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Chip Amps Amplifiers based on integrated circuits

Project Cute 16w
Project Cute 16w
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Old 23rd October 2017, 11:57 AM   #11
flyingfishtw is offline flyingfishtw  Taiwan
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Quote:
Originally Posted by AndrewT View Post
Many here use between 40kHz and 1MHz
But the consensus seems to be around 150kHz to 300kHz.
I use 160kHz (RC=1us) to 234kHz (RC=680us), or ~ one decade above 20kHz

400r + 270pF gives RC=108us
Thankx for the good idea. I replaced the buffer stage 270p to 1nF(from my stash), Done and Done. Originally I put 270pF bcs I don't want the dac output overshoot.

The result is pretty sweet, doesn't effect sound quality at all, and now hanging signal cable doesn't act like RF receiver. Why do you mention RC, normally I calculated it by f = 1 / 2piRC
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Old 23rd October 2017, 03:00 PM   #12
AndrewT is offline AndrewT  Scotland
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the RC is built into your formula: F-3dB frequency = 1/ 2pi RC
using RC allows very quick comparison of filters.
It is common to use RC in many filters, rather than to refer to the frequency, eg. in FM tuners the time constant for the HF emphasis/de-emphasis is either 50us, or 75us, in tape recording and RIAA one sees RC time constants.
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Old 24th October 2017, 11:35 PM   #13
flyingfishtw is offline flyingfishtw  Taiwan
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Default Cute 16w is just moody

Quote:
Originally Posted by PRR View Post
I have no doubt it "may" oscillate. Multi-stage amplifiers love to do that. Often not the circuit you designed, but the physical layout, including bypass caps at key points.
You're so right about this. If I don't connect the Zobel network to GND, turn the volume up, it will have 2 volt DC output, not very stable. and I put 5.1 ohm base stopper on the first stage bjt, even worse, on the 'right condition', it oscillate like no tomorrow.

I haven't solder the feedback capacitor yet.
Just with Zobel everything is fine.
What a moody amp.
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Old 14th November 2017, 08:42 PM   #14
flyingfishtw is offline flyingfishtw  Taiwan
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Oh well, it's not fine, it's a nasty demon. If I put laptop above the board and turn on a fan, it will oscillates if I turn the volume knob.

3 conditions have to meet to oscillate. I tame it with just Iron Core Bead thingy on the power supply input and it's fixed, no silent pops when I turn on fan or other stuff.
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Old 15th November 2017, 08:55 PM   #15
flyingfishtw is offline flyingfishtw  Taiwan
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Are there any way to increase output voltage swings from op amp besides BTL?
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Old 16th November 2017, 08:07 AM   #16
AndrewT is offline AndrewT  Scotland
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Many opamps use a supply range upto +-15Vdc, some go to +-18Vdc and a few go to +-22Vdc.
The maximum output voltage into a high impedance load is ~ 1/3rd (one third) of the rail to rail supply voltage.

If you use the boosted form of supply you can go much higher than that 1/3rd limit.
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Old 16th November 2017, 08:55 AM   #17
flyingfishtw is offline flyingfishtw  Taiwan
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Quote:
Originally Posted by AndrewT View Post
Many opamps use a supply range upto +-15Vdc, some go to +-18Vdc and a few go to +-22Vdc.
The maximum output voltage into a high impedance load is ~ 1/3rd (one third) of the rail to rail supply voltage.

If you use the boosted form of supply you can go much higher than that 1/3rd limit.
Interesting how you put everything. 1/3rd you mean like my op amp with +- 18V DC, the output is roughly +-17, so 34Vp-p/2.828 = 12Vrms roughly 1/3 DC voltage.

What about the boosted form of supply? can you recommend some configurations? Thank you sir.
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Old 28th December 2017, 04:57 PM   #18
flyingfishtw is offline flyingfishtw  Taiwan
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My power supply, 2200uF for Vcc2 , +pi filter to LM317.
It's a bit aggressive. and you guys are right,
hiss noise should be my least concern,
even hum is my least concern,

I try to install everything in a case .

The light Buzz I mentioned earlier, it was from the line power itself, it can be rejected by using line emi filter. And another buzz was caused by output channel way too near transformer.

But the real demon in the picture is ground loop from laptop to usb DAC to amp, when I try to connect the board to earth ground which I don't have in the house plugs, and notebook, every switching power supply shares the same extension plug. That was some nasty monster....

When I connect 10 ohm from signal GND to earth GND, it has 5xmV, then I try different resistors, about the same voltage. and when I measure the resistance between signal gnd and earth gnd on the 50 ohm resistor it shows like 110 ohm. Don't know why's that, doesn't look like ohms law.

I float the signal gnd for now with 2k resistor parallel 0.1uF + 2 diode back to back, don't know if it's a okay idea.
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File Type: jpg PS schematic.jpg (91.0 KB, 50 views)
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Old 28th December 2017, 05:02 PM   #19
flyingfishtw is offline flyingfishtw  Taiwan
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With my pi filter, it works wonderfully for differential rejection, but I don't know how to make common mode rejection filter.
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