BluesBreaker Resistors, which prefered?

[Nick C.]

See http://www.generalguitargadgets.com/pdf/ggg_mbb_sc1.pdf

I've been searching all over to make sense of the feedback resistors R2 and R3 in the BluesBreaker circuit. Why did Marshall change from 27k, 33k to 4k7, 3k3? Or was it the other way around. Seems to me that the bigger resistors would give much less gain and much more bass. Big changes. Am I correct on this? Which setup is preferred?

Please no try them both and see what you like answers

Thanks

Nick

[jayp5150]

I'm still learning the role of what's what, but it appears that those are not functioning as feedback resistors, but rather to form filters for tone-shaping.

However, I may be way off (but that's why I'm here lol, to learn).

[Nick C.]

They are part of the divided negative feedback circuit that sets the gain of the 1st opamp and creates a r-c high pass filter.

Here's an excellent link

http://gaussmarkov.net/wordpress/parts/op-amps/op-amps-4-divided-negative-feedback/

[jayp5150]

See? I learned something. 

I guess I just saw the resistor with a cap to ground, and that's the first thing I thought of.

Thanks for the link.

[Nick C.]

I had the BB bread boarded with the smaller resistors and tried the big resistors last night. While there is some differences they are small and both set ups are good.

Big resistors=
-less distortion but smoother and good for blues and even gives a nice rock OD when maxed.
-more low end but still not that much

Small resistors=
-more range of distortion, clearer, but somewhat harsher
-bright clear highs, even less low end

Both suffer from lowish volume due to the diodes and filtering with no recovery, but I can live with it.

Now that you have my opinions, what's yours? Which one separates the collector from his money?

[LHC]

See http://www.generalguitargadgets.com/pdf/ggg_mbb_sc1.pdf

I've been searching all over to make sense of the feedback resistors R2 and R3 in the BluesBreaker circuit. Why did Marshall change from 27k, 33k to 4k7, 3k3? Or was it the other way around. Seems to me that the bigger resistors would give much less gain and much more bass. Big changes. Am I correct on this? Which setup is preferred?

Please no try them both and see what you like answers

Thanks

Nick

Hi,

my first post here, because I'd like to answer and asked a similar question in a german diy-forum recently.
I experimented with the values of the several schematics I found on the net and you can see, which I like the best, in my schematic:

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/icebreaker.png.html

Please note the additional resistor R4 - 10k.
Somewhere I read, the first Bluesbreaker from '91-'92 had these values ...

R2 - 4k7
R3 - 3k3
C4 - 47pF

... and from '92 -'94 these:

R2 - 27k
R3 - 33k
C4 - 10pF

Whether the C4 was 10pF in later bluesbreakers, as commented on your GGG-schem, or just a typo and should mean 100pF - I don't know.  But 10pF was way too bright for me in that position and is mostly 100pF in similar schematics. It would be nice, if someone could clarify this.

Because the vintage version with the small resistors was too harsh and low gain to me with a strat, I changed the values in the vintage BB to 

R2 - 27k
R3 - 33k
C4 - 100pF
R4 - 10k (additional)

It is my favorite overdrive since then.

Greetings.

[Nick C.]

LHC- thanks for the reply. This is interesting, the small resistors were original. I've been leaning to go that way as it works a little better with my setup. With the bigger resistors I felt that it was a little too similar to my modified sd1 which is very close to a Tube Screamer with more lows. I've seen a lot of reviews where people call it a very "amp like" pedal. I don't know about that, but it's a good low distortion pedal.

[StephenGiles]

But I think you should have used 1/4% resistors