[darren adcock]

Hi.

So i've found myself a bit poor for a few weeks and want to try and make a bunch of utility modules for my synth as I think I have a lot of the parts in my workshop.

I drew this up after reading Ray Wilsons op amp articles. Is it correct? Is there a better way of achieving what I want? I'd like to have it interchangeable so I can pass Control voltages though it also (I can make swith bypassess for the caps) I've not drawn a circuit up from scratch before, but it's about time I learned as much as possible about op amps. My graphics card keeps crashing so I've drawn it up by hand. Ignore the scribble to far right.

 

[Audioguru]

It passes AC signals, not DC control voltages. Since there is only one input then it mixes nothing.
If you bypass the coupling capacitors then it amplifies the DC input up to 30.86 times up to about +10V.

 

[darren adcock]

My intention is that I would like it to have one input that can then be split into 3 outputs. All i need is attenuation on these outputs. I see, is it because I said "control voltages" you mentioned mixing? Ok, that would be too high an amplification as most of the cv inputs I will be using want to recieve -5v/+5v. Maybe i'm expecting too get too much from this having both DC and AC. Would it be more adviable to have seperate modules?

 

[davenn]

Maybe i'm expecting too get too much from this having both DC and AC.

yes
this is an audio splitter audio = AC
as AG said, the circuit would have to be altered to be used for DC, then it wont be any good for an AC signal

 

[darren adcock]

Ok great. Thanks.

 

[Audioguru]

The output from an opamp can drive hundreds of devices if their resistance is fairly high. Then a "splitter" is not needed.

So you do not need a mixer and you do not need a splitter. Do you need an opamp?

I am confused. You showed an AC circuit with one input and three outputs then talk about many cv inputs and mixing and splitting something.

 

[darren adcock]

The output from an opamp can drive hundreds of devices if their resistance is fairly high. Then a "splitter" is not needed.

So you do not need a mixer and you do not need a splitter. Do you need an opamp?

I am confused. You showed an AC circuit with one input and three outputs then talk about many cv inputs and mixing and splitting something.

ok sorry. It's a bit late for me now. I will attempt to reword and be clearer tomorrow with your concerns in mind.

 

[darren adcock]

I'll keep this as an ac line splitter. So interms of audio when the signal gets split the volume decreases? Yes thinking about this I can see that isn't the case for DC. Keeping this seperate here ill stop it being so confusing (along with me still learning to use the correct termiology). I'll post up seperately the DC/CV expander seperately.

 

[Audioguru]

An audio splitter can have attenuation, gain or the same level outputs as the input. You can "split" one signal to feed hundreds of devices without using any parts. The signal source must have a low impedance (like the output of an opamp) and the devices must have a high input impedance (like the input of an opamp).

 

[darren adcock]

An audio splitter can have attenuation, gain or the same level outputs as the input. You can "split" one signal to feed hundreds of devices without using any parts. The signal source must have a low impedance (like the output of an opamp) and the devices must have a high input impedance (like the input of an opamp).

So in terms of an audio splitter is what I have drawn above ok? I don't expect it to be perfect. My intention is to run through a bunch of op amp based utility circuits.

 

[Audioguru]

You have an opamp on the left driving three opamps that drive volume controls. The opamp on the left can drive many volume controls by itself without any additional opamps. But the additional opamps can have different gains if you want.

I would simply increase the gain on the opamp on the left so that the volume control needing the most signal level gets it without an additional opamp then use a resistor in series with each other volume control to reduce their maximum levels without adding any opamps on the right side.

You will not even need the opamp on the left if the signal source has a fairly low impedance.

 

[darren adcock]

You have an opamp on the left driving three opamps that drive volume controls. The opamp on the left can drive many volume controls by itself without any additional opamps. But the additional opamps can have different gains if you want.

I would simply increase the gain on the opamp on the left so that the volume control needing the most signal level gets it without an additional opamp then use a resistor in series with each other volume control to reduce their maximum levels without adding any opamps on the right side.

You will not even need the opamp on the left if the signal source has a fairly low impedance.

Thanks AG. I will make what you have said also.

I was worried if I split the signal I'd get volume loss which is why I added the extra opamps. Adding them was also a bit of learning via repetition also.

I feel like i'm at a stage in learning where raher than copying chematics or asking you guys for solutions/schematics I should be trying to draw them on my own and see if they are correct via here. Is this a good approach or I worry it will be too time consuming for you guys.

 

[Audioguru]

Take an opamp that has negative feedback which causes its output impedance to be 0.1 ohm (it is probably less).
Then "split" its output to drive ten 22k ohm loads. Does "splitting" cause a volume loss? How much is the level at each of the loads?
The voltage divider is (22k/10) / [(22k/10) + 0.1 ohms]= 0.99995 times. The tiny loss is almost unmeasurable.

 

[darren adcock]

Take an opamp that has negative feedback which causes its output impedance to be 0.1 ohm (it is probably less).
Then "split" its output to drive ten 22k ohm loads. Does "splitting" cause a volume loss? How much is the level at each of the loads?
The voltage divider is (22k/10) / [(22k/10) + 0.1 ohms]= 0.99995 times. The tiny loss is almost unmeasurable.

That's really helpful thanks AG. Loads of circuit space just opened up right there!