I am looking at your last version. a few comments:
a) Vce on T2/T3 appear to be too small. Ic going through T1/T5 is about 1.6ma. so voltage drop over R4/R8 is about 750mv. Voltage over R8 is about 700mv (voltage over D1/D2). As such, Vce on T2/T3 is about 650mv. I tend to run them a little bit higher (in the 1.5v range). part of the reason is high degenerate resistors R4/R8: i use 22ohm in general.
b) this is less of an issue with CCS but I usually set the current going through the Vbe resistors at about 1/10 of the current going through the whole Vbe setup. In this case, I would dial them up about 10x. Using a small capacitor here (0.1-1u) will help as well.
c) R16/R19 seem to be too big.
d) I usually make R21 identical to R22, for reasons I elaborated in my post earlier. I also used the same value for R20 and R22. IRFP140 class mosfets drop about 4ma (peak) gate current at 20khz, and I usually run my driver stage at about 15 - 20ma.
e) game resistors for the mosfets are very small. I use 110ohm to just slow down the mosfets.
Hope it helps.
a) Vce on T2/T3 appear to be too small. Ic going through T1/T5 is about 1.6ma. so voltage drop over R4/R8 is about 750mv. Voltage over R8 is about 700mv (voltage over D1/D2). As such, Vce on T2/T3 is about 650mv. I tend to run them a little bit higher (in the 1.5v range). part of the reason is high degenerate resistors R4/R8: i use 22ohm in general.
b) this is less of an issue with CCS but I usually set the current going through the Vbe resistors at about 1/10 of the current going through the whole Vbe setup. In this case, I would dial them up about 10x. Using a small capacitor here (0.1-1u) will help as well.
c) R16/R19 seem to be too big.
d) I usually make R21 identical to R22, for reasons I elaborated in my post earlier. I also used the same value for R20 and R22. IRFP140 class mosfets drop about 4ma (peak) gate current at 20khz, and I usually run my driver stage at about 15 - 20ma.
e) game resistors for the mosfets are very small. I use 110ohm to just slow down the mosfets.
Hope it helps.
tlf9999 said:
a) In practice the current through R4 & R8 is about 1.3mA. I prefer to have larger value resistors here for better linearity. No reason why the amp would not work with a variety of values here.
b) I am not sure which part of the amp you are talking about, i.e. which Vbe.
c)Yes, these in fact can be removed and replace with links but T10 and T9 actually need very little drive, because there is less load on them than if they were driving a transistor output stage. The base resistors afford some protection to previous stages. But hey each to his own.
d)The value of R21 was selected during bench tweaking. I found the 100 ohm value gave the best performance in terms of symmetry, clipping and linearity.
e) I use lower value gate resistors in order to keep the drive impedance to these FETs low. The FETs used have a fairly high input capacitance. If FETs with a lower input capacitance are used then higher value resistors could be used. Again each to his own.
Thank you for your observations.
Cheers
hello guys
Again, i like this schematic but the power level is too high for me. I only need a power around 100 - 150w maximum.
My question is how can i reduce the power but keep the performace?
A solution is to reduce the supply voltage and the number of power transistors (to use only two pairs or even one pair of MOS-FETS)
Another solution is to reduce the gain of the amplifier (and perhaps the number of output transistors?)
I like the idea of reducing the gain but i don't know if that is the best solution because i have no experience in designing power amplifiers.
Again, i like this schematic but the power level is too high for me. I only need a power around 100 - 150w maximum.
My question is how can i reduce the power but keep the performace?
A solution is to reduce the supply voltage and the number of power transistors (to use only two pairs or even one pair of MOS-FETS)
Another solution is to reduce the gain of the amplifier (and perhaps the number of output transistors?)
I like the idea of reducing the gain but i don't know if that is the best solution because i have no experience in designing power amplifiers.
cd-i said:
Sorry cd-i
Forgot to answer your question.
If you use +/- 50 volt rails this module will deliver just over 110 watts into 8 ohms.
You will need a transformer with 38 volt windings plus a 25 amp bridge rectifier and a minimum of 10,000 uF capacitors per rail per module.
You can use the existing board layout and just use 4 FETs.
You could reduce the gain of the amplifier by changing R17. The value of this resistor divided by 1000 (R18) gives you the gain. I would not go below 22k.
Cheers
hello, quasi
I made up my mind. I will build the amplifier developed by you and presented here
http://www.diyaudio.com/forums/show...8232#post498232
Obviously I will build the schematic posted by you at the end of that thread after you worked your magic on it
I will also use the printed circuit board you designed for this schematic.
At first i will build the amplifier "as is" and after i see it working i will try to reduce the power.
Anyway this will take some weeks due to my school exams session that begins next week.
Thanks for your help.
I made up my mind. I will build the amplifier developed by you and presented here
http://www.diyaudio.com/forums/show...8232#post498232
Obviously I will build the schematic posted by you at the end of that thread after you worked your magic on it
I will also use the printed circuit board you designed for this schematic.
At first i will build the amplifier "as is" and after i see it working i will try to reduce the power.
Anyway this will take some weeks due to my school exams session that begins next week.
Thanks for your help.
Hey cd-i
The link you posted did not work, I presume you mean this one.
www.diyaudio.com/forums/attachment.php?s=&postid=601021&stamp=1111237713
The link you posted did not work, I presume you mean this one.
www.diyaudio.com/forums/attachment.php?s=&postid=601021&stamp=1111237713
Hi Quasi,
Can you pls send pcb layout of your high power version ?
http://www.diyaudio.com/forums/showthread.php?postid=708177#post708177
thanks,
roland.ong@vishay.com
Can you pls send pcb layout of your high power version ?
http://www.diyaudio.com/forums/showthread.php?postid=708177#post708177
thanks,
roland.ong@vishay.com
funberry said:
Adrian,
I just stumbled on your post. I have been using Vicor and Eta SMPS for audio power amps. What I did to prevent the sagging on load peaks is just what we used to do with linear supplies: put a hefty cap at the output. The SMPS doesn't seem to care, they will initially charge the caps with a limited current, but after that it is OK. I used 4700uF per supply voltage with no ill effects and no lock-outs. Did you ever try something like that?
Jan didden
rolandong said:
Sorry Rolandong, this board is not properly designed yet. If you are patient I will design it over the next few weeks. If you are looking for a compact high power amp and cannot wait then try the one linked below. The thread is called "power amp under development".
Cheers
www.diyaudio.com/forums/showthread.php?postid=600264#post600264
www.diyaudio.com/forums/attachment.php?s=&postid=601021&stamp=1111237713
Hi Jan
Supplying the PWM controller from an external power supply has usually solved this problem for me. It's actually better if this supply can deliver some current (100-200mA), and has a large filter cap, because the controller will need to drive a MOSFET from this rail, and it may take a 1A peak to charge Cgs.
You'r right, this definitely takes care of the problem too.
However, half of the reason I go with SMPS is to get rid of the big, heavy, expensive power transformer. The other half, is to get rid of the big, clumsy, expensive filter capacitors.
I like slim cases, 4-5cm high.
I've shoved in as many smaller, 4cm dia capacitors as I could fit, in parallel, in a previous slim design, but I still need to leave room for good air circulation.
Adrian
Supplying the PWM controller from an external power supply has usually solved this problem for me. It's actually better if this supply can deliver some current (100-200mA), and has a large filter cap, because the controller will need to drive a MOSFET from this rail, and it may take a 1A peak to charge Cgs.
You'r right, this definitely takes care of the problem too.
However, half of the reason I go with SMPS is to get rid of the big, heavy, expensive power transformer. The other half, is to get rid of the big, clumsy, expensive filter capacitors.
I like slim cases, 4-5cm high.
I've shoved in as many smaller, 4cm dia capacitors as I could fit, in parallel, in a previous slim design, but I still need to leave room for good air circulation.
Adrian
BTW, speaking of air circulation:
When you make compact amps, you often have to provide fan cooling.
And because fans mean noise, and I like to run my fan well below rated speed.
I'll supply 7-8 V to a 12V computer fan; This shouldn't work, because the speed is electronically controlled, but it does work. At that speed, I hear no noise coming from the fan even with my ear close to it.
The lowest Voltage at which most of these fans will reliably start is 3-4 V, and I go 3 volts or so above that.
Adrian
When you make compact amps, you often have to provide fan cooling.
And because fans mean noise, and I like to run my fan well below rated speed.
I'll supply 7-8 V to a 12V computer fan; This shouldn't work, because the speed is electronically controlled, but it does work. At that speed, I hear no noise coming from the fan even with my ear close to it.
The lowest Voltage at which most of these fans will reliably start is 3-4 V, and I go 3 volts or so above that.
Adrian
Regarding the fan problem,
a good idea is to control the fan speed with a pwm or something similar, (if you have a microcontroler in your design) And you can spin the fan with variable speed depending of the heat sink temperature.
And with that microcontroler you can do a lot of useful things in that amplifier.
You can implement the protections circuit, a digital tone and volume control or even a remote control...
A simple PIC microcontroller is enough to do all those things
a good idea is to control the fan speed with a pwm or something similar, (if you have a microcontroler in your design) And you can spin the fan with variable speed depending of the heat sink temperature.
And with that microcontroler you can do a lot of useful things in that amplifier.
You can implement the protections circuit, a digital tone and volume control or even a remote control...
A simple PIC microcontroller is enough to do all those things
funberry said:
yes i agree with suppliyng the fan with a lower voltage than it's nominal value, but you may experince some problems due to dust accumulation in the fan.
Is better to use some control circuitry around that fan to monitor it's RPM and at start-up use a higher voltage for a second or two and after that you can reduce the voltage at a lower level.
You have to be careful if you use forced cooling in a tight enclosure. A failure of the fan could be a disaster for your amplifier.
Anyway I don't trust fans.....
cd-i said:
a motor does that natively: when a DC motor is stationary, it has very low resistance so a large current goes through it. When it starts to rotate, it kind of functions like a electricity generator and the current going through it goes down to the point that it is just enough to maintain the motor's speed.
I have used a thermistor to control a DC motor.
I think to be safe, any amp should have a thermal switch on the heatsink to shut down the amp in case of a disaster.
Analog Devices make a neat little Temperature-to-PWM converter,
the TMP05, in SOT23 package.
I've been meaning to use them in my amp, but the dumb method works so well, I just can't get myself to use the smart method now. I wanna save the TMP05's for something else.
I have a thermal shutdown relay. The amp could have run safely without the fan, but I want to have the flexibility to place it in between books, and shelves, and other tight spaces.
Yeah, the dust, tell me about it. Once a year I have to open it up and dust it. But that's good practice for the heat sink anyways, whether or not you use a fan. A 1mm dust layer on any heat sink is destructive enough to warrant periodic removal. But I have to do that with my computer case (six fans in that one) anyways once a year, so think of it as spring cleaning.
Adrian
the TMP05, in SOT23 package.
I've been meaning to use them in my amp, but the dumb method works so well, I just can't get myself to use the smart method now. I wanna save the TMP05's for something else.
I have a thermal shutdown relay. The amp could have run safely without the fan, but I want to have the flexibility to place it in between books, and shelves, and other tight spaces.
Yeah, the dust, tell me about it. Once a year I have to open it up and dust it. But that's good practice for the heat sink anyways, whether or not you use a fan. A 1mm dust layer on any heat sink is destructive enough to warrant periodic removal. But I have to do that with my computer case (six fans in that one) anyways once a year, so think of it as spring cleaning.
Adrian
Hi Quasi,
I have a huge transformer intended for the super leach (65-0-65 (20A secondary), about the same supply as your high power design. I'm impressed about the simplicity and compact design of mosfets so i thought of giving it a try.
I'm willing to wait for any updates.
Just a suggestion: why not class-g output stage for higher efficiency.
rgds,
roland
I have a huge transformer intended for the super leach (65-0-65 (20A secondary), about the same supply as your high power design. I'm impressed about the simplicity and compact design of mosfets so i thought of giving it a try.
I'm willing to wait for any updates.
Just a suggestion: why not class-g output stage for higher efficiency.
rgds,
roland
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