Splicing circuits together and another beginner question

Started by RandomRedLetters, July 31, 2005, 03:01:11 AM

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RandomRedLetters

Well Ive built an Electra Distortion with suscessful results and Im probably going to wire one into my guitar permanently with a push-pull pot for a switch.

On the otherhand Id like to make a nice stompbox version so how would I go about adding some tone controls and a booster stage? How would I add say something like the AMZ Mosfet Booster or any other booster circuit to my distortion circuit? Could I just link the output of one to the input of the other without disrupting anything? Same with the tone circuits?

I work with electronic parts on a daily basis, but Im 19 and I really dont have the knowledge as to why certian parts in certian places make things sound better, so I really just going off any schematics I can find.

Also what would you recommed as a second project that isnt a distortion pedal? I was thinking an MXR Phase 45 clone maybe.

Threefish

I'm still a bit of a noob myself, but I've built an AMZ mosfet booster, and it's a winner. Great clean boost up until about 90percent rotation, then overdrive. Sounds great.
If you're after tone control, why don't you try a tonemender at runoffgroove.com ? Haven't built one myself, but it's says (and what these guys say you can trust ooh yeah) got clean boost with a tonestack. Sounds like a good addition to something like the electra.
As for where these would be in your chain from guitar to amp - experiment. However order you put these various circuits in will vary the sound a little. If you wanted to box up the electra with something else, It's probably best to to literally put the two separate circuits in the same box, with all the controls that each have. Of course you'll have the output of one (where the output jack would be) going into the input of the other with no jack between them, and you may end up with a few pots that vary the volume, but the'll do it in different ways. I've done a couple of boxes that have two circuits in there, and by doing them on two seperate boards inside your enclosure you can always separate them and rebox them how you like if your tastes or ideas change. The great thing about DIY - you can do whatever you want to.
Experiment, play around, but be careful - ITS ADDICTIVE!!!
"Why can't I do it like that?"

Mark Hammer

The thing to pay attention to when sticking/grafting circuits in series is the bias voltage.

Since the brunt of guitar circuits use a single-ended power supply (one battery), in order to have a "middle" for the audio/AC signal to swing back and forth, a voltage equal to one half the supply (4.5vdc) is used to "fake" having a bipolar (+/-V) supply.  In effect, your signal is sitting on top of a 4.5v DC voltage.

This makes life easier AND more complicated at the same time.  Why?  Well, it's simpler because using only a single battery simplifies life as far as stuffing things into small boxes, turning batteries on and off with an input jack, etc.  But at the same time, it becomes more complicated because you need to keep asking yourself "Do I have my signal suitably centred here?".

You will notice that op-amps and many transistor circuits will have capacitors in  series with the input and output.  These are intended to block DC.  In part, one blocks DC to sort of wipe the slate clean.  If you have stage A and stage B, with a cap between them, you will likely see stage B re-biased with a path to Vref.  Conversely, if there is NO cap between them, you may not see any re-biasing of the second stage.  The key is to assure there is something like 4.5v there.  There is no point in adding 4.5v on top of 4.5v.  There is also no point in accepting a bias handed down from a preceding stage if that part of the circuit introduced error in the bias.  For instance, it may be the case that the preceding stage  produces an error of 1v in the bias voltage simply by the way it achieves gain. how much gain was aimed for, and its unique properties.  Do you want a 5.5vdc reference/bias for the next stage?  Maybe not.  So a cap follows the first stage to block the DC bias voltage, and the next stage is rebiased again...properly.

I am telling you this because most guitar circuits are designed by people who are "blindfolded".  They have absolutely no idea what you are feeding the circuit, and where you are sending it.  Consequently they provide DC blocking at both the input and output for safety's sake.  Do *you* need it if you are directly wiring A to B on the same board?  Not necessarily.  If circuit A "ends" in a 10uf cap and 100k resistor to ground and circuit B "begins" with a 1meg resistor to ground, a .1uf input cap and 10k input resistor, you can probably skip the 10uf cap, 100k and 1meg to ground (which are in parallel anyways, making the 1meg redundant and pointless), and just tack the .1uf cap to the output of the preceding stage.

It is a little more complicated than I describe in each specific instance, but the general principle that much of what gets tacked on to the ins and outs of presumed standalone pedals can safely be scrapped when wiring things directly together...as long as you pay attention to bias voltages.

RandomRedLetters

For others who will read this post heres what Im thinking: Electra Distortion and an EH booster combined
http://img.photobucket.com/albums/v213/nothingone/electra.gif