Double D Bounce and 4049 "tuning"

[Matt505]

Hello,
Thanks to all the good info/folks here, I've waded into fx building and am having a blast!
For the latest, I was looking for a good distortion pedal that stays "smooth", without the "fizziness" a lot of hi gain pedals seem to have. The sound clip I heard for the "Bounce" channel for ROG's Double D really sounded good, so I breadboarded it up, and hot damn! This thing cooks!
Now, not that I'm unhappy with the sound, but I'd like to understand the circuit a bit more, so I have a couple questions:

1) With the gain at 0, there is still a considerable amount of crunch (which also sounds great!). Is this from the input stage JFET? I just went with a 10k drain resistor instead of the 50k trimpot, b/c that's what I saw on the layout pic. I think I was getting about 4.4V there, I'd always heard ~1/2 supply voltage is what you want, so left it as is, without understanding "why". So if I wanted the gain knob to allow for more cleans, do I increase the drain resistor to lower the JFET gain?

2) The Double D description says:
Caps were used over the inverters to mellow the clipping out. We've implemented Mark Hammer's suggestion of rolling the treble back more in earlier clipping stages and less in subsequent ones. This helped bring out the amp-like sounds and removed the harsh, "fizzy" high end of the bare circuit.
Again, not that I'm unhappy with the sound, but if I wanted to accentuate more T,M, or B, how would I go about modifying those feedback caps/resistors? I just would like to understand the 4049 "voicing" approach.

Thanks!
Matt

[esdiezy28]

Nice questions Matt! I've been looking over several hex inverter based circuits since I got my 4049UBE's in about a month ago.

To Question #1 with a 10k Drain Resistor yes, you are getting some crunch. Some general numbers for this include a ratio between the Drain Resistor and the Source Resistor. Take a look at the Fetzer Valve on http://www.runoffgroove.com/fetzervalve.html. This will explain calculating the gain of a FET. And I think with a J201 your voltage at Drain can be from 4.5-7V. Try increasing your source resistor on the FET to 1k and have the bypass capacitor on the source with a switch to toggle on and off.

To Question #2, I'm not as informed about this but I think your gain stages in the 4049 are forming a filter, I think a low pass seeing as it rolls out your high frequencies, right? Then here with the math   Frequncy= 1/[6.28 X (x)Mohms X (y)uF]        That is frequency is equal to one divided by two pi (i subbed in 6.28) times resistance in Mega Ohms times capacitance in micro Farads. I have no idea how to attenuate the frequencies for bass, treble, or mid. Only seems like you can roll out more or less high frequency by changing your capacitor size, but don't quote me on that, I just don't know how to do that.

Hope I've helped some! Best of Luck! ToNy

[suprleed]

Does anyone know of any good reading on hex inverters in relation to making gain/boost/distortion circuits?  I've been meaning to start experimenting with them but haven't been able to find much info on them.  I haven't been able to get much from the datasheet either.  Does anyone have any suggestions, links, etc. of a good place to start?

Thx

[Matt505]

Tony, thanks for the response! Well, I can vouch for the Bounce/DD, it is awesome! Seems like the other 4049 ckt that comes up a lot is the Red Llama...
Ahh, thanks for pointing me back to the fetzer discussion, lots of good info there! Increasing the source resistor is an easy test...
The bypass cap on a switch -- so it's like a preamp tube cathode bypass, where it provides a gain boost across certain frequencies, right? So if I take it out, it should drop the gain for most of the freqs involved?

As for the voicing stuff, sounds like it's the same as for other circuits, in terms of the filter caps/resistors...I guess I wasn't sure if things were somehow "different" when using the 4049 as opposed to an opamp or whatever  I saw 4049 = inverters, not "amplifiers", so wasn't sure...I could start messing around with those caps, but I really do like the "smoothness" at highest gain, so probably best not to mess with perfection! 

[esdiezy28]

yes, the bypass cap works on the same principle as with cathode bypass in tubes. The bypass cap and resistor form a high pass filter. Frequencies above the high pass corner frequency get maximum gain from the stage. If you take out the bypass cap then the circuit will work more like the fetzer valve circuit. Using a bypass capacitor removes the tube like frequency curves that a FET can produce, but it is a nice "boost" and I have made the fetzer valve circuit and used the toggle bypass cap. Not a whole lot of difference but it did add "presence" to my sound, hard to describe but I could tell it was different than without it. I think for the versatility that putting a toggle switch on your bypass cap is a worthwhile one, IMHO. You say you like its "smoothness" when you have the gain cranked to max? Then I would definately leave the cap sizes alone. Don't mess with a sound your happy with!

[tackleberry]

Im not sure with the 3 gain stages in the bounce channel its possible to get no gain or clean. The one I built I messed with the caps between stages to tweak the tone. I messed with the small value bypass caps on the gain stages but didnt notice any real difference. I got better results with a tone control between the last stage and the volume on each channel. The treble was a bit much so I added some high pass filters with a switch for treble boost between the tone and volume control. Im pretty happy with how it turned out.

[Matt505]

Tony - thanks again for your response, I'm definitely keeping the stock values for the feedback caps! Did you decide on a 4049 build?
I think I'll read up more on the various filters and such, I'm often curious "how'd they pick those values?" I'm sure a lot of 'taste-testing' goes into it...

TB - which 'style' TC did you put in? I'm on the fence there, I'm leaning toward keeping this a 2-knobber and just using guitar/amp TCs...

Thanks,
Matt

[esdiezy28]

No, I'm not sold on a particular build as yet. The "Double D" and "3 Legged Dog" both from www.runoffgroove.com both look awesome. Type in 4049UBE for a search on here, I found there is someone, I forget who, who showed a bunch of different stages he's tested with a 4049 inverter stages, including boosts, diodes in the inverter loop, and even how to use a stage as a buffer. Just got my Valvecaster working last night! Sounds awesome!

[tackleberry]

I went with the BMP single tone knob. Only so much room on this pedal for controls. But with the switchable high pass filters gives more variation. Also I socketed most of the caps so I could change em as needed. The stock version got muddy with all the bass it allowed thru. And the stock version really needs something to tame the treble. I also put switched clipping diodes on the jiggle side with the AMZ saturation control. I can get just as much distortion with jiggle as bounce this way or just have OD.

[snap]

No, I'm not sold on a particular build as yet. The "Double D" and "3 Legged Dog" both from www.runoffgroove.com both look awesome. Type in 4049UBE for a search on here, I found there is someone, I forget who, who showed a bunch of different stages he's tested with a 4049 inverter stages, including boosts, diodes in the inverter loop, and even how to use a stage as a buffer. Just got my Valvecaster working last night! Sounds awesome!

those were brett, stm, and WGTP!

[MohiZ]

As the Double D is intended as a two-channel distortion, maybe the Bounce section isn't intended to work that well with lower gains. I breadboarded the thing today and while getting quite a nice lead sound I thought the bass was a bit too "flabby" and, while not overly trebly, there were still too many odd harmonics to my ear. Oh well, maybe the 4049 isn't my thing.

[WGTP]

http://www.aronnelson.com/gallery/main.php/v/WGTP/Red+Rooster.GIF.html?g2_imageViewsIndex=1

Mostly I got this stuff from STM, Brett, Gez, Puretube, Frank Clark, etc.   It's at the threshold of my understanding limit. 

[darthpoodle]

I know this is an old thread but still have some questions. I too have built the double d and it is my first real build. Really new to this and my knowledge is limited. I too find it too flabby and bass heavy. Without getting too complicated is there a simple mod (cap or resistor change) to tame the bass in the circuit?

[WGTP]

Just about anytime there is a cap in the circuit path, you have an opportunity to "adjust" the bass content.  Basic ruff filter theory.

To reduce the bass, reduce the size of the cap.  Halving it raises the bass roll off frequency by a factor of 2 or 1 octave.  

To increase the bass, increase the size of the cap.  Doubling it lowers the bass roll off Frequency by a factor of 1/2 or 1 octave.

There are limits to how much bass a circuit will have, so you can't "add" bass where there isn't any.  It will depend on how much was originally removed in the original design.

It is also a function of the resistance in the area, so halving or doubling that can make changes.

Changing the bass content pre-distortion sounds different than changing it post-distortion or mid-distortion

May want to change it in several places in the circuit for different roll off rates at different frequencies.

Not so suprisingly, the negative feedback loop works in reverse and does the same stuff to the high frequencies. 

Low pass filter in the feedback loop and high pass filter in the direct signal path.  6db/octave or higher when combined in different stages.                 

As Aron has always said, use sockets and experiment.  

[darthpoodle]

where to start is my question. I am not too good with reading schematics and looking at it there are several places to start. At the end of the chain or the beginning? What's going to give me the best bang for the buck. I guess I could socket all seven in that side of the chain but that cuts down on playing time. I guess I am being lazy.

[WGTP]

I should have acknowleged Mark Hammer's contributions in the earlier post.

I really like the CMOS distortions.  How about emulating SHO stages with one?

Anyway, I would start with the 220n caps.  Replace one or both with a 100n cap (this way you don't have to use such big 220n caps).  You can also try values in between 220n & 100n.

You could also lower the cap at the beginning of the CMOS stage cascade.  It seems small already...

Lowering the cap at the end retains the same level of bass distortion, but reduces the overall bass.

Doing it earlier on in the signal chain reduces the bass distortion (providing more dynamics) and provides a less "wooly/flabby" sound.  That is my preference.    

[WGTP]

Sometimes you can tighten the straps on those Double D's and get a little more Jiggle and a little less bounce.  I think it raises the Q and frequency.   

[Brymus]

Sometimes you can tighten the straps on those Double D's and get a little more Jiggle and a little less bounce.  I think it raises the Q and frequency.   

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