GGG MXR Envelope Filter BASS mods? Mark Hammer? Anyone?

[boogietube]

Are there any bass mods for the MXR Envelope Filter project at GGG? I am building this for my bassist. I am building the mods version. I suspect that the range mod would lower the operating frequency range. Is this enough for the effect to be used by my bassist? I will eventually be using a paralooper to blend the effect in if this makes any difference.
The reason that I specifically asked for Mark Hammer is because I've read lots of his posts here and on other sites and he seems to have this knowledge of a electronics demi-god.
Thanks for anyone who helps out!!!
Sean Harris

[boogietube]

Come on guys? Too simple for ya? Please help?
Sean

[Bernardduur]

The range mod will raise the frequency range; I guess when you double the value of the filter caps it gets in the region of a bass.

[Mark Hammer]

No deification, please.  Management doesn't allow it.

You are correct in mentioning the range shift and corresponding caps.  The Envelope Filter already has a somewhat bass-friendly range, but I imagine it wouldn't hurt to make those default 1000pf cap in the filter sections 1500pf or maybe even 1800pf instead.

The other thing to consider is that, while the EF has a nice range of attack times, bassists generally want a faster decay than guitarists do because they are not going to use the pedal to filter a strummed and sustained chord.  In which case, if you are building from Francisco Pena's recently updated "A-Gua" layout OR JD's layout at GGG, you will likely want to alter the value of R17 from its current value of 1M.  C9 and R17 set the speed of the upsweep and downsweep.  Making R17 smaller in value will accelerate the speed with which the filter returns to the starting point.  I'm going to suggest that a 390k-470k fixed resistor in series with a 500k pot (or trimpot if you find something you're happy with) will let you get a range of decay speeds that will make your bass sound more "punctate" (i.e., a quick on and off event).

Finally, bass canput out some whomping signal levels, making it sometimes difficult to dial in just the right sensitivity/threshold setting.  Consider changing the Threshold pot from a 500k unit to a 1M unit so that you can cope better with higher amplitude input signals.

[boogietube]

Thanks fellows!!
Mark - sorry for the embarrasment - NOT!!
I've read so many of your posts and they are both insightful and comprehensive.
After I have wired this up I will give all of your suggestions a try one at a time. I'll post comments on them for the benefit of you and maybe other bassists on the forum.
Thanks Again!!
Sean

[boogietube]

Jeepers !!! I just realised that you live in Ottawa, Ontario. Holy crap!!
So do I!!
Small world.
My band is called The MoonMovement in case you get out.

www.themoonmovement.com

Sean

[Mark Hammer]

Neat!  I don't get out much, but we'll have to convene this summer.  There are a bunch of us here.

I'm kind of tied up for the next month with personal and work stuff but certainly later in June is a go.  I have a couple of A-Guas you can compare yours to.  Glad to be of assistance.

[ReCoC]

Hello everybody. I've built the mxr EF from GGG for my bass. I have to questions:

You are correct in mentioning the range shift and corresponding caps.  The Envelope Filter already has a somewhat bass-friendly range, but I imagine it wouldn't hurt to make those default 1000pf cap in the filter sections 1500pf or maybe even 1800pf instead.

1. Because i'm not very keen of electronics, which is the filter section. Which one is the cap i have to change?

2. My filtered signal is dropped compared to the bypassed one. What can I do about that?

[ReCoC]

Anybody??

[Pushtone]

The build reports on the Tonepad.com MXR EF page might be helpful for you both.

Everything in the Tonepad reports applies to the GGG versions.
From what I can tell all resistors and caps are numbered the same in both versions.

From those build reports the part substitutions that address the loss of bass and level are...
R1-1k
R2-100k
R16-62k
C2-1uF
C4-0.01uF

Made the changes to my GGG MRX EF build and it sounds much better.
Before it lost a little level and sounded thinner than the bypass signal.

Read the TP reports for the GGG project.

[Mark Hammer]

Hello everybody. I've built the mxr EF from GGG for my bass. I have to questions:

You are correct in mentioning the range shift and corresponding caps.  The Envelope Filter already has a somewhat bass-friendly range, but I imagine it wouldn't hurt to make those default 1000pf cap in the filter sections 1500pf or maybe even 1800pf instead.

1. Because i'm not very keen of electronics, which is the filter section. Which one is the cap i have to change?

2. My filtered signal is dropped compared to the bypassed one. What can I do about that?

C6 and C7 are the two caps that set the filter range.

R1 (3k6) and R2 (200k) work like a sort of volume pot to slightly reduce the output level.  Drop R1 to 3k3 and raise R2 to 220k and that will give a little more level.  It'll probably reduce headaches too since 3k6 and 200k are not the most common resistor values out there.

[ReCoC]

sorry to bother again but I've got so many different anwers and i don't know which one to try.
If I install a booster in line with the EF will it work ok? Should I put it before or after the filter?

[Mark Hammer]

A little bit of boost before the EF is not essential but can be useful.  Keep in mind that you want the sort of input level to the EF that will permit a large portion of the "Threshold" (sensitivity) pot's range to be useful to you.  If the input is too low then only the 4:00-5:00 portion will be useful, and if the input is too hot, then only the 7:00-8:00 portion will be useful.  A modest bit of boost (e.g., gain of 3-5) might make the unit more responsive to your playing style, and improve the S/N ratio a bit.  Just don't go crazy with the boost or it will misbehave.

[ReCoC]

so you suggest that i put a booster (eg LPB1 from tonepad) before the EF input. Where exactly? Before C3 cap? wouldn't it be better if i put at the output with a pot to control the overall output level? After R1 for example?

[Mark Hammer]

Presumably, any boost in signal level applied at the input will show up at the output.  Remember that this is not like a Distortion+ where the clipping diodes limit how much volume there can be regardless of input boost.  In this instance, if the input is louder, the output will be louder.  Since the EF circuit itself is capable of producing/adding some hiss, best S/N ratio will be achieved by sticking a bit of clean gain up front, rather than at the output where it will simply boost the acquired hiss. 

This principle is true of just about ANY pedal.  The only cases where post-boost makes sense is when the effect results in a serious reduction in output level and you need to compensate by bringing the level back up again.  Obvious cases are those where some sort of passive tone circuit is used that results in considerable passive loss (e.g., Big Muff) or where germanium clipping diodes to ground seriously reduce signal level in service of distortion.  Other instances would include those where the effect produces signal loss but clean performance can only be achieved by feeding the circuit modest input signals.  Other than those and some other obscure circumstances, your default strategy should always be to stick your gain at the input.

[ReCoC]

ok. Help me with one more thing please...
I'm gonna build an LPB1 from tonepad and put it before the filter. Well my thoughts are:
To build it without an input and output capacitor and stick it after C3 of the MXR. Is this right? Will it work?
Also if I don't use the input capacitor shall I leave the 2M2 resistor or dismiss it?
As I mentioned this pedal is for bass. So if I change the C3 of the MXR to 0.47uF is it going to be better?

[Mark Hammer]

1) If you are going to stick a booster in there, then why not do the "smart thing" and install a DPDT toggle for bypassing the filter so you can use the main stompswitch to get you either a straight booster OR a booster+filter?

2) If you think #1 is a sensible thing to do then the following is probably also sensible:

• build the booster as if it were a wholly different effect in series with the filter
• leave the 2M2 resistor on the LPB-1 in place to avoid popping
• increase the 390R resistor in the LPB-1 a bit (say 470R) to reduce the gain since it will be too easy to overdrive the filter into "frozen sweep" (getting stuck at the extreme of the sweep range)
• leave C3 in place to decouple the booster's output from the input resistors on the filter
• increase the 500k Threshold pot on the filter to 1meg so you can use a boost without "sweep freeze" - you will still be able to dial in sweep with unboosted inputs

[ReCoC]

1) If you are going to stick a booster in there, then why not do the "smart thing" and install a DPDT toggle for bypassing the filter so you can use the main stompswitch to get you either a straight booster OR a booster+filter?

That's a really good idea but i dont want to do this. I'm really bored with this project and i want to get over with it! I'm thinking of using them together.
I'll just try the rest you said....
thanks....

[Mark Hammer]

Then just get it working but make sure you leave a space in the chassis in case you want to stick a toggle in later on.  "Space" means not only panel space between existing controls, but panel space where the toggle won't bump into other things under it inside the box.

[ReCoC]

Then just get it working but make sure you leave a space in the chassis in case you want to stick a toggle in later on.  "Space" means not only panel space between existing controls, but panel space where the toggle won't bump into other things under it inside the box.

I've got it working today and it works great! I've got a problem though with the new mod! The decay pot you suggested! I just don't see any difference. I want to try to lower R17 to 300k and put a 1M pot. What do you think?
Oh about the space... I don't think I have to worry about that because the box is kind of huge!