I think I've just added another pedal to my "to do" list.

[RaceDriver205]

Yeah, ill add my approval too, for its simplicity you can get a good decent sound.
Good example sound clip of it using BAT46 diodes at www.tothemax.web1000.com, under 'FXDemos'. Bottom of page, under "Delay",  the sound clip titled "reverb" setting.
Would put a direct link, but web1000 doesn't allow it.

[Fret Wire]

500KC would be the reverse log dist. (gain) pot. Usually "C" deontes rev log. As far as the diodes, thats something I noticed in this ckt. I've never a/b'd 270's & 34a's in other ckts, so I don't know if it applies across the board in other ckts.

[Mark Hammer]

Said it before and I'll say it again, the reverse log taper of the gain pot was to get the gain through the "useless" part as quickly as possible with a pot of that high a value.  Just about any 100k pot linear or log, will provide as much dialability.

Do the math.  With a 1M feedback resistor and 1M+4k7 in the ground leg, between the "-" input and gnd, the op-amp has a gain of around x2.  Not enough to get the diodes clipping unless the input signal is SUPER hot and already boosted.  With the same pot turned down to half the resistance (500k), the gain is now a death-defying x3.  Drop it down by half again to 250k and you have an equipment/marriage/hearing/lease-destroying boost of x5.  Still no diode-clipping.

You really don't get any sort of appreciable diode-clipping, even with power chords, until you start getting into the range of x10 gain or so, which is a ground resistance of just over 100k plus the 4k7 fixed series resistor.  The reverse-log or "C" taper simply gets you past that first 900k in a really big hurry.  So why knock yourself out about it?  Go immediately and directly to the part of the gain range that matters.  Get a 100k pot and be done with it.  I suppose some might still find a reverse log or perhaps linear, is just the taper for them in terms of dialing in sounds with some precision, so don't feel confined to one taper or another.  The main point is that if you can take that last 100k of resistance and spread it around the entire rotation of a pot, you have accomplished 90% of the job that tnhe reverse log was intended to address.  If you were putting in an order somewhere and needed to buy a pot anyways, I suppose you can spend the money.  But if you have 100k pots just sitting around without anything to do and want to finish the pedal, don't bother ordering; use what you've got.

[Fret Wire]

Mark, if you use a 100k lin, the smaller gain range is still going to be bunched up towards the end. Have you ever actually marked off 100k and checked the level through an amp? Or is it keyboard and math? How do you get quickly past the first useless 900k with a 500k pot. You seem to be deciding how much gain everybody wants. What you always suggest is fine for bedroom playing where you'll be using the majority of the pedal's distortion instead of the amps. What about an amp that has a fair amount of overdrive? Mesa, Marshall, etc. Even a dimed tweed champ won't need that much gain to get a useable dist. sound. Don't forget that whether the 500k pot is all the way down or not, your sound is still affected by the eq of the pedal (bass rolloff). Randy Rhodes supposedly used it more the eq, not heavy on the gain. What if someone wants to just build an authentic D+? For someone who always suggests ckt mods for more flexibility, this is one case where you always suggest less flexibility, not even knowing the posters rig. I hope it's not just for the sake of argument with me, I couldn't care less.

It suprises me that people still don't know the original pot values and tapers of such a simple ckt. I know I've done nothing to confuse that issue. We should at least get some kind of speaker's fee for popping up in every D+ thread. Would this be BUM+? Mod a ckt before you even build it or know how it's going to react with the posters rig?

[Mark Hammer]

We should at least get some kind of speaker's fee for popping up in every D+ thread.

  You can have my share, brother.

I think your points are well-taken, and certainly if someone desparately WANTS "vintage", go for it.  My sense is that people want it not so much for its lower gain sounds, though.  I'm not telling anyone to do that, I'm just reading what people say and say they want.

To the best of my knowledge, the "original" used a 1M reverse log taper pot for gain.  That may have been changed since 1978, but the use of reverse-log, and the purpose of it appears to remain constant.  The reverse-log taper produces some substantial changes in resistance in the first 1/3 of rotation as you move clockwise, and then "simmers down".  If it were a linear taper, then all the useful changes in gain would be crowded into the last 1/10 of rotation (an arc of <30 degrees).  Taking the resistance of that last 1/10 and spreading it across the latter 2/3 instead makes it more dialable for the user.  The first 1/5 to 1/3 of the range (even with a reverse-log pot), however, still remains pretty useless for the vast majority of players.

The qualifier here is that, as any experienced and adventurous D+ builder can attest, it is virtually *impossible* to make it sound clean.  Lift the diodes and set the gain to minimum and it is still gritty.  I still think we need to collectively explore the role of the biasing circuit (there is 2meg of series resistance between V+ and the noninverting input!) to see what that is doing to a 741, but the point is that the pedal still introduces coloration even when set in a manner that ought not to do so.  Of course, my counterpoint would be that this coloration is still present and accounted for, and not really any different, when the gain is set to around 10, well before the diodes start to seriously kick in.

Your point about how much gain is needed to extract more edge from an amp is spot on.  My tweed Princeton doesn't take all that much boost to start singing.  On the other hand, I'd rather do it with a dedicated straight boost pedal, and have a separate distortion pedal for....distortion.  And unless they simply lack the funds or pedalboard space, I imagine a great many players would do that too.

As for the EQ-ing effects of the Dist+ (and I've lost count of the number of times I've fielded requests about how to defeat that!), that also doesn't really kick in until the gain starts to go up noticeably.  At lowest gain (R = 1M+4k7), the .047uf cap yields a rolloff well below 20hz.  Even with R = 100k, the rolloff still is only below around 33hz.  It's not until the gain pot starts to have a resistance dipping below 50k (plus the 4k7 of the series resistor, giving a gain of about x19) that you start to get bass rolloff which is clearly audible on most guitars on most amps (below around 62hz).  Again, using a 100k pot instead of 1MegC doesn't deprive one of the accompanying bass rolloff that some (but not all) prize their Dist+ for.

In sum, I'm not going to knock anyone for using the stock value pot.  It doesn't become a lesser pedal by doing so, not by any stretch of the imagination.  At the same time, use of a plain vanilla 100k pot doesn't decrease what the Dist+ does or is capable of by more than maybe 5%, if that, so no one should feel like they are somehow settling for anything substandard if they look in their bin and that's all they have.  100k is not *better*, it's just not discriminably *worse* in most applications.

[formerMember1]

I have been interested in this pedal these past weeks too.  BUt i mainly play a strat.

So how does the DOD250 sound with a strat? or is it better with a HB/les paul guitar?

just looking for opinions...

BTW, buying a new DOD250 for $39.99 at Musiciansfriend.com and modding it to '77 specs doesn't seem bad at all.

[MartyMart]

Sounds great with a strat ( mostly what I use, though have a couple of HB gtrs too )
Probably gets "cleaner" with a lower output strat/tele too
I had several Dist+/250 circuits, like Liquid drive, Ross Dist, Dist+ and they all came alive
and much more useful when I discovered 500KC pots   HIGHLY recommended !
( thanks smallbear )

MM.

[formerMember1]

Cool thanks Marty! 

[RaceDriver205]

it is virtually *impossible* to make it sound clean

I had to use a 1Meg for gain, as there was no 500K 9mm pot (had to use 9mms). With it wound right down, the output sound is very clean, and it can be used as a clean boost. At least, if my memory serves me right.

Can't one just use a lin pot, and turn it into a pseudo-rev-log pot using the info at geofex.com?

[Burstbucker]

Thanks again to all that have contributed to this thread.

So, as far as some of you guys are concerned, this pedal will sound better using a non-polarised 1uF box cap instead of the stock 1uF polarised Tantalum cap?

[MartyMart]

Thanks again to all that have contributed to this thread.

So, as far as some of you guys are concerned, this pedal will sound better using a non-polarised 1uF box cap instead of the stock 1uF polarised Tantalum cap?

Yup !
RDV may still have some for sale, I bought a bunch from him and they are small enough for most
circuits 6mm x 5mm x 1cm high, he had 680n's also, about the same dimentions

MM.

[Torchy]

ESR (http://www.users.zetnet.co.uk/esr/) have 1uF 63V box poly's (metallized polyester), slightly smaller than that at £0.25p.

[Fret Wire]

Good post Mark, points well made. You're far too diplomatic with my cranky edged post. Yes, I never thought of it as a clean boost either.

Yes the biasing is definitely something to explore further. Everyone concentrates on diodes and such. I also am interested in hearing how everybody adjusts their od/dist's. Bedroom/clean style vs incremental style. In one case the pedal is providing all the dirt, in the other case, the amp is doing most of the work and the pedal is providing the last bit of dirt. Big difference in touch response and feel between the two methods. I have quite a few amps and only one has a master volume. So I've always adjusted incrementally. Except fuzz's of course.

Ritchie, like Marty said, the 250 sounds fine with a strat. You can take a new one and replace the 4558 with a 1458, ditch the pf smoothing cap, and it'll be more like the original. Add a switch to go between yjm308 + 250 input caps, and it will be more versatile.

Burst: Panasonic ECQ-V 1uf caps are real small for their uf value. Digi-Key carries them. They're the ones Keeley is always refering to on his site.

[WGTP]

Do I hear a 250K reverse audio taper pot.

OK, I couldn't resist any longer.  This Rat dual leg thing is too much fun to sim.  For dual leg Dist+

Similiar gain/Rat like response 4.7K/22n leg and 47K/47n leg

Similiar gain/Bigger Bottom 4.7K/22n leg & 22K/100n leg

More Gain/Rat like response 2.2K/47n leg & 22K/100n leg

More Gain/Biggest Bottom 2.2K/47n leg & 10K/100n leg

The first leg sort of controls the highs and mids and the second leg the mids and lows

If there is too much gain, reduce the 1Meg resitor in the feeback loop to 470K or even 220K 

Feel free to mix and match values, or use pots or switches 

[formerMember1]

Ritchie, like Marty said, the 250 sounds fine with a strat. You can take a new one and replace the 4558 with a 1458, ditch the pf smoothing cap, and it'll be more like the original. Add a switch to go between yjm308 + 250 input caps, and it will be more versatile

Thanks Fretwire, that is the method i will probably choose.  Probably have to change the diodes, change some of the mylar caps to ceramic etc...  But I don't need help on that, i can figure it out with some schemes,  I am just blabbing...

[Mark Hammer]

RE: tantalum caps in 1590B-sized MXR pedals in general.

People can feel perfectly free to show me contradictory evidence and make my face turn a bright beet red, but.....

In light of the size of the pots, switches and jacks used in those MXR pedals stuffed into 1590B-sized boxes, MXR's choice was to use those caps types that could be easily bent on their sides to produce a flatter-profile board.  This would allow it to be easily stuffed into that box on top of the other existing parts (noted above).  This translated into frequent and regular use of both ceramic disc and tantalum capacitors in their pedals, rather than plastic or electrolytic types.  I can vouch for the fact that in 1978-80, the typical 1-10uf/16-25v cap was virtually always about 1/3 smaller in tantalum than in radial electrolytic form.  Generally more expensive too, but if it made the difference between being able to close the box easily...or not....you sprung for the extra 20 cents a cap or whatever.  Historically, you see box-type plastic caps as the 1590BB-sized boxes start to come out.  The sole exception to this rule of thumb that I am aware of was the 6-band equalizer, which used board-mounted slider pots, not stompswitch, and had to fit all components in the spaces between the pots

There are two aspects to this design move.  One is that if one wants to produce an authentic replica, then ceramic disc and tantalum are what you aim for....whether you need to conserve space or not.  The other is that ceramic disc and tantalum may not be the best choices for audio reasons and that "better" caps should be chosen wherever possible. The in-between compromise is that things like power-supply related caps can be electrolytic while polarized caps in the signal path can remain tantalum or ceramic if the builder/user is aiming for authenticity.  For instance, ane electrolytic cap betwen V+ and ground should not impact on tone,, whereas a tantalum output cap in the Dist+ *MAY* yield something sonically different.

[Toney]

I also am interested in hearing how everybody adjusts their od/dist's. Bedroom/clean style vs incremental style. In one case the pedal is providing all the dirt, in the other case, the amp is doing most of the work and the pedal is providing the last bit of dirt. Big difference in touch response and feel between the two methods.

Valid point, totally agree.
Stage volume/house level. Two separate worlds in the case of drive and tube amps and its often the missing vital info with build reports

Love the dist+. have it with si diodes on mostly (switch)...but Ge's sound best whan the amp is pushed hard.