I see First Watt will be selling the F8 amplifier.
[FONT=Arial, sans-serif]Originally created almost 6 years ago, the F8 is a stereo two-stage single-ended Class A amplifier using the NOS Toshiba 2SJ74 P channel Jfets and SemiSouth R100 SiC power Jfets for signal gain, plus IRFP240 Mosfet mu-follower current sources, for a total of three devices per channel.[/FONT]
[FONT=Arial, sans-serif]It is similar to the J2 amplifier, but has only one front end transistor instead of six, operated as a current feedback amplifier (CFA) as opposed to the J2's voltage feedback (VFA) differential input. This front end is more consistent with the single-ended approach to amplifier design and yields a purer second harmonic character, less distortion with lower negative feedback, greater bandwidth and higher damping factor.[/FONT]
[FONT=Arial, sans-serif]The owner's manual can be downloaded here: F8 Owner's Manual[/FONT]
[FONT=Arial, sans-serif]Availability is September 2020 at a list price of $4000.[/FONT]
[FONT=Arial, sans-serif]Originally created almost 6 years ago, the F8 is a stereo two-stage single-ended Class A amplifier using the NOS Toshiba 2SJ74 P channel Jfets and SemiSouth R100 SiC power Jfets for signal gain, plus IRFP240 Mosfet mu-follower current sources, for a total of three devices per channel.[/FONT]
[FONT=Arial, sans-serif]It is similar to the J2 amplifier, but has only one front end transistor instead of six, operated as a current feedback amplifier (CFA) as opposed to the J2's voltage feedback (VFA) differential input. This front end is more consistent with the single-ended approach to amplifier design and yields a purer second harmonic character, less distortion with lower negative feedback, greater bandwidth and higher damping factor.[/FONT]
[FONT=Arial, sans-serif]The owner's manual can be downloaded here: F8 Owner's Manual[/FONT]
[FONT=Arial, sans-serif]Availability is September 2020 at a list price of $4000.[/FONT]
we hope and we urge
Rich Pa, relaxed Pa, more freebies to amused Greedy Boyz
That depends on who is making the list:
Pa-
1A Relaxed Pa
1B Rich Pa
2. Freebies to Greedy Boyz
GB-
1. Freebies to Greedy Boyz
2. Freebies to Greedy Boyz
3. Freebies to Greedy Boyz
Such a clever trick to break conventional wisdom of complementary parallel push-pull differential. A right approach to simplification for improve performance. Who is scared of caps anyway?
Pa-
1A Relaxed Pa
1B Rich Pa
2. Freebies to Greedy Boyz
GB-
1. P channel sony sit3 vfet GB
2. N channel sony sit3 vfet GB
Pa-
1A Relaxed Pa
1B Rich Pa
2. Freebies to Greedy Boyz
GB-
1. P channel sony sit3 vfet GB
2. N channel sony sit3 vfet GB
I think the pass labs forum has been a little quiet with anticipation...I can’t wait for the f8, I notice that the f8 and about half of the other first watt amps product less power into 4 ohms, even though they are stable into very low impedance (would the f8 put out 7-8 watts into 2ohms?) Since this in my mind also goes against convention or maybe expectation is there a reason for this?
F8 is current limited to around 2.75A pk.
That is what limits the power into lower impedance loads.
F4, F5, M2, F6, F7 (BA2, BA3) don't have these types of issues.
The others do.
The way around this issue is to bias the circuit higher, but then you need a better power supply, bigger transformer, and larger heatsinks (possibly dual mono in a larger chassis, or monoblocks)
That is what limits the power into lower impedance loads.
F4, F5, M2, F6, F7 (BA2, BA3) don't have these types of issues.
The others do.
The way around this issue is to bias the circuit higher, but then you need a better power supply, bigger transformer, and larger heatsinks (possibly dual mono in a larger chassis, or monoblocks)
Last edited:
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Joined 2009
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I also wonder about this.
Obviously there is bass roll off to consider, so choosing the right size is important.
Then there is ESR and impedance between 20 Hz to 20kHz
Current capability.
Stability with heat
Longevity
Distortion measurements
All these issues give me a brain aneurysm.
If there was some kind of agreed methodology to test some of this stuff, I would do it.
Obviously there is bass roll off to consider, so choosing the right size is important.
Then there is ESR and impedance between 20 Hz to 20kHz
Current capability.
Stability with heat
Longevity
Distortion measurements
All these issues give me a brain aneurysm.
If there was some kind of agreed methodology to test some of this stuff, I would do it.
Regarding output cap...
Read this thread:
25W Class A amp with Lateral MOSFETs
In fact this is a kind of F8 with bipolar input and driver ;-)
All the misinformation about electrolytics in the signal path disapears when you listen to music through this amp...if you listen to "reviews" on the internet, you will be lost
Read this thread:
25W Class A amp with Lateral MOSFETs
In fact this is a kind of F8 with bipolar input and driver ;-)
All the misinformation about electrolytics in the signal path disapears when you listen to music through this amp...if you listen to "reviews" on the internet, you will be lost
What order of priority for those?
1. Relaxed Pa
2. Relaxed Pa
3. Relaxed Pa
We know that you do all this stuff because it's "what keeps you going in life" and you really enjoy it, obviously. But, you've already created enough projects to last EVERYONE (including certain Serbian members
) a lifetime, even ones that require unobtanium parts
Each channel has two parallel 10,000 uF 50V Panasonic electrolytics
bypassed by 1.5 uF polypropylene.