Re: Why the demanding PS?
The reason for "so much ripple" is that the bias current at idle is very high for Class A amps. The bias current at idle for the Class AB AKSA is much lower.
If you are messing around with PSUD2 you know that if you increase the current produced by the power supply, the ripple for a given Cap value, will increase.
To reduce the ripple at the high bias current of the Pass designs large power supply caps are needed. Nothing is wrong with that, it's just the way it is.
Later BZ
nowater said:
The reason for "so much ripple" is that the bias current at idle is very high for Class A amps. The bias current at idle for the Class AB AKSA is much lower.
If you are messing around with PSUD2 you know that if you increase the current produced by the power supply, the ripple for a given Cap value, will increase.
To reduce the ripple at the high bias current of the Pass designs large power supply caps are needed. Nothing is wrong with that, it's just the way it is.
Later BZ
Dont' forget that capacitor charge is given by: Q=CV, and that the energy stored is equal to the charge muliplied by the potential (E=QV). The stored energy is therefore E=CV^2.
Thus, at lower voltages, we need a much larger capacitance value to achieve the same level of energy storage. 100,000uF may seem like a big value, but at 15V, it's not really that much compared to something you might see in a 50W 'conventional' amplifier like the AKSA. Think about the typical PSU cap used in a 50W tube amp...
nowater:
The PSU doesn't need to be too fancy. The Aleph-X doesn't care much about it's PSU, since it has good PSRR and if the active current sources are set to 50% accurately, then no AC signal currents will flow through the power supply at all! This pretty much eliminates the need for fancy capacitor types, though I've included a small footprint on the PCB for a little 47-220uF panny FC or BG. It's mostly there to help with RF supression and to lower the impedance after the power comes in through the lead wires / connectors etc. The main power supply caps should be selected for long life and high ripple current.
I recommend a single pi stage only, it seems to be overboard to go with a two-stage pi filter, when you can easily achieve less than 5mV ripple with a single pi filter. I've tested the amp with a C-only filter, and it's happy running with 430mV ripple, producing only a quiet hum out of the woofer of my 89dB speakers. I had to get quite close to hear it... At 105dB, you'll probably want to cut the hum right out, so a CRC or CLC is definitely what you'll need. Be mindful of magnetic flux from power inductors though. I also recommend you use the LM329 voltage reference with a ZVP3310 for Q6.
You can simulate half the PSU. See the attached PSUD file of my CLC power supply, using a Hammond 156B inductor. I'm actually going to build my final amps using CRC instead, but this is a good starting point...
Thus, at lower voltages, we need a much larger capacitance value to achieve the same level of energy storage. 100,000uF may seem like a big value, but at 15V, it's not really that much compared to something you might see in a 50W 'conventional' amplifier like the AKSA. Think about the typical PSU cap used in a 50W tube amp...
nowater:
The PSU doesn't need to be too fancy. The Aleph-X doesn't care much about it's PSU, since it has good PSRR and if the active current sources are set to 50% accurately, then no AC signal currents will flow through the power supply at all! This pretty much eliminates the need for fancy capacitor types, though I've included a small footprint on the PCB for a little 47-220uF panny FC or BG. It's mostly there to help with RF supression and to lower the impedance after the power comes in through the lead wires / connectors etc. The main power supply caps should be selected for long life and high ripple current.
I recommend a single pi stage only, it seems to be overboard to go with a two-stage pi filter, when you can easily achieve less than 5mV ripple with a single pi filter. I've tested the amp with a C-only filter, and it's happy running with 430mV ripple, producing only a quiet hum out of the woofer of my 89dB speakers. I had to get quite close to hear it... At 105dB, you'll probably want to cut the hum right out, so a CRC or CLC is definitely what you'll need. Be mindful of magnetic flux from power inductors though. I also recommend you use the LM329 voltage reference with a ZVP3310 for Q6.
You can simulate half the PSU. See the attached PSUD file of my CLC power supply, using a Hammond 156B inductor. I'm actually going to build my final amps using CRC instead, but this is a good starting point...
A2 transformer
Hi, I was wondering if my 35V secondery transformer could be some how used in a high power AX. The problem with AX circuit is there are too many options out there and considering the fact that, It is in fact a blessing for some pros, But us newbes are in fact left in the dust scraching our head or maybe I should just speak for my self.
If any body could help me decied what to do If I want to built an high power AX using CRCRC layout at the PS with the same transformer. How do I calculate the R in the PS if I want to shed a few volts. My speaker impeadence is 4 ohms.
Please help
Regards.
SAAD//
Hi, I was wondering if my 35V secondery transformer could be some how used in a high power AX. The problem with AX circuit is there are too many options out there and considering the fact that, It is in fact a blessing for some pros, But us newbes are in fact left in the dust scraching our head or maybe I should just speak for my self.
If any body could help me decied what to do If I want to built an high power AX using CRCRC layout at the PS with the same transformer. How do I calculate the R in the PS if I want to shed a few volts. My speaker impeadence is 4 ohms.
Please help
Regards.
SAAD//
You should start with deciding how much power you want from the amp. Let's say you want 40W per channel. Since your voltage-limited max power works out to (2*VMax/sqrt(2))^2/Impedance, you really only need ±9V into the speaker. To give yourself some headroom, you might say you want ±10V or ±12V rails.
You say your trafo is 35V on the secondary, is that 35V single, or 35V in series, or 35V in parallel? If it's 35V in series, you are in luck: this is just about the right voltage. Allowing .7V for (Schottky) rectifier drop, you would get about 11.7V rails with a C filter. If it's 35V in parallel or single secondary, this is too high. You need a different transformer for this application.
Supposing you want a CRC filter, you need to decide how much current you require. Using your designed idle current, multiply by R to get the allowable voltage drop in the filter. Then fiddle with R and C until you get good attenuation at the ripple frequency of 120Hz.
You say your trafo is 35V on the secondary, is that 35V single, or 35V in series, or 35V in parallel? If it's 35V in series, you are in luck: this is just about the right voltage. Allowing .7V for (Schottky) rectifier drop, you would get about 11.7V rails with a C filter. If it's 35V in parallel or single secondary, this is too high. You need a different transformer for this application.
Supposing you want a CRC filter, you need to decide how much current you require. Using your designed idle current, multiply by R to get the allowable voltage drop in the filter. Then fiddle with R and C until you get good attenuation at the ripple frequency of 120Hz.
It's a 1000va 35V+35V transformer. I have two of these and thinking about making two mono blocks. I got the chasis done and waiting for the AX boards. These are hifizen/gratacu boards. Can you please let me know what are mods needed for my amps to put out 200wpc; like how many IRFP240 am I going to need per channel. I have this schematic but not sure of the power rating at 4 ohms. Please feel free to comment or suggest on it to make it work for my amp.
Thank you.
SAAD//
Thank you.
SAAD//
There are a few threads you need to look at for this information. For calculating power you want this thread by Wuffwaff. For more general information on a high powered Aleph-X you need to check one of the "High Powered Aleph-X threads. Here's one of them, and here's the original.SI said:It's a 1000va 35V+35V transformer. I have two of these and thinking about making two mono blocks. I got the chasis done and waiting for the AX boards. These are hifizen/gratacu boards. Can you please let me know what are mods needed for my amps to put out 200wpc; like how many IRFP240 am I going to need per channel. I have this schematic but not sure of the power rating at 4 ohms. Please feel free to comment or suggest on it to make it work for my amp.
Thank you.
SAAD//
Yes it would be a shame. So, Do you think I can use these transformers, without loosing 200 watts at the filter ?
JWB, I think I saw some where that you had some issues with your AX, Have you had a chance to hammer
out your problems ? Does yours looks any thing like the scematic I posted(I found it the forum) ? Is it possible to have an AX that is stable at 8-2 ohm load, in other words the output remains the same or gets higher with lower impedance ?
Guys what do you think of these encloser ? Are big enough for high power AX ?
Regards
SAAD//
JWB, I think I saw some where that you had some issues with your AX, Have you had a chance to hammer
out your problems ? Does yours looks any thing like the scematic I posted(I found it the forum) ? Is it possible to have an AX that is stable at 8-2 ohm load, in other words the output remains the same or gets higher with lower impedance ?Guys what do you think of these encloser ? Are big enough for high power AX ?
Regards
SAAD//
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SI said:
Impressive cases you made.
What is the estimated heat dissipation of the heatsinks you have?
If you want to use a rail voltage of 28V you’ll loose a lot of power in your CRCRC filter because you will need to bias the amp at about 10A to give you 200W at 4 ohm.
You will need at least 16 mosfets and preferably 20 to keep the dissipation per fet under 30W.
Each amp will consume 560W and with heatsinks rated at 0.07°C/W each amp will have a temperature of 62°C at 23°C ambient. With 0.14°C/W heatsink temp. will be more then 100°C
If you really want that high power at 4ohm I recommend lowering the rail voltage and this means buying other toroids. Or nice big Papst fans.
Did you look at the AXE spreadsheet?
Re: Big is Good
I have very demanding set of speakers. These are my pride and joy(old pair of AR-9). You can see part of them in the picture.
I'm using the scare tactic (building the amp in front of them) to see if I can tame them.
About the tow motor : I might hit you up on the offer.
Regards.
SAAD//
SGregory said:I'm glad I not the only one that likes big amps.
I'll have towmotor for sale soon once I get mine into position.
Scott
I have very demanding set of speakers. These are my pride and joy(old pair of AR-9). You can see part of them in the picture.
I'm using the scare tactic (building the amp in front of them) to see if I can tame them.
About the tow motor : I might hit you up on the offer.
Regards.
SAAD//
The one and only spreadsheet can be found in the AlephX wiki:
http://www.diyaudio.com/wiki/index.php?page=Aleph-X
Look under section 5.3
http://www.diyaudio.com/wiki/index.php?page=Aleph-X
Look under section 5.3
bigger is better
Here's the first picture of the power supply of the AX 1000 version (someone has to be the first, a pity it isn't american) I dont wan't any ripple so I put in quite a few stubby's. I problably stack them in two layers, as with the toroids.
Next week the powercompany is going to upgrade the powerlines to my house, because they expect problems with the needed currents.
Springgreetings from Holland,
Jojo (aka dutch Yoyo)
Here's the first picture of the power supply of the AX 1000 version (someone has to be the first, a pity it isn't american) I dont wan't any ripple so I put in quite a few stubby's. I problably stack them in two layers, as with the toroids.
Next week the powercompany is going to upgrade the powerlines to my house, because they expect problems with the needed currents.
Springgreetings from Holland,
Jojo (aka dutch Yoyo)
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