3 Transistor HP Amplifier with low dist

[shattered_dream]

Which wattage should the fransformer have ?
And about a volume pot. Which one would you recommend ?

 

[jasonRF]

Hey Lineup, what is the point of C6? Removing it doesn't seem to do anything in the sim...

I’m not Lineup, but I didn’t see an answer to this yet. Anyway, it filters out some of the power-supply ripple, so less of it ends up getting fed into the amp. Using jargon, it improves the power supply rejection ratio (PSRR).

Love this amp, but haven’t soldered it up yet. Other projects in the queue ahead of it!

 

[avtech]

It was answered in the post directly following that one:

https://www.diyaudio.com/community/...p-amplifier-with-low-dist.359267/post-7036705

 

[lineup]

Hey Lineup, what is the point of C6? Removing it doesn't seem to do anything in the sim...

What schematic do you refer to?
Most probably that cap is like it is said: Filter supply to achieve better PSRR. Power supply rejecting ratio.

Now if you have a clean and good supply, there is not so much need for that cap.
For example if you use LM317 to regulate voltage.

 

[lineup]

Here I post the latest schematic of 3-transistor amplifier I have.
Suitable transformer is 12VAC when used with LM317.
When you rectify such a transformer you get like 17VDC or even a bit more.
The add LM317 to get 12.0 Volt supply.

 

[widea]

Here I post the latest schematic of 3-transistor amplifier I have.
Suitable transformer is 12VAC when used with LM317.
When you rectify such a transformer you get like 17VDC or even a bit more.
The add LM317 to get 12.0 Volt supply.

Thank you Lineup!
I noticed the filter at the input consisting of R10 and C5 is not necessary but C4 highly likely is. What is your opinion about this?

 

[avtech]

Both are necessary - the input filter (R10-C5) is a low pass to ensure the amp doesn't get HF and oscillate. I added C4 experimentally when first building Lineup's design because I found the amp was unstable without 220-330pF. It may have been down to the layout so if you have an oscilloscope, you can always test different values or omit and see how it behaves.

 

[BucketInABucket]

Thanks for the help people, I understand why that cap's there now

 

[widea]

Both are necessary - the input filter (R10-C5) is a low pass to ensure the amp doesn't get HF and oscillate. I added C4 experimentally when first building Lineup's design because I found the amp was unstable without 220-330pF. It may have been down to the layout so if you have an oscilloscope, you can always test different values or omit and see how it behaves.

Hi Avtech. I do not have an oscilloscope to verify whether it is oscillating or not but it is my impression the input filter can be left out because of the use of C4. Anyway, so far so good without the input filter

 

[knauf1919]

You can do it without any component that you consider useless. 😎
It is your choice and no one can convince you. In fact, it is a bad thing to impose your own opinions on someone who thinks differently.
It's freedom!!! 🥳🤩🥳

 

[widea]

You can do it without any component that you consider useless. 😎
It is your choice and no one can convince you. In fact, it is a bad thing to impose your own opinions on someone who thinks differently.
It's freedom!!! 🥳🤩🥳

Haha of course Knauf1919! Just curious

 

[avtech]

I personally prefer to limit the frequencies entering the audio chain by using the LPF. Even with the LPF and no C4 my amp oscillated badly, so I keep both on mine.

But DIY is a 'choose your own adventure', and as Knauf says, Freeeedom!!

 

[marin cornel]

Hello,
I managed to finish this wonderful project. I present you some pictures:

 

[byutea]

This is my latest project. I'm implemented the amplifier to XIAO DAP (by @blue__seven) project

the amp is use 9v from boost converter

 

[sumeshak]

This is my latest project. I'm implemented the amplifier to XIAO DAP (by @blue__seven) project
View attachment 1096218

the amp is use 9v from boost converter
View attachment 1096219

Nice project!
Can you share some details of the DAC?
Is it possible to DIY such a DAC?

 

[byutea]

Nice project!
Can you share some details of the DAC?
Is it possible to DIY such a DAC?

Thanks
the DAC is TDA1387 (nxp) with simple JFET I/V, i2s signal buffered by 74hc125.
TDA1387 is common used as DIY DAC project.

 

[sumeshak]

Thanks
the DAC is TDA1387 (nxp) with simple JFET I/V, i2s signal buffered by 74hc125.
TDA1387 is common used as DIY DAC project.

Ok. Thank you

 

[merlin el mago]

Here I post the latest schematic of 3-transistor amplifier I have.
Suitable transformer is 12VAC when used with LM317.
When you rectify such a transformer you get like 17VDC or even a bit more.
The add LM317 to get 12.0 Volt supply.

Same schematic for 300 ohms headphones?

 

[lineup]

Same schematic for 300 ohms headphones?

Sorry to kept you waiting.
Now I am working on a 300 Ohm version.
It will be posted here.

What transformer do you have?
I am planning using an 15VAC transformer, as 300ohm needs a bit more voltage but less current.
The regulated voltage will be 15VDC.

If you have already a 12VAC transformer I make the circuit for that.

 

[merlin el mago]

Don't worry, no problem, thank you.