Having experienced F2 (lite), and currently running a ZV9 without feedback, I'd like to point out that they make me happier (than feedback circuit). Besides killing distortion, negative feedbacks seems also to kill some life of music, imho.
Of course it would depend on the speakers used. I've tried Fostex FE206e in an ML TL and a Visaton B200 in the OB.
Both being fullrangers, they may prefer the lower damping the non-feedback amps provide. (as Nelson also pointed out in his article about transconductance amps)
Distortion? Ah, yes...
I've experimented with my ZV9, feedback vs. no feedback before I decided which variant I like. (no aleph CS)
Well, if you crank up the volume, ZV9 WITH feedback sounds better. Tighter, more controlled, everything on its place, clear. Really good.
Until you...
Lower the volume, load the output with 10-15 ohm resistor, and suddenly...(beside higher gain) some magic appears. Some notes that sounded "solid" become "airy" and simply float in the air.
I noticed that, by adjusting output load resistor (beside altering gain) it also affects this "airiness". Up to your taste. At some point you begin to like this too much; increase the volume and notes gently start falling apart, blurring the image and reminding you that there's no free lunch...
Leave Aleph as it is. If you have efficient fullrange speakers , and still want a feedbackless amp, build an F2. 😉
Regards,
Vix
Of course it would depend on the speakers used. I've tried Fostex FE206e in an ML TL and a Visaton B200 in the OB.
Both being fullrangers, they may prefer the lower damping the non-feedback amps provide. (as Nelson also pointed out in his article about transconductance amps)
Distortion? Ah, yes...
I've experimented with my ZV9, feedback vs. no feedback before I decided which variant I like. (no aleph CS)
Well, if you crank up the volume, ZV9 WITH feedback sounds better. Tighter, more controlled, everything on its place, clear. Really good.
Until you...
Lower the volume, load the output with 10-15 ohm resistor, and suddenly...(beside higher gain) some magic appears. Some notes that sounded "solid" become "airy" and simply float in the air.
I noticed that, by adjusting output load resistor (beside altering gain) it also affects this "airiness". Up to your taste. At some point you begin to like this too much; increase the volume and notes gently start falling apart, blurring the image and reminding you that there's no free lunch...
Leave Aleph as it is. If you have efficient fullrange speakers , and still want a feedbackless amp, build an F2. 😉
Regards,
Vix
I have efficient speakers- Edgarhorn Slimlines (100db), but they are not full rangers.
Just wanted to tweak the Mini I am getting and the future ones I build to be more like the J. I don't need tons of gain from the feedback.
Maybe Choky still has Babblefish boards?
Or maybe build F4 when I get around to building an active preamp (maybe use the preamp built into my Benchmark DAC1 until can build something else?)?
Just wanted to tweak the Mini I am getting and the future ones I build to be more like the J. I don't need tons of gain from the feedback.
Maybe Choky still has Babblefish boards?
Or maybe build F4 when I get around to building an active preamp (maybe use the preamp built into my Benchmark DAC1 until can build something else?)?
winslow said:
I already posted this above, but I'll try again, throwing more words into this post since I don't seem to do "brevity" well.
To reduce the negative feedback, increase the value of the resistor that goes from the output to the backside of the front end differential, meaning the device whose Gate points towards the output stage. Alternatively, you could reduce the value of the resistor that goes from the backside device's Gate to ground. Either will work. Or do both at the same time.
Sorry I can't give you the part numbers for the feedback resistors, but it's been a really long time since I did the Mini-A and I don't even try to memorize part numbers. Not to mention the fact that I've done a lot of other circuits since then and they tend to crowd out the older things.
The two resistors together form a voltage divider. The ratio of the two determines how much of the output signal gets fed back to the differential, hence determining the amount of feedback.
Lowering the open loop gain is another matter entirely. That requires a more careful approach and, in this case, the selection of different active devices. There are a lot of different parameters that come into play and you have to balance everything against everything. More particularly, I designed the Mini-A as a cut-down Aleph 3. Some of the things that I chose to do then I would do differently now, but that's pretty much true for anything, assuming that hindsight is 20/20 or even anything close to it.
Later on came the "official" version from Nelson; one of the Zen series (I forget which one, but you can scan through the Zens and figure it out pretty quickly). Then came the "J" front end, which I had considered as a Version 2 of the Mini-A, but was tied up in Version 751 of my unending quest for a satisfactory active crossover and I never got it done.
The "J" provides less open loop gain, simply by using a JFET instead of a MOSFET for the front end. It also has the extra "cool-factor" of coming from Nelson instead of yours truly.
Open loop gain is inherent in the design of the circuit. It involves the value of the front end load resistor, the bias current, the transconductance of the device and--in case that's not enough to drive you nuts--there's always the output stage, which in an Aleph also supplies voltage gain (as well as current gain). Assuming for the moment that you leave the output stage alone whether it's mine (the Mini-A) or Nelson's (the Zen or First Watt "J" Aleph), the front end is pretty much where you're going to determine the open loop gain. If you want to lower the open loop gain of a Mini-A, substitution of something like a 2SJ109, two 2SJ74s, or two 2SJ103s is a really good place to start, but keep in mind that the output stage bias is dependent on the voltage across the front end load resistance.
Grey
winslow said:
look at attached pic
this is one way of doing it - introducing some source degeneration ( local feedback) ........ how much without penalties , and will you have any benefits , dunno
try it - maybe you'll like it
winslow said:
yes I have ; but - you can easily made your mini with jfet input .
if you are desperate - you know how you can find me , but I told you how to made it cheap 😉 ........ anyway - my pcbs weren't made as GB batch , so they can't be cheap as GB ones .
winslow said:
that is question for which only you can give an answer ;
don't be surprised in six (or even less months ) if everyone start dismantling own F4 ........ to make new Papa's jewel .......
Attachments
I would never suggest such a thing! Those sound like some really cool amps you have planned -- I hope you will post some pics once they are done.
JJ
Trying to rein in a MOSFET's gain by adding degeneration at the Sources will work, but I don't know if any of the Mini-A or Zen boards have a space for the necessary resistors. This gets back to something I said above, the idea of trying to redo a Mini-A once you've already got PC boards in hand is going to be really difficult. Any of the likely JFETs have a different pinout from the IRF9610--or in this case, no place to put resistors.
My understanding was that the original poster already had boards in hand. Assuming that they were made from my original schematic or either of Nelson's versions, there weren't any degeneration resistors at all.
Grey
My understanding was that the original poster already had boards in hand. Assuming that they were made from my original schematic or either of Nelson's versions, there weren't any degeneration resistors at all.
Grey
GRollins said:
I have bad habit - when I'm answering to someone , somehow I presume that he has some brain left ........
Grey - don't be so serious .....
daughter boards , mini ones - are answer for that problem
edit:
same as you - I also hate to see (or conclude ) that some ppl are making all these gadgets - same as puzzle , without knowing what TF is going on ......
but - fortunately - thread starter isn't of ones who started new thread every 10 mins
Yes sir, I have a couple pairs of Brian's boards. I'm not sure of the origins of the boards in the amp the woman bought for me for my birthday present- have to wait and see when it comes as to what they are.
Maybe this is a bad idea...people don't seem to think it is a good idea. Was just thinking the real A-J had 15 dB less NFB, what could I do to lower it on what I have....if I could even do it at all with the boards I have.
So would the boards I have be suitable for the JFET front end conversion? I have BillWW's conversion schematic saved, so I would just put those parts in the same locations in my boards as he did in his?
Thanks guys...my background is more math and prior to that chemistry...not as knowledgeable of electronics as you guys. But I try.
Maybe this is a bad idea...people don't seem to think it is a good idea. Was just thinking the real A-J had 15 dB less NFB, what could I do to lower it on what I have....if I could even do it at all with the boards I have.
So would the boards I have be suitable for the JFET front end conversion? I have BillWW's conversion schematic saved, so I would just put those parts in the same locations in my boards as he did in his?
Thanks guys...my background is more math and prior to that chemistry...not as knowledgeable of electronics as you guys. But I try.
winslow said:
maybe I partially answer to this , we typed in same time ..........
anyway - look - is it of any help to you ..... it's anyway buried somewhere in hysteric Bab J thread ........
Thanks, I had just discovered that as you were typing.
Now, these 2SJ109 JFets are pretty tough to find aren't they? And the 176s need to be bought in bulk and matched? But I could use 2SJ74s since they can be bought prematched?
Now, these 2SJ109 JFets are pretty tough to find aren't they? And the 176s need to be bought in bulk and matched? But I could use 2SJ74s since they can be bought prematched?
winslow said:
74 , yes .
ask ruach ;
buy them ( and 170, too ) in quantity ......... and match your own ;
if you are infected with this drek , known also as Audio related DIY - they will be useful......... later 😉
Thanks.
You guys make this board. The support here is top notch and the best I've seen on home audio based boards.
If you ever need car audio help, I'd be more help there since that is where most of my audio back ground is at.
You guys make this board. The support here is top notch and the best I've seen on home audio based boards.
If you ever need car audio help, I'd be more help there since that is where most of my audio back ground is at.
MikeW said:
Hey, fella...get thee behind me Satan, and all that. The last thing I need is another project. Got 'em stacked up waist-high as it is. Besides:
1) If I were to do a zero feedback Aleph, I'd want to start from scratch. I'm not even sure it's possible/practical to do such a thing. I'd hoped to devote a brain cell to it today, but Wyatt was cranky and just generally disagreeable and I never had a moment of peace.
2) I don't see a tidal wave of posts demanding a zero feedback Aleph. Which isn't a problem, in that I know that I'm in a very, very tiny subset of the overall audio group because I seek low-to-no feedback. Didn't expect a lot of response. Didn't get a lot of response. Wasn't surprised.
Thanks for the offer, though.
And Happy New Year, while we're at it...
(How's your JC-3 coming along?)
Zen Mod said:
1) I have no brain left. According to some, I didn't start even start with a brain.
2) I use daughter boards, but am reluctant to recommend them because there's not much room on most of the Mini-A boards I've seen. I suppose people could use perf board, but I seem to be one of the few who actually cook up their own PCBs. Either way, you can still run into clearance problems.
3) Your last two points are clearly a shameless attempt to get me to comment on another thread. I won't fall for it.
winslow said:
1) I don't think the idea of a low-to-no feedback circuit (LTNF? I'm getting tired of writing that out--need a cute acronym, but I'm too tired to come up with something) is bad. I wouldn't have spent the better part of the last year developing a no feedback amp if I thought so. It's just that it isn't necessarily a trivial project when the base circuit is an Aleph. Tube amps are ideal for this sort of exploration because they're so stable. Solid state is far more prone to instability and other nuisance characteristics (the Aleph circuit is far better behaved in this sense than many others) that make life difficult for those who want to reduce feedback.
2) My official education is in geology and psychology, neither worth a plugged nickel when designing a circuit. Nobody is born knowing this stuff, it's just a question of trying something, then sitting back and thinking about what you've just done for a while so that the lesson sinks in (Zen Mod, you are hereby directed not to read that as commentary on other threads. Understand me?).
Feedback is full of things that are obscure and counterintuitive. Even bringing up the concept of a no-feedback circuit will get you in hot water in some circles. (Me? I'm fearless. I box with the bears at the zoo. Would have done a round or two with that tiger over in California, except the cops done the poor critter in. Oh well...)
None of this is meant to discourage you from trying...just don't expect amazing results the first time out. Feedback isn't a random thing that you can just arbitrarily pluck from thin air. You have to approach it as an integral part of the whole design. Set some goals, fiddle with the circuit, and see what you get. It's a great way to learn.
Grey
GRollins said:
hehe
1) I meant that thread starter certainly have some brain left .........
someone who is hangin' here from 2001 and 2003 certainly have not , and that just can't be questionable in any way ..........
3) no - it isn't attempt to that ; just tiny skaska ......... as a reminder how life can be un-complicated ..... and that somewhat , somehow can be fun to learn .... and teach ........
ya remember my own hysteria , when I was puzzled - how on earth eeeny weeny 7 legged critter can drive 2 or 3 massive gates ?
that was for massive
, no lessRegarding the current required to drive MOSFETs:
The no-feedback circuit I've been piddling with uses MOSFETs in the output stage. I played with different amounts of current in the driver stage, but to make a long story short the distortion dropped around .1% just by biasing the driver stage harder. Trivial, perhaps, when you intend to use feedback to cover your tracks, but crucial when you're not.
N.B.: This is in reference to an entirely different topology. The amount of drive required for an Aleph will be somewhat less in the sense that part of my current is consumed by the resistive load I use to bring down the gain and to "center" the DC offset. On the other hand, my driver stage is push-pull vs. the Aleph's single-ended drive, which makes for somewhat lower distortion. It's not an apples to apples comparison, so don't over generalize.
How much drive am I using, you ask?
100mA for two output pairs.
Clearly, this isn't feasible for JFETs, unless you intend to use the Lovoltech (aka Qspeed) power JFET, but there's no P-ch device, and you'd have to cascode it in order to protect it from the voltage, and since there's no P-ch, you'd have to turn the Aleph upside down and use P-ch outputs...uh, well...perhaps some other day.
Grey
The no-feedback circuit I've been piddling with uses MOSFETs in the output stage. I played with different amounts of current in the driver stage, but to make a long story short the distortion dropped around .1% just by biasing the driver stage harder. Trivial, perhaps, when you intend to use feedback to cover your tracks, but crucial when you're not.
N.B.: This is in reference to an entirely different topology. The amount of drive required for an Aleph will be somewhat less in the sense that part of my current is consumed by the resistive load I use to bring down the gain and to "center" the DC offset. On the other hand, my driver stage is push-pull vs. the Aleph's single-ended drive, which makes for somewhat lower distortion. It's not an apples to apples comparison, so don't over generalize.
How much drive am I using, you ask?
100mA for two output pairs.
Clearly, this isn't feasible for JFETs, unless you intend to use the Lovoltech (aka Qspeed) power JFET, but there's no P-ch device, and you'd have to cascode it in order to protect it from the voltage, and since there's no P-ch, you'd have to turn the Aleph upside down and use P-ch outputs...uh, well...perhaps some other day.
Grey
well - two old farts polutin' other's thread ........ 😉
imagine crazy mind ........
someone here (not me) , decided to make split choke loaded preamp ...
ion the end - that preamp is real bstrd ..... jfet ltp (nothing really new under the sun) , with mosfet outputs ..... loaded with split choke .
pretty same old story for toob boyz , but somehow odd for not toob boyz
anyway - what's really odd - current through output stage(s) - 150mA each side
do not try to connect that gadget with anyone here .......
imagine crazy mind ........
someone here (not me) , decided to make split choke loaded preamp ...
ion the end - that preamp is real bstrd ..... jfet ltp (nothing really new under the sun) , with mosfet outputs ..... loaded with split choke .
pretty same old story for toob boyz , but somehow odd for not toob boyz
anyway - what's really odd - current through output stage(s) - 150mA each side
do not try to connect that gadget with anyone here .......
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