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

[cgibsong002]

pin 7 is 7.36V (these tests are taken with a slightly dead battery at about 8V)
pin 3 is 3.18V

w/ no power, i'm getting about .1 to register at R5. my meter doesn't have small settings of AC voltage. only 200 and 600. but with power (is that correct), minimum gain, and at pin 6, I'm getting about 7.4VAC regardless of strumming or not. With max gain this number doesn't change.

I'm guessing the two DC voltages would be correct assuming a better battery was used. Would this affect my bad AC results, or is this likely something else?

[Mark Hammer]

I'm losing my sense of scale here.  When you say "i'm getting about .1 ", do you mean .1 millivolts, or .1 volts?

You should not be getting 7.4VAC at the pin 6 output.  First, your supply voltage is only 7.36V, and the output can't be greater amplitude than the supply voltage, right?

Even assuming that the 7.36 vs 7.4 difference is simply measurement error (i.e., the same thing, measured at a different point in time, being slightly different but essentially the same), a 741 should not swing from rail to rail.  Indeed, with a 9V supply, most op-amps are not going to be able to swing further than maybe +/-3.5V (i.e., 7vAC).  So, getting 7.4vAC from a humble 741 powr3d off 7.4VAC, means you are either measuring wrong**, or that V+ is connected to something it shouldn't be.

**And, for all their many benefits, when one has leads flying all over the place on a breadboard, placing your probe in exactly the right spot to measure something is generally not one of them.

[cgibsong002]

i'm not quite sure how to interpret the AC readings. for dc, i have ranges of 200m, 2,20,200,and 600. for ac, it appears i have simply 200 and 600. i was using the 200 setting.

[Mark Hammer]

Hmmmm, we may need a different meter.  You want to be able to read AC voltages in the range of 10 to a few hundred millivolts. If the most sensitive range you have for AC is 200V, then small wonder it wold appear to be "stuck" and not responding to the input signal.

Can I ask what brand/model of meter it is?  It might be possible to suss out what it can and can't do by looking at an on-line picture of it.

[cgibsong002]

Yeah it would seem odd that it would only measure ac voltages that high.. I can't see why you'd need to measure such large voltages with such a cheap device. Maybe there's another way. Here's the dmm http://www.amazon.com/W-Sperry-DM350A-Function-Multimeter/dp/B000ET5VYC

[Mark Hammer]

The manual ( http://www.sperryinstruments.com/documents/products/dm-350a.pdf ) suggests that you won't have the resolution you need to do effective troubleshooting on audio devices.  The 350 will have a resolution of 1/10V AC, which is not going to be helpful.

I hate to be the bearer of bad news, but it might be worth your while to spring $20 (sometimes much less) for another meter that will let you read smaller instrument-level AC signals.  Your meter will certainly be more than adequate for reading DC levels, but it comes up a little short for reading audio signals.

On the other hand, that doesn't mean we can't debug this one unless you have such a meter, eh?

[cgibsong002]

Hm.. no, I don't have another meter here    I wish I had realized the AC thing before.. I just bought it recently for this purpose. Oh well, it was only a few bucks, I'll get another on my next order. But for now, is there a way we can use mainly DC voltages to trouble shoot? Also a bit of extra info, I'm not sure if this means anything or not, but there is a noticeable popping through the amp when I touch a string. Maybe something is falsely grounded?

[Mark Hammer]

The other approach to take is to simply use an audio probe.  If you have a guitar cable that can be plugged into the amp but have probe-like contacts on the other end, you can strum your guitar (or provide any other source of reasonable audio input signal, like a radio, MP3 player, etc), and "listen" to the signal at various vantage points.

Since what you hear is dependent on the amp volume settings, among other things, it is perhaps not quite as informative as accurate voltage readings, but at least you can verify that there is audio signal successfully reaching here and here, but not there.

[cgibsong002]

Hmm.. unfortunately where I am I don't have an extra cable to take apart, unless I take apart my footswitch.

Am I thinking incorrectly, or on a pot, if I have a resistance across 1 and 2, should I not have the remaining resistance across 2 and 3? I'm not sure if I'm making this up or if it was different pots we were using in class. But I'm not getting any readings of resistance on 1 and 3 or 2 and 3. Wonder if its bad, and if it is, if that would be causing the issue.

edit: nope, wired the output direct without the potentiometer and no difference. I'm going to go over my whole circuit again and check all the component values.

EDIT! after taking a look at the vero layout, I noticed what I thought was wrong in the first place. I guess I didn't have the input wired correctly (unless some other random thing that I did fixed it). I wired the positive input to the non grounded side of R1, rather than to the 9v source as I previously had it. Volume knob works, gain trimmer works.

Now on to the fun stuff I guess. As is, this thing really didn't do what I was looking for. Maybe a bit of extra harmonics on the low E pinches, but aside from that, just a bit extra gain, a decent sustain improvement, but most harmonics are still everything but existent, unlike they were with the ZW OD. Also, the noise level compared to the improvement was not a good proportion, although I'd assume some of that can be attributed to breadboarding rather than proper wiring. If I'm thinking this correctly, my trimpot is the same thing as a regular gain knob. Even with the gain a touch under max (max was unbearably noisy), it still wasn't half as nice as how my ZW was with gain off.

So where can we go from here? I've got more or less a distortion plus on a breadboard. I want to turn this into more or less a ZW OD, or something with the gain/harmonic characteristics of that.

[Mark Hammer]

Semi-congrats.

When you say "noise", do you mean hum or hiss, or both?

[cgibsong002]

Semi-congrats.

When you say "noise", do you mean hum or hiss, or both?

If I remember correctly, it was just like my normal amp's hum, but louder. it was when the gain trim was on full that it was just crazy feedback and hiss when not being played. but I'm not sure if full gain is a concern.

I take it as an accomplishment. I built my first pedal following a real schematic. I built my first pedal on a breadboard. Now hopefully you or one of you can help me in turning this into more of what I'm looking for.

[cgibsong002]

i hope a bump is allowed 

[Mark Hammer]

If you get "crazy feedback", it sounds like the circuit is unstable in some manner.  Which, again, suggests something is not right.  I'm wondering if the sensible thing to do is not to just make yourself a board for a Dist+ or perhaps follow one of the tested stripboard/vero layouts that someone has posted, and use the replacement values discussed here.  If you know the layout is verified, then that at least removes a few areas of doubt and reduces the troubleshooting required.

[cgibsong002]

If you get "crazy feedback", it sounds like the circuit is unstable in some manner.  Which, again, suggests something is not right.  I'm wondering if the sensible thing to do is not to just make yourself a board for a Dist+ or perhaps follow one of the tested stripboard/vero layouts that someone has posted, and use the replacement values discussed here.  If you know the layout is verified, then that at least removes a few areas of doubt and reduces the troubleshooting required.

I've looked at both the SD-1 and ZW layouts, and they are both very, very different from the distortion plus schematic. Will it really be possible to modify the + into something with the characteristics of an SD-1 (once I get the board right), or would I be better off going the other route?

[ddpawel]

I'm just waiting until someone modifies Marshall MG15 to get JCM800 

[cgibsong002]

I'm just waiting until someone modifies Marshall MG15 to get JCM800 

If you're going to take the time to ridicule somebody who is simply trying to learn, why don't you take the time to actually help out and give some suggestions?

[twabelljr]

How about just building the actual ZW-44, leaving the 1meg Gain pot out of the circuit. Just have the the 33k (R6) tying the ends of D1 and D2 together. That would be minimum gain. Then leave out the 20k Tone pot out, and in its place put 2 - 10k resistors in series where the tone pots lugs 1 and 3 would connect, then jump from the middle of the 2 10k's to C3. That should be the same as having the tone at 12:00 setting, unless the Tone pot has some weird taper. (or use a 20k trimpot for tweaking, to keep it inside the enclosure). Wire up the volume as normal and you will have a one knob (vol), minimum gain, tone at noon ZW Overdrive.
http://analogguru.an.ohost.de/193/schematics/Mxr_ZakkWylde.gif

[cgibsong002]

How about just building the actual ZW-44, leaving the 1meg Gain pot out of the circuit. Just have the the 33k (R6) tying the ends of D1 and D2 together. That would be minimum gain. Then leave out the 20k Tone pot out, and in its place put 2 - 10k resistors in series where the tone pots lugs 1 and 3 would connect, then jump from the middle of the 2 10k's to C3. That should be the same as having the tone at 12:00 setting, unless the Tone pot has some weird taper. (or use a 20k trimpot for tweaking, to keep it inside the enclosure). Wire up the volume as normal and you will have a one knob (vol), minimum gain, tone at noon ZW Overdrive.
http://analogguru.an.ohost.de/193/schematics/Mxr_ZakkWylde.gif

Thank you very much! That's more of less what I wanted to do, but didn't know exactly how to go about doing that. I found this vero layout... which is obviously completely different from the schematic you linked to. But I thought I read somewhere that it was verified. http://www.olaolaonline.net/page.php?image=20110104182044_wylde_my_vero.gif
Does anyone know of a verified vero for the ZW? I read that torchy had one, but I can't seem to find it. I'm thinking this schematic is a bit out of my breadboarding capabilities, unless maybe I can try breadboarding that more simple one from renegadrian

[twabelljr]

That layout is very similar to the schematic. Opamp pins 1,2,3 on schem are 5,6,7 on vero and 5,6,7 are 1,2,3 which is no big deal since it is a dual opamp. You would have to hook R6 to the drive pot D1 strip (move the lower end up one strip so it is connected to the 2nd and 3rd strips like the diodes). Ignore the drive pot. Substitute a trimpot for the tone control. The layout compared to the schematic looks pretty good just bouncing back and forth between pics. Renegadrian does good work. The input transistor is even there on the vero although it is not labeled. The vero also does not use assymerical clipping. Easy enough to add a clipping diode though.

[cgibsong002]

That layout is very similar to the schematic. Opamp pins 1,2,3 on schem are 5,6,7 on vero and 5,6,7 are 1,2,3 which is no big deal since it is a dual opamp. You would have to hook R6 to the drive pot D1 strip (move the lower end up one strip so it is connected to the 2nd and 3rd strips like the diodes). Ignore the drive pot. Substitute a trimpot for the tone control. The layout compared to the schematic looks pretty good just bouncing back and forth between pics. Renegadrian does good work. The input transistor is even there on the vero although it is not labeled. The vero also does not use assymerical clipping. Easy enough to add a clipping diode though.

Ohh.. I just realized on the schematic that that's just one op-amp. I thought it was two op amps and two transistors, while the vero was 1 and 1. Ok, I think I can work with this. Looks like I should only need a few parts possibly. What type of transistor is that? I have a tran from my LPB-1 layout.. or do I need two anyway?