suggested caps for YJM tone change

[BMJ]

Hello fellow tone chasers'

I have a YJM (DOD 250) overdrive that has been modded with a 1458 chip and C2 removed and looks like C3 has been changed as well.
My question(s) -

(1) the cap in C3 in C3 says "103J 100.L: what is its value ?

(2) the cap in C1 says "2A473J what is its value ?

(3) I am wanting to take some of the top end off of the tone (less fizz more honk) which cap do I change ? (C3 is my guess ?) and any suggestions for values ?

hopefully these are legit questions that can possibly be answered here in this forum, thanks in advance for any help what so ever :-)

[Mark Hammer]

Clearly novice questions, but absolutely legit.

103 implies 10 followed by three zeros.  That's 10,000pf to you and me, or .01uf.  473 is, you guessed it, 47 followed by three zeros or 47,000pf, commonly known as .047uf.

The classic DOD250 has no feedback cap in parallel with the 1M feedback resistor (which will be between pins 1 and 2 or pins 6 and 7 of the chip).  Placing a small value cap in paralle with that resistor will remove some treble.

It also has a .001uf (102) cap in parallel with the clippping diodes.  While it is supposed to remove fizz, obviously it doesn't remove enough for your tastes.  Small wonder.  In tandem with the 10k resistor just ahead of those diodes, it rolls off starting at just under 16khz.

If you place a 47pf cap in parallel with the 1M feedback resistor, that will start to roll off the signal hitting the diodes at around 3.4khz.  Increasing the value of the .001uf cap to .0033uf will add a second rolloff on top of that, starting around 4.8khz.  Those two changes, combined, should get you an overdrive that enough bite and crunch, but does not send you running for the treble or presence knob on your amp..

[BMJ]

thank you for the reply and help !

looking at this schematic:



originally my circuit had C2 (which has been removed) which is what you are referring to as the "cap in parallel to the 1M feedback resister" ?

also I take it that C6 is the "cap in parallel with the clipping diodes" ?

TIA again   

[Mark Hammer]

Actually, C2 was there to prevent fizz.  It just isn't a high enough value.  Yes, you identified the caps correctly.

[BMJ]

Ok, so I put a 47pf cap in the C2 hole set and it wound up being just a tad dark..

but using my "other" strat (the one with the .022uf cap on the tone pot) it is pretty much right on the money !  which is cool as that strat was mostly un-usuable with my live rig being too bright (works awesome with though with the direct recording setup)
so it looks like I will have break out the soldering iron and pull the strings on my main strat for some modification........
additionally someday I will get some 55hz h30's for my cab which will centralize things even further  

but in the mean time -

signal chain as follows:

strat - deja vibe - vox wah - early 70's thomas organ cry baby circuit for notch filter - custom NKT275 fuzzface with "69" mods - YJM 308 modded - digitech delay - 1987X plexi - Marshall 4X12 w/ stock (well broken in) GT75's (10 ga speaker wire and reverted to mono only mod)

here's what it sounds like: www.blindmojojohnny.com/PoTdemo.mp3


thanks again for all the help !

[Steve Mavronis]

If you are using a 1458 (which is a dual 741 inside) you really don't need C2 at all. The original 250 Overdrive didn't have that. I only did steps 1, 3, and 4 on my YJM308 and it sounds exactly like a grey spec 250 clone that I had previously built. But experiment if you want a different sound.

Also there no need to do the full 'mojo' mod involving cutting and re-routing traces, in my opinion. So I removed those extra steps in my revised graphic guide. Too much work for no 'real' imaginary change in what you'll hear.