This is a review and detailed measurements of the Topping Pre90 balanced and unbalanced preamplifier. It was kindly sent to me by the company. The base preamplifier with ability to switch between RCA and XLR inputs costs US $599. There is an extension that gives you four (4) more inputs (three balanced and one unbalanced) for another $250.
Splitting the functionality into two boxes is rather unique:
View attachment 98412
Unfortunately there is no immediately switch to select an input. You have to cycle through them using the "SEL" button on the left.
Remote control is provided for volume which in turn mandated relay based stepped attenuator which is quite a "high-end" feature. For any kind of home system use remote is mandatory in my book so it is great to see it implemented here. There are other cool features like setting a pre-input gain or maximum safe playback level.
The back panel shows the unusual configuration with the umbilical cord connecting the two:
View attachment 98413
As you see mains power supply is built-into it as it should in this price category.
Overall fit and finish is very good.
For my testing I exclusively focused on XLR input and output.
Topping Pre90 Measurements
As usual I setup preamplifiers for "unity gain" meaning what voltage I put in, is what comes out. On Pre90 that meant setting the volume to -6 dB instead of zero. That gives us this eye popping output:
View attachment 98414
Distortion is whopping -25 dB lower than best case threshold of hearing. Combined noise+distortion as represented by SINAD is 5 dB better than said threshold. And this includes the noise from my analyzer. Likely the actual performance is fair bit better.
Suspecting some of the good noise figure comes at the expense of lower than normal input impedance, I jacked up the default 40 ohm output impedance of my Audio Precision analyzer to 200 ohm. The result was that the output from the Pre90 dropped down to 3.6 volts (instead of 4). One click on the volume control compensated for that nicely and give me the same good performance just as well:
View attachment 98416
So there is really no penalty to the lower input impedance.
I wanted to test the effect of the external box so I selected one of its inputs and ran the dashboard again (with 40 ohm impedance);
View attachment 98424
As you see the external input works just as excellently as the internal input.
EDIT: here is the RCA performance:
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Signal to noise ratio (combined with my analyzer input) is 21 bits and rises to almost 22 bits with full volume:
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Note that Topping advertises much higher numbers. They do that by using a noise amplifier, measuring the results with AP, and then dividing the output by the gain of the noise amplifier. By doing so the remove the effect of Audio Precision analyzer's self noise and get much higher SNR. That is customary in chip industry. For us to keep things consistent we will continue to test as we have as any performance above what I am showing is academic anyway.
Note that the Pre90 can go up to +10 dB gain. Doing so though has a penalty in overall noise. To show the effect of output level/gain, here is a sweep:
View attachment 98435
As you see you can get to 8 volts while maintaining the full performance of the preamp. There is more gain left if you want to drive an amplifier like
Benchmark AHB2 in low gain or
Purifi without its input buffer.
Frequency response is almost flat to 80 kHz:
View attachment 98436
There is a bit more droop in my measurements vs Topping. Not sure why but it is immaterial.
Crosstalk was more than good enough for what we need but shy of the best that can be done:
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Intermodulation distortion test is as good as the best I have tested, the
Benchmark HPA4:
View attachment 98439
Same is the case for SINAD vs frequency:
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Conclusions
Seems like the revolution we have had in high performance headphone amplifiers has bled into preamplifiers. I love it because I have a Reel Reel tape deck that I like to use occasionally in my system along with my usual DAC. Sadly hardly any premplifier could keep up with said DAC so I was degrading the performance of it to have the ability to play another analog source. With the Pre90, that compromise is no more. It is an instrument grade, more transparent than transparent, preamplifier. Other than Benchmark HPA4, I don't think it has an equal no matter how much money you spend. In that regard, it is quite a value as well although obviously not "cheap" as compared to desktop products.
It is my pleasure to strongly recommend the Topping Pre90. If you needed to have another source beside your DAC to play in your system, you now have a wonderful way to accomplish that with zero impact on performance.
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