The F4 gives about the same distortion numbers balanced
or not for any given wattage short of just below the SE
clipping point.
You can get lower distortion yet by:
1) decreasing the Source resistors (more careful matching
reuired for that)
2) More bias (more sinking)
3) more devices (more devices...)
1 and 3 will increase the DF.
or not for any given wattage short of just below the SE
clipping point.
You can get lower distortion yet by:
1) decreasing the Source resistors (more careful matching
reuired for that)
2) More bias (more sinking)
3) more devices (more devices...)
1 and 3 will increase the DF.
Variac said:
I admit that I had some drinks last night when I was one-finger punching the computer keyboard. And, it was around 2 o'clock early in the morning . . .
With amps of Papa's projects, I always start with high bias, and reduce it little by little, monitoring the sound to the level of a good compromised satisfaction, without sensing any distortion numbers. I usually sit down on total about 1.5A class A bias ^^.
Just my habit ^^.
P1 is there to adjust the bias as it controls the dc differential voltage between the gate pins of Q3 (Q4/Q5) and Q6 (Q7/Q8) while the mid point between Q3 and Q6 always remains at zero voltage (or almost zero). I must be right as long as it is true that the bias level is depending on the Vgs value.
Wishing you a good success!
Nelson Pass said:The F4 gives about the same distortion numbers balanced
or not for any given wattage short of just below the SE
clipping point.
You can get lower distortion yet by:
1) decreasing the Source resistors (more careful matching
reuired for that)
2) More bias (more sinking)
3) more devices (more devices...)
1 and 3 will increase the DF.
3) How much more?
Manuel
How low do you want your damping factor?
For any given design the output device--in this case the IRF MOSFET--and its associated Source resistor will have some characteristic impedance. Just to make things easy, let's say that every complementary pair has an impedance of 1 Ohm. After that it's just a case of impedances in parallel:
1 pair would have an impedance of 1 Ohm
2 pairs would have an impedance of .5 Ohms
3 pairs would have an impedance of .33 Ohms
4 pairs would have an impedance of .25 Ohms
5 pairs would have an impedance of .20 Ohms...etc.
Obviously, it's a diminishing returns sort of thing. Given that the F4 has no feedback, the Zout is what it is. It's set by the topology and parts choices you made.
Grey
For any given design the output device--in this case the IRF MOSFET--and its associated Source resistor will have some characteristic impedance. Just to make things easy, let's say that every complementary pair has an impedance of 1 Ohm. After that it's just a case of impedances in parallel:
1 pair would have an impedance of 1 Ohm
2 pairs would have an impedance of .5 Ohms
3 pairs would have an impedance of .33 Ohms
4 pairs would have an impedance of .25 Ohms
5 pairs would have an impedance of .20 Ohms...etc.
Obviously, it's a diminishing returns sort of thing. Given that the F4 has no feedback, the Zout is what it is. It's set by the topology and parts choices you made.
Grey
Variac,
I confess that I got lost several posts back. Let me see if I've got this straight. You want to build a dedicated balanced stereo F4, right? I think I saw that your speakers were pretty efficient, so that works in your favor.
Two questions:
--What impedance are your speakers?
--What is your target power?
(These may have been posted earlier, but Wyatt's kicking and being a distraction and I'm having trouble feeding him and doing this at the same time.)
Yes, IRFP140s will be fine.
Grey
P.S.: Don't fret about heat. You have a decent heatsink, you have fans, the bias is adjustable. Some combination of those factors will get the job done.
I confess that I got lost several posts back. Let me see if I've got this straight. You want to build a dedicated balanced stereo F4, right? I think I saw that your speakers were pretty efficient, so that works in your favor.
Two questions:
--What impedance are your speakers?
--What is your target power?
(These may have been posted earlier, but Wyatt's kicking and being a distraction and I'm having trouble feeding him and doing this at the same time.)
Yes, IRFP140s will be fine.
Grey
P.S.: Don't fret about heat. You have a decent heatsink, you have fans, the bias is adjustable. Some combination of those factors will get the job done.
Yes, there's a limit, but where the limit is becomes a bit complicated. Different people will give you different answers as to how much current is required to drive a given amount of capacitance. The basic question is one of slew rate, which would seem to be one of those things that everyone could agree on...only it's not.
My personal feeling is that the F4 is pretty cool the way it is. If I were going to start strapping on more output devices, I'd want to look at beefing up the first stage. Nelson (and I'm putting words in his mouth, here) will very likely tell you that the front end is sufficient to drive at least two or three more pairs of outputs without alteration. Other people will have other opinions.
My suggestion is to ask yourself exactly what your goal is. Are you wanting to add output devices simply to increase the damping factor? Are you looking for more power into a low impedance? Are you trying to spread out the heat across the heatsink? Adding devices just to be adding devices is a waste of time and current. Do it intelligently.
Bear in mind that damping factor is one of those diminishing returns things. A damping factor of 1000 is not 1000 times better than a damping factor of 1. Even more damning, some tube amps (with pretty poor damping factors) have very tight bass indeed, much better than some solid state amps with far higher damping factors.
If you really want to do a number on the damping factor, think in terms of adding a front end and enclosing the output stage in a feedback loop. The more practical--though less impressive numerically--way is to choose Nelson's option for reducing the Source resistors.
Grey
My personal feeling is that the F4 is pretty cool the way it is. If I were going to start strapping on more output devices, I'd want to look at beefing up the first stage. Nelson (and I'm putting words in his mouth, here) will very likely tell you that the front end is sufficient to drive at least two or three more pairs of outputs without alteration. Other people will have other opinions.
My suggestion is to ask yourself exactly what your goal is. Are you wanting to add output devices simply to increase the damping factor? Are you looking for more power into a low impedance? Are you trying to spread out the heat across the heatsink? Adding devices just to be adding devices is a waste of time and current. Do it intelligently.
Bear in mind that damping factor is one of those diminishing returns things. A damping factor of 1000 is not 1000 times better than a damping factor of 1. Even more damning, some tube amps (with pretty poor damping factors) have very tight bass indeed, much better than some solid state amps with far higher damping factors.
If you really want to do a number on the damping factor, think in terms of adding a front end and enclosing the output stage in a feedback loop. The more practical--though less impressive numerically--way is to choose Nelson's option for reducing the Source resistors.
Grey
The question is always how much damping is enough? For many of us we have not had the opportunity to listen to various combinations of amps and speakers to really know where that "enough" lies. I do know that my A75 controls the bass of many of the speakers I have heard, more control than the Alephs. Since the First Watt line is intended for high sensitive speakers the F4 may have enough control for those drivers. The unity gain and no feedback is very attractive. I am bi-amping at the moment with Zen V8 and A75. The A75 has way more gain than I need, but the bass is great. I think fullrange high sensitivity is in the future, PM6C!?
Thanks Nelson for the never ending quest.
BDP
Thanks Nelson for the never ending quest.
BDP
Veteran's board
When looking, at the drawing, i had to look 'through' the paper, when drawing the pcb by hand right ??? Otherwise i had to 'mirrorflip' it ?
When looking, at the drawing, i had to look 'through' the paper, when drawing the pcb by hand right ??? Otherwise i had to 'mirrorflip' it ?
I tend to agree (reluctantly, until now) Having been listening to Fostex units costing less than 100$ for some time, I must say that I am impressed. Here is a link to some very nice drivers. These drivers should satisfy anyone's demands about craftmanship and so onBDP said:
I wonder what can be achieved with a pair of those, in a finely tuned speakerbox?Feastrex
Steen
steenoe said:I tend to agree (reluctantly, until now) Having been listening to Fostex units costing less than 100$ for some time, I must say that I am impressed. Here is a link to some very nice drivers. These drivers should satisfy anyone's demands about craftmanship and so on
Feastrex
Steen
steen,I'll soon have pair of Sonido's,so I can pass my experiences to you; if memory serves me well........searching now.......http://www.diyaudio.com/forums/sear...by=lastpost&sortorder=descending&pagenumber=1
with honest approach-there is no need to two drivers cost you arm and leg.......
to achieve dynamics even with sensitive speakers you either need big horn or OB with bass augmentation.........or good 12"-15" coax in big box.........
anyway,except in case with OB+ 15" bass,anything bellow 8" is just a toy.......thinking of degree of compromise
if you live in small japanese (or serbian
) room ,there is some purpose in small driver....but if you live (listen) in something bigger room.......
Hi,
Just an observation. In my experience, more damping factor does not always mean better sound, or better bass, if you like. This is especially the case if you use FR drivers. They seem to prefer a higher Zout.
I've built a ZV9 without feedback, and loaded the output with 7.5 ohm resistors. Therefore, it damping factor should be around 1 (one) if I am not mistaken. This works best for my Visaton B200's.
Regards,
Vix
Just an observation. In my experience, more damping factor does not always mean better sound, or better bass, if you like. This is especially the case if you use FR drivers. They seem to prefer a higher Zout.
I've built a ZV9 without feedback, and loaded the output with 7.5 ohm resistors. Therefore, it damping factor should be around 1 (one) if I am not mistaken. This works best for my Visaton B200's.
Regards,
Vix
Well, i had been listening to the F4 with the Abby clones for about 3 hour's Sunday, at steenoe's place. I AM IN NO Doubt, it's the best setup i have ever listenet to The perspective is sooo great from the F4's, every little detail just comes through here, There has been a little doubt about Steenoe being crazy or not, regarding his 'review' with theese F4's, but he is not. End of quistion.
So i am just now in a little doubt, whether or not, they must be the one's i had to build.
Steenoe was kind enough to lent me his 25watt's Babelfish, so that i could hear at home, wheater or not it's enough for my loudspeakers. Well i tried to set this up today
(With an unbalanced BoSoZ + Unbalanced babelfish) and i must say, that the sound from this little monster, is very good. I think they are capable of driving my loudspeaker's till theire half strenght or so (maybe a little lesser than that) I don't know for sure, if a setup of a fully balanced F4 2xmonoblock's (along with a balanced BoZoS) then will be able to do that job ???
I have posted a picture of my setup with steenoes Babelfish.
Jesper
The perspective is sooo great from the F4's, every little detail just comes through here, There has been a little doubt about Steenoe being crazy or not, regarding his 'review' with theese F4's, but he is not. End of quistion.So i am just now in a little doubt, whether or not, they must be the one's i had to build.
Steenoe was kind enough to lent me his 25watt's Babelfish, so that i could hear at home, wheater or not it's enough for my loudspeakers. Well i tried to set this up today
(With an unbalanced BoSoZ + Unbalanced babelfish) and i must say, that the sound from this little monster, is very good. I think they are capable of driving my loudspeaker's till theire half strenght or so (maybe a little lesser than that) I don't know for sure, if a setup of a fully balanced F4 2xmonoblock's (along with a balanced BoZoS) then will be able to do that job ???
I have posted a picture of my setup with steenoes Babelfish.
Jesper
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