod this pedal to give more output level?

Thanks in advance.

[antonis]

Can't find a clear circuit diagram but oversizing last op-amp NFB resistor might help..
(with simultaneously undersizing the NFB cap by the same ratio, if you wish to maintain LPF cut-off frequency..)

[Rob Strand]

Bringing the dead back to life... hehehe

I'm playing a lot with my Boss ODB-3 lately and a problem arose. One of my basses have a really hot output and the pedal, even with the level control on maximum, can't give me unity level. How can I mod this pedal to give more output level?

Thanks in advance.

Do you want more gain with the blend set to clean or set to overdrive?   From what I can see the clean side has some gain already so you might need more gain on the overdrive side?

The output of the overdrive preamp has a voltage divider R18 1.5k and R19 820 ohm which limits the level of the overdrive signal.   You can up the gain about 2dB by changing R18 to 1k and R19 to 1k.   You can up the gain by about 5dB by swapping R18 to 820 ohm and R19 to 1.5k.   Personally I'd go for the 2dB boost.  Note both these mods maintain a 500 ohm impedance from the divider so it does not change the frequency response of the voicing network.

[Guga Ramone]

Rob Strand, I'm ok with the signal blend, I just need more overall output volume.

I'm gonna try that, antonis! BTW, this is the schematic I'm reading right now:



Thanks, guys!

Edit to correct image link.

[antonis]

BTW, this is the schematic I'm reading right now

Reading a long time ago deleted image is kind of mojo, isn't it..?? 

[Guga Ramone]

Oops! Image fixed. Thanks!