This is a review and detailed measurements of the Fosi Audio HD-A1 amplifier. It costs US $200 on Amazon including Prime shipping. It was kindly sent to me for testing by member @IowAudio. He has a review of it on youtube.
The front is not bad for a budget product:
The font could use some help but you don't listen to that. Nice to have a volume control as many budget amps don't have one.
The back panel connectors are unusually high quality:
Oddly the power switch is on the left (right above).
There are no safety or regulatory certifications which is always a concern for mains operated product.
In use the unit was quite robust, never shutting down or getting overly warm.
Company advertises that the topology is similar to Marantz's HDAM amplifier stage. Whether that is the case or not, I have not tried to investigate:
The amplifier is Class AB and uses a toroidal transformer which makes it quite heavy and sturdy for its size.
Amplifier Audio Measurements
As usual we test for noise and distortion by asking the amplifier to produce 5 watts into 4 ohm load using a 1 kHz signal:
This is not good. We have tons of power supply related spikes (left of our 1 kHz tone) and harmonic distortion after our tone. I suspect this is a low feedback design and as such, is not very linear. No wonder then that the ranking amount all the amplifiers tested is almost at the bottom:
There is some talk about it being tube like so maybe that is the excuse for poor performance.
Noise performance is not great either:
Frequency response and crosstalk on the other hand are very good:
But our 32-tone signal resembling "music" is not:
Power into 4 ohm load does not meet spec:
It gets closer though if we allow more distortion:
Naturally power drops with 8 ohm load:
Conclusions
The Fosi HD-A1 amplifier promises more from its looks and weight than it delivers in transparency. Then again there is some pretension of tube line sound and such so maybe this is intentional. The high distortion and noise don't do much for me so it is not something I can recommend. But I didn't want to give it the lowest score because I don't know if there is anything better in this power range and price.
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As always, questions, comments, recommendations, etc. are welcome.
The panthers have heard that Covid virus doesn't hurt them much so they want to throw a summer party. I have saved up enough money from donations to buy them steaks to eat. But need to get a hazmat suit for me so I don't catch the virus and for that, I need money, and lots of it! So please donate generously using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The front is not bad for a budget product:
The font could use some help but you don't listen to that. Nice to have a volume control as many budget amps don't have one.
The back panel connectors are unusually high quality:
Oddly the power switch is on the left (right above).
There are no safety or regulatory certifications which is always a concern for mains operated product.
In use the unit was quite robust, never shutting down or getting overly warm.
Company advertises that the topology is similar to Marantz's HDAM amplifier stage. Whether that is the case or not, I have not tried to investigate:
The amplifier is Class AB and uses a toroidal transformer which makes it quite heavy and sturdy for its size.
Amplifier Audio Measurements
As usual we test for noise and distortion by asking the amplifier to produce 5 watts into 4 ohm load using a 1 kHz signal:
This is not good. We have tons of power supply related spikes (left of our 1 kHz tone) and harmonic distortion after our tone. I suspect this is a low feedback design and as such, is not very linear. No wonder then that the ranking amount all the amplifiers tested is almost at the bottom:
There is some talk about it being tube like so maybe that is the excuse for poor performance.
Noise performance is not great either:
Frequency response and crosstalk on the other hand are very good:
But our 32-tone signal resembling "music" is not:
Power into 4 ohm load does not meet spec:
It gets closer though if we allow more distortion:
Naturally power drops with 8 ohm load:
Conclusions
The Fosi HD-A1 amplifier promises more from its looks and weight than it delivers in transparency. Then again there is some pretension of tube line sound and such so maybe this is intentional. The high distortion and noise don't do much for me so it is not something I can recommend. But I didn't want to give it the lowest score because I don't know if there is anything better in this power range and price.
-----------
As always, questions, comments, recommendations, etc. are welcome.
The panthers have heard that Covid virus doesn't hurt them much so they want to throw a summer party. I have saved up enough money from donations to buy them steaks to eat. But need to get a hazmat suit for me so I don't catch the virus and for that, I need money, and lots of it! So please donate generously using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/