SE source operation
Nelson, or anyone else for that matter, care to elaborate on why nomadic ground resistors degrade performance with SE sources?Are we talking about resistors from Sources to ground here (an obvious no, no) or others, e.g. from gates of input devices? I'm not clear why the latter should have any significant effect given that they are effectively connected to a virtual earth in this application.
Ian.
Nelson, or anyone else for that matter, care to elaborate on why nomadic ground resistors degrade performance with SE sources?Are we talking about resistors from Sources to ground here (an obvious no, no) or others, e.g. from gates of input devices? I'm not clear why the latter should have any significant effect given that they are effectively connected to a virtual earth in this application.
Ian.
When you put resistance off the Sources of the
diff pair I recall that you start drawing the
cross-coupled error off to ground and you reduce
the effect, but I seem to recall that this does not
particularly apply to resistance going to the
output nodes, probably because, given the right
values, this error is also present there, and the
differential error current doesn't flow.
In any case, this is not a big effect. Originally the
resistance to ground was included to help stabilize
the circuit back when it had more gain stages.
diff pair I recall that you start drawing the
cross-coupled error off to ground and you reduce
the effect, but I seem to recall that this does not
particularly apply to resistance going to the
output nodes, probably because, given the right
values, this error is also present there, and the
differential error current doesn't flow.
In any case, this is not a big effect. Originally the
resistance to ground was included to help stabilize
the circuit back when it had more gain stages.
So, here is the schematic for the Aleph-X that I build.
Given the recent posts, I will probably give the 4,7k value
for the famous resistors another try.
Given the recent posts, I will probably give the 4,7k value
for the famous resistors another try.
rtirion,
Thanks for the post. Your schematic looks really good. (And thank-you GRollins and Mr. Pass). I look forward to building one up soon.
I have one question regarding bias. If I wish to run more class AB than A, what is the best method of adjusting this schematic to have the unit run cooler (I was thinking of having +/-25V rails)? I understand from previous posts, etc., that increasing R3,R10,R25,R29 from 0.22 to 0.39 will reduce current and the amp will run cooler, but this is at the expense of reduced power output. Can you maintain same power and run less into class A?
Thanks, Robert
Thanks for the post. Your schematic looks really good. (And thank-you GRollins and Mr. Pass). I look forward to building one up soon.
I have one question regarding bias. If I wish to run more class AB than A, what is the best method of adjusting this schematic to have the unit run cooler (I was thinking of having +/-25V rails)? I understand from previous posts, etc., that increasing R3,R10,R25,R29 from 0.22 to 0.39 will reduce current and the amp will run cooler, but this is at the expense of reduced power output. Can you maintain same power and run less into class A?
Thanks, Robert
Aleph's cannot run Class AB as such because they are single ended. However you can increase the current source AC gain above the standard 50% which has a similar effect but will also effect the sound. No free lunch! In the schematic 2 posts prior, you decrease the values of R9 and R20 until you get what you want.
Hi everyone
Great job on the schematic, But I can't help seeing that it has quite a lot of elements from the Aleph 3, 4, 5 designs.
In the patents for the Aleph X, it shows a folded cascode driver stage.
I don't see one here....
I can see the cross coupling as with the orginal patent, so I guess in essence this design would function pretty much the same. Anyway I was just curious as to why the folded cascode was not used in this design.
Great Job!🙂
Anthony Holton
www.aussieamplifiers.com
Great job on the schematic, But I can't help seeing that it has quite a lot of elements from the Aleph 3, 4, 5 designs.
In the patents for the Aleph X, it shows a folded cascode driver stage.
I don't see one here....
I can see the cross coupling as with the orginal patent, so I guess in essence this design would function pretty much the same. Anyway I was just curious as to why the folded cascode was not used in this design.
Great Job!🙂
Anthony Holton
www.aussieamplifiers.com
rtirion
I see your diagram shows 12 volt rails - some questions:
1. What bias current are you using (per channel)?
2. What PSU design are you using?
3. What is the voltage and power ratings of your transformer(s)
4. What actual voltage to you get out under load?
5. What power output do you get into 4 and 8 ohm loads?
Thanks (in anticipation).
Nix
I see your diagram shows 12 volt rails - some questions:
1. What bias current are you using (per channel)?
2. What PSU design are you using?
3. What is the voltage and power ratings of your transformer(s)
4. What actual voltage to you get out under load?
5. What power output do you get into 4 and 8 ohm loads?
Thanks (in anticipation).
Nix
At the moment I use a test supply with a variac. You can't live without one of these variac's when experimenting with these little amplifiers.
🙂
So I adjust the variac for 12 Volt per rail under load and that's about it.
The Aleph-X pulls aprox. 4,5 Amps out of this supply when idle.
Rating of the transformer is 500va.
I have not yet measured the outut power of the amp. Will do so in the coming weeks.
I am working on a solution for the final supply. This solves the problem of low voltage, high va rating. (try finding a tranformer of let's say 500va with 9 or 10v secondaries.)
🙂
So I adjust the variac for 12 Volt per rail under load and that's about it.
The Aleph-X pulls aprox. 4,5 Amps out of this supply when idle.
Rating of the transformer is 500va.
I have not yet measured the outut power of the amp. Will do so in the coming weeks.
I am working on a solution for the final supply. This solves the problem of low voltage, high va rating. (try finding a tranformer of let's say 500va with 9 or 10v secondaries.)
rtirion
I can buy 250VA transformers with 2 x 9V secondaries for a good price. Thinking of using one transformer per channel with a pi filter with 50,000uF per rail. Seems like that would do fine.
With your 12 V rails, what power output do you get into 4 and 8 ohm loads?
BTW how did you decide on your output devices (IRFP150N)?
Nix
I can buy 250VA transformers with 2 x 9V secondaries for a good price. Thinking of using one transformer per channel with a pi filter with 50,000uF per rail. Seems like that would do fine.
With your 12 V rails, what power output do you get into 4 and 8 ohm loads?
BTW how did you decide on your output devices (IRFP150N)?
Nix
IRFP150N were leftovers from an ALEPH. They worked
pretty good in the ALEPH, so I have used them again.
Some time ago, I did a comparison between IRFP140,
IRFZ44N and IRFP150N in a ZEN and they were
the best sounding to me. They are reasonably priced too.
Power measurement will be done in coming weeks.
Can not promise a date, sorry. (To be honest, it is not
on the top of my list)
pretty good in the ALEPH, so I have used them again.
Some time ago, I did a comparison between IRFP140,
IRFZ44N and IRFP150N in a ZEN and they were
the best sounding to me. They are reasonably priced too.
Power measurement will be done in coming weeks.
Can not promise a date, sorry. (To be honest, it is not
on the top of my list)
Preparing to build my AlephX-
I am gathering parts together to start building my Aleph-X monoblocks... here is the plan.
I have IRFP-240's for the output stage. I would like to run 4 pairs per side, with a bias current somewhere around 6.25 amps per side. My rail voltage will be about 16 volts loaded (I'm using seperate 13.5 volt transformers for each rail) This would put me at about 125 watts into my speakers minimum impedance of 3.2 ohms. I figure I should be able to put out about 50 watts into 8 ohms, going by "uncle bear's rule of thumb".
Now, the problem I am having is this...
I try to model the circuit using circuitmaker student version (that may be the problem itself) but it dosen't seem to want to work. I could never get the zen circuit to simulate either. I have a few questions about what to look for in the circuit, and I hope that someone will help me out. First, will there be any problem hanging more transistor pairs on the output, keeping the front end the same? Will this affect the feedback loop? It dosen't seem like it would, since the voltages will stay about the same. Second, will upping the supply voltage a little upset the circuit? I was assuming that I should adjust the load resistors for the differential pair. Is there any reason not to push a little more current through the differential pair, to reduce the distortion a little? Also, what DC voltages am I looking for on the output of the differential pair?
I think I have a fair understanding of how the circuit works, and I am confident that I can get it to work. I would rather ask these things from those who know more about it, so I can avoid any unnecessary frying of components... any help would be much appreciated. Thanks.
Steve
I am gathering parts together to start building my Aleph-X monoblocks... here is the plan.
I have IRFP-240's for the output stage. I would like to run 4 pairs per side, with a bias current somewhere around 6.25 amps per side. My rail voltage will be about 16 volts loaded (I'm using seperate 13.5 volt transformers for each rail) This would put me at about 125 watts into my speakers minimum impedance of 3.2 ohms. I figure I should be able to put out about 50 watts into 8 ohms, going by "uncle bear's rule of thumb".
Now, the problem I am having is this...
I try to model the circuit using circuitmaker student version (that may be the problem itself) but it dosen't seem to want to work. I could never get the zen circuit to simulate either. I have a few questions about what to look for in the circuit, and I hope that someone will help me out. First, will there be any problem hanging more transistor pairs on the output, keeping the front end the same? Will this affect the feedback loop? It dosen't seem like it would, since the voltages will stay about the same. Second, will upping the supply voltage a little upset the circuit? I was assuming that I should adjust the load resistors for the differential pair. Is there any reason not to push a little more current through the differential pair, to reduce the distortion a little? Also, what DC voltages am I looking for on the output of the differential pair?
I think I have a fair understanding of how the circuit works, and I am confident that I can get it to work. I would rather ask these things from those who know more about it, so I can avoid any unnecessary frying of components... any help would be much appreciated. Thanks.
Steve
I am gathering parts together to start building my Aleph-X monoblocks...
"I try to model the circuit using circuitmaker student version (that may be the problem itself) but it dosen't seem to want to work."
Maximum of 50 devices per design (any type);
"First, will there be any problem hanging more transistor pairs on the output, keeping the front end the same? Will this affect the feedback loop? It dosen't seem like it would, since the voltages will stay about the same. "
The open loop gain and bandwidth will change.
"I was assuming that I should adjust the load resistors for the differential pair. Is there any reason not to push a little more current through the differential pair, to reduce the distortion a little? Also, what DC voltages am I looking for on the output of the differential pair?"
Yes there is a reason. For the same gate to negative supply voltage for the output stage, the gain for the front end will decrease for lowering the drain load resisitor values as the bias current is increased. DC voltage depends on the output stage bias current and source resistor values.
"I think I have a fair understanding of how the circuit works"
From the nature of your questions, I wonder..... Why not build
one of the proven Aleph designs first to get a little experience with a proven design before tackling a project of this depth? I see
many on the forum want to design amps without the experience of constructing, debugging, and tweaking a known design. Learn to walk before trying to run. I know I will get hate mail, but I say this in all sincerity. The Aleph designs are great and would make a much easier project and you will be happy with the results.
H.H.
"I try to model the circuit using circuitmaker student version (that may be the problem itself) but it dosen't seem to want to work."
Maximum of 50 devices per design (any type);
"First, will there be any problem hanging more transistor pairs on the output, keeping the front end the same? Will this affect the feedback loop? It dosen't seem like it would, since the voltages will stay about the same. "
The open loop gain and bandwidth will change.
"I was assuming that I should adjust the load resistors for the differential pair. Is there any reason not to push a little more current through the differential pair, to reduce the distortion a little? Also, what DC voltages am I looking for on the output of the differential pair?"
Yes there is a reason. For the same gate to negative supply voltage for the output stage, the gain for the front end will decrease for lowering the drain load resisitor values as the bias current is increased. DC voltage depends on the output stage bias current and source resistor values.
"I think I have a fair understanding of how the circuit works"
From the nature of your questions, I wonder..... Why not build
one of the proven Aleph designs first to get a little experience with a proven design before tackling a project of this depth? I see
many on the forum want to design amps without the experience of constructing, debugging, and tweaking a known design. Learn to walk before trying to run. I know I will get hate mail, but I say this in all sincerity. The Aleph designs are great and would make a much easier project and you will be happy with the results.
H.H.
Member
Joined 2002
this may not be nice to do but if your trying to use the soft and it mazes out at 50 pcs AG your circuit maker program why dont you get the Crack so that you can use all of it and save up some money to buy it so that way your not just pirateing soft.. AH hem PRotel is good AHEM crack..
LOL
LOL
Harry,
Thanks for the answers.
I didn't think about the open loop gain increasing. One of the reasons I get on here and ask a few dumb questions is that it helps me to sort out stuff that I overlooked in the first place.
As far as the simulation goes, it isn't that I run out of parts. I was using more of a zen design, without the aleph current sources; a simplified version of the circuit.
So, maybe I could kill two birds with one stone here- lower the gain of the front end by running a higher bias current and lowering the value of the load resistors, and balance that out with my addition of paralleled output devices, which would increase the open loop gain. Is there anything wrong with this thinking?
Would this affect the "X" feedback scheme?
As far as testing the circuit, how much open loop gain am I looking for, and how much feedback is being applied? Would there be anything wrong with building the circuit without the x feedback, measuring the open loop gain, and then calculating the feedback resistors?
If you're willing to bear with me here, I would appreciate the help. I will build these one way or another, but it would really be nice to have a little expert advice.
Steve
Thanks for the answers.
I didn't think about the open loop gain increasing. One of the reasons I get on here and ask a few dumb questions is that it helps me to sort out stuff that I overlooked in the first place.
As far as the simulation goes, it isn't that I run out of parts. I was using more of a zen design, without the aleph current sources; a simplified version of the circuit.
that one hurt- right in the gut! But, when you're right, you're right. At the same time, I have an oscilloscope and other test equipment, and I'm willing to dive in head first and take a few chances. So, instead of pushing me toward something else, let's just assume that my mind is made up on building these, and I would like to figure out how to make them work. It's my money after all, right?
So, maybe I could kill two birds with one stone here- lower the gain of the front end by running a higher bias current and lowering the value of the load resistors, and balance that out with my addition of paralleled output devices, which would increase the open loop gain. Is there anything wrong with this thinking?
Would this affect the "X" feedback scheme?
As far as testing the circuit, how much open loop gain am I looking for, and how much feedback is being applied? Would there be anything wrong with building the circuit without the x feedback, measuring the open loop gain, and then calculating the feedback resistors?
If you're willing to bear with me here, I would appreciate the help. I will build these one way or another, but it would really be nice to have a little expert advice.
Steve
Simetrix intoduction simulator.
Steve
Why not try Simetrix intoduction simulator, it is a very esay sim to use, the max limit of of nodes is very high.
I have simulated most of the Zen´s and Aleph´s with or without X.
I have bulid a nuber of amps, and all behavied close to the simulator when we are talking about bias, voltage and curret swing, but i don´t beleve the simulating of bandwith and espially not noise, thou i havn´t checked.
Harry
As allways 🙂 🙁 😀 😡 😕 😱
You are stirring up the minds, but i am shure you mean it well, so i gess it´s ok if one can take it. I am pretty shure, that Steve will build this thing anyway. So help him and the rest of us!🙂
Steve
Why not try Simetrix intoduction simulator, it is a very esay sim to use, the max limit of of nodes is very high.
I have simulated most of the Zen´s and Aleph´s with or without X.
I have bulid a nuber of amps, and all behavied close to the simulator when we are talking about bias, voltage and curret swing, but i don´t beleve the simulating of bandwith and espially not noise, thou i havn´t checked.
Harry
As allways 🙂 🙁 😀 😡 😕 😱
You are stirring up the minds, but i am shure you mean it well, so i gess it´s ok if one can take it. I am pretty shure, that Steve will build this thing anyway. So help him and the rest of us!🙂
Wow, this thread cooled off quick. Everyone must be building instead of reading, haha.
Well, I was able to finally simulate a Zen type circuit, actually Aleph without the variable current sources. I have a few questions about what I am seeing.
First, in Grey's original post he said that he put an adjustment in for the absolute dc offset, so that the gates of the output transistors were setting at 0 volts. When I simulate the original Aleph (minus variable sources- so a zen with split supplies) I am able to zero out the OUTPUT of the output Mosfets, but the circuit dosen't want to work with the gates at 0V potential. I understand that it is not a problem in a bridged circuit to have a DC potential on each output, as long as they approximately equal, but why is the X design different in that the output is setting up at a higher potential. I would have thought that it would be the same as an Aleph- at approx. ground potential at idle.
So, I have good luck simulating the zen/aleph circuit, but everything goes to hell when I bridge it and use the crossed feedback resistors and 30 ohm resistors to ground. The DC balance is excellent, but the signal is mangled, no matter how I adjust the front end bias current. Does anyone know what is wrong, or is the simulator just not able to handle a bridged X type circuit? It seems to never work when I try to bridge ANY circuit. Any suggestions? (besides trying a simpler design)
Steve
Well, I was able to finally simulate a Zen type circuit, actually Aleph without the variable current sources. I have a few questions about what I am seeing.
First, in Grey's original post he said that he put an adjustment in for the absolute dc offset, so that the gates of the output transistors were setting at 0 volts. When I simulate the original Aleph (minus variable sources- so a zen with split supplies) I am able to zero out the OUTPUT of the output Mosfets, but the circuit dosen't want to work with the gates at 0V potential. I understand that it is not a problem in a bridged circuit to have a DC potential on each output, as long as they approximately equal, but why is the X design different in that the output is setting up at a higher potential. I would have thought that it would be the same as an Aleph- at approx. ground potential at idle.
So, I have good luck simulating the zen/aleph circuit, but everything goes to hell when I bridge it and use the crossed feedback resistors and 30 ohm resistors to ground. The DC balance is excellent, but the signal is mangled, no matter how I adjust the front end bias current. Does anyone know what is wrong, or is the simulator just not able to handle a bridged X type circuit? It seems to never work when I try to bridge ANY circuit. Any suggestions? (besides trying a simpler design)
Steve
