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Onboard Guitar Preamp


rokeros

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I recently took apart my yamaha pacifica 312MKII (Great little player) hoping to change to change the pickups to GFS texas (neck, middle) and the filteron hum (bridge).

THen i discovered that I have some spare parts from goodness knows what?, but then it came to me that I could pssibly add a preamp or onboard distortion. This is where my mind stops when I read the preamp on perfboard on (www.diyguitarist.com) with an opamp. As this is meant to be a subtle guitar effect. Do you think it is possible to switch the opamp to a JRC4558D or RC4588P. If this possible to convert the preamp to a dist. that would be great!

P.S. I remember seeing somewhere on the net but can't find, about stacking opamps on top of each other like 5 or 6 a pile to create some amazing overdrive. If someone knows what I mean, it would be appreciated if one could pinpoint me to that site. Thx

:D:DB)

Edited by rokeros
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Yep, there are single and dual opamps. The JRC4558 supposedly makes the Tube Screamer sound likes it does, but most of that is hype. There is some merit to this claim, as the JRC4558 is a BJT opamp, and it does distort differently than a JFET type like a TL072. You can actually see this on a scope, but I can't really hear a difference myself.

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WOw.

Do you think I could use a 25k pot instead of 50k? And fo you think that I could get a clearer pic of the schematic and layouts? Thanks.

All I am trying to achieve with your tutorial is to recreate an overdriveish in replacement of my pacifica tone knob rather than make a booster

EDIT : I am stupid! I managed to scroll down your page (paul) to find that PDF file. :D

Edited by rokeros
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Its just that I deserve to have more wins than loses, get my point?

I built a tube screamer. It was swell, then I checked with my dad (i'm 16) and he said it was fine. Then it screwed up. Since then, I built 2 more Ts-808 circuits and it doesn't get any better.

I am just naturally born not to deal with complex circuitry. THe most I can handle is a PCB or a standard guitar schematic. No MORe...

So anyways....I spent over USD$80 buying parts when I could get the exact circuit from a new behringer Tube screamer stomp box to put inside my own shell.

BTW...if anyone here had used soldering flux...does anyone get very very very sleepy after inhaling a bit of soler fumes?

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$80?! woa man... ur being ripped off!

What exactly is the problem wth ur tube screamers? have you tried going across particular components with a multimeter to check they are working ok? There's a good debugging section on diystompboxes.com if you're having trouble.

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BTW...if anyone here had used soldering flux...does anyone get very very very sleepy after inhaling a bit of soler fumes?

You should never have to use a separate soldering flux with electronic circuitry.

Not necessarily. I've used flux many times in assembly and rework. Helps the solder flow a little better and allows you to get in and get out fast. Just clean the excess off when you're finished, is all.

rokeros, try figuring out what went wrong with your circuit. You seem to give up a little too easily sometimes. Go through the schematic and check every component and connection. Make sure your signal path matches the schematic. When I was starting out, and I still do this anyway, try making the circuit look exactly like the schematic when you lay it out on the board. It makes it so much easier to troubleshoot what you're doing and assembly is so much cleaner.

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well, i kinda altered some components due to a lack of materials

oops - and at first when i plugged it in, the bettery made the circuit make sizzle sounds and release fumes.

The switch is a dpdt on/on (IDK Japan)

The IC is a RC4558P

the 100pf was changed to a 47pf

470k to 510k

0.22uf is a tantalum (that might have cause the problem)

and the pot is B25k. Is the diagram on layout showing the pot from above or below?

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at first when i plugged it in, the bettery made the circuit make sizzle sounds and release fumes.

That sounds like a battery hooked up backwards.

0.22uf is a tantalum (that might have cause the problem)

Highly unlikely. And that should have been a 0.022uF cap, not 0.22uF

Is the diagram on layout showing the pot from above or below?

I can never remember how to wire those variable resistors. You want the gain to increase when you turn the pot clockwise. If it's doing the opposite, just take the one wire on the far side of the pot and switch it to the opposite side of the pot.

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...the bettery made the circuit make sizzle sounds and release fumes...
Been there, done that! Opamp circuits are deceptively simple in appearance, but they require a dual polarity bias setup that has confounded many beginners ( we won't talk about my early failures, as in destroying an entire pack of five 741s before I got the bugs ironed out :D ), and perfboard can be tricky as well (at least for me). The trick is to allocate at least double the build time for rechecking and debugging before you even power up your first gadget. Anybody can solder some leads together, but making the results work as intended is where you learn! Have you tried Don Tillman's Discrete FET Guitar Preamp? It's very robust, sounds really nice, and is almost an order of magnitude simpler than any opamp circuit - it might be a great way to put one in the Win column, and restore your confidence, so you won't have to quit altogether! Hang in there, it gets easier, I promise!
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A great way to learn and get your circuit building skillz in order is to buy a good quality breadboard. Instead of soldering, you just snap the components in place and test your layout before actually moving everything over to perf/PC board and burning stuff up.

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