feedback on my design

[keantoken]

I have designed my own amp. It currently takes 100K input impedance
and I was wondering if this was pretty good for a second design attempt. I don't really know all the widely used imedances or 'standards' so if you want to give me a list that I can write down or something like that, please do. I was making this on my simulator so if something isn't quite right please tell me. You can't crank the gain up very high or else since the transistor isn't biased exactly the negative portion of the wave will start to do wierd things. The diodes are what biases the transistor, so if I could get some more diod models maybe I could find some better ones. I have commented the nominal resistances to keep the distortion under control on the schematic. Here it is:

[Tim__x]

This amp won't be very linear, must float with regard to the singal source, and certainly won't drive an 8 ohm speaker with component values shown.

Take a peek at some standard common-emitter amp schematic for inspiration.

[keantoken]

oops... I have seen common-emitter circuits and their simplicity doesn't appeal to me... Though I guess that for small-signal amplification they would work with minimal distortion. What I don't like about one-transistor arrangements is that you have to bias them perfectly if you want good sound which usually will take some component count if you want to use it for something other than small signal (at least with my transistors, which are low-end which I have to cope with ). I like symmetrical arrangements like symasm4 or the 4QD-TEC one here: http://www.4qdtec.com/pwramp.html. This one is cool because it uses a self-biasing chain. If I sound like a complete idiot who doesn't have any experience, please let me know. Also, I have been trying to develope another amplifier based on the 4QD-TEC one and I was wondering, don't amplifiers that float good have more of a tendancy to oscillate? Meaning that the speakers will scream at you from larger distances away when your holding a mic? I know about positive and negative feedback, are there any good ways that I can suppress oscillation without affecting the circuit's behavour majorly? I like straigt-forward designs that don't add any "flavour" to the sound so that I can apply my own effects. If you have any good, simple amplifier schematics that you think I will like, please post. Gosh... I need to learn how to make stuff that works ...
BTW, is this circuit useful for anything except for absolutely nothing?

[Tim__x]

I assumed you wanted a single transistor stage, like the one you posted. The circuit will produce sound, but not very well.

What exactly are you wanting to amplify, and what load are you wanting to drive?

These two pages make a spectacular introduction to amplifier design.

http://sound.westhost.com/amp-basics.htm
http://sound.westhost.com/amp_design.htm

P.S. You schematic is a common-emitter amp, just with a... unusual bias generator.

[keantoken]

oops... I have seen common-emitter circuits and their simplicity doesn't appeal to me... Though I guess that for small-signal amplification they would work with minimal distortion. What I don't like about one-transistor arrangements is that you have to bias them perfectly if you want good sound which usually will take some component count if you want to use it for something other than small signal (at least with my transistors, which are low-end which I have to cope with ). I like symmetrical arrangements like symasm4 or the 4QD-TEC one here: http://www.4qdtec.com/pwramp.html. This one is cool because it uses a self-biasing chain. If I sound like a complete idiot who doesn't have any experience, please let me know. Also, I have been trying to develope another amplifier based on the 4QD-TEC one and I was wondering, don't amplifiers that float good have more of a tendancy to oscillate? Meaning that the speakers will scream at you from larger distances away when your holding a mic? I know about positive and negative feedback, are there any good ways that I can suppress oscillation without affecting the circuit's behavour majorly? I like straigt-forward designs that don't add any "flavour" to the sound so that I can apply my own effects. If you have any good, simple amplifier schematics that you think I will like, please post. Gosh... I need to learn how to make stuff that works ...
BTW, is this circuit useful for anything except for absolutely nothing?

[keantoken]

You posted before I posted that last post... As for the load, I was thinking on trying to drive an 8-ohm to test it and when I knew it was safe try it as a preamp maybe. I am trying to amplify my microphone so I can have some louder sound (so that I don't have to amplify it digitally which is a pain). I got the "unusual bias generator" from the 4QD-TEC schematics, it seemed like an easy way to bias low-requirement circuits and if your good enough maybe make something better. This appeals to me because, unlike a resistor, the bias will fluctuate less when the supply voltage changes. This is why the 4QD schematic can work over a large supply range.

[Tim__x]

That part of the 4QD-TEC schematic is a constant current source, it's designed to source (technically sink in this case, but who cares ) a constant current regardless of the voltage on the collector, it's not designed as a bias circuit for any kind of linear voltage amplifer.

Voltage divider biasing does give pretty poor PSRR, but automatically adjusts bias to the best level.

[sawreyrw]

keantoken,

This amplifier can't possibly work. The output impedance is way too high; the output coupling cap is way too small; etc. In addition, the biasing is very questionable. There is no way you will get any appreciable power into the load.

Low output impedance is one of the reasons most power amps use emitter (or source) followers. Your amp might work if you use emitter followers, and if it is biased properly.

I don't wish to be negative, but you asked for comments.

Rick

[johndiy]

umm i agree this amp is like those you often find on internet
it wont work well umm
the op is way too loaded with 8ohms you'll need high sensitivity
headphones to hear any sound

john

[keantoken]

I guess I'll try something different