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Chip Amps Amplifiers based on integrated circuits

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Old 11th September 2019, 12:05 AM   #11
pelanj is offline pelanj  Czech Republic
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I tried to re-arrange for single supply. Does it look OK? I am pretty sure that this could be improved. The coupling caps intentionally limit the bandwidth as I would like to try this with MF/HF horns.
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Old 11th September 2019, 02:10 PM   #12
sgrossklass is offline sgrossklass  Germany
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You mistakenly made R2 a 4.7 ohm instead of R8. Should be the other way round.

I don't think C1 = 1µ is a good idea, it would upset current sharing at lower freqs. Not a conventional signal path coupling cap, this one. Change C4 instead.

R31 should have at least 10 µF in parallel, 47 µF would be better.
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Old 11th September 2019, 02:38 PM   #13
Elvee is offline Elvee  Belgium
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As Grossklass said.

here is the corrected circuit:
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Old 11th September 2019, 08:10 PM   #14
pelanj is offline pelanj  Czech Republic
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Thank you both for corrections!
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Old 11th September 2019, 09:17 PM   #15
pelanj is offline pelanj  Czech Republic
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Elvee, I still have one question - is there any reason why the output capacitor is placed like it is on your drawing? This way, there would be DC potential at the speakers terminals - or am I wrong? I use Speakon connectors, not banana plugs, but still this makes me feel a bit unsafe (for the amp, not for me).
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Old 11th September 2019, 09:41 PM   #16
Mark Tillotson is offline Mark Tillotson
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R4 needs to be 4.7 ohms, remember...


Yes, normally the coupling cap is before the speaker, it won't affect performance, just look unprofessional!

Last edited by Mark Tillotson; 11th September 2019 at 09:44 PM.
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Old 13th September 2019, 07:59 AM   #17
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by pelanj View Post
is there any reason why the output capacitor is placed like it is on your drawing?
In fact, I started by redrawing the circuit with a capacitive virtual ground, driven by the DC level of the amp, but I realized I was going to gain nothing and I changed my plan to a more conventional solution -and I left one of caps where it stood-
Electrically, it works identically, but for a practical circuit, it should be on the output side.

Again, some reminders:

-This is not a complete amplifier, just a precision unity gain buffer; to build an amplifier, you need to add a voltage amplifier in front (opamp.... )
-R2 should be halved for regular 317's: the models I used in the sim only have half the capacity
-This is a class A circuit, meaning a high quiescent current and dissipation.
The heatsink(s) should be dimensioned accordingly.
Fortunately with regulators, if the cooling is insufficient, they go in protection mode and shut down
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Old 13th September 2019, 12:16 PM   #18
pelanj is offline pelanj  Czech Republic
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I actually need a unity gain buffer, my source is 2 V RMS and the DSP can boost it to 3 V RMS and that is more than I need for my 110 dB/W horns. I will actually try to reduce the voltage and maybe halving the resistor will not be necessary at all, since 1 W into 8 ohms is my goal. I have some heatsinks ready since I want to evaluate this circuit together with the single MOSFET followers, resistor, choke and CCS loaded.
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Old 13th September 2019, 05:01 PM   #19
Elvee is offline Elvee  Belgium
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For 3V rms into 8 ohm, a 3.3 ohm resistor should indeed be sufficient, and the supply can safely be reduced to 18V, maybe less.

This will seriously ease dissipation concerns.

With a reduced supply voltage, it might be useful/necessary to scale R1 & R5, to 150 and 27 ohm for example, to keep a sufficient slewrate
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