Author Topic: 9v to bias volt?? Question for the pros  (Read 3306 times)

9Lives

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9v to bias volt?? Question for the pros
« on: February 10, 2012, 02:13:18 PM »
so I'm hacking the gain stage from the tubescreamer to put into another pedal. I actually have half of the lm13600 to work with but I just don't understand.. I can't amplifiy the same way, I'm missunderstanding. But I can do this with a dual op amp. Only prob is there is a 10k resistor coming from 4.5v bias?? It works good on my tester bc I have 9v and 4.5v sockets but when I put on a pcb and put it into a pedal, how am I going to get that 4.5v?? Making sense?

madbean

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Re: 9v to bias volt?? Question for the pros
« Reply #1 on: February 10, 2012, 02:23:25 PM »
Actually, none at all...I'm sorry I'm lost.  ;)

What LM13600? Is the pedal some kind of phaser or envelope filter? What exactly are you trying to accomplish? Sorry----I just can't figure out what you are describing here.

9Lives

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Re: 9v to bias volt?? Question for the pros
« Reply #2 on: February 10, 2012, 02:32:07 PM »
ok srry man, I know I'm all over the place. The tonepad cp9 compressor. It uses half of the lm13600 and leaves the other half for mods. What I want to do is add a gain stage as a grit control. I tried using the 13600 but I'm just dumbfounded. So I went to my comfortzone. Tl072. But in the schem of the tube screamer a 10k res comes off the "bias 4 5v" just trying to figure out how to come up with that 4.5v if I put this gain stage on a radioshack pcb. Is that a lil better?

mgwhit

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Re: 9v to bias volt?? Question for the pros
« Reply #3 on: February 10, 2012, 03:26:22 PM »
I think you're just talking about a Voltage Divider.  You use two resistors (one in series, one to ground) to lower the input voltage.  Make the two resistors equal (in the Green Bean: R18=10k, R19=10k) and you effectively halve the input voltage: 9V -> 4.5V.

The entire point is to give the op amp a DC reference voltage half-way between its +V and -V pins, so that your AC signal can be amplified in both (positive and negative) directions. The voltage divider trick is a way to compensate for the fact that (most) pedals just use ground (0V) on the -V pins of their op amps.  Check out the Boneyard for an example of a pedal that skips the voltage divider and provides its op amp 9V and -9V.

madbean

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Re: 9v to bias volt?? Question for the pros
« Reply #4 on: February 10, 2012, 03:50:36 PM »
Jeh, got it now. You can pull the bias voltage right off the CP9. The two 10k resistors (to the right of the 9k1 on the schem) form the voltage divider. Tie that to your 10k that connects to the non-inverted input of your TS stage. Or, just add two extra 10k resistors on your daughter PCB tied to the 9v supply and create it's own bias supply. If you do this, use a 10uF cap from the second 10k to ground to give it a little filtering.



jubal81

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Re: 9v to bias volt?? Question for the pros
« Reply #5 on: February 10, 2012, 05:06:59 PM »
Does this mean that if you wanted more headroom from a compressor, you could replace the supply with a 1044 dual voltage system and the VB bias voltage is now connected to the GND?
"If you put all the knobs on your amplifier on 10 you can get a much higher reaction-to-effort ratio with an electric guitar than you can with an acoustic."
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9Lives

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Re: 9v to bias volt?? Question for the pros
« Reply #6 on: February 10, 2012, 08:39:57 PM »
yall are freakin genius man. It's like an encyclopedia that answers my questions. Let me ask you this bean. If I tie off of that resistor on the cp9 board that won't mix the signal in any kind of way will it? Or is the 10ks on cp9 strictly voltage? If I just hook the wire going to the daughter around one of the leads and solder it down that will be good enough? This comps gonna be badass. To bad I fried the first one :/ and why am I having no luck trying to make this off the OTA? Breadboarding it I tried everything (i could think of) and if I decide to use the tl072 should I go ahead and add the tone section to? Keep in mind. I have to put this gainstage and pot on a switch. Bc when I turn it down all the way it's still a lil distorted. And one last question. I was going to  insert this right before the level pot. Is there a better place for this gain stage? I know if I put it before the compression it will amplifiy the noise.. Right?