idea
the idea behind that circuit was to combine some already
working designs. The output section is very similar to the
proven Pass/Thagard A-75. The idea of leaving the amount
of overall feedback to the builders choice fascinated me and
therefore I implemented this feature with R30 and R47 (XX).
How it works can be read in the Pass/Thagard article in
AudioAmateur or at passdiy.com. I simply adapted their
frontend to modern Mosfets. The amount of bias (ClassA)
can be adjusted easily by trimming R39 and R51 to about
0.14 volts across one of the 0R33 source resistors. This
amount of bias is good for 25W RMS ClassA and leads to
about 180W to be handled by the heatsinks, 15W per fet.
For thermal stability T11, T14 must be mounted on the
heatsink near the output devices.
The trimming of the CCS´s is needed for offset adjustment
after a reasonable warm up time. To achieve best results
both inputs should be grounded during adjusting R1, R3.
The amp is capable of about 200W/8R and 400W/4R RMS.
The only tricky thing is the PSU. I use a hammond toroid with
1000VA and 48V CT. and a small one 2x 15V (independent!)
for the auxiliary PSU (+-55V) Powercaps are 4x Siemens
47mF/40V
Uli
the idea behind that circuit was to combine some already
working designs. The output section is very similar to the
proven Pass/Thagard A-75. The idea of leaving the amount
of overall feedback to the builders choice fascinated me and
therefore I implemented this feature with R30 and R47 (XX).
How it works can be read in the Pass/Thagard article in
AudioAmateur or at passdiy.com. I simply adapted their
frontend to modern Mosfets. The amount of bias (ClassA)
can be adjusted easily by trimming R39 and R51 to about
0.14 volts across one of the 0R33 source resistors. This
amount of bias is good for 25W RMS ClassA and leads to
about 180W to be handled by the heatsinks, 15W per fet.
For thermal stability T11, T14 must be mounted on the
heatsink near the output devices.
The trimming of the CCS´s is needed for offset adjustment
after a reasonable warm up time. To achieve best results
both inputs should be grounded during adjusting R1, R3.
The amp is capable of about 200W/8R and 400W/4R RMS.
The only tricky thing is the PSU. I use a hammond toroid with
1000VA and 48V CT. and a small one 2x 15V (independent!)
for the auxiliary PSU (+-55V) Powercaps are 4x Siemens
47mF/40V
Uli
Neat idea, uli!
Regarding the power supply, you could of course use a voltage
doubler to generate a raw +/-70VDC, which you can filter and/or
regulate down to +/-55V. This eliminates the need for a separate
transformer and its associated wiring, mounting, and fusing.
If the finished amplifier has audible background hum or can't
make full output at high frequencies, you could reduce the 100R
value between the sources of the input diff pair to increase the
open loop gain of the voltage section and make the feedback
loop more effective. Also, as you've referenced both input gates
to ground, I don't think you'll need the 630R to ground at the
sources of the input diff pair.
I'm curious as to why you referenced the cascode gates to the
filtered output stage supply rails rather than to a zener string in
the front end section. Does this ensure that the voltage section
will clip before the output stage does?
Regarding the power supply, you could of course use a voltage
doubler to generate a raw +/-70VDC, which you can filter and/or
regulate down to +/-55V. This eliminates the need for a separate
transformer and its associated wiring, mounting, and fusing.
If the finished amplifier has audible background hum or can't
make full output at high frequencies, you could reduce the 100R
value between the sources of the input diff pair to increase the
open loop gain of the voltage section and make the feedback
loop more effective. Also, as you've referenced both input gates
to ground, I don't think you'll need the 630R to ground at the
sources of the input diff pair.
I'm curious as to why you referenced the cascode gates to the
filtered output stage supply rails rather than to a zener string in
the front end section. Does this ensure that the voltage section
will clip before the output stage does?
many questions
Hi Uli,
great job You did on the PCB layouts!!
Me too wonder why You hooked up the drivers gate drive to the output power supply and not to a fixed reference at the frontend.
Somehow I can`t follow why the driver should clip before the output.
Moreover I assume that the gate potential of the drivers may fluctuate and thereby gets modulated when the output stage leaves Class-A range.
Do You mind to explain what exactly is the reasoning behind this arrangement?
Also could You please tell a bit more about the sound in comparison to Your Aleph 2`s (unless bottom range) ?
When You compared the X-Amp. with the Aleph-2 did You run the X-Amp. with or without feedback?
What kind of speakers have You used for the comparison (sensivity - among other characteristics)?
Is there any kind of noise/hum in operation or any louder pops during power-on/off?
Sorry for all the questions without being able commenting something useful to Your great efforts.
Hi Uli,
great job You did on the PCB layouts!!
Me too wonder why You hooked up the drivers gate drive to the output power supply and not to a fixed reference at the frontend.
Somehow I can`t follow why the driver should clip before the output.
Moreover I assume that the gate potential of the drivers may fluctuate and thereby gets modulated when the output stage leaves Class-A range.
Do You mind to explain what exactly is the reasoning behind this arrangement?
Also could You please tell a bit more about the sound in comparison to Your Aleph 2`s (unless bottom range) ?
When You compared the X-Amp. with the Aleph-2 did You run the X-Amp. with or without feedback?
What kind of speakers have You used for the comparison (sensivity - among other characteristics)?
Is there any kind of noise/hum in operation or any louder pops during power-on/off?
Sorry for all the questions without being able commenting something useful to Your great efforts.
Re: many questions
great job You did on the PCB layouts!!
>> Thanks!
Me too wonder why You hooked up the drivers gate drive to the output power supply and not to a fixed reference at the frontend.
Somehow I can`t follow why the driver should clip before the output.
Moreover I assume that the gate potential of the drivers may fluctuate and thereby gets modulated when the output stage leaves Class-A range.
Do You mind to explain what exactly is the reasoning behind this arrangement?
>> The reason is, that in my opinion there is no modulation as
the driver stage is completely decoupled thru the cascoded
stage, in fact I built it first on a test board before drawing
and it worked, but you are free to modify this part of course!
replace the 100R resistors with a reference to 20Volts
below the 55.
Also could You please tell a bit more about the sound in comparison to Your Aleph 2`s (unless bottom range) ?
When You compared the X-Amp. with the Aleph-2 did You run the X-Amp. with or without feedback?
>> I prefer not to include the outpustage in the NFL.
I like the Aleph mids better, BUT bottomend is superior!
I believe the main difference stems from the complementary
source follower output compared to the Aleph thus the
far better basscontrol IMHO.
What kind of speakers have You used for the comparison (sensivity - among other characteristics)?
>> Home brew 4way D´appollito 2x 12" 0-95Hz 18dB Xover
2x 6,25" Kevlar mids 95-800 18dB, 2x 2" dome (Alu)
800- 3000 18dB, Neodym dome tweeter (2x - 1front, one
switchable in the back)
Sensitivity is about 89-90 dB/W/m
Charakter: tweaked to 21Hz -3dB!!!
Is there any kind of noise/hum in operation or any louder pops during power-on/off?
>> NO, Trick: shortcutrelay between the gate - lines during on/off
Sorry for all the questions without being able commenting something useful to Your great efforts. [/B][/QUOTE]
This forum is made for such questions, everybody posting circuits
is proud to explain them !
Uli
great job You did on the PCB layouts!!
>> Thanks!
Me too wonder why You hooked up the drivers gate drive to the output power supply and not to a fixed reference at the frontend.
Somehow I can`t follow why the driver should clip before the output.
Moreover I assume that the gate potential of the drivers may fluctuate and thereby gets modulated when the output stage leaves Class-A range.
Do You mind to explain what exactly is the reasoning behind this arrangement?
>> The reason is, that in my opinion there is no modulation as
the driver stage is completely decoupled thru the cascoded
stage, in fact I built it first on a test board before drawing
and it worked, but you are free to modify this part of course!
replace the 100R resistors with a reference to 20Volts
below the 55.
Also could You please tell a bit more about the sound in comparison to Your Aleph 2`s (unless bottom range) ?
When You compared the X-Amp. with the Aleph-2 did You run the X-Amp. with or without feedback?
>> I prefer not to include the outpustage in the NFL.
I like the Aleph mids better, BUT bottomend is superior!
I believe the main difference stems from the complementary
source follower output compared to the Aleph thus the
far better basscontrol IMHO.
What kind of speakers have You used for the comparison (sensivity - among other characteristics)?
>> Home brew 4way D´appollito 2x 12" 0-95Hz 18dB Xover
2x 6,25" Kevlar mids 95-800 18dB, 2x 2" dome (Alu)
800- 3000 18dB, Neodym dome tweeter (2x - 1front, one
switchable in the back)
Sensitivity is about 89-90 dB/W/m
Charakter: tweaked to 21Hz -3dB!!!
Is there any kind of noise/hum in operation or any louder pops during power-on/off?
>> NO, Trick: shortcutrelay between the gate - lines during on/off
Sorry for all the questions without being able commenting something useful to Your great efforts.
[/B][/QUOTE]This forum is made for such questions, everybody posting circuits
is proud to explain them !
Uli
Uli,
How does this mosfet x200 design relate to the other dynamically biased x schematic you posted on the “X100 backengineered here” thread? Is one an improvement on the other? Did you build both? Do you suppose that with the dynamically biased current source the highs and mid will improve. Is the amp on the “X100 backengineered here” push pull or single ended?
I know you stated that you like the Aleph mid better. Does it image as will as the Aleph? Are the differences in sound between the Aleph and the X only very suttal or is it a night and day type of difference? Does this amp have the lighting fast attacks and decays that the owner manual of the true x amp speaks of.
Do you really need the CR circuit on the plus and minus output to prevent resonation or is it just a leftover from the a75? Is this amp optimized for 180watts of bias or can it be biased anywhere (within its limits)? I can see from the silk screen that the two input mosfets are mounted on a heat sink. Do they have to be mounted on the same heatsink ?
The dilemma I face is that, if power consumption was of no concern I would just build an XA100, but the power dissipation is 300watts per channel. I am only 23 years old, however a lot of the time I still fall asleep lissning to my system (maybe a sleep mode would help here). I don’t want to build a 30 watt XA because I fear it may be underpowered for my system (maybe an AX60 would be ok, that’s about 200watts idle). That’s why I’m looking at push pull.
Leve Hajdu
How does this mosfet x200 design relate to the other dynamically biased x schematic you posted on the “X100 backengineered here” thread? Is one an improvement on the other? Did you build both? Do you suppose that with the dynamically biased current source the highs and mid will improve. Is the amp on the “X100 backengineered here” push pull or single ended?
I know you stated that you like the Aleph mid better. Does it image as will as the Aleph? Are the differences in sound between the Aleph and the X only very suttal or is it a night and day type of difference? Does this amp have the lighting fast attacks and decays that the owner manual of the true x amp speaks of.
Do you really need the CR circuit on the plus and minus output to prevent resonation or is it just a leftover from the a75? Is this amp optimized for 180watts of bias or can it be biased anywhere (within its limits)? I can see from the silk screen that the two input mosfets are mounted on a heat sink. Do they have to be mounted on the same heatsink ?
The dilemma I face is that, if power consumption was of no concern I would just build an XA100, but the power dissipation is 300watts per channel. I am only 23 years old, however a lot of the time I still fall asleep lissning to my system (maybe a sleep mode would help here). I don’t want to build a 30 watt XA because I fear it may be underpowered for my system (maybe an AX60 would be ok, that’s about 200watts idle). That’s why I’m looking at push pull.
Leve Hajdu
Hi Leve,
The "X-Amp" is classic push-pull full complementary output.
The "backengineered" amp is single ended complementary
ouput (only IRFP240 are active)
As the driverstage is very similar the difference is a single
sourcefollower (IRFP240) + CCS (IRF9140) against full
complementary source followers.
The X-Amp can be driven class AB wheras the other can only
be driven class A (+ a little extra aleph power from the
dynamic CCSs)
Thus You can easily achieve 400W RMS into 4 R with the the X200!
The idle current is up to Your choice (and money for heatsinking
of course)
Uli
(EDIT): Yes I built the X200, no I just prototyped the SE version
The "X-Amp" is classic push-pull full complementary output.
The "backengineered" amp is single ended complementary
ouput (only IRFP240 are active)
As the driverstage is very similar the difference is a single
sourcefollower (IRFP240) + CCS (IRF9140) against full
complementary source followers.
The X-Amp can be driven class AB wheras the other can only
be driven class A (+ a little extra aleph power from the
dynamic CCSs)
Thus You can easily achieve 400W RMS into 4 R with the the X200!
The idle current is up to Your choice (and money for heatsinking
of course)
Uli
(EDIT): Yes I built the X200, no I just prototyped the SE version
Hi Uli,
I built a pair of Aleph X for mid and tweeter. Now I'm looking for ideas for amp to power the woofer, which covers 200Hz and below. Sounds like your "X200" could be a good candidate. Do you like the bass with your amp? Did you compare it with other design? For the moment, I'm drivng the bass with a Proceed HPA2, but I would like to put a DIY amp in there.
Thanks...
I built a pair of Aleph X for mid and tweeter. Now I'm looking for ideas for amp to power the woofer, which covers 200Hz and below. Sounds like your "X200" could be a good candidate. Do you like the bass with your amp? Did you compare it with other design? For the moment, I'm drivng the bass with a Proceed HPA2, but I would like to put a DIY amp in there.
Thanks...
Hi Niner,
Bass performance is IMHO very similar to a wellbuilt Aleph X.
The point is the extra power you get from this X design and
littlr bit better damping factor.
I believe XA is best of both worlds used fullrange.
As bass amplifier the X is more cost effective, does not radiate
that much heat and sucks not so much power out of the wall.
Uli
Bass performance is IMHO very similar to a wellbuilt Aleph X.
The point is the extra power you get from this X design and
littlr bit better damping factor.
I believe XA is best of both worlds used fullrange.
As bass amplifier the X is more cost effective, does not radiate
that much heat and sucks not so much power out of the wall.
Uli
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