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Class D Switching Power Amplifiers and Power D/A conversion

TPA3250 somebody is listening?
TPA3250 somebody is listening?
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Old 1st April 2018, 10:35 AM   #271
strongbow60 is offline strongbow60  Sweden
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Join Date: Jul 2017
Same revision and date on mine, with a blue board for volume.
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Old 1st April 2018, 10:56 AM   #272
strongbow60 is offline strongbow60  Sweden
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Warning, the following is just my very subjective experience, no measurements (except volume).

Yesterday I compared my FX502PRO amp against my self built amp with TPA3255EVM.
The TPA3255 amp uses a linear power supply with quality toroid and filter capacitors, DC filter on the mains side, noise filter on the line input and so on. The FX502S is standard and uses the 24V/4A power supply that comes with the amp. Not entirely fair.

I used the same equipment in the whole test, just switching cables between listing sessions. The FX502S have a higher gain so I had to adjust the volume control between sessions.
My speaker are a pair of XTZ99.26, floor standing speakers with89dB/W efficiency and an impedance between 4 and 8 ohms. Listening volume was about 70-80 dB at one meter from the speaker, it should not have been very taxing for the smaller amp.

The sound
They are sound-wise clearly both from the same family. But the sound from the FX502S is a bit muddy, it lacks precision in the bass, even if there was a fair amount of rumbling bass to it, just not the same amount of low level bass I am
used to from the EVM board. Resolution in the whole spectrum is lacking, the
sound comes mostly from a point in between the speakers, not so much a sound stage.
I would say that it is an OK amplifier and definitely worth the money, but that's about it.

Then I swapped the op-amps from the NE5532 to the much better LME49720NA and things started to lighten up! Now there are much better resolution in the whole spectrum and there is the impression of a wider sound stage. The bass is not so dominant, it is the midrange (voices) and the treble that benefits most from the new op-amps. It might be even better from another several hours burn in. Time will tell. Later I will also check for any high frequency oscillation on the output of the LME op-amp's.

Still it is no match for the TPA3255EVM which shows that there is much more to an amplifier than the op-amp's and the TPA IC. Sound wise the EVM amplifier is much more balanced, more dynamic and have better resolution over the whole audible spectrum with a much deeper and better defined bass, better sound-stage and a calm and authority that speaks of class. I still is not nearly as good as the best class AB amplifier I have had, but that was a magnitude more expensive amplifier.
Now, if I could only swap the op-amp's to a LME49720....
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Old 1st April 2018, 02:22 PM   #273
impuls60 is offline impuls60  Norway
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Thanks for the comparison Strongbow. I have the same speakers and I feel that the sensitivity is closer to 86-87db. These speakers sounds muddy on moderate to high levels with the tpa3116 and a 70W rms tube amp. Mye 3e audio 3255 is the only amp I've used that truly brings out the true performance out of these speakers! I can play much louder than before and no midrange distortion at high volume. The traces and chokes on the tpa3255 is much more beefier and the psu caps are much larger also.
I just recently recommended the FX502PRO to a friend of mine which was really impressed with a modded tpa3116 on his speakers. I think input impedance matching could explain the bass difference. Using a turntable with its own preamplifer gave a huge difference in dynamics between a NAD stereo amp and the tpa3116. The tpa3116 gave great dynamics and bass, even on low volumes. When we used a Cambridge audio dac as source the difference was almost gone!
I'm looking forward to hearing the FX502PRO soon and do more comparisons . On the pcb pictures it looks that the FX502PRO has bipolar electrolytics on the input side, could you confirm this?

Last edited by impuls60; 1st April 2018 at 02:30 PM.
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Old 1st April 2018, 05:11 PM   #274
strongbow60 is offline strongbow60  Sweden
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Quote:
Originally Posted by impuls60 View Post
On the pcb pictures it looks that the FX502PRO has bipolar electrolytics on the input side, could you confirm this?
No idea, but it's likely, just like TPA3255. The two caps close to the op-amp's are 100 uF which i think is on the large side for input caps. It all depends how close they follow TI:s example circuit.
The volume control is 100k (92k measured) but the input impedance is probably around 10k.
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Old 2nd April 2018, 11:26 AM   #275
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Hi Friends from North

thanks for your impression!...i will get my amps hopefully in 2 weeks.
go ahead with compare with some other amps and sources.

thanks

chris
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Old 2nd April 2018, 02:52 PM   #276
forestsgump is offline forestsgump
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Join Date: Dec 2017
I am writing in here if you have FX502Spro:

could NE5532 on FX502Spro a fake ? - Page 5,6

~ Calling for your awareness &
~ Rally your support to check on yourside if true
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Old 2nd April 2018, 05:17 PM   #277
strongbow60 is offline strongbow60  Sweden
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Maybe, or not. Just buy some genuine ones and have a try.
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Old 2nd April 2018, 05:23 PM   #278
DJDestiny is offline DJDestiny  Singapore
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Join Date: Feb 2011
Quote:
Originally Posted by KaffiMann View Post
In short: The TPA3250 is better than the TPA3116.

Is it much better? That depends on your application.
It is slightly more powerful, you can get probably 2x25w nearly clean power (guesstimate somewhere between 0.01-0.001% distortion) in 8 ohm with the included PSU.
Whereas the TPA3116 also gives 2x25w in 8 ohms but at 21V max, and 10% distortion.

It seems to be a slightly better designed PCB, there may be some power conditioning going on (not tested), there is a pre-amp stage containing the well known NE5532, seemingly well optimized for modern use at 0.775mv specified input voltage.
Many TPA3116 seem to be set to very aggressive gain settings making it more noisy than it has to be, and there is often no pre-stage on the stuff sold cheap on ebay.
TPA3116 at 24V is not 10% distortion. Nowhere close. At about 25W, it is less than 0.1% for the lower frequencies and about 0.05% for 20K.

That is right before the onset of distortion however.

Quote:
Originally Posted by FauxFrench View Post
TPA3250 is from the top-of-the-range series. As I would expect from what I see in the advertisement, cooling may be a problem. A rather small heatsink enclosed in a small cabinet without vents - technically not optimal. There is this general perception that class D amplifiers do not have cooling issues. This is not true, they are just less than for class AB amplifiers.

As someone wrote about the TPA3116D2: it may make noise ("hiss"). I have such a TPA3116D2 amplifier board and initially a 50K potentiometer was used. I shunted the TPA3116D2 inputs (at the output from the potentiometer) with 4K7 resistors and the "hiss" disappeared.
Perhaps back then it was but the top of the range is the TPA3255 now.

Last edited by DJDestiny; 2nd April 2018 at 05:35 PM.
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Old 2nd April 2018, 05:52 PM   #279
irribeo is offline irribeo  Netherlands
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tpa3255 is worst in tpa32xx serie, but it is the most powerfull
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Old 2nd April 2018, 06:53 PM   #280
DJDestiny is offline DJDestiny  Singapore
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Quote:
Originally Posted by irribeo View Post
tpa3255 is worst in tpa32xx serie, but it is the most powerfull
It's still the top of the range.

At 10W @ 8 ohms they're basically indistinguishable
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