Need help with Mark Hammer's ggg EF440 bass mod.

[bigandtall]

I just got a ggg EF440 clone and I'm not wild about how it sounds on bass. It's just too subtle and sucks out all of the bass from the signal. The person I bought it from (part of a package deal) already did the mod where he changed C6 and C7 from .022uf to .1uf. I checked under the hood to confirm this.

Anyway, on the ggg page is Mark's suggestion for making this pedal more bass-worthy and I'd just like to see if someone can clarify this for me:
http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=119&Itemid=26

4) If you want to use if with bass, stick a small-to-medium value (say, 10k) resistor in series after C8, and run another similar-value resistor from the R1/R2 junction to the free end of the resistor after C8. Now run a 100k terminating resistor to ground. That will mix in some straight signal with the swept filter so you don't lose bottom during the sweep. Note that since the dry signal is tapped before processing, and since the filter build around IC1B is inverting, the filter will be subtracted from the dry signal at the output, yielding a swept notch. Very funky in its own right. You may have to tinker with mixing resistor values to get a decent balance or simply stick in a trimpot and tweak.

Here's my interpretation of what he's saying: solder in a 10K resistor after C8 and wire that to a resister that you wire between R1 and R2. He says to connect it at the "junction" and I'm not sure what that means. Do I solder it to the trace on the PCB, or just make my own connection by soldering in the resistor? Also, the end of C8 connected to the signal out from the PCB. If I just have a resistor in series connected to the junction, how does the signal ever get out of the PCB? Should I be connecting it to an out somehow?

Thanks for any help: here's the ggg layout:

http://www.generalguitargadgets.com/pdf/ggg_ef440_lo.pdf

[Mark Hammer]

1) For "unpopping" purposes, the unit needs a terminating resistor to ground anyways, so let's go with 100k.

2) What I suggested was to simply blend the unprocessed signal and filter signal at a "mixing node".  You will stilll have an output.  This just bumps that output over by a single solder joint.

3) If you are able to drill a small hole in the populated board without damaging anything, here's what to do:

• unsolder the output lead from point "O"
• drill a small hole just to the right of point "O"
• install a 10k resistor, vertically (i.e., pointing up with one lead bent right over) between point "O" and the new hole
• solder a 100k resistor from the lead poking out through the new hole to the nearest ground point; slip some wire insulation or shrink tubng over the exposed lead so the resistor doesn't short out against anything
• solder a 10k resistor from anywhere along the trace between R1 and R2 (lots of space there) to the lead sticking out of the new hole, takiong the same protective steps to insulate the exposed leads of the added resistor
• reconnect your output wire to this new junction ot 3 resistors poking out of the new hole

There are obviously neater and messier ways to do this, so you may very well find yourself doing it once, deciding it is too bulky, desoldering and resoldering more neatly.  You can use 1/4w resistors but may find that it ends up neater and fitting your existing space by using 1/8w resistors.

[bigandtall]

Mark,
That clears it up for me. Thanks for responding and giving me the proper terms so that I can look everything up.

Are there any other mods that you would recommend to make this pedal sound better on bass? I'm not sure why, but nobody seems to suggest changing the input and ouput caps. Is there a reason for this?

[Mark Hammer]

In the vast majority of cases, input and output caps provide more than enough bandwidth.  It's really only a few cases, and principally discrete fuzzes, where input and output cap values are chosen to restrict low end so as to elicit a different sort of behaviour from the circuit.  Keep in mind that when a pedal is produced by a larger company, they tend to think in terms of the entire signal chain.  So, if the user is going to be running our booster into our fuzz into our filter into our chorus, how do we assure that at the end of it they have all the bandwidth they need?  That's why you'll see most pedals having a bass rolloff at the input somewhere not too far above DC (e.g., 4hz).  It's in anticipation of the cumulative effect of having 10 pedals in a row with a 1/2db rolloff at 40hz or whatever.

Reading over what is posted at GGG, I think that pretty much covers what might make it more effectively suited to bass.  There are really only 4 things to concern oneself with:
1) Is the range of sweep appropriate for the instrument?
2) Is the sensitivity appropriate to the source's typical level?
3) Is there any risk of momentary loss of critical information? (one of the reasons why so many bass players prefer a filter that can either blend in clean or else is a lowpass that will not lose bass content)
4) Do the adjustments available allow suitable "dialability"?

The comments of mine that are posted on GGG cover all that.  I suppose the only thing I would add to it is that bass likes a faster decay than guitar does.

[bigandtall]

Thanks Mark. That clears it all up. I'm working on a bass paralooper that will blend in a clean signal to all of my effects. Hopefully, that will make everything sound better in the end.

[bigandtall]

Finally did this mod and I'm getting a lower signal coming through without any auotwah on it 

When I have more time, I'll have to go through it all again and make sure I did it right... though I think I did. Not sure if I shorted something out along the way.

[Mark Hammer]

Now that you mention it, you should expect  a bit of volume drop, since the way in which clean and filter are being combined, will result in a swept notch.  This was a really dumb suggestion on my part.  My apologies for directing you to it without thinking it through.

If it were the case that the clean signal (or filter, for that matter) was inverted by an additional op-amp stage prior to blending, then you'd get a wah superimposed on top of additional clean signal above and below the passband.

Just out of curiosity, how does the swept notch sound?

[bigandtall]

It actually sounds fairly clean... just at a much lower volume.

Would you suggest that I just put everything back to how it was and focus on building my blend pedal?

[bigandtall]

No worries for the misdirection either... just trying to get a hang of the whole mod thing. Maybe someday I'll spot these kinds of things ahead of time.

[bigandtall]

I double checked and there is a little bit of funky notched sound if you turn the range all the way up. I'm not sure that the volume drop is worth it, though.