Help with beginner overdrive?!?!

[kevinh92]

This is my first post on here so bare with me. I am pretty new at building my own pedals. Had pretty good luck modding preexisting circuits. Not so much with building my own pedals. Anyway, I decided to try a simple overdrive pedal from modkitsdiy, the Thunderdrive. I don't like the whole idea of using terminal strips and grounding the pedal with a screw so I tried to use point to point wiring, but I am having several problems. First, my ground doesn't seem to be adequate because the signal gets much louder as I move things around but it is usually very week. Second, the gain pot seems to do absolutely nothing. I turn it back forth. Nothing. Third, I have no signal at all when I bypass the pedal. I'll post pictures of it. Maybe someone can help me. Please excuse the wiring and soldering. Like I said, I'm pretty new at this. Thank you guys.

The schematic is here:  http://www.modkitsdiy.com/sites/default/files/product_files/the_thunderdrive_schematic.pdf

[duck_arse]

hello and welcome, kevin.

as we always say, go here, follow instructions, come back and tell. do you have a multimeter?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[kevinh92]

No, I don't currently have a DMM. One is in the mail on the way. I realize it would REALLY help my situation if I had one. Until it arrives, I was really hoping someone might spot a simple error from the pictures and schematic. Thanks for the reply duck_arse!

[induction]

Several thoughts:

Are you sure you have the lugs wired correctly on the input jack? It's hard to tell from the pictures, but it looks like you are taking your circuit input from the ground lug, and using the signal lug as circuit ground. You're also using all three lugs of an input grounding jack as if it were a stereo jack. This will leave one of the lugs floating when a plug is inserted.

It also looks like you might have the distortion pot wired wrong (again, hard to tell from the pictures).

Finally, you appear to be relying on the case to connect the different ground points together. There may be enough paint and oxidation on that enclosure that this conductive pathway will be unreliable or simply discontinuous.

[Mark Hammer]

Oh man.  That solder job reminds me of the pics I saw of webs that spiders made under the influence of LSD!

More importantly, it bears a striking resemblance to the way that EHX used to build their first pedals!  My small-box Muff Fuzz was exactly like that, with "flying components".

So, either you're very high, or well on your way to a successful entrepreneurial career I the pedal industry.  As far as "baring with you", I think you should buy me dinner and take me to a movie first, and THEN we'll discuss "baring".

Gentle ribbing aside, I think you may find that rebuilding it on a piece of either perfboard, pad-per-hole board, or vector board, will lend itself to a) fewer errors (if there are any) in the build, b) understanding the circuit a little better, and c) being able to locate where mods and such can be introduced.  And, while not any sort of requirement, I always find that using some sort of colour-coding of wires helps me to be able to follow things when looking at an installed (or pre-installed) circuit board.  I like to use white for input and blue for output, and things like yellow/orange/brown wire for treble/middle/bass controls.  Things like that can help to visually organize the innards of a pedal.  But again, not a requirement, just an example of things one can do to assist oneself in thinking through troubleshooting and installation.

The distortion pot doesn't adjust gain so much as pad down the input signal.  As such, one might expect a change in tone as it is adjusted, but not a huge change in signal level.

Stompswitches can often appear to be properly wired up and not function properly, baffling many.  Although the immediate response is to blame the switch, the failure can often be a byproduct of the soldering job done by a novice; specifically the consequences of the application of too much heat during installation.  I made a little demo video that explains and illustrates a lot of what to do about it, that many seem to find useful: http://www.youtube.com/watch?v=6uhDKFhqYnw

The Thunderdrive is about as simple a clipping circuit as it is possible to make.  Once you get it working, you may wish to try a few modifications to get it functioning in a more pleasing manner.  For example, you can play with the diodes to get different degrees/qualities of clipping.  You can also consider sticking different small-value capacitors in parallel with those diodes to roll off some of the annoying parts of the higher frequencies.

I think you're going to find that the battery in your pedal runs down very quickly.  The picture seems to show that you are using a closed-circuit mono input jack.  Traditionally, input jacks are stereo, with the black lead from the battery clip going to the "ring" connector/lug on the jack.  What that does is leave the battery disconnected from ground until a standard mono plug is inserted.  Once you insert a mono plug the part of the jack that would otherwise only make contact with the ring part of a stereo plug, now makes contact with the shaft part of the plug and is thus connected to ground, and now powering up the circuit.  Although the jack you are using DOES have three lugs, it is not stereo, but closed-circuit mono.  That means that when you take the plug out, the battery ground connection is going to the input of your circuit.  And when you insert your plug, the battery ground is not really connected to anything.  Or so it would appear from the picture.

My own best recommendation would be to use some appropriate heat sinking, desolder the parts, and rebuild on a piece of board, so that what you build can more or less "look" like the schematic drawing, making it easier to assure that connections are going where they should.  It's also a good idea to make sure the component leads are not shorting out against either the backs of the pots, or the sides of the box.  I simple piece of cardboard placed between the board you build the circuit on, and the back of the pots, can do that.

Have no fear, we'll get you through this.

[kevinh92]

Thanks induction,

To be completely honest, I read the schematic to the best of my ability, but this was my main resource: http://www.modkitsdiy.com/sites/default/files/product_files/k-950_thunderdrive_instructions.pdf
I tried to make my circuit look like the finished product in the manual. That was probably my first mistake. Also, here is a better picture of the distortion pot. Maybe you can tell a little more from this picture. Thanks again!

[kevinh92]

Mark,
excuse the "bare" comment lol Thanks so much for your reply. Yeah, I knew that soldering was messy. I totally didn't realize that wasn't a stereo jack. That's what I meant by spotting simple errors! I'll take down the circuit and see if I can do a better job. So it sounds like the error lies with my sloppiness and not so much with the actual layout of the pedal? And possibly some crappy grounding? Thanks!

[induction]

Ok. The distortion pot appears to be wired correctly. The rest of my post (and Mark's) still stand.

[nate77]

Welcome to the forum man. This isn't any direct help for this particular build but I'll throw it out there anyway. The modskitsdiy stuff is a bit confusing IMO. The circuits themselves are straightforward but they become hard to linearly follow the circuit path and logical order and function of the components. Also, the eyelet style construction is still considered point-to-point and serves the function of keeping everything secure and appropriately spaced. With all of the components floating around in the enclosure, you'll forever have issues with your signal grounding out. I've done a few of those kits back in the day and I've come to find that they are expensive and fairly low quality effects, buts that's neither here nor there. Another problem with not using the eyelet boards to tie everything to is that trying to debug this box ones very tedious because its difficult to clearly see the signal/power path. Good luck man.

[kevinh92]

Thanks for the input, Nate. Does anyone have any specific mods that know of to tame the harshness of the pedal or at least make it more pleasant? Also, I would like to add a dc power jack. There's a link to adding on modkitsdiy.com but it's for the Thunderdrive Deluxe which uses a 3pdt. Is it still basically the same principle? Do I need center pin negative or positive?

[Mark Hammer]

The parallel capacitor I suggested in my previous post can be used to "tame the harshness".  I suggest starting with .01uf, and either making the value a little smaller if too much treble is lost, or increasing the value if you want to remove even more treble.

Some might also be able to suggest capacitor values to place in parallel with the 2meg (probably 2.2meg) resistor to help along with that.

[kevinh92]

Thanks everyone for the input. After giving it some thought, I've decided to abandon the Thunderdrive in favor of the Trotsky Drive from Beavis Audio. I've ordered some perfboard so I intend to do a much better job this time. I'll post back with results once those parts are in. No doubt I'll have more questions. Thanks in advance.

[Mark Hammer]

You're welcome.  I think you'll have better luck with the perfboard.  Much easier to keep track of connections in 2-dimensional space, as opposed to 3-D.  And, as noted earlier, easier to keep component leads from accidentally shorting out against other things.

The Trotsky Drive is nearly identical to the Thunderdrive you were working on.  The chief differences, apart from the suggested Russian transistor (that you may have some difficulty sourcing), are that:

1) there is no variable resistance on the input/base of the transistor, as in the Thunderdrive;
2) there IS a variable resistance on the collector of the transistor;
3) there is a small resistance (i.e., non-zero) on the emitter;
4) the treble-cutting cap I suggested is included.

Essentially, you can think of the one as a slightly modded version of the other.

Mark's handy-dandy tips for working with perf:

• Keep the leads of your more expensive and harder-to-replace components long.  So, if you're going to connect that 680R resistor to the emitter of the transistor, try to wrap the emitter lead around the resistor before soldering and snipping, rather than the resistor around the transistor.  That way, if you need to remove the components to re-use or re-install, you'll still have enough lead left on the components you care more about.
• figure out where you want to your off-board wiring to go...first, and work backwards from there.
• keep track of all ground connections, and verify after building that all those grounds are connected with each other.

[kevinh92]

Thanks for all your help, Mark. You're the man. Lol I picked the Trotsky because it was similar in build and difficulty to the Thunderdrive, but with some useful changes. Can't wait to get started and do it right this time

[kevinh92]

Well, just like I figured. I finished the Trotsky Drive and guess what. MORE PROBLEMS! haha  I have normal guitar signal with the pedal bypassed but when I engage the pedal, I get an extremely weak signal and when I flip the spst switch, I get an even weaker signal. I'm sure I've made some simple wiring or soldering blunder. I have a DMM now, but being the total noob that I am, I'm not finding it to be much help. As usual, here are some pictures.

[Gus]

I am not a fan of the biasing used in the circuits in this posts.

The collector to base feedback/bias resistor sets the DC bias AND is part of the gain setting AND the value depends on the hfe/beta of the transistor

[peterg]

Kevinh92 - take aa look at the thread duck_arse posted. He was the first to replay to your original post. This will explain what info to provide in order to get some help. Also take a look at this thread for perf board layout tips:
http://www.diystompboxes.com/smfforum/index.php?topic=96544.0

[Gus]

A thread somewhat about this type of biasing
http://www.diystompboxes.com/smfforum/index.php?topic=104613.0