Hi!
I've built me (for my ghetto blaster project) a high-pass GC, using a circuit from the nationals on-line filter calculator, like this:
With the following values:
R1 3200 K
R2 240 K
R3 2.2 K
R4 0.1 K
C1 2.2 nF
C2 2.2 nF
It should give a a xo-frequency of about 75 - 80 Hz with a Q of 0.6
Supply voltage is +- 35 V (25 - 0 - 25 toroid), with only GC-like 2 * 1000 uF at the pins of the IC, which is an OPA458.
When I turn on the amp, with no signal and no load connected, nothing happens (OK), supply voltages are OK, but at the output pin I have nearly the full positive output rail!
Has anyone some suggestions? This is the first time I am trying to use those filters... And I have to be finished until friday evening, since I want to use the blaster in my skiing holidays...
Thanks,
Arndt
I've built me (for my ghetto blaster project) a high-pass GC, using a circuit from the nationals on-line filter calculator, like this:
An externally hosted image should be here but it was not working when we last tested it.
With the following values:
R1 3200 K
R2 240 K
R3 2.2 K
R4 0.1 K
C1 2.2 nF
C2 2.2 nF
It should give a a xo-frequency of about 75 - 80 Hz with a Q of 0.6
Supply voltage is +- 35 V (25 - 0 - 25 toroid), with only GC-like 2 * 1000 uF at the pins of the IC, which is an OPA458.
When I turn on the amp, with no signal and no load connected, nothing happens (OK), supply voltages are OK, but at the output pin I have nearly the full positive output rail!
Has anyone some suggestions? This is the first time I am trying to use those filters... And I have to be finished until friday evening, since I want to use the blaster in my skiing holidays...
Thanks,
Arndt
Hi!
Yeah, I meant the OPA 548...
Actually I found a mistake by back-engineering (drawing a diagramm by the connections I made)...
The feedback resistor (R3) is not from output to negative input , but to positive input...
On all of my four ICs...
Can not change it right now, maybe later...
Thanks anyway,
Arndt
Matttcattt said:
Yeah, I meant the OPA 548...
Actually I found a mistake by back-engineering (drawing a diagramm by the connections I made)...
The feedback resistor (R3) is not from output to negative input , but to positive input...
On all of my four ICs...
Can not change it right now, maybe later...
Thanks anyway,
Arndt
Hi!
Is it somehow possible to lower the DC offset? Problem is, whenever I raise the resistance from negative input to ground, the gain decreases...
Is there a way to avoid this change in gain and filter characteristics, but still dropping DC offset (I want to achieve at least <100 mV)?
Thanks,
Arndt
Is it somehow possible to lower the DC offset? Problem is, whenever I raise the resistance from negative input to ground, the gain decreases...
Is there a way to avoid this change in gain and filter characteristics, but still dropping DC offset (I want to achieve at least <100 mV)?
Thanks,
Arndt
Re: Re: Problems with HP GC, urgent
Hi!
I have used small feedback resistor values because is was adviced to do so in this thread:
active XO GC
Can I use "normal" feedback values without risking instability?
Only two days unti this has to work...
Bye,
Arndt
Hi!
moamps said:
I have used small feedback resistor values because is was adviced to do so in this thread:
active XO GC
Can I use "normal" feedback values without risking instability?
Only two days unti this has to work...
Bye,
Arndt
Cradle22 said:
The gain is determined by a *ratio* of the feedback resistor to the resistor from the inverting input to ground. So, if you want to increase the value of the inverting-ground resistor, you simply increase the feedback resistor by the same factor!
It seems to me, however, that you will want to reduce the values of those two resistors in order to reduce your DC offset.
Good luck!
Hi!
I know how to calculate the feedback resistors. And I would say that it is easier to reach lower DC offset by increasing the values, but still there was this statement of someone who said that the feedback resistors should be small in a sallen-key topology, which should lead to a better rolloff at the XO frequency.
Don't know if I have the time to do some more work on this today, and tomorrow I'm off for Saas Fee (which is what I've built this thing for in the first run)...
Bye,
Arndt
Nappylady said:
I know how to calculate the feedback resistors. And I would say that it is easier to reach lower DC offset by increasing the values, but still there was this statement of someone who said that the feedback resistors should be small in a sallen-key topology, which should lead to a better rolloff at the XO frequency.
Don't know if I have the time to do some more work on this today, and tomorrow I'm off for Saas Fee (which is what I've built this thing for in the first run)...
Bye,
Arndt
Hi!
Well, looking at the thomson application notes for the TDA2030A, where they implement something like I want to do, I realize that they also added polarized caps in series to the output, which is also a (not preferred) way to get rid of DC offset...
But since sound quality is not of highest priority on my wish list, I will also try that (it should still be better than the average boombox out there).
Bye,
Arndt
Well, looking at the thomson application notes for the TDA2030A, where they implement something like I want to do, I realize that they also added polarized caps in series to the output, which is also a (not preferred) way to get rid of DC offset...
But since sound quality is not of highest priority on my wish list, I will also try that (it should still be better than the average boombox out there).
Bye,
Arndt
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