Simple Bluesbreaker MK I volume/gain/tone mod

[MartyMart]

This is a very nice circuit, with a good tone and seems to work best infront of a LOUD amp, some complain
about a general lack of volume and gain, so here's a couple of ideas that should work well and sound great.

Volume recovery stage :
This can be done a few ways, either by using a BJT stage like the last "Big Muff" stage, a Jfet gain stage
or with half of a second TL072 setup with a gain of X 2 or so ( which gives us something else in a minute ! )
Tack this on to the volume pot's wiper, where the circuit output to jack would be directly to the 0.1uf cap
( C10 on the GGG schem  )
If you do use a second TL072 then one half could be used as a buffer at the front of the circuit, just like Jack
Ormans "simple IC buffer"
CAVEAT : There is not enough space/ connections to use another IC in an original BB MKII but there is enough
space in the enclosure to add a simple vol recovery stage on a small piece of perf/vero either side of the footswitch !!

Gain increase :
I came across this on my DIY build by simply not having the correct resistor value ! , in place of R10 in the GGG
schem which should be a 220k, use a 270k or 330k for a slight gain increase.
What also sounds good IMO in conjunction with this is to replace one of the 1N4148's with a 3mm red LED, mine had
a forward voltage of 1.2v, so you end up with antiparallel pair of 2 x 1N4148 and 1 x 1N4148 with 1 x 3mm red LED
watch the anode and cathode when adding the LED !
You get an additional small volume increase from this and a change of sound from the asymetrical clipping arrangement
and slightly decreased onset of clipping.
You could go much further with this but IMO you will loose the essence of the BB by adding too much extra gain, it's meant
to be a quite "mild" OD, so leave it doing it's job the way it does best !

Tone change :
Several people have commented that the BB is best used with the tone control way down at 9/10 o'clock due to excess
top end.
You can roll out some of the high "hash" by using a small cap to ground after R9, such as a 2n2 to 10n , find a value that
you like the effect of with use of a socket.
Also changing the two tone caps that connect to Vref and the vol pot , C8/C9 - from 0.1uf's to 0.22uf or 0.33uf should bring
the range down enough to get more use from the tone pot's settings above 9 o'clock.
I hope this is useful to some and enjoy your new BB MK I 
Marty.

[frokost]

Regarding the gain increase mod; what does this do to the noise level? I too like the Bluesbreaker a lot, but I felt that there wasn't much to it unless the gain control is maxed. I tried to solve this with a booster in front of the circuit, but thre result of this was so much hiss that it became hard to use with the gain control set at much more than it's minium  .

Thanks for the info!

[John Lyons]

Thanks Marty.
I was planing a BB build so these notes will come in handy.

John

[frankclarke]

Marshall completely changed the tone stack on the BB2, looks like it might be louder: http://thebin.free.fr/FSTBX/bb2.pdf

[MartyMart]

frokost :
It's a slight increase and doesn't add any additional noise at all, the circuit has a good "voice" of it's own
so I dont advise that you try and make it into a Dist+ or something, just built one for a more heavy gain
sound.

John : No problem, I have not done all these changes so I hope the ideas will work out fine !

Frank : Thanks, I hadn't seen the BBII schem before, it looks like quite a different beast , I still find these
original "black box" Marshall pedals to be better than the new stuff in general.

[frokost]

Thanks, Marty. One day I'll have to open it up again. I tried the booster idea so that I could get a bit more useful range from the gain pot, but it was somewhat unsuccesful. I tried to put a MOSFET booster in front of an original Bluesbreaker just to see if it was the combination of Boost -> BB that was noisy or if it was something with my layout. It wasn't my layout.... So if your way leads to less noise, I'll have to try it because, as you say, this thing has a nice voice of it's own. Great pedal!

[Michael Weidenauer]

My favourite mod to the BB 1 is a bass boost switch that adds a 22nF-cap in parallel to the input cap and one 10nF-cap in parallel to the 10nF that connects the 27k resistor(from OA-pin2) to ground. This opens up the bottom and also gives a slight increase in gain and will cure the problems with too pronounced treble.
Now you will be closer to a boogie-style sound.

If the pedal now sounds to scooped for you and you want back Marshall midrange again then put a 10nF-cap in parallel to the cap that connects the 33k resistor to the 27k.

Another Tip: Using good film-caps in this circuit really lowers the intermodulation-distortion that to the original units suffered from in their highest gain settings.

A recomended build for everyone,
Michael

[Gus]

or you could reduce the resistor values between the gain stages and maybe change the cap size to move the highpass

note the way the gain control adjusts the gain in both sections
If one does not want the stock mute function connecting the center of the 4.7Ks to ground one can make both the .22uf one cap and both the 4.7Ks one resistor

stock 9.4K .11uf

1/2piRC

4.7K .22uf

At 9V power supply a tl072 should have no problem driving 4.7K