Hi,
I checked the power supply without connecting it anywhere. It measures +/- 35V. But when I connect it to the amplifier, the voltage drops to about 30 and 25V when measured after the 10 ohm resistors. But still the voltage across the 10 ohm resistor remains zero.
And yes, I am using the same power supply for both modules.
A little later, I removed the light bulb from the transformer input circuit and switched on. No smoke (thank God) but still the voltage across the 10 ohm resistors is 0. I checked after the 10 ohm resistors and it measures 42V between the positive rail and ground and about 28V between the negative rail and ground. I just don't get it. What am I missing?
Vivek
I checked the power supply without connecting it anywhere. It measures +/- 35V. But when I connect it to the amplifier, the voltage drops to about 30 and 25V when measured after the 10 ohm resistors. But still the voltage across the 10 ohm resistor remains zero.
And yes, I am using the same power supply for both modules.
A little later, I removed the light bulb from the transformer input circuit and switched on. No smoke (thank God) but still the voltage across the 10 ohm resistors is 0. I checked after the 10 ohm resistors and it measures 42V between the positive rail and ground and about 28V between the negative rail and ground. I just don't get it. What am I missing?
Vivek
Hi Guys;
Having some reading across half of this forum and also Google to understand better and to learn more as somebody start to have headache with my dumb question-sorry for that-just want to learn.
I need confirmation on this - from my digging so far based on my module i.e pwr with 53Vdc
1. I should get Vdc reading @44Vdc (let say on Pos rail side) across the 100r means 9v drop as I'm using 3 pairs. (Previously posted is actually value measured from Gnd point to point after the 100r)
2. As I'm using 0.47 for the source resistor as to set the 30mA per FET pair based on 44Vdc, I should get at around 6mV across either R30, R32 and R34 or can it be measure across R29, R31 and R33?
Guide me and correct me on this and I will proceed to check without funny question...
Many Thanks
Having some reading across half of this forum and also Google to understand better and to learn more as somebody start to have headache with my dumb question-sorry for that-just want to learn.
I need confirmation on this - from my digging so far based on my module i.e pwr with 53Vdc
1. I should get Vdc reading @44Vdc (let say on Pos rail side) across the 100r means 9v drop as I'm using 3 pairs. (Previously posted is actually value measured from Gnd point to point after the 100r)
2. As I'm using 0.47 for the source resistor as to set the 30mA per FET pair based on 44Vdc, I should get at around 6mV across either R30, R32 and R34 or can it be measure across R29, R31 and R33?
Guide me and correct me on this and I will proceed to check without funny question...
Many Thanks
Hi Hari
No it shouldn't. A switch on delay is set mainly by the 330k resistor and the 470uF capacitor. The rising voltage is fed via a 56K resistor to the base of Q4.
Possible causes of your fault include an open cct capacitor or short cct Q4 and or Q5. Do you have a diode across the relay coil?
Cheers
Q
No it shouldn't. A switch on delay is set mainly by the 330k resistor and the 470uF capacitor. The rising voltage is fed via a 56K resistor to the base of Q4.
Possible causes of your fault include an open cct capacitor or short cct Q4 and or Q5. Do you have a diode across the relay coil?
Cheers
Q
satcure,
As just noted by Quasi, you need to use 10R and 1R (noted by AndrewT) to properly bias the mosfets.
In my understanding,
1) the 100R is for pre-biasing safety purposes only.
You adjust the voltage to 9V.
2) the 10R is for proper biasing of the mosfets.
You adjust the voltage to 0.9V
3) the 1R (and/or 0.1R) is for more precise biasing.
You adjust voltage to 90mV.
If you're done on these, your amp will be good for sonic
testing.
As just noted by Quasi, you need to use 10R and 1R (noted by AndrewT) to properly bias the mosfets.
In my understanding,
1) the 100R is for pre-biasing safety purposes only.
You adjust the voltage to 9V.
2) the 10R is for proper biasing of the mosfets.
You adjust the voltage to 0.9V
3) the 1R (and/or 0.1R) is for more precise biasing.
You adjust voltage to 90mV.
If you're done on these, your amp will be good for sonic
testing.
quasi said:
I found it
The 470uf cap and the 56K in parallel were both not connected to ground
It was an error in my pcb layout. The switch on delay is now working. But the dc detect part does not seem to be working. I used a 9V power supply to inject the dc but the relays are not turning off.Hari
quasi said:
Quasi
The dc supply I'm using for injecting the dc voltage shares the same ground. I've connected the ground of the supply to that of the dc detect board. For the dc detect, I have an onboard supply.
Meanwhile, check out this dc detect circuit that was published in Elektor a very long time ago and which I'm using in my present amp.
Hari
R21 in Nmos200
What is the purpose of R21 in the schematic of Nmos200?
I am in the progress of putting this amp together and in the meantime I have modelled it in my simulator (Multisim 10).
The resistor R21 on 100 ohm just seems to bring assymetrical clipping (negative clip before positive) and also assymetric distorsion (cross distorsion when going positive to negative) when biasing, unless a much higher quisent current is choosen compared when this resistor is not there at all.
Maybe I have missed it in this or some other thread but it's a lot of threads to read and search through
Soon I have the real stuff to measure on but any explenation before is welcome.
What is the purpose of R21 in the schematic of Nmos200?
I am in the progress of putting this amp together and in the meantime I have modelled it in my simulator (Multisim 10).
The resistor R21 on 100 ohm just seems to bring assymetrical clipping (negative clip before positive) and also assymetric distorsion (cross distorsion when going positive to negative) when biasing, unless a much higher quisent current is choosen compared when this resistor is not there at all.
Maybe I have missed it in this or some other thread but it's a lot of threads to read and search through
Soon I have the real stuff to measure on but any explenation before is welcome.
Hi Radioman62,
One of the characteristic drawbacks of this topology is that the positive going output swing will clip before the negative going swing. This has to do with the gate voltage requirements of the FETs where the gate must be +4 to +6 volts more than the source. When the source approaches Vcc there is simply no voltage left for the gate drive and the output clips.
The 100ohm resistor serves to also limit the drive to the negative rail FETs so that a degree of symmetrical clipping is achieved. I know it's not perfect but in practice performs ok.
Cheers
Q
One of the characteristic drawbacks of this topology is that the positive going output swing will clip before the negative going swing. This has to do with the gate voltage requirements of the FETs where the gate must be +4 to +6 volts more than the source. When the source approaches Vcc there is simply no voltage left for the gate drive and the output clips.
The 100ohm resistor serves to also limit the drive to the negative rail FETs so that a degree of symmetrical clipping is achieved. I know it's not perfect but in practice performs ok.
Cheers
Q
Thanks Quasi, that explains it. Also, I have very little experience of Mosfets.
This quirk doesn't show up in the simulator, even though I got the IRFP260 Spice model from the International Rectifier
.
I hope to have a working "real" amp this weekend to do tests on. Can't wait to see real scope pictures from my old Tektronix T912
I am in looong progress of doing my own ampdesign which use On Semi's ThermalTrak BJT devices, but your NMOS200 was a perfect easy to do project and a way for me to really have a chans to listen to a Mosfet amp for the first time. Iwas a bit to fast though ....
When I etched the PCB board I thought that the copperside was the side where you could read the texts "Vpos" and "Vneg" the right way. When two cards where done and drilled I saw that everything was mirrored, exept the texts "Vpos" and "Vneg"...
It's not a big problem though. I have to solder the output transistor the other way, so when the heatzink is in place they are hiding beneath.
I will report back when I have something to give in this project.
By the way, is there any posts on measured data on this amp? Such as distortion and signal to noise etc.
This quirk doesn't show up in the simulator, even though I got the IRFP260 Spice model from the International Rectifier
.I hope to have a working "real" amp this weekend to do tests on. Can't wait to see real scope pictures from my old Tektronix T912
I am in looong progress of doing my own ampdesign which use On Semi's ThermalTrak BJT devices, but your NMOS200 was a perfect easy to do project and a way for me to really have a chans to listen to a Mosfet amp for the first time. Iwas a bit to fast though ....
When I etched the PCB board I thought that the copperside was the side where you could read the texts "Vpos" and "Vneg" the right way. When two cards where done and drilled I saw that everything was mirrored, exept the texts "Vpos" and "Vneg"...
It's not a big problem though. I have to solder the output transistor the other way, so when the heatzink is in place they are hiding beneath.
I will report back when I have something to give in this project.
By the way, is there any posts on measured data on this amp? Such as distortion and signal to noise etc.
Hello
Also, I have very little experience of Mosfets.
I dont understand in Quasis Design Nmos 350 MKII.....
I think the Emitter voltage T11 MJE 350 will be about - 75V,this is to high, the gate from Mosfets T13,T15,T17 connected (with gate resistors) with T11 will get -75 V and Mosfets blow up < 1 second .
I dont understand this, i think T13,T15,T17 N-Channel mosfets will blow up < 0,1 second ....after switch on power board
For example, If i queck Voltage with 220 OHM resistor and Digital Multimeter from - 75 V to Ground the Voltage is about - 75 V.
How that can function, I pleased me about a detailed explanation
Also, I have very little experience of Mosfets.
I dont understand in Quasis Design Nmos 350 MKII.....
I think the Emitter voltage T11 MJE 350 will be about - 75V,this is to high, the gate from Mosfets T13,T15,T17 connected (with gate resistors) with T11 will get -75 V and Mosfets blow up < 1 second .
I dont understand this, i think T13,T15,T17 N-Channel mosfets will blow up < 0,1 second ....after switch on power board
For example, If i queck Voltage with 220 OHM resistor and Digital Multimeter from - 75 V to Ground the Voltage is about - 75 V.
How that can function, I pleased me about a detailed explanation