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Class D Switching Power Amplifiers and Power D/A conversion

Full digital amplifier with chip STA326
Full digital amplifier with chip STA326
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Old 7th February 2018, 05:27 PM   #351
JMF11 is offline JMF11  France
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Quote:
Originally Posted by Nanoloop View Post
It could be that the output filter on the amp is designed for 4 ohm and your speakers are 8 ? This would give an sparkly/grainy/brittle edge to the sound but it wouldn't have an effect on the bass. That should be superb. If not, move the speakers or change rooms. ;-)
Thanks for your answer Nanoloop, and sorry for the late feedback.

So I understand from your message that from your perspective, it should not be a "generic flaw" from the STA326 (not delevering flesh / warmth).

I wanted to check if some have experienced similar feeling.

Best regards,

JMF
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Old 7th February 2018, 11:01 PM   #352
Nanoloop is offline Nanoloop  Hong Kong
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Originally Posted by JMF11 View Post
Thanks for your answer Nanoloop, and sorry for the late feedback.

So I understand from your message that from your perspective, it should not be a "generic flaw" from the STA326 (not delevering flesh / warmth).

I wanted to check if some have experienced similar feeling.

Best regards,

JMF
I've only tried one version of the STA326 and that with two different speakers so far - Klipsch and Kef - and what I hear is the colouration of the speakers/room more than anything else. Perhaps others who have tried more versions of this amp will comment.
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Old 8th February 2018, 01:18 AM   #353
forestsgump is offline forestsgump
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Audeo point out another thread : Original Apogee datasheet design shows have 2 different inductor config cater to 4 & 8 Ohms, however D8 uses a castrated version of the filter intended for 8 Ohm speakers (D8 uses simliar inductor values from STA326/STA328 datasheet which only shows 8 ohm inductor config).

IF YJ uses similar inductor config as D8/STA326/328, then on contrary: 8 ohms speakers on YJ should be correct, as it is having 8 ohms inductor config.
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Old 8th February 2018, 03:03 AM   #354
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Nanoloop View Post
Perhaps others who have tried more versions of this amp will comment.
In my experiments with these amps the bass in particular is very sensitive to the power supply. The stock SMPSU sucks pretty bad for bass, it really needs a discretely regulated supply - I use an EF fed from a TL431 shunt reg.
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Old 8th February 2018, 03:07 AM   #355
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Originally Posted by audeo View Post
...The end result is good enough for me: now I have to stick my ear into the speaker to hear the hiss whereas before I could hear it from a meter apart.
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Originally Posted by audeo View Post
By the way, Apogee's datasheet on this chip says: "Note, digital and power ground planes must be combined under the IC". And, as far as I remember, in Alientek D8 they made a single huge ground plane all around the chip. So, perhaps, isolating output power MOSFET's ground pins from digital signal ground with some choke would further help reducing hiss. But that would take a lot of effort and I did not even think of trying to do that.
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Originally Posted by audeo View Post
This hiss does not depend on gain unless it is set to absolute zero. Try to feed something very quiet (but non-zero) to your amp and set gain to +1 and you'll get that noise floor we are talking about. Or, if you have D8, you can select AUX as its input while nothing is connected to it and get virtually the same result (ADC adds very little noise of itself). When digital stream to STA326 contains zeroes it usually (unless configured otherwise) switches its outputs off by shorting all speakers to the ground and thus you won't hear anything at all.
The listening test verdict is out (non-qualitative):
Comparing (non A/B blind - placebo?) & referencing earlier comments:

1. D8 music instrument definition seems better to FX502Spro
(Optical digital source 16bit 44.1Khz -> Xmos U8 I2S-> STA326/8 D path amplification VS analog source-> ADC path -> TPA3250 D path amplification)

2. D8 much noiser than FX520Spro
D8 without mod noise-floor found at aux, but hiss could be hear for gain +1, ard 1 meter on my 6 ohms 86dB. Affirmed gain +0 speaker cut-off
However it is quiet on toslink digital-inputs; guess D8's ADC path was affect by smps V-reg noise? eg. hiss not started from STA326/8 amplifier.
FX502Spro impressive quiet featherlight hiss, maybe partly due to using LDO V-reg AMS1117 for 3.3V, LM317 for 24 V-reg.

Will guess have do the smps inductor noise removal mod.
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Old 8th February 2018, 03:12 AM   #356
Nanoloop is offline Nanoloop  Hong Kong
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Quote:
Originally Posted by forestsgump View Post
Audeo point out another thread : Original Apogee datasheet design shows have 2 different inductor config cater to 4 & 8 Ohms, however D8 uses a castrated version of the filter intended for 8 Ohm speakers (D8 uses simliar inductor values from STA326/STA328 datasheet which only shows 8 ohm inductor config).

IF YJ uses similar inductor config as D8/STA326/328, then on contrary: 8 ohms speakers on YJ should be correct, as it is having 8 ohms inductor config.
Easiest and most accurate way to calculate and graph the effect of different output filter designs/values with different impedance speakers is to use TI's spreadsheet calculator. Free download. Free use. It rocks.

LCFILTER-CALC-TOOL Class-D LC Filter Designer | TI.com
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Old 8th February 2018, 03:30 AM   #357
Nanoloop is offline Nanoloop  Hong Kong
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Originally Posted by abraxalito View Post
In my experiments with these amps the bass in particular is very sensitive to the power supply. The stock SMPSU sucks pretty bad for bass, it really needs a discretely regulated supply - I use an EF fed from a TL431 shunt reg.
What's an EF ?

I mostly use an LT1083 with the YJ 2.0 - sounds surprisingly good - ultrafast diodes with snubbers, 13,200uF pre regulator cap bank, zener at the base. I'm going to start using an AMB Sigma11 I made last night. I hooked it up and noise from the amp is the same as LT1083 despite S11 being a lower noise psu. I expect dynamics to be better - we'll see.
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Old 8th February 2018, 03:33 AM   #358
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Quote:
Originally Posted by Nanoloop View Post
What's an EF ?
EE shorthand for 'emitter follower'. Sounds remarkably similar to your 'pre reg....zener at the base' except I use the TL431 as a programmable zener.
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Old 8th February 2018, 03:54 AM   #359
Nanoloop is offline Nanoloop  Hong Kong
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Thanks! I think I might try that with the LT next time. I've tried using an LM317 as a constant current source into a TL431 for a low power head amp - sounds very clean and tonally neutral - it's a good psu.
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Old 8th February 2018, 04:07 AM   #360
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I've also tried the LM317 as CCS into a TL431 on a number of designs. Found its sometimes difficult to keep the LM from oscillating, depending on the voltage drop across it. I normally put resistors in series to limit the drop to 4V or so across the LM317. Doing this mod to the input stage PSU of my Xindak integrated amp made a very noticeable improvement to PRaT, previously the input opamp had been fed just from LM317/337s.
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