Hi everybody,
I just wanted to show you all a truly amazing power amp I have been building for the last couple of months, with very good specs...
power.........................225w/4 ohm, 160w/8 ohm
slew rate...................115V/us!!!
freq. response.............10Hz-105kHz (-3dB)
THD............................0.004% 100W RMS/8 ohm
..................................0.008% 180W RMS/8 ohm
..................................0.009% 240W RMS/4 ohm
TIM.............................0.005% 140W RMS/8 ohm (50Hz/7KHz 4:1)
s/n..............................>100dB (100W RMS)
Damping factor..............>450 (150W RMS/8 ohm)
It is called "Sigma" and it has been designed by Dr. Borivoje Jagodic from Serbia. Unfortunately, his web site is mainly in serbian http://bas.elitesecurity.org/.
He is a very helpful and understanding person, also an excellent english speaker, you can contact him by mail.
Anyway here is the schematic http://bas.elitesecurity.org/sigmasema.pdf
Its amazing slew rate is almost twice as big as Brystons 4B SST (60V/us) which is twice as powerful as Sigma.
Minimum figures to meet Jung and Pass criterion for audio quality is 65V/us for an amp of 250Watt/4Ohm, 200kHz bandwidth.
As you can see Sigma is fantastic...
The stabilized +-75V PSU. 12x4700uF, 35A rectifier...
Populated PCB. The output transistors used are matched Hitachi 2sk1058 and 2sj162 power mosfets.
Both pcbs together, as a mono block with custom 220V:57V 500VA transformer.
The two mono blocks finished driving my Dynaudio BM15 speakers.
The back panel is custom laser cut and engraved from plexi.
The cases are aluminium, also custom made...
I haven't done any measurements yet, since I have no admittance to the expensive equipment needed. I will post the results as soon as my university starts and the labs open.
Many thanks to Dr. Jagodic for this exceptional design, it truly sounds BEAUTIFUL...
I just wanted to show you all a truly amazing power amp I have been building for the last couple of months, with very good specs...
power.........................225w/4 ohm, 160w/8 ohm
slew rate...................115V/us!!!
freq. response.............10Hz-105kHz (-3dB)
THD............................0.004% 100W RMS/8 ohm
..................................0.008% 180W RMS/8 ohm
..................................0.009% 240W RMS/4 ohm
TIM.............................0.005% 140W RMS/8 ohm (50Hz/7KHz 4:1)
s/n..............................>100dB (100W RMS)
Damping factor..............>450 (150W RMS/8 ohm)
It is called "Sigma" and it has been designed by Dr. Borivoje Jagodic from Serbia. Unfortunately, his web site is mainly in serbian http://bas.elitesecurity.org/.
He is a very helpful and understanding person, also an excellent english speaker, you can contact him by mail.
Anyway here is the schematic http://bas.elitesecurity.org/sigmasema.pdf
Its amazing slew rate is almost twice as big as Brystons 4B SST (60V/us) which is twice as powerful as Sigma.
Minimum figures to meet Jung and Pass criterion for audio quality is 65V/us for an amp of 250Watt/4Ohm, 200kHz bandwidth.
As you can see Sigma is fantastic...
An externally hosted image should be here but it was not working when we last tested it.
The stabilized +-75V PSU. 12x4700uF, 35A rectifier...
An externally hosted image should be here but it was not working when we last tested it.
Populated PCB. The output transistors used are matched Hitachi 2sk1058 and 2sj162 power mosfets.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Both pcbs together, as a mono block with custom 220V:57V 500VA transformer.
An externally hosted image should be here but it was not working when we last tested it.
The two mono blocks finished driving my Dynaudio BM15 speakers.
The back panel is custom laser cut and engraved from plexi.
The cases are aluminium, also custom made...
I haven't done any measurements yet, since I have no admittance to the expensive equipment needed. I will post the results as soon as my university starts and the labs open.
Many thanks to Dr. Jagodic for this exceptional design, it truly sounds BEAUTIFUL...
Downloaded the schematic and like the design (differential VAS)
This amp brings back memories of a kit I assembled in 1989.
Yours uses the more modern 1058/162 outputs while
mine had the old TO-3 laterals.
The sound of them hitachi's were SWEET ,the highs were
the best to hear.
VERY nice board, did you draw/ layout them out by yourself??
If you could, post your softstart,DC protect and regulated PS
schematics for us.
It looks like you are TRUE DIY ,start to finish ,Good work..OS
This amp brings back memories of a kit I assembled in 1989.
Yours uses the more modern 1058/162 outputs while
mine had the old TO-3 laterals.
The sound of them hitachi's were SWEET ,the highs were
the best to hear.
VERY nice board, did you draw/ layout them out by yourself??
If you could, post your softstart,DC protect and regulated PS
schematics for us.
It looks like you are TRUE DIY ,start to finish ,Good work..OS
The PCB layout of the power amp was given to me by the designer, Dr. Jagodic.
The softstart was from Elliot Sound Projects http://sound.westhost.com/project39.htm
so was the DC protection circuit
http://sound.westhost.com/project33.htm
I couldn't get the dc protection circuit to work for a week, so I gave up.
Instead I bought the Velleman K4700 kit, which is fantastic. It protects from dc an oscilations, it also saved my speakers during testing.
The PCB layout for these two circuits, I made my self, I could mail them to anyone interested.
here is the +-75V PSU.
The softstart was from Elliot Sound Projects http://sound.westhost.com/project39.htm
so was the DC protection circuit
http://sound.westhost.com/project33.htm
I couldn't get the dc protection circuit to work for a week, so I gave up.
Instead I bought the Velleman K4700 kit, which is fantastic. It protects from dc an oscilations, it also saved my speakers during testing.
The PCB layout for these two circuits, I made my self, I could mail them to anyone interested.
here is the +-75V PSU.
An externally hosted image should be here but it was not working when we last tested it.
Seems there's some fun going on.
The 75V rails are good for more than 300WRMS into 8 ohms, however the 6 A fuse cuts that down to about the half of that.
Of course the maximum power into low loads is then also severely cut down and 225W are not possible into 4 ohms, but only less than 100 WRMS?
What am I missing here? Or is that really a strange power concept?
Have fun, Hannes
I hate being the party pooper, but there's something very fishy with this project.
At 8ohm and 160W output you need about 100Vpp in the load. Allowing 5V reserve means all you need is +/-55V. Then why using +/-75V?
At 100Vpp in the load and 4ohm you need 25A peak. The 2SK1058/2SJ162 are rated at Idmax=7A, for two pairs that's 14A. Chances are high this thing is going to blow in your face at max power into 4ohm load and only the forgiving nature of the laterals will save you from a fire.
At 4ohm load the max power dissipation will occur at 50Vpp in the load and that's about, on top of my head, some 160W, that is, an average of 40W/tranny. That's a lot to cool down.
Under the same conditions, Vds is about 30V and Id about 6A or 3A per tranny. You are driving the trannies very close to the SOA limit, and that's before any power derating (it assumes that trannies are at 25 degrees which is certainly not going to happen). So chances are high the amp will blow well before reaching the max power into 4ohm.
At +/-75V don't even bother to calculate what's going to happen. The thing is going to blow in your face ASAP. The only survival chance is if the power supply has a significant sag, but this will drastically affect the amp performance. The PSRR is not very good in this design.
If you want to meet those numbers I would suggest adding at least two more pairs of output devices and reduce the supply voltage to max. +/-60V.
At 8ohm and 160W output you need about 100Vpp in the load. Allowing 5V reserve means all you need is +/-55V. Then why using +/-75V?
At 100Vpp in the load and 4ohm you need 25A peak. The 2SK1058/2SJ162 are rated at Idmax=7A, for two pairs that's 14A. Chances are high this thing is going to blow in your face at max power into 4ohm load and only the forgiving nature of the laterals will save you from a fire.
At 4ohm load the max power dissipation will occur at 50Vpp in the load and that's about, on top of my head, some 160W, that is, an average of 40W/tranny. That's a lot to cool down.
Under the same conditions, Vds is about 30V and Id about 6A or 3A per tranny. You are driving the trannies very close to the SOA limit, and that's before any power derating (it assumes that trannies are at 25 degrees which is certainly not going to happen). So chances are high the amp will blow well before reaching the max power into 4ohm.
At +/-75V don't even bother to calculate what's going to happen. The thing is going to blow in your face ASAP. The only survival chance is if the power supply has a significant sag, but this will drastically affect the amp performance. The PSRR is not very good in this design.
If you want to meet those numbers I would suggest adding at least two more pairs of output devices and reduce the supply voltage to max. +/-60V.
Hello Renx,
My first thought on seeing this was "Hitachi application note" and "Maplin kit" circa 1980 ? and examining a copy of that project does show a large similarity.
I am sure it sounds very good indeed, those lateral FET's are my device of choice.
As to the performance figures, I must say I find the slew rate figure hard to believe, and agree with syn08, a quarter of a killowatt from a pair of 7 amp laterals--maybe but for how long
It's perhaps a bit unfair to critise without actually building and measuring it. Nice job building it by the way-- makes a change to see a real project, not just a simulation
My first thought on seeing this was "Hitachi application note" and "Maplin kit" circa 1980 ? and examining a copy of that project does show a large similarity.
I am sure it sounds very good indeed, those lateral FET's are my device of choice.
As to the performance figures, I must say I find the slew rate figure hard to believe, and agree with syn08, a quarter of a killowatt from a pair of 7 amp laterals--maybe but for how long
It's perhaps a bit unfair to critise without actually building and measuring it. Nice job building it by the way-- makes a change to see a real project, not just a simulation
Juergen Knoop said:
The average supply current (that may blow the fuse) is the peak current through the load divided by PI (3.14). Which makes, for 4ohm and 100Vpp, 50V/4ohm/3.14=4A The trannies will protect the fuse but will not survive the peak current due to the SOA limitations.
Actually I made an error in my previous post, the peak current is 12.5A not 25A, but this is assuming a pure resistive load. In a typical speaker reactive load, chances are good you will still need 25A peak current.
"as it should take only Milliseconds to burn the fuse"
http://littelfuse.com/data/en/Data_Sheets/312_318.pdf
As we can see, a 6A fast acting fuse will open up in less than 10 seconds at 200% of rated current.
At 135% or rated current it will open up in less than one hour.
At rated current it will hold for four hours (minimum).
With ± fuses, the RMS speaker current may be 1.414 times the rail fuse rating (the fuse gets to 'rest' on alternate half cycles).
The correct fuse size for this amp that runs on ±80V is 5A, and note that the one set of fuses feeds both channels (third fuse is the line fuse).
http://littelfuse.com/data/en/Data_Sheets/312_318.pdf
As we can see, a 6A fast acting fuse will open up in less than 10 seconds at 200% of rated current.
At 135% or rated current it will open up in less than one hour.
At rated current it will hold for four hours (minimum).
With ± fuses, the RMS speaker current may be 1.414 times the rail fuse rating (the fuse gets to 'rest' on alternate half cycles).
The correct fuse size for this amp that runs on ±80V is 5A, and note that the one set of fuses feeds both channels (third fuse is the line fuse).
Hi,
The rail fuses after the main smoothing can pass enormous output currents, well in excess of the nominal fuse rating.
I tested a ClassA Krell Klone KSA100 biased to 2.6A fitted with an F5A fuse in each supply rail.
These F5A fuses allowed continuous outputs of 32.1Vac into 4r0 (=11.3Apk, 257W) and 30.1Vac into 2r0 (=21.3Apk, 453W).
I have suggested that the rail fuse rating be selected to pass about half the peak output current into the specified load. Quasi has suggested using half the rms output current.
Using the half peak current suggests that an F5A fuse would allow upto 250W into 4r0 and Quasi's rule would indicate that F4A is generally high enough for a similar power output.
The rail fuses after the main smoothing can pass enormous output currents, well in excess of the nominal fuse rating.
I tested a ClassA Krell Klone KSA100 biased to 2.6A fitted with an F5A fuse in each supply rail.
These F5A fuses allowed continuous outputs of 32.1Vac into 4r0 (=11.3Apk, 257W) and 30.1Vac into 2r0 (=21.3Apk, 453W).
I have suggested that the rail fuse rating be selected to pass about half the peak output current into the specified load. Quasi has suggested using half the rms output current.
Using the half peak current suggests that an F5A fuse would allow upto 250W into 4r0 and Quasi's rule would indicate that F4A is generally high enough for a similar power output.
It's not Rds on that is the limiting factor.richie00boy said:
It's the gate drive voltage which needs an overhead of between 5V and 8V when delivering maximum power.
As an aside.
2pair of 100W lateral FETs would make an excellent 8ohm capable amplifier able to deliver 150W+ into any 8ohm speaker.
But, for 4ohm capability, 3 or preferably 4pair would be needed to approach excellence.
160W to 225W (+1.48dBW) when going to half impedance indicates that this amplifier is struggling with a 4r0 load and don't even think about using a severe reactance speaker as a load.
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