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Class D Switching Power Amplifiers and Power D/A conversion

TPA3255 - all about DIY, Discussion, Design etc.
TPA3255 - all about DIY, Discussion, Design etc.
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Old 11th November 2018, 09:31 PM   #921
voltwide is online now voltwide  Ireland
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Join Date: Jan 2010
Quote:
Originally Posted by MirageZA View Post

My question - is it worth to try? Coming from old school amplification, a little bit of negative feedback is good. How about 3255, can I expect lower noise floor (less hiss in my case).
In my view, PFFB is more elegant solution than coil/caps mods on the output.

Many thanks for your help!
Alex
My answer is NO! - for several reasons
Certainly you could reduce hiss with additional feedback. But at the expense of gain, i.e. input sensity.
TPA3255 is a real low noise device, so if you are experiencing noise you should trace its source instead of reducing power stage gain. More often than not noise originates from the input source, so the first question was: Does it disappear with shorted input terminals?
PFFB as stated by TI application implicates significant gain reduction of TPA3255 and that must be compensated with accordingly increased input level. As a consequence the driving OPA must deliver more output level at lower THD to improve performance in PFFB configuration.
And looking at the THD performance of TPA3255 w/o PFFB I consider these mods not worth the effort.
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Old 13th November 2018, 08:16 PM   #922
MirageZA is offline MirageZA  South Africa
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Join Date: Dec 2015
Location: Sandton
Quote:
Originally Posted by voltwide View Post
My answer is NO! - for several reasons
Certainly you could reduce hiss with additional feedback. But at the expense of gain, i.e. input sensity.
TPA3255 is a real low noise device, so if you are experiencing noise you should trace its source instead of reducing power stage gain. More often than not noise originates from the input source, so the first question was: Does it disappear with shorted input terminals?
PFFB as stated by TI application implicates significant gain reduction of TPA3255 and that must be compensated with accordingly increased input level. As a consequence the driving OPA must deliver more output level at lower THD to improve performance in PFFB configuration.
And looking at the THD performance of TPA3255 w/o PFFB I consider these mods not worth the effort.
Fair enough, I will check the noise after I remove NE to swop for OPA. If TPA3255 is dead silent, will look into power supply options for OP amps, have low noise LT1084 regulator, might give it a whirl.
Thanks!
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Old 13th November 2018, 09:11 PM   #923
seez is offline seez
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Join Date: Mar 2011
Hi All, this is my first post, I have been only lurking around here till now.

I have a question on connecting a REL Quake subwoofer to TPA325x (BTL - I think it matters).
REL recommends leaving the ground wire floating and only connecting other two to + speaker posts. The same scheme is advised for A/B class balanced amps.
Is this connection fine with TPA325x and will it have an effect on THD or stereo speakers SQ? The input impedance of the REL amp is around 10K ohms. Would it interact somehow with LC filter in the amp?

REL faq:
https://relsupport.zendesk.com/hc/en...ection-Methods

a discussion on similar issue (though not class d):
http://forums.stevehoffman.tv/thread...estion.485994/
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