Simple gain circuit...electronic gurus needed

[augerpro]

I was looking at building a simple gain circuit for use in a biamped 3way to to match the woofer level with the mid/tweet due to baffle step. The rest of the XO would be passive. So a active/passive hybrid. This circuit would be placed between the preamp and the amp. So I check Linkwitz's site and found the variable gain circuit. Now this just looks like a voltage divider to me, ie it can lower the level of the signal. I'm looking to raise the woofer, not lower the mid/tweet to match the them...am I missing something? How do I do this?

Now that I think about it, wouldn't this require a transformer to step up the voltage? Could the average joe build something simple to do this that wouldn't sound like garbage?


PS could someone point me to an AB switch for comparing speakers. Retail or a simple diy circuit? Thanks

[cotdt]

wouldn't it be better to lower the output of the mid/tweeter? opamps begin to impart their own sound when they are used for gain purposes.

[BobEllis]

http://www.linkwitzlab.com/filters.htm#5 shows two baffle step circuits. Be sure to provide well regulated power and bypass the rails with 100 nF as close to the power pins as possible.

[augerpro]

Well...I don't know. I mean the DCX and whatnot does this and no one complains so...if i'm going to drop the sensitivity of the mid/tweet I might as well build a regular passive XO.

[augerpro]

Thanks Bob. That does look like what I need :T . I'm thinking that this isn't as simple as I thought...I have no idea what your advice meant ops: So this filter would have to have a power supply? Makes sense. Would it need this buffer circuit Linkwitz lists first? It seems very simple but I have no experience with this sort of thing. I can understand the equations well enough I think, just not the actual circuit building part of it.

[BobEllis]

You don't need a separate buffer if you keep component values in the range of those shown. You could easily build this circuit on a small piece of perfboard like the project boards Radio Shack sells. Linkwitz uses the shelving low pass circuit as his buffer in many of his designs.

I have a spreadsheet here that helps with the calculations. The site is going down in a couple of weeks as I change ISPs.

The power supply could be as simple as a bridge, filter caps and a data sheet LM317/337 regulator. LM7815 and 7915 regulators are a bit noisier, but may be acceptable, too.

Bypassing simply means connecting a 100 nf cap from each rail pin to ground as close to the chip as possible. Tolerance isn't a factor, but use a polyester or polypropylene cap. Mouser and Digikey are good parts sources.

[augerpro]

Bob you the man! I'll dig into this at your site a bit more. Thanks again!

[BobEllis]

No, SL, Jon Marsh and Zaph are the men. I just managed to dumb it down a bit

[chasw98]

Brandon:
If you do not want to go to the hassle of building your own external power supply just for an opamp or 2, you can usually find +-15 volts available in most electronic gear. Almost all Behringer components will have a bipolar supply that you can tap off of for use for a couple of opamps. Just be sure to put the bypass caps Bob talks about in as close to the power supply pins of the opamps as possible.

Or if you want a very good, inexpensive supply, look here http://www.skycraftsurplus.com/index...ROD&ProdID=890

Chuck

[augerpro]

Hey Chuck thanks for the link. I don't mind using prebuilt for the PSU as long as the quality is good. Is that part good quality?

For now digging around Bud's and Rod Elliots site to learn what the heck I'm doing. My biggest problem is time. It's summer and between work, house work, and other hobbies I don't know if I can give myself a decent crash course in basic electronics. I'll post my progress in this thread. Thanks everyone for the help so far.

[chasw98]

Hey Chuck thanks for the link. I don't mind using prebuilt for the PSU as long as the quality is good. Is that part good quality?

For now digging around Bud's and Rod Elliots site to learn what the heck I'm doing. My biggest problem is time. It's summer and between work, house work, and other hobbies I don't know if I can give myself a decent crash course in basic electronics. I'll post my progress in this thread. Thanks everyone for the help so far.

Yes, it is a very good power supply and it is even better because of the surplus price. The one drawback to it is the size and how to mount it since it is an open frame supply. It will fit in a 2 space rack unit, but then the actual circuit you are using is only about 2 inches by 2 inches so it is kind of overkill. I like them because they are easy to use and prototype with till you get the circuit doing exactly what you want and can then build a supply to fit the requirements so to speak.

Chuck