Can someone check my schematic and tell me if it should work

[wsgarner]

I'm in a quest for a clean boost with some treble/bass EQ and an alternate distortion circuit. I never did find one I liked, so I took some schematics I have found here and other places and came up with my own. Bad thing is, I'm not circuit goo-roo so I have no idea if it will actually work like I want it to. So, I'm asking if someone can look this thing over and tell me if should be ok or not.

[alanlan]

You need to bias your op-amp + inputs to half rail or thereabouts - you should see this in loads of op-amp circuits running of a single 9V rail.

[wsgarner]

alanlan,
Thanks for the reply. OK, Bias the opamp: I think your talking about the curcuit with 3 resisters and a cap going into the + lead of the opamp??? I've seen this before, ya.

OK, which opamp do I do that to. the first one or all of them? The EQ curcuit is one I found on another site and I think I do recall that having the bias'ing your talking about (that is if it's what I'm thinking it is), I didn't think I would need that so..... I'll go back to that schematic tomorrow and look at it, I have the web link on my laptop and I don't want to have to drag it out and boot it up right now.

The Distortion circuit is all but a direct copy of a curcuit I found called "Destortion Plus" (and yes that web link is my laptop too). So I think that opamp should OK unless the schematic I found isn't correct.

Any way, thanks again. Let me know if you think we're talking about the same thing (BIAS'ing thing). In the mean-time, I'll do some digging around this evening and see if I can find that for sure.

Scott

PS:
AHHHH! I found that EQ curcuit and I don't see the bias thing your talking about on it. Here's the link: http://www.generalguitargadgets.com/pdf/ggg_eq6b_sc.pdf

And the Distortion curciut was on the same site. Here's the link to it: http://www.generalguitargadgets.com/diagrams/dist_plus_sc.gif This is the one that I saw the bias'ing thing on. It has the resisters and cap into the + lead of the opamp on it. Is this what you were talking about???

[amz-fx]

I would use the 20k eq-taper pot for the bass and treble controls. Smallbear stock:

http://www.smallbearelec.com/Detail.bok?no=463

You'll get a smoother feel for the control as it sweeps to either side of the flat (mid) position.

Also, on the Bass control, the gyrator has a 0.033uF capacitor on the plus input of the opamp, and that should be 0.0082uF instead.

You can check it with my bandpass eq calculator: http://www.muzique.com/lab/gyrator.htm

regards, Jack

[alanlan]

You need to bias each op-amp + input separately.  The chances are that if you've seen an EQ circuit it may have had dual supplies i.e. +/- 15V (especially if it's from a mixing desk or similar) in which case the + inputs would be tied to ground via a resistor or direct connection.  This can't be done if you've only got a single rail i.e. 9V.

The gain of both your op-amp stages at DC is unity so if you apply 4.5V to the + input you will get the same DC level out.  As it stands the first stage op-amp will be sitting at close to 0V so any signal will be heavily clipped on the bottom.  The second stage isn't biased at all at DC because there is no DC path for bias current, so who knows what it might be doing - you need to correct these bias problems to get a sensible outcome.

[wsgarner]

OK alanlan/amz-fx,
I really appreciate the help. I think I've got it now, take a look:

[slacker]

Looks cool, be interesting to see how it turns out
You've got your 4.5 bias connections slightly wrong. The top 2 opamp sections need to be connected to 4.5volts through their own resistor not both through the same one. The bottom ones in the EQ section can be connected straight to 4.5volts with no resistor.

I hope you don't mind but I've edited your picture to show how it should be, because it will probably make more sense.



I'll remove it if you're not happy, and I'll get rid of it in a few days anyway.

[wsgarner]

Slacker,
Mind!!?? He** (heck) no! I appreciate the changes!!! Like I said in the original post, I'm not circuit goo-roo! I'll take all the help I can get! I stole these circuits and bunched them together.

I'm in search of that perfect tone. One for rhythm (I have it) and one for lead (I don't have it). The only reason I added the distortion circuit here is so I have a backup if I ever need it.

I use a DOD fx55c on my board. I love the gain from that thing (real nasty), but to get the tone out of it I want I have to put an EQ just after it and kill allot of the mid's. What I'm shooting for with this thing is to give me a boost for leads and be able to bring some of the upper mid's back and maybe add a little bottom end to cut through the mix (not sure if 2Khz for Treble filter is right for what I want, I'll have to build it and see).

I'm cannibalizing a Boss HM-2 to build this thing (I just hate the sound out of it and the case is just right). All I need to do now is figure out what kind of foot switch that thing has in it so I can wire it in.

Again,
Thanks to all for the help.
Scott