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Old 16th December 2009, 11:21 AM   #11
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Quote:
Originally Posted by tinitus View Post
Low impedance preamp load ?
Sorry, I can't picture this in that context - can you explain better? Thanks!
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Old 16th December 2009, 11:55 AM   #12
tinitus is offline tinitus  Europe
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Well, say you have two amps each with maybe like 10khz input impedance
And you paralel them into the same preamp output
The preamp will see a 5kohm load instead of 10kohm
Some tough preamp designs will be fine, but many wont

You may have amps with higher input impedance, like say 20kohm
But then, you are talking about multiple amps, more amps than just two
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Old 16th December 2009, 12:07 PM   #13
tinitus is offline tinitus  Europe
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Originally Posted by theAnonymous1 View Post
What's wrong with using a single amplifier for all the drivers?
Oh, I may have misunderstood it
I read it as one amp each driver, like someone suggested

I can see now it probably means ONE single amp only

Last edited by tinitus; 16th December 2009 at 12:20 PM.
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Old 16th December 2009, 12:22 PM   #14
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Quote:
Originally Posted by tinitus View Post
Low impedance preamp load ?
Not sure I follow that question.

He mentioned there will be 21 drivers per side @ 6-ohm each. If he made 7 sets of 3 parallel drivers, that would make a combined load of ~14-ohm.

I don't see any major problem with a final 14-ohm load; unless he planned on doing some sort of power tapering using the gain of each individual amp.

EDIT: Didn't read your last post until after I finished.

Last edited by theAnonymous1; 16th December 2009 at 12:24 PM.
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Old 16th December 2009, 03:10 PM   #15
oublie is offline oublie  United Kingdom
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Power tapering is one of the reasons i'm going this route.

the other is to try and keep all the connections parallel if possible.

it is my understanding that series and series/parallel can have adverse effects on speakers and is a technique used in the live perfomance world to change the sound on amplified guitars etc. Apparently it can lead to an 'edgier' sound which of course i don't want.

It would be easy for me to just wire the drivers in a mixture of parallel and series and run them of 4.8 ohms - 5 parrallel - 4 X series or some other configuration with a single driver on 6 ohms. but this wont allow me to taper adequately. In sets of 3 i can at least tweak to a certain extent.

It's really all about flexibility allowing me to test a number of different configurations and getting the best sound a diyer can achieve within a pretty tight budget.
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Old 16th December 2009, 05:29 PM   #16
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Well, out of the two small boards you previously mentioned, I would have to go with the MPS7720. I've heard the other 2W amp produces a nasty amount of noise.

Be aware the MPS7720 has capacitor coupled outputs (single supply, single ended). It should be fine at 2R if you keep the supply voltage low enough (hopefully).
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Old 16th December 2009, 09:24 PM   #17
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Quote:
Originally Posted by theAnonymous1 View Post
Not sure I follow that question.
Sorry, I thought it was explained

It was related to a previous suggestion of using multiple amps, or I mistakenly thought it was
I misunderstood, maybe because of a bit shortened english
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Old 16th December 2009, 10:29 PM   #18
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With that many drivers, you may need more power than you realise
I would say a minimum of 30watt/8ohm, making 100watt into 2ohm
Any good AB amp with just 2 or maybe 4 tough output devices will do that, with a big heatsink

But you may realise that even if it survives 2ohm, it may loose some of its quality
With 2ohm, it might just be only 1.8ohm, or even 1.5ohm
2.5-3ohm might work much better

Im not sure why you say "on a tight budget", with that many 4" and electrostatic tweeters
What is a tight budget
Every time I have calculated such with even much less drivers, it gets expencive very fast, even with relatively cheap drivers

Last edited by tinitus; 16th December 2009 at 10:36 PM.
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Old 17th December 2009, 01:20 PM   #19
oublie is offline oublie  United Kingdom
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Quote:
Originally Posted by tinitus View Post
With that many drivers, you may need more power than you realise
I would say a minimum of 30watt/8ohm, making 100watt into 2ohm
Any good AB amp with just 2 or maybe 4 tough output devices will do that, with a big heatsink

Im not sure why you say "on a tight budget", with that many 4" and electrostatic tweeters
What is a tight budget
Every time I have calculated such with even much less drivers, it gets expencive very fast, even with relatively cheap drivers

I think i'll go with the sure 4X 100w boards and try one with 2 mids in parallel to start with test for a week or 2 and if all is okay ill order all that i need with a couple of spares. They seem to offer the best bang for buck and having too much power wont cause as much of an issue as too little will.

As for tight budget - my 40th birthday presents consist of

64 4" wharfdale full range drivers
2 15" dayton dvc subs
one cerwin vega cv 2800 (not ordered yet)

i already have the step up transformers and 4 other amps for the tweeters and the custom metal will be ordered after xmas.

now thats a proper birthday present even though my birthdays not until march i hope to unveil the finished speakers at the party - I love my wife
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