Re: Re: quasi's post #1899
Hi everyone,
I am, thanks for your effort, and thanks for pointing out, John. 😉
Yet I'm unsure of the relevance for my work on the website prototype, as Quasi likely won't use it.
See? 😱
I'm sure Quasi will tell the thread which way his website development needs will go when the time is ready for him.
Cheers,
Sebastian.
Hi everyone,
I am, thanks for your effort, and thanks for pointing out, John. 😉
Yet I'm unsure of the relevance for my work on the website prototype, as Quasi likely won't use it.
See? 😱
I'm sure Quasi will tell the thread which way his website development needs will go when the time is ready for him.
Cheers,
Sebastian.
Web Update
Hi folks,
Updated the web site a bit tonight.
In the power selection table, I have downgraded acheivable powers a little to better reflect a real world practical build. I have also taken advice from John (OQTR) and AndrewT and have inserted suggested fuse ratings. I have also applied some values for R6 & R17.
Note; my approach is a bit different. I have tried to return to more common values for resistors (E12) and fuses.
Cheers
Q
PS. Sebastian, you are welcome to transfer any information you like to your (better) web site.
Hi folks,
Updated the web site a bit tonight.
In the power selection table, I have downgraded acheivable powers a little to better reflect a real world practical build. I have also taken advice from John (OQTR) and AndrewT and have inserted suggested fuse ratings. I have also applied some values for R6 & R17.
Note; my approach is a bit different. I have tried to return to more common values for resistors (E12) and fuses.
Cheers
Q
PS. Sebastian, you are welcome to transfer any information you like to your (better) web site.
Hi,
I posted an update in the Leach thread on power and fusing.
I drove 311W into 4r0 using F3.1A rail fuses.
They both survived a non reactive load with peak currents hitting 12.4Apk.
I wonder what instantaneous peak currents will flow into a reactive load and when there is a sudden change in drive voltage.
The suggestion is that the apparent impedance of the speaker can fall to 35% to 40% of the nominal impedance.
If this were applied to our fusing requirements then peak currents into 4ohm speakers could approach 25Apk. What value of F rated fuse do we fit for that duty?
F4A or F5A or F6A?
Using half peak requires F6A to push 300W into 4ohms.
Using half RMS requires F5A.
Take your pick with your amps and speakers. See how long they last. But always safer to start slightly smaller using Quasi's half rms value and hope there is little if any nuisance tripping.
BTW,
what happens to output offset if the ONLY damage is one blown rail fuse?
I posted an update in the Leach thread on power and fusing.
I drove 311W into 4r0 using F3.1A rail fuses.
They both survived a non reactive load with peak currents hitting 12.4Apk.
I wonder what instantaneous peak currents will flow into a reactive load and when there is a sudden change in drive voltage.
The suggestion is that the apparent impedance of the speaker can fall to 35% to 40% of the nominal impedance.
If this were applied to our fusing requirements then peak currents into 4ohm speakers could approach 25Apk. What value of F rated fuse do we fit for that duty?
F4A or F5A or F6A?
Using half peak requires F6A to push 300W into 4ohms.
Using half RMS requires F5A.
Take your pick with your amps and speakers. See how long they last. But always safer to start slightly smaller using Quasi's half rms value and hope there is little if any nuisance tripping.
BTW,
what happens to output offset if the ONLY damage is one blown rail fuse?
Hi Andrew,
I always yank each fuse out, one at a time and measure the DC offset. It helps to use reverse biased diodes to ground from each supply after the fuses to prevent the rail from reversing in polarity. This also helps the DC offset remain closer to ground.
-Chris
I always yank each fuse out, one at a time and measure the DC offset. It helps to use reverse biased diodes to ground from each supply after the fuses to prevent the rail from reversing in polarity. This also helps the DC offset remain closer to ground.
-Chris
anatech said:
Chris could you post for my education a schematic segment of what you described?
Regards,
John L. Males
Willowdale, Ontario
Canada
26 June 2007 22:50
Official Quasi Thread Researcher
Hi John,
I don't have anything to draw on handy at the moment. I'll describe it differently then.
Assuming you have a positive and negative fused rail (one each). After the supply fuse (towards your circuit) you install a 1N4007 from that point to your dirty ground, the diode does not normally conduct. The same thing is repeated for the negative rail, the diode also installed so it normally does not conduct.
By doing this you protect the circuit. Sometimes when a fuse fails on a rail, the (say positive) rail might be pulled to some value between the (negative for example) rail and ground. This may destroy electrolytic caps and cause some junctions in semiconductors to conduct heavy currents. This may not kill a device outright, but it may damage the device so that it becomes leaky or noisy. The DC parameters may also shift (such as DC beta in a transistor).
So, with diodes installed, the greatest voltage in the opposite polarity you would see should be less than 1 volt.
-Chris
I don't have anything to draw on handy at the moment. I'll describe it differently then.
Assuming you have a positive and negative fused rail (one each). After the supply fuse (towards your circuit) you install a 1N4007 from that point to your dirty ground, the diode does not normally conduct. The same thing is repeated for the negative rail, the diode also installed so it normally does not conduct.
By doing this you protect the circuit. Sometimes when a fuse fails on a rail, the (say positive) rail might be pulled to some value between the (negative for example) rail and ground. This may destroy electrolytic caps and cause some junctions in semiconductors to conduct heavy currents. This may not kill a device outright, but it may damage the device so that it becomes leaky or noisy. The DC parameters may also shift (such as DC beta in a transistor).
So, with diodes installed, the greatest voltage in the opposite polarity you would see should be less than 1 volt.
-Chris
Many power amps have diodes between the output and supply rails to handle surges due to load inductance . These probably would be enough for this purpose.
What about in built protection diodes of some power devices ? Good enough for the same purpose ?
What about in built protection diodes of some power devices ? Good enough for the same purpose ?
Hi ashok,
Those go from supply to speaker output. That is another thing I normally design into all amplifiers. What is needed here are diodes from supplies to a hard ground.
Hmmmm, those diodes would work if the output was shorted.
-Chris
Those go from supply to speaker output. That is another thing I normally design into all amplifiers. What is needed here are diodes from supplies to a hard ground.
Hmmmm, those diodes would work if the output was shorted.
-Chris
Hi ashok,
Don't feel bad. I have moments like that often.
Hi Bonsai,
The type of diode I use depends on where it is and how much power is lying around just waiting to go the wrong way. For smaller amps I use 1N4007. I use these because they are almost the same price as lower voltage units and I don't want to stock different types. For larger amps I might use 1N5408 types from the speaker output to the supply busses. A 1N4007 is normally all that's needed from supplies to ground. If they short, even better (the fuse is already blown).
-Chris
Don't feel bad. I have moments like that often.
Hi Bonsai,
The type of diode I use depends on where it is and how much power is lying around just waiting to go the wrong way. For smaller amps I use 1N4007. I use these because they are almost the same price as lower voltage units and I don't want to stock different types. For larger amps I might use 1N5408 types from the speaker output to the supply busses. A 1N4007 is normally all that's needed from supplies to ground. If they short, even better (the fuse is already blown).
-Chris
now I am confused
about websites of the nmos amp-
which website should I look now-well the problems are the resistors and their different values
Quasi is your website the right one or...?
thanks
and why are the resistors in power suply?i think they are there for discharging the caps, but why is this so important?
about websites of the nmos amp-which website should I look now-well the problems are the resistors and their different values
Quasi is your website the right one or...?
thanks
and why are the resistors in power suply?i think they are there for discharging the caps, but why is this so important?
smokingmachine said:now I am confused
which website should I look now-well the problems are the resistors and their different values
Quasi is your website the right one or...?
thanks
and why are the resistors in power suply?i think they are there for discharging the caps, but why is this so important?
Smokingmachine,
If I may jump in.
Quasi's website is the only one to refer to and is up to date and is maintained up to date. sek's site was just a prototype and not a live site yet and may not be. My site is very old and I have had hosting technical problems in its administration so I have not been able to update it, my life issues for number of months aside.
I am not sure what resistors you are refering to. There are two possible purposes for resistors in a amp power supply.
One is used to discharge the filter capacitors. This is important for two reasons. Discharging for safety reasons so if you have to go into the amp a long time after it is turned off the dangerous current stored in the filter capacitors has been discharged. That said you still have to be aware of this hazzard and know how to check if there is still a charge and if so how to bleed the capacitors off safely, but faster so you can work on the amplifier.
The second possible purpose of resistors is in combination with small value film capacitors to filter out certain undesirable noise "garbage" that some believe improves the sonics of the amplifier. The garbage is generally noise from the AC line, filter capacitors, transformer, et al.
Regards,
John L. Males
Willowdale, Ontario
Canada
27 June 2007 23:19
Official Quasi Thread Researcher
Hi,
Exactly.
Quasi, you might want to check out the JS-Kit Widget.
It's not exactly a guest book, but I already commented on the nineties thing... 😉
PS: I updated my prototype site in order to clarify.
Exactly.
Quasi, you might want to check out the JS-Kit Widget.
It's not exactly a guest book, but I already commented on the nineties thing... 😉
PS: I updated my prototype site in order to clarify.
MOSFET Rating
Hello,
I thought it may have been discussed in this thread, but it apears it has not. What I like to know is if the Rail Voltage is +- X does the MOSFET Vdss need to be at least 2*X or at least X? I know there should be a margin of safety, so for the purpose of this question skip any safety margin as I will absolutely ensure there is sufficent safety margin.
I seem to recall reading somewhere else over a year ago that the answer was 2*X. If that is case it would be helpful to understand the reason(s) for the 2*X Vdss MOSFET rating as I do not understand why if the answer is in fact 2*X.
Regards,
John L. Males
Willowdale, Ontario
Canada
30 June 2007 22:52
Official Quasi Thread Researcher
Hello,
I thought it may have been discussed in this thread, but it apears it has not. What I like to know is if the Rail Voltage is +- X does the MOSFET Vdss need to be at least 2*X or at least X? I know there should be a margin of safety, so for the purpose of this question skip any safety margin as I will absolutely ensure there is sufficent safety margin.
I seem to recall reading somewhere else over a year ago that the answer was 2*X. If that is case it would be helpful to understand the reason(s) for the 2*X Vdss MOSFET rating as I do not understand why if the answer is in fact 2*X.
Regards,
John L. Males
Willowdale, Ontario
Canada
30 June 2007 22:52
Official Quasi Thread Researcher
Hi,
interesting design... i wanna try...
but... theres something bothering me... the cost...
man, FET transistors were too expensive here in our country...
how about, instead of using FET's,,, i use common output transistors... how shall i incorporate it?
thanx...
regards,
Riche🙂
interesting design... i wanna try...
but... theres something bothering me... the cost...
man, FET transistors were too expensive here in our country...
how about, instead of using FET's,,, i use common output transistors... how shall i incorporate it?
thanx...
regards,
Riche🙂
mos-fet voltage rating
The most logical answer on this problem should be Vdss = 2x
The worst case for the amplifier is when the amplifier is overloaded and one bank of fet's are conducting. In this way the other bank of transistors sees the whole supply voltage minus the voltage drop across the load. An extreme case should be a short circuited load or an inductive kick of the load which adds to the supply voltage.
This is the way i see things... if I'm wrong please correct me.
The most logical answer on this problem should be Vdss = 2x
The worst case for the amplifier is when the amplifier is overloaded and one bank of fet's are conducting. In this way the other bank of transistors sees the whole supply voltage minus the voltage drop across the load. An extreme case should be a short circuited load or an inductive kick of the load which adds to the supply voltage.
This is the way i see things... if I'm wrong please correct me.
sorry guys,
what I said in the previous post about amplifier overloading and inductive kicks only applies to the BTL amplifiers. (my mind was at full bridge switching supply)
For single ended amplifiers the load only have a small influence on the Vdss rating of the MOS-FET's.
But still, the output transistors should be rated to at least 2x supply voltage because the conducting mos-fet applies the other branch of the power supply to the non conducting one (minus D-S voltage drop). In this way the non conducting mos sees the whole power supply voltage across it's drain - source terminals.
what I said in the previous post about amplifier overloading and inductive kicks only applies to the BTL amplifiers. (my mind was at full bridge switching supply)
For single ended amplifiers the load only have a small influence on the Vdss rating of the MOS-FET's.
But still, the output transistors should be rated to at least 2x supply voltage because the conducting mos-fet applies the other branch of the power supply to the non conducting one (minus D-S voltage drop). In this way the non conducting mos sees the whole power supply voltage across it's drain - source terminals.