Diodes to Ground with Cap Question

[WGTP]

In the standard Distortion +/ Rat, etc. what happens when a Cap is placed between the diodes and ground?  I'm sure the value of the cap will determine which frequencies are effected, but let's say the bottom 2 octaves.  I'm thinking the lows will get clipped less, but does it "boost" the lows volume???  In other words, could this be used for a bass boost effect???   

[Mark Hammer]

Imagine you had a large value pot (hmmm, say 1M) to ground between the diodes and ground.  Why should the signal clip/clamp under these circumstances?  At the same time, why should it be attenuated?

Placing a cap between diodes and ground is a bit like sticking in a large value pot whose value gets smaller the higher up the frequency is.

The question is, what happens to those different frequencies?

Keep in mind that although in an abstract sense, high frequencies are lower amplitude, hence generally well below the clipping threshold of those diodes anyways, they are still sitting ON TOP OF lower frequency AC.  So, imagine I had a large amplitude 0.1hz component.  Any HF component sitting on top of that would be below clipping threshold at some points, and present an amplitude peak well above clipping threshold at other points.

Consequently, my hunch is that there would be preferential, but inconsistent clipping of mids and highs.

[petemoore]

  I think I ended up with a .22uf for a subtle yet noticable increased definition/volume level of lows..not clipped.
  Careful selection of what's going into the diodes and the cap value btw them and Gnd. so that there is a small 'overlap' of freq's let in to freq's clipped [less than subtle setup may provide more clean bass than you want]...adjustments to values and dials all influence this mod, it took careful setup to get where I liked it.

[Caferacernoc]

I agree, I've experimented with the same thing. It works, but you need to choose the cap value carefully or it will sound weird.

[gez]

Reply No 6:

http://www.diystompboxes.com/smfforum/index.php?topic=10754.0

[WGTP]

Thanks for the quick responses.  I tried it last night with the last clipping stage of a dual op amp clipper and it worked very well.  I didn't have time to fine tune, but it definitely increases bass response and since there are previous clipping stages, the bass doesn't get cleaned up too much. 

I also tried using  a cap in the feedback loop, without a resistor.  6db/oct. bass boost to balance the pre-distortion bass reduction. 

I guess one thing that distinguishes different distortions is the amount of distortion that occures at different frequencies.  Given the same overall EQ balance at the end, varying amounts of distortion can occur in the bass/mids/highs, etc. 

To me, the bass has plenty of sustain without lots of distortion, but the highs need some help.  I don't want ice pick treble though. 

Anyway, nice way to get some bass back, without having to use an active filter or 4 part notch filter.   

[Steben]

Yes looks like a solution for the midhump problem of pre bass cut and post treble cut in many OD's. Tried to implement this too. This way you clip more natural Freq's but leave the bass alone. Maybe worth while in a feedback clipper too? Or mod you BMP by decreasing those caps in series with the diodes which is the same idea.

[MartyMart]

How difficult would this be :
Freq splitter, so everything under say 150 Hz stays clean and the rest goes
through the feedback loop etc, gets distorted and joins back with the low end
afterwards  ??
Two paths and two opamps should do ....  !  "Blend pot" with a dual gang perhaps
A nice "full range" sound with only mids/highs crunched  ?

Marty.

[Steben]

150hz is still too low. Will leave some mud out, but won't do the job.
450hz is better. It's the frequency I like Tube screamers to aim at instead of 720.

[WGTP]

Reading the John Simonton thread, I once again looked that the Quadra Fuzz which splits the sound spectrum into 4 seperate clipping stages "bands" and provides for varying amounds of distortion and volume for each.  Cool idea using a TS type distortion w/LED's circuit for each stage.  You could mod it to use a different clipping stage for each "band".  Diodes in loop, diodes to ground, symmetrical/asym etc. 

May have to try a 2 band version as suggested.  450Hz sounds like a good frequency to start with.  TS for Highs and Dist.+ for Lows.   

[H S]

The Blackbox Ultraviolet has three parallel bands of distortion.

A couple years ago I built a diodes-to-ground fuzz with a cap and an inductor in series with the clipping diodes.  I don't have the information with me about the values, but I think the midpoint was about 1.3kHz.  It had a scooped-mids metal sound.  At the time, I concluded that I could get close to the same sound with a Boss Metal Zone MT-2, the one with the three-band EQ.

[MartyMart]

Reading the John Simonton thread, I once again looked that the Quadra Fuzz which splits the sound spectrum into 4 seperate clipping stages "bands" and provides for varying amounds of distortion and volume for each.  Cool idea using a TS type distortion w/LED's circuit for each stage.  You could mod it to use a different clipping stage for each "band".  Diodes in loop, diodes to ground, symmetrical/asym etc. 

May have to try a 2 band version as suggested.  450Hz sounds like a good frequency to start with.  TS for Highs and Dist.+ for Lows.   

WOOAH MOMA  that is a BIG circuit ... !!
I think two bands will do 
WGTP .... any "tips" here ??

Marty.

[RickL]

I built a Quadra Fuzz a while ago expecting exactly what you describe - being able to adjust the amount of clipping and volume on each frequency band - but my results were disappointing. I expected to be able to get, for instance, clean bass, heavily distorted mids and lightly distorted highs but what I got was a fuzz with a four-band tone contol.

It's been a while (more than a year, maybe two) since I've played with it so my memories may be faultly but my general impression was that while it sounded okay, it wasn't worth the bother of the huge build. If someone else has had dramatically different results it would encourage me to dig mine out and re-evaluate it and check to see it I had a working, but not working quite correctly unit.

I used a hand drawn layout that I found somewhere on the net. Good luck finding it, but if you do I seem to recall that the wiring on one of the regulators was incorrect. Also, in case you're not aware, PAiA sells a kit for it.

[gez]

450hz is better. It's the frequency I like Tube screamers to aim at instead of 720.

Same here (to my ears).

[Steben]

Of course there is always the possibility of clean and distorted in parallel each with a decent tone control. It even doesn't have to be just one stompbox. MOSfet boost with tone control in parallel with TS (at 450Hz ) to a mixer for example.

[brett]

Hi.

450hz is better. It's the frequency I like Tube screamers to aim at instead of 720.

Ah yes, grasshopper, there's a reason why 440 Hz is called *middle* A.
It's also a nice area to base a truly gutsy solos.  Think of how many times Jimi played in that area (e.g. purple haze intro and hey joe solo).
cheers

[Steben]

grasshopper?

[JimRayden]

Hmm, imagine a "Frequency Divider And Mixer Box", or shortly, the FreqDAMB.

The guitar signal comes in, it gets divided into octave-wide bands. Plus the two bands that are "X and lower" and "Y and higher". Each octave has it's own output jack and input jack, for external effects loops. Then you have a volume control for each section, and a master volume.

That would become a fairly large project, but would yield some interesting results. Of course, if octaves are not enough, you can have lots of more and tighter bands. What about an effects loop for every friggin' note on the fretboard. 

----------
Jimbo

[WGTP]

I haven't tried the Quadra-Fuzz, but the review above seems to be the common result.  It may be that filtering of the seperate "bands" needs to be sharper/higher Q.  I haven't messed with 2 bands yet, but that is in the works. 

Haven't seen or thought of using an inductor/cap notch filter for the diodes, cool idea.   

R.G. and others have advocated that  octive EQ before and after the clipping stage has a very significant effect, maybe more so than the clipping stage.  I think they are right.  I might need to focus more on EQ's, but they aren't as sexy.   

It occured to me that using both an non-inverting and inverting op amp to blend would result in them being out of phase.  So if the lows on one were rolled off and the highs on the other, you would get a NOTCH where the to come together, due to the out of phase situation.  Hmmm.  Might also get a bunch of undesireable noise too...

I have been pleasantly suprised by the effect of using a cap to ground between LED's in the last clipping stage.  Seems to add a "tube ampish" quality to it.  The standard practice of rolling off the lows thru the clipping stage to smooth things out, leaves the bass under represented and the Cap mod boosts it back leaving the bass with less distortion than the highs and mids. (seems to be the way larger amps seem to work)   

I can see how it might be less effective with a single clipping stage.