Hi,
I'm looking at upgrading parts in an active subwoofer crossover that I currently have. I would like some input on it's current opamps and what I should swap them with.
The power for this unit is supplied with a 24VAC transformer. There are only 2 1N400X diodes in the power supply section, so I assume it's a single 24VDC power supply. I don't think there is a voltage regulator there, but worst-case scenario would indicate that the opamps would need to be able to handle a +24VDC supply.
There are four MC33078 DIP8 dual-opamp chips, made by ST, on the main board and it looks like they drive the high-pass / low-pass outputs. The spec sheet says it has a large output voltage swing (+14.3V/-14.6V), but I'm not sure if this is critical. It looks like they are all bypassed pretty good because there a little of .1uF caps surrounding these opamps.
There is also an LM324 DIP14 quad-opamp chip on the main board, also made by ST. It's not apparent what this is used for, but it provides a large voltage gain (100db) and a very low supply current (376uA). Thinking about it, it's probably for the gain stage.
Finally, there are two MC33179 quad-opamp chips (DIP14) on a sub-board along with 4 pots. The pots are used to adjust hi-pass frequency, low-pass frequency, phase and gain. The only unique quality that I can really see on this one is its ability to drive a 600ohm load. I would think this is to handle the different impedances from the pots. It's also a bipolar device (but the others could be bipolar, too).
I don't intend to use the high-pass outputs, so I'm not really worried about frequancies above 200Hz or so.
Recommendations are welcome.
I'm looking at upgrading parts in an active subwoofer crossover that I currently have. I would like some input on it's current opamps and what I should swap them with.
The power for this unit is supplied with a 24VAC transformer. There are only 2 1N400X diodes in the power supply section, so I assume it's a single 24VDC power supply. I don't think there is a voltage regulator there, but worst-case scenario would indicate that the opamps would need to be able to handle a +24VDC supply.
There are four MC33078 DIP8 dual-opamp chips, made by ST, on the main board and it looks like they drive the high-pass / low-pass outputs. The spec sheet says it has a large output voltage swing (+14.3V/-14.6V), but I'm not sure if this is critical. It looks like they are all bypassed pretty good because there a little of .1uF caps surrounding these opamps.
There is also an LM324 DIP14 quad-opamp chip on the main board, also made by ST. It's not apparent what this is used for, but it provides a large voltage gain (100db) and a very low supply current (376uA). Thinking about it, it's probably for the gain stage.
Finally, there are two MC33179 quad-opamp chips (DIP14) on a sub-board along with 4 pots. The pots are used to adjust hi-pass frequency, low-pass frequency, phase and gain. The only unique quality that I can really see on this one is its ability to drive a 600ohm load. I would think this is to handle the different impedances from the pots. It's also a bipolar device (but the others could be bipolar, too).
I don't intend to use the high-pass outputs, so I'm not really worried about frequancies above 200Hz or so.
Recommendations are welcome.
ainami said:
I don't intend to use the high-pass outputs, so I'm not really worried about frequancies above 200Hz or so.
Recommendations are welcome.
so why do you want to improve anything? noise issues?
Well, from what I've read, there is a lot of difference between opamps at that low of a frequency. The Burr-browns usually are described as softer or more "tuby" at the bottom end, as opposed to the Analog Devices opamps.
What I ended up deciding on is to replace the four MC33078's with AD823's. They seemed to be regarded as having a tighter bottom end than the bb's. The crossover is for a home theater application, so I don't want a loose bottom end. The circuit also requires something that will run off a single supply at 24V. I did measure the supply pin of the opamps at 24V, so the power supply is not regulated at all.
The LM324 is getting replaced with a OP484 (Analog Devices), which seems be a better solution for a quad opamp using a single supply. There a lot of negative feedback on the LM324.
I left the MC33179's alone because they seem to be regarded as pretty good. Also, I couldn't find a supplier for them, so I can't switch back if the new ones don't work. The OP484's above seemed like a good solution for this, but I don't know how they react at 600 ohms (which the MC33179 is designed for)
What I ended up deciding on is to replace the four MC33078's with AD823's. They seemed to be regarded as having a tighter bottom end than the bb's. The crossover is for a home theater application, so I don't want a loose bottom end. The circuit also requires something that will run off a single supply at 24V. I did measure the supply pin of the opamps at 24V, so the power supply is not regulated at all.
The LM324 is getting replaced with a OP484 (Analog Devices), which seems be a better solution for a quad opamp using a single supply. There a lot of negative feedback on the LM324.
I left the MC33179's alone because they seem to be regarded as pretty good. Also, I couldn't find a supplier for them, so I can't switch back if the new ones don't work. The OP484's above seemed like a good solution for this, but I don't know how they react at 600 ohms (which the MC33179 is designed for)
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