Well I just got the Pass today. Apparently needs a lot of break in... the highs are not smooth at all, rather aggressive still. Right now the mids are already good. Mr Pass said something that makes me curious: that with 4 ohm speakers the pure class A sounds better. Here is one question: even with my 4 ohm 87 db speakers, listening at night I guess I'm just using a few watts, well inside the pure class A abilities of the X250.5. In that situation is there any reason that would make the XA30.5 sound better? Since at low volumes the X250.5 doesn't leave class A anyway, and considering the bigger power supply and maybe better parts, shouldn't I assume that X250.5 outperforms the XA30.5 at low listening volumes?
Thiels have always been known for a slightly aggressive top
end and many customers have had to adjust to that, finding that
they like it after some time. Changing an amplifier can cause
you to revisit that experience.
The XA30.5 will beat out the X250.5 for the first 20 watts or so
because it has a much higher bias, and this is particularly
true of low impedance loads. (I used Thiel 3.6's to voice the
original Aleph 0, and they were 2 ohms across the board).
I suggest you take a look at the article Leaving Class A
posted at Pass Laboratories which discusses this in detail.
😎
end and many customers have had to adjust to that, finding that
they like it after some time. Changing an amplifier can cause
you to revisit that experience.
The XA30.5 will beat out the X250.5 for the first 20 watts or so
because it has a much higher bias, and this is particularly
true of low impedance loads. (I used Thiel 3.6's to voice the
original Aleph 0, and they were 2 ohms across the board).
I suggest you take a look at the article Leaving Class A
posted at Pass Laboratories which discusses this in detail.
😎
Give it a good break-in period of time - I would say 1 week for this purpose. Then, it will perform best after 2 hours warm up
Cheers,
nAr
Cheers,
nAr
Thank you this is really helpful! So the high bias is key... maybe that explains why my Audionet amps sound so bad with the Thiels. Maybe low impedance loads require high bias to sound good... it is strange though, what are the advantages of having lower bias ? Is it simpler to make ? At least I guess that AB amplifiers can't have a too high bias or is it just much harder to combine? Also I gotta check what bias means, my intuition tells me it has something to do with current...
And by the way, the highs are starting to sound much better after playing my break-in SACD for 4 hours... some nice transparency already, though not much "air" yet...
My room has boomy bass and I really need thin and tight bass control, which is why I'm a bit afraid of the XA30.5 (maybe I'm wrong...) even though I understand that I wouldn't even use the power of the XA30.5 because I'm sitting close to my speakers.
Just read Leaving Class A, answered many questions. I'm gonna read all the articles! There is one other thing I want to know, does setting the gain of the preamp at the highest level mean that I will get more pure class A operation from the X 250.5? I can set any number from -80db to -140db. Usually set it at -80, especially because I use an old Vacuum State modded SACD player with very low gain.
you can feed your X250 either wit preamp with variable gain or with water hose - you'll not change factory set parameters of amp
disclaimer - amp will last much longer if you don't feed it with water hose
Thanks JulienG!🙂
I have the same speaker, following the discussion I know now better why F4 and Pumpkin was the best combination from the First Watt DIY line, F4 does not emphasize the highs like F5 ( see Nelson comments for the hot highs of Thiel speakers) and by upping the bias to the highest possible value allowed by my heatsinks I could get a good bass.....🙂🙂
I have the same speaker, following the discussion I know now better why F4 and Pumpkin was the best combination from the First Watt DIY line, F4 does not emphasize the highs like F5 ( see Nelson comments for the hot highs of Thiel speakers) and by upping the bias to the highest possible value allowed by my heatsinks I could get a good bass.....🙂🙂
I just saw your signature ....... that's J - Two Kings ?
Exactly Zen Mod J twokings is the favorite amp......
I got your pumpkin boards and all the others today I am very happy.....😀😀😀😀
Seems that my next power amp will be the XA100.5... or if I don't wanna spend the money maybe a second hand class A Plinius...
Measurements
I estimated the Thiel CS2.4's voltage sensitivity to be slightly higher than both average and specification, at 88dB(B)/2.83V/m. However, despite Wes Phillips' conjecture that this speaker is not too hard to drive, its impedance plot (fig.1) indicates that the CS2.4 demands a lot of current from amplifiers. Not only does its impedance drop to 2.73 ohms at 600Hz, but it stays significantly below 4 ohms from 100Hz to 50kHz, and there is a difficult combination of 4.5 ohms magnitude and –45° electrical phase angle at 80Hz. Thiel CS2.4 owners should make sure they have a good 4 ohm–rated amplifier to drive this speaker
My X250.5 is starting to sound better after 100 hours... something puzzles me though, I just realized that there is some steady AC noise inside the amp that I can hear sometimes in the silences. Is this normal?
In the silence? I'm three meters away and I hear it. I used to have a Simaudio amp that had that too, louder though. Could it be because of dirty AC lines?
I think it needs to be toed-in for both to point at the listener for better vocals...although the highs might be too much?
(p)resuming that Donuts are humming ...... only Papa can answer that for sure ;
but , I think that his xformers are certainly flawless with clean AC , so you probably have dirty AC - few hundred mV-s of DC
there are numerous posts with DC block filters around
look at this , made by Mighty ZM :
DC Block - diyaudio.rs
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If you have lamp dimmers or similar sorts of appliance
controls using Triacs, you will find that their switching is
not perfectly symmetric which tends to leave some DC on
the line, which makes for transformer noise.
When they are off, the line is quiet, and it could be your
neighbor if you share a mains transformer.
😎
controls using Triacs, you will find that their switching is
not perfectly symmetric which tends to leave some DC on
the line, which makes for transformer noise.
When they are off, the line is quiet, and it could be your
neighbor if you share a mains transformer.
😎
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