I am tweeking a CA trem on my bread board now. I have been trying to figuring out the best way to increase the gain. When increase the gain of the 2nd side of the TLO72 by increasing the feedback resistor, I start getting an audible ticking sound from the oscillator (i guess).
How can I get more volume without the ticking?
I am using a MAX1044 to supply the -9v/+9v to the TLO72 using a battery, if that makes any difference. And the battery may be running a little low, around 7-8 volts.
If memory serves, this is likely not one of those things you want to run on a MAX1044, simply because of the current requirements. It's not a current hog, by any means, but my guess is that the current sucked from the supply by the LFO creates spikes in the power lines to the op-amp. Certainly the drop in battery voltage is placing the entire circuit at risk for sudden current demands in one part of the circuit creating audible noise in other other parts.
There are a few things you might consider, other than reverting back to dual batteries.
One is to take a bit of the treble out of the output signal and make the tick more tolerable by means of a cap in the feedback loop of the output stage. Since you said you wanted more output, let's stick a 10k resistor in there for a little more oomph. With a 10k feedback resistor, let's stick a 2200pf cap in there for a rolloff around 7.2khz.
A second thing to consider is to isolate/decouple the power lines of the op-amp from those of the invertor. E.g., consider putting 47R resistors from the power source to the V+/V- pins of the op-amp, and 10uf caps to ground. from those same pins. The basic idea is that whenever there is a surge of current demand from the invertor, the op-amp has enough current stored in those caps to tide it over. I forget what Craig put in for power-line decoupling for the 4049, but if he didn't have anything, do the same thing for that as well.
Thanks!
The reason I want to use the MAX1044 was to save space so that I could fit the circuit into a Hammond B-size enclousure. And, it doesn't seem to hurt, as long as I don't increase the gain of the 2nd opamp.
I think I may be better of increasing the feedback R on the input of the circuit (1st side of the opa, that way I will not be amplifying the ticking caused by the LFO.
But I was thinking that my affect the input impedance, if what I remember from my class on opamps is correct. If so maybe a input buffer may help.
Of course since I am fairly new to this, I could be all wrong.
If the ticking is a consequence of what happens to the power feeding the dual op-amp, then which stage you add the gain to will make no difference. Note that BiFet op-amps have better noise specs when using higher value resistors, and devices like the NE5532 and 4558 have better noise specs when using smaller value resistances. If you are using a 4558 or 5532, you may be better off from a hiss perspective to add your gain to the 2nd stage, since doubling the gain raises the feedback resistor value minimally. Doubling the gain of the first stage moves you to a higher value quickly.
On the other hand, it's not like there is a whole lot of hiss to worry about in this circuit. Personally, I find in mine that there is actually more than enough gain for my needs using stock part values.
The CLM6000 was always the standard part for this circuit, but I'm wondering now if there aren't lower-current LEDs or optoisolators one could use to modulate the LDR without hampering attempts to run it off a single ended supply. Certainly, one could lower current needs by means of lowpower op-amps. Maybe, between that and a superbright LED/LDR that only needed 1/4 the current, you could easily operate the thing off a single 9v and a MAX1044.
Mark, I added the 47 ohm and the 10uf caps to the +v/-v pins of the opamp. Also added 10uf from the ground to each power supply, like I was supposed to according to the Anderton schem. That allowed me to increase the gain of the opamp on the first stage with no noticeable ticking!
Instead of increasing the feedback R (100k), I decreased the input R to 10k. So now I have a gain of 10 at the input. This helps to boost the signal so that I will have the same volume when the trem is set to its deepest setting, as when it is bypassed. Which,btw, was the original problem. BTW, how would I calculated input impedance of the opamp, I can't find it in my book?
Also I am using a Vactec VTL5C3, instead of the CLM600. It may use less current than the CLM600, I don't have the specs on the it.
I may try increasing the gain of the second stage of the opamp, to see which works better, and try using a 4558 instead to the tlo72.
Thanks again for your help.
Mark, I added the 47 ohm and the 10uf caps to the +v/-v pins of the opamp. Also added 10uf from the ground to each power supply, like I was supposed to according to the Anderton schem. That allowed me to increase the gain of the opamp on the first stage with no noticeable ticking!
Instead of increasing the feedback R (100k), I decreased the input R to 10k. So now I have a gain of 10 at the input. This helps to boost the signal so that I will have the same volume when the trem is set to its deepest setting, as when it is bypassed. Which,btw, was the original problem. BTW, how would I calculated input impedance of the opamp, I can't find it in my book?
Also I am using a Vactec VTL5C3, instead of the CLM600. It may use less current than the CLM600, I don't have the specs on the it.
I may try increasing the gain of the second stage of the opamp, to see which works better, and try using a 4558 instead to the tlo72.
Thanks again for your help.