Mytek HiFi Brooklyn AMP+ power amplifier Measurements

Sidebar 3: Measurements

Other than "+" appended to the name on the amplifier's top and bottom plates, the Brooklyn AMP+ appears identical to the original Brooklyn AMP that was reviewed in the September 2018 issue. I summed up the earlier amplifier's behavior on the test bench by writing "Mytek's Brooklyn AMP is a tiny powerhouse offering respectable measured performance." I used my Audio Precision SYS2722 system (see the January 2008 "As We See It") to test the Brooklyn AMP+. Like its predecessor, the AMP+ has an output stage operating in class-D, so I inserted Audio Precision's auxiliary AUX-0025 passive low-pass filter between the test load and the analyzer. This filter eliminates RF noise that could drive the SYS2722's input circuitry into slew-rate limiting, and I used it for all the tests other than frequency response.

The Brooklyn AMP+ is specified as having a voltage gain of 23 or 29dB, selectable with one of the rear-panel DIP switches. (Setting DIP switch #1 to On allows the amplifier's settings to be adjusted with the switches; otherwise, it is controlled with the Mytek Control app via the rear-panel USB port. I tried both methods.) The voltage gain into 8 ohms measured very close to the specification at 22.9dB and 28.9dB for both balanced and unbalanced inputs. In Bridged mode, the gain was 6dB higher in both gain settings, as expected.

Both sets of inputs preserved absolute polarity (ie, were noninvert-ing) in Normal mode, and the Bridged mode was noninverting when the positive output was taken from the left channel's positive output terminal. The input impedance was 19.8k ohms from 20Hz to 20kHz for the balanced inputs, and 17k ohms at 20Hz and 1kHz for the unbalanced inputs, the latter dropping slightly at 20kHz, to 15k ohms. The output impedance in Normal mode, including a 6', spaced-pair speaker cable, was very low at 0.085 ohms at 20Hz and 1kHz, but rose to 0.3 ohms at 20kHz. As a result, the modulation of the Brooklyn AMP+'s frequency response with our standard simulated loudspeaker was very small in the audioband (fig.1, gray trace). Into 8 ohms (blue and red traces), the response peaked by +0.9dB between 40kHz and 50kHz, before rapidly rolling off to reach –3dB at 80kHz. (The original Brooklyn AMP rolled above 25kHz.) The ultrasonic peak, which is due to the passive low-pass filter that follows the amplifier's class-D output stage, was absent into 4 ohms (cyan and magenta traces) and 2 ohms (green trace). The response into 2 ohms was down by 0.7dB at 20kHz.

421Mytekfig01

Fig.1 Mytek Brooklyn AMP+, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).

The ultrasonic peak into higher impedances is associated with a slight degree of leading-edge overshoot with a 10kHz squarewave (fig.2), but the overshoot is critically damped, with no ringing evident. Channel separation was excellent, at 100dB in both directions below 1kHz, and still 73dB at the top of the audioband. Without the AP low-pass filter there was 98mV of ultrasonic noise present on the Mytek's output, which is significantly lower than with the original Brooklyn AMP, which had 315mV of noise present. With the AP filter, the unweighted, wideband signal/noise ratio, taken with the single-ended inputs shorted to ground, was 78.5dB (average of both channels) ref. 1W into 8 ohms. The S/N ratio improved to a very good 84dB when the measurement bandwidth was restricted to 22Hz–22kHz, and to 86.8dB with an A-weighting filter in circuit. Other than the inevitable ultrasonic noise produced by a class-D design, this is a quiet amplifier. Spectral analysis of the low-frequency noise floor (fig.3) revealed no AC-supply–related harmonics.

421Mytekfig02

Fig.2 Mytek Brooklyn AMP+, small-signal 10kHz squarewave into 8 ohms with Audio Precision AUX-0025 low-pass filter.

421Mytekfig03

Fig.3 Mytek Brooklyn AMP+, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (left channel blue, right red; linear frequency scale).

Mytek's website specifies the amplifier's maximum power as 250Wpc into 8 ohms (24dBW), 300Wpc into 4 ohms (21.7dBW), and 400Wpc into 2 ohms (20dBW). Defining clipping as when the THD+noise in the output reaches 1%, I measured the clipping power with both channels driven into 8 ohms as 265W (24.23dBW, fig.4). However, when I tried to measure the clipping power into 4 ohms, the Mytek went into protection mode at 210.4Wpc into 4 ohms (20.2dBW, fig.5). Similarly, the AMP+ went into protection mode at 103.7W into 2 ohms (14.14dBW, not shown). In both cases, the amplifier turned itself on again as soon as I reduced the level of the input signal.

421Mytekfig04

Fig.4 Mytek Brooklyn AMP+, distortion (%) vs 1kHz continuous output power into 8 ohms.

421Mytekfig05

Fig.5 Mytek Brooklyn AMP+, distortion (%) vs 1kHz continuous output power into 4 ohms.

I examined how the Brooklyn's THD+N percentage varied with frequency at 20V (equivalent to 50W into 8 ohms, 100W into 4 ohms, and 200W into 2 ohms). The THD+N was extremely low in the bass and midrange into 8 and 4 ohms (fig.6), with the usual rise in the treble due to the decrease in open-loop voltage gain as the frequency increased. Note the higher level of distortion with the right channel driving 4 ohms (magenta trace) than the left (cyan trace). This graph doesn't show how the THD+N percentage varied into 2 ohms, as the amplifier went into protection at this output voltage.

421Mytekfig06

Fig.6 Mytek Brooklyn AMP+, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red) and 4 ohms (left cyan, right magenta).

The THD+N waveform at 50Wpc into 8 ohms (fig.7) suggests that the distortion signature is primarily third harmonic in nature. This was confirmed by spectral analysis of the amplifier's output while it drove 50Hz at 50Wpc into 8 ohms (fig.8). The third harmonic was a little higher in the right channel (red trace), but the second and higher-order harmonics all lay at or below –100dB (0.001%). As implied by fig.6, when I drove the 50Hz tone at the same voltage into 4 ohms the third harmonic increased in level in the right channel but was still relatively low at –74dB (0.02%, fig.9).

421Mytekfig07

Fig.7 Mytek Brooklyn AMP+, 1kHz waveform at 50W into 8 ohms, 0.003% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

421Mytekfig08

Fig.8 Mytek Brooklyn AMP+, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (left channel blue, right red; linear frequency scale).

421Mytekfig09

Fig.9 Mytek Brooklyn AMP+, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (left channel blue, right red; linear frequency scale).

Despite the decrease in top-octave linearity shown in fig.6, when tested with an equal mix of 19 and 20kHz tones and the signal peaking at 100Wpc into 4 ohms, the Mytek produced low levels of intermodulation distortion (fig.10). The difference product at 1kHz lay at –94dB (0.002%) in the left channel (blue trace) and at –100dB (0.001%) in the right channel (red trace). The higher-order intermodulation products all lay close to or below –80dB (0.01%).

421Mytekfig10

Fig.10 Mytek Brooklyn AMP+, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 4 ohms (left channel blue, right red; linear frequency scale).

Like its predecessor, Mytek's Brooklyn AMP+ is indeed a tiny powerhouse. It matched the measured performance of the original Brooklyn AMP in most ways but with a wider small-signal bandwidth and a lower level of ultrasonic noise. Even with its hair-trigger protection circuit, it will offer sufficient power into low-impedance loudspeakers with music signals.—John Atkinson

COMPANY INFO
Mytek Audio
148 India Street, 1st floor
Brooklyn, NY 11222
(347) 384-2687
ARTICLE CONTENTS

COMMENTS
tonykaz's picture

"best sounding" in the next few years ?

Thats a Strong extrapolation but coming from you I'd tend to embrace it. ( probably because I want it to be true )

I'm anxious to see the Class D Schiit and/or the Audio Research offerings.

Fingers crossed,

Tony in Venice Florida

ps. that lit front panel might be enough to push this device into a Buy-it-Now! event ( along with: Made in Poland, of course )

georgehifi's picture

"best sounding in the next few years ?"
"Thats a Strong extrapolation but coming from you I'd tend to embrace it. ( probably because I want it to be true )"

Follow what amps are using the new GaN fet as outputs, and it's believable.

Cheers George

a.wayne's picture

Class D amplifiers can’t pass Squarewaves so how do they have a perfect TF ..?

Regards

That Other Guy's picture

a bit edgy.

a.wayne's picture

https://www.stereophile.com/images/421Mytekfig02.jpg

Like its predecessor, Mytek's Brooklyn AMP+ is indeed a tiny powerhouse. It matched the measured performance of the original Brooklyn AMP in most ways but with a wider small-signal bandwidth and a lower level of ultrasonic noise. Even with its hair-trigger protection circuit, it will offer sufficient power into low-impedance loudspeakers with music signals.—John Atkinson

Ohhh please John , its an 8ohm amplifier and barely will sink sufficient current to deal with 4 ohm loads forget 2 .

Regards

Ortofan's picture

... the $2K NAD C 298 class D power amp, which uses the Purifi amp modules?
Tests have shown that it is capable of a continuous output of 260W @ 8Ω and 516W @ 4Ω.
https://nad.de/wp-content/uploads/2020/11/NAD_C298_Test_Stereo.pdf

John Atkinson's picture
Ortofan wrote:
Will there soon be forthcoming a review of the $2K NAD C 298 class D power amp, which uses the Purifi amp modules?

Kal Rubinson reviews the C298 in the June issue.

John Atkinson
Technical Editor, Stereophile

JRT's picture

I am looking forward to reading Kal's review, and your measurements and associated comments.

JRT's picture

From the NAD press release at the link below, "The Eigentakt modules are manufactured by NAD under license from Purifi, allowing NAD to optimise these specifically in combination with the custom designed power supply and input stages of the C 298."

https://nadelectronics.com/nad-intros-c-298-power-amplifier-with-purifi-eigentakt-amplification/

So there are no Purifi Eigentakt amplifier modules utilized within the NAD C 298, rather are modified designs manufactured under a technology license. It will be interesting to see if the design modifications and optimizations were more toward improving cost or performance, or perhaps both.

If somebody does not need to bridge the modules, they might do well to consider the Audiophonics LPA-S400ET which uses two off the shelf Purifi Eigentakt 1ET400A amplifier modules, one Hypex switch mode power supply module SMPS1200A400, and Audiophonic's in-house design interface board. Price is €1,124.17 plus S/H (taxes/duties?) from France. I have no affiliation. There are similar competing products from others, but Audiophonic's looks to be nicely assembled and includes cooling slots that some others seem to not include. The interface board includes balanced differential input and single ended input, includes a couple of choices in gain, and includes facility to bypass the input stage to drive the modules directly with outboard gear (if that upstream device can swing 10_Vrms differential output across a 2_kOhm load).

Richard Dev's picture

A review of a $2500 power amplifier, based on listening to only vinyl sources and two high sensitivity speakers from the same manufacturer?

tonykaz's picture

This reviewer doesn't own any 16/44 does he? I still love him and I'm a digital shirt pocket music lover.

Those Horns are wonderful,

Mr.KM is wonderful for his insights, he's one of my 4 candidates for Audiophile of the Year 2021 along with Mr.JA1, Mr.HR and the Audiophiliac!

Tony in Venice Florida

thatguy's picture

If it is any consolation the RP600M speakers aren't 'that' sensitive. This site measured them at 89.6 not the claimed 96.

But I do get your point that with a 250wpc class D amp it would be nice to also throw some really hard to drive speakers at it.

tonykaz's picture

Today Mr.Stoddard said: looks like the Sol will not continue in production.

I'm not giving a accurate quote here, just paraphrasing .

Schiit are doing a broadcast from the Texas Location, a tour of the Building with workers working and a rather long Q&A for Jason from the Audience.

Seems like the Sol is too much of a commitment ( my summary ).

I agree, my Retail outlet, Esoteric Audio, was a Turntable, Arm & MC Cartridge Specialist . It was great fun that involved Tons of critically technical workings accompanied by ample room for disruptions in quality. We maintained a complete diagnostic service.

1985 CDs killing vinyl was an emotional relief. ( for my family )

Today, I feel for the Vinyl people as Chad's beautiful and pricy offerings require all the best & priciest vinyl paraphernalia and a significant monthly purchase budget.

Tony in Venice Florida

Jim Austin's picture

First, it's not certain yet, although it's very likely that the Sol will be discontinued.

Pure speculation here, on my part, but I suspect we'll see it again, or a version of it, once supply chains stabilize and they've had a bit more time to refine the design--not so much from a functional standpoint but from a sustainability standpoint: They need a 'table they can consistently and successfully build. Profitably, too.

Jim Austin, Editor
Stereophile

ken mac's picture

I'm really sorry and puzzled to hear that news. I thought the Sol was unbeatable for the $$$$. I really enjoyed my time with it.

Michael Fremer's picture

If they really are discontinuing the SOL they should license or give it away to someone else to manufacture. When correctly set up it sounded great for so little money. Yes it was “fiddly” but so was Heifetz!

tonykaz's picture

Thank you for writing back.

Mr.Stoddard explains that they are now selling 10X more than they forecasted and are experiencing acute Supply issues in every area.

They are also doubling in Factory Size with the two locations being 1,000 miles apart. ( I would NEVAH sign-off on an arrangement like that, these guys are designers not manufactureres )

I also suspect that these guys aren't Transducer specialists either. This player should've Sale-priced at $2,500 ( in my estimation ).

Overall, Schiit is HigherEnd Audio's Tesla type Company except they are growing much faster than their supply chain ( which seems one to two years behind )

For all us Schiit owners, Schiit gear sells for 80% of New Prices on eBay, residual values are outstanding.

Schiit is a Smash Success.

I was surprised that Stereophile reviewed the Sol but not surprised that Schiit can't quite make the darn things.

I wonder what a Cost Analysis would reveal.

Tony in Venice Florida

ps. Mr. Stoddard appears to have resigned himself to managing a Run-a-way demand situation accompanied with a backordering dilemma .

ken mac's picture

Well stated!

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