Post by vonFrenchie on Jul 25, 2007 20:15:59 GMT -5
Hey everybody. I have a Ibanez hollowbody. Its an awesome guitar but lately I've been experimenting with stereo sound, usually one input is distorted and the other clean. The only problem with this is the way I go about doing it. Since its a hollowbody, its new, and its summer so I'm lazy, I have my acoustic pick up sitting (just sitting, no mounting device) in between the actual pickups. It sounds great but its kind of a hassle.
How can I get the stereo functionality without buying an expensive stereo tuner or modifying my guitar? I'd prefer not to tape the acoustic pickup in place because the idea of duct tape sitting on my guitar for extended periods of time is not a great one to me. I was thinking of a simple split box. How can I build it without getting any extra noise, or is this not a good idea?
Do you just want to take a single guitar output, and feed it to two amps?
If so, a metal box with three jack sockets in it. All the ground lugs are connected together, as are all the hot lugs. The sockets are interchangeable and1 cord from each goes to guitar, amp1 and amp 2. Id put it near to the amps, so the amp to box leads are fairly short..
Well, you could also just run to radio shaft and buy a 1/4" TS splitter cable. You may not like the results, tho...
Your guitar will be seeing (likely) half the impedance it's used to, which might cause some loading of your pickups. You'll also likely have some degredation in treble response.
Most people prefer to buffer a guitar signal before it's split. A lot of people will also want to buffer the signal after it's split, for a total of 3 buffer circuits (1 in + 2 out). You really don't need the output buffers unless you're gonna split a few times. The output Z of a simple op amp buffer is extremely low, so you don't have so much to worry about with loading. The only issue would be if the input Z of the amps were wildly different. I think that will just cause the signals to be out of balance, like one louder than the other.
Simpler still would be to use an unmodded commercial effects pedal (Boss, Dod, etc.) in bypass mode. Plug the guitar into that and the radio shaft y cable out to your individual signal chains. Course if the pedal happened to be stereo (a chorus or whatever) you could save yourself the agrivation of dealing with those kids down there...
And then there's the question, are you actually just wanting to split the guitar signal as it appears at the out jack today? Somehow, I think you want something more.
I've got no ideas on how you might semi-permanently attach your pickup to your guitar. I've got the opposite problem. Want to stick a l'il killer in my acoustic. Maybe that's not exactly opposite...
There are several ways that you can re-wire your guitar to be able to get a stereo output. Would obviously require either replacing your jack with a TRS, unless you want to add a second TS. Then you've got options. Easiest way is to just wire one pickup to T and one to R and call it a day.
Or you could search around here, the topic has come up a few times.
Post by vonFrenchie on Jul 25, 2007 23:31:41 GMT -5
My whole plan is to hopefully not touch the electronics of the guitar itself. Its a hollowbody and I dont want to try to get the electronics out only to not be able to get them back in. The only unmodded pedals I have are being used in the distorted channel, and one of them is actually modded (Boss "SD-808", Rocktron Metal Planet, Vox V847).
The buffers are a possibility. Id prefer the simple metal box like John said but the way Ashcatlt made it sound that may mess with my source tone, which is awesome as is.
So as for the buffers. I'm thinking a nice metal box, I'll call the T-Box from now on, with a signal buffer at the input and outputs. Then the outputs will be connected to my amp, two channel/four input Peavey 400, (so nice for this). Then balanced to my liking. Sounds easy. Anyone disagree, or have words of wisdom?
I'll analyze the Basic Buffers page to find what I need.
Post by vonFrenchie on Jul 25, 2007 23:48:01 GMT -5
Here's my first shot at it.
I chose MPF102 because it was recommended in the "Dr. Quack" schematic from which this was taken from. Its basically the fourth image on the "Basic Buffers" page, tripled. Once I slap a 9V battery in there with the (-) connected to the input ground I am set, in theory. Anyone disagree, or have words of wisdom... or warning?
Post by vonFrenchie on Jul 26, 2007 14:06:33 GMT -5
Well my concern is that the tone will dwindle when its plugged into two amps. Accentuating the treble (as your nifty 20' buffer cable seems to do) is no problem with me. You can always tone down what you have, but you can't add what you don't. If I lose treble right at the T-Box I can't just add it later without messing up the bass and mids.
So that being said. Is only one signal buffer is needed (if any of course) and not the three that I have drawn? Also on your, John, first drawing you're using a J201, but on the buffer cable you're using an MPF102. Are these virtually interchangeable? I know I have some MPF102s sitting around so I'd prefer to use what I have instead of special ordering parts. If so I think I'll go with your drawing and instead of one stereo output I'll simply install two mono outputs.
What you've got there will work. It's going to have a 500K input impedance. The one JohnH linked to is the same basic circuit, but the biasing resistors are bigger, giving an input Z of 1.1M, which is "safer*" for HBs.
Since you've got three of these things in your circuit, i think I'd take the time to make a Vr source (the top of the basic buffers page) and use the second buffer circuit on the page. The more resistors you've got, the more heat noise you'll get. Might be neglibible, but best to err on the side of caution.
You don't need all three of the DC blocking caps (the three caps between the buffers). You can delete the one coming out of the first buffer. You might want to experiment with the values of these caps, as they will affect the low frequency response of the circuit. I built mine (just a single) with those values and haven't had a problem, but I haven't tried to use it for bass, either...
I think also that you don't need a full 1M input Z on the output buffers. The out Z of the first is going to be extremely low, and smaller resistors would contribute less noise.
I'd probably use a quad op-amp in this application, but some people prefer the discrete circuit like you've got it. You could use the fourth op amp for a global clean boost or overdrive.
edit - i think you ninja'd me there, and changed your mind in the process. I did mention above that you don't really need the output buffers to split two ways, especially if both chains will be presented with similar input Zs.
Last Edit: Jul 26, 2007 14:15:09 GMT -5 by ashcatlt
Post by vonFrenchie on Jul 26, 2007 15:34:31 GMT -5
Uh... yeah, not so stereo but you've caught me. It actually sounds, when it works which is about 90% of the time, amazing. The other 10% the acoustic pickup falls forward into the strings. My whole plan is to use my acoustic pickup for my acoustic and simply duplicate the sound of the actual pickups.
vF I think the need for buffers will depend on the input impedance of the amps. But having a buffer is a safer bet, and i use them alot in my guitars and stomp boxes. I think a single buffer is fine, these JFET source follower circuits can have very low output impedance and so can drive lots of other inputs.
The source follower configuration is very forgiving of circuit component values. R2 you can raise, I often use 30k to 100k, and its still low output impedance, due to the route through the JFET. The optimum biasing resistors R1 and R3 vary for different JFETs, due to different gate/source bias voltages.
With both R1 and R3, you can choose them to set the voltage across R2 at just above half the supply, about 5V is good. For the buffer cable however, I could only use one biasing resistor to ground, which was why I needed an MPF102, with its high Vgs. Heres some values for three different JFETs that Ive tried:
JFET-------Vgs-----R1----R2----R3 MPF102---2.5V----1M----22k--omit, or MPF102---2.5V----1.5M--47k--3.9M 2N5457---1.5V----2.2M--47k--3.3M J201-------0.75V--2.2M--47k--2.2M
Ive tuned them to give input impedances in the range 1M to 1.3M, and put in a lower R2 value than I use for built-in buffers, to give even more driving power. JFETs are very variable devices, so the optimum for each specimen may vary, but as I said, these circuits are very forgiving, so I believe these values will be fine. Theres two MPF102 versions, one which takes the opportunity to delete R3.
The R2 values can vary widely. R1 and R3 can be changed to achieve different input impedances, keeping the ratio between them. Im sure with that, you can find something suitable in the spares box!
Its the right bits, but not hooked up right! Are you thinking of actually building a buffer cable (JFET in the jack plug), with two output sockets? If so, that would be a very useful gadget and will let you experience the full zing of your pups, into one or two or more amps. The main tone effect is due to the signal getting to a JFET befor etravelling through a long guitar cord.
Or, will you use that circuit all within a box near the amp? Then the guitar cord is still affecting tone, as it usually does, giving you nearer to the sounds that you are used to.
Either way, the connection to the guitar is to the gate, ie, the arrowed connection on the JFET diagram
Post by vonFrenchie on Jul 26, 2007 21:01:21 GMT -5
Well I was thinking of building a buffer cable... minus the cable. I couldn't quite tell from the drawing you made so I simply guessed. I'm just glad I guessed here and not while I was making it. Looking back at it I didn't notice that the actual notation was in blue, on the right side of the label, oops. So it would look like this, after fixing my mistake of course.
Post by vonFrenchie on Jul 27, 2007 12:16:09 GMT -5
Is there any way (complication is my middle name) to add a volume knob right before the output? Would it just be the same as a volume on a guitar?
It may seem like a silly idea but right now I have my amp perfectly balanced, all my pedals are set up so that no matter if they are on or off the volume is the same, the amp channels are set up to be balanced. I would like to just be able to tweak the volume right at the source.
Would this drive my pedals less, ie less distortion like turning the volume down on the guitar itself, or would they remain the same?
You can have a volume control at the buffer if you want one, a 100k after the buffer would be OK. But it would be very much the same as the guitar volume control, except that you would not get significant treble loss as you reduce volume, which can (in some cases) happen on guitar volume controls unless they have treble-bleed caps.
I think with that, I'd drop the value of the 33k resistor down to say, 18k, and increase the output cap to 1uF or more.
But these buffer designs have very close to exactly x1 gain, so even without a volume control, it should not affect your level balances.