zachary vex pedal question (not a schem)

[csmatt45]

Hi,

a friend of mine has a super duper. It sounds great of course. Was just wondering if someone could explain how to cascade a couple of clean boosts together. I'm not requesting a zvex schematic, I just like the way the duper cascades the two together with a mast volume, and wanted to try it with my favorite boost, Gus's NPN boost.

Thanks,

Matt

[Johnny G]

its pretty simple

just run one after the other. have an output volume on each of them so you have the pot after the first boost as a gain control and the second pot as a master volume

Z uses mosfets for his boosts so if you're looking for that kind of breakup sound you could start there however any 2 clean boosts after each other should work fine

may be worth building the circuit but socketing the transistor slots to try out different trannies. and they dont have to be the same type. ive had some great tone out of running a mosfet based booster into a germanium transistored rangemaster clone......really need to get around to building it into one box

[csmatt45]

thanks, but I think thats a bit different than the duper setup. I'm looking for 2 separate clean boost volumes, with a master volume between them (3 pots total). I believe the mast vol is a 50k that is attached to the second boost when it is used alone, but also acts as a master for the first when engaged.

BTW I hope I'm not stepping on anyone's toes getting this detailed about it, and again, I'm not trying to copy his clean boost, I just thought it was a beautifully simple idea that'd be cool to apply to a pedal I make.

please let me know if this is not OK to do in the forum.

Matt

[bass_econo]

Do a search for "dual boosters" or "2 booster" or similar.  There are a lot of posts on this.  Also there are a lot of layouts out there as well.  Below are 2 but I'm sure there are more.


Dual LPBs (Nabo's layout) -

http://aronnelson.com/gallery/NaBos-Layouts/doubleLPB2


Dual AMZ boosts (ustomp layout) -

http://ustomp.com/index.html?menu=2&section=8

[csmatt45]

thanks, but same thing, those don't have a master pot. Need 2 boosts, 1 mast, 3 pots total.

Thanks anyways!

Matt

[bass_econo]

Not sure, but I don't think you are going to find an exact copy of of the ZVex pedal... You may need to look up "master volume mod" etc and add it to the above... Or just buy the ZVex pedal.

[Mark Hammer]

Okay, picture starting to gel a bit.  I'm getting the sense you want a single MASTER master-volume.

When it comes to so-called "clean" boosters (and I call them "so-called" not because *they* aren't clean, but because the consequences further down the signal path often are not; after all people want them to push their amp into clipping without introducing coloration from an outside source), there are essentially 2 parameters to control: gain applied, and attenuation applied.

If the gain stage is "clean", then as long as the taper on the attenuation control is convenient and usable, there should be no need to adjust the gain of the stage unless it is to adapt to very different input signal levels (e.g., line-level synth output vs voice mic).  If the gain stage is being used to produce some degree of coloration internally (i.e., what leaves is more distorted than what went in), then I can see needing a gain-adjust control, but if clean is what you want then all you need is a level-setting pot on the output, right?

Okay, so imagine we have 2 cascaded "clean" gain stages.  If the gain of stage 1 and 2 is set reasonably then there is no reason why we can't run stage 1 full out into stage 2, right?  If the gain of stage 1 or stage 2 is such that any additional multiplication of that gain (e.g., if stage 1 = x200 and stage 2 = x 20, then their combined gain will easily exceed the voltage swing possible from a 9v battery unless you're trying to amplify bioelectric signals in the microvolts) is certain to produce clipping of some type, then a gain-adjustment is advisable.

What this suggests is that a cascaded pedal where stage 1 has fixed gain (but an output attenuator) and stage 2 has variable gain and an output attenuator, would be capable of delivering all possible ranges of tempered (i.e., pretty damn clean) and overdriven tone.  This arrangement lets you:
a) trim back the output level of stage 1 and set stage 2 for modest gain so that, multiplied, they provide as huge a volume boost as is feasible from that power supply,
b) run stage 1 full output into stage 2, with stage 2's gain set high enough to exceed requirements for clean sound, and the output attenuator trimming back for a reasonable output level.

There are your 3 pots: Level A, Drive/gain B, and Level B.

Where you may want to think harder is in terms of what sort of user capabilities you want.  For instance, do you want to be able to bypass stage 1?  Do you want to be able to engage/bypass EITHER gain stage?  Note that if you had a true bypass switch governing stage 2, you could easily switch between some fixed output level of stage 1, and some fixed utput level of stage 1 going into stage 2, since there is a "master" volume on the output of each stage.  Set your gains right for each stage, and you should be able to swap back and forth between maximum clean gain from stage 1 and heavily overdriven (but modest volume) tone from stage 2.

Make sense?  If it does, you can pretty much do this with just about any boost circuit.  I'm not guaranteeing you will like the coloration, but you will have that sort of functionality.  Bear in mind as well that you have no obligation to use the identical circuit for each gain stage.  If you felt like it, you could use a bipolar or op-amp for stage 1 and a MOSFet, mu-amp, or whatever for stage 2.  The key tasks would be to identify:
a) the gain or gain range appropriate to the function of each,
b) what sounds better going into what,
c) suitable value for the attenuator pot between stages,
d) optimal coupling between stages,
e) your "ideal" switching scheme.

Incidentally, while requesting some schematics can be a bit touchy or even inappropriate, there is absolutely nothing wrong with asking the question "How could I achieve the same functionality?"  Absolutely nothing at all.   The means for achieving a specific user goal may be legally protected IP, but there is nothing protected about the goal itself.  Perhaps more importantly, asking how pedal X does something gets you one answer, but asking "how could I accomplish X?" may well get you many different answers to choose from.  Clearly, one approach buys you more than the other.  But then, I take it from your query that you knew that.

[ryanscissorhands]

I did this very thing, only with a few more bells and whistles. I did a dual AMZ MOSFET booster, each with 2 knobs, boost and volume. (Just add 100K audio pot to ground for master at the end). I also added an FX loop on each channel. It turned out pretty good.

One thing that is really sexy is running them on a bi-color LED.



http://diystompboxes.com/sboxforum/viewtopic.php?t=33519&highlight=amz

Check it out. . .

[csmatt45]

wow, thanks mark (and the rest), I'll have to read your post again a few times so I can better grasp it's meaning. I'm still a "paint by #s" DIY'er but I'm starting to grasp it a bit. Thanks for your time putting in such a detailed answer.

I'll let you know how it goes...

Matt

[robotboy]

Dual Mosfet Booster

Dual Mini-booster

Dual Mosfet + Mini-booster

I'm definitely going to build one of the above, but I can't decide which. Adding a master volume should be just a pot from output to ground with the wiper working as the new output.

[bass_econo]

Now that it's being talked about, I went and listened to the sound clips on ZEX's site and I'm not sure that it would be something I would want.  It is an interesting pedal just not something I need for me!!  

Does the AMZ dual boost (or any other) sound like that?  I would want something that sounds a little more "natural?".  If what I would get would be similar I think I will look to something else, like a boost and overdrive.  Or  I think I would like one as a buffer at unity gain for the first and just use the 2nd as the boost.

Anyone have any soundclips of a dual AMZ boost or like?

[bigjonny]

I did the MOSFET Boost + Mini Booster that robotboy was so nice to point out.  Sounds good, but gets distorted when the two are ganged up (of course).  The problem with running two boosters, cascaded is that you run into limitations of the 9V power, and thus get distortion no matter how "clean" they are to start with.  You might consider running @ 18V?

Or, if you really want three levels, why not some stomp switches that put multiple volume controls in the path from the output of the circuit board to the output jack?  Then you can use one MOSFET boost (or whatever), and simply choose how many volume control pots you send it through before sending it to the output jack -- cheap easy and effective.  Alternatively/additionally, you could toggle the gain state on the MOSFET boost -- just read the bottom of Jack Orman's MOSFET Boost page.  Instead of disconecting R6 from ground, change R6 to another pot ...

With one booster, you won't have (many) over-voltage problems.

The Mini Booster is a gain-then-attenuate booster.   With the gain its set at, by itself, it adds a bit of distortion.  A dual MOSFET boost is probably what you're after, since its perceptually "clean".  

Tim Escobedo's got some great boost suggestions on his Circuit Snippets page.  Probably your best bet is to build a few (or a heap!) of individual boosters, and combine two that sound good.

I propose that b/c of its high inpedance input, gain control, and perceptual cleanness, the MOSFET boost is a good "1st stage" booster.  My guitar sparkles a lot more even @ 1:1 gain.

[robotboy]

How much more gain does the mini-booster have than the mosfet? Is the distortion of the two combined harsh clipping, or is it still musical and pleasing to the ears? I used to own a SHO and when cranked to the max, it was way too distorted for my taste. If a single boost running off 9V can probably raise my guitar's output voltage to 7V, maybe two boosters would be overkill...

[bigjonny]

To my ears the MOSFET has more perceived boost -- but we're talking a bit, here.  Probably b/c is sounds less "clippy" than the Mini, and has higher input impedance.  That sheen, as attested in another thread is quite nice.

Even though I did a double boost, its probably more practical to do a single booster where you can toggle in how MUCH boost is happening.  I usually do NOT cascade them in live situations (too overpowering for my bandmates!), unless its time for a LOUD solo.

Its the peaks of the signal that first cause distortion.  The RMS (Root Mean Squared -- a fancy average) of the signal is MUCH lower.  You still need that headroom to not clip, which is why I suggest an 18V supply.

Jack Orman has an article about this.  read it, and you'll also see why its better to control Gain, rather than Volume, for your purposes.

I think you'll be much happier with the MOSFET boost.  The Mini Booster has a fixed gain, and that gain is set to distort, slightly.  It's a sweet sound, but it definitely provides a color.  This is why I did a MOSFET + Mini.

Since it seems like you want minimal coloration, I stand firm in my opinion:
Mod a booster so that you can toggle between a few pots.  If its a MOSFET, you can toggle between two Gain states (eg 1:1 and whatever your pot is set to), and two Master volumes.

Be sure to check out Escobedo's Utility Boost and Duende schematics, too.  They might give you ideas.

[robotboy]

Thanks for the very helpful reply. I'll probably try the mosfet boost with the suggested mod. It sounds like exactly what I need since I already have an amazing sounding natural gain provided by my Rivera amp. That way I can just kick it up a notch when I need to cut through. My amp has a builtin boost, but it provides too much gain and goes into crunch territory. I'm a big fan of smooth overdrive.

[bigjonny]

It occurs to me that you might be better suited to reduce your guitar's overall volume if your amp already has heaps of gain...  This can be done before the preamp, as Dragonfly suggests in his Clean Machine, or in the effects loop, as DIY Guitarist suggests in the Solo Pro.

Reducing pre-preamp will affect your gain, and thus your tone (this could be good, or not).
Reducing pre-power amp (effects loop) will preserve the sound of the preamp, but simply make it quieter (or not).  If your pushing your power amp into clipping this will also affect your tone.  If the power amp is running "clean", this will likely NOT affect your tone.

Both builds are so simple and cheap, I suggest trying both...

[bass_econo]

Yeah me too.  What Robotboy is talking about in the SHO distortion is what I didn't like (to my ears that is).  I think I will go with the single mosfet with the mods as well.  

OR...  Has anyone tried the dragonfly's Deluxe Sparkle Boost?  It had sort of the same set up ---> http://aronnelson.com/gallery/album18/deluxe_sparkle_boost

[robotboy]

Seems like a neat idea... having your guitar's volume throttled at 75% most of the time and then de-throttling it for solos, etc... I'll have to try it.

[bigjonny]

... having your guitar's volume throttled at 75% most of the time and then de-throttling it for solos, etc...

I find keeping a slightly-less-than-ridiculously-loud volume in reserve works out nicely.  I turn my amp up louder than I think I'll need, and use my volume knob to control things.  I should probably build Dragonfly's Clean Machine and/or the Solo Pro, too!  One of those things I keep meaning to do, but keep just using my guitar's knob.

For completeness, I'll refer you to Dragonfly's original thread where he introduced the Clean Machine.

[Eirik]

I built the sparkleboost a couple of weeks ago. I'm thinking of building anotherone into the same enclosure. It's a very nice booster but it isn't as super hard on as the super hard on though