another Ampeg Scrambler Volume Question

[johnadon]

I hate to ask this since there are so many posts relating to low output volume on Scrambler builds, but I can't say I've found a definitive answer. The Scrambler was one of my first builds (a wonderful choice since you really get a great idea of the freakish possibilities with DIY), but I've always been stumped by the less-than-unity output I attained. I built one for a friend and it suffered from the same problem. It appears from the posts I've read that there must be a build error on my part, but I find it hard to believe I could make the same build error twice (famous last words) using the same simple layout, which has been verified many times over (the Tonepad layout http://tonepad.com/getFile.asp?id=31). I did note the problem with the reversed electrolyte that was present at one time.

In short I absolutely lust over this pedal but would like to attain unity volume. It seems the two solutions that appear most often are 1.) correct one's stupid build error or 2.) add a booster at the end. In particular the LPB1 has been mentioned as a nasty complement.

I like the idea of adding a booster so this is more of an (newbish) academic question, but I'm curious if increasing the value of R15 and R10 to ground would increase the volume? The are the resistors to ground on either side of the blend pot that sends the blend to output.

Sorry if this has been answered in full before, and thanks to anyone who can provide a little bit of info. I'm still learning after a year and a half. :-) Work intervenes way too often. :-)

-John

[Mark Hammer]

Sure, take a crack at hiking up R10/R15 to maybe 100k, and see if that conserves a little more signal for you.  Personally, I find mine is plenty loud, though it must be said that the circuit itself is not intended to be dramatically louder than bypass because there is no volume-level adjustment, only tonal balance.

The Scrambler has always suffered from having no "sensitivity" adjustment that might determine how easily the octaving portion is set into obvious doubling.  I'm wondering if the value of R3 can be played with, or perhaps an emitter-to-ground cap with a variable resistor?  One of your transistor wunderkinds is going to have to confirm that for me.

[johnadon]

Thanks for the reply, Mark. I think I'm going to try it out just for kicks seeing as my floor is already littered with tools and components at the moment. I've been tidying up old circuits.

[johnadon]

Well, that turned out to be quite an interesting exercise, especially since it highlighted how my assumption was based mostly on habit. I love turning things up all the way.

I concentrated on differing values for R15 on the tonepad schematic since the dirty side of the circuit was where I was noticing less than unity volume. Increasing the value of that resistor - even removing it from the circuit altogether - had very little effect on the output. Lowering the value to lower than 5K did lower the volume. In the end, I reinstalled the resistor at the default value.

Here's where it gets interesting: I almost only ever use my scrambler with the blend turned all the way dirty and with the texture maxed. I began to play with those controls and discovered that the unit really does output at unity at almost any setting other than the max settings. As a matter of fact, when set to clean you can't even hear a volume change when switching the pedal on and off. I imagine there is some sort of gating (? I'm not sure of the proper terminology here?) causing the apparent less-than-unity output when the unit is at max, and I was basing my opinion solely on those settings. In the end, I think my Scrambler probably works exactly as it's intended, and I'm not sure I'm going to bother to put a booster on it at all, especially since I usually run it into one fuzz or another. Definitely a 'cleanup' project I can leave for later.

[johnadon]

Ha! Just found the remnants of an AMZ Mosfet Booster in my junk box so I have no excuse not to pop in a control.

[Mark Hammer]

This is why the Scrambler needed an input sensitivity control.  When pushed hard, it "implodes".  On my "Scrambler Plus", where I have what is basically a Dist+ ahead of the Scrambler and use the D+ circuit as a kind of "signal conditioner", I can hit the Scrambler with a bigger than usual signal.  Turning the Mix and Texture controls up easily results in an "imploded" signal that is much lower than normal.  If I leave the Texture at min, however, and crank the D+ portion of the overall circuit, turning the Mix/Blend pot over to effect-max DOES give a volume boost, relative to effect-min.

[johnadon]

Interesting. I've always run my scrambler before my standard distortion pedals since they smooth out the Scrambler output somewhat whenever I feel the need to do so. It also brings the Scrambler output to whatever level the distortion pedal is set to. I'm not sure I've ever run a distortion in front of the Scrambler at all, come to think of it!

I did pop in the AMZ Mosfet Booster at the output last night and that thing can really drive an amp now. It could probably drive a car as well if I could patch it in somehow. :-)

[Mark Hammer]

I've blathered on about it at perhaps excessive length, but I simply can't say enough about how productive the combo of a simply diode clipping stage and a Scrambler is.  One of the things that a D+/DOD250-like front end adds is the capacity to adjust how long the octaves take to emerge or to fade out.  Keep in mind that the diode clipping of what the Scrambler sees as the input signal imposes a certain consistency of level as you turn the distortion (clipping) up.  Since the lower harmonics tend to exist at substantive levels for only a brief period when using a clean signal, the pre-clipping lets them linger a longer while, so there is an advantage to using a pre-clipping circuit over and above merely sticing a compressor ahead of the Scrambler.  Additionally, if one sticks in some treble-taming as part of the pre-clip circuit (e.g., changing the typical .001uf cap in parallel with the clipping diodes for one in the .0033-.0047uf range, then what you end up doubling is primarily the fundamental and lower-order harmnics, rather than middle and upper harmonics and their usual irritating fizziness.  That's why I refer to the D+ front end as "signal conditioning"; it's getting the guitar signal ready for the Scrambler to do a better job at what it does.

BTW, if you are going to do this, change the gain pot in the D+ front end for 50k-100k linear, and change the .047uf cap for .22-.47uf.

[johnadon]

Sorry for the delay in replying. I think I have a Dist+ in my old circuits box, and I've really got to try patching it in. I just dug up some of your posts about using the Dist+ as a front end and it sounds like a real extension to the capabilities of the Scrambler - which already ranks among my faves in the first place. :-)

[Mark Hammer]

And I have to post some sound samples.

[alex frias]

As Mr Hammer said and others confirmed, the use of another smooth clipping circuit like Dist+ or a TS before the unit may enhance the effect and add new possibilities. Very distorted fuzzes I don't think so inspiring as the more mellower sounding distortions in this particular case. I found the compressor sustainer, like the Dynacomp, a good combination, but not as rich as the mellower drives.

What I am now really into is feed the scrambler input with my EPM (Perculator version), you can control a lot of things with just guitar controls like pickup selector switch and volume knobs. You even control the "birth" of the octaved up sound.

Excellent suggestion!