This is a review and detailed measurements of Rogersound Labs (RSL) ia255.1 stereo class D amplifier. It is on kind loan from a member and costs US $125.
The look is fine. The switches have very positive feedback. There are tone controls but alas, I wish there was a tone defeat. In my sample, center position was not the same as flat response, requiring very fine tuning. Back side shows one of the features many ask for:
The amp has a proper high pass filter for the mains. Its frequency is a bit high at 90 Hz. It is likely to be right for typical small desktop speakers. Speaker terminals are small as is typical of the class but I still managed. Forgot to take the picture of the external power supply which is roughly the size of the amplifier itself.
Unusually so in this class is inclusion of USB input.
RSL ia255.1 Amplifier Measurements
I adjusted the volume for 25 dB gain (see review picture for position) and drove the RCA inputs:
This is decent results and only slightly below average of all amplifiers tested. Was hoping USB digital would improve things but did the opposite:
It severely increases noise causing SINAD to drop by some 15 dB which is huge. So I abandoned that and performed the rest of the tests using RCA.
Noise performance is good for the class. There are amps that do better to be sure but this is not embarrassing.
Channel separation was actually very good:
As I noted, I had to mess with tone controls to try to get a flat response. This is the best I could do:
I was impressed that the load dependency only occurs well outside of audible band. I tested the high pass filter and it has a 3 dB point of about 100 Hz -- close enough.
The "grass" in multi-tone is variable -- something I don't usually see:
Fortunately it is lowest where our hearing is most sensitive (2 to 5 kHz).
Power sweep shows modest power output and varying distortion levels:
Again, this is something I have not seen before. There is some kind of secondary distortion that sets in around 5 watts. You can see this much more clearly as we perform the same test but at different frequencies:
The rise in distortion with power level before clipping made it impossible to run my peak and max power ratings. The unit would only produce 1 or 2 watts before reaching 1% THD+N. You can see this in 40 Hz measurement:
Finally, the amp is sort of stable other than some kind of glitch early on:
Conclusions
Being also a speaker company, the ia255.1 provided the correct high/low pass filtering for mains and subwoofer channels. Dashboard performance is good for class as is the noise level. Distortion though, is somewhat unpredictable and rises quite high at higher frequencies. Competing amps also do that but not to this extent. So some refinements are needed for hopefully the next version. I was impressed with lack of load dependency -- something the company doesn't advertise and is an issue in budget class D amplifiers.
On strength of functionality and some of the measurements, I am going to Recommend the RSL ia255.1 stereo amplifier.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The look is fine. The switches have very positive feedback. There are tone controls but alas, I wish there was a tone defeat. In my sample, center position was not the same as flat response, requiring very fine tuning. Back side shows one of the features many ask for:
The amp has a proper high pass filter for the mains. Its frequency is a bit high at 90 Hz. It is likely to be right for typical small desktop speakers. Speaker terminals are small as is typical of the class but I still managed. Forgot to take the picture of the external power supply which is roughly the size of the amplifier itself.
Unusually so in this class is inclusion of USB input.
RSL ia255.1 Amplifier Measurements
I adjusted the volume for 25 dB gain (see review picture for position) and drove the RCA inputs:
This is decent results and only slightly below average of all amplifiers tested. Was hoping USB digital would improve things but did the opposite:
It severely increases noise causing SINAD to drop by some 15 dB which is huge. So I abandoned that and performed the rest of the tests using RCA.
Noise performance is good for the class. There are amps that do better to be sure but this is not embarrassing.
Channel separation was actually very good:
As I noted, I had to mess with tone controls to try to get a flat response. This is the best I could do:
I was impressed that the load dependency only occurs well outside of audible band. I tested the high pass filter and it has a 3 dB point of about 100 Hz -- close enough.
The "grass" in multi-tone is variable -- something I don't usually see:
Fortunately it is lowest where our hearing is most sensitive (2 to 5 kHz).
Power sweep shows modest power output and varying distortion levels:
Again, this is something I have not seen before. There is some kind of secondary distortion that sets in around 5 watts. You can see this much more clearly as we perform the same test but at different frequencies:
The rise in distortion with power level before clipping made it impossible to run my peak and max power ratings. The unit would only produce 1 or 2 watts before reaching 1% THD+N. You can see this in 40 Hz measurement:
Finally, the amp is sort of stable other than some kind of glitch early on:
Conclusions
Being also a speaker company, the ia255.1 provided the correct high/low pass filtering for mains and subwoofer channels. Dashboard performance is good for class as is the noise level. Distortion though, is somewhat unpredictable and rises quite high at higher frequencies. Competing amps also do that but not to this extent. So some refinements are needed for hopefully the next version. I was impressed with lack of load dependency -- something the company doesn't advertise and is an issue in budget class D amplifiers.
On strength of functionality and some of the measurements, I am going to Recommend the RSL ia255.1 stereo amplifier.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
