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Best Class Amp for 4ohm Speakers?
Best Class Amp for 4ohm Speakers?
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Old 9th February 2017, 01:58 AM   #1
blippio is offline blippio
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Default Best Class Amp for 4ohm Speakers?

Hi All-

I'm a total noob but have been very interested in building an amp to drive a set of 4ohm speakers. Is there an amp topology that is better suited to driving lower impedance speakers?

I've been researching the Boenicke W5 and am much more of a woodworker than an electronics guy; I plan on building a clone of these speakers as they are way out of my price range ($5000 - $10,000 pr)

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These don't seem to be the most sensitive speakers... Details from his website:

Boenicke W5 Standard
Sensitivity: 83-86 dB / watt / m depending on frequency
Nom. impedance: 4 ohms

5.25″ long throw bass driver, tuned to 65*Hz,*1st order crossover
3″ widebander, 1st order high pass filter, Rear ambient tweeter

As far as wattage I do not know?! I remember reading a review where Boenicke himself stated that "they love power"... I'm including the specs on the three drivers of the speakers here, which should help:

Fountek FE85 (full range front driver)
Power Handling (RMS): 12 Watts
Power Handling (max): 25 Watts
Impedance: 8 ohms
Sensitivity: 85.7 dB

Tang Band 13-1761S (rear tweeter)
Power Handling (RMS): 12 Watts
Power Handling (max): 25 Watts
Impedance: 8 ohms
Sensitivity: 85.7 dB

Peerless SLS (side woofer)
Power Handling (RMS): 80 Watts
Power Handling (max): 150 Watts
Impedance: 4 ohms
Sensitivity: 87.8 dB

Oddly enough these drivers are very inexpensive (given the speakers' price) but the overall result has been rated very highly. The internals are more high-end (wiring, crossover parts)

The thing I like about these speakers is the look (I admit I'm a sucker for the aesthetics), their size, and their apparent sound :great imaging/soundstage, great tone--all surprising considering their small size. Maybe these are some of the characteristics I'm looking for in an amp? (in addition, of course, to the engineering/specs required to drive these)

Last edited by blippio; 9th February 2017 at 01:10 PM. Reason: adding more info...
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Old 9th February 2017, 03:09 AM   #2
kct is offline kct  Canada
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Best Class Amp for 4ohm Speakers?
Well, you need to provide a little more info.

Can you provide some info on the speakers you want to operate the amp with ? Model, Make ect.

What is your power requirement at 4 Ohm ?
10W
100W
1000W
?

What expectations do you have for sound quality ?

Would you be happy with Class D or do you need a Class AB or Class A ?

So far pretty much any amp of the above classes can drive a 4 Ohm load.

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Old 9th February 2017, 12:52 PM   #3
sgrossklass is offline sgrossklass  Germany
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Not so much a matter of topology but rather of implementation. A lower-impedance load needs less voltage but more current, and crossover distortion needs to be better-controlled. So in an AB amplifier, expect somewhat higher bias currents than just 30 mA, emitter resistors of 0.22 ohms tops, maybe doubled-up (or beefier) output transistors and somewhat lower supplies.
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Old 9th February 2017, 01:23 PM   #4
blippio is offline blippio
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Doing further research some say the Goldmund Job 225 (Class A/B) as well as the Wyred4Sound mINT (Class D) pair with these speakers well... Any designs that are similar to these that would be recommended?

I've been looking at the SAKSA board and am curious about Pavel's PAO3 as well as "The Wiener" board

Any input welcome!

Last edited by blippio; 9th February 2017 at 01:39 PM. Reason: double post
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Old 9th February 2017, 02:05 PM   #5
blippio is offline blippio
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Pics of the Boenicke W5 btw...

boenicke-walnut3.jpg

boenicke-walnut4.jpg

boenicke-internal.jpg
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Old 9th February 2017, 02:17 PM   #6
picowallspeaker is offline picowallspeaker  Italy
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You seem to forget that the crossover do the splt for all the drivers.
You haven't mentioned it yet.
The (lateral) sub does the ( very low ) frequencies
the front speaker does the most important range ( 0.1 -15 k Hz)
The rear tweeter ( what does a rear tweeter do )
needs some passive components to filter out the mid and low frequencies.

Doesn't a classical 3 way with drivers arranged to emit frontally amuse anyone ?
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Old 9th February 2017, 02:21 PM   #7
picowallspeaker is offline picowallspeaker  Italy
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OMG ! the tw is on the binding posts !
Doesn't this thread belong to multi-way/fullrange forum(?), as it seems you're most interested on the maple/oak/cherry finish rather on the tehnical side of the things.
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Old 9th February 2017, 02:39 PM   #8
turk 182 is online now turk 182  Canada
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your clone is likely to wind up with a few birth defects unless you have a really good handle on speaker design software and simulators.
and if your speaker choices T/S parameters don't match what was used in the original changing the box vent is going to likely be necessary.
should be an interesting journey...

oh wait i forgot your on about an amp to drive 4 ohm speakers with, without knowing if your crossover/speaker combo may or may not present a reactive load or a bad dip in the impedance to the amp how does one decide what amp topology to go with...?

Last edited by turk 182; 9th February 2017 at 03:02 PM.
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Old 9th February 2017, 02:59 PM   #9
blippio is offline blippio
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LOL, birth defects for sure but I'll hopefully come out with at least 9 fingers after this project (though I'd prefer to keep my 10)

I was definitely planning on leveraging the expertise here when considering the crossover, though there is a very detailed thread on several who have treaded here before me (unfortunately google translate makes it a bit of a challenge to learn this new hobby!)

crossover.png

There will surely be a little reverse-engineering and sleuth work involved, and the possibility of hiring someone for crossover design has entered my mind

@ Picowallspeaker: Yes, it looks like an unconventional design--but the size is perfect for me (and I can't help but liking the wood either!)... I have a tendency to jump headlong into new hobbies, I'm hoping to learn a lot with this project...
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Old 9th February 2017, 03:14 PM   #10
picowallspeaker is offline picowallspeaker  Italy
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There are some projects with that subwoofer ( or similar ) on the P.E. website, in the DIY section.
Bookshelf | Parts Express Project Gallery
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