Doubt with Active Sub Controller

[hernanstafe]

I was looking at project 48 on Rod Elliot's Page, and when looking at the schematic and the pcb i noticed that there are some electrolitic caps in the pcb that are not shown in the schematic...why is this? just to protect the circuit for being copied or they're not necessary or what?

http://sound.westhost.com/project48.htm#1

[phase_accurate]

One can only see two foil caps on Rod's PCB so is assume that four of these are used as the 4.7 uF coupling caps.

I have seen someting interesting recently: The original ELF patent has run out at least in Europe.

Regards

Charles

[rabbitz]

I'd say they are just the power / bypass caps for the opamps. He does the same thing with the P88.

It will be the electros and some ceramics across the rails.

[hernanstafe]

ok guys but...should i put those electrolytics anywhere? or shouldn't i?!

[MJL21193]

If you follow the schematic exactly you will have no problem - there isn't anything missing. Disregard the electros in the photo as this is a pic of his prototype.

[rabbitz]

The prototype PCB is the same as the final ones he sells. C1 to C4 are signal caps and C5 to C9 are filter and bypass caps which are needed.

Full details are shown in the P48 construction article but you need to buy a PCB to access this info.

[macboy]

Originally posted by MJL21193
If you follow the schematic exactly you will have no problem - there isn't anything missing. Disregard the electros in the photo as this is a pic of his prototype.

The schematic is definitely missing power supply bypass caps for the opamps. You need some.

[REFUGE]

I'm looking at my P48 PCB and I see spaces for 9 caps and the circuit diagram shows 4. I wrote to Mr. Elliot asking for additional info re: the caps. He said the information is available on the secured sight which I have not yet found.
There are two caps #C7 and #C8 that are definitely the size and shape of filter caps.
What is the secured site he mentioned? Anybody know?

[hernanstafe]

And! I've asked for an active sub filter schematic here and the replies i got where about taking a look to that schematic, which is useless since there are parts missing. I need one of those filters, which also sum up left and right channels. Does anyone have a COMPLETE, WORKING schematic for a sub filter?

[macboy]

OK, so first off you need to understand that P48 is probably not what you want unless you read the article very carefully and understand exactly how the circuit is designed to be used. It is not a simple crossover, it is primarily a very special EQ designed for use with a specific type of subwoofer. That is, a subwoofer which has been intentially built into a box that is "too small" (according to traditional design methods) so that its resonant frequency is higher than the frequencies it will be used at. If you try to use this circuit with a conventional subwoofer, you will not only be disappointed with the performance, but will also be likely to damage your subwoofer.

There are no fewer than 3 crossover projects on Rod's site, any of which could be used as a subwoofer crossover after the correct filter component values are chosen. In general, Rod's projects' schematics do not include a power supply, but he usually refers the reader to one of his power supply projects. In addition he rarely includes (necessary) power supply bypass capacitors in his schematics, but he includes them on his PCBs. Usually, all that you need to do is add a 10 uF 25 V cap between each of the two power rails and ground (one pair for each opamp), noting correct polarity of course. Other than that the circuits he puts up are generally functional as described in the articles.