But then why is a higher current - lower Z impedance path sometimes preferred
even on a VFA ?
Conversely , I use a higher Z - lower current split path on my ND.
The small signal stages , and even the VAS is low current.
Not the "burning hot" typical CFA.
OS
Lower impedance gives less noise and more authority. For CFA's lower impedance is more ideal, but one must find a compromise betveen performance and heat
Why would the feedback node of the CFA necessitate high heat, that would seem to be an over simplification of the two different feedback methods between CFA and VFA?
In CFA you get better slew with lower impedance, but there's a practical limit to how far you can go. Kindhorn, I have built them all and listened to them, my findings are totally independent of OS reached similar findings. I would like a fusion of qualities, base-end from leach paired with the soft and liquid mids and highs from the diamond input CFA. That would be an awsome amplifier.
I said some time ago to make a tri-amp, but no one seemed to share that sentiment. Making a cross-over electronically in front and combine them to achieve the qualities you summed up. I wish some one would start a thread and proceed to make it a reality Soon. 😀
If it were a computer system that needed some software I would do it in a heart beat. But my skill level is like 25 cents compared to most others. OS and Bob Cordell are 100 dollar bills comparably to my skill sets in amp design. More like a Cleveland ($1000) compared to a George Washington Quarter, not dollar bill.
Krisfr,
My plan is just that, but a bi-amp system rather than a tri-amp. The only real difference is that you need a third amplifier section and an additional xo. I'm working with some others who will do the active dsp network design, I am like you not capable of pulling that off. But I will add if you are only trying to make a simple active xo it isn't that hard to do a simple opamp based Saleen Key network in whatever order you want, 2nd, 3rd or 4th. I have some simple boards that can do it for a 4th order xo that are not very big and rather simple in design. I just want to go beyond that simple implementation and have other corrections that aren't easy to do in an analog circuit.
I bought the little xo boards on Ebay for really cheap. All it takes is a bunch of resistors and some inexpensive 5532 opamps to make it work.
My plan is just that, but a bi-amp system rather than a tri-amp. The only real difference is that you need a third amplifier section and an additional xo. I'm working with some others who will do the active dsp network design, I am like you not capable of pulling that off. But I will add if you are only trying to make a simple active xo it isn't that hard to do a simple opamp based Saleen Key network in whatever order you want, 2nd, 3rd or 4th. I have some simple boards that can do it for a 4th order xo that are not very big and rather simple in design. I just want to go beyond that simple implementation and have other corrections that aren't easy to do in an analog circuit.
I bought the little xo boards on Ebay for really cheap. All it takes is a bunch of resistors and some inexpensive 5532 opamps to make it work.
or use a minidsp.
miniDSP 2x8 kit | miniDSP
miniDSP 2x8/8x8 Box | miniDSP
I understand wanting to make the bits when bringing a product to market but for one off home use this thing works great. Or just a resellable stop gap until your homemade crossover is ready.
miniDSP 2x8 kit | miniDSP
miniDSP 2x8/8x8 Box | miniDSP
I understand wanting to make the bits when bringing a product to market but for one off home use this thing works great. Or just a resellable stop gap until your homemade crossover is ready.
The minidsp does crossover as well as some DSP. My main system uses two pair of amps. The buffer/preamp drives one pair of amps directly. Passive crossover to mid bass and planer tweeter. The preamp also sends signal to the minidsp. This drives a second pair of amps for the bass. Two 15"woofers per side. The speakers are open baffles so there is a lot of power required to make good bass.
I also have a party system.....Active three way using another 2x8 minidsp 2" compression driver.....16" midbass in a ported box and a pair of horn loaded lab 15s for sub woofers. Neighbors watch out......
I also have a party system.....Active three way using another 2x8 minidsp 2" compression driver.....16" midbass in a ported box and a pair of horn loaded lab 15s for sub woofers. Neighbors watch out......
The current (low Z) of the output stage is the direct player in a CFA's feedback ,
not a fixed current (CCS) gated by that same feedback signal (VFA).
The heat is the byproduct of taking this "shortcut". My "split" path
on the ND is REAL cool , not much more than a lower Z "aggressive" VFA
feedback.
Nice thing , it still retains CFA properties (300V/us slew).
Actually , I "stole" this from a Russian member that came to the forum
with a 40 device "superamp" design. (there , I came clean).
OS
OS,
So with your split path feedback circuit does that contain a capacitor in the feedback or is it still just resistors as in a CFA?
So with your split path feedback circuit does that contain a capacitor in the feedback or is it still just resistors as in a CFA?
About impedance of the feedback, its a matter of the influence of base (VFA) parasitic capacitances or emitter (CFA) ones. The impedance of the feedback has to be low in such a way that this low pass filter does not have a phase influence on the resulting feedback signal at HF.
On a practical point of view, the low impedance of the emitter impedance oblige anyway a low impedance serial resistance in the feedback bridge. It has a positive influence too about EMI/RFI rejection in the feedback path.
It is easy to make simulations to understand those behaviors of both topologies.
On my side, I believe the main difference depends on the "current on demand" behavior of the CFA. It is "expansive" while VFAs are "compressive", so better for transients and fast edge (slew rate) signals. VFA is better on a distortion point of view and PSRR at low frequencies.
On a practical point of view, the low impedance of the emitter impedance oblige anyway a low impedance serial resistance in the feedback bridge. It has a positive influence too about EMI/RFI rejection in the feedback path.
It is easy to make simulations to understand those behaviors of both topologies.
On my side, I believe the main difference depends on the "current on demand" behavior of the CFA. It is "expansive" while VFAs are "compressive", so better for transients and fast edge (slew rate) signals. VFA is better on a distortion point of view and PSRR at low frequencies.
On my side , I don't have a VFA that comes close ... except the wolverine
at 20K.
Only a couple VFA's that exceed the psrr .
(below 1/2).
I have NO VFA or CFA that goes sub ppm from 500hz to 5Khz (like the ND).
Some serious cancellation of distortion going on here !
OS
Attachments
Ohh ND, so you learned some Housekeeping tricks, still The VAS driven cascode has super gainn, so you end up with a greatdeal of feedback and Very very Good data, apart from The VAS, this is very close to my latest CFA, still the base performance and drive of the music will be better in the Leach types.
You really need to try the IPS, I showed you (and you improved with a driven casode) that one is the fusion of good's
The gain of one ops I published on the Cordel thread, also deserves some focus. A novel way of making a good performing OPS, a real goodie for the non feed back voltage stage brigade.
You really need to try the IPS, I showed you (and you improved with a driven casode) that one is the fusion of good's
The gain of one ops I published on the Cordel thread, also deserves some focus. A novel way of making a good performing OPS, a real goodie for the non feed back voltage stage brigade.
Yours is next , Miib.
I'll soon get bored with the simple perfection of the "ND". 🙄
If I used the super-pair cascode VAS with a leach input stage , would I not have
A true "leach ND". The only difference would be the feedback method ?
PS - a spare ND board will be "hyper tuned" (with an OPS) to put on
RN marsh's AP analyzer - we'll see if it beats the blameless.
OS
I'll soon get bored with the simple perfection of the "ND". 🙄
If I used the super-pair cascode VAS with a leach input stage , would I not have
A true "leach ND". The only difference would be the feedback method ?
PS - a spare ND board will be "hyper tuned" (with an OPS) to put on
RN marsh's AP analyzer - we'll see if it beats the blameless.
OS
But you cheated, using CCs and cascoded Darlingtons for the VAS 🙂
As the PSRR of a CFA is better at HF than a VFA, and you addressed the PSRR issue at low frequencies the way it has to be (rail side), this is, on my point of view, one of the best amps i have seen on all the aspects.
I will try to do a version of it next month, for my own use, damping the input diamond stage, and (if it helps), adding a base stopper to the base of the second Darlington of the VAS, and using a MOS power stage. Will try to avoid this "2ways" feedback path for the beauty of the principle ;-)
I have this buffer http://www.diyaudio.com/forums/anal...s-simple-error-correction-superbuffer-28.html i want to use this in combination with a volume potentiometer .
I wonder witch IPS is more suitable for this.
Opinions please.
I wonder witch IPS is more suitable for this.
Opinions please.
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