# I need help with an audio amplifier.

Discussion in 'Analog & Mixed-Signal Design' started by ConstructionK88, Jul 28, 2018.

1. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
Thank you. Want you and everyone to know none of this will be wasted. I will be studying everyone's equations. Also what circuit were you referencing in this post?

2. ### Audioguru Expert

Dec 20, 2007
10,605
1,182
It hasn't been designed yet. Two complementary power transistors and two or three little NPN transistors.

3. ### MrChips Moderator

Oct 2, 2009
17,316
5,333
What @Audioguru means is that it doesn't apply to any one design. It is the basic analysis of any audio amplifier with a push-pull output stage.

4. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
If tip41/42 with c1815(have a lot of these as well) would work I'd create it. If you had an idea for a schematic I might be able to create it just from experiments with different values of resistors and caps.

5. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
As I asked Audioguru if you have a rough schematic I'll try to make it and see how it goes if it's possible with tip41/42 and c1815s. I have plenty of both.

6. ### sghioto Active Member

Dec 31, 2017
528
73
Actually it has been! The "Lil Tiger"
How many times do I have have to mention this.

ConstructionK88 likes this.
7. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
AHHHHHHH! I WILL BUILD IT! ALSO I DON'T KNOW HOW TO MAKE EMOJIS ON HERE! FRUSTRATED AND HAPPY YALL ARE HELPING ME FACES!!

8. ### Audioguru Expert

Dec 20, 2007
10,605
1,182
The Lil Tiger in post #110 produces 5W into 8 ohms when powered from 24V but do you want to carry around four 6V lead-acid batteries?
With two 6V batteries producing 13.2V I calculate an output of only 1.1W into 8 ohms because the design is using darlington transistors that have a lot of voltage losses.
A 4 ohm speaker would almost double the power to 1.9W.
Bridging two of these amplifiers would produce about 6.7W into 4 ohms with a 13.2V supply.

Compound transistors should be used for less voltage loss and fewer diodes. Then it will produce much more power.

9. ### sghioto Active Member

Dec 31, 2017
528
73
The TS claimed he would use 18 volts. At this voltage the power out is just under 4 watts at 4 ohms
SG

10. ### sghioto Active Member

Dec 31, 2017
528
73
That's true but is the example you posted correct? Seems like that would only work using a dual supply maybe. I can't find any examples of that type of output configuration.
Below I posted a working circuit using a different compound configuration driven by a LM386-4, 2.125 watts at 12 volts and 5.5 watts at 18 volts with a 4 ohm load.
SG

Last edited: Aug 13, 2018

Apr 5, 2008
18,682
3,633
Hello,

I just came accross a weird schematic that uses an opamp as driver for power transistor (founs in electuur):

They claim an output power of about 6 Watts @ 0.01 %

Bertus

Last edited: Aug 10, 2018
12. ### sghioto Active Member

Dec 31, 2017
528
73
Doesn't seem like much power for a 36 volt power supply.
SG

13. ### Audioguru Expert

Dec 20, 2007
10,605
1,182
Boy oh boy I made a messy error on the compound transistors, I corrected it.

Elliot sound Products has many audio projects and uses single supplies and dual polarity supplies on them. Some use compound transistors.

Many power amplifier ICs have datasheets that show booster transistors at the positive and negative supplies for the IC like this one that produces 29W at low distortion into 4 ohms, or maybe 16W into 8 ohms.

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14. ### Audioguru Expert

Dec 20, 2007
10,605
1,182
The problem with using an opamp or an LM386 power amp to drive emitter-follower transistors or compound transistors is that the opamp and LM386 already have the voltage loss of emitter-follower outputs. Then the voltage losses are doubled resulting in less output power.

15. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
I wouldn't mind bridging them for less battery weight, also i should have mentioned that when I said carry around, I really meant it'll be on casters like a rolling luggage bag. My apologies but I use 3/4in birch for all my "pretty" wood projects and that stuff is heavy. Most everything like you're used to seeing in prefab speaker boxes is particle board with a plastic or thin wood veneer making it very light. If I build it, it will be quite solid. So more batteries aren't an issue. Even with just 2 it'll weight around 30lbs. However if you know a circuit that would work about the same with a 12volt supply I'll try it as well.

16. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
Also I'm not sure what you mean by compound transistors?

17. ### sghioto Active Member

Dec 31, 2017
528
73
Not really. The LM386 worked better than a single transistor driver. The output from the TIP drivers clipped before the output of the LM386.
SG

18. ### sghioto Active Member

Dec 31, 2017
528
73
See post 213.
SG

19. ### ConstructionK88 Thread Starter Member

Jul 25, 2018
148
2
OK wow. I have seriously been missing a lot of posts on my thread. I just read 6 I never got alerted to and never noticed and they are at the same time of some of my posts. I'm going to apologize if I've repeatedly asked the same thing over because I'm getting posts hours after the time stamp

20. ### sghioto Active Member

Dec 31, 2017
528
73
Well when you get over 200 post it happens.
SG