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OK, got it. Torben, thats the ones, the coupling capacitors!
Thanks
Morning Torben,
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.
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'...![]()
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.?
hi,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.
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
EDIT: Just found out, when the sound card is doing nothing, it has like 2V at the output, would that do anything like this?
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.