We knew that from the performance and from the PFFB traces visible on the bottom of the PCB.
From Post 1078.
From Post 1078.
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Topping PA5 Review (Amplifier)
- Thread starter amirm
- Start date
What kind of music files do you use to keep phase shifts unchanged up to 300kHz? What kind of speakers, microphone? Are you saying that the amp must keep the phase up to 300kHz, however the signal source may be 10 - 100 x degraded in this regard?
Digital audio files do not need to be at 600kHz data rate to have 300kHz phase accuracy. Although there is 768khz rate dats files. Also much faster for DSD and other formats. Typical clocks that control ADC’s and DAC’s run at 12MHz and have typically 50ppm stability and jitter measured in the picoseconds range. More than enough to preserve phase accuracy to 3usec (300kHz).
DS23MAN
Active Member
Please read the tech note on PFFB carefully, Ti states the THD improvement is max 5 db with pffb. So it is not only PFFB!We knew that from the performance and from the PFFB traces visible on the bottom of the PCB.
From Post 1078.
And you seem to believe that the captured music has the same "phase accuracy" in microphone paths. Do you have an idea how their response looks like? And have you ever analyzed the "768kHz data files" for their spectral content? So where does it end?
Just received and test it. I connected with SU-9 via XLR(female) to TRS cable and speaker JBL Stage A130, amplifier power more than enough for listen loud 80dBA(measured with UNIT-T UT353 sound level meter) at middle range (3m).
I'm not report subjective review as some may not want to hear it. But I promised to buy the next class AB amp that @JohnYang1997 will release soon. I respected your R&D result.
Anyway, the build of speaker binding post connector very loosen. I need to open cover to fix it from inside. Thank @genfreeciv for internal picture ,it made easier to find how to open it. It need to be more qc for this price level.
I'm not report subjective review as some may not want to hear it. But I promised to buy the next class AB amp that @JohnYang1997 will release soon. I respected your R&D result.
Anyway, the build of speaker binding post connector very loosen. I need to open cover to fix it from inside. Thank @genfreeciv for internal picture ,it made easier to find how to open it. It need to be more qc for this price level.
KSTR
Major Contributor
Post Filter Feedback is a design technique, not a specific circuit. The passive TI example is just one simple variation with a lot of specific conditions, like not loosing too much circuit gain and simplicity of the compensation (2-pole).
The tough thing with heavy PFFB is the compensation scheme, you need a higher order feedback loop (3rd order minimum) to have still some gain for correction at 5kHz++ without running into stability issues. Running the main LC resonance at the highest possible frequency helps (~50kHz in this case).
KSTR
Major Contributor
Only depends on the maximum level you can get before you run into current clamping or thermal issues. This is true for all amplifiers.
A dip to 2.9Ohm in a small frequency range is not going to be problem.
KSTR
Major Contributor
@xrk971,
so you design your power amplifiers with unrestricted bandwidths of 1Mhz and higher, basically capable for AM transmitter duty?
And you want to tell us that a reasonable bandwith restriction to, say ~40kHz (on both channels) is audible wrt soundstage and localization?
Also, you can hear the difference in DAC's imaging filter with the same magnitude response but one being minimum phase and the other linear phase?
And, what's the bandwidths of your tweeters (and the matching, not to forget)?
Where is the serious evidence of audibility of all this?
so you design your power amplifiers with unrestricted bandwidths of 1Mhz and higher, basically capable for AM transmitter duty?
And you want to tell us that a reasonable bandwith restriction to, say ~40kHz (on both channels) is audible wrt soundstage and localization?
Also, you can hear the difference in DAC's imaging filter with the same magnitude response but one being minimum phase and the other linear phase?
And, what's the bandwidths of your tweeters (and the matching, not to forget)?
Where is the serious evidence of audibility of all this?
BoredErica
Addicted to Fun and Learning
Would you mind explaining why maxing the volume on the dac and turning down the amp makes a difference, and why this is more important for unbalanced interconnects? I always found this confusing. Do I turn the volume down on the dac, the amp, the preamp (if there even is one in the system), or digitally.
KSTR
Major Contributor
Fair enough.Because...
Topping PA5 Review (Amplifier)
Topping PA5 manual available here: https://www.tpdz.net/newsinfo/575024.html
"Only have rca output on DAC. Is it possible to DIY a rca to TRS balanced cable? Will this work?
It should but you won't get maximum power unless the DAC can produce 2.5 volts (some can, most cannot)."
KSTR
Major Contributor
With unbalanced connections any mains leakage current that flows through the RCA cable shield causes a voltage drop which is part of the signal as seen by the receiving end.
Thus, the higher the signal level on the line the larger the ratio of signal to noise (hum/buzz).
With balanced, the problem is less severe but still there.
General rule for signal transmission with cables is: always use the highest possible signal levels. Of course not so high as to overload/clip the input of the amp before it has a chance to attenuate it.
BoredErica
Addicted to Fun and Learning
Seems like the volume knob is an extra bonus for me then. I think I can go without a preamp and just use the volume knob on the amp!
TI note only has a passive PFFB implementation. That's why I've said before that this level of performance can be only done with an active PFFB.
Looks like they've figured out how to implement active PFFB properly.
Take a look at this TI Support thread
I already read this thread before and I thought back then that this is cdsgames which is the designer of Allo
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KSTR
Major Contributor
Pretty sure the PA5 is a composite with some opamp being the master and the class-D chip being the power slave. Which makes a bit easier to squeeze out the last bit of loop gain even at higher frequencies, ~5kHz.
TNT
Active Member
- Joined
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Yet, there is virtually no spectral content above 15k from an orchestra at a normal listening position.
From the TI thread... "We are developing a hiend amp based on tpa3255 (under 400$ including linear PSU 250W" ..
This PSU is only 38x4= 152VA (~watt)...
Allo?
//
restorer-john
Grand Contributor
What about the 15kHz (45kHz BW) THD dip? An aberration in the AP?
That suggests an LF and HF separate FB network, perhaps trimmed for minimum THD at specific frequencies. There were a bunch of designs that utilized similar topologies in the 1980s, including some non-NFB, direct distortion cancelling offerings.
I guess it is related to the bandwidth limiting in the AP-filter.
Here is another measuremet of the PA5, but with a 20 khz bandwidth - so a bumb at the 6+ khz.
KSTR
Major Contributor
AP abberation? No ;-)
The decrease around 1W is the result of many factors but I don't think there is special trimming involved. Composite or passive PF feedback is always split in AF and HF sections, otherwise no compensation possible.
By the way, I could be wrong and the PFFB is passive (PPFFB) but perhaps higher order than 2nd. As long as the input (into the PPFFB) can be driven high enough (say 10Vrms with frontend OpAmps running from +-15V) the feedback factor can be increased significantly but limited of course by the 21dB "open loop" gain of the chip.
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