Enleum AMP-23R Measurements

This unit was loaned to me to test by a friend.
Content and analysis made possible thanks to support from https://headphones.com, and https://patreon.com/goldensound supporters.

Chit-Chat:

The AMP-23R is the successor to the Bakoon AMP-13R. A 25 watt speaker amp in a compact chassis, with headphone output included.

It has a few interesting design aspects, such as having a volume control that directly adjusts the gain of the amplification stage itself instead of simply attenuating the signal, and also it uses no negative feedback whatsoever.

Using no negative feedback inherently means that it’s not going for ultra-high measurements, but subjectively there are many who prefer the sound of amplifiers using little to no negative feedback.

Bakoon had a history of producing some quite unique products, even being one of the very few companies to produce a full current-mode amplifier, so it’s no surprise to see some quite interesting and unique design aspects here too.

Another interesting feature on the AMP-23R is its ‘JET2 Bias’ circuit, which uses a combination of an ADC and DAC to constantly monitor and correct the bias of the transistors in response to various external factors such as temperature. This means that the amp should perform identically from the moment it’s switched on and will not need warmup.

Measurements:

Test Setup:

– Audio Precision APx555 B-Series Analyzer
– Amplifier was warmed up for 6 hours before measuring.
– AudioQuest Mackenzie RCA interconnects
– Neurochrome Headphone Dummy Load
– Amplifier set to Low Gain for all tests
– Full reports containing additional data and test configurations are attached
– Exact analyzer configurations for each measurement are detailed in the full reports
– All measurements shown below are taken with a 32 ohm load in low gain unless otherwise specified

Full Reports:

Reports available here (These contain 4v unity gain, and 700mv test results, please check you’re looking at the right ones when comparing!):

Gain: 22.5dB (High), 7dB (Low)

Output impedance: 0.8 Ohm

Power:

Unfortunately I completely forgot to do a power test before the amp left. It is coming back to me later for a full review though so I’ll update this then.
Officially however, it can supply 25W into 8 ohms, and 6.25W into 32 ohms.

1khz 2V input 2V Output 32 ohm:

At 2V into a 32 Ohm load there’s a fair amount of harmonic distortion. Near equal amounts of 2nd and 3rd order.
As mentioned earlier, this amp employs zero negative feedback, low THD+N is NOT what it’s going for and NOT why people are buying this.
But….this performance is actually somewhat misleading, read on to see why.

1khz 2V input 2V Output 300 ohm:

Performance between a 300 ohm and 32 ohm load is extremely close.
Now what if we look at a realistic listening level of 700mV?

1khz 2V input 700mV Output 32 ohm:

What’s interesting is that at 700mV performance is practically identical to at the higher level of 2V. Whereas on many amps distortion level (and sometimes profile) will change depending on level.
This is likely because the Enleum AMP-23R volume control actually alters the gain of the amp, rather than attenuating the signal. This means that performance should in theory remain pretty much identical regardless of what volume you have the amp set to.

BUT, whilst testing, I did notice something unusual. The AMP-23R does not seem to perform quite so well with higher, or even standard 2V level RCA inputs. Its IMD vs input level graph for example looks like this:

This is pretty typical for a lot of amps. The higher the input level, the higher the output level. And at somepoint once the amp starts working too hard, performance starts to drop the more you push it. Crank the volume up too far and distortion might start to rise.
But on the 23R, this graph remained exactly the same even when I set the volume very low. Meaning it couldn’t be correlated to the amp output level, but instead the input level.
So I reduced the input signal to 0.3V and this is what we got:

1khz 300mV input 700mV Output 32 ohm:

Performance gets a big jump! And not only in absolute level, but notice the actual structure of the distortion.
Where we previously had equal 2nd and 3rd order harmonics, we now have a ‘triode-like’ profile with 2nd order prominence, then falling 3rd and 4th order. A profile which many would regard as subjectively preferable, as odd-order harmonics are generally agreed to be subjectively much less pleasing than even-order.

I try to avoid putting subjective commentary in the measurement posts unless I feel it’s necessary or appropriate, but here I think that’s the case.
To me the 23R sounded notably better when the DAC feeding it had about 8-10dB of DSP headroom/volume control applied, with things coming across less ‘dense’, slightly more neutral, and having better clarity of separation between elements.

If you have a 23R it’s worth playing about with this, you can pretty much ‘tune’ the amp by increasing/decreasing your DAC volume between -0dB and -10dB (assuming your DAC outputs about 2V on RCA).

The remainder of this post is showing tests with normal 2V line level, as that’s how most people are using it and I want to keep my test methodology consistent. But there is a PDF full report done with a 300mV input level instead of 2V if you are interested.

THD+N / Frequency:

Total harmonic distortion does not change to any notable degree vs frequency.

SINAD/THD+N vs output level:

IMD (SMPTE) vs Output Level:

Crosstalk:

Crosstalk is quite high.

1khz Square Wave:

Multitone:

When input level is lowered to 0.3V the multitone is much much cleaner, dropping around 15dB in many areas.