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Here is an additional self biased approach - by Andrea Ciuffoli:
Amplifier End by Andrea Ciuffoli
Audio Asylum Thread Printer
Yes you're right and good that you say that.
Right now I prefer Mosfets in the second stage. The simulated circuit is a little bit more stable with the Mosfets. And the distortion are also a little bit better.
The Gateresistors with 10 ohm is no error.
An externally hosted image should be here but it was not working when we last tested it.
Open loop and closed loop:
An externally hosted image should be here but it was not working when we last tested it.
Another benefit of using TO-220 MOSFETs in the second stage is the range of output power levels they can safely support, should you ever want to scale up. IRF9510s can drive output stage rails up to 60V (150W) or so, while IRF9610s can go to around 120V (600W). 😱
Yes, it's amazing how easy you can scale the circuit. 🙂
I'm using the IRF9510 because I have some in stock. The IRF9610 are very similar. In the simulation without any major differences.
This is my first Layout:
An externally hosted image should be here but it was not working when we last tested it.
That was not easy, I've changed the layout several times before I was somewhat satisfied.
That's the power supply board. 2 x 11mF for the poweramp and 2x 2.2 mF for the driver. The amplifier board and the power supply board fit on one 160mmx100mm board.
... and that was easy to layout 😉
An externally hosted image should be here but it was not working when we last tested it.
... and that was easy to layout 😉
The prototype is finished and makes a very good impression 🙂
First of all, there is no hum and no noise.
This is unfortunately no soft switcher. When the amplifier is switching on you can hear a little bang. 😱
Switch on, right after the amp has a quiescent current of 160mA, after 10 minutes is it about 100mA. Thereafter, the quiescent current stays stable.
I changed the 2SA1930, the current source and bias control, for BD140.
If the aluminum plate is very hot, the idle current decreases slightly. The scheme seems to be working.
I have testet a bit:
10kHz, with 100nF and 1µF at 8 Ohm
It seems to be stable.
1kHz Sinus in overdrive:
Cut by app. +/-38V
This is the proto:
The board:
And of course I heard music. What can I say ... the best, the handsomest, the winner ... 😀
First of all, there is no hum and no noise.
This is unfortunately no soft switcher. When the amplifier is switching on you can hear a little bang. 😱
Switch on, right after the amp has a quiescent current of 160mA, after 10 minutes is it about 100mA. Thereafter, the quiescent current stays stable.
I changed the 2SA1930, the current source and bias control, for BD140.
If the aluminum plate is very hot, the idle current decreases slightly. The scheme seems to be working.
I have testet a bit:
10kHz, with 100nF and 1µF at 8 Ohm
An externally hosted image should be here but it was not working when we last tested it.
It seems to be stable.
1kHz Sinus in overdrive:
Cut by app. +/-38V
An externally hosted image should be here but it was not working when we last tested it.
This is the proto:
An externally hosted image should be here but it was not working when we last tested it.
The board:
An externally hosted image should be here but it was not working when we last tested it.
And of course I heard music. What can I say ... the best, the handsomest, the winner ... 😀
congrats 🙂
btw, are you using double power supply, like needed with tube amp circlotrons, or is the symmetric +/- supply doing the same 😕
btw, are you using double power supply, like needed with tube amp circlotrons, or is the symmetric +/- supply doing the same 😕
Nothing that a simple cap. multiplier can't cure. Otherwise, very nice
Shure? At which point?
Wow, that was fast! How did you get the boards so quickly - do you make them yourself?
If you want, you can probably get rid of the "pop" at turn-on by removing all DC offset from the circuit as discussed earlier.
Also, I don't know if this will be a problem, but if your power transformers pass any common-mode noise, you may see it from each output terminal to ground. If so, a common mode line filter at the AC power input may help.
Again, very nice work!
If you want, you can probably get rid of the "pop" at turn-on by removing all DC offset from the circuit as discussed earlier.
Also, I don't know if this will be a problem, but if your power transformers pass any common-mode noise, you may see it from each output terminal to ground. If so, a common mode line filter at the AC power input may help.
Again, very nice work!
At power supply line. Like this:
An externally hosted image should be here but it was not working when we last tested it.
Q5 is a cap. multiplier and time constant R7/C4 makes sure that PS voltage rises slowly enough to avoid turn-on thump.
In my best times around 11,5 sec in 100 meter 😀
Yes, if the structures are so rude, a circuit board is quickly etched by myself.
I have the opamp in suspicion. 😡 I will test it tomorrow...
No, not yet, but i will eye it.
Thanks 🙂
Yes, and it is so easy to scale up into higher power. You only need a bigger supply and more or stronger Mosfets.
Thank you, juma.
Yes, this is realy easy...I will test it and repot 🙂
Re: DC Offset
Just in case you need it later for testing, here's a simple tool that you can jumper into the circuit to remove absolute DC offset.
Just in case you need it later for testing, here's a simple tool that you can jumper into the circuit to remove absolute DC offset.
Hi Joe,
I've tested your circuit and it works. Unfortunately, the voltage is not very stable and wobbles around zero volts. I have just reduced the values of the resistors (R5, 11) to 220 ohms. Now I have a stable voltage of about 0.5 volts to ground.
The offset on the speaker is 40mV. (The first stage is not matched.)
But that changed nothing against the popping.
After I disconnect the supply from the driver the Amp switches on with silent. I will put in a soft start for the driver-supply like juma said.
I've tested your circuit and it works. Unfortunately, the voltage is not very stable and wobbles around zero volts. I have just reduced the values of the resistors (R5, 11) to 220 ohms. Now I have a stable voltage of about 0.5 volts to ground.
The offset on the speaker is 40mV. (The first stage is not matched.)
But that changed nothing against the popping.
After I disconnect the supply from the driver the Amp switches on with silent. I will put in a soft start for the driver-supply like juma said.
Hi moschfet,
Thanks for the feedback. The circuit may work better with a current source in place of the pot, but is probably not worth pursuing if it doesn't help. I hope the soft-start on the driver solves the problem.
Joe
Thanks for the feedback. The circuit may work better with a current source in place of the pot, but is probably not worth pursuing if it doesn't help. I hope the soft-start on the driver solves the problem.
Joe
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From the findings above, I've circled the problem. I've installed a softswitch for the second differential amplifier circuit. Only three additional components and the amplifier turns on quietly.
The amp sounds much better... 😎 😉
The softswitch is from C4, R33 and Q3 and drives the constant current source for the power up slowly:
So far so good.
Let's see if I can do some meaningful THD measurements.
The amp sounds much better... 😎 😉
The softswitch is from C4, R33 and Q3 and drives the constant current source for the power up slowly:
An externally hosted image should be here but it was not working when we last tested it.
So far so good.
Let's see if I can do some meaningful THD measurements.
Unfortunately, I realized that my sound card can not record. It is the Prodigy HD. Drivers problems? I do not know. After trying several unsuccessful hours... I've taken my onboard soundcard. 😡
Another problem: The amplifier operates as a bridge. And the line input is unbalanced. So I measured the amp to ground.
So see the measurements not to serious 😉
I am using Arta. First, only the sound card. Then through the amplifier:
1Watt 8ohm:
The amplifier sounds much better than it seems
Another problem: The amplifier operates as a bridge. And the line input is unbalanced. So I measured the amp to ground.
So see the measurements not to serious 😉
I am using Arta. First, only the sound card. Then through the amplifier:
An externally hosted image should be here but it was not working when we last tested it.
1Watt 8ohm:
An externally hosted image should be here but it was not working when we last tested it.
The amplifier sounds much better than it seems
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