My first project -> MXR Distortion+

[Fumi SG]

Hi there,

I'm going to build my own MXR Distortion+, but I want to change the circuit a little bit. I want to stick an extra pair of diodes (2x 1N4148) next to the original 1N270. I want to choose them by using a switch, so I can choose between the original pair of 1N270's and the other 1N4148's.

Because the 1N4148's have a higher output, I want to place a 5k resistor at 'the end' of the pair.....

Here is my 'modified' schematic.




Well, is this possible (following this schematic)?? And what kind of switch do I have to take, I'd like it as simple as possible! :wink:

[Fumi SG]

nobody?

[jimmy]

hey, it looks good to me! i dont think that whacking a resistor between the diodes and ground will give a volume drop (i may be wrong). i cant think of a good solution to that right now so ill move on. you'll need a SPDT switch for that connection.

try it and see

cheers
Jim

[Gringo]

Looks like it will work fine

I would use a 5k trim pot to adjust the amount of clipping of the second pair, but that's just me  :twisted:

Also, consider to use a cap just like in the original diode pair, since the silicon diodes are more "rough", to my ears at least, and the cap helps smooth the harshness.

Edit: Seach for RDV's HMP, it has quite a variety of clipping arrangements.

[Mark Hammer]

Actually, mine already HAS a GE-SI switch, and it works just fine.

Note the following, however.  The 10k output pot is simply inadequate.  Switch it for a 50k or 100k pot.  The reason is that the 10k resistor ahead of the diodes, in conjunction with a 10k pot, makes the circuit act like a 20k pot turned down halfway.  Under these circumstances you will NOT get any appreciable volume from a pair of GE diodes unless you crank it all the way.  You'll get more volume from the SI diodes, to be sure, but will find the GE setting sorely disappointing.

Second, scrap the tantalum cap after the op-amp.  No need to use it unless you're MXR in the 70's trying to make the profile of the board as flat as you can and slide it under fat-ass pots inside a 1590B.   Let me be completely clear about this: MXR used tantalum caps for physical size reasons and not sonic ones.  Electrolytic caps of 25 years ago were physically bigger, and tantalums were prized for their ability to be smaller than a similar-value electrolytic and also for the manner in which they could be easily bent over on their side to form a flat profile.

Third, your schematic shown implements the treble-reducing .001uf cap for the GE "position" but not for the SI position.  Given the amount of potential gain in the circuit, and the treble boost provided by it, I can assure you with utmost confidence that you will want a fizz/hiss-reducing cap with the SI diodes as well.  So, leave the cap on always, and simply switch the diodes.

Finally, take a look at Jack Orman's article at his AMZ site ( http://www.muzique.com ) on "warp" controls.  You'll find it useful.

[rodriki1]

It is perfectly possible. Any H-H switch will do it.

Try to put 4 diodes. 2 diodes 1n4148 in series, having clipping level about 1.2V at each phase.

Try to Raise de source voltage. Experiment!!!!

try....

http://geocities.yahoo.com.br/rmfidelis/TubeSimulator.html

[Fumi SG]

thnx guys... I also posted this at other forums and they said this schematic was a bit to hard for me. But heah, I like challenges! :wink:

So my idea is going to work, I'm pleased with that.

@Mark Hammer: You say I should just scrap the 1µF tant. cap and put nothing else in place? And that 0.001µF cap in the SI-position, I saw that yesterday by myself and I have changed it already.

@rodriki: I don't get your idea I think. Can you explain it in a different way??

I will keep this topic updated if there is any progression or if I have some more questions, and I WILL have questions!

[Fumi SG]

well... Here's my second question. It's a really simple one about the jack-sockets. On the other forum I was told to use a stereo-socket, so that it would work as an on/off switch. But then, I have no idea how to wire this.  Can anyone explain it as simple as it gets, it would be nice if you could explain it with a drawing/schematic.

What I do know is that the negative pole from my battery has to be wired to the mid pole of my stereo-socket. That's about it!

[Bernardduur]

That's it; wire the negative of the battery to the mid part of the jack. When you put a non stereo plug in the jack the mid connects to the sleeve thus grounding the unit and feeding the negative pole.

Nice idea with the diodes. I added a 12 selecter wheel in my D+ clone (Coron Distortion 10) so I could switch between all kinds of clipping diodes (Ge, Si, Ge+Si, LED's, etc.)

[Fumi SG]

well... my problem is, how do I wire the socket to the circuit. When you have soldered your negative to the mid part of de socket, you have to other poles that also have to be wired. Which one do I have to wire on what part of the circuit. I really don't get it...

Remember that I also have a DPDT swich! :wink:

[Mark Hammer]

@Mark Hammer: You say I should just scrap the 1µF tant. cap and put nothing else in place? And that 0.001µF cap in the SI-position, I saw that yesterday by myself and I have changed it already.

My apologies.  I forgot how new you were to this.  What I meant was "Use just a regular electrolytic capacitor and don't bother with trying to find a tantalum one".  Sometimes people here can get a little nuts about trying to *perfectly* copy something older that had actually used certain parts for reasons unrelated to tone.  Just trying to save you a headache.

Keep us posted of how things are going so we can nurse you through this.

[Bernardduur]

.... hmm

on the tips of the jack you should wire the input wire (or output wire, depends on what jack), on the sleeve you should wire the ground.

As for the switch, a 3PDT (TPDT) is wired the same as a DPDT with some extra row for LED switching

Check with a multimeter how the switch switches.

[petemoore]

well... Here's my second question. It's a really simple one about the jack-sockets. On the other forum I was told to use a stereo-socket, so that it would work as an on/off switch. But then, I have no idea how to wire this.  Can anyone explain it as simple as it gets, it would be nice if you could explain it with a drawing/schematic.

What I do know is that the negative pole from my battery has to be wired to the mid pole of my stereo-socket. That's about it!

 >>Stereo jack input switch trick..
 when you plug a mono 1/4'' plug into a stereo jack, the sleeve and ring get connected by the sleeve of the mono plug...by connecting the sleeve to circuit ground, and the ring to the power supply circuit, the power supply circuit is switched on/off through the ring/sleeve when a plug is in/out of the jack. the tip connection [plug to jack] is made also.

[Fumi SG]

I have figured it out already. I made a drawing and posted that one on another forum. There they said it would work.  But that was just a DPDT-switch, but I want a LED that shows me if my stompbox is on or off... So I just made another schematic. Will this work??

[Bernardduur]

Nice pic!

[Mark Hammer]

What you show *should* work just fine.  But please, please, PLEASE (to quote James Brown) verify that the solder lugs on the stereo jack go where you THINK they do.  Not all manufacturers use the same layout of solder lugs on stereo jacks.  The ground lug is obviously easy to identify, but you would not be the first person to have problems because what you THOUGHT was the solder lug for the tip was actually for the ring, and vice versa.  Make sure you visually trace the lug to the plug contact, or else use your DMM to establish what lug goes to what plug contact.

The other thing to note is that while a 1k current limiting resistor for the LED will at least prevent it from being burnt out, you may want to consider a higher value or a different LED or both.   I'll try and be brief because we have beaten this one to death with a stick already.

LEDs are rated for their brightness in "millicandles" (mcd).  Over the years, manufacturers have found ways to make brighter and brighter LEDs that don't simply burn up at that brightness.  The fact that they can BE brighter does not mean you NEED them that bright as status indicators.  Older lower-brightness LEDs would require more current to be adequately visible, and for that a 1k resistor would provide perhaps the maximum amount of current limiting tolerable (i.e., a resistor >1k would limit the current flowing through the LED too much, yielding an LED that wasn't bright enough).  Newer high-brightness LEDs, though, can be more than adequately visible using much less current.  The advantage is that you don't use up the battery as fast.  If you can, try and find an LED with a brightness rating of at least 2000mcd.  This will let you easily get away with a resistor of 10k or more sometimes, drastically reducing current consumption by the LED.  Alternatively, whatever you manage to score, before install it in the pedal, stick a 25k trimpot between the LED and the power, set the resistance to maximum, and gradually back off on the resistance until you hit a brightness you think you can live with.  Make a note of the trimpot's resistance at that point and fidn the standard resistor value that comes closest and use that.  In some circuits, the indicator LED can use almost as much current as the circuit itself, so it pays to use what's available to drop current needs for status indicator down to the lowest possible.

[Fumi SG]

so, in other words. If I install a LED of at least 2000mcd and a 10k resistor, I'll save more of my batterypower. Right??

What is the plug-contact, is that the 'large thing' sticking out?? The lug that's connected to it should be ground.


I hope I can get my bits 'n pieces tommorow, but I'm not shure. I hope so, then I can start working on it!

[Mark Hammer]

so, in other words. If I install a LED of at least 2000mcd and a 10k resistor, I'll save more of my batterypower. Right??

Bingo!

What is the plug-contact, is that the 'large thing' sticking out?? The lug that's connected to it should be ground.

By "plug contact" I mean the thing the phone plug actually touches.

[Fumi SG]

yep, 'the large thing'! :mrgreen:

I no longer have any questions. For so far!! Once I have all my parts (I hope tommorow!) I can actually start building it. I'm dying to get started! :lol:  If there is any progress I'll post it here, I'll keep you guys updated. :wink: