GotNoRice
100+ Head-Fier
- Joined
- Oct 14, 2003
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I noticed on Amazon that they had the Fosi P2 marked all the way down to about $40 or so. Since it is compatible with EF95/6J1/6AK5 tubes, of which I have plenty, I thought that it would make an interesting experiment to see what this super cheap tube amp could do. I didn't see any dedicated thread about this amp, and only a few brief mentions here and there, so I thought I would make a thread.
https://fosiaudioshop.com/products/...utput-protection-for-headphones-fosi-audio-p2
Out of the box, it came with a pair of Chinese 6K4 tubes and a pair of ancient JRC 5532D OpAmps.
I will say that the 6K4 tubes sounded better than I thought they would. They left a better impression than other Chinese tubes i've had in the past such as the stock 6J1 tubes that came with my Little-Dot I+ and the similar 6J1 tubes that came with my FX Audio TUBE-01. I tried a reliable set of GE 6AK5W tubes and they sounded very good and at least as good as the 6K4 tubes. I tried a pair of 6DT6 tubes which leave grid 3 floating when used as EF95 tubes and that caused a humming in my Little-Dot I+, but in the Fosi P2 they seemed to not have any issues being used in this mode. I tried my 6HA5/6HM5 tubes, which are EF95-compatible triodes and some of my favorites in the Little-Dot I+. They gave great results but ultimately the tube that I found sounded best was the similar 6HQ5 Triodes. In the Little-Dot I+ I always felt that the 6HA5/6HM5 Triodes had the edge over the 6HQ5 but in the Fosi P2 it seemed to be the oposite.
When it came to opamps, the stock JRC 5532D OpAmps were not horrible but pretty mediocre. I tried switching them out with a pair of OPA627 OpAmps (two single OpAmps on a small adapter board) and also LM4562 OpAmps. I thought that the LM4562 OpAmps sounded the best, but i'll admit that i'm biased toward them since they are my long-time favorites. Both were improvements over the JRC 5532D and there were no compatibility issues.
It's greatest weakness seems to be an overall lack of output power. At louder volumes, and especially with bass heavy music, it wasn't too difficult to drive the amp into soft-clipping. It comes with a fairly small 12v 1.5A wall-wart style external power adapter. I tried swapping it out for a 12v 3A adapter I had since it already had a compatible connector. Even with double the current, the upgraded power supply didn't seem to make any difference as to when the unit would clip. So despite the stock tiny external power adapter, I don't think that's actually the bottleneck. My Sony MDR-XB700 headphones (24-Ohm), my Beyerdynamic DT770-Pro (80-Ohm) and my Beyerdynamic DT990-Pro (250-Ohm) all felt under-powered with this amp. But it was mainly an issue during heavy bass. Depending on your listening level and the music you listen to, you might not hit it's power output limits. For me, switching back to my Little-Dot I+ and having the increased output power back was a real breath of fresh air.
Overall, I was pretty surprised at how good it sounded considering it's price. I think that it would make a good first headphone amp for someone on a minimal budget who is just looking to dip their toes into things like tube rolling and OpAmp swapping, since this unit allows both. Despite it's shortcomings I think it's still worth it for the price. It's so small and slim, especially with the external power adapter, it might actually make an interesting option for traveling and using with my laptop.
https://fosiaudioshop.com/products/...utput-protection-for-headphones-fosi-audio-p2
Out of the box, it came with a pair of Chinese 6K4 tubes and a pair of ancient JRC 5532D OpAmps.
I will say that the 6K4 tubes sounded better than I thought they would. They left a better impression than other Chinese tubes i've had in the past such as the stock 6J1 tubes that came with my Little-Dot I+ and the similar 6J1 tubes that came with my FX Audio TUBE-01. I tried a reliable set of GE 6AK5W tubes and they sounded very good and at least as good as the 6K4 tubes. I tried a pair of 6DT6 tubes which leave grid 3 floating when used as EF95 tubes and that caused a humming in my Little-Dot I+, but in the Fosi P2 they seemed to not have any issues being used in this mode. I tried my 6HA5/6HM5 tubes, which are EF95-compatible triodes and some of my favorites in the Little-Dot I+. They gave great results but ultimately the tube that I found sounded best was the similar 6HQ5 Triodes. In the Little-Dot I+ I always felt that the 6HA5/6HM5 Triodes had the edge over the 6HQ5 but in the Fosi P2 it seemed to be the oposite.
When it came to opamps, the stock JRC 5532D OpAmps were not horrible but pretty mediocre. I tried switching them out with a pair of OPA627 OpAmps (two single OpAmps on a small adapter board) and also LM4562 OpAmps. I thought that the LM4562 OpAmps sounded the best, but i'll admit that i'm biased toward them since they are my long-time favorites. Both were improvements over the JRC 5532D and there were no compatibility issues.
It's greatest weakness seems to be an overall lack of output power. At louder volumes, and especially with bass heavy music, it wasn't too difficult to drive the amp into soft-clipping. It comes with a fairly small 12v 1.5A wall-wart style external power adapter. I tried swapping it out for a 12v 3A adapter I had since it already had a compatible connector. Even with double the current, the upgraded power supply didn't seem to make any difference as to when the unit would clip. So despite the stock tiny external power adapter, I don't think that's actually the bottleneck. My Sony MDR-XB700 headphones (24-Ohm), my Beyerdynamic DT770-Pro (80-Ohm) and my Beyerdynamic DT990-Pro (250-Ohm) all felt under-powered with this amp. But it was mainly an issue during heavy bass. Depending on your listening level and the music you listen to, you might not hit it's power output limits. For me, switching back to my Little-Dot I+ and having the increased output power back was a real breath of fresh air.
Overall, I was pretty surprised at how good it sounded considering it's price. I think that it would make a good first headphone amp for someone on a minimal budget who is just looking to dip their toes into things like tube rolling and OpAmp swapping, since this unit allows both. Despite it's shortcomings I think it's still worth it for the price. It's so small and slim, especially with the external power adapter, it might actually make an interesting option for traveling and using with my laptop.
