Assistance in wiring a simple circuit?

[things]

OK, got it. Torben, thats the ones, the coupling capacitors!

Thanks

 

[Torben]

OK, got it. Torben, thats the ones, the coupling capacitors!

Thanks

OK, cool. Hope it works out. Post again when you see whether it works or not.


Good luck!

Torben

 

[Torben]

Morning Torben,

Morning Eric,

I believe that 'things' is asking 'where' do I connect my output ground [0v].?

You connect the Output ground [0v] to the Sound Card 0V.

. . .and also to gnd on whatever you connect the amplifier output to, right?


Torben

 

[ericgibbs]

Morning Eric,
. . .and also to gnd on whatever you connect the amplifier output to, right?
Torben

hi,
Its best to avoid a common point that is 'high' wrt to the psu ground [and signal source]
due supply currents flowing in that common wire.

Any changes in current flowing in the 'common' wire will cause a voltage change at the 'high' common point.
The opa will 'see' this change in common level as a signal change.

I expect you know this already, perhaps it may help 'things'...

 

[Torben]

hi,
Its best to avoid a common point that is 'high' wrt to the psu ground [and signal source]
due supply currents flowing in that common wire.

Any changes in current flowing in the 'common' wire will cause a voltage change at the 'high' common point.
The opa will 'see' this change in common level as a signal change.

I expect you know this already, perhaps it may help 'things'...

I *think* I know what you mean. But just to be sure I have to ask: if the power supply ground is connected to the amplifier ground, and the amplifier ground is connected to the next device's ground, then no voltage difference can appear between them, right?

Are you saying that there is a common high point in this circuit? Or is this something about floating grounds which I haven't learned yet?

Sorry if these seem like basic questions (they are, I know) but I'm still working on gathering my theory (and experience).


Torben

 

[Torben]

One more question: why would the deliberate +5.1V DC bias given by the Zener be useful?


Torben

 

[ericgibbs]

One more question: why would the deliberate +5.1V DC bias given by the Zener be useful?


Torben

hi,
The way I read the circuit, not being 100% sure of the input signal, is that the -5V, sets the postive limit of the output signal level via R3.

IF the input signal is 0V thru +5v [dont know for sure] then the output signal would swing down to zero volts.
Not knowing what he is trying to do makes it hard to follow.
I think what he trying to do is to get the 'square' wave signal from the sound card before the filters
and to amplify that prefilter signal to a 0/+5V level.

Perhaps he could tell us what he's trying to do.?

 

[Torben]

hi,
The way I read the circuit, not being 100% sure of the input signal, is that the -5V, sets the postive limit of the output signal level via R3.

IF the input signal is 0V thru +5v [dont know for sure] then the output signal would swing down to zero volts.
Not knowing what he is trying to do makes it hard to follow.
I think what he trying to do is to get the 'square' wave signal from the sound card before the filters
and to amplify that prefilter signal to a 0/+5V level.

Perhaps he could tell us what he's trying to do.?

I had the same thoughts. I was working under the assumption that because he's skipping the coupling caps he wants to connect to something which isn't another piece of audio gear.


Torben

 

[ericgibbs]

I *think* I know what you mean. But just to be sure I have to ask: if the power supply ground is connected to the amplifier ground, and the amplifier ground is connected to the next device's ground, then no voltage difference can appear between them, right?

Are you saying that there is a common high point in this circuit? Or is this something about floating grounds which I haven't learned yet?

Sorry if these seem like basic questions (they are, I know) but I'm still working on gathering my theory (and experience).


Torben

hi,
A diagram explains it best.

The problem to avoid is the power supply current for the devices flowing in the signal ground lines.
These device currents cause voltage drops in the ground wiring which can be seen as a change in signal level in sensitive amplifiers,
if the amplifier uses a connection point away from the psu 0V.

In theory by grounding, in whats known as a Star ground connection back at the psu these 'ground loops' can be minimised.

 

[Torben]

hi,
A diagram explains it best.

The problem to avoid is the power supply current for the devices flowing in the signal ground lines.
These device currents cause voltage drops in the ground wiring which can be seen as a change in signal level in sensitive amplifiers,
if the amplifier uses a connection point away from the psu 0V.

In theory by grounding, in whats known as a Star ground connection back at the psu these 'ground loops' can be minimised.

Hi Eric,

Gotcha! Once you put it in terms of "ground loop" I got what you meant. I've had to deal with ground loops in audio (stage and studio) situations but just wasn't thinking about it in this context. Makes total sense.

Thanks!


Torben

 

[things]

hey guys. Just finishing up the circuit now. let me explain exactly what I am doing.

Well, basically, you all know that a sound card, is basically a digital to analogue converter. I have a laser projector, that uses galvanometers to control the beam. They are setup in a X/Y configuration, and are controlled by a +5/-5 volt signal. Since the real lasershow controllers are VERY expensive, it has been discussed that you can use a sound card do do that. SO basically, you just take the signal DIRECTLY from the DAC chip on the sound card (Before the coupling capacitors at the output).

This then gives you a raw analogue signal, which is what you want. Now, one of you 2 may know, but what EXACTLY does that circuit do? Does it just amplify the signal?

The reason I am asking, is that driving the galvo's from the sound card DIRECTLY works, but the output is quite distorted. Is there anything in that circuit, that would somehow optimise the output? I am thinking this, because the output image size, with just the sound card is reasonable, and I dont know why they are so distorted.

Any idea's?

THanks

 

[Torben]

hey guys. Just finishing up the circuit now. let me explain exactly what I am doing.

Well, basically, you all know that a sound card, is basically a digital to analogue converter. I have a laser projector, that uses galvanometers to control the beam. They are setup in a X/Y configuration, and are controlled by a +5/-5 volt signal. Since the real lasershow controllers are VERY expensive, it has been discussed that you can use a sound card do do that. SO basically, you just take the signal DIRECTLY from the DAC chip on the sound card (Before the coupling capacitors at the output).

Hi Things,

It sounds to me like the laser projector has a control input which has 2 connections: signal (+-5V) and gnd. Is this correct? If so, I would think that you want the signal centred on gnd, which as far as I can see would mean just connecting straight out of the sound card outputs (i.e. don't skip the coupling caps) and lose the Zener. I may well be missing something here--I'm just a hobbyist. There are lots of real EEs on the forum.

This then gives you a raw analogue signal, which is what you want. Now, one of you 2 may know, but what EXACTLY does that circuit do? Does it just amplify the signal?

As I read it, with both pots centred, it inverts the signal and amplifies it by 3.5 times.

[Edit: With the 5.1V Zener in place it also imposes a +5.1V DC bias on the signal.]

The reason I am asking, is that driving the galvo's from the sound card DIRECTLY works, but the output is quite distorted. Is there anything in that circuit, that would somehow optimise the output? I am thinking this, because the output image size, with just the sound card is reasonable, and I dont know why they are so distorted.

Any idea's?

THanks

How is it distorted? What does it do that you do not want?


Torben

 

[ericgibbs]

hi,
What voltage do you measure at the input of you amp [the signal line] when you have no audio input drive to the sound card.?
I suspect its +5V, can you measure and let us know.

What voltage drive levels do the galvo's require.? and whats the galvo resistance.?

 

[Torben]

Good points, Eric. I guess it would be good to get an idea of what is actually being driven.

Anyway, I'm off to bed. Hope you guys get this figured out.


Torben

 

[things]

Hi, I am not using the amp right now, but by "distorion", I mean the output pattern/image is really messed up. For example, if I try get it to draw a regular circle, it comes out as a circle, but with ALOT of loops in it. almost like its "pulsing" somehow.

EDIT: the circle comes out kinda like this, but more even and with more loops:

**broken link removed**



EDIT: Just found out, when the sound card is doing nothing, it has like 2V at the output, would that do anything like this?

 

[ericgibbs]

EDIT: Just found out, when the sound card is doing nothing, it has like 2V at the output, would that do anything like this?

That explains the purpose of the -5V offset voltage.
Set the R3 pot so that the output of the OPA is zero when the sound card has no audio input.

Keep the OPA gain set R4 low for starters.
What are you driving the input with, signal/freq etc.

Ask again:
What voltage drive levels do the galvo's require.? and whats the galvo resistance.?

 

[things]

I am not driving the GALVO's directly, the galvo's have thier own little amplifier. So basically, I am supplying the galvo amplifier with a signal, which they then control the galvo.

The galvo amps state: Input: +-5VDC differential

they have a input for a + signal, and - signal.

 

[ericgibbs]

I am not driving the GALVO's directly, the galvo's have thier own little amplifier. So basically, I am supplying the galvo amplifier with a signal, which they then control the galvo.

The galvo amps state: Input: +-5VDC differential

they have a input for a + signal, and - signal.

hi,
Is this the way you have the galvo differential amps connected when using the galvo's.

Are you driving the stereo inputs of the sound card with quadrature signals for the circle.. sine on left chan. cos on right chan.?

EDIT: you must remove the +2V offset, thats the purpose of the OPA circuits.

 

[things]

Oh man, I was just laughing soo hard, I was wondering why t wasnt working, then I find that I didnt link the -15V to the op-amps LOL.

Anyway, one problem I have now, is that I am getting like 12V on the output!!! :O

Maybe its a problem with having the sound card ground hooked to the ground of everything else, and not just straight to the output?

Here is how its currently wired:

**broken link removed**

 

[ericgibbs]

hi,
With no audio input, adjust R3 to cancel the fixed +2V coming from the sound card.
This is a MUST else the galvo's will be off zero angle at rest.

It should be possible to make the outputs pin#1 on both the TL072 to be zero.

If you cant set it to zero, recheck the wiring.