Newbie with a question

[Surfcaster]

Hi, I've built a couple pedals from kits, done some modding of purchased pedals, built a tube amp from a PCB and tweaked on some tube amps, but have never built a pedal from scratch.  One pedal I tweaked successfully was a DOD FX55 Distortion a friend gave me a few years ago, but it's not all that stable and I feel I could do more with it, so I wanted to try breadboarding one then build from scratch.

But I really only know enough to be dangerous, so might need a bit of help.

Here is the schematic I found online as a starting point:  http://farm8.staticflickr.com/7187/6819506718_db011a6e4d_z.jpg

My question has to do with the IC in the lower left corner...it looks like it's just involved in switching and the LED.  I'm wondering, if I use a 3PDT switch for true bypass and the LED, do I need that IC at all?  Could I just leave it out, or will that mess up other parts of the circuit?

Thanks,

[Govmnt_Lacky]

I'm wondering, if I use a 3PDT switch for true bypass and the LED, do I need that IC at all?  

Short answer is NO!

Long answer is that the 4007 IC in your schematic is used for switching the effect and LED on and off. Often times, it is cheaper for a manufacturer to use an IC and associated components than it is to use a 3PDT. This, and it is "quieter."

[Hemmel]

Short answer is NO!

Long answer is that the 4007 IC in your schematic is used for switching the effect and LED on and off.

I was about to answer the same thing but saying it might have to do with Vbias, but then I saw that it doesn't, as Vbias is done through R5 R6 and C15.
However, what would come in to the left of R24 ? Vcc from the junction of C17 and R26 ?

[nocentelli]

...I wanted to try breadboarding one then build from scratch...

It might be more rewarding to build a simpler circuit than the DOD, but with the same basic topology that is more DIY-friendly. With the DOD, you've got an input and output buffer that aren't strictly necessary if you're not using the buffered bypass system: Using two dual op amps is therefore over complicating your potential breadboard adventures.

If you take a look at the Wampler Ecstasy schematic that's available online it has the same sort of circuit, with clipping diodes in a feedback loop followed by clipping diodes to ground. With the Ecstasy, one or two switches allow you to choose both or either diode pairs for a wider variety of different clipping sounds. The DOD pedal has the second opamp as an active tone control, whereas the Wampler pedal has a bass boost control on the first op amp (it's shown as a single 10k resistor, but should be a 10k pot wired as variable resistor), followed by a passive treble cut/boost pot (similarly drawn as a pair of 12.5k resistors, should be a 25k pot wired as a voltage divider with lug 2 connected to a 22n cap->ground). If you like the single knob DOD tonestack more, you could always omit the volume control from the DOD scheme, use the DOD schematic second stage and follow it with the volume control direct to output.

[Surfcaster]

The only reason I'm starting with the DOD schematic is because I liked the tone I got after tweaking the FX55...swapped out some diodes for LEDs, added some caps across the gain stages to smooth out the distortion, added a tone control.  When I saw the FX55b had incorporated some of these elements in its design, I thought its schematic might be a place to start.  But one of the things I wanted to play around with was adding a more involved tone stack.  So maybe the Ecstasy is a good place to start.  I could always see what happens when you substitute some of the diodes with LEDs in that design.

The other idea I had was to build something based on the Marshall Guv'nor...got the schematic from the General Guitar Gadgets site.  It does look quite a bit simpler, and is already drawn for the 3PDT.

I guess I could also try Hemmel's suggestion of connecting Vcc to the other side of R24.  I've pretty much got the breadboard plan laid out for the DOD, so I might just give it a shot and see what happens.  If it doesn't seem to be working out, I've got some other options to try.

[GibsonGM]

Good luck with whatever you do, Surf, but for ease of assembly, I might try a Distortion +, then a Tubescreamer, then the Guv'nor, and THEN that FX55....that way, you'd be entering the from-scratch opamp-based distortions in 'sequence', by complexity.  And all the help you might ever need is RIGHT HERE!     You will learn how they all work, the different topologies, you can mod them and see how things change (what effects what) and ultimately, all others are pretty much just mods of those.  You'll never wonder again if you do it in that order, but it's up to you, of course.

Don't forget to do at least one transistor Fuzz, just to cover the bases, ha ha!   

[Surfcaster]

Thanks for the advice, GibsonGM.  I'll consider doing that.  I'd need to order additional components to build those pedals.  

I looked into it briefly and saw the Op Amp for the Distortion + was about $5, seems a bit steep just for a breadboard build!

But it looks like I could probably get all the extra components I'd need for the TS (and some mods for it) for about $6 plus shipping...the only problem is shipping is almost as much as the order, which just rubs me the wrong way!  But I might go ahead and do that...it might be fun to play around with those designs.

[GibsonGM]

     $.73, my friend!    All ya need is an LM741:  http://www.newark.com/jsp/search/results.jsp?N=422&Ntk=partnumbers&Ntt=LM741CN&Ntx=mode+matchall&ref=lookahead

Find one of the threads that deal with "what parts should I keep on hand?", and then you can build ALL of these whenever you like!  The only things I 'order' anymore are enclosures and 3PDT switches.

Think about stuff like this:

Capacitor 'kit'
various electrolytic caps, 1uf, 10uf, 22uF, 100uf, 470uf.....
common opamps (like, 10 each)
3 full sets of resistors
1N914 and 1N34 diodes
some 1N4001 diodes
package of MANY NPN switching transistors (5088's too)
bunch of 1/4" jacks
bulk pack of assorted LEDS, and LDRs

and so on.

[garcho]

^ big +1

You think you can feel the desire to breadboard something, to tweak, to source parts, and then just walk away from this *hobby* after one build? Ha! You're in deep, son.  

[rutabaga bob]

Yeah - he's hooked! 

[Surfcaster]

Yeah, I'm sure I'm hooked...I mean after I built my last amp I felt I had all the amps, pedals and guitars that I wanted/needed.  But the desire to build is stronger than I had thought.  My first impulse was to build a new amp, but I'm not ready to spend that kind of cash at the moment, so this seemed like a better option for the moment.  I'll probably end up getting some of those kits eventually....

[duck_arse]

if yer postage and handling charges are more than yr parts order, order more stuff!

[Mark Hammer]

I'll hold my opinions of the FX55 to myself since distortion is a matter of rig and personal taste.

That said, there is an awful lot about the circuit linked to that can be safely carved away.  If you use a stompswitch, all that is really required is the stuff around U2a and U2b.  The rest is superfluous, and has to do with FET switching, buffering of the switches, yadda yadda.  In the same way that Jack Orman (and so many others after him) were able to pare the TS-9 down to a pair of op-amps and little more, this circuit can be similarly pared down.

C1 and R1 would now go directly to U2a's input.  R10 would go directly to C6.  All the stuff around Q2, unnecessary.  U2b's output from pin 7 goes directly to R3.  And there you go, a much simpler circuit.  Personally, I'd stick a second diode in series with D4 and another in series with D5, just so that the output from that stage is a little hotter than the forward voltage of D1/D2.  So, the extra dioes could be germanium or schottky.  Alternatively, if you have a bunch of diodes and a meter, just pick the ones with the highest forward voltage for D4/D5, and the ones with the lowest forward voltage for D1/D2.

[Surfcaster]

I'll hold my opinions of the FX55 to myself since distortion is a matter of rig and personal taste.

Oh, I agree...IMO, the pedal in stock form is horrible.  I find it hard to believe anyone actually bought one!  (But then I wasn't playing guitar in those days...I suppose the options were fairly limited)

So when this friend gave it to me, after trying it I tossed it in a box.  But then later I thought it would make a great platform to try some mods on...I could learn a little something, and maybe even end up with a useable pedal.  And after a while, much to my pleasant surprise, I did end up with something I found very respectable!  But its NOT the same pedal at all!

Thanks for the information...I think I will apply that to my breadboarding and see how it goes!  My parts are arriving this evening...woohoo!!  

[GibsonGM]

if yer postage and handling charges are more than yr parts order, order more stuff!

^^^This!  You can make 20+different things from just a few basic components ) 

AND create NEW things of yer own!

[PRR]

> Here is the schematic I found

One drawing-error right off the bat: IC1A needs some resistor from +In to Vbias, or it will stick and be sick.

[Surfcaster]

> Here is the schematic I found

One drawing-error right off the bat: IC1A needs some resistor from +In to Vbias, or it will stick and be sick.

Thanks for pointing that out.  However, based on Mark Hammer's suggestion, I've removed IC1 from the circuit completely. 

I am, however, wondering about pins 4 and 8 on IC2.  In looking at the schematic on the data sheet for the LF353, it looks like these pins are for voltage...pin 8 for +ve and pin 4 for ground...is that right?

And if so, what +ve voltage would I send to pin 8...would it be Vcc?

[Surfcaster]

BTW, I got my components last evening.  I decided to start with the Guv'nor, just because I've never heard one and am very curious about it.  I just about have my breadboard populated, just need to add the last few components, then wire up the external connections for jacks, pots, switches and power.  We've got a busy weekend, so I may not be able to get to it until Sunday. 

I'm very curious to find out if my breadboard layout is accurate...little nervous about that, actually...

[garcho]

I'm very curious to find out if my breadboard layout is accurate

Draw them out first on graph paper, or with DIYLC or something. It also makes troubleshooting wayyy easier.

[Surfcaster]

Draw them out first on graph paper, or with DIYLC or something. It also makes troubleshooting wayyy easier.

I found an image of the breadboard that I printed out and drew it out on there before I started populating the board.  So now it's time for a real world test I guess!