I am not bothering with a regulated supply on the Aleph-X. The reason is simple: the Aleph-X draws a constant current from the supply at all times, so there is practically nothing to regulate. A CRC filter will easily take power supply ripple levels down to the 50mV range or less. After the application of PSRR, which is pretty good in the Aleph-X, thanks to it's balanced topology, this miniscule ripple should have basically nil effect on the circuit.
A second point to consider is to save the complexity and cost of a regulated supply and apply that gain elsewhere, such as in upgraded components. Besides, one of the cornerstones of the Pass designs is their simplicity, and I think it is counter to this philosophy to add complexity where it isn't needed.
That said, I see no technical reason against the use of an actively regulated supply. You may be up against the law of diminishing returns, but if you're looking to extract every last ounce of performace out of your circuit, then by all means, go for it!
A second point to consider is to save the complexity and cost of a regulated supply and apply that gain elsewhere, such as in upgraded components. Besides, one of the cornerstones of the Pass designs is their simplicity, and I think it is counter to this philosophy to add complexity where it isn't needed.
That said, I see no technical reason against the use of an actively regulated supply. You may be up against the law of diminishing returns, but if you're looking to extract every last ounce of performace out of your circuit, then by all means, go for it!
Thanks for your suggestion, Peter and hifiZen.
I think I'll do without regulated PS first, but leave rooms to add the regulators at a later time. I built two pairs of Zen V4, and very impress with the sound from such a simple circuit. The Aleph-X will comare head to head with a Krell FPB-300. Other than both are Class A, they are very different amp. I want to see how good a DIY amp can be, with just a fraction of cost.
Another question, would you guys put a cap (as big as physically possible) right next to each output & CS mosfets? I have someone said that is the best, which gives quick current discharge when it's needed. I love to see someone's layout and wiring.
niner
I think I'll do without regulated PS first, but leave rooms to add the regulators at a later time. I built two pairs of Zen V4, and very impress with the sound from such a simple circuit. The Aleph-X will comare head to head with a Krell FPB-300. Other than both are Class A, they are very different amp. I want to see how good a DIY amp can be, with just a fraction of cost.
Another question, would you guys put a cap (as big as physically possible) right next to each output & CS mosfets? I have someone said that is the best, which gives quick current discharge when it's needed. I love to see someone's layout and wiring.
niner
Did you see this?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5980
That was my intention too. Caps as close to output devices as possible. What else can be better?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5980That was my intention too. Caps as close to output devices as possible. What else can be better?
For what it's worth, I ordered in a bunch of the Panasonic FC caps from Digikey and will be putting one near each output device. Whether it will help or not, I can't say, but I can't see a mechanism where it will hurt.
The current source I used is the same one that Nelson uses in the Alephs. This circuit was derived directly from the Mini-A, which in turn was nothing more than a cut-down Aleph with a few parts recalculated. By all means, toss in a more complicated current source if you like, but I'm not sure whether it will be audible in an amplifier. Basically, I'd think that the primary difference would be residual noise, and these amps just aren't all that noisy.
Now a preamp, on the other hand, might be able to show off the quietness of a good current source...
Grey
The current source I used is the same one that Nelson uses in the Alephs. This circuit was derived directly from the Mini-A, which in turn was nothing more than a cut-down Aleph with a few parts recalculated. By all means, toss in a more complicated current source if you like, but I'm not sure whether it will be audible in an amplifier. Basically, I'd think that the primary difference would be residual noise, and these amps just aren't all that noisy.
Now a preamp, on the other hand, might be able to show off the quietness of a good current source...
Grey
Well, its together and adjusted.
I ended up with about 15 mV DC offset Speaker + and -.
Any one care too explain the relavence of the abs. DC offset between speaker + or - and gnd. (dumb newbe question).
I have not had a chance to listen to the little guy yet,
or do I have anything to compare it too because I don't think it has enough wattage behind it to drive my power hungry Martin Logans.
Well, off to the wood shop with Grey to make some book shelf speakers.
I ended up with about 15 mV DC offset Speaker + and -.
Any one care too explain the relavence of the abs. DC offset between speaker + or - and gnd. (dumb newbe question).
I have not had a chance to listen to the little guy yet,
or do I have anything to compare it too because I don't think it has enough wattage behind it to drive my power hungry Martin Logans.
Well, off to the wood shop with Grey to make some book shelf speakers.
Attachments
Great work, guys.
Now here's a little layout tip for lowest noise in X
amps:
Make all the parts location and wiring identical in
layout AND location between the two halves of the
circuit. That way all the noise pickup is identical between
the two halves of the circuit.
For example, on the XA200 the outputs of the two halves
are found next to each other on both sides of the amplifier,
and the traces going to and fro are identical, one on the
top, the other on the bottom of the board.
Now here's a little layout tip for lowest noise in X
amps:
Make all the parts location and wiring identical in
layout AND location between the two halves of the
circuit. That way all the noise pickup is identical between
the two halves of the circuit.
For example, on the XA200 the outputs of the two halves
are found next to each other on both sides of the amplifier,
and the traces going to and fro are identical, one on the
top, the other on the bottom of the board.
quote:
--------------------------------------------------------------------------------
Originally posted by nobody special
I think Grey was talking about the absolute DC voltage between either + speaker and ground, or - speaker and ground, which is set by adjusting the current source on the front end, and should be as close to 0V as is possible. The reason you set the offset relative to ground is to keep as much voltage swing as possible.
--------------------------------------------------------------------------------
Now when you mentioned it... I was planning on increasing the current through the input differencial to about 30mA and effectively I choose 300ohm drain resistors (for 5V drop). If I'm doing that, will I have a trouble with obtaining 0V absolute offset? I didn't expect that changing the front end current changes offset. If it does, how it works then?
I asked it before but since Mr. Pass is here maybe a better answer could be obtained. If the current changes absolute offset, how it happens?
__________________
--------------------------------------------------------------------------------
Originally posted by nobody special
I think Grey was talking about the absolute DC voltage between either + speaker and ground, or - speaker and ground, which is set by adjusting the current source on the front end, and should be as close to 0V as is possible. The reason you set the offset relative to ground is to keep as much voltage swing as possible.
--------------------------------------------------------------------------------
Now when you mentioned it... I was planning on increasing the current through the input differencial to about 30mA and effectively I choose 300ohm drain resistors (for 5V drop). If I'm doing that, will I have a trouble with obtaining 0V absolute offset? I didn't expect that changing the front end current changes offset. If it does, how it works then?
I asked it before but since Mr. Pass is here maybe a better answer could be obtained. If the current changes absolute offset, how it happens?
__________________
You always end up having to adjust either the bias
current going into the diff pair or the load resistors
off their Drains, no matter what.
If you are capacitively coupled at the input, or if the
DC source impedance is the same for both inputs from
the source, then a bit of absolute DC offset is OK. If the
value of DC gets large, it cuts into the maximum swing.
The same is not true if you have DC coupled inputs and
the DC source impedances are not the same, in which
case absolute DC gets translated into differential DC
and your speaker will start seeing it.
current going into the diff pair or the load resistors
off their Drains, no matter what.
If you are capacitively coupled at the input, or if the
DC source impedance is the same for both inputs from
the source, then a bit of absolute DC offset is OK. If the
value of DC gets large, it cuts into the maximum swing.
The same is not true if you have DC coupled inputs and
the DC source impedances are not the same, in which
case absolute DC gets translated into differential DC
and your speaker will start seeing it.
Hey wessol.....
I'm dying here, (ok, I'm just super anxious) does the pcb work properly? I'm thinking about having a batch of these pcbs custom made with all the bells and whistles. Your pic seems to indicate that you are using the latest pcb artwork. Is this so? Did you have to make any alterations? A small quantity batch of pcbs would cost around eighty dollars a pair. If the quantity were increased to 100 pieces, the cost would drop dramatically; a forty dollar board is reduced to less than four! Perhaps others would care to join in the purchase? But, without your input, I'm reluctunt to spend the dough.
John Inlow
I'm dying here, (ok, I'm just super anxious) does the pcb work properly? I'm thinking about having a batch of these pcbs custom made with all the bells and whistles. Your pic seems to indicate that you are using the latest pcb artwork. Is this so? Did you have to make any alterations? A small quantity batch of pcbs would cost around eighty dollars a pair. If the quantity were increased to 100 pieces, the cost would drop dramatically; a forty dollar board is reduced to less than four! Perhaps others would care to join in the purchase? But, without your input, I'm reluctunt to spend the dough.
John Inlow
Pass DIY Addict
Joined 2000
Paid Member
Aleph X
Let's see now.....
1. The schematics I have seen are not what I would called fully fleshed out designs. By that I mean fully tested and characterized for stablity, bandwidth, DC stability, ect....
2. The design is patented and very current technology by one of the the most talented designers around. Selling PCBs would be considered a violation of patents for a commercial puposes. Many would considerer it gross ingratitude for Mr. Pass's contributions to this forum, legal isssues aside. I believe the DIY projects from Passlabs are documented as such, and that this is not one of those projects. I don't remember Mr. Pass posting schematics for this one.
3. I don't know who I would trust to design a PCB in light of these considerations.
4. Maybe someone can borrow one of the new Passlabs active crossovers, reverse engineer it, and publish the documentation for all. After all, intellectual property seems to be such an outmoded concept here.
I am very curious to hear other opinions on this, including the "ME TOO!' freeloaders. I would also like to hear Mr. Pass and Mr. Rollins weigh in on this. I probably know enough to design a PCB for this but wouldn't even think of doing it.
Fred Dieckmann
Let's see now.....
1. The schematics I have seen are not what I would called fully fleshed out designs. By that I mean fully tested and characterized for stablity, bandwidth, DC stability, ect....
2. The design is patented and very current technology by one of the the most talented designers around. Selling PCBs would be considered a violation of patents for a commercial puposes. Many would considerer it gross ingratitude for Mr. Pass's contributions to this forum, legal isssues aside. I believe the DIY projects from Passlabs are documented as such, and that this is not one of those projects. I don't remember Mr. Pass posting schematics for this one.
3. I don't know who I would trust to design a PCB in light of these considerations.
4. Maybe someone can borrow one of the new Passlabs active crossovers, reverse engineer it, and publish the documentation for all. After all, intellectual property seems to be such an outmoded concept here.
I am very curious to hear other opinions on this, including the "ME TOO!' freeloaders. I would also like to hear Mr. Pass and Mr. Rollins weigh in on this. I probably know enough to design a PCB for this but wouldn't even think of doing it.
Fred Dieckmann