Hello,
I just completed the MXR Distortion Plus circuit from Tonepad. Everything works, but the distortion only seems to really kick in at the extreme range of the pot. I've actually never played through a "real" Distortion Plus. Is this the way the distortion should behave? If not, what could I have screwed up to cause this?
Also, I was wondering if anyone has built this project with germanium diodes. I noticed that Small bear carries the 1N270 diodes, and the mods section of diystomp says that the germs are less harsh than the diodes Tonepad calls for. I was able to take the harshness out with a cap over the output pot terminals, but I thought it would be interesting to try to germ diodes to see if there is any difference.
Thanks,
John
The reason for the distortion occuring in the last bit of the pot is because of the taper of the pot that you used. A reverse audio taper pot will give a more gradual climb into distortion, or you can wire a regular audio pot backwards(you'll just have to think backwards when you turn it) to get the same thing. I left mine as is because it's not too big a deal to me.
The diodes are purely a matter of preference. Some are quite happy with Si diodes in the Dist+. Others(like me) prefer Ge diodes for their smooth sound. Socket them and have fun figuring it out for yourself.
Regards
RDV
I'm at the xact same point of Dist+ building.
I used a 'regular' 1 meg [not the reverse taper specified, and the Dist level can be adjusted through it's proper range [It would seem, because it gets extreme] but most of the change in the range is at the very end on the pots travel...N/P as far as I'm concerned, a different taper pot would certainly provide a different taper to the knob.
Yes diodes...Ge types are probably going to cut output level and provide harder [closer to the center of the linear swing] clipping.
Well mine of course has a 8pin IC used as diode/cap to ground socket. Also the board is well secured in the shallow box, I'll be trying out different diodes for another day or so I imagine...I like to play and retune after each diode swap that doesn't immediately sound like S.
I just posted a general question about what specific diodes are like in the Dist+ by others...titles Dist + Diodes...it should still be on the BYOSB forums page 1...
If you use a 100K linear taper pot for gain you don't notice the taper issues at all. The 1M isn't necessary in my opinion, maximum gain is achieved when the pot is reading 0 ohms resistance. The only thing you're gaining by using a 1M is more "clean" room on the gain pot - now why would you want that on a distortion pedal? :)
Jim
Quote from: Jim JonesThe only thing you're gaining by using a 1M is more "clean" room on the gain pot - now why would you want that on a distortion pedal? :)
The way a lot of people use them is for a semi-clean boost(even though I don't) which is why you would want to be able to reduce the gain that far.
RDV
I can't imagine a Distortion + sounding very good in that application, RDV? Although, as with anything music-related "to each is own" I guess. :)
Jim
The main reason for Dist+ IMO is it's internally generated distortion.
I tried it with the gain pot all the way down, part way down etc. just seemed like a dull sounding booster. Cool, usable [I guess] but not all that desirable to 'go after'.
Quote from: Jim JonesI can't imagine a Distortion + sounding very good in that application, RDV? Although, as with anything music-related "to each is own" I guess. :)
Maybe the term semi-clean booster is not right, what people do is use it as a distortion booster or lead booster, with the gain down & volume up. Randy Rhodes, & Yngwie Malmsteen are two of the more famous users who do(did) this. It works well, actually.
RDV
I just don't see it working very in that capacity at all - it's not like the Distortion + is a "loud" pedal - there just doesn't seem to be enough output.
Randy Rhoads - what a killer talent, but one of the worst guitar tones in history...
Jim
The most common pot values were 500k rev. log and 50k log. Mxr did put some out with 1m and 10k, though you won't get much volume with the 10k. You will definately hear a difference between ge and si diodes. When they're at spec, you'll even hear a slight difference between the 1N34a's and the 1N270 Ge's. Even an MXR reissue will benefit from replacing the si diodes with the above Ge's. I guess I'm one of the few that likes the original circuit values (including the 741 IC). I just sub metal film for the resistors, tants, and ceramics, but keep all vaues original.
If you want to really want to experiment, get the duel layout board (Dist.+/MicroAmp) Tonepad has. It uses the 4558 dual, so you can to town subbing IC's and diodes.
Jameco has 1N270's very reasonable:
http://www.jameco.com/cgi-bin/ncommerce3/ProductDisplay?prmenbr=91&prrfnbr=1340&cgrfnbr=697&ctgys=503;520;697;
Quote from: Jim JonesI just don't see it working very in that capacity at all - it's not like the Distortion + is a "loud" pedal - there just doesn't seem to be enough output.
I used 500K/100K.
Mine boosts like crazy if you crank both knobs! :wink:
For boost mode just take the volume ALL the way up, and bring up the gain until something starts smoking and there you are. :shock:
RDV
Thanks so much for the responses, I have many options it seems...
I think the first thing I'll try is putting a 100,000 K resistor in parallel with the gain pot, this should make the range from 0 to ~90000K which should give me the behavor Jim described. If this isn't what I'm looking for, I'll try a 500K reverse audio pot.
One thing I didn't understand from RDV's post was using a regular audio pot. Wouldn't this make things worse? Isn't the change in resistance fastest (per amount turned) near 0 ohms (max gain in this case)?
I'm going to check out the germ diodes too.
Thanks,
John
QuoteOne thing I didn't understand from RDV's post was using a regular audio pot. Wouldn't this make things worse?
I'll see if I can clarify.
If you wire a audio taper pot
Backwards, then you will have a
reverse audio taper, only the pot will be backwards, it will go down as you turn it up(and visa-versa).
Also read this:
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm
RDV
RDV,
Thanks for your post, I'm definitely going to read that article when I get a chance. Looking at the diagram of the 4 different pot styles, it looks like the audio taper would be the one that would fit this application. From 0 - 1/2 turn the resistance increases very slowly, so if this pot was put in backwards, as you suggest, it would give good sensitivity to the small area where distortion begins (near 0 ohms).
The reverse audio looks like in would always be fast near 0 ohms, so it would never provide good sensitivity right? Or maybe my brain's just not working properly ;)
Anyway thanks, this will probably be clearer to me when I get a chance to read the article!
John
Nevermind, I think I understand. I was thinking "backwards" in terms of which way the dial would turn on the pedal, but I think you mean that wiring from the wiper to lug 3 will always be the inverse of lug1 to the wiper.
Quote from: john1056The reverse audio looks like in would always be fast near 0 ohms, so it would never provide good sensitivity right? Or maybe my brain's just not working properly ;)
John
No, the reverse log was the original spec (500K). Remember, this is a simple circuit, so it's been modded to death. Now, many of the personal mods are now listed as original. 500k rev. log and 50k log are the original spec values. Someone reversed engineered a unit with 1m and 10k pots, and now, most every schematic shows those values. In other words, they were just re-copied. They (1m & 10k) were not the most consistant value used. A small company like MXR used a few different values because of what was available at the time.
I tried the 100K resister in parallel with the 1M pot last night by sticking the resister leads in the little holes in the pot lugs of the 1M pot (to adjust the pot range to ~100K). The result was a surprising high pitch squeal. I can't figure out why this would happen since the 100K resister should only be able to alter the circuit by lowering the resistance. Since the pot can go to 0, it's strange that this is a problem. Maybe I shouldn't be sticking things in those little holes? I used the little holes a few nights ago to experiment with cap values to cut the high end in the volume pot (as described in the mods section). That seemed ok.
Quote from: Fret WireNo, the reverse log was the original spec (500K). Remember, this is a simple circuit, so it's been modded to death. Now, many of the personal mods are now listed as original. 500k rev. log and 50k log are the original spec values. Someone reversed engineered a unit with 1m and 10k pots, and now, most every schematic shows those values. In other words, they were just re-copied. They (1m & 10k) were not the most consistant value used. A small company like MXR used a few different values because of what was available at the time.
I think I understand why reverse is right for this circuit. If you take a reverse log pot and wire it between the wiper and lug3 you get the desired behavior. With the knob turned full left you have max resistance (500K). In the middle (12:00) you are already past 90% of the total resistance (based on the diagram in the secret life of pots), so the resistance would be < 50K. From this point to full right the resistance would move very quickly to 0.
just a tip~
try red LED's for clippers... (fairchild i beleive)... it brushes on tht subject @ GGG, in the OD 250 page...
it is actually alot smoother than SI diodes in my opinion... i am a low gain tone wizard type..? and i went with the red leds in mine.
also~
do a search mark hammer shed some pretty good light on the dist+ pot taper about a year ago..
hth,
I've used a 500K linear pot for gain... and i hear something only at maximum gain :/... from 1% to 99% of the pot = *nothing*
The 100k log pot i've used for volume seems to work.. but at max the volume is veeery low... i have to turn drastically up amp volume to hear something...
please.. help me :(
when i bypass it.. it works perfectly.. so i think jacks wiring is right..
oh i've used DOD250 schematic with YJM308 variations..
I tried this, and would again, if DIST +ing.
I Found tones in diodes much better, plus it opened up the sound and helped add a touch of twang!
WQhat a nice pot to plant in a Dist+ clipping diode arena.
Quote from: DavideI've used a 500K linear pot for gain... and i hear something only at maximum gain :/... from 1% to 99% of the pot = *nothing*
The 100k log pot i've used for volume seems to work.. but at max the volume is veeery low... i have to turn drastically up amp volume to hear something...
please.. help me :(
when i bypass it.. it works perfectly.. so i think jacks wiring is right..
oh i've used DOD250 schematic with YJM308 variations..
Davide,
When I built this pedal, at one point I had exactly the behavior that you are seeing - I could hear a little sound if my amp was cranked. The problem in my case was that I had blown out the OP Amp. I'm not sure how I did it, but I had a few grounding problems with my input as well so I guess I could have fried it trying to troubleshooting that. Anyway I would first short the board to make sure the problem is there (put a little peice of wire between the out and in pins of your bypass switch and see if it acts like the bypass is on), if so swap I different OP Amp if you have one. Make sure your don't have your OP Amp in wrong, from what I've read that will fry it for sure. Other than that I would double check the continuity of the components, and make sure something isn't wired wrong.
John
Thank you :) i'm going to try and tell ya
ah, if someone is interested for the malmsteen variation i've modified the dod250 pcb ('cause of the different IC with two op amps instead of one)
(http://utenti.lycos.it/auledimandos/DOD308PCB.jpg)
(thanks to ggg where i took the 250 pcb)
Tha's what I use them for these days.
Got some batches from RS, for early build stuff. Now I use them to test cct's before I put in something like a TL072 or a 4558.
I usuallly wait till I'm about [hopefully] half the way through de-bugging before I put the 'nice one in. same thing with transistora, whenever possible I use a component I know works, but will probably not be the one I'll want in there.
so.. :)
i've tried to bypass in and out pins of my switch when the effect is on... and it sounds as bypassed, clear and loud...
when i remove the bypass it sounds distorted but with a veeeery low volume :/...
and my gain pot (a 500k linear) works only at maximum gain...
Unfortunatly that means the problem is definitely on your board. I don't know what to suggest other than just checking all the connections between components with a meter to make sure there isn't a bad joint somewhere. I would try to swap a different Opamp in though, especially if you've socketed it.
everything on the board seems ok.. i think i've fried the ic.. i dont know how but probably i did :P.. i'll try with a new one.. and i'll substitute the lin gain pot with a reverse wired log pot..
Hi,
With this design, if you are only interested in the top 10% or 5% of the rotation of a 1 Meg gain pot. You could just use a 100K or 50K pot for gain. Where it is located in the circuit, maximun gain is when the pot is at zero.
Regards,
Will
mmm
i've replaced the IC with a new one.... but no improvements...
i still can hear the distorted sound but only at maximum amp volume...
i'll try with new pots...
Hi Davide,
I know it sounds nasty, but I bet you anything there's a wiring error in your circuit. They're frustrating as hell to find but when you do it's like you climbed Everest. :)
Jim
i think you're completely right :P
but i've checked it many many and many times...
it was perfeclty working.. but i connected to ground ring's output jack instead of sleeve.. so i connected sleeves of both jacks with a wire to test... and it worked great... since i've corrected the mistake 'bout the output jack it does this trange joke.... and when bypassed there arent problems.. so i think jacks wiring is right.. and i havent changed anything else :/