Preparing for first opamp build

Mr Goat

Member
2016-02-03 12:50 pm
Sweden
Hey!

So i have decided i want to build my own op-amp for a pair of dt990's 250ohm.

I do have basic knowledge how to solder and i have basic electric knowledge, But i have a feeling this wont be enough to build a relatively good amp. So i want to learn more about the parts needed, how a basic and more advanced op-amps work, How to understand what will fit my needs. Pretty much all that jazz so i know what i will be doing before i start the build.

Also, where do you recommend i turn to get IC's, and other parts i cant find on the Swedish website where i know i can get a hold of components like resistors etc?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am

Mr Goat

Member
2016-02-03 12:50 pm
Sweden
Welcome to diyAudio :)

Always try an buy semiconductors from reputable suppliers such as Mouser, Digikey, Farnell, Radio Spares and so on. There are many many fake devices from less reputable suppliers.

You would do a lot worse than to study the O2 headphone amplifier,
http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html

And also to study general opamp theory ;)

Is a cmoy enough to power the dt990? or do i have to build something like the Objective 2?
The reason im not all that about the O2 is that i have to import the pcb, so if i can get a more simple amp that can still power the dt990's?
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Probably not... or at least not to very high volume.

I believe the DT990's use 250 ohm drivers which although it makes them more of an 'easy' load on an amplifier, it also means you need more voltage to drive them to high levels.

That said, something like a CMOY running on a higher voltage (say 18 volts) would probably be fine.

If you look at the O2 circuit diagram and study the output stage then that is really all you need. Two opamps such as the 4556 running on a -/+ 9 volt supply would work well and would also allow you to add gain if needed. A single rail supply (so that is a single 18 volt rail as opposed to a split supply of +9 and -9) would require the amp to be AC coupled.

(Once you understand a bit about the theory of opamps then you can easily alter any circuit to make it do just as you want)
 
So long as the circuit is decoupled well it should work OK.

Be careful how you wire up the power supply.
Power should come in on one side to smoothing capacitors and exit on other side to op-amp circuit. If you dont you will get hum.
I got caught out with a USB mixer circuit that way. I just mixed in power supply with op amp circuit and got 1 volt of hum on output with no input signal. The charging impulses into the smoothing capacitors modulates the ground.

RS Components and Farnell are my preferred suppliers.