ampli mosfet irf 540 + irf9540 - Page 2

xcicc · 17th March 2009, 01:41 PM

again

xcicc · 17th March 2009, 01:43 PM

the last...

xcicc · 17th March 2009, 01:44 PM

Quote:

Originally posted by Zen Mod
search for Papa's Citation 12

I have not found anything, please post the link?
thanks

xcicc · 17th March 2009, 01:47 PM

Quote:

Originally posted by BV
Change R5 to 820R or 1k( or change R3 to 8.2k or 10k). This schematic needs (to work correct) supply voltage about +-35V.

ok, I agree even though I do not think it will change anything.
ok I agree the power supply should be 30 +30 v but I have only a 15 +15 v I do not think that this is to affect the circuit
thanks

Zen Mod · 17th March 2009, 02:08 PM

Quote:

Originally posted by xcicc

I have not found anything, please post the link?
thanks

http://www.passdiy.com/pdf/citation.pdf

Corax · 17th March 2009, 03:34 PM

Oh xcicc, you can do better than this.
Please try to imagine if someone can trace through your amp by seeing just these kind of picture. The picture from the component side is fine, but I wish I would've found the same (complete) picture just from the copper side (and mirrored, to make an overlay, would be almost perfect). Your PCB drawing with some sort of silkscreen to identify which component is located at which place would make in addition things much easier for me/us.

Nevertheless, I still guess that the fault is located at the BIAS circuit. Either the routing is incorrect or T3 is blown.
I still doubt that at all pins of both MOSFETs you're able to measure +22V. I guess aou mean +22V at T5 and -22V at T6?! Otherwise it would make no sense at all - i.e. +22V at the -22V rail.

And again, what is the voltage between the Collector and Emitter of T3 and/or between the Gates of the two MOSFETs?

xcicc · 17th March 2009, 03:46 PM

Quote:

Originally posted by Corax
Oh xcicc, you can do better than this.
Please try to imagine if someone can trace through your amp by seeing just these kind of picture. The picture from the component side is fine, but I wish I would've found the same (complete) picture just from the copper side (and mirrored, to make an overlay, would be almost perfect). Your PCB drawing with some sort of silkscreen to identify which component is located at which place would make in addition things much easier for me/us.

Nevertheless, I still guess that the fault is located at the BIAS circuit. Either the routing is incorrect or T3 is blown.
I still doubt that at all pins of both MOSFETs you're able to measure +22V. I guess aou mean +22V at T5 and -22V at T6?! Otherwise it would make no sense at all - i.e. +22V at the -22V rail.

And again, what is the voltage between the Collector and Emitter of T3 and/or between the Gates of the two MOSFETs?

I hope that this picture is more useful, later I will make some of measurements .
thanks
I just added the picture with some value...

mjf · 17th March 2009, 04:56 PM

hello.
have a look at t4 if it is built in wrong
or the connection from its' collector to the other parts is lost/broken......
greetings.......

CBS240 · 17th March 2009, 04:57 PM

Hi

There are a few problems that stand out to me. First off, IRF540 and IRF9540 are not really complements (if there really could be complements of these type of transistor

) in terms of relative transconductance. These mosfets are of vertical type and need thermal compensation. T3, the bias servo, is intended to track the temperature of the outputs to keep the bias from running away. I don't see T3 mounted to the heatsink or outputs.....

About the circuit around T3.... The pot should connect between base and emitter in series with R12 with the wiper shorted to one side because if the pot ever fails such as the wiper becomes open, then T3 turns off and the outputs will be smoked like bad "tobacco" thru a hookah. Then there is the case of the outputs not having source resistors. These are important for stability, especially with the DC bias. The point of which the feedback node is taken from between the output source resistors (that you don't have) is important for fb symmetry and stability. Speaking of frequency stability, gate resistors are necessary for each mosfet as physically close to it as possible. Better yet, a gate Zobel filter. Speaking of Zobel filter, for the output, it is in the schematic, but I don't see it on the PCB.

If you get some spare time, you should skim through
this paper. Some good info

Corax · 18th March 2009, 09:11 AM

Well xcicc, if you have -12.63V at the Emitters of T1 and T2 the differential amp at the input won't work. Have you noticed that the pin assignment for the MPSA92 transistors is mirrored to the BC238?! Either the Emitter and Collectors of T1 and T2 are (accidentally) swapt or they are burned. Since these Transistors are PNP and they should conduct a little bit the voltage level at the Emitters must be somewhat positive but never negative.

Furthermore for the functionality of the amp Source resistors, as CBS240 mentioned, are not really or absolutely necessary. However it is true that they could better stabilize the BIAS circuitry. Until now, we don't even have a running amplifier with a working DC BIAS, so we should proceed step by step.

Another point are the (series) Gate resistors CBS240 mentioned. They would prevent unwanted oscillation of the amplifier. They could and should be inserted. However I've seen many (even) professional linear amplifier not having those. That's also a question of design and if there is i.e. local negative feedback introduced or not besides other factors like PCB design, component selection and so on.

Strange is also that some voltages in the circuit extend the measured voltages of the rails? How could this happen xcicc?

17th March 2009, 04:57 PM	#19
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Hi There are a few problems that stand out to me. First off, IRF540 and IRF9540 are not really complements (if there really could be complements of these type of transistor ) in terms of relative transconductance. These mosfets are of vertical type and need thermal compensation. T3, the bias servo, is intended to track the temperature of the outputs to keep the bias from running away. I don't see T3 mounted to the heatsink or outputs..... About the circuit around T3.... The pot should connect between base and emitter in series with R12 with the wiper shorted to one side because if the pot ever fails such as the wiper becomes open, then T3 turns off and the outputs will be smoked like bad "tobacco" thru a hookah. Then there is the case of the outputs not having source resistors. These are important for stability, especially with the DC bias. The point of which the feedback node is taken from between the output source resistors (that you don't have) is important for fb symmetry and stability. Speaking of frequency stability, gate resistors are necessary for each mosfet as physically close to it as possible. Better yet, a gate Zobel filter. Speaking of Zobel filter, for the output, it is in the schematic, but I don't see it on the PCB. If you get some spare time, you should skim through this paper. Some good info __________________ All the trouble I've ever been in started out as fun......

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17th March 2009, 03:34 PM	#16
Corax diyAudio Member Join Date: Feb 2005 Location: south of lower saxon	Oh xcicc, you can do better than this. Please try to imagine if someone can trace through your amp by seeing just these kind of picture. The picture from the component side is fine, but I wish I would've found the same (complete) picture just from the copper side (and mirrored, to make an overlay, would be almost perfect). Your PCB drawing with some sort of silkscreen to identify which component is located at which place would make in addition things much easier for me/us. Nevertheless, I still guess that the fault is located at the BIAS circuit. Either the routing is incorrect or T3 is blown. I still doubt that at all pins of both MOSFETs you're able to measure +22V. I guess aou mean +22V at T5 and -22V at T6?! Otherwise it would make no sense at all - i.e. +22V at the -22V rail. And again, what is the voltage between the Collector and Emitter of T3 and/or between the Gates of the two MOSFETs?

17th March 2009, 04:56 PM	#18
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. have a look at t4 if it is built in wrong or the connection from its' collector to the other parts is lost/broken...... greetings.......

18th March 2009, 09:11 AM	#20
Corax diyAudio Member Join Date: Feb 2005 Location: south of lower saxon	Well xcicc, if you have -12.63V at the Emitters of T1 and T2 the differential amp at the input won't work. Have you noticed that the pin assignment for the MPSA92 transistors is mirrored to the BC238?! Either the Emitter and Collectors of T1 and T2 are (accidentally) swapt or they are burned. Since these Transistors are PNP and they should conduct a little bit the voltage level at the Emitters must be somewhat positive but never negative. Furthermore for the functionality of the amp Source resistors, as CBS240 mentioned, are not really or absolutely necessary. However it is true that they could better stabilize the BIAS circuitry. Until now, we don't even have a running amplifier with a working DC BIAS, so we should proceed step by step. Another point are the (series) Gate resistors CBS240 mentioned. They would prevent unwanted oscillation of the amplifier. They could and should be inserted. However I've seen many (even) professional linear amplifier not having those. That's also a question of design and if there is i.e. local negative feedback introduced or not besides other factors like PCB design, component selection and so on. Strange is also that some voltages in the circuit extend the measured voltages of the rails? How could this happen xcicc?