Iyremenko said:
If you put the zeners on the "outside" (as desirable for better suppression of parasitic oscillation), you want to have a gate drive circuit that has some degree of current limiting, so that in the event of an output short the driver does not try to drive the load through the zener diode. This can be as simple as some additional small resistance between an emitter-follower bipolar driver and the place where the zener is.
Bob
Again the usual para-philology! Each one expresses costless criticism. As we say in Greece, each one says his long and his short. Sakis knows what means that please Sakis can you translate what means this in English? In this and in many other cases we need SOLUTIONS and not COMMENTS. Please, mercy on us! Well Sakis, did you notice the second reply of N. Pass? First he is confirmed – something which i had said to you in our contact by phone – that the use of the 2 zeners between G-S it is enough for protecting mosfets from spikes. Do you have check it? Second, he gives a solution to the negative offset that appears in the amplifier’s output. “Drop D1 and the output swings more positive”. Above i quote a revision of your circuit according an old application of RCA which seems to be very close to it. Also change this MJE340 in the VAS with a TIP47. These MJE340 and 350 used as pre or main drivers. TIP47 is a better device in this place. Trust me. And C9 is a Miller compensation device. I thing there is no need for the extra 100pF around VAS. If you have oscillations after the VAS try to increase the value of C9 to solve it. And you may experiment hardly with these solutions offered to you. Nothing it comes without labour. It is not our work to make this circuit. Make your circuit safe; don’t leave it at its luck. Çave you thought ever what it could happen if your amplifier it was found near dimmer packs with hard RF emissions from TRIACS? I wish you success.
Fotios
Fotios
Wait for a moment please! Just now, I took answer from the author of this project Mr. Borivojie Jagodic in a question that I placed to him. His answer I believe that it reverses what we discuss up to now regards to the output stage.
This is my question to Mr. Jagodic
Mr. Jagodic, because so many fuss exists the last month about the practical application of your LEGEND amplifier by our friend Sakis from Greece, i tried to give a help by redrawing your original plan which posted to me by Sakis before one month. I ask your comprehension for my intervention in your intellectual property, but the drawn under this manner it is a standard in audio amplifiers theoretical design as you know, to be easy comprehensible. I hope to not be angry with me, and i ask - if you have the kindness - from you to confirm that the values of components and the circuit nets and nodes are connected correctly in my redraw.
Kind Regards
Fotios Anagnostou
And this is the answeer from Mr. Jagodic
Hello Fotios!
I can confirm that your drawing is correct except that you added 4 resistors of 0,18 ohms (not existing in my schematic) of which two are correctly positioned in sources of upper units, but two lower ones are in drains ?! They won't be of much use there. Visual analogy to complementary configured output stages is not enough to provide functionality and right purpose.
Regarding all that "fuss" you mentioned, I decided from the first moment not to comment anything. My friendly extended hand and help I gave from my heart from the first contact, were "turned" upside down, many things were misinterpreted and published that way, my design abused without even minuscule intention to ask for my permission (at least!)....... Hence, I don't see a point of any further involvement in any way!
This is my question to Mr. Jagodic
Mr. Jagodic, because so many fuss exists the last month about the practical application of your LEGEND amplifier by our friend Sakis from Greece, i tried to give a help by redrawing your original plan which posted to me by Sakis before one month. I ask your comprehension for my intervention in your intellectual property, but the drawn under this manner it is a standard in audio amplifiers theoretical design as you know, to be easy comprehensible. I hope to not be angry with me, and i ask - if you have the kindness - from you to confirm that the values of components and the circuit nets and nodes are connected correctly in my redraw.
Kind Regards
Fotios Anagnostou
An externally hosted image should be here but it was not working when we last tested it.
And this is the answeer from Mr. Jagodic
Hello Fotios!
I can confirm that your drawing is correct except that you added 4 resistors of 0,18 ohms (not existing in my schematic) of which two are correctly positioned in sources of upper units, but two lower ones are in drains ?! They won't be of much use there. Visual analogy to complementary configured output stages is not enough to provide functionality and right purpose.
Regarding all that "fuss" you mentioned, I decided from the first moment not to comment anything. My friendly extended hand and help I gave from my heart from the first contact, were "turned" upside down, many things were misinterpreted and published that way, my design abused without even minuscule intention to ask for my permission (at least!)....... Hence, I don't see a point of any further involvement in any way!
Nelson Pass said:
Unfortunately I was referring to the maximum output swing,
and not the offset at output.
As said to me Sakis by phone the amplifier presented negative offset (about 200mV in static condition i.e. without signal in input) and i supposed that it is translated in more negative swing in output under dynamic condition i.e. with signal in input. According to this thought i translated what you wrote for the “Drop of D1”. That is to say it will resolve also the problem of dc offset. However now mr. Jagodic said to us that the 2 resistors in the drains of the lower Mosfets they are placed wrong and it should connected in sources. This puts the things somehow in their place.
Fotios
Why the need of source resistors?
I want to express a query because I do not know many things about Mosfets except from my inverter welding machine. Why they need resistors in sources (corresponding to the emitter resistors of BJTs)? In BJTs we know that the emitter resistor offers thermal feedback to stabilize the current flow. Mosfet as we know it has by itself automatic current balance according to its case temperature. Well why there is the need of thermal feedback by a resistor?
I want to express a query because I do not know many things about Mosfets except from my inverter welding machine. Why they need resistors in sources (corresponding to the emitter resistors of BJTs)? In BJTs we know that the emitter resistor offers thermal feedback to stabilize the current flow. Mosfet as we know it has by itself automatic current balance according to its case temperature. Well why there is the need of thermal feedback by a resistor?
Re: Re: Why the need of source resistors?
O.K. i get. I believed that the increase or the reduction of current is linear. On the contrary as soon as his temperature reaches in a limit, then the Mosfet it drops abruptly the current that flows through it.
Thanks
Fotios Anagnostou
Nelson Pass said:
Except that it doesn't. Mosfets will increase their current with
temperature until you reach rather high currents, so a Source
resistor is commonly used to stabilize this and to help make
parallel devices share more evenly.
O.K. i get. I believed that the increase or the reduction of current is linear. On the contrary as soon as his temperature reaches in a limit, then the Mosfet it drops abruptly the current that flows through it.
Thanks
Fotios Anagnostou
Actually, there is no abrupt alteration with temperature. At
fairly high currents, a Mosfet will show little or no temperature
dependence, and at higher currents, the characteristic will tend
to decrease the current with rising temperature, all pretty
gradually. The problem of course is that the current involved is
very much higher than the average bias current, so the
coefficient for bias with increasing temperature is positive.
fairly high currents, a Mosfet will show little or no temperature
dependence, and at higher currents, the characteristic will tend
to decrease the current with rising temperature, all pretty
gradually. The problem of course is that the current involved is
very much higher than the average bias current, so the
coefficient for bias with increasing temperature is positive.
just to make sure that it is working.
opinions and comments
to answer fotios point about opinions i will use a greek joke ......
it goes like that in greece ......opinion is like assho**s !!! every body has his own !!!!!!!
if you like some statistics this project is in the air in the forum and people are looking at it since last october !!!!!!!!!
various posts of me and others seriously involved with this project exist as i said from october ...with schematics pictures improovements and goes on
if you listen to what i was told in all this time you are going to lough your brains out ......meaning that many people very well familliar with a part of the amplifier made various suggestion regarding one part of the amplifier ...like ltp or vas or ccs and goes on ......
the truth is that nobody put the all thing together or even notice any suggestion for the ltp example will have also side effects to othere division also
frugment of knowledge coming from NELSON PASS ....FOTIOS ... ANDREW T ....QUASI .... CARLOS DESTROYER X .....AND EVEN ROD ELLIOT made the picture come together
of course since i have no design skills and after a lot of testing and almost practice of six month ...it seems that we are getting just a litle closer !!!!!
yet again and for one more time thank you all people !!!!!
to answer fotios point about opinions i will use a greek joke ......
it goes like that in greece ......opinion is like assho**s !!! every body has his own !!!!!!!
if you like some statistics this project is in the air in the forum and people are looking at it since last october !!!!!!!!!
various posts of me and others seriously involved with this project exist as i said from october ...with schematics pictures improovements and goes on
if you listen to what i was told in all this time you are going to lough your brains out ......meaning that many people very well familliar with a part of the amplifier made various suggestion regarding one part of the amplifier ...like ltp or vas or ccs and goes on ......
the truth is that nobody put the all thing together or even notice any suggestion for the ltp example will have also side effects to othere division also
frugment of knowledge coming from NELSON PASS ....FOTIOS ... ANDREW T ....QUASI .... CARLOS DESTROYER X .....AND EVEN ROD ELLIOT made the picture come together
of course since i have no design skills and after a lot of testing and almost practice of six month ...it seems that we are getting just a litle closer !!!!!
yet again and for one more time thank you all people !!!!!
With few words Mosfet output current is dependent from its junction temperature. What interests me is the following: Suppose that we have a pair of complementary Mosfets and a pair of complementary BJTs with the same Vce, Ic, Pd. If we place the BJTs in a heatshink smallest than they need for the Pd that they have, i know sure that they will be burned. If we make the same with the Mosfets, these will not be burned; simply they will decrease their output current. Thus the only loss in the case of Mosfets will be the reduction of output power. On the contrary with BJTs the consequence will be worse as these will be destroyed. Rightly up to here? Consequently with Mosfets we do not face the case of thermal destruction. Where i want to go. If i make an amplifier with Mosfets and also i make economy in heatshinks i will have a loss of output power in the worst case. On the contrary if i do the same with BJTs (we suppose that does not exist auxiliary circuit of thermal cut–off or thermal reduction) then BJTs will meet their fate that is to say they are destroyed. Thus with the use of Mosfets in output can some constructor to deceive us? The reason that i wrote these, are because something like this it happened to me. In my entire career i deal with P.A. systems and sometimes it happened i have 3 or 4 amplifiers Mosfet of some well known British company. Because these operate in conjunction with certain BJT amplifiers of the same power, i noticed that the output of Mosfet was decreased after 2 or 3 hours of operation compared to BJT. This happened before 20 years. Then, i was noticed that no one American company use Mosfets in her amplifiers. The same happens up today, with the difference that no one constructor of P.A. amplifiers worldwide use Mosfets more (as i know). From then i was stopped entrusting Mosfets even if it was very fashion. Thus i did not deal again with them and devoted to the old but trusty BJTs.Nelson Pass said:Actually, there is no abrupt alteration with temperature. At
fairly high currents, a Mosfet will show little or no temperature
dependence, and at higher currents, the characteristic will tend
to decrease the current with rising temperature, all pretty
gradually. The problem of course is that the current involved is
very much higher than the average bias current, so the
coefficient for bias with increasing temperature is positive.
Regards and thanks for information
Fotios Anagnostou
Hi,
it took me a while to realise that FETs exist in two basic forms.
I just could not get my head around what folk were describing because I was unaware of the Vertical & Lateral difference in parameters.
When finally, this V & L thing fell into place it all started to make sense.
Fotios,
do some reading/experimenting. Pay particular attention to Vgs and temperature vs Id. Try it and see what happens. Unfortunately Laterals are expensive but you are less likely to destroy them due to thermal runaway, with care you should be able to control power dissipation and thus temperatures.
it took me a while to realise that FETs exist in two basic forms.
I just could not get my head around what folk were describing because I was unaware of the Vertical & Lateral difference in parameters.
When finally, this V & L thing fell into place it all started to make sense.
Fotios,
do some reading/experimenting. Pay particular attention to Vgs and temperature vs Id. Try it and see what happens. Unfortunately Laterals are expensive but you are less likely to destroy them due to thermal runaway, with care you should be able to control power dissipation and thus temperatures.
thanks andrew t
since you declaired that you dont really like this circuit and thats very ok with me but may be your opinion will be also critical in this post .....
given as a fact that i am ok with the amp the way it end up and i am happy with it do you think that aditional zeners as shown in the above circuits will prevent some ammount of abuse on this amp ???
since you declaired that you dont really like this circuit and thats very ok with me but may be your opinion will be also critical in this post .....
given as a fact that i am ok with the amp the way it end up and i am happy with it do you think that aditional zeners as shown in the above circuits will prevent some ammount of abuse on this amp ???
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