Question about the LM383 7-watt audio amp.

[Electric Rain]

Is the LM383 audio amp IC cascadable? If so, how would I go about adding a second or third one to this schematic?: https://www.aaroncake.net/circuits/amp.htm Thanks.

Rain

 

[Juglenaut]

You will run into what is called a brick wall if you are going to cascade op amps.

 

[Electric Rain]

Why is that? What would happen?

 

[Juglenaut]

I think 3-4 is the limit, it will hit a max of 80 dB gain or abouts, that is what I learned.

Bridging is different, but also has stand alone issues.

 

[Nigel Goodwin]

Is the LM383 audio amp IC cascadable? If so, how would I go about adding a second or third one to this schematic?: https://www.aaroncake.net/circuits/amp.htm Thanks.

Perhaps you should tell us what you are trying to achieve?, the question really doesn't make any sense!.

 

[Electric Rain]

...Um... not to be rude Nigel, but isn't it obvious? I simply want to double or tripple the wattage of the amp that I posted the schematic of. But I want to do it by cascading the IC that was used in the schematic.

Rain

 

[Nigel Goodwin]

...Um... not to be rude Nigel, but isn't it obvious? I simply want to double or tripple the wattage of the amp that I posted the schematic of. But I want to do it by cascading the IC that was used in the schematic.

No it's not obvious :lol:

Simply because it doesn't work like that! - so your question was totally meaningless.

An audio power amplifier can do no more than output a voltage limited by it's power rails, by bridging two amplifiers you can effectively double this voltage - but the same constraints apply!.

So assuming you have a 12V supply rail the absolute MAXIMUM voltage that can be delivered is 12V peak to peak (actually less, due to losses in the amplifier - but I'll assume 12V for ease!).

12V p-p is 4.24V RMS, you calculate the power by squaring that (giving roughly 16) then dividing by the speaker impedance. In this case 16/4 gives 4W into 4 ohms, or 16/8 gives 2W into 8 ohms.

Cascading two amplifiers means putting them in series, this is a stupid thing to do with two power amplifiers (you would use an opamp for the first one instead), and would only increase the voltage gain of the system - no increase in power whatsoever!.

If you wanted to increase the power you need to do one of two things, increase the supply rail, or lower the speaker impedance. Either of these will probably require updated amplifier components.

What sort of power are you looking for?, into what impedance?, and from what supply voltage?.

 

[Electric Rain]

Well, excuse me for not being on the same level of electronic knowledge as you. :roll: Nigel, it wasn't a pointless question, because the question was asking if it's possible to cascade the IC for a higher wattage. You act as though my question was "I know that you can't cascade the LM383 to double the wattage of this circuit, but how do you cascade the LM383 to double the wattage of this circuit?" :lol: THAT'S a pointless question. Where are you coming from when you say it's a pointless question Nigel? Or are you just put-off by my new signature or something? 8)

Rain

 

[Juglenaut]

Bridge it

 

[Electric Rain]

Bridge it

Does this simply consist of building two circuits, wiring together the input of them and the outputs of them? This will double the wattage? Thank you.

Rain

 

[Nigel Goodwin]

Well, excuse me for not being on the same level of electronic knowledge as you. :roll: Nigel, it wasn't a pointless question, because the question was asking if it's possible to cascade the IC for a higher wattage. You act as though my question was "I know that you can't cascade the LM383 to double the wattage of this circuit, but how do you cascade the LM383 to double the wattage of this circuit?" :lol: THAT'S a pointless question. Where are you coming from when you say it's a pointless question Nigel? Or are you just put-off by my new signature or something? 8)

If you try asking for what you want, it works a LOT better - your use of cascade didn't make any sense at all - if you had asked how to get more output power by using multiple LM383's it would have made sense!.

But you still need to give more details, what voltage rail are you using?, what speaker impedance?, and what power do you want?.

I previously mentioned bridging, by bridging two amplifiers you get double the output voltage, which gives twice the power into twice the impedance. If you're wanting to do this you may as well use a different IC, there are plenty bridged amplifiers available in a asingle IC package.

I've no problems with your signature, like most of the world I've no interest which loony the USA have as a president!.

 

[Electric Rain]

I've no problems with your signature, like most of the world I've no interest which loony the USA have as a president!.

Well, I guess that is true. It's not as though it makes any difference to you one way or another, being as you live in England.

Anyway, I'll be using 8 ohm speakers most likely, and 12VDC. Here's the thing though... I want to build an amp that will be strong enough to fill a small room with sound. I've got no clue if 2 watts or 50 watts will be enough. This will be my first amp and I don't really have a stereo system that shows off it's power with a big "300 Watts" or "500 Watts" printed in big shiny letters on the front. So I don't have anything to compare it with. Chances are, 8 watts is plenty. Especially with the amp being only for one channel, so I'll actually have 16 watts of power. I have a small TV in my bedroom, that only has one speaker. (So it's line level input.) That one speaker simply kills me. I want stereo sound for my room. That is all. Nothing especially loud or extremly clear. So what do you suggest for power? :?: I'll probably just end up using a pair of amplified computer speakers. :lol:

Rain

 

[audioguru]

Anyway, I'll be using 8 ohm speakers most likely, and 12VDC.
Chances are, 8 watts is plenty. Especially with the amp being only for one channel, so I'll actually have 16 watts of power.

Rain

Never mind the title of the project, it's just plainly wrong!
Where are you going to get 8W from? Not from this amp. Didn't you hear Nigel?
This amp gives only 4W into 4 ohms, or 2W into 8 ohms, with a 12V supply. This puny amount of power is accompanied with horrible-sounding 10% distortion because manufacturers overdrive amps to get big false numbers.
Get a better amp with honest spec's.

 

[Electric Rain]

Hey hey... calm down. 8) Like I said, I'll probably just use a pair of amplified computer speakers anyway. One last thing, can I use a pair of amplified computer speakers with line level output?

 

[Nigel Goodwin]

Hey hey... calm down. 8) Like I said, I'll probably just use a pair of amplified computer speakers anyway. One last thing, can I use a pair of amplified computer speakers with line level output?

Yes, they will probably be just one or two watts anyway, the figures on computer speakers are unbelievably over exaggerated!.

If you're happy with the volume of your TV, 2W per channel would probably be enough for you - although don't expect any decent bass out of 2 inch speakers and 2W :lol:

 

[Electric Rain]

Nah, I don't need that much base with that little room I have. Thanks for your help guys.