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Topping PA5 Review (Amplifier)

daniboun

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Hi,

My opinion : this could be a bridged chip , with 4 quality inductors and some flat wires and it matters !
I would say it is a TPA3250 chip bridged or less obviously a MA12070 Merus bridged.

The amp gives 48W / 8R and 83W / 4R
The TPA3250 is a 70-W / 4R stereo module with 38V max supply... (the PA5 has a 38V / 4A power brick PSU)

We don't see the OP amps by the way... maybe under the D-01 enclosure ? differential op amps?? )))



You can see here that flat inductors perfom usually better than the other (at least with TPA3251 chip) :



inductor_cmp.png


Also interesting to read :

 
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Calleberg

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Nah. The IMD is already shown to be practically inaudible, and the HD in this region would only be 2nd and 3rd order. Both are not easy to discern and at their levels we can expect from this amp, won't be audible at all in the high treble region.

Do you have an example of where the "IMD is shown to be inaudible". Don't get me wrong, I'm normally in the same camp as you, you know, where the sensible people are :) so just curious.
 

daniboun

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Here a TPA3251 with differential OP amps, could help to compare... (OPA1632 + OPA1612)


 

xrk971

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Those look like CoilCraft or Wurth flat copper inductors - same as the ones I use on my TPS3255. Funny that they ground off the name and model number. It’s no secret.

I see a 4 gang pot. So that means the stuff under the epoxy potted D-01 block are just some opamps doing straight balanced gain. What would be interesting is to check to see if the PFFB trace goes to the input of the TPA3255 or the D-01 block. If it goes to the block, it might be a composite amp with a Class D slave stage. Interesting.

I am pretty sure it is a TPA32XX.

I see MOSFETs for remote power switch on/off from small front panel low voltage switch.
 

daniboun

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Those look like CoilCraft or Wurth flat copper inductors - same as the ones I use on my TPS3255. Funny that they ground off the name and model number. It’s no secret.

I see a 4 gang pot. So that means the stuff under the epoxy potted D-01 block are just some opamps doing straight balanced gain. What would be interesting is to check to see if the PFFB trace goes to the input of the TPA3255 or the D-01 block. If it goes to the block, it might be a composite amp with a Class D slave stage. Interesting.

I am pretty sure it is a TPA32XX.

I see MOSFETs for remote power switch on/off from small front panel low voltage switch.

This is what I assumed above about the D-01 block... Topping is hiding some "secrets OP amps". Most of diyers are using OPA1656 and OPA1612 with the TPA325X. Amir has demonstrated in several tests that the OP amps had little influence on the measurements, at least concerning FET-Input or Bipolar-input type OP amps.
I guess if Topping hides the OP amps, it's probably because they've found a new kind of OP amps that combine well with the audio chip we're trying to guess )))) This is why I was thinking of differential OP amps)
At the same time, I think the PFFB circuit is also hiding under the D-01 box....

I share your opinion, it's silly to have filed the specs of the inductors.... CoilCraft or Wurth I agree )
 

0bs3rv3r

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Seems to be a common thing. I have a very cheap phono amp where they filed off the opamp numbers.
 

HammerSandwich

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If it goes to the block, it might be a composite amp with a Class D slave stage. Interesting.
Considering Topping's more recent headphone amps? That's almost certainly correct. And a really smart way to build a top-value power amp.
 

genfreeciv

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Clean build, the ribbon cable from the TRS inputs is not going to satisfy proper audiofools though :) Layout looks like "TPA INSIDE" First Class LC filter components, with what I suspect is intelligent placement of Inductors. 5 Segment Pot by the looks of it? The 5th segment might be a switch. Is there a CLICK in either extreme of that pot?
There is no CLICK in eigher extrime of the pot.
 

338h10

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Yes this would work, but depending on how the input stage circuitry is wired, you may be using only half of the amp as it grounds one half of a bridged output amp in the worst case, or not fully using the common mode noise rejection feature afforded by balanced line inputs. If the circuitry performed a balanced to single ended conversion internally, and then back to balanced output to drive the amp internally, then this would still be utilizing both sides of the balanced amp’s output. Since it has a volume pot, I suspect this is true as a volume control would most naturally be done on a single ended signal vs requiring a quad gang pot (which is expensive and hard to keep balanced). The easy way to give this amp SE input is to use an RCA to TS adapter. It shorts the ring and the sleeve together.

For example:
Has this been tried? I.e., using a single-ended source with PA5?
 

typericey

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I’m currently using the PA5 ( source being a D90SE ) , powering my JBL L100 classics. The sound is crystal clear with plenty of power. I’m happy to report that there is absolutely no hiss or interference from my speakers. It is dead quiet with my ear next to the tweeter. An inky black background in audiophile garble i suppose.

The topping combination provides a very neutral, see-through sound that is very enjoyable. It does really help one “see” into the recording without detracting from the usual audiophile tropes of speed, transparency, detail and bass slam ( if it’s in the recording that is ).

I reckon topping could have fooled us all if they placed the amplifier in a larger, more intricate case with large shiny buttons and charged four times the cost and it would still sell. Pretty glad they didn’t do that. I look forward to the higher end power amplifier that is in the works.

What a time to be an audiophile!

Nice. I have a 4312SE and am also planning to get a PA5 to drive them. They have 90dB sensitivity, 6 ohms. If it all works out, I can sell my Rotel integrated which I am sure the PA5 will out-measure (except for power).
 

merelyok

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Nice. I have a 4312SE and am also planning to get a PA5 to drive them. They have 90dB sensitivity, 6 ohms. If it all works out, I can sell my Rotel integrated which I am sure the PA5 will out-measure (except for power).
Pretty sure it will have no trouble powering it properly!
 

xrk971

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We can also infer from the fact that 4 audio grade 10uF electrolytic caps are used between the pot and 4 more between the D-01 block and the amp that this is very close to a TPA32XX implementation. The fact that there is a DC blocking cap shows that the opamps are running single rail and at 24vpp (since the rail cap of the DCDC buck converter followed by linear voltage regulator are 25v rated).

Now I believe the potted block D-01 contains opamps arranged as a balanced line receiver / buffer, followed by more opamps for a gain stage (9dB), followed by a opamps arranged as a balanced line driver. Probably OPA1642 (could be almost any low distortion, low noise, high performance dual package opamp) . All running 24v single rail. The TPA32XX has modified PFFB for about 10dB intrinsic gain. Overall gain is 19dB. For amp to output 68Vpp requires that the opamps swing 21.5Vpp (assuming amp is 10dB gain). Hence 24v rail should be sufficient to hit clip. TPA32XX provides built in DC offset protection, thermal protection, shorting protection. The relays between the input jacks and the pot provides anti pop turn on delay protection.

Since a 4 gang pot (Alps RK09 series) is used (5th section is just base for main knob shaft, 4 pins on left side) linearity of volume tracking and CMRR for bal input will not be perfect at partial volume levels. Best performance will be achieved at max volume and use preamp to control volume.

Edit: heatsink removed and all is revealed. That is TPA32XX for sure. Even the 22k current limit setting resistor is there to allow max current to be achieved.


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Edit: after studying the underside of the PCB I see that the PFFB traces go to the end pins on the D-01. So it looks like the PFFB is implemented via AC coupling where the distortion is more important. At lower DC frequencies, the feedback is not important. I take back what I said about where PFFB loop is. It does look like the amp may actually be a composite amp design now. Please see feedback traces below.

A9A90511-E4C1-4C63-993C-89FBA4A6D920.jpeg
 
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