Hi Kanwar,
Arrrrgggghhh! Please cut out the professional nonsense. It's making me sick.
I repaired Pro amps for over 20 yrs. There are many on this board that did the same and some who designed the darn things. They are just an object, a tool.
Things that make a good "pro amp" are high efficiency, reliability and light weight. All are well built with overdesigned output stages for standard acceptable loads. Many are designed for "road work" and some in stationary appliciations.
If you want to design amplifiers that will put up with m o r o n s connecting them with improper loads - fine. That does not lessen any other amp or make yours somehow superiour. They will be heavier, that's for sure. What you are doing is encouraging poor sound practices. Your business, your viewpoint, don't rub it in any more.
There are countless amp racks with 30 + yr old amps, running fine in them. That sounds like a good amp to me. Some may sound bad now, but they were the best at the time.
-Chris
Arrrrgggghhh! Please cut out the professional nonsense. It's making me sick.
I repaired Pro amps for over 20 yrs. There are many on this board that did the same and some who designed the darn things. They are just an object, a tool.
Things that make a good "pro amp" are high efficiency, reliability and light weight. All are well built with overdesigned output stages for standard acceptable loads. Many are designed for "road work" and some in stationary appliciations.
If you want to design amplifiers that will put up with m o r o n s connecting them with improper loads - fine. That does not lessen any other amp or make yours somehow superiour. They will be heavier, that's for sure. What you are doing is encouraging poor sound practices. Your business, your viewpoint, don't rub it in any more.
There are countless amp racks with 30 + yr old amps, running fine in them. That sounds like a good amp to me. Some may sound bad now, but they were the best at the time.
-Chris
PS:
SOA is the process where one limits output device current as a function of voltage across the output device. It is well known especially in bjt's that at higher Vce the current allowed is much LESS than the Pc would suggest. A 200W device may be able to carry 10A at 20 Vce, but NOT 2.5 A at 80V, but only say 1A at 80V. SOA limiting oftem includes one or two breakpoints in the allowed Ic/Vce curve to follow as closely as possible the device SOA curve to get the max power out of a given device without danger of overload.
Why is that important? Especially with complex loads, due to phase shift between load voltage and load current, the output voltage may be positive while the current is negative, in other words, the bottom device is "sucking" current while the Vce of the bottom device is very high because of the pos output voltage. That is a condition that would invite secondary breakdown, resulting from exceeding the SOA. So, for real-world complex (speaker) load and bjt output stages, you need SOA protection to be safe and to get max output power. With more ohmic simple loads (as in active speakers) and with MOSFET outputs (that have much less or no secondary breakdown problems) it is less of an issue.
Jan Didden
SOA is the process where one limits output device current as a function of voltage across the output device. It is well known especially in bjt's that at higher Vce the current allowed is much LESS than the Pc would suggest. A 200W device may be able to carry 10A at 20 Vce, but NOT 2.5 A at 80V, but only say 1A at 80V. SOA limiting oftem includes one or two breakpoints in the allowed Ic/Vce curve to follow as closely as possible the device SOA curve to get the max power out of a given device without danger of overload.
Why is that important? Especially with complex loads, due to phase shift between load voltage and load current, the output voltage may be positive while the current is negative, in other words, the bottom device is "sucking" current while the Vce of the bottom device is very high because of the pos output voltage. That is a condition that would invite secondary breakdown, resulting from exceeding the SOA. So, for real-world complex (speaker) load and bjt output stages, you need SOA protection to be safe and to get max output power. With more ohmic simple loads (as in active speakers) and with MOSFET outputs (that have much less or no secondary breakdown problems) it is less of an issue.
Jan Didden
All eyes on me!!!!!
Dear Jan you are missing a point !
The Zeners at the gate of mosfet have two work assignments...
1. They protect the gate from overvoltage occuring from spikes or transients resulting from spurious Turn-ON of equipments .
2. They protect the MOSFET in the EVENT of SHORT CIRCUIT...HOW?
Here it goes:
In a closed loop amp with Mosfet output stage , when the short circuit is encountered, then the output tends to drive the short circuit due to the feedback action, then the GATE DRIVE VOLTAGE at the Gate Terminals of the Mosfet Rises Abruptly so as to enable the Mosfet to Conduct the Large Current to Drive the Dead Short, Which results in Increase in the Temperature of DIE and also the maximum current conduction limit of mosfet is exceeded and it gets destoryed in no time....
But if we implement a Zener On the Gate to Source terminal of Mosfet Such that Its Clamp Voltage Value is Set according to the SOA, so that Mosfet conducts only a small amount of current..because the Gate voltage is now limited by Zener and the Current Conduction in a mosfet is Directly proportional to gate Voltage...Hence the Drain current from the mosfet is now limited and Falls under the Safe value to protect itself to some extent. and After That the protection circuit kicks and does its job..
Traditional Mosfet amps use Zeners [especially 12V]to Just protect the Gate of Mosfets from overvoltage, But...If you choose the Value say 5.6V - 6.2V Zeners [in our amps] these limit the output current to about 4 - 5 amperes peak per Mosfet and saves them from overcurrent condition..
Similarly , if the Value is choosen to be 12V for Zeners they would not assist in safeguarding the mosfets in Event of Short Circuit because at 12V of gate drive the Mosfet saturates Fully....
I Hope You would now agree with me..
K a n w a r
janneman said:
Dear Jan you are missing a point !
The Zeners at the gate of mosfet have two work assignments...
1. They protect the gate from overvoltage occuring from spikes or transients resulting from spurious Turn-ON of equipments .
2. They protect the MOSFET in the EVENT of SHORT CIRCUIT...HOW?
Here it goes:
In a closed loop amp with Mosfet output stage , when the short circuit is encountered, then the output tends to drive the short circuit due to the feedback action, then the GATE DRIVE VOLTAGE at the Gate Terminals of the Mosfet Rises Abruptly so as to enable the Mosfet to Conduct the Large Current to Drive the Dead Short, Which results in Increase in the Temperature of DIE and also the maximum current conduction limit of mosfet is exceeded and it gets destoryed in no time....
But if we implement a Zener On the Gate to Source terminal of Mosfet Such that Its Clamp Voltage Value is Set according to the SOA, so that Mosfet conducts only a small amount of current..because the Gate voltage is now limited by Zener and the Current Conduction in a mosfet is Directly proportional to gate Voltage...Hence the Drain current from the mosfet is now limited and Falls under the Safe value to protect itself to some extent. and After That the protection circuit kicks and does its job..
Traditional Mosfet amps use Zeners [especially 12V]to Just protect the Gate of Mosfets from overvoltage, But...If you choose the Value say 5.6V - 6.2V Zeners [in our amps] these limit the output current to about 4 - 5 amperes peak per Mosfet and saves them from overcurrent condition..
Similarly , if the Value is choosen to be 12V for Zeners they would not assist in safeguarding the mosfets in Event of Short Circuit because at 12V of gate drive the Mosfet saturates Fully....
I Hope You would now agree with me..
K a n w a r
Hi Kanwar,
Yes that OK - but you are using very high transconductance devices with high input C and production spreads. this 6.2V is quite low for your reasons but do you match devices? Can they get an overvoltage pulse to speed turn-on (charge that large gate C)?
You have obviously chosen a good balance.
Cheers,
Greg
Yes that OK - but you are using very high transconductance devices with high input C and production spreads. this 6.2V is quite low for your reasons but do you match devices? Can they get an overvoltage pulse to speed turn-on (charge that large gate C)?
You have obviously chosen a good balance.
Cheers,
Greg
Hi GREG,
I dont know why do we have a good Chemistry between us, besides the Fact that we havent seen or met each other !......
Yeah we use High TransConductance mosfets and there C is high too....we do match the devices but to about 10% Tolerance max.
Since the MAX voltage at gate is limited by the Zeners, So as to derive a good Transient response at output , we opt to parallel many Devices and use Push-Pull Drivers to enhance both Turn-ON & Turn-OFF Of Devices....Whereas in Conventional designs the turn -ON is Active but turn -Off is merely done passively by Gate driver resistor[bleeder resistor of driver stage]. in our case both periods are enabled actively...
A single Mosfet cant give you even a rail to rail swing with limited gate drive voltage with low impedance loads, but if you parallel them the output current adds and result in excellent combination of Transient spur attack!
Wishing you a Nice and Happy life,
K a n w a r
I dont know why do we have a good Chemistry between us, besides the Fact that we havent seen or met each other !......
Yeah we use High TransConductance mosfets and there C is high too....we do match the devices but to about 10% Tolerance max.
Since the MAX voltage at gate is limited by the Zeners, So as to derive a good Transient response at output , we opt to parallel many Devices and use Push-Pull Drivers to enhance both Turn-ON & Turn-OFF Of Devices....Whereas in Conventional designs the turn -ON is Active but turn -Off is merely done passively by Gate driver resistor[bleeder resistor of driver stage]. in our case both periods are enabled actively...
A single Mosfet cant give you even a rail to rail swing with limited gate drive voltage with low impedance loads, but if you parallel them the output current adds and result in excellent combination of Transient spur attack!
Wishing you a Nice and Happy life,
K a n w a r
Never use zeners to 'limit' current in mosfets....
.....as voltage drive to the devices is needlessly curtailed even when they are not in danger...
'Zener-limiting' current in a power mosfet to '4A or 5A' regardless of the voltage across it is near-perverse, as these devices may well be able to pass 30A at low Vds!
In general, 'overkill' design, and the use of zener diode 'limiting' falls in the category of what people prefer to grasp with their hands rather than with their minds....
.....as voltage drive to the devices is needlessly curtailed even when they are not in danger...
'Zener-limiting' current in a power mosfet to '4A or 5A' regardless of the voltage across it is near-perverse, as these devices may well be able to pass 30A at low Vds!
In general, 'overkill' design, and the use of zener diode 'limiting' falls in the category of what people prefer to grasp with their hands rather than with their minds....
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