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Topping PA5 II Stereo Amplifier Review
- Thread starter amirm
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That doesn't really answer the question "why?". You could feed the balanced input just fine from an unbalanced source.
Roland68
Major Contributor
How exactly do you feed a truly balanced (and required) input from an unbalanced source?
I'd be really interested to know.
Roland68
Major Contributor
You can try it, but two TPA235x amplifiers on a single power supply could negatively influence each other.
Run two separate cables from the power supply to the amplifiers, each at least as long as the original cable. This should work. You can also use the cable from the defective power supply for this purpose.
Also note that the original power supply is only rated for one amplifier; it has no reserve power. With two amplifiers, you could easily permanently overload it, which could also lead to failure.
The TPA3521 and 3255 amplifier chips each has 4 amplification channels. The usually configuration is to run them in 2-channel BTL (bridge tied load) mode to double the output voltage swing with the same power supply voltage.
For that, one of the channels must receive an input that is in opposite polarity from the other. Since the output of both channels are referenced to the same ground, tying a normal polarity output channel with a reversed polarity output channel gives the BTL output. Therefore for single ended inputs, where the negative input is tied to ground and is of no use to drive the reversed polarity channel, an op-amp is used to generate the reversed polarity signal for the input to the channel.
[Edit]
In the TI eval module implementation, the signal flows are as follows (note that the TPA chips are inverting amplifiers, therefore the input signals are inverted by the op-amps):
SE input:
The +ve input is inverted by op-amp U5A and goes to IN-A (amp channel A input) of the TPA chip.
It also feeds U5B which inverts the U5A output and generates the reversed polarity input for IN-B (amp channel B input) of the TPA chip.
DIFF input:
The +ve input is inverted by op-amp U5A and goes to IN-A (amp channel A input) of the TPA chip.
The -ve input is inverted by op-amp U5B and goes to IN-B (amp channel B input) of the TPA chip.
Therefore, both op-amps are utilized by the SE and DIFF modes. Just that the SE -ve signal goes through both op-amps, whereas all the other ones go through just one op-amp.
For that, one of the channels must receive an input that is in opposite polarity from the other. Since the output of both channels are referenced to the same ground, tying a normal polarity output channel with a reversed polarity output channel gives the BTL output. Therefore for single ended inputs, where the negative input is tied to ground and is of no use to drive the reversed polarity channel, an op-amp is used to generate the reversed polarity signal for the input to the channel.
[Edit]
In the TI eval module implementation, the signal flows are as follows (note that the TPA chips are inverting amplifiers, therefore the input signals are inverted by the op-amps):
SE input:
The +ve input is inverted by op-amp U5A and goes to IN-A (amp channel A input) of the TPA chip.
It also feeds U5B which inverts the U5A output and generates the reversed polarity input for IN-B (amp channel B input) of the TPA chip.
DIFF input:
The +ve input is inverted by op-amp U5A and goes to IN-A (amp channel A input) of the TPA chip.
The -ve input is inverted by op-amp U5B and goes to IN-B (amp channel B input) of the TPA chip.
Therefore, both op-amps are utilized by the SE and DIFF modes. Just that the SE -ve signal goes through both op-amps, whereas all the other ones go through just one op-amp.
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In my particular use case (Vinyl and CD) I would ideally prefer to connect my primary source (Vinyl) to the Balanced input since it gives a notionally shorter (without N5532 op amp) signal path.
However since my cartridge outputs only 2mV and my phono preamp has gain of 41.5dB, and the Balanced input of the PA5 II provides 19.2dB gain versus 25dB for SE, any potential improvement yielded by the shorter signal path is overcome by the hiss from my phono preamp, when the PA5 II is turned up well past 2 o'clock to achieve an acceptable volume level.
Perhaps with a higher output cartridge and/or phono preamp with higher gain I might benefit from connecting my Vinyl source to the Balanced input.
Or perhaps the influence of the N5532 op amp on the sound of the amplifier is so negligible as to be not worthy of consideration.
However since my cartridge outputs only 2mV and my phono preamp has gain of 41.5dB, and the Balanced input of the PA5 II provides 19.2dB gain versus 25dB for SE, any potential improvement yielded by the shorter signal path is overcome by the hiss from my phono preamp, when the PA5 II is turned up well past 2 o'clock to achieve an acceptable volume level.
Perhaps with a higher output cartridge and/or phono preamp with higher gain I might benefit from connecting my Vinyl source to the Balanced input.
Or perhaps the influence of the N5532 op amp on the sound of the amplifier is so negligible as to be not worthy of consideration.
Sorry, cannot buy any power supplies in the HRP series over here in the uk.
You said that this is the best power supply for amplifiers, what do you think makes it so, and can any of these mods be applied to the stock pA5 II power supply
Roland68
Major Contributor
You don't need to post a reading tip for me. I wanted to know how you plan to do it without electronics, because that's not possible.
The link refers to symmetrical data transmission, in which the signal is then desymmetrized and further processed as SE. This only serves external signal transmission to eliminate interference.
That's exactly not the case with TPA325x-based amplifiers; these amplifier ICs require a truly symmetrical signal, consisting of an inverted and non-inverted signal, not just a potential difference.
@NTK was kind enough to post the excerpts from the datasheets for you.
In simple terms, the TPA325x is about symmetrical signal processing, and you're referring to symmetrical signal transmission, two areas that have nothing to do with each other.
I've been running my PA5 (first generation) since day one with RCA cables and a converter board with two DRV134s directly in front of the PA5. This is the correct application for driving a truly balanced device via a SE signal. And this is exactly what the OPAmps in the other TPA325x devices are needed for, as is also intended by the IC manufacturer TI.
What do you mean it is not possible? Just connect the hot lead of the unbalanced output to the + (non-inverting) input, and source ground to the - (inverting) input.
They have nothing to do with each other? Do you know what "balanced" means? Did you actually read and understand the Putzeys piece?
Sure, you can do that if you want to. It is not needed.
Please re-read the reply by @NTK
Roland68
Major Contributor
The Mean Well HRP series is a power supply designed for industrial applications that require high inrush power/currents or have short-term power peaks, such as CNC milling. The HRP series is now in its 3rd generation. HRP 150%, HRP N 250%, HRP N3 350%. The % number indicates the power that can be delivered for 5 seconds, based on the nominal power.
Related to 4 amps/150 watts, for example, this means for 5 seconds: HRP 6A/225W, HRP N 10A/375W, HRP N3 14A/525W.
This is ideal for audio applications, as these power supplies are particularly well-suited to meeting the high pulse/power requirements, especially in the low-frequency range.
Therefore, these power supplies should never be oversized in audio applications, as this would only reduce efficiency and increase power consumption. The big advantages are also their stability, reliability, and durability. I've been using several HRP power supplies for my amplifiers (including PA5/II) for over two years, which had previously been in 24/7 industrial use for several years.
You can order such power supplies from Mouser or Digi Key. In the UK, you just have to google it; you could, for example, ask at ecopacpower.co.uk.
eBay is also a good source, for example, for used power supplies.
You can of course also use other power supply series, such as Mean Well UHP, LRS, MSP, some of which are available on Amazon.
You can't modify the original Topping switching power supply; such power supplies are complex designs that can't be easily modified.
Audiophonics offers the original power supply at a very reasonable price, but I don't know if they ship it to the UK. Perhaps someone can bring it to you.
TOPPING Switching Power Adapter 38V 4A GX12
Roland68
Major Contributor
Maybe we're just talking past each other.
We're talking about TPA325x-based amplifiers that only have one balanced input, like the original PA5. That's not a pro audio device and doesn't have a balanced input suitable for pro audio.
You're referring to this circuit diagram, which is completely correct and clear. (I hope I'm allowed to post the excerpt?)
But that refers to the receiver duly subtracting the potentials of the two wires. That doesn't exist in the original PA5.
Gamerpaddy was kind enough to publish the circuit of the PA5 before the TPA325x; see also the circuit diagram of the PA5 input in the Topping PA5 fix - D01 Module Replacement for everyone thread.
How do I get the required inverted signal with a cable whose circuit diagram, in the case of the original PA5, looks like this?
Zwischen dem Kabel und dem TPA325x ist dann nur noch das 4 kanal Lautstärkepoti und die verlinkte Schaltung.
Maybe, yes.
For an input to be truly balanced, it needs to be differential. That is why I always talk about "balanced/differential", because while electrical engineers know what "differential" means (and why it is essential in this context), laypeople seem only to (vaguely) understand "balanced".
Yes. A differential input stage.
Then it isn't differential. How can it then be balanced?
A balanced input has two terminals, neither connected to earth. That means than they have to also be differential - one of them has to be inverting - otherwise you would not get any output signal.
I think there is some confusion regarding which type of input signals the TPA chips need when operating in the bridged (BTL) mode.
Disclaimer first: The schematic for the input circuit I showed in post #1105 was from the TI EVM (evaluation module). Topping may not necessarily implemented theirs the same way.
To drive the TPA chip in BTL mode, the input signal needs to be symmetric. A symmetric signal means that the +ve and -ve lines are equal in magnitude but opposite in polarities when referenced to ground. It is not the same as differential (which means the input circuit only cares about the difference between the +ve and -ve input lines and not care how much or whether they are offset from ground). Balanced refers to having the same impedance to ground for the +ve and -ve lines.
From: Wikipedia
The input circuit as shown in the TPA EVM schematic in post #1105 (with the jumpers set for DIFF inputs) will turn the differential input signal into a symmetric input. In the SE mode the circuit generates a symmetric input from the SE input.
Disclaimer first: The schematic for the input circuit I showed in post #1105 was from the TI EVM (evaluation module). Topping may not necessarily implemented theirs the same way.
To drive the TPA chip in BTL mode, the input signal needs to be symmetric. A symmetric signal means that the +ve and -ve lines are equal in magnitude but opposite in polarities when referenced to ground. It is not the same as differential (which means the input circuit only cares about the difference between the +ve and -ve input lines and not care how much or whether they are offset from ground). Balanced refers to having the same impedance to ground for the +ve and -ve lines.
From: Wikipedia
The input circuit as shown in the TPA EVM schematic in post #1105 (with the jumpers set for DIFF inputs) will turn the differential input signal into a symmetric input. In the SE mode the circuit generates a symmetric input from the SE input.
Thanks ! Did you notice any improvements in sound quality with the meanwell HRP versus the stock PA5 II power supply
I am looking at the Mean Well HRP-450-36 because i have three PA5 II amps being used in a 5.1 audio set up The HRP-450-36 looks to have three voltage outputs, could this one power supply be used to power all three amps without deteriorating sound quality. There is a screw on the left for voltage adjustment, could this raise the voltage to 38 volts
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Seavovk
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MEAN WELL UHP-500-36 also a very good option (active PFC function,slim and fanless design, 95% efficiency), it is possible to increase the output voltage to 38 volts with a built-in variable resistor, as a result you will receive 38V 13A . Or MEAN WELL UHP-350-36 with which you can get 38V 9A.
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Roland68
Major Contributor
But with the HRP N3 300 Watt, you get over 31 amps, or over 1000 watts, for up to 5 seconds.
This is a huge advantage in the audio sector, where high pulse power has its advantages.
The 36-volt HRPs can all be set to 38 volts.
Do you feel sound quality may improve using HRP versus the stock power supply
And is it possible to power three PA5 II amps from the HRP as it has three outputs, or is this a bad idea
And is it possible to power three PA5 II amps from the HRP as it has three outputs, or is this a bad idea
TI recommends that the oscillator clocks be synchronized when a single power supply is used to power multiple amplifiers.
IOW, not recommended.
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