Thanks Dennis.
I mailed Mr Pass and he had a good point. With 4 ohm speakers bridged will play louder but parallel will give less distorsion.
I have no need to play really loud so I will go parallel as a start.
Thanks everyone for your feedback. For a 8 ohm speakers bridged would be a non brainer.
I was running directly from my DAC (at the time a PS Audio Perfectwave MKII), although once I sold off my 300b amplifiers after building the F4 I bought a Don Sach's build of the SP14 6sn7-based preamp kit:
Vacuum Tube Audio SP14 preamp by Don Sachs
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And if only I could pick an amplifier based on THD specifications... would have made the process much, much easier. Can't argue with your ears unfortunately.
Also, I'll note that I did not say that I thought any of the above amplifiers sounded bad. I certainly liked the XA-25. The only one I didn't appreciate was the Lyngdorf... just sounded like the music was "blended" for lack of a better term. Definitely made me anti-digital processing.
How is the gain on the Don Sachs? I’ve built a lot of Tubes4hifi gear and I’ve wanted to upgrade from the SP-12 to a Don Sachs SP-14.
I have two F4s and Cornwall IIIs. Would there be enough gain for 2?
I'm a little confused by this and wondering if the quote might have been misquoted or summarized?
In balanced bridged mode wouldn't there be less 2nd harmonic as it would cancel out? Since there is normally more 2nd harmonic distortion than higher order I would guess the peak distortion to be lower from balanced bridge operation. I suppose the lower damping factor from bridging would lead to more undesirable distortion and certainly the ratio of desirable to undesirable would be adversely affected.
My personal experience is that I greatly prefer the sound of parallel operation, but I don't believe that it is due to less distortion but rather more distortion, or at least more of the desirable variety. A big part of the goodness of Pass amplifiers is the designed in negative phase 2nd harmonic distortion and in the case of the F4 temporal clarity from the lack of any feedback. Perhaps the almost unique total lack of feedback would result in higher distortion in bridged mode for the F4 if not other amplifier topologies? I'm certainly not going to bet against Nelson, just trying to learn and clarify what I think I know.
Ignorance is bliss
Knowledge is creative freedom
being somewhere in the middle along the path is simply dangerous
Thanks Stephen.
But can it not be that the F4 amp or actually most amps have more distortion the lower the speaker impedance? In parallel mode the 4 ohm speaker will be seen as 8 ohm. And in bridged they will be seen as 2 ohm. Is that the proof of pudding?
An amplifier with sufficient current reserves and delivery devices wouldn't necessarily have more distortion into a lower impedance load. That said when comparing Parallel or bridged configuration of the same reserves and devices, yes there will be the potential for more distortion as the current or voltage limits are reached, but if you keep the volume down below the limits of the design the balanced bridged configuration will still be cancelling out much of the 2nd harmonic.
The point I guess behind all this relates to
It isn't so much the total or the peak distortion that matters to our ears as much as the ratio of the harmonics or the quality of the distortion. Some may actually be pleasing and the removal of it perceived as less desirable to listen to.
Having auditioned an XA25 for several weeks prior to building my F4 mono blocks, I can say that if $$$ wasn't an issue I would want both.
The point I guess behind all this relates to
It isn't so much the total or the peak distortion that matters to our ears as much as the ratio of the harmonics or the quality of the distortion. Some may actually be pleasing and the removal of it perceived as less desirable to listen to.
Having auditioned an XA25 for several weeks prior to building my F4 mono blocks, I can say that if $$$ wasn't an issue I would want both.
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I lose some gain from using the balance controls and could survive the volume level at full swing, but don't think that would be true if both channels were at max levels (I have to turn down both to different levels to even out my room). Assuming Don's version doesn't change basic operating, the sp14 "puts out 20v p-p".