Low Distortion Audio power amplifier

Thread Starter

Adgj533

Joined Feb 27, 2018
21
Hi guys im new here, Need some help with an amplifier im building and I have a few questions. I have the schematic and ill attach the PSpice simulation files
1) why is the output clipping around 20V?
2) I want to implement this on a breadboard, should I use 3.5mm to split cables to connect phone as input and output to a speaker?
3) in the simulation I used basic parts but how can I order parts using the simulation to implement this, kinda confused on this. I dont wanna order random parts and waste money( im talking about transistors,diodes,zeners etc)
 

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Thread Starter

Adgj533

Joined Feb 27, 2018
21
Hi Albert, Thanks for your input yeah i was changing values and trying to fix it, but value of R10 doesnt matter, I tried 1 and 1k, I get the same clipping around 20V.
 

DickCappels

Joined Aug 21, 2008
6,542
Your power supply is only ±22 volts. That leaves only 2 volts of headroom for the output circuits to work with. That's actually pretty good for a bipolar amplifier. Try increasing your power supply voltages.
 

DickCappels

Joined Aug 21, 2008
6,542
I agree with Alberthall -when you load the output those 1k resistors will be a problem.

I cannot make out the part number of Q3. Is it a Darlington?
 

Thread Starter

Adgj533

Joined Feb 27, 2018
21
oh ok, I will change to 1ohm then, I got a 60Watts 6 ohm speaker at home, would that be sufficient, ?
Also idk what type of transistors to use because this is a project for school so prof gave the schematic, i just need to put it on a breadboard and show him that it works. Im pretty sure its not darlington pairs.
for the transistors im gonna go with 2N3904 and 3906. thats available at my school hopefully it works
 

crutschow

Joined Mar 14, 2008
25,270
for the transistors im gonna go with 2N3904 and 3906
The output transistors need to be power types, otherwise your maximum power into a 6Ω speaker will be about 100mW and the transistors will likely get zapped.
Try something like a TIP31 and TIP32 for the output transistors.
 

Audioguru

Joined Dec 20, 2007
11,249
On the other website the schematic is much clearer. He wanted to buy the parts at Digikey but the huge high voltage Oriental driver transistors are not available there. Since the predriver currents are low then I recommended any little transistors.
 

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Audioguru

Joined Dec 20, 2007
11,249
How long do I have to hang around AAC before I get the schematic-descrambler code? (I'm not referring Ag's)
I think the schematic that is impossible to see anything is a Multisim simulation because it has lines going up and down and around instead of being straight. It also has ground and power wires all over the place instead of symbols which make all the parts far away and tiny. I don't know why schools use Multisim as a simulator and schematic messing-up program.
 

ebp

Joined Feb 8, 2018
2,332
Conventional audio amps like that are probably one of the easiest of moderately-complex circuits to draw in a way that makes the flow of signal conspicuous. Except for the feedback path and the AB bias circuit, they are beautifully symmetric when built with complementary devices. I find the schematic at #1 nearly incomprehensible, and it isn't because I don't understand how the circuit works (except the switch - I'm a bit baffled by it).
 

Thread Starter

Adgj533

Joined Feb 27, 2018
21
Hey its the friendly neighborhood hero Audioguru again, whats up man lol. So do I need TIP31 or can i u use 3904/06?
 

Thread Starter

Adgj533

Joined Feb 27, 2018
21
How long do I have to hang around AAC before I get the schematic-descrambler code? (I'm not referring Ag's)
Hey man sorry about the circuit schematic, I did kinda quick in PSpice, the schematic Audioguru posted was from my prof. now that I think about it, i shoulda posted that. My mistake.
I just wanted to show you guys how I did the simulation or maybe i did something wrong in the sim.
Thanks for your feedback
Cheers
 

Audioguru

Joined Dec 20, 2007
11,249
Your PSpice schematic is hard to follow since its ground and power supply wires are all over the place instead of being symbols, and since the PNP transistors are still upside-down but re-wired to be connected correctly.

Since you are simply copying an existing circuit then I guess your professor did not teach you how to design one.
The pre-driver transistors in the original circuit are Oriental high voltage power transistors that are not available here.
They drive driver and power transistors that have a minimum current gain of 1000 so the 18V peak voltage into an 8 ohm speaker requiring 18V/8 ohms= 2250mA needs only 2.3mA from the pre-driver transistors and their 1k collector resistors need only 18mA. You don't need a high voltage transistor in a 44V circuit and you don't need a power transistor when the current is only 2.3mA + 18mA= 20.3mA and the heating in the pre-driver transistors is puny so the 2N3904 and 2N3906 (625mW, 40V, 200mA) transistors will be fine. Somebody on this website or on the other website said that the 2N3904/2N3906 (250MHz !) might not be fast enough. I think the amplifier will be fine without them and the driver and output transistors can be changed around to be Sziklai pairs.
 

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Thread Starter

Adgj533

Joined Feb 27, 2018
21
Your PSpice schematic is hard to follow since its ground and power supply wires are all over the place instead of being symbols, and since the PNP transistors are still upside-down but re-wired to be connected correctly.
Hey man thanks for the input, I will try to do it better next time, I didnt know how to change the direction of the arrow in Pspice, thats why, how did u do that?
 

Audioguru

Joined Dec 20, 2007
11,249
A PNP has the arrow pointing to the base inside it. An NPN has the arrow pointing away from the base inside it.
PSpice never learnt that positive is up and negative is down.
 

ebp

Joined Feb 8, 2018
2,332
It's been so long since I've drawn a schematic, I don't remember which way up the emitters are on the PNPs in my library. I just assume that any part is likely to require rotation and or mirroring. I have four variants for each bipolar - E&C up & down, both to the side, E up/down C to the side, C up/down E to the side. It takes a few minutes to add new symbols to the library (something I typically had to do for every new project) but it makes schematics neater and allows tighter packing of the symbols which leaves more clear space for ref designators & values (& sometimes one or two other details) and names on nets. I would never allow a schematic with colored anything, except for highlighting for special reason, out into the wild. Color is to aid in drawing and not for publication. But I make some very colorful layers in my PCB PDFs.
 
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