Topping LA90 Discrete Amplifier Review

[capslock]

That is an interesting offer, but I live in Russia, so I doubt I will be able to sell you anything easily. T

Too bad, at least for the time being it would be too difficult.

I am very familiar with coil whine. My favorite notebooks are the Dell Latitude 7275 and 7285 of which I own several. They are passively cooled, so coil whine which is modulated into a staccato stands out, and they all do it to varying degree. And the display of the head unit of my car does it, in that case it is the high voltage supply for the CCFL. It is a constant whine with components at 11 kHz, 13 kHz etc. Whoever designed the voltage converter must have been deaf. I took the unit apart, changed a ceramic cap to foil and drenched the coil in very thin epoxy. That made it better but not completely silent.

 

[babadono]

I have 4 LA90s and 2 B200s and none have an objectionable whine or buzz being emitted by their power bricks. Perhaps I am just fortunate. However I do have in the same equipment rack a digital crossover that emitted a quite objectionable buzz. It is definitely the SMPS. I had to unmount it from the metal bosses it was mounted on and re mount with foam rubber blocks and double sided tape. The SMPS was making the whole chassis vibrate. The chassis no longer vibrates but the faint buzz of the SMPS remains......
Still lovin' the Toppings.....

 

[RandomEar]

Just to put this into perspective: There are multiple Hypex amps which also suffer from SMPS whine noises [1, 2, 3]. So even supposedly "high quality" units can be affected.

 

[Le_Passager]

It is a constant whine with components at 11 kHz, 13 kHz etc. Whoever designed the voltage converter must have been deaf.

Absolutely agree. Thank you everyone for your feedback and sharing your observations!

I have 4 LA90s and 2 B200s and none have an objectionable whine or buzz being emitted by their power bricks. Perhaps I am just fortunate.

I suspect there might be a certain dependence on the local electrical grid conditions. The probability that one user could get 'lucky' with six power supply units while another (like me) gets unlucky with four units is incredibly slim. It is also highly unlikely that the manufacturer would intentionally send me replacements from some "B-stock" after I specifically reached out to them regarding noise issues.

So even supposedly "high quality" units can be affected.

So, it seems to be highly situational. Apparently, at this stage of technology, there is no universal switching power supply (SMPS) design that can guarantee completely silent physical operation for absolutely everyone under all conditions.

 

[RandomEar]

So, it seems to be highly situational. Apparently, at this stage of technology, there is no universal switching power supply (SMPS) design that can guarantee completely silent physical operation for absolutely everyone under all conditions.

Yes, mostly. I think it's less a question of technology and more a question of design effort, quality control (including tolerances of supplied parts) and manufacturing process control. I'm sure it can be avoided, but it may increase the manufacturing costs.

 

[dcolak]

My two Topping LA90 Discrete have a strange problem.

When the volume is in bypass mode ON and bridge mode is ON, with XLR cables in but no music playing, if I slowly move the pot from minimum to maximum I get a LOT of white noise and whining sound. At some positions of volume pot noise gets lower, at some it gets louder. All that with volume pot bypassed!

If I disable volume pot bypass (bypass OFF), there is no noise, no matter in which position is the volume pot.

Anyone else noticed the same problem?

 

[Le_Passager]

My two Topping LA90 Discrete have a strange problem.

When the volume is in bypass mode ON and bridge mode is ON, with XLR cables in but no music playing, if I slowly move the pot from minimum to maximum I get a LOT of white noise and whining sound. At some positions of volume pot noise gets lower, at some it gets louder. All that with volume pot bypassed!

If I disable volume pot bypass (bypass OFF), there is no noise, no matter in which position is the volume pot.

Anyone else noticed the same problem?

Well, another interesting symptom. I can say for myself that I've never observed anything like this. My two LA90 Disctere were always used with the volume control bypass enabled. The amplifiers never responded to turning the volume control (when it was disabled). Although, to be honest, sometimes I did turn this volume controls, cause they move very nicely and pretty.

Could you please tell me how long you've noticed this problem, and how long have you been using this pair? Have there been any recent changes in your system or power suply grid? Perhaps, based on this, more professional users will be able to suggest something more precise.

 

[dcolak]

Well, another interesting symptom. I can say for myself that I've never observed anything like this. My two LA90 Disctere were always used with the volume control bypass enabled. The amplifiers never responded to turning the volume control (when it was disabled). Although, to be honest, sometimes I did turn this volume controls, cause they move very nicely and pretty.

Could you please tell me how long you've noticed this problem, and how long have you been using this pair? Have there been any recent changes in your system or power suply grid? Perhaps, based on this, more professional users will be able to suggest something more precise.

No changes in the system. I never touched volume pots before, while bypass was on. Usually, my volume pots were on minimum, while bypass was on.

This time, I was switching between bypass on and off and pots were not on minimum and there it was, white noise on speakers, with no input signal.

While the noise is there, if I switch to another INPUT, noise disappears (no cables connected to other inputs).

Very strange. I thought maybe cables are creating the problem (RCA to XLR) but... why would volume pot position in bypass ON mode create noise?

The noise is there even if the RCA->XLR cables are not connected to the DAC, just plugged into amps.

I think this must be a case of cables acting as RF antennas? I noticed, if I put my hand on LA90 case, noise disappears. Still, very puzzling why would vol pot position have any influence in vol pot bypass on mode

 

[babadono]

Hmmmm..yes very strange. Can you clean the bypass switch? Deoxit or similar. And I suppose the Volume pot as well. So noise is present when volume pot is bypassed, the full gain of the LA90 is being used when in that mode. What about when not bypassed but turned up all the way? This would be the same as bypassed or very close. Curious what RCA to XLR cables are being used? How are they wired?

 

[dcolak]

If it is NOT bypassed, noise is NOT present at any vol pot position.

Only when it is bypassed I get noise at different vol pot positions.

The RCA end of cable is not connected to anything, but even when it is connected to dac, the noise is there, although lower. Very strange. Turn off bypass and all the noise is 100% gone and the amp is dead silent.

 

[babadono]

ok....Hmmm....since Topping is so secretive about their circuitry we are all just guessing. Educated guesses maybe but guesses nonetheless. I run all mine balanced. I could as an experiment dis connect the balanced cabling and plug in RCA to XLR cables temporarily to see if mine behave the same. The RCA/XLR cables I have are wired correctly for unbalanced output to balanced input. Again we do not know what Topping does circuit wise right at the input. Again what cables are you using? How are they wired?

 

[dcolak]

ok....Hmmm....since Topping is so secretive about their circuitry we are all just guessing. Educated guesses maybe but guesses nonetheless. I run all mine balanced. I could as an experiment dis connect the balanced cabling and plug in RCA to XLR cables temporarily to see if mine behave the same. The RCA/XLR cables I have are wired correctly for unbalanced output to balanced input. Again we do not know what Topping does circuit wise right at the input. Again what cables are you using? How are they wired?

Not sure about the cables bought them on amazon.com

https://www.amazon.com/WJSTN-Shielded-Twisted-Oxygen-Free-Conductors/dp/B0C1L2MQG3?pd_rd_w=QernU&content-id=amzn1.sym.a17d2b69-5d25-4d1d-9e89-ce7360646089&pf_rd_p=a17d2b69-5d25-4d1d-9e89-ce7360646089&pf_rd_r=KZ3HCEGGSA790JCDR9XH&pd_rd_wg=OWlyY&pd_rd_r=b2787142-8f4d-4a1a-983f-2baa6cb99be5&pd_rd_i=B0C1L2MQG3&ref_=pd_bap_d_grid_rp_0_1_ec_t&th=1

 

[babadono]

Ok. Manufacturers video on Amazon shows 2 different wiring schemes. This is confusing. Take XLR end shell off and see if in fact pins 1 and 3 are tied together there. They should not be. They should only be tied together at the RCA outer shell connection.

 

[babadono]

@dcolak you are using the LA90s in bridge mode? And you have the little shorting cable that ties the 2 negative outs together installed? Which gain setting are you using?
When I get a round tuit i want to dup your settings exactly.

 

[dcolak]

@dcolak you are using the LA90s in bridge mode? And you have the little shorting cable that ties the 2 negative outs together installed? Which gain setting are you using?
When I get a round tuit i want to dup your settings exactly.

yes, lower outputs are shorted. high gain. I will check the cables when I get home

 

[babadono]

Ok I hooked up one of my LA90s with a RCA to XLR cable. It was the amp that drives the mid frequency horn on the left speaker in my set up.It is set in mono (bridge) mode with the shorting cable. I could not make it make any noise with the RCA end open. No matter the setting...hi or low gain, volume bypassed or not, sweeping the volume pot through its whole travel.

 

[babadono]

Thought about it and went and did it again but with a Jensen Transformer dummy plug attached to RCA end of cable. Basically puts a1K load between RCA center pin and shield simulating the output impedance of an unbalanced output. Still quiet as a church mouse. In fact the channel hooked up this way was DEAD quiet as opposed to the normal channel through all its mixer pre amps and digital crossovers. Love these Toppings!

 

[MBO]

I’ve owned both the B200 and the LA90, and there was absolutely no noise from the power supplies. I have just one reservation regarding the sound quality with the switching power supplies; these amplifiers ought to sound vastly better with traditional power supplies.

 

[antcollinet]

these amplifiers ought to sound vastly better with traditional power supplies.

I can't think of any valid reason why that should be so.

 

[dcolak]

Thought about it and went and did it again but with a Jensen Transformer dummy plug attached to RCA end of cable. Basically puts a1K load between RCA center pin and shield simulating the output impedance of an unbalanced output. Still quiet as a church mouse. In fact the channel hooked up this way was DEAD quiet as opposed to the normal channel through all its mixer pre amps and digital crossovers. Love these Toppings!

Hm, that means both of my LA90D's developed the same problem at the same time... or, you have no RF radiation that those cables could pick up?