0R22 vs 0R47
The lower R gives slightly more headroom but on the downside it makes thermal stability of the output stage more difficult to achieve.
0R33 is the best compromise for this design, closely followed by 0R47. 0R22 might work OK but you'd need to test carefully.
The lower R gives slightly more headroom but on the downside it makes thermal stability of the output stage more difficult to achieve.
0R33 is the best compromise for this design, closely followed by 0R47. 0R22 might work OK but you'd need to test carefully.
PCB Fabricator
Hallo Friends.
I would fully agree your experience Hugh, but if i go, after put in dimensions of
board, to calculate the shipping coast i came up to 35$ to Germany.
New customer first order 10 free boards- that doesn't work for me.
So i was looking to kikipcb too- and end up with 26$ all inclu with
Singapur post.
Any of us have to watch shipping cost.
Zener and 4148 i could help, but to late now i see.
I need other missing parts- not much better than you. 😛 😀
Bangla.
Hallo Friends.
I would fully agree your experience Hugh, but if i go, after put in dimensions of
board, to calculate the shipping coast i came up to 35$ to Germany.
New customer first order 10 free boards- that doesn't work for me.
So i was looking to kikipcb too- and end up with 26$ all inclu with
Singapur post.
Any of us have to watch shipping cost.
Sorry Patrick, couldn't know that you missing any parts- with that one and
Zener and 4148 i could help, but to late now i see.
I need other missing parts- not much better than you. 😛 😀
Bangla.
Hallo Friends.
I would fully agree your experience Hugh, but if i go, after put in dimensions of
board, to calculate the shipping coast i came up to 35$ to Germany.
New customer first order 10 free boards- that doesn't work for me.
So i was looking to kikipcb too- and end up with 26$ all inclu with
Singapur post.
Any of us have to watch shipping cost.
Sorry Patrick, couldn't know that you missing any parts- with that one and
Zener and 4148 i could help, but to late now i see.
I need other missing parts- not much better than you. 😛 😀
Bangla take a lookl at : Dirt Cheap Dirty Boards
25$ for 10u up to 100x100mm by selecting Protoboard incl shipping
Marc
Hi Marc,
When you set a higher source resistor on a mosfet you reduce the transconductance. Put another way, more voltage at the gate is needed to achieve an increase of current. This is because more current through the source resistor drops more voltage, and a marked increase of gate voltage wrt to the BOTTOM of the resistor is the higher, the voltage dropped across the resistor is more, and a little more voltage is increased also across gate and the source, but the dominant voltage drop is across the resistor.
This is interesting, because these days there are very high transconductance mosfets available with up to 30A/volt (20 Siemens) transconductance and even more. This means that if there were no source resistor, an increase of 1V across the gate from say 4.1V to 5.1V the current through the drain/source would increase from say 0.1A up to 30.1A! But if you put in a 0.47R source resistor, this sort of additional current would hugely reduce the voltage between gate and source, which cannot happen, so the result is that the overall increase of current is rather less than you would expect based entirely on the Gm of the device. Since Rdson of a mosfet is often less than 0.1R, and down to as low as 10 milliohms, the source resistor starts to dominate the transconductance. In fact the relationship of the transconductance is the reciprocal of the source resistor.
Try this thought experiment. Use a mosfet with say 100S, a huge, almost ridiculous figure but helpful for this explanation. Let us put another voltage on the gate wrt the BOTTOM of the 0.47R source resistor. We set it up to 100mA quiescent at 4.15V. Now, increase the current with a 5.15V from gate to bottom of source resistor. We know that the mosfet might be passing 100A more or more if there were NO source resistor, so most of this 1V must be across this resistor, not across the mosfet. Add 1V across the 0.47R resistor, and we pass another 2.12A. That is, the reciprocal of the source resistor value, 1/0.47. In truth the mosfet will have a much smaller transconductance than 100S, it might be 6S (IRFP240), so some of this voltage will show an increased from Vgs. But in this situation, you can see that the transconductance will be hugely reduced by a larger source resistor, in this example it will be less than 2.12, it might be around 1.8S. With less current flowing through the mosfet when you increase an extra voltage on the gate, it shows that the transconductance is lower and therefore the quiescent current is much easier to set on a real push pull (or SE) amplifier.
Cheers,
Hugh
When you set a higher source resistor on a mosfet you reduce the transconductance. Put another way, more voltage at the gate is needed to achieve an increase of current. This is because more current through the source resistor drops more voltage, and a marked increase of gate voltage wrt to the BOTTOM of the resistor is the higher, the voltage dropped across the resistor is more, and a little more voltage is increased also across gate and the source, but the dominant voltage drop is across the resistor.
This is interesting, because these days there are very high transconductance mosfets available with up to 30A/volt (20 Siemens) transconductance and even more. This means that if there were no source resistor, an increase of 1V across the gate from say 4.1V to 5.1V the current through the drain/source would increase from say 0.1A up to 30.1A! But if you put in a 0.47R source resistor, this sort of additional current would hugely reduce the voltage between gate and source, which cannot happen, so the result is that the overall increase of current is rather less than you would expect based entirely on the Gm of the device. Since Rdson of a mosfet is often less than 0.1R, and down to as low as 10 milliohms, the source resistor starts to dominate the transconductance. In fact the relationship of the transconductance is the reciprocal of the source resistor.
Try this thought experiment. Use a mosfet with say 100S, a huge, almost ridiculous figure but helpful for this explanation. Let us put another voltage on the gate wrt the BOTTOM of the 0.47R source resistor. We set it up to 100mA quiescent at 4.15V. Now, increase the current with a 5.15V from gate to bottom of source resistor. We know that the mosfet might be passing 100A more or more if there were NO source resistor, so most of this 1V must be across this resistor, not across the mosfet. Add 1V across the 0.47R resistor, and we pass another 2.12A. That is, the reciprocal of the source resistor value, 1/0.47. In truth the mosfet will have a much smaller transconductance than 100S, it might be 6S (IRFP240), so some of this voltage will show an increased from Vgs. But in this situation, you can see that the transconductance will be hugely reduced by a larger source resistor, in this example it will be less than 2.12, it might be around 1.8S. With less current flowing through the mosfet when you increase an extra voltage on the gate, it shows that the transconductance is lower and therefore the quiescent current is much easier to set on a real push pull (or SE) amplifier.
Cheers,
Hugh
Last edited:
Protoboard incl shipping Marc
Thank you Marc, very kind.
That helps me a lot- is it your choose for your PCB?
Hugh- very interesting teaching lesson.
After collecting any information about gm it is a fully clear view now-
That i have to write down to keep in mind.
Zen Mod in Pass Forum is playing with sourse Resistors, and he is setting the
Output on "STEROID" that way, but i understand now it is very sensible
game.
Very helpful! Thank you.
Bangla.
Thank you Marc, very kind.
That helps me a lot- is it your choose for your PCB?
Hugh- very interesting teaching lesson.
After collecting any information about gm it is a fully clear view now-
That i have to write down to keep in mind.
Zen Mod in Pass Forum is playing with sourse Resistors, and he is setting the
Output on "STEROID" that way, but i understand now it is very sensible
game.
Very helpful! Thank you.
Bangla.
Thank you Marc, very gracious of you!
Bangla,
Thank you, this is a good exercise for me because technical writing actually helps me get my thoughts together, helps me with my language too which is slowly improving after a stroke some years back.
I use 0.47, 0.33, and 0.22 in my source resistors. As you go down, you find that the quiescent is very high at start up, slowly reducing as the temp compensation brings it down and the mosfets warm up. This is tricky to get right too. On the QUASI you can see the system Ranchu and I use to control this quiescent; a Vbe multiplier (BD139) and a 3.3V zener.
Ciao,
Hugh
Bangla,
Thank you, this is a good exercise for me because technical writing actually helps me get my thoughts together, helps me with my language too which is slowly improving after a stroke some years back.
I use 0.47, 0.33, and 0.22 in my source resistors. As you go down, you find that the quiescent is very high at start up, slowly reducing as the temp compensation brings it down and the mosfets warm up. This is tricky to get right too. On the QUASI you can see the system Ranchu and I use to control this quiescent; a Vbe multiplier (BD139) and a 3.3V zener.
Ciao,
Hugh
Hallo Hugh.
I have read about your stroke- if movement in mind, combined with writing your thoughts helps- we all happy to learn from you and give inspiration to you. It's very kind
to share with us- one learned more/faster the other less/slower- so it is.
The tricky bias is likewise Nelson use in M2- given a voltage reference in a simple way-
only possible to know with much experience- i like that stuff- holds me waked up.
Cheers Bangla.
I have read about your stroke- if movement in mind, combined with writing your thoughts helps- we all happy to learn from you and give inspiration to you. It's very kind
to share with us- one learned more/faster the other less/slower- so it is.
The tricky bias is likewise Nelson use in M2- given a voltage reference in a simple way-
only possible to know with much experience- i like that stuff- holds me waked up.
Cheers Bangla.
Thank you Marc, very kind.
That helps me a lot- is it your choose for your PCB?
Hugh- very interesting teaching lesson.
After collecting any information about gm it is a fully clear view now-
That i have to write down to keep in mind.
Zen Mod in Pass Forum is playing with sourse Resistors, and he is setting the
Output on "STEROID" that way, but i understand now it is very sensible
game.
Very helpful! Thank you.
Hi Bangla,
I use them three time in past month other if not tested i won't give adress
Marc
Chat in live with them.Hallo Friends.
I would fully agree your experience Hugh, but if i go, after put in dimensions of
board, to calculate the shipping coast i came up to 35$ to Germany.
New customer first order 10 free boards- that doesn't work for me.
So i was looking to kikipcb too- and end up with 26$ all inclu with
Singapur post.
Any of us have to watch shipping cost.
Sorry Patrick, couldn't know that you missing any parts- with that one and
Zener and 4148 i could help, but to late now i see.
I need other missing parts- not much better than you. 😛 😀
They offer other economical shipping way
PCB
Thanks Thimios.
project for me.
Thanks Thimios.
, sure it is, i will test that- must find out the really wished/needed
project for me.
Sitopway Technology Limited
I used sitopway for the slewmaster group buys. I don't know how they compare for just a few boards. Kevin was the rep I dealt with. I had good experiences.
I used sitopway for the slewmaster group buys. I don't know how they compare for just a few boards. Kevin was the rep I dealt with. I had good experiences.
Still on MOSFET ...
Still on MOSFET ...
I have several irfp044N would be useful in this AMP ?
http://www.hestore.hu/files/irfp044n.pdf
Still on MOSFET ...
I have several irfp044N would be useful in this AMP ?
http://www.hestore.hu/files/irfp044n.pdf
Thiago,
I would recommend you look at the Fairchild mosfets at Digikey.com. This IRFP044N dates from 1997, and the Fairchild trenchfets are quite cheap and much higher voltage and power, more suitable for a power amp.
Try the FQA38N25 and FQA40P15. These are a similar power but rated at 280W, I use them in one of my commercial amps, very good devices and inexpensive.
Hugh
I would recommend you look at the Fairchild mosfets at Digikey.com. This IRFP044N dates from 1997, and the Fairchild trenchfets are quite cheap and much higher voltage and power, more suitable for a power amp.
Try the FQA38N25 and FQA40P15. These are a similar power but rated at 280W, I use them in one of my commercial amps, very good devices and inexpensive.
Hugh
BanglaH: I just received the (Prasi layout) PCBs in the post. Thank you!
Now I need to read thread for notes on any changes or deviations from the silkscreen. If there is a summary of needed changes for this amp to work can someone point it out please?
Now I need to read thread for notes on any changes or deviations from the silkscreen. If there is a summary of needed changes for this amp to work can someone point it out please?
Hallo X.
Now i can good sleep, ufff!
If you need part information- it is an Excel doc any pages back- should be all in there.
Thimios not used C8 and you can carefull playing with paralleling R9 with 33-68pF- Mica.
My idea is solder R9 under board- let the legs a bit longer above and solder the Mica there.
I have to do it if parts received.
Happy soldering.
Cheers Bangla.
Now i can good sleep, ufff!
If you need part information- it is an Excel doc any pages back- should be all in there.
Thimios not used C8 and you can carefull playing with paralleling R9 with 33-68pF- Mica.
My idea is solder R9 under board- let the legs a bit longer above and solder the Mica there.
I have to do it if parts received.
Happy soldering.
Cheers Bangla.
I deduced that I have board Rev 3. Parts list and schematic here:
http://www.diyaudio.com/forums/soli...imentary-mosfet-amplifier-34.html#post4765108