Thanks to a friend bringing a lot of cargo in for me I’ve been busy finishing/progressing projects - some of them four years in the making - including Ben’s project. Fun times. Put together the power supply from the cast-off Krell amplifier I used for my M2X in 2019 with some bits of wood lying around and the Hammond chokes the good doctor transported for me. So, another step further along. Just the chunks of aluminum now….and the FE 2022 Ben likes above when they come back into stock.
Output of the PS is 59.4 VDC. So, in the ballpark. And there’s a grill to go around the entire thing - can’t have any more lizard’s trespassing…
Output of the PS is 59.4 VDC. So, in the ballpark. And there’s a grill to go around the entire thing - can’t have any more lizard’s trespassing…
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I am starting to think the only audible distortion is that of the output stage and that the volt. gain stage distortion doesn't really matter. I m 50% sure of it.I have some very low distortion amplifiers that sound very good, so go figure...
I’m 100% sure that I don’t know if it matters. After building lots of tube and SS designs with all kinds of distortion I thought I knew.
I just bought an XA-25 and if you know this design you know it’s distortion products are way down in the grass, and certainly not even-order dominant.
It’s fabulous sounding: I listen to album after album, never looking for that “right” track. It truly is remarkable sounding in my system.
I just bought an XA-25 and if you know this design you know it’s distortion products are way down in the grass, and certainly not even-order dominant.
It’s fabulous sounding: I listen to album after album, never looking for that “right” track. It truly is remarkable sounding in my system.
Nice! That looks like one of the best amps out there right now. My perception is that low distortion isn’t bad in itself as long as higher order products (4th onwards) are much lower than the lower order products (2nd and 3rd). Also, a really linear gain stage or output stage can unmask what’s in front and behind it and then you can hear what should be improved. This happens with loudspeakers too, where really linear and low distortion speakers show you what’s down the chain. Fun stuff 
Thank you Greg and ra7! Sometimes I think that the use of heavy negative feedback is also somehow bad sounding. Bad this seems to be only half of the story.
The XA25 seems to be an amazing amplifier. I just had a conversation with the the boss of Spatial Europe (has the rights of Spatial in the US), and he mentioned some amplifiers working very good with these high efficiency open baffles, which were tubes, but also pass gear, and he named the XA25 as a very fine amplifier!
I'm looking forward to a SIT powered follower, this is why I'm here. (The F4 just keeps me using it, and it wasn't the only Firstwatt amp!)
The XA25 seems to be an amazing amplifier. I just had a conversation with the the boss of Spatial Europe (has the rights of Spatial in the US), and he mentioned some amplifiers working very good with these high efficiency open baffles, which were tubes, but also pass gear, and he named the XA25 as a very fine amplifier!
I'm looking forward to a SIT powered follower, this is why I'm here. (The F4 just keeps me using it, and it wasn't the only Firstwatt amp!)
Stereophile's measurements of XA25: Stereophile XA25 Measurements
It looks like mainly third harmonic at 1000Hz, nearly equal second and third at 50Hz.
I am in agreement with ra7. Keep those higher order harmonics out of the music. I have gone lower and lower with distortion and for me, the sound and music have improved at each step.
One way to keep the higher harmonics out of the music is to have a combination of power amplifier and speakers that allow the amplifier to operate at low power output at normal listening levels. Many people believe in low, low powered amplifiers for high sensitivity speakers. That may not be the best if it forces the amplifier to operate at its upper limit of power and distortion at normal listening levels.
And distortion at all stages of the music reproduction chain matters.
It looks like mainly third harmonic at 1000Hz, nearly equal second and third at 50Hz.
I am in agreement with ra7. Keep those higher order harmonics out of the music. I have gone lower and lower with distortion and for me, the sound and music have improved at each step.
One way to keep the higher harmonics out of the music is to have a combination of power amplifier and speakers that allow the amplifier to operate at low power output at normal listening levels. Many people believe in low, low powered amplifiers for high sensitivity speakers. That may not be the best if it forces the amplifier to operate at its upper limit of power and distortion at normal listening levels.
And distortion at all stages of the music reproduction chain matters.
It’s really unusual in how it reminds me of a SET and yet has none of the draw backs of a tube amp. The soundstage is very wide and deep: sonic elements appear deeper into the recording than I have heard with any of my amps. There’s a lot of energy appearing all over the soundstage at once.
The XA-25 is a love letter to First Watt / First Watt DIY from Pass Labs: three stages, I believe 2SJ313 / 2SK2013 on the front end and two IXYS pucks on the output and no degeneration on those devices.
I think it’s fair to say that this amp is one of Nelson’s greatest achievements.
The XA-25 is a love letter to First Watt / First Watt DIY from Pass Labs: three stages, I believe 2SJ313 / 2SK2013 on the front end and two IXYS pucks on the output and no degeneration on those devices.
I think it’s fair to say that this amp is one of Nelson’s greatest achievements.
It depends, for ex all currently available DACs sound the same to me. I guess I am lucky. However, to your point about efficiency, lowering resistive losses in the crossover by going to 8ga inductors? HUGE difference. All kinds of micro details appearing.And distortion at all stages of the music reproduction chain matters.
