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Please help me learn from my first amp idea.
Please help me learn from my first amp idea.
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Old 6th August 2012, 05:45 AM   #1
JZatopa is offline JZatopa  United States
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Join Date: May 2003
Location: Chicago
Default Please help me learn from my first amp idea.

So I recently built both an 02 amplifier and a 1969 JLH amplifier and have been enjoying both quite a bit. The JLH is very impressive even when compared to the F5 I built about 8 months ago but now I want to try something different. Attached is a schematic of an idea I had for an amp. I am not sure if it is a good idea, bad idea or if it would even work. My first question is, would this amplifier work as I drew it? If not, why? If the amp would work could you show me some other similar designs and tell me about their pros and cons? I am not an engineer so I don't really have anyone I could take this to to teach me about what I did right or wrong.

A little about the thought that went behind this. I started thinking about the JLH and how it might be improved. The way I understand it, NP combined the first stage and the phase splitter section of the amp to make the PLH. Instead of that I decided to try to swap in a supposedly "invisible" front end bassed on the O2 amplifier and use one of the opamps to invert the phase. I did not make any calculations and just made an assumption that if the front end can drive a pair of headphones, a pair of output devices should be just as easy. If I were to build such an amp, I would possibly use semisouth jfets on the output. I would also consider keeping the front end on it's own battery based power supply to limit noise on the front end. let me know what you guys think.
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Old 6th August 2012, 08:00 AM   #2
Mooly is offline Mooly  United Kingdom
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Please help me learn from my first amp idea.

I can see your reasoning but I'm afraid there are problems for high quality audio with a circuit like this.

Q1 is an NPN device and so the opamp output driving it would just turn this hard on putting supply across the speaker.

If Q1 were PNP...

The output transistors are not enclosed in any feedback network and so distortion would be very high.

There is a "dead zone" of -/+0.7 volts where the output devices are non conducting, Cross over distortion ! There is no means of accurately setting a forward bias to overcome this.

But don't let any of that put you off Keep trying and thinking and experimenting.

Edit... have a look at this circuit to see how a pair of transistors can be added to an opamp output. It's only the start though
Help with basic amp design

Last edited by Mooly; 6th August 2012 at 08:06 AM. Reason: More info and link
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