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Old 13th November 2006, 01:29 AM   #1
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Default Amplifier Gain Question

I have a 3-way loudspeaker where I want to purchase (or make) a separate amp for my passive low pass network (bass woofer) and use my Aleph 2 for the mid and tweeter section.

Yes, I know active is the best way to go, but it is not in my cards right now.

The reason I want to do this is that my bass speaker is 3db less efficient than my mid/tweeter combo.

My question is, if my Aleph 2 (100w) has 26 db gain, to get 3db more from a bass amp (using the same signal from the pre) what specs should I look for? Do I just look at gain values or does watt rating play a role too?

Thanks for any help you may provide.

~S
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Old 13th November 2006, 02:08 AM   #2
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As you probably already know, listening to your system at full 100 watt levels is difficult to do, especially if it is music you are trying to listen to.

You also probably know that you only need to increase the lesser level of your bass speaker by 2 or 3 db ... of sound pressure level ... to get into better balance with the other drivers.

Now if you actually listen at much more civilized liestening levels, and you only have to increase your bass woofers a couple of db, then you may really only need to change the levels between your (future) bass amp and your middie/tweeter amp.

Whether you actually need to have something like 200 watts for the bass woofers is, of course, a matter of taste, but what you are really trying to do is balance the sound pressure levels of your system and not necessarily just add another, large amp. (200 watts being about 3 db increase over 100 watts , theoritically (as a voltage increase, not necessarily a sound presure level increase).)

Additionally, your bass speaker may be of a nature that increasing the power level by a single db or so may be all that is required ... since you may discover that your bass speaker increases in efficiencies with increased power applied and increasing your wattage from 100 watts to, say, 120 watts may be all that is required ... for your taste and your prefered listening levels ... or maybe you really only need to have a more efficient amp suitable for the bass speaker.

My advise, since you seem to like your Aleph 2, is to get another Aleph 2 for your bass speaker (set). This way you will not have too many suprises or disappointments in the results ... and by simply running the Aleph associated with the bass speakers at a modestly higher level, your expectations will be accomplished.

Of course you might just consider changing you speaker cabinet wiring (crossovers).

(I might also suggest consultation at the Pass Labs forum located elsewhere here at DIYAudio ...)

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Old 13th November 2006, 02:21 AM   #3
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Thanks very much FastEddy.... somehow I knew there would not be an easy answer for this one. I do appreciate your detailed answer.

I was hoping to get away with buying an old ADCOM GFA555 for the bass as it took me 3 years to build my Aleph!!!! I just don't like padding down the mid in the passive xover.

I think I will just experiment and maybe borrow various amps and see what it sounds like.

Thanks again.
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Old 13th November 2006, 02:30 AM   #4
v-bro is offline v-bro  Netherlands
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I would say go for Class D for the bass http://www.41hz.com

To start easy and low cost on a very good functioning type of crossover look for r/c filters (google on "pllxo")...
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Old 13th November 2006, 02:42 AM   #5
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Hmmm... have you heard any of these? Might be a fun project. The Amp 2 just might be the ticket.

Thanks for the link.
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Old 13th November 2006, 02:48 AM   #6
v-bro is offline v-bro  Netherlands
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I have heard many amps with the same brand of chip in it (called "Tipath"), all these amps share ultra detailed sound and good LF control. I just purchased four AMP32's from them, they're really cute.
But presently I'm still using an amp with the same chip as AMP9.

The really high powered amps I haven't had the honour to try yet....
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Old 13th November 2006, 06:45 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
can your speakers be bi-wired?

If so you can bi-amplify them as well (the passive variety not active).

When you add that extra amp feeding only the bass driver you can adjust the bass amp for the extra 3db of gain that you need.
3db =1.414times, so your existing set-up with 26db of gain (20times) stays the same and the new bass amp gets 29db of gain (20*1.414=28.3Times) 28times will be close enough.

If you cannot bi-wire then you need to modify your crossover to separate the low pass from the rest.
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Old 13th November 2006, 07:36 PM   #8
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" ... I was hoping to get away with buying an old ADCOM GFA555 for the bass as it took me 3 years to build my Aleph!!!! I just don't like padding down the mid in the passive xover. ..."

Go for it!! Decent specs, eBay specials = US$200 to US$350 ...

(You might keep exploring around: v-bro 's suggestions about considering Class-D are right in the bass / sub woofer area of quality you will need to keep up with the Alephs' ... You might just end up putting a Class-D right inside your bass speaker box ... :>)
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Old 13th November 2006, 07:52 PM   #9
v-bro is offline v-bro  Netherlands
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Active bass speakers YUMMIE!
'specially with class D...

But if you can get a good deal on the ADCOM, go for it! They are pretty good....

You can always decide to build a class D amp later, maybe you should try a small one first like AMP6 from http://www41hz.com
It will always come in handy for a pair of computer speakers or an upgrade for your alarm clock......
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Old 14th November 2006, 01:29 AM   #10
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Thanks for all the replies and suggestions.

Yes, my plan was to use the low pass section of the passive xover separately with another amp. I was hoping that there was an easy way to decipher the amp specs so I could predict the extra 3db I need.

One is to split apart an Adcom 555, build an additonal power supply and mount the mono amps to my speakers. Then, down the road I will add a digital xover - probably a Xilica 1030, as they come in separate channel versions designed to be mounted in a speaker cabinet and with a wireless ethernet router I can modify the xover using my laptop wirelessly..... but I am a ways off that....
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