Around Christmas I picked up one of the M-86 Classic Distortion pedals for $29 at GC, but as it basically sounded like the first half of the gain knob of the Rat model on my PODxt Live, I don't think I've plugged it in since. I did open it up, and after seeing pics of the Distortion III's guts, they're definitely the same thing, mine's just sort of gift-wrapped in black.
Has anyone tried any mods on either of these? They have a Motorola MC33178 IC and a tantalum cap, though I don't know what value and I haven't seen a schematic yet.
Here's the schematic:
http://analogguru.an.ohost.de/001/schematics/Mxr_Distortion-III.gif
Removing C4 seems to be a popular mod.
Anyone know of different op-amps to try?
If its a dual op-amp with standard pin configuration the usual suspect will work...
JRC4558
RC4558
JRC4559
TL072
TL082
TL2272
NE5532
Burr Brown fancy ICs
Hello
Can anyone comment about what audible difference removing the C4 will do? I had picked up one but it is more of a overdrive than a distortion, to me. I have the drive pegged 100% and still looking for more. Thinking about selling it (un-touched) unless the c4 mod will help or another (easy) hot rodding mod otherwise, off it goes.
Any insight is appreciated, S
I wish I had picked one up. I love stuff like this.
Quote from: stompbox steve on April 28, 2009, 03:19:44 PM
Hello
Can anyone comment about what audible difference removing the C4 will do? I had picked up one but it is more of a overdrive than a distortion, to me. I have the drive pegged 100% and still looking for more. Thinking about selling it (un-touched) unless the c4 mod will help or another (easy) hot rodding mod otherwise, off it goes.
Any insight is appreciated, S
It is definitely more of an overdrive. Removing C4 will increase the highs (which are way too low for my taste) and the noise.
Assuming the linked-to schematic is accurate, C4 rolls off treble frequencies above 72hz. Kinda low, dontcha think? Personally, I wouldn't stick anything in there higher than .01uf. That will roll off starting at just under 1.6khz. If you need mellow, then I suppose I'd accept .033uf for a 480hz rolloff. That will still provide some bite because the rolloff is a shallow 6db/octave.
Don't waste your breath or time on the op-amp choice. VERY little about this unit, besides maybe noise or battery-consumption, will depend on op-amp choice. This is principally because the clipping diodes are NOT in the feedback loop, like the Tube Screamer, but are after the output, going to ground.
If you want to invest time with some chance of reaping tonal rewards, I suggest reading the document on TS-9 tone control mods, over at Jack Orman's site: http://www.muzique.com/lab/tstone.htm
I love in this forum that people actually answer with useful info, not like other places. Everyone's input is always appreciated.
I will crack it open and see how I feel. The tone mod might be more than what I am looking to do. At this point I am leaning to sell it, but deep in my heart I can't let any pedal go...
my name is Steve and I am a pedal-holic.
1/ 2 Pi RC, 1/ 6.28 X (10 x10^3) x (.022 X10^-6)
723hz
Bah!! You're right. it's 22n, not 0.22u. So yeah, sleepy-head :icon_rolleyes: here totally agrees with Gus's math :icon_biggrin:; bump the rolloff freq up by 10x from what I said earlier.
However, the recommendation remains the same to both check out Jack's article and consider making the value of that cap a little smaller (something between 22n and 10n, like 15n or 18n) to permit just a bit more bite.
Quote from: Mark Hammer on April 30, 2009, 10:09:33 AM
However, the recommendation remains the same to both check out Jack's article and consider making the value of that cap a little smaller (something between 22n and 10n, like 15n or 18n) to permit just a bit more bite.
Or even set up the rolloff at something like 10kHz so that it only rolls off noise. Something like 2n2 or 1n would work for that.
Is the Classic Distortion being sold any more??
My local CG sold out immediately and Christmas time and never had them back in since. :(
I put in a .01uF in mine yesterday. Now it has enough highs available when needed without being too bright. Works for me. :icon_biggrin: Thanks for the tips!
Hi! This is an old thread, I know, but still seems like the right place to post this, and it might even benefit someone... :)
I have a Distortion III that has been subject to all kinds of modding experiences, here are some of my findings:
To get more gain and a juicier bottom end, place:
R4 1,2 k
C2 4,7 uF
(I also installed a "boost" switch to change between these and original values)
The above mod and a red/yellow led combo at clipping stage will get quite a nice Marshall type distortion.
My other mods:
op-amp 4558P (the original MC33178P is not bad at all, but I prefer this)
C4 reduced to 4,7 nF (more openness and treble control)
C6 raised to 100 nF (more bass)
Switch to disable clipping diodes
Switch to select original diode clipping or red/yellow led clipping
My DIII is already quite versatile (3 switches, each making a big change in sound) - but it still has a hole empty for a miniswitch to add something selectable... Any ideas? ;)
Adding in diodes in the first opamp's feedback loop?
Maybe something from one of these:
www.muzique.com/lab/tstone.htm
www.muzique.com/lab/zenmos.htm
How does the LED clipping sound?
I tried to add clipping in the first opamp's feedback loop, but I didn't really find anything usable. It may be because I only tried 1N4148's (singles, doubles, triples) and some LEDs. Germaniums etc. might get me somewhere (generally, I'm not a fan of the germanium sound). Should the achievable effect be really prominent or really subtle? Maybe I should pop the pedal open and really try to dig in deep with more diodes. I was a bit tired when experimenting, so maybe I wasn't putting my all into it.
LED clipping is really cool in my opinion. It gives a louder sound than (the usual) silicon diodes, and the distortion has a bit more flexibility and airyness than silicon, which is more squashed. Different colour LEDs have different operating voltages, and mixing them gives a softer, asymmetrical clipping (tubey sound) with more harmonics. My favourite LED clipping sound is the red / yellow combination. I'd say it's very much a high gain Marshall-sound.
For metal lead work, the pedal sound really good with clipping disabled, too.
By the way, my ultimate goal with this pedal is to have one single distortion / overdrive unit that does pretty much everything from mellow blues sounds (the original setup) to high gain heavy rock, and I think I'm getting all that. I think the basic sound structure of the DIII is fantastic - a big, ballsy sound that can be tailored to the taste. 8)
I bought one of the MXR Classic Overdrive pedals.I found out that the builder of the pedal put a secret black switch inside.I unsoldered the switch and put in a SPDT(on-on switch).Know you can switch from the stock mode to another mode that has less volume,and less of a mid hump with softer clipping.
Quote from: soupbone on September 04, 2010, 06:11:12 AM
I bought one of the MXR Classic Overdrive pedals.I found out that the builder of the pedal put a secret black switch inside.I unsoldered the switch and put in a SPDT(on-on switch).Know you can switch from the stock mode to another mode that has less volume,and less of a mid hump with softer clipping.
I know about the switch inside (it changes it from the ZW-44 circuit to the Custom Shop OD circuit), but I don't understand what you did. Are you saying you put an EXTERNAL switch on the pedal to switch between the modes?. It's a little unclear.
Al
Quote from: zombiwoof on September 04, 2010, 03:43:13 PM
Quote from: soupbone on September 04, 2010, 06:11:12 AM
I bought one of the MXR Classic Overdrive pedals.I found out that the builder of the pedal put a secret black switch inside.I unsoldered the switch and put in a SPDT(on-on switch).Know you can switch from the stock mode to another mode that has less volume,and less of a mid hump with softer clipping.
I know about the switch inside (it changes it from the ZW-44 circuit to the Custom Shop OD circuit), but I don't understand what you did. Are you saying you put an EXTERNAL switch on the pedal to switch between the modes?. It's a little unclear.
Al
You just take out the switch.It has 3 holes that it is connected to.Cut off 3 pieces of wire solder them to the blank holes,then solder the 3 wires to the 3 lugs of a spdt switch(on-on).You're done!!(you do have to drill a hole in the enclosure though for the switch).
Quote from: Jurbo on August 19, 2010, 04:28:12 PM
Hi! This is an old thread, I know, but still seems like the right place to post this, and it might even benefit someone... :)
I have a Distortion III that has been subject to all kinds of modding experiences, here are some of my findings:
To get more gain and a juicier bottom end, place:
R4 1,2 k
C2 4,7 uF
(I also installed a "boost" switch to change between these and original values)
The above mod and a red/yellow led combo at clipping stage will get quite a nice Marshall type distortion.
My other mods:
op-amp 4558P (the original MC33178P is not bad at all, but I prefer this)
C4 reduced to 4,7 nF (more openness and treble control)
C6 raised to 100 nF (more bass)
Switch to disable clipping diodes
Switch to select original diode clipping or red/yellow led clipping
My DIII is already quite versatile (3 switches, each making a big change in sound) - but it still has a hole empty for a miniswitch to add something selectable... Any ideas? ;)
Hey! Great post.
I`m really interested on trying this mods on my DIII aswell, is there a chance to see some pictures of yours?
To see how it`s been done would be very helpfull.
Thanks.
Martin
Hey Martin - here's a lowdown of my mods. The modding and experimenting process took its toll on the pedal pcb (for example, removing the opamp was terrible and caused damage), so there are a couple of destroyed copper traces (replaced with wire) and a general messy look, but the thing is alive and stronger than ever, so... ;)
Here's a view of the controls - I added three switches:
(http://s1.postimage.org/cfLp9.jpg) (http://www.postimage.org/image.php?v=gxcfLp9)
- Gain Hi / Std (Hi gain or Standard gain)
- Lift / Clip (this removes or engages diode clipping - the lift mode is great too, as the opamp screams by itself, too)
- LED / Orig. (if Clip is selected, this toggles between LED clipping (red + yellow) and the original diode clipping)
To understand the changes and the actual soldering points better, you should study the schematic by Gottfried Divos.
In the process, quite a few components have been switched from the top side of the PCB to the bottom side (for a good reason or no reason...).
Gain switch selects either the original R4 + C2 chain (2,2kOhm + 100 nF) or a juicier R4 + C2 chain (1,2 kOhm + 4,7 uF), placed between opamp pin 6 and ground.
The two clipping related switches connect/remove stuff between ground and D1/D2. You can see the original diodes and LEDs on the bottom side.
For easy opamp changing, I installed an 8-pin socket. I like the TI 4558P best.
For easy treble cap changing, I installed a socket for C4 (I actually have 2,2 nF there, not 4,7 nF, giving even brighter sound).
For easy bass cap changing, I installed a socket for C6 (but the caps I like are so large, that the 100 nF cap (big green square) had to be soldered to the bottom side).
A couple of wires on the bottom side are fixes for broken traces.
(http://s1.postimage.org/cfNUi.jpg) (http://www.postimage.org/image.php?v=gxcfNUi)
(http://s1.postimage.org/cfXSS.jpg) (http://www.postimage.org/image.php?v=gxcfXSS)
(http://s1.postimage.org/cg1S9.jpg) (http://www.postimage.org/image.php?v=gxcg1S9)
(http://s1.postimage.org/cg6Rr.jpg) (http://www.postimage.org/image.php?v=gxcg6Rr)
(http://s1.postimage.org/cgekS.jpg) (http://www.postimage.org/image.php?v=gxcgekS)
At one point I also had an adjustable Big Muff eq installed, with a trimmer (tone pot) inside the pedal and a switch on top to engage/remove the Muff mid scoop. I removed it, because it took too much volume away and I don't know how to design a necessary amplification stage for it. Anyway, that leaves me with an extra hole for a switch, if I decide to try yet something extra for this pedal. By the way, these mods with all the sound evaluations took my one week's spare time, but it was really educative and I learned a lot. And I think the sounds are killer!
Hey!
Thank you so much for the pictures!
I will try to do the same to mine.
I really love this pedal, but i feel like it could have more gain, you know?
Will try it and send photos!
Thanx again!
Has anyone tried to lift clipping diodes fom bias to ground? Whats happened? Stronger clipping? Or is it wrong in this circuit?
Removing the clipping diodes will not result in more clipping. You will get an increase in volume, though.
In original version diodes are connected to bias. I asked who connected them to ground, not lift totaly!!! I know what disconnect will do - more volume and op-amp clipping.
Ah...a misunderstanding on my part.
could you take off the stock pots and add better quality pots and attach wires to them to make the pedal more durable?
You could, but D-taper pots are hard to find. I think the pots they have in there are fine for durability. As long as the nuts are tight and you aren't rough on the pots, they should be okay.
Quote from: AndrewSeth9115 on March 08, 2011, 08:10:39 PM
could you take off the stock pots and add better quality pots and attach wires to them to make the pedal more durable?
My opinion is Don't Fix It If It Ain't Broke!.
Al
I built the Dist III today and I did these mods:
C4: 10nF. The stock 22nF is just too low/middy. I strongly advise against removing this as it will turn the tone knob into a high-shelf knob with way too much highs!
C2: 220nF. Brings back your low-end. Much like the fat mod found on tubescreamers
D1 & D2: Germanium! I tried 1N60 but settled on 1N270's. Removes the modern high-gain sound and adds a vintage character to the pedal.
Overall, I'm quite impressed with this overdrive. Now let's see how long this one will stay on my pedalboard ::)
Quote from: Harold on July 10, 2011, 12:01:28 PM
I built the Dist III today and I did these mods:
C4: 10nF. The stock 22nF is just too low/middy. I strongly advise against removing this as it will turn the tone knob into a high-shelf knob with way too much highs!
C2: 220nF. Brings back your low-end. Much like the fat mod found on tubescreamers
D1 & D2: Germanium! I tried 1N60 but settled on 1N270's. Removes the modern high-gain sound and adds a vintage character to the pedal.
Overall, I'm quite impressed with this overdrive. Now let's see how long this one will stay on my pedalboard ::)
Does changing D1 and D2 to germanium lower the output of the pedal?.
Thanks.
Quote from: zombiwoof on July 10, 2011, 02:59:23 PMDoes changing D1 and D2 to germanium lower the output of the pedal?.
Thanks.
Is sure does! Using 2 parallel pairs of germaniums in series should increase volume, but remain "vintagy". I'll be the next thing I'll try!
This was one of the first threads I found on this topic. Although it's very old I want to state s.th. here after trying out various mods. This pedal can be seen as a very effective unit to tighten up your sound using drive level at 0 and output level almost maxed in front of the crunch or overdrive channel of your amp.
C4 mod to a lower value makes sense if u miss some highs or brilliance in your tone. I have done this and kept it at 10nf.
C2 mod to bring back the low end makes no sense at all for people who wanna tighten up the sound. The stock capacitor there makes a very good job. You can tighten up any normal passive humbucker to pure metal tone for broken riffage. Only if you really want to use it in front of your clean channel this mod makes sense.
Reducing R4 will give you more gain but you'll never end up with turning this into a high gain pedal.
Lifting the clipping diodes: Bravo! This gives you an almost mesa boogie - like, slightly wah-like tone and attack.
Some people might still find this thread via search engines, so those are my little bits on this topic.