DIY Sub amp recomendations??

[.::Jonesy::.]

hi,
Im sure this has been mentioned quite a few times, but i did a quick serch and didnt find to much of revelance.
I have a HT set up but need a decnt sub and amp, the amp and creading the box and so forth are of no real issue, but i cant seem to find a cheap off the shelf sub amp, in australia.
I was wondering if there wa any good DIY amps that i could use for this. I only plan to use one sub 10 or 12 inch, and my amplifier has a sub out socket.
I can solder circuit borads and do a bit but dont know too much thus i like the Gainclone design, could a gainclone design amp be used, also why have i not seen any specs for the output for a gainclone, everone seems to be building them but i have not seen any power ratings (have i just missed them).
thanks for youre help,
PS if their is a thread that has covered this already please let me know so i can save everone time.
jonesy

[soundNERD]

I am working on this, the board layout is complete, and I am hoping to etch and assemble the board today and see how it comes out.

It uses 2 3875 chips bridged. The chips both run in non-inverted mode, but a DRV134 chip inverts one amp and not the other.

Finally, there is a crossover using the LM833 Audio OPAMP. The crossover gain and frequency is adjustable.

Hopefully not too much to ask

[Jye]

Here is some good reading

http://www.national.com/an/AN/AN-1192.pdf#page=1

I'm looking at making a 100W Parallel Circuit later for a sub that will go with some tangbands.

Hope this helps
Jye

[carlmart]

Originally posted by soundNERD
The chips both run in non-inverted mode, but a DRV134 chip inverts one amp and not the other.

Are you using both outputs of the DRV134 or just the inverting one? On the latter case it would be a waste to use that chip.


Carlos

[soundNERD]

Yes, I am, otherwise, like you said, its a waste.

I have both amps in NI mode with the inverting output going to one amp and the non inverting going to the other chip.

If you do not have one of those, you could probably rig a dual opamp into there if the pins are right and invert one, or try and mess with the amps to make one invert.

[carlmart]

Originally posted by soundNERD
Yes, I am, otherwise, like you said, its a waste.

I have both amps in NI mode with the inverting output going to one amp and the non inverting going to the other chip.

If you do not have one of those, you could probably rig a dual opamp into there if the pins are right and invert one, or try and mess with the amps to make one invert.

If you are doing like you said, it's not a waste: it's as how it should be. Inverting output to one amp, non-inverting output to the other. That's what bridging is.

The fact that you are using a NI mode on the amps is also right and it's what I would do.

The advantage of using the DRV134 is that you do the bridging with more precision than when using two singles or a dual op-amp. Very much like what you would do with a transformer.


Carlos

[soundNERD]

yep

exactly why i did that.

Hopfully it will make a difference with a sub.


While were talking about the 3875, does it work ok with a 4ohm? according to the graph on the datasheet, it can't do 4ohm. Is this true? If so I guess I'm going with a 3886.

One more question, how would a bridged 541 be for a sub? I want to use a 549, but my PS is too high voltage for it. Would I get more power bridging a 541 into a 8ohm sub than a 3886?

thanks!

[soundNERD]

On the 541, to remove to current limit, do I just get rid of the resistor? Or do I need a larger resistor?

[cjd]

If I remember correctly (I've read this a few times here and elsewhere):

The 3875 wants less input voltage to handle 4ohms IIRC. 18VA trafo is usually recommended, though 22V is a good balance between 4ohm and 8ohm performance.

In this case, the 3886 does seem better suited to the application, particularly if you ever find yourself with a 4ohm driver.

C

[soundNERD]

Forget the 3875, too low power and too high minimum impedence.

Now, heres the design with a opa541. Should be about 150W into 8ohm (4ohm each amp)??

Let me know what you think.

heres the copper layout