16ohm Goodman Axiom with class d amp - diyAudio
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Old 29th January 2015, 03:54 AM   #1
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Default 16ohm Goodman Axiom with class d amp

My question: what is likely to happen to the performance of a class D into a 16ohm speaker load such as my much loved and well cared for Goodman 201s.

Searching manufacturer sites has not helped because the specs for the Class D amps & chip sets (e.g. TAS5630) that the amps they are based on give the performance into 4 & 8 ohm speakers.

The chip set specs show some but not a great deal difference for 4 or 8 ohm in say THD vs power or frequency response even the output power does not seem linear with load.

My plan is to replace my own build Bailey (circa 1968) amp with a class D. At this stage I am looking at an assembled board based on TAS5630 (with my own added limiter to protect the speakers) but not finalised yet.
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Old 29th January 2015, 10:44 AM   #2
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Hi,
I'm not an expert in class D. But I would not be worried about the 16 Ohms vs 8 or 4 Ohms, as a higher impedance is an normally an easyer load.
And as FR drivers are often known for irregularities in frequency response, I think it would be a marginal effect.
Off topic , I've made many projects with FR : Lowther, Goodmans 201, axiom 80, Fertin field coil being the best ... until I discovered Earl Geddes speakers. A non-return loudpeaker trip, be careful
Alain
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Old 29th January 2015, 10:13 PM   #3
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Thanks Alain, had an interesting read of Geddes site, but my aim is to keep my Goodman's in their K12 enclosures.

The higher resistance 16ohm is usually perceived as easier on the amp and extrapolating the curves of the TAS5630 it looks like I should get:
1) perhaps lower distortion across most of the range
2) less power - not an issue with my speakers
3) better efficiency - of interest as I generate my own electricity, but magnitude renders the point somewhat moot.

What I really hope for is to run the amp in the 1-10W region which will give a THD that approaches that of the Bailey.

Real question is will the Class D drive 16ohm or spit the dummy?
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Old 29th January 2015, 11:22 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

For an amplifier capable of 8 ohm drive, 16 ohms is a walk in the park.
Of course you'll only get a 1/2 of the power (perhaps a bit more).
Efficiency is unlikely to improve, though less power will be drawn.

If you can, get an amplifier that likes 8 ohms and doesn't like 4 ohms.
At lower powers that is hard, as they are all optimised for cars.

Use the maximum supply voltage specified for the amplifier.

rgds, sreten.

Personally I'd go push pull class A for 10W into 16 ohms.
E.g. The DoZ http://sound.westhost.com/project36.htm
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Last edited by sreten; 29th January 2015 at 11:29 PM.
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Old 30th January 2015, 05:05 AM   #5
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Quote:
Originally Posted by Charles809 View Post
Thanks Alain, had an interesting read of Geddes site, but my aim is to keep my Goodman's in their K12 enclosures.

The higher resistance 16ohm is usually perceived as easier on the amp and extrapolating the curves of the TAS5630 it looks like I should get:
1) perhaps lower distortion across most of the range
2) less power - not an issue with my speakers
3) better efficiency - of interest as I generate my own electricity, but magnitude renders the point somewhat moot.

What I really hope for is to run the amp in the 1-10W region which will give a THD that approaches that of the Bailey.

Real question is will the Class D drive 16ohm or spit the dummy?
Don't see why any class D would not drive 16 ohms , strange thing however is that TI doesn't show a frequency response graph at different impedance's in their datasheet .
Only 80kHz bandwith is mentioned . The output filter will have an influence on the frequency response with 16 ohm speakers, as I can't see any feedback after the output filter in the schematics , so how much will the HF response rise around 20 kHz ?
Probably Easy to fix swapping some inductors and capacitors .

Cheers ,

Rens
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Old 31st January 2015, 06:36 AM   #6
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thanks, it may need a bit of trial and error with matching the output filter
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