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Old 8th May 2013, 10:38 PM   #1
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Default Component Selection Help for DC Coupled Amp

Greetings,

In my application, I am driving a square pulse into an 8 Ohm impedance load. I have a 24V/5A single supply. I am aiming for 10-15W output. Any rising edge rate that could beat my current amp's performance of 66us/V would be an improvement.

I have observed the voltage droop in the output of an amp lacking DC coupling, so I will be trying a MOSFET switch circuit out soon. However, once I am able to produce a square wave, I need to amplify a square wave that has exponentially damped rising and falling edges, and that's why I am looking for a long-term DC coupled amplifier solution. At least that's what I have convinced myself.

I found this unspecified schematic for a DC coupled amp with negative feedback. Other than the gain being specified as (R4+R3)/R3, there are no values assigned to the components. I am reaching out to the community to gain help with specifying the components.


I have found a properly annotated 15W Death of Zen schematic by shaan that I believe would suit me, yet it requires a dual +/-20V supply.

Could someone please provide some guidance? Thank you!
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Old 9th May 2013, 09:58 AM   #2
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
24Vdc supply will allow ~ 8Vac into a high impedance load.
Expect <=7Vac into a speaker load or 8ohms resistor.
Max Power = 7*7/8 = 6W.
If you are using a square wave output then the heating effect of the squarewave is double the sinewave power. i.e. 12W of squarewave power into 8r0.
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Old 9th May 2013, 10:21 AM   #3
ilimzn is offline ilimzn  Croatia
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Location: Zagreb
I think you need to wite up exactly WHAT you are doing, not how you want to do it. Driving a square wave into a load is not the same as any arbitrary waveform, there are other methods to do this, not just linear amplification.
Besides your 'DC couple amp' is DC coupled between stages but OBVIOUSLY AC coupled on input and output - and for DC conditions (see input, output and emitter caps!). If you want vadiable gain then this is not the ampo for you as changes in gain require re-calculating ALL the components. Have a look at fast op-amps instead.
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Old 9th May 2013, 02:33 PM   #4
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Thanks for the replies.

AndrewT - Looks like it is worth building and testing this circuit, based on the performance specs. I need a fixed gain of 2X.

ilimzn - I need to amplify a square wave with nonlinear rising/falling edges at a fixed 2X voltage gain (6dB?) into an 8 ohm load.

Can anyone help me specify the values of all the components please?
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