Topping LA90 Discrete Amplifier Review

[Rottmannash]

I see what looks like 4 smaller transistors on each side and 2 much larger ones. Are the larger ones for the output channels?

 

[theREALdotnet]

Two black rectangular boxes seem to be advertised Topping secret.

Topping “gain cell”?

 

[osscar]

I don't like that the capacitors are so close to the emitter resistors (they can get hot)...and practically pressed against the plastic housings of the relays. Also, the ribbon cable is "sandwiched" between the resistor and the filter capacitor...

 

[sarumbear]

I think you are missing the point. standards exist for a reason.
every other hi-fi amp uses XLR and/or RCA.
but Topping uses much less common things like 1/4 jacks, see other amps they produce.

at least in this case it's compatible with XLR, better than nothing.

1/4" jack is also a standard.

 

[restorer-john]

And Topping decides to use PCB material as an output transistor clamp to the heatsink- again.

If you needed even the tiniest indication that they have no idea how to attach an output transistor to a heatsink in a power amplifier....look no further. Absolute clowns.

 

[theREALdotnet]

And Topping decides to use PCB material as an output transistor clamp to the heatsink- again.

I believe these are ceramic thermal pads, or something like that.

If it were me, I’d use Gelid thermal compound.

 

[Sokel]

And Topping decides to use PCB material as an output transistor clamp to the heatsink- again.

If you needed even the tiniest indication that they have no idea how to attach an output transistor to a heatsink in a power amplifier....look no further. Absolute clowns.

View attachment 279186

My guess is that they put it there to avoid direct heat to the caps and resistors that are close,not to secure the clamping.
Even as it seems they are overtightened..

 

[Sokel]

I believe these are ceramic thermal pads, or something like that.

If it were me, I’d use Gelid thermal compound.

They are printed like PCBs,they don't look ceramic,specially bending like that.

 

[thulle]

I believe these are ceramic thermal pads, or something like that.

Fastening ceramic materials by bolting down the sides? What are you basing that on?

 

[theREALdotnet]

They are printed like PCBs,they don't look ceramic,specially bending like that.

Oh, that part! I thought John meant the material between the transistors and the heatsink. Well, that beats me. Looks like thermal shielding of sorts. The curse of the miniature form factor, I guess.

 

[theREALdotnet]

If it looks too small to be true, it probably is. And I thought Purifi amps where impossibly small, but they’re mostly air inside.

 

[Sokel]

Oh, that part! I thought John meant the material between the transistors and the heatsink. Well, that beats me. Looks like thermal shielding of sorts. The curse of the miniature form factor, I guess.

John probably suggests the long debated in diyAudio:
That case expands differently than the (main) pcb board with heat so in the long term...

 

[Deleted member 48726]

So we have, in real terms, a three input power amplifier with a 'massive' 41wpc@8R amplifier stage that hits the wall so hard it shuts down. Wow. Impressive. Not.

40wpc per channel was pretty much the minimum, the absolute bare minimum entry into high fidelity in the early 1970s! 40wpc amplifiers were less than $150(US) and they were a genuine, under-rated 40wpc. And that was with speakers boasting 90-95dBSPL@1W/M sensitivity. Most two ways these days are 80-87dB.

This is kid's basement stuff.

Yeah, all these tiny amps. getting reviewed here makes people move their perspective. The numbers are good, yes. But please.. Has HiFi really moved from the floor to the desk next to the 1440p monitor with a sub to rest your feet on?

No grudge against Amir though. -Taking into consideration of freight and weight. But hasn't ASR eventually grown so that full size 43 cm. amps can be tested regularly?
I wouldn't mind sponsor deals as long as they are transparent.

 

[restorer-john]

They appear to be using scraps of PCB material to clamp the output devices to the heatsinks, and the heatsinks are incorrectly profiled with the 'fins' in the horizontal plane.

 

[Deleted member 48726]

The "impedance" (really, thermal resistance) of a heat sink should not be confused with its "thermal capacity" (thanks to it being a large block of metal that takes energy to heat up). What really matters is not instantaneous absorption of heat, but rather steady-state heat dissipation, which is a function of many factors, incl. shape, spacing and surface treatment of fins, not just the overall surface area. If this amp produces roughly 100 W of heat, those two small heat sinks with horizontal fins, even when (poorly) edge-coupled to an aluminum case, will hardly be sufficient to dissipate it to maintain a reasonable junction temp of the output transistors (let alone not cook the rest of the circuitry inside). And, this will be even more of a problem in the silver model.

Yeah, and sealed air is an exceptional insulation method.

 

[Doodski]

I see what looks like 4 smaller transistors on each side and 2 much larger ones. Are the larger ones for the output channels?

Yes, the larger transistors are the output transistors.

 

[wwenze]

Test data on horizontal vs vertical fins:

http://thermalsoftware.com/vert_vs_horz_sink.pdf

However I can still understand going horizontal because of looks... and because have you ever cut yourself with the top corner of a heatsink pointing up?

Add: Looking a bit further I notice most of the heatsink is enclosed inside the chassis anyway... that does throw a wrench in the calculation and expectation. I would still say vertical fins would allow the convection to create a bigger thermal / pressure gradient and push the hot air away

 

[Triliza]

Yeah, all these tiny amps. getting reviewed here makes people move their perspective. The numbers are good, yes. But please.. Has HiFi really moved from the floor to the desk next to the 1440p monitor with a sub to rest your feet on?

No grudge against Amir though. -Taking into consideration of freight and weight. But hasn't ASR eventually grown so that full size 43 cm. amps can be tested regularly?
I wouldn't mind sponsor deals as long as they are transparent.

I never had a desktop setup, just headphones, but what do you have against desktop, isn't it better that people can get quality sound when working or doing stuff in their pc/workspace?

Full size amps are tested regularly, today we had another review. And better not to go the way you are implying in the last sentence (if I understand correctly what you are saying), the companies send stuff to be tested and they are tested, just because you don't find these products interesting doesn't mean other people feel the same.

 

[Doodski]

There appears to be white thermal compound used with silicon heat pads.

 

[restorer-john]

There appears to be white thermal compound used with silicon heat pads.

Why not simply use a large washer/plate under the device mounting screw instead of a scrap of pcb material?