Aha. Yes, clever little nugget of information, Nelson. Kind of a corollary to what I mentioned several posts back, that any asymmetry in the magnetic flux passing through such a "mirror-image" symmetrical board would not be rejected. A double-sided PCB using mainly surface-mount parts would give the best folded symmetry, since each side could be very nearly identical.
Fabrizio's design is very nice indeed!
Fabrizio's design is very nice indeed!
Well, a ground plane isn't a necessity in an application like this. I guess you could do a 3 layer board with the ground plane sandwiched in the middle. In fact, ground plane construction isn't necesarily of benefit at all for this circuit...
(hehe, this should stir things up)
(hehe, this should stir things up)
Symmetry
Wouldn't perfect symmetry require that all pairs
of transistors is totally identical in transfer?
To what degree can one acheive this?
Without matching? With matching?
Wouldn't perfect symmetry require that all pairs
of transistors is totally identical in transfer?
To what degree can one acheive this?
Without matching? With matching?
I have a very hard time visualizing what Nelson is talking about.
Group theory has never been my strong point and that maybe a reason.
Anyways this cartoon illustrates my thinking: the only way to null out the stray flux would be to have the transformer on the symmetry axis of the board. If one moves off axis all bets are off.
On the other hand flux lines are anisotropic so even that won't do it.
I am confused.
Edit:
this cartoon is really useless! Sorry
Group theory has never been my strong point and that maybe a reason.
Anyways this cartoon illustrates my thinking: the only way to null out the stray flux would be to have the transformer on the symmetry axis of the board. If one moves off axis all bets are off.
On the other hand flux lines are anisotropic so even that won't do it.
I am confused.
Edit:
this cartoon is really useless! Sorry
Attachments
Actually, it's not bad. Gets the job done...
Assuming the thick black vertical line through your cartoon board is the PCB axis of symmetry, then yes, you'd want the transformers centered on a plane perpendicular to the board, and which passes through this axis.
You can imagine two loops formed by some circuit traces... one a mirror image of the other, symmetrical around the centerline. At the centerline itself, there is no flux component perpendicular to the board, so there will be no net magnetic flux through the area of a loop here. But, toward the sides of the board, there will be some perpendicular component of magnetic flux from the trafo. You've got the direction "arrows" right, showing that flux going into the page on one side will be symmetrical (ideally) with the flux coming out of the page on the other side. Thus, the current induced in these two circuit loops will be equal and circulate in opposite directions: one clockwise, the other counter-clockwise (the currents are mirror images of each other). Since the ciruit is also mirrored, the net effect of these currents will appear at the speaker terminals as a common-mode signal, and be have no effect on the loudspeaker.
Now imagine if we fold that PCB down the middle and flatten it. If the PCB were infinitely thin, and our circuit traces were perfectly symmetric, then the loops formed by circuitry in each half of the circuit would be physically occupying the same space. In reality, they're separated by a thin bit of fibreglass, but it's pretty close. What happens here is, any magnetic flux through one loop would be exactly the same flux flowing through the other loop, and will induce exactly equal effects in each half of the circuit, again inducing only common-mode signals which get rejected at the speaker. What's special about folding the circuit is that now it doesn't matter where that transformer (or any other magnetic field source) is. The circuit loops in each half of the circuit are so close together that they will always have nearly exactly the same flux through them, inducing mirror-image currents, and producing common-mode effects only.
Assuming the thick black vertical line through your cartoon board is the PCB axis of symmetry, then yes, you'd want the transformers centered on a plane perpendicular to the board, and which passes through this axis.
You can imagine two loops formed by some circuit traces... one a mirror image of the other, symmetrical around the centerline. At the centerline itself, there is no flux component perpendicular to the board, so there will be no net magnetic flux through the area of a loop here. But, toward the sides of the board, there will be some perpendicular component of magnetic flux from the trafo. You've got the direction "arrows" right, showing that flux going into the page on one side will be symmetrical (ideally) with the flux coming out of the page on the other side. Thus, the current induced in these two circuit loops will be equal and circulate in opposite directions: one clockwise, the other counter-clockwise (the currents are mirror images of each other). Since the ciruit is also mirrored, the net effect of these currents will appear at the speaker terminals as a common-mode signal, and be have no effect on the loudspeaker.
Now imagine if we fold that PCB down the middle and flatten it. If the PCB were infinitely thin, and our circuit traces were perfectly symmetric, then the loops formed by circuitry in each half of the circuit would be physically occupying the same space. In reality, they're separated by a thin bit of fibreglass, but it's pretty close. What happens here is, any magnetic flux through one loop would be exactly the same flux flowing through the other loop, and will induce exactly equal effects in each half of the circuit, again inducing only common-mode signals which get rejected at the speaker. What's special about folding the circuit is that now it doesn't matter where that transformer (or any other magnetic field source) is. The circuit loops in each half of the circuit are so close together that they will always have nearly exactly the same flux through them, inducing mirror-image currents, and producing common-mode effects only.
Thank you for your advices Nelson, Chad & Grataku.
🙂
It's interesting what you said about the magnetic field interaction, especially what Grataku exposed and Chad commented.
Question: if I put the PCB perpendicular to the trafo symmetric axis so that both have their centre on the same axis, are the components and traces in a good and specular situation, lookin from a magnetic point of view?
In my view, I think that this situation should be the best possible (except for a different supply case), is not?
Thank you again!
Fabrizio
🙂
It's interesting what you said about the magnetic field interaction, especially what Grataku exposed and Chad commented.
Question: if I put the PCB perpendicular to the trafo symmetric axis so that both have their centre on the same axis, are the components and traces in a good and specular situation, lookin from a magnetic point of view?
In my view, I think that this situation should be the best possible (except for a different supply case), is not?
Thank you again!
Fabrizio
Lazy *** Question...
This threads has gone over 1000 posts so far and that has gone past my attention and retention span by now - shop, girlfriend etc, etc.
Anyway, I spend some of my after hours listening here at my triangular corner placed computer workstation, with multiple shelves above the PC monitor containing a televish, veeseearrr, cd player of the week, and a 1964 Panasonic all tube Am/Fm reciever (the matching MFB speakers are in the garage) driving a pair of quite ok Boston 6 1/2" two ways mounted on springs on the benchtop so I am in nearfield and don't usually run much audio power at all (if I really want to crank it, I think I've got about 10W+10W).
So my thoughts are turning towards building a point to point low power (5 to 10W) version of the Aleph-X for this purpose.
So, can somebody point me to the appropriate current SOTA circuit and recomendations for appropriate mods to run nicely at low supply voltages/low power ?.
I have spent plenty of listening hours on Aleph '0' amps in the past and I liked what I heard - a baby version tickles my interest.
Thanks in advance, Eric.
This threads has gone over 1000 posts so far and that has gone past my attention and retention span by now - shop, girlfriend etc, etc.
Anyway, I spend some of my after hours listening here at my triangular corner placed computer workstation, with multiple shelves above the PC monitor containing a televish, veeseearrr, cd player of the week, and a 1964 Panasonic all tube Am/Fm reciever (the matching MFB speakers are in the garage) driving a pair of quite ok Boston 6 1/2" two ways mounted on springs on the benchtop so I am in nearfield and don't usually run much audio power at all (if I really want to crank it, I think I've got about 10W+10W).
So my thoughts are turning towards building a point to point low power (5 to 10W) version of the Aleph-X for this purpose.
So, can somebody point me to the appropriate current SOTA circuit and recomendations for appropriate mods to run nicely at low supply voltages/low power ?.
I have spent plenty of listening hours on Aleph '0' amps in the past and I liked what I heard - a baby version tickles my interest.
Thanks in advance, Eric.
shielding
I know that iron can block a magnetic field. A 1/8" sheet of ferrous metal between the ps and the pcb should be effective. What is the downside to this approach?
John Inlow
I know that iron can block a magnetic field. A 1/8" sheet of ferrous metal between the ps and the pcb should be effective. What is the downside to this approach?
John Inlow
After sleeping on it I think I understand it. It makes you wonder how could it be done in the past without X! 😉
Why Use Sheild?
to place a circuit behind a shielding
or distance it from a magnetic field?
That would take the satisfaction out of your acheivment
in solving this serious problem.
The true fighters, of course likes to create problems.
Than they can figure out 😕 how to solve them.
😉 that is the TRUE spirit 😉
What is the funcarpenter said:
to place a circuit behind a shieldingor distance it from a magnetic field?
That would take the satisfaction out of your acheivment
in solving this serious problem.
The true fighters, of course likes to create problems.
Than they can figure out 😕 how to solve them.
😉 that is the TRUE spirit 😉
childhood experiment......
When I was a child in school, I read of an experiment that involved the use of a threaded needle, a pocket knife and a magnet. The idea was to suspend the threaded needle into mid air with the use of the magnet over the top of the needle; the needle's thread was taped to a counter top or desk, or what have you. Once the needle was suspended, one would slice through the magnetic field with the pocket knife. You guessed it, the needle would fall back to the counter top. The pocket knife doesn't become a magnet, or the needle would remain suspended. Also, this is a trick used to create a wrist watch that is unaffected by magnetism.
John Inlow
When I was a child in school, I read of an experiment that involved the use of a threaded needle, a pocket knife and a magnet. The idea was to suspend the threaded needle into mid air with the use of the magnet over the top of the needle; the needle's thread was taped to a counter top or desk, or what have you. Once the needle was suspended, one would slice through the magnetic field with the pocket knife. You guessed it, the needle would fall back to the counter top. The pocket knife doesn't become a magnet, or the needle would remain suspended. Also, this is a trick used to create a wrist watch that is unaffected by magnetism.
John Inlow
Re: Lazy *** Question...
The current schematic is on page 23 posted by rtirion.
mrfeedback said:
The current schematic is on page 23 posted by rtirion.
I worked a bit more on the schematic, and decided to include 8 output devices on the pcb. It makes it a bit big, but it doesn't really matter, since I am just using it for prototype pcbs. Here is a pic.
Is this a good way to wire up the output stages? I don't want to mount the mosfets to the main board, but instead attach wires to the board. I was going to use higher current terminal blocks. Would these be alright?
I am still working on the output circuit, and I think that I have the placement the way I want to, and I just need to start looking back over it to see if I got the circuit tied together correctly.
Any opinions on this? How much power do you think each channel could run with 8 devices? I would like to aim for 100W into 4 ohms if possible
--
Brian
Is this a good way to wire up the output stages? I don't want to mount the mosfets to the main board, but instead attach wires to the board. I was going to use higher current terminal blocks. Would these be alright?
I am still working on the output circuit, and I think that I have the placement the way I want to, and I just need to start looking back over it to see if I got the circuit tied together correctly.
Any opinions on this? How much power do you think each channel could run with 8 devices? I would like to aim for 100W into 4 ohms if possible
--
Brian
Attachments
It looks good. Even if you want to use wires, why not spread the output devices for the whole length of the board. This leaves the option to somebody who wants to mount them directly.
Brian,
it would be better if you tried to keep the source resistor further away from the mosfet. It's good to finally see big traces.
it would be better if you tried to keep the source resistor further away from the mosfet. It's good to finally see big traces.
I will space them out some more and isolate the source resistor a bit more. I initially had the groups of resistors orientated lower, and I just changed them so that I could move it over, but forgot to do it.
Is 3W enough for the output resistors attached to the mosfets? I am using 5W for my aleph 2...
--
Brian
Is 3W enough for the output resistors attached to the mosfets? I am using 5W for my aleph 2...
--
Brian