modding an LPB-1 into a... ZW OD? Tube screamer?

[cgibsong002]

Ok. So once upon a time, I ran a ZW OD pedal into my marshall 3203 stack. I maxed the volume on the OD, left the tone at 12, and zero'd the gain. more or less a clean boost. It gave me insane pinch harmonic power and sustain that would last for days. It turned my amp into a monster. But unfortunately, it sucked low end tone and made it noisy enough that I only wanted to use it on solos. So I eventually moved on and forgot about it.

Next, I tried building an LPB-1 clone, hoping it would do the same for me that the ZW OD did, minus the noise and low end suck. After you all helped me with my first pedal build from scratch, I finished the LPB-1 clone. Unfortunately, it didn't do what the ZW OD did for me. It added plenty of gain, yet somehow did nothing to help my sustain or harmonics. It was really only a big change on the clean channel.

So I want to mod the LPB-1 into something a bit different. Or at the very least, use my existing case and layout and just change the circuit. As I only need a volume pot (like I didn't use the other 2 on my ZW), I figure I have a good base to start with. Can you guys think of any modifications or additional I can do to my lpb-1 circuit to give me the results I desire? Or should I build maybe a modified OD or tube screamer circuit that only uses one pot?

edit: also, I just got a recommendation for a MXR micro amp. have never used one, but maybe that's something to consider as the layout is the same as the lpb-1

What do you guys think?
Thanks a lot! I'm sure you'll come through again  

[Mark Hammer]

Well, you can't mod an LPB-1 into any of those others.  A bit like modding a garage into a yacht.  I mean, it can be done, but is more trouble than just making the yacht.

Sounds to me like what you are searching for is something that provides a hint of overdrive, and whatever modest compression comes from that clipping, with tone-shaping that is better suited to the way you want to push your amp.

My gut tells me you'll want to tinker with the basic MXR Distortion+/DOD250 structure.  So, a single op-amp medium-high gain driver, pushing some diodes (and probably 3 or 4), with well-chosen tone-shaping caps to trim the fizzies and retain the bottom.  Make one and we'll talk component values afterward.

[cgibsong002]

yeah I figured I'd most likely be just building another new circuit from scratch, no big deal. Just figured I'd ask.

So do you know how the Distortion plus compares to the ZW OD? I have a feeling MXR just made the ZW out of a distortion + and added more gain and a tone knob? And since I don't need drive or tone, they should be quite similar? I just want to be sure I'm building the right thing here.

[petemoore]

  A glance at layouts or schematics shows the LPB/Microamp/OD circuits to be quite different.
  The DIST+ or OD 250 are nearly identical, compare schematica.
  Either can fit on the same basic board which fits in most boxes, I use 'em.
  Use 100k L pot for gain is recommended, a third knob can = useful treble control, or preset HF cut works as well.

[Govmnt_Lacky]

So do you know how the Distortion plus compares to the ZW OD? I have a feeling MXR just made the ZW out of a distortion + and added more gain and a tone knob?

From what I have read... the ZW44 was based loosely or "borrowed" from the SD-1 pedal.

[Mark Hammer]

Insomuch as it has the added tone control, yes the ZW OD is more in the TS/SD-1 vein.  What I got from the OP's note was that he wants a simple boost that is "pre-calibrated" to push his amp a certain way.  That only really needs a single op-amp section to do, although if he wants more flexibility, a second stage with variable tone shaping will obviously provide that.

the other reason I recommend the basic D+/250 structure is that this territory has been mined so extensively that the OP will have no shortage of good informationa available to make wise choices from.

[MikeH]

To me it sounds like what you really need is a noise gate.  The guy from killswitch does basically what you described.  He has a tube screamer (Which is really more of what the ZW is... More so than a Dist+ anyway) and he runs it in the loop of a Boss NS-2.  I actually got to see his rig up close- it was a TS-5 at the time, and he had it set about how you described; Vol way up, gain at less than 1, and the tone kind of up there too.

[cgibsong002]

Well... I probably could get the desired results I wanted with a ZW OD, a 6 band, and noise gate.

But I want to build my own pedal, and kind of come up with my own design. I also want this dead simple. Volume knob only.

If i base it off the distortion plus, can I simply replace the gain knob with a large resistor instead, to simulate the gain knob on zero? and then since the distortion plus is quite simple, I'd imagine it would be a good basis to be able to modify different components to better tweak it to my tastes? As in if I say it's too treble-y, you guys would be able to help me replace a certain cap with a different one? Or if it needs a bit more gain you guys can help me in determining a resistor to switch out?

Correct me if I'm wrong here, because I honestly am a noob to this, but I am also confident enough that I can achieve what I want through my circuit knowledge and your guys' help. I had nearly the exact results that I wanted with the ZW OD with the volume maxed, the tone at 12, and the gain at 0. The Distortion plus is a bit different and has no tone knob. I'd like to further simply get rid of the gain knob on the distortion plus by replacing it with a set resistor (I'd imagine a 1M ohm would do exactly this). And then once I have nothing but a drive knob, how big of a difference is there really between the ZW and the distortion plus? Could I not change some values around or add some components to get my desired sound?

Thanks guys. Sorry if this sounds complicated. I'm very excited to try to work on something more or less original and come up with something that I can say I built. Of course, you guys are the gurus here and I'm learning, so I look forward to your suggestions and advice.

[Mark Hammer]

I think you'll want a trimpot so that you can set the gain accordingly to get juuuuuuuuust the barest hint of distortion, and then tinker with the cap to ground (in parallel with the diodes) and the cap in the feedback path of the op-amp, to get the tonal spectrum you need to tease out the sort of distortion you want from the amp.

The principle to always keep in mind is that the dstortion you get out of something is a function of the spectral content, and the relative amplitude of the spectral elements, that you feed in.  Introducing a bit of clipping in the to-be-built pedal/booster, with some suitable lowpass filtering, will shift the balance in the harmonic content of what you feed the amp towards lower order harmonics.  The clipping also provides a hint of compression/leveling that assures a more constant signal hitting the amp for a few more milliseconds.

The ZW uses diodes in the feedback loop of the op-amp, and the D+/250 uses them going to ground.  Sightly different flavour, but in your application I don't think it will matter all that much.  Just make sure the .047uf cap from the inverting pin to ground is at least .1uf if you want any appreciable bottom, and make sure you use a 100k output volume pot.

[cgibsong002]

I think you'll want a trimpot so that you can set the gain accordingly to get juuuuuuuuust the barest hint of distortion, and then tinker with the cap to ground (in parallel with the diodes) and the cap in the feedback path of the op-amp, to get the tonal spectrum you need to tease out the sort of distortion you want from the amp.

The principle to always keep in mind is that the dstortion you get out of something is a function of the spectral content, and the relative amplitude of the spectral elements, that you feed in.  Introducing a bit of clipping in the to-be-built pedal/booster, with some suitable lowpass filtering, will shift the balance in the harmonic content of what you feed the amp towards lower order harmonics.  The clipping also provides a hint of compression/leveling that assures a more constant signal hitting the amp for a few more milliseconds.

The ZW uses diodes in the feedback loop of the op-amp, and the D+/250 uses them going to ground.  Sightly different flavour, but in your application I don't think it will matter all that much.  Just make sure the .047uf cap from the inverting pin to ground is at least .1uf if you want any appreciable bottom, and make sure you use a 100k output volume pot.

I think we can make it work 

I get what you're saying about the gain. But I literally had the gain on my ZW on zero, not at all above. But of course, that doesn't mean it was not there at all... so maybe I'll start with an 800K resistor instead of a 1M and see how that works? I really just don't want that drive knob there. If it takes some unsoldering and resoldering of a single resistor to find the right value... it's really no big deal.

Could I do something similar to what you said, and use the diodes in the opamp rather than to ground, but using the schematic of the MXR, and kind of combine the two?

[Mark Hammer]

At "zero", the ZW-OD has a gain of 8x.  At least in the op-amp stage.  I'm no bloody good at calculating gain for transistors, and the input stage looks like it has some gain too ( http://analogguru.an.ohost.de/193/schematics/Mxr_ZakkWylde.gif ), so that multiples with the 8x for even more.  The upshot is that at the 7:00 setting you probably were experiencing some light clipping in the ZW-OD and not pristine "clean boost".

How much gain is needed to achieve light clipping?  I can't say precisely, but I imagine that in most instances, when using a pair of silicon diodes, we're looking at minimum 20x, and more likely 30x.  A stock Distortion+/250 ranges between <10x and a max of 214x.  A stock TS has a max gain of 118x.

If you set the minimum gain for just under 50x or so (fixed resistor of 220k) and tack on a 500k trimpot for dialing purposes, and stick a 2+1 silicon diode complement as the clipping element (instead of the 1+1 germanium that the Dist+ has), you will have wads of output to pummel the amp's input stage.  Instead of the .001uf cap, traditionally shown in parallel with the diodes, stick a 3900pf-6800pf cap to ground (larger trims more treble fizz).  Instead of the 10pf cap in the feedback loop like the stock Dist+ has, use a higher value, like the ZW-OD.  It uses 120pf, which may be a little large for ouor purposes, so try 47pf-68pf for starters.

[Derringer]

I think we can make it work 

I get what you're saying about the gain. But I literally had the gain on my ZW on zero, not at all above. But of course, that doesn't mean it was not there at all... so maybe I'll start with an 800K resistor instead of a 1M and see how that works? I really just don't want that drive knob there. If it takes some unsoldering and resoldering of a single resistor to find the right value... it's really no big deal.

Could I do something similar to what you said, and use the diodes in the opamp rather than to ground, but using the schematic of the MXR, and kind of combine the two?

Do you have a breadboard? If not, get one, it's a must.
Then breadboard up what Mark's saying. I bet the first try will get you at least 90% of the way there and then you can adjust a few components to get it completely customized to your taste before committing to solder.

[cgibsong002]

At "zero", the ZW-OD has a gain of 8x.  At least in the op-amp stage.  I'm no bloody good at calculating gain for transistors, and the input stage looks like it has some gain too ( http://analogguru.an.ohost.de/193/schematics/Mxr_ZakkWylde.gif ), so that multiples with the 8x for even more.  The upshot is that at the 7:00 setting you probably were experiencing some light clipping in the ZW-OD and not pristine "clean boost".

How much gain is needed to achieve light clipping?  I can't say precisely, but I imagine that in most instances, when using a pair of silicon diodes, we're looking at minimum 20x, and more likely 30x.  A stock Distortion+/250 ranges between <10x and a max of 214x.  A stock TS has a max gain of 118x.

If you set the minimum gain for just under 50x or so (fixed resistor of 220k) and tack on a 500k trimpot for dialing purposes, and stick a 2+1 silicon diode complement as the clipping element (instead of the 1+1 germanium that the Dist+ has), you will have wads of output to pummel the amp's input stage.  Instead of the .001uf cap, traditionally shown in parallel with the diodes, stick a 3900pf-6800pf cap to ground (larger trims more treble fizz).  Instead of the 10pf cap in the feedback loop like the stock Dist+ has, use a higher value, like the ZW-OD.  It uses 120pf, which may be a little large for ouor purposes, so try 47pf-68pf for starters.

is a trim pot one of those potentiometers that you solder directly to the pcb? if so, yeah, i agree, that'd be perfect. allows me to do minor tweaking if I want, but doesn't clutter up the physical layout of my pedal on the outside.

and let me see if i'm understanding correctly. if i was simply simulating a distortion plus with the gain on zero, something like an 800K or a 1M resistor in place of the pot would be ok... but you're trying to give this pedal some characteristics of the ZW, which likes has more gain than the + , even with the dial on zero... and that's why i need less resistance than something like 1M?

and yes, I do have a breadboard. i'll definitely build it on there first.

i'll update in a second with a list of components, can somebody double check to make sure I'm not missing anything? and perhaps add a few extra things that i might possibly need? i don't have a bin full of extra components, so i want to make sure i can try to order as much as i can at the same time.

what do you mean by 2+1 diode?

here's my list... look good? i already have all the other components to build the pedal. i just need the components for the circuit.



•   10K linear taper pot
•   LM741 op amp
•   1MΩ (x5)
•   10KΩ (x2)
•   4.7KΩ
•   .001uF (x2)
•   .01uF
•   .047uF
•   1uF/35V tantalum (x2)
•   10pF
•   1N914 diode (x2)
•   Mods
o     220KΩ
o     500K trimpot
o     2+1 silicon diode (?)
o     3300pF multilayer ceramic
o     4700pF
o     5600pF
o     6800pF
o     47pf
o     56pF
o     68pF

[Mark Hammer]

Yes, that's what a trimpot is, and is for.

I think we have liftoff.

[cgibsong002]

Yes, that's what a trimpot is, and is for.

I think we have liftoff.

i'm a genious!  we use those all the time in circuits lab, the teacher just calls them potentiometers. i figured they were just cheap ones (compared to a standard audio pot), but now i understand their application.

how's my list look?

[Mark Hammer]

Okay, looking over your list, and the discussion, I made some changes to the basic drawing (thank you to JD Sleep for the basic drawing, copied from GGG, that I modified for this purpose).

The parts that are different from stock are shown in violet.  I was originally thinking of adjusting the gain via the feedback path, but the ground leg works just as well.  The output pot can also be 50k, though 100k is probably better.  The gain trimpot can be whatever you want, from 500k down to 50k, and it will still work fine.  Taper is immaterial in this application since it will be a preset.  For C4, bigger gets you more bass.  For C5 and C7, higher values get you less treble and a "rounder" tone.

[cgibsong002]

Very cool of you, and thanks very much. I'm about to get some sleep for the night, so don't have time to compare contrast, but is that schematic the same as this vero layout (the second fixed one)? http://www.diystompboxes.com/smfforum/index.php?topic=74691.msg607418#msg607418

obviously aside from your changed values.

i really don't think this will be too difficult to achieve. looking at the vero layout, it looks quite simple. and due to that, it looks like a great base to be able to breadboard it and adjust and tweak. i'll try ordering the parts tomorrow.

[blooze_man]

Before Zakk got his signature overdrive, he used the SD-1. So basically I'm agreeing with those who said to check it out.

[56335130]

you can see the mxr type dist(rat)has the clipping diode between the second triode and the out put and it's lead to ground
but the sd1 or ts or zw44 has the clipping diode parrel to the first ic...
so tey the ts or sd board
ds+ give you more hard dist,not harmics

[Renegadrian]

Have you tried to add a couple of diodes at the LPB output?! try 1n4148 or LEDs.