Topping LA90 Review (Integrated Amplifier)

[JSmith]

If that's the case then using the combination input connector was a serious mistake.

The input socket is like one of these connectors from what I can see... XLR/TRS;

JSmith

 

[Deleted member 46664]

The input socket is like one of these connectors from what I can see... XLR/TRS;

JSmith

A little reading might help .... DB Pages: Balanced Audio

 

[JSmith]

A little reading might help

You mean this part I gather...

This, of course, has the down side that you've got to be very careful what you're plugging in where. Plugging a TS cable into a TRS output could damage your equipment.

JSmith

 

[solderdude]

If there really is an internal rail-splitter in linear class-A/B we'd still have some useless power dissipation, being just an undriven bridge half. Large local bulk caps after the splitter do help... but not much for very low frequencies. The amp isn't DC coupled but what happens with, say, a <20Hz "earthquake" mono signal at full blast?

If split locally, why then the 3-prong DC supply connectors? This style is available in 2-, 3- and 4-pin variants. Maybe the 3-pin was simply the cheapest they could get?

I was merely commenting what the possibilities are.
1: the power supply is secretly +/-32V (which would be logical but most bricks are single supply voltage)
2: Rail splitter, when this is done using a splitter that cab source/sink 5A then you would not need large capacitors.
3: Internal DCDC converter

Hoping @JohnYang1997 tells us what he (they) did.

 

[Toku]

Porbably. At least that's what Topping states: "compatible with XLR and TRS interfaces", not explicitely mentioning TS here.

OTOH, a balanced input by sheer definition must handle unbalanced signal as well with no problems, otherwise it's just not a viable balanced input whose definition is to subtract out any common-mode signel (when driven with TS unbalanced cable then the common-mode signal is simply half of the differential signal).

Offering TRS input invites users to plug in TS inputs (or RCA to TS adapters) and therefore it would be very strange if TS really isn't allowed (aka creating problems). Or did they state that just because the leakage current from their PSU is very high which easily creates noise in unbalanced interconnects?

This is Topping and as we have seen for the PA5 Inpus they may do things in a non-conformant style and provide little technical detail about connection / input topology and its limiting values.

What is the reason for forcibly connecting an unbalanced signal to an amplifier dedicated to balanced input?
If you just want to make a sound, you can use it like that. But I don't think LA90 is needed for such applications.

 

[solderdude]

Are any amps configured as a current source? Audio amps are (to my knowledge) always voltage sources.

I think the confusion is from the feedback topology, current feedback or voltage feedback. In both cases the output is always a voltage source.
I would assume this is nested feedback (a bit like the LM3886 from Tomchr ?)

 

[Deleted member 46664]

You mean this part I gather...

Those jacks are INPUTS.

 

[Deleted member 46664]

What is the reason for forcibly connecting an unbalanced signal to an amplifier dedicated to balanced input?
If you just want to make a sound, you can use it like that. But I don't think LA90 is needed for such applications.

Okay... so you're about half way through updating your system ... you have your LA90 ... but still have an unbalanced DAC ... There's no reason you can't use it, if those inputs are correctly configured.

Stuff like this is done all the time in pro audio... how do you think they connect a guitar to a console?

Balanced Audio

The ins and outs of balanced audio

dbpages.ca

 

[NTK]

Apologies in advance if I missed it but what was the sensitivity of the speakers used for this table?

For the ANSI/CTA-2034-A standard, the required power is calculated in a roundabout way, and not from the speaker sensitivity. Below is the example report presented in the ANSI/CTA-2034-A document. I'd guess/assume the graphs and numbers come from the same example speaker instead of just some random numbers, but I can certainly be wrong.


The required power numbers seem a bit high to me, as from the on-axis frequency response curve the speaker looks to be quite efficient (I estimate to be 92 dB / 2.83 V / 1 m).

Per the standard, instead of using speaker sensitivity, the required power is calculated using the input voltage to generate the maximum usable continuous SPL. Unfortunately, the information required to back calculate the required power wasn't given in the document (or I couldn't figure it out myself). Therefore, I am unable to verify their numbers. I have also never seen a complete (full) CTA-2034 report -- only the spinorama part, and therefore never saw real numbers of an actual speaker.

 

[DHT 845]

So it is class AB amp?
On audiophonics site they say class D / T in data sheet section...

 

[PoorishDecision]

That's a really cool little amp, I'd say with the right speakers it'd be awesome. I don't really see the issue with the power rating tbh, I used a naim/craft 25w pre power class a for a while and it ran everything well. I'd be curious to hear it running some high efficiency floorstanders

 

[JSmith]

A little reading might help

What you were actually referring to may have assisted the conversation. Text only discussions are prone to misunderstandings.

Doesn't it depend on the circuit topology in some cases?

Maybe @Toku can elaborate further on the previous comment in this context.


JSmith

 

[solderdude]

For inputs it really does not matter. You can safely connect the - input to ground in both truly balanced (so not ground referenced common) as well as differential that is ground referenced. In both cases the signal is on the + input and the screen becomes the - (be it tied to ground/common or not)
There could be differences in ground loops but that is another matter and downside of RCA.

 

[Deleted member 46664]

What you were actually referring to may have assisted the conversation. Text only discussions are prone to misunderstandings.

Go back and actually READ at the page this time ...
There are even pretty pictures to help you along.

 

[pjug]

It depends which 2 of the 3 pins across are measured. Pick the +/-32 and you get 64.

But he measured against the third pin too, of course!

 

[Ra1zel]

High gain is 20dB. How do people who want to use it with RCA drive it to full power?

 

[antcollinet]

High gain is 20dB. How do people who want to use it with RCA drive it to full power?

They use a preamp, or they don't.

 

[JSmith]

Go back and actually READ at the page this time ...

No need to be condescending, it's just a friendly discussion mate. Feel free to PM me if you wish to discuss the matter further.


JSmith

 

[PeteL]

They use a preamp, or they don't.

While it's true for many low level sources, may you explain tour reasoning?

In 4 Ohms: V =sqrt( P*R) = =14.97V

20 dB Gain= 10X

14.97/10= 1.497 V

Most RCA/unbalanced Dacs from toppings or other can give 2V. Yes if we are talking general consumer equipment it's not the case, especially vintage stuff. But what where you talking about exactly by absolutely needing a preamp?

 

[KSTR]

What is the reason for forcibly connecting an unbalanced signal to an amplifier dedicated to balanced input?

Well, as I said, the whole idea of a balanced input is cancelling principle, that is to look only at the difference signal between pins. You're not forcing anything when, say, one pin is at ground like it is the case here.

Therefore, a "balanced input" only working properly with signal-balanced drive is impossible. Either it's balanced or it is not, no in-betweens.