Nature of design
Cmon, it's nature of design, you get trade-offs... (I'm talking from "numbers" perspective, not subjective sound quality)
First, trade off between HF and LF. Second, when you work with bipolars, verticals or laterals, you'll know that it is difficult to get very good "damping" with laterals. I think the root cause is the relatively low transconductance of the laterals...
And of course it is subjective/relative, meaning that you have to compare with something (bipolar design, or try the SKA amp for vertical), and that the most important component in the chain, the speaker, should not something very easy to drive...
And then, IMO, the "correct" sound of bass is relatively unknown. In the past I really like the general bass sound of mosfet amps, later I found that it was unnatural. Today, with hi-fi we like to compare with real instruments like kick drum for bass. And you know that many bass that we (like to) hear (in the past) was not correlated with any instruments sounds...
Cmon, it's nature of design, you get trade-offs... (I'm talking from "numbers" perspective, not subjective sound quality)
First, trade off between HF and LF. Second, when you work with bipolars, verticals or laterals, you'll know that it is difficult to get very good "damping" with laterals. I think the root cause is the relatively low transconductance of the laterals...
And of course it is subjective/relative, meaning that you have to compare with something (bipolar design, or try the SKA amp for vertical), and that the most important component in the chain, the speaker, should not something very easy to drive...
And then, IMO, the "correct" sound of bass is relatively unknown. In the past I really like the general bass sound of mosfet amps, later I found that it was unnatural. Today, with hi-fi we like to compare with real instruments like kick drum for bass. And you know that many bass that we (like to) hear (in the past) was not correlated with any instruments sounds...
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Hmmm, The SKA is the most unnatural sounding of all the amps I have built. Not sure why you choose that one as an example of verticals. Mile's vertical amp designs sound much more natural as do Valery's. YMMV
FX8 Zobel
BTW, Terry and Miles, have you confirmed with measurement that the zobel (I think 4R7 and 100n) is right on?
BTW, Terry and Miles, have you confirmed with measurement that the zobel (I think 4R7 and 100n) is right on?
Yes, you still miss the driver transistors 😉 That's orange cap is a Philips MKT, right? I usually avoid MKT in zobel position. The other white 100n (MMK) looks like a ceramic and they might be better switching the positions?
Yes I have many of them too from the Crescendo era.
May be it doesn't matter. I just use my intuition that MKT is not the right cap for HF stabilization duty. The other one (100n on the CCS) is not critical but here I prefer MKP. This amplifier is not perfect in term of stability (my guess is that the phase margin is no more than 70), so everything must be done precisely: PCB track, zobel values, cap type, etc.
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I'm not criticizing. I have built this amp with 3 different output transistors. (It also means 3 different PCBs)
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Sorry, I don't have any pictures. Too many projects, don't have motivation to install Samsung Kies or whatever is required to take and post pictures 🙂
I can confirm that. I built an original kit from "ska-audio.com", and the sound is quite boring. I don't know why so many people seem to find that amp "so good". In my ears that amp doesn't do anything right. But I guess it's a matter of taste. 😀
Yes, verticals/hexfets are not suitable for low current application due to the high input capacitance. Nelson Pass uses them in class-A amplifiers.
For big transistors, when complementary pair is required, I think IRFP240/9240 is about the best. But I don't have this pair and have never used them. I have better big transistors (for big class-A) like this, but N-Channel only (so for single ended/follower).
For complementary pair of hexfet amps, I use smaller mosfet (TO-220AB), which is even better than LATFET. Don't ask me what they are. They are 10A device (bigger than J50 which is 7A), 4x the transconductance of J50, half of J50 input capacitance, I think lower rds-on. SOA is not a problem even in class-A.
In an amplifier, nothing can beat a good transistor.
Don't worry Terry,i see many guys here who want only to take and give nothing.🙁
In what way does it sound unnatural? Many people like it so what are it's redeeming features?
I second Terry's and Thimios's post. when you build someone's design, you post pics, your impressions, plus your gratitude (becoz you are not so capable[atleast I am not]), .... see my builds... you will see acknowledgement, impressions and thanks to the designer...
reg
Prasi
BTW, Thimios, have you built FX8, nice little amp.. I am awaiting your impressions too😉.
reg
Prasi
BTW, Thimios, have you built FX8, nice little amp.. I am awaiting your impressions too😉.
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No prasi, unfortunately not.
We have many problems in Greece.
Personally I'm jobless for about 3 years now...