AX100 100W Aleph-X Monoblocks

[Luke]

Hi Graeme,

Ive been following this thread for a while and i just reread it all tonight.

If I ever build my aleph-x Ill be following this thread, it looks like youve made it easier for us not so experienced diyers. This project is abit intimidating.

I do have one question, I worked out your outputs are running at about 15watts dissipation. From memory I think Nelson runs things at 25 watts per device. Isnt it easier for the jfet front end to drive less gates?
Do you think using your schematic with 25 volt rails and 12 outputs with 6 amps bias would work ok with your jfet front end.


cheers arthur

[gl]

Hi Arthur,

I'm always happy to hear that what I've done is useful to others.

The 15W number for 540ma of bias through each MOSFET is what I calculate as well. I chose a number that is lower than the typical Nelson number because my heat sink design is not as efficient as the typical PassLabs heat sink design.

I assume that when you say 12 outputs and 6A of bias that you mean a monoblock single channel amp with 12 output MOSFETs and 12 Aleph CCS MOSFET's and 500ma of bias through each transistor? If that's the case then I would say that the dual JFET front end would probably work.

Cheers,
Graeme

[Luke]

The 15W number for 540ma of bias through each MOSFET is what I calculate as well. I chose a number that is lower than the typical Nelson number because my heat sink design is not as efficient as the typical PassLabs heat sink design.

Ah I thought that might be the case, I luckily have some quite chunky sinks.

I assume that when you say 12 outputs and 6A of bias that you mean a monoblock single channel amp with 12 output MOSFETs and 12 Aleph CCS MOSFET's and 500ma of bias through each transistor? If that's the case then I would say that the dual JFET front end would probably work.

Yes thats what I mean. I would be tempted to try mosfets first just to realise what the fuss is about with these jfets

[gl]

Your plan to build a MOSFET front end first is wise. There is more collective experience around here with that topology. Build your amp and get through all the other basics first, like physical layout, heat, and grounding stuff.

Graeme

[space2000]

Originally posted by gl
Here is the schematic.

The circuit is essentially the original Aleph-X as shown in the schematic at the beginning of the Aleph-X thread. I have retained the original part numbering. All of the changes made have been discussed by others at various times in various threads. There is nothing new here. The original circuit has simply been reworked to provide an amplifier appropriate to a specific requirement.


The following changes were made:

1) Rail voltages were increased to about 26 - 27V. The CLC type supply uses 68KuF/50V - 1mH - 68KuF/50V filters on each rail. The inductors are Madisound Sledgehammers. Yes they probably are saturating - but they look so cool. There is a great deal of discussion on the Aleph-X thread about sagging transformer secondary voltages under heavy load. I did not experience this. The transformers have a slight soft buzz that's only audible up close.

2) The output device complement was changed to 20 IRFP240's per monoblock or 5 transistors per quadrant and bias was initially set to .5 amps per transistor for a total of 5 amps. These were matched to within .01V in sets of 10.

3) Output source resistors were set to 1 ohm @ 1% to help equalize the dissipation on each output transistor because of the separate heatsink plates. They are 2W Ohmite NI wirewound types chosen because they were one of the better and less expensive units in the catalogs.

4) The CCS sense resistors R2, R3, R42, and R43 were changed to .47 ohms because I had a pile of them. Extra resistors r50, R51, R52, R53, R54, and R55 were added.

5) R16 and R30 were changed to 220K to give a gain of 26dB with a balanced input.

6) Pots V1 and V3 were adjusted and then they and the original 47K resistors were swapped for single fixed values. 82K gives 500ma of bias per device @ 13W of dissipation. 100K gives 540ma per device.

7) R12 and R34 were adjusted for 50% CCS AC current gain. I used the NP method given in the Aleph-X builders thread. First, 475 ohm resistors with 1K pots in series were substituted for R12 and R34. R12 and R34 were then disconnected and with a 100Hz sine wave input the AC voltage across R6 and R41 was measured. R12 and R34 were then reconnected and the pots adjusted so that the AC voltage across R6 and R41 drops to half it's former value. The R12 and R34 pot/resistor networks were removed and measured and fixed resistors substituted. The measured value was 853 ohms and I created this with 634 ohms + 221 ohms which I had on hand, otherwise the closest 1% value is 845 ohms.

When NP describes this process he states that the input level should be set to give 16VRMS across an output load resistor. I couldn't get anywhere near this value without serious clipping. The highest unclipped value I could get was 12V measured with an AC voltmeter. At first I thought something was wrong because this appeared to be way too low. But after I thought about it I figured that with a rail to rail voltage difference of 54V I would start seeing clipping at 48V under ideal circumstances. With the CCS gain at zero I would lose 50% of the current at clipping so the clipping point drops by half. Add to that I was using an unbalanced input so half again. So 12V output at clipping was probably correct.

8) 4.75K MacMillan resistors were added. This resistor value is for me the one big mystery in the circuit. Like it says in the WIKI this value is traded off against the value of the output grounding resistors. Common mode performance is traded off against DC offset performance.

If I had the opportunity to request one breadcrumb from NP it would be the corresponding MacMillan values for the 100 ohm output resistors in the XA series.

9) Several other resistor values were changed in accordance with NP breadcrumbs scattered around in the Aleph-X and Aleph-X builders thread.

10) R21 was deleted.

11) R14, R17, and R31 were increased because of the higher rail voltages.

12) 4.7uF PP input caps and 100K resistors were added to the inputs.

13) 220uF caps were added to each rail on the PCB. A 4.7uF cap was added across D1. These changes were made because similar parts appear in the photos of the XA160 and XA200 that have been posted here or included in various magazine reviews.

14) The rectifier bridges are individual IXYS FRED type soft recovery diodes. There are two bridges in each amp for the two center tapped transformer secondary windings. The outputs of the bridges are paralleled at the first filter cap. This seems to work fine.


Whenever possible individual ground wires were run to a single star ground. There are three ground connections to the PCB: one to each group of input (+ and -) related grounds and a third which collects the power supply connections including the CCS. The RCA jack is insulated from the chassis and its ground pin is connected to pin 3 of the XLR and then pin 3 of the XLR has a separate wire back to the star ground. The star ground is connected to a frame ground (near the IEC inlet) through a CL60. The IEC inlet ground is connected to the frame ground.

I copied the input filtering scheme from the Aleph 60 more or less. Next time I will buy a filtered inlet regardless of what it costs!

I hope that some of this information is helpful to the next builder. If anyone sees anything wrong here please post.

Regards,
Graeme L.

hi,

i saw your circuit design. i want to follow this circuit as i can arrange easily all mosfets. i have question about input and output connection.

i can see there are in and out have (+) and (_) .

which should be atching to the the CD and speaker?

should i connect Cd into (+ ,GND) and speaker to the (+, GDN)?

my cd player is non inverted.
as i have done aleph-3 there are only + and GND to out and input.

thanks.
michael

[space2000]

Originally posted by gl
Here is the schematic.

The circuit is essentially the original Aleph-X as shown in the schematic at the beginning of the Aleph-X thread. I have retained the original part numbering. All of the changes made have been discussed by others at various times in various threads. There is nothing new here. The original circuit has simply been reworked to provide an amplifier appropriate to a specific requirement.


The following changes were made:

1) Rail voltages were increased to about 26 - 27V. The CLC type supply uses 68KuF/50V - 1mH - 68KuF/50V filters on each rail. The inductors are Madisound Sledgehammers. Yes they probably are saturating - but they look so cool. There is a great deal of discussion on the Aleph-X thread about sagging transformer secondary voltages under heavy load. I did not experience this. The transformers have a slight soft buzz that's only audible up close.

2) The output device complement was changed to 20 IRFP240's per monoblock or 5 transistors per quadrant and bias was initially set to .5 amps per transistor for a total of 5 amps. These were matched to within .01V in sets of 10.

3) Output source resistors were set to 1 ohm @ 1% to help equalize the dissipation on each output transistor because of the separate heatsink plates. They are 2W Ohmite NI wirewound types chosen because they were one of the better and less expensive units in the catalogs.

4) The CCS sense resistors R2, R3, R42, and R43 were changed to .47 ohms because I had a pile of them. Extra resistors r50, R51, R52, R53, R54, and R55 were added.

5) R16 and R30 were changed to 220K to give a gain of 26dB with a balanced input.

6) Pots V1 and V3 were adjusted and then they and the original 47K resistors were swapped for single fixed values. 82K gives 500ma of bias per device @ 13W of dissipation. 100K gives 540ma per device.

7) R12 and R34 were adjusted for 50% CCS AC current gain. I used the NP method given in the Aleph-X builders thread. First, 475 ohm resistors with 1K pots in series were substituted for R12 and R34. R12 and R34 were then disconnected and with a 100Hz sine wave input the AC voltage across R6 and R41 was measured. R12 and R34 were then reconnected and the pots adjusted so that the AC voltage across R6 and R41 drops to half it's former value. The R12 and R34 pot/resistor networks were removed and measured and fixed resistors substituted. The measured value was 853 ohms and I created this with 634 ohms + 221 ohms which I had on hand, otherwise the closest 1% value is 845 ohms.

When NP describes this process he states that the input level should be set to give 16VRMS across an output load resistor. I couldn't get anywhere near this value without serious clipping. The highest unclipped value I could get was 12V measured with an AC voltmeter. At first I thought something was wrong because this appeared to be way too low. But after I thought about it I figured that with a rail to rail voltage difference of 54V I would start seeing clipping at 48V under ideal circumstances. With the CCS gain at zero I would lose 50% of the current at clipping so the clipping point drops by half. Add to that I was using an unbalanced input so half again. So 12V output at clipping was probably correct.

8) 4.75K MacMillan resistors were added. This resistor value is for me the one big mystery in the circuit. Like it says in the WIKI this value is traded off against the value of the output grounding resistors. Common mode performance is traded off against DC offset performance.

If I had the opportunity to request one breadcrumb from NP it would be the corresponding MacMillan values for the 100 ohm output resistors in the XA series.

9) Several other resistor values were changed in accordance with NP breadcrumbs scattered around in the Aleph-X and Aleph-X builders thread.

10) R21 was deleted.

11) R14, R17, and R31 were increased because of the higher rail voltages.

12) 4.7uF PP input caps and 100K resistors were added to the inputs.

13) 220uF caps were added to each rail on the PCB. A 4.7uF cap was added across D1. These changes were made because similar parts appear in the photos of the XA160 and XA200 that have been posted here or included in various magazine reviews.

14) The rectifier bridges are individual IXYS FRED type soft recovery diodes. There are two bridges in each amp for the two center tapped transformer secondary windings. The outputs of the bridges are paralleled at the first filter cap. This seems to work fine.


Whenever possible individual ground wires were run to a single star ground. There are three ground connections to the PCB: one to each group of input (+ and -) related grounds and a third which collects the power supply connections including the CCS. The RCA jack is insulated from the chassis and its ground pin is connected to pin 3 of the XLR and then pin 3 of the XLR has a separate wire back to the star ground. The star ground is connected to a frame ground (near the IEC inlet) through a CL60. The IEC inlet ground is connected to the frame ground.

I copied the input filtering scheme from the Aleph 60 more or less. Next time I will buy a filtered inlet regardless of what it costs!

I hope that some of this information is helpful to the next builder. If anyone sees anything wrong here please post.

Regards,
Graeme L.

hi,

i saw your circuit design. i want to follow this circuit as i can arrange easily all mosfets. i have question about input and output connection.

i can see there are in and out have (+) and (_) .

which should be atching to the the CD and speaker?

should i connect Cd into (+ ,GND) and speaker to the (+, GDN)?

my cd player is non inverted.
as i have done aleph-3 there are only + and GND to out and input.

how about the voltage? can i apply 29vdc on it? is there any things need to be change?

thanks.
michael

[Zen Mod]

Originally posted by space2000



.......

considering what type of questions you asking.........

you are not ready for X amp ;

spend two weeks at least in reading related threads ......... go to Papa's site and download EVERY pdf you can .......... and read ;

point is that you learn something building amps , not just to have amp .

[space2000]

Originally posted by Zen Mod



considering what type of questions you asking.........

you are not ready for X amp ;

spend two weeks at least in reading related threads ......... go to Papa's site and download EVERY pdf you can .......... and read ;

point is that you learn something building amps , not just to have amp .

Hi,

*This reminds me, one person says don’t open often any new thread, go to the related thread to ask. now, I got this. *

At first I have to say I am not an electronics engineer. If I am expert, I wouldn’t ask any question here, I would answer questions. This is the reason to ask this kind of stupid question here. May be it’s odd question to you or too cheap question to you. I just asked question and you replied to me go and read “this and that” you are not ready for X amp”. I am really very much disappointed about your writing.

[tryonziess]

Space2000, The Aleph circuit and Aleph-X circuits are not your standard run of the mill designs. Though the Aleph is user friendly the Aleph-X circuit can be quite difficult to tame.
The question you asked concerning the hookups has to do with balanced and single ended amplifiers.
It would save you much money and headache to take Zen Mods suggestion to heart.
I am by no means expert in this field and started out with a few chip amp builds and progressed to some nice Leach amps. I will build the A-75 design before tackling the aleph-X.
Some of the very much experienced builders on this forum have had good luck with the X but they know how to tweek the little things and know when things are not right.
Good Luck Tad

[Zen Mod]

Originally posted by space2000



......... I am really very much disappointed about your writing.

you were asking for fish ;

I pointed you where ocean is and how to learn fishing ;

be disappointed .