Dist+ or DOD 250 or Ross Distortion?

[akc1973]

Hi Folks,

I've got a GGG Distortion PCB and I'm tossing up which circuit I should build on it. Do you guys have any preferences between the MXR Distortion +, the DOD 250 or the Ross Distortion? I already have built a ROG Omega (my fave pedal ever), and have a FAB distortion.

Thanks in advance,

akc1973

[Electron Tornado]

The Dist +, etc, are so similar that you can have the best features of each. It's such a simple circuit that it's easy to add some mods to your build. Take a look at this article:  http://www.premierguitar.com/articles/mxr-distortion-plus-mods-1

Here's one component the article doesn't really discuss: C4 in the Dist +, (and the Ross, I think) is 1uF, the DOD 250 uses 10uF there, if I recall. Some people think the DOD 250 sounds "warmer" than the Dist +. If you like both, you can make them switchable. I found 4.7uF to be a happy medium for me.

Some people claim to hear differences in tone between the 741 and a TL071 op amps. I don't. However, either one of those is suitable for this circuit.

Have fun!

[Elijah-Baley]

I'm building a dod250, work in progress. I don't know the (I think little) differences between these pedals, so I can't give to you a very good answer, but I can tell you what I know.

TL071 could be a less noise replacement (less noise in the Micro Amp, too).
I'm using an UA741CN, but I still can't anything about noise at this moment because my version has less gain than original. I'm trying to come out a mod with low and high gain switch. Actually, the tone seems nice, my opinion of course.

If you have a breadboard you could hear the three configuration, testing it with the different components.

[Mark Hammer]

They are all pretty much the exact same pedal.  Here are differences that matter:

The MXR uses germanium diodes, and the DOD uses silicon.  Germanium have a lower clipping threshold than silicon.  This will yield more audible clipping at any given gain setting, but it also means the output level is lower.  So, if you want the sound of the pedal alone, germanium is better.  If you want the pedal to have more output and drive the amp harder (i.e., the sound you prefer is a product of pedal + amp), then silicon is better.  If you only want modest clipping and a hot output, then raise the threshold even higher by subbing a silicon+germanium in series for each Ge diode shown.  

The MXR unit exploited the weaknesses of the 741 op-amp.  Many here have reported that they have fo8und it nigh impossible to get a clean sound from the thing, even without the clipping diodes.  I suspect, but cannot confirm, that this is partly a product of the 1M pair that sets the Vref/bias voltage.  That pair provides a very low bias current, which may bring out the dirty-ish qualities in the 741.  I'll leave it to the EEs here to confirm or refute that hypothesis.  If I'm right, then the MXR is sort of a "double-clipper", in that it takes an already dirty signal, and clips it again, with diodes.  Use of a better-quality op-amp likely won't get you that, and use of a higher-current Vref (e.g., by using a 20k+20k pair, instead of 1M+1M) might not, either.

Non-inverting op-amp gain can be set by either the feedback resistance, or the ground-leg resistance, or both.  The feedback resistance interacts with any feedback cap such that, as gain is increased, top end is diminished.  The ground-leg resistance interacts with any capacitance it is in series with such that, as gain is increased, bass response is diminished.  All three of these pedals lose bottom end as you crank the gain, so one regularly sees (as is shown in the Wampler mod article) recommendations to increase the .047uf cap to something higher, like .1-.47uf.

Though I can not confirm it, my sense is that MXR elected to use the ground leg to set gain, and forfeit bass with increased gain, because pickups at the time tended to be less attentive to noise (i.e., few, if any, hum-rejecting or lo-noise single-coil options available), such that decreasing the amplification of any 60-cycle hum as you turned up was considered a good thing, rather than a forfeiture.  The seemingly brighter tone as gain was increased also allowed a 2-knobber to provide a broader range of tones.

All 3 units can present with an annoying fizz, because they do not take steps to tame the top end.  If one adjusts gain via the feedback resistance, as Brian shows in the mod article, one keeps bass as gain is increased.  But what he doesn't show is any feedback cap to smooth out the highs, as happens on a Tube Screamer.  Consider sticking a cap in the position that GGG shows as C5.  I'd personally recommend a value between 47pf and 100pf, with values of 22pf or less delivering improvements in chip stability but nothing you can actually hear as a tonal change.  Sticking a 3300pf (.0033uf) cap in parallel with the clipping diodes will also help to warm up (fizz down?) the tone.  The feedback cap in tandem with the 2nd cap to ground will bring out a nice growl from the unit, instead of the shriek it normally produces.

Finally, the 10k volume pot shown in some drawings posted around really ought to be a higher value, like the 100k that GGG shows.  If you decide to use the more traditional ground-leg approach to gain change, that GGG shows, then 500k reverse log is not really that essential.  Its original intent was to allow the pedal to magically transform from a modest semi-clean booster to an overdrive....in the days when few pedalboards would have more than 3 pedals on them.  These days, that seems moot.  A 100k pot will provide sufficient control over degrees of overdrive.

[Quackzed]

another small point about opamp choice is that many prefer the sound of these pedals with the older 741 chip (me included) because the speed of the transition from clipping to not clipping is slower and therefore smoother. newer chips may be slightly less noisy, but the increased fidelity in the high end isn't always a good thing and the older chip can sound smoother/ less harsh.
germanium diodes do indeed clip at a lower threshold, and sound smoother and warmer at low gains, overdrivey but as mark stated, you lose more output volume. where silicon you get a little more output volume for boosting whatevers next but the clipping is a bit harsher or fizzier.
also as stated the output volume of a germ dist+ can be less than unity with lowest gain settings( barely clipping) so a 100k volume pot is just a good idea if building one, you can always get less volume but a little more is a big plus for germanium diodes as they can be lower than unity at low gains...
i'd build a dist+, it's the original design... i use my germ dist+ all the time. its a good solid distortion without any heavy toneshaping at lower gains and at high gains it rolls off lows nicely to keep it tight, no bass flooded swampy distortion with the gain up...

[Mark Hammer]

I suppose another compromise is to simply insert a smallish-value resistor between the germanium diode pair and ground, if you want somewhat less clipping and more output.  It's an interesting trick I swiped from some other designs, and it works well.  Doesn't produce nearly the huge difference in output that yu get fr switching between different combinations of diodes, and it is simple to defeat by merely bridging the added resistor.

[Quackzed]

  it's funny you should mention that, i went as far as to add a diode ladder onto one, like adding a resistor to the diode pair, but a 10kish to ground after the first si' diode pair, then a 1k after the second si' pair, so at the first pair threshold, its only halfclipped/half clean-ish, then at the second pair its 'mostly clipped, but a little softer than no resistor...
i think i ended up letting more opamp clipping through, as there wasn't enough headroom to just hear the diode ladder alone...
but its very dynamic this way, you don't hit a hard volume threshold- so if you lean on it it gets louder as well as more distorted... to a point.
to the op: i'd go stock at first, i use my stock one more often, you can always try different mods later ...

[petey twofinger]

i did my first one stock , but added a switch to change over to a set of 3mm red leds intsead of the stock clipping diodes .

i do not use the stock mode much , ever

there is a decent volume boost when i switch over , i compensate for that with the volume knob but ... i dont use the diodes .

i feel it offers enough gain with my set up , it seems very pick sensitive ,  i would say this is my favorite mod  but i didnt try anything that mark mentioned .

i would describe the stock sound as compressed and 80's ish . the leds , much more open , much less fizz but also its more of an over drive now . i dont use a ts so ... this works really well for me , but i am a fan of the cot 50 as well . this sound paired with some trem and a bit of reverb works really well .

[Mark Hammer]

Incidentally, if one includes the suggested 47-100pf feedback cap, and the cap in parallel with the clipping diodes, that will reduce audible noise substantially, reducing any real advantage provided by using other "better" op-amps.

And FWIW, I've made Dist+ units with a SWTC tone control on them and that works well, albeit at the forfeiture of a bit of output level.

[aron]

To me, the Dist+ etc... they really need a tone control as you say. The simple mods section applies very well with this pedal.

[Electron Tornado]

To me, the Dist+ etc... they really need a tone control as you say. The simple mods section applies very well with this pedal.

The circuit is so bare bones that it really gives a lot of room for mods. One could go so far as to add pre and post clipping tone controls. The signal drop due to a passive tone control can be overcome with either a single transistor gain stage or a dual op amp.

[akc1973]

Thanks for all the detailed responses, guys! 

I'll let you know what I end up doing.

akc1973

[petemoore]

 Input cap and what it's fed [SC / HB etc..booster?
Treble control at the end.
Set gain and adjust clipping diodes.
Drop voltage and boost the input !
I like the input cap on an offboard wire, or large value on the board to be trimmed by a series cap and possible switch..
Treble control is cap>10k pot>Gnd. type, try .01uf or smaller, or SWTC.
I have best results with it being pretty to very hard distorted, adjusting it 'outside' the circuit by putting boost, distorting booster and compression circuits before it, but just the treble and volume at the output work out well with the fixed ~high gain setting.

[aron]

I have a ROSS distortion and I tacked on the Sonic Distortion tone control on the end.

[pinkjimiphoton]

to me, the ross has the best overall tone. a simple tone control is a great feature, but ya may wanna try adding a big muff pi type with the added midrange control. lets ya really get on top of it.

i liked the lm308 in this circuit best, followed by the 741... the older metal can ones sound a little looser to my ear than the more modern chips, but not enough to really matter. ne5534 sounds good too in these, lower noise floor and a somewhat sweeter distortion.

i like an asym clipper on these too, one side ge and the other side a pair of 914's or whatever in series on the other...smoother distortion to my ear, not as fuzzy as a dis + can be, but not as tite as the dod. led's can sound really good on the dod circuit too, the one i built had ge on one side, none in the middle, and led's on the other side...all very useful.

this is a great circuit to mod, and real toneful. keep the leads to pots short, it can oscillate pretty easily!!!

[zbt]

Another my DOH! moment





and what's more, this alien Ross which should be sunbathing on the beach






isn't it the same as YJM308, what does Curly Ribs 4558 taste like?
I seem to be missing the relation between db and Hz or I misinterpreted the data



while it looks good in the picture, in reality the 1M/500K gain pot seems a bit odd




if I draw the pot in linear step, it spike at 8 - 10 (the drawing use NT term, one louder)
For 500K the gain jump from 11, 19 to 214, is this another trick?
kind switch without click?
because Yngwie Malmsteen play all max out? DOH! (another no or one knob)

I try to change to 250K 100K 50K
I think for 10K the frequency field is wider (230Hz - 720Hz) gain (69 - 214)
To make 720Hz  in the middle, try 5K in series with 2K2 (470Hz - 1539Hz) 
only the gain goes up to (140-456) and isn't this distortion



looks good? cause I havent test yet, but it is equation right
DOH! or probably three knob

this board are more versatile, but only for single op amp
https://www.madbeanpedals.com/projects/_folders/VFE/pdf/VFE_Distortion3.pdf

i liked the lm308 in this circuit best, followed by the 741... the older metal can ones sound a little looser to my ear than the more modern chips, but not enough to really matter. ne5534 sounds good too in these, lower noise floor and a somewhat sweeter distortion.

this look interesting 

[zbt]

good Lord!

He makes max all to ten, and He use humbucker 

[Mark Hammer]

A late teaching colleague used to get load-out gigs at various concerts around town.  He was surprised to find out that many cabs in the mountain of Marshalls that Kiss had on stage were actually empty, and many of the amp heads were just parked, unpowered, atop those cabs.

[Steben]

I suppose another compromise is to simply insert a smallish-value resistor between the germanium diode pair and ground, if you want somewhat less clipping and more output.  It's an interesting trick I swiped from some other designs, and it works well.  Doesn't produce nearly the huge difference in output that yu get fr switching between different combinations of diodes, and it is simple to defeat by merely bridging the added resistor.

Resistors are the key it seems. Adding resistance in series with silicon diodes mimicks the germanium curve closely but with higher output... Shockley...

[zbt]

A late teaching colleague used to get load-out gigs at various concerts around town.  He was surprised to find out that many cabs in the mountain of Marshalls that Kiss had on stage were actually empty, and many of the amp heads were just parked, unpowered, atop those cabs.

May be, sponsored by Boze ... accoustimass Sir

For NE5534 inside there is transistor at + and - input, would not it act like preclipping?
also if I remember reading ETI amp, also take a cap between can reduce slewrate,
maybe we can apply to 741 to make it like 308