Twenty-Two Sevenths - Wow!

[tcobretti]

I built it using Gaussmarkov's layout.  I used 220p caps in the feedback loops, and I used 22n caps in the tone stack because I have never liked the stock tone stack.  The layout I used has both the gain switch and the scoop switch built into it.  A while back I was modding my Russian BMP when it died altogether, and I didn't like it enough to figure out what went wrong.  So, I used the enclosure and pots from it for the 22/7.

Disclaimer: I've never been a fan of the BMP.  It's a little too tame for my tastes.  I like unruly fuzz that erupts out of the speakers, and the BMP has never come close to the other fuzz classics IMO.

I really like this pedal.  It has a nastiness that separates it from the BMP.  It reminds me a little of my Tone Bender Mk II, but with way more gain.  Speaking of which, it has a ton of gain and mine would oscillate if both the gain and volume knobs were anywhere close to maxed out.  I'm not sure how necessary the extra gain switch is; on mine it didn't affect the tone all that much but it did raise the noise floor substantially and contributed to the oscillation.  Speaking of which, mine is pretty freaking noisy.  Not only hiss, but mid freq noise.  I have a hunch that the larger caps I used in the feedback loops are contributing to the noise.  The tone knob worked much as I intended, but the scoop switch didn't do as much as I expected, which I figure is probly because of the different caps I used in the tone stack.  That said, it does have an effect on the tone and makes the tone knob a bit more flexible.

This is a great pedal.  Anybody who likes fuzz needs to try it out, even if you aren't a big fan of the BMP.  Yun definitely needs to build one and try out all his crazy mods.  Yun: I'm pretty sure this thing is right up your alley.

I'll try to post sound clips, but it may be a few days from now.

STM, thanks for another great pedal, and thanks Gauss for the layout!

[Meanderthal]

I've never been a fan of the BMP.  It's a little too tame for my tastes.  I like unruly fuzz that erupts out of the speakers

OMG! If you're serious, this thing must be absolutely lethal! Because the BMP is certainly a rip-snorter that could be described as an unruly fuzz that erupts from the speaker! 'Course, they're all different...

Sounds like a REALLY good one! Gonna have to go on The List...

[gaussmarkov]

sweet.   

[tcobretti]

I've spent some time with 3 different BMPs: 70s transistor based, 90s Black Russian, and the new Little Big Muff.  Of these, the LBM was my favorite, but they all are a little too smooth and refined for my tastes.

With the 22/7, if I crank the tone knob all the way it reminds me of the Orpheum Fuzz.  It's not quite as nasty, but it's definitely a good 60s fuzz sound.

The only BMP I haven't checked out is the Opamp, and I'm thinking about practicing my PCB layout skills on that one.

[stm]

I used 220p caps in the feedback loops, and I used 22n caps in the tone stack because I have never liked the stock tone stack.

Do you mean you replaced BOTH tonestack caps with 22n?  Did you maintain the values of the resistors?
In this case the resulting tonestack is way different and it is to be expected that the extra 33n cap which turned the original tonestack into the Swollen Pickle tonestack will have little effect.

The layout I used has both the gain switch and the scoop switch built into it.

There is a single switch for the tonestack. Its second pole is connected to compensate the gain when the swollen pickle mode is enabled since its aparent volume is a bit less.  It is just a refinement and you can live without it, since you can compensate the slight gain difference with the LEVEL control. The wiring of these two switches is such that when one half is open the other is closed.

Speaking of which, it has a ton of gain and mine would oscillate if both the gain and volume knobs were anywhere close to maxed out.  I'm not sure how necessary the extra gain switch is; on mine it didn't affect the tone all that much but it did raise the noise floor substantially and contributed to the oscillation.  Speaking of which, mine is pretty freaking noisy.  Not only hiss, but mid freq noise.

You should resort to the gain resistors used in the first version of the 22/7: a 100k input resistor with a 1Meg resistor in the feedback loop in the first amp stage. This works better and it is simpler.

[tcobretti]

I did use 2 22n caps in the tone stack.  In the Duncan Tone Stack sim it seemed like it smoothed out the scooped curve of the normal BMP tone stack.  Do you have a recommendation for a more appropriate cap value for the scoop switch? 

Thanks for the help with the switchology, I'll mess with that tonight.

I'll try the 100k input resistor and see if it helps with the noise.  That said, I don't mind it like it is.  It's still usable.

Thanks again!

[gaussmarkov]

The layout I used has both the gain switch and the scoop switch built into it.

There is a single switch for the tonestack. Its second pole is connected to compensate the gain when the swollen pickle mode is enabled since its aparent volume is a bit less.  It is just a refinement and you can live without it, since you can compensate the slight gain difference with the LEVEL control. The wiring of these two switches is such that when one half is open the other is closed.

sorry, i am confused.  in the rev. 1.3, there is a simple switch for the "CLASSIC SCOOP" and rev 1.2 had a different gain section.  so i put in a second simple switch in my layout for the two versions of gain.  where is the two-pole-switch version of the twenty-two sevenths?

cheers, gm

[stm]

I did use 2 22n caps in the tone stack.  In the Duncan Tone Stack sim it seemed like it smoothed out the scooped curve of the normal BMP tone stack.  Do you have a recommendation for a more appropriate cap value for the scoop switch? 

OK, now I understand what you're after.  The original BMP tonestack has a moderate notch (-7dB) around 1 kHz.  The Swollen Pickle has a deep notch (-17dB) around 500 Hz, giving a heavy metal characteristic to the sound.  Your mod flattens the notch for a more balanced fuzz sound.  

There is a simple way of having these three responses simultaneously, if you like, or you can just leave whatever works best for you.  Currently switching in the 33n cap changes from the original to the swollen pickle response.  If instead of switching in the 33n in parallel to the 10n cap you switch a 6n8 cap in parallel with the 3n3 cap you'll have essentially flat response and the TONE will simply alter the balance between bass and treble.

So, you can implement three responses simultaneously by simply using a DPDT switch with three positions (center off).  One pole will be used to add the 33n cap in parallel with the 10n on one side, while the other pole switches the 6n8 cap in parallel with the 3n3 cap on the other extreme.  Center switch position will give the stock BMP response.  Hope this makes sense.

I'll try the 100k input resistor and see if it helps with the noise.  That said, I don't mind it like it is.  It's still usable.

Remember that the 100k input resistor goes along with the 1M feedback resistor and 150p (or 220p) feedback cap.

Thanks again!

You are most welcome.

[stm]

sorry, i am confused.  in the rev. 1.3, there is a simple switch for the "CLASSIC SCOOP" and rev 1.2 had a different gain section.  so i put in a second simple switch in my layout for the two versions of gain.  where is the two-pole-switch version of the twenty-two sevenths?

cheers, gm

Hi GM, sorry there is such a confusion.  The dual pole CLASSIC/SCOOP switch was introduced in rev 1.4.  The input stages have experimented changes also within different revisions.

Please keep in mind that the 22/7 was designed and tested in a rush for September's FX-X.  After the rush, it became another ROG project under development and it has experimented several changes due to the creative process that takes place when doing our usual teamwork to polish a circuit until we are satisfied with it for release. You can see the different revisions as snapshots of the creative process in action.  All revisions are worthy (as far as I know none of them is buggy), however there are some differences in gain, capacitors and overall response.

The final development of the 22/7 got postponded a couple of times when we started working in Thor and then in Omega.  We are currently working on the 22/7 again in order to make an official release, however it may take some weeks until it's ready.  At this time I'd say rev 1.2 is a safe and nice version to build--consider it a sneak preview.  From there, you can try to increase the interstage coupling capacitors to taste and adjust the feedback filter caps, which is where most of the tuning is to be expected.  Also, my previous post about a third option for the tonestack opens another area for investigation.

Cheers.

[gaussmarkov]

sorry, i am confused.  in the rev. 1.3, there is a simple switch for the "CLASSIC SCOOP" and rev 1.2 had a different gain section.  so i put in a second simple switch in my layout for the two versions of gain.  where is the two-pole-switch version of the twenty-two sevenths?

cheers, gm

Hi GM, sorry there is such a confusion.  The dual pole CLASSIC/SCOOP switch was introduced in rev 1.4.  The input stages have experimented changes also within different revisions.

thanks, stm.  no worries!  i will take care to mark the layout that i made as a rev. 1.2/1.3 and to note that it is not ROG work-in-progress.  if there's any confusion, it is mine. 

cheers, gm

[tcobretti]

The tone switch idea is great.  That seems like a good mod for every BMP.