Which is the most important part of a stereo system?

There is no most important component. They call it a stereo “system” for a reason. My own approach is to figure out what the weak link is and address that next. It’s a never-ending project and the improvements get smaller and smaller but my ability to hear them gets better and better. 
That said,I can remember getting three big jumps in SQ over the past 20 years, that you might cogitate over before chasing boxes. 

1. A hospital grade wall outlet. A genuine WTF moment. No PC ever made as much difference as the outlet itself did.
2. Antivibration under the pre-amp. Iin my system it has mattered there more than anywhere else.

3. Perfect Path contact enhancer applied as the maker recommends it. An astonishing product, but you’ll never find it again. The maker died this winter and apparently the formula passed on with him. The entire community should be sad about that one. It turned out I purchased one of his very last tubes. 
but that is with my system. For someone else it might be something else. Tthere is no magic amp or pre or speaker out there that will transform a system. 
I could add a fourth — a well produced  recording. The better your system is,the more you are at the mercy of the production quality of whatever you’re listening to.

The room. 
I’ve head so-so systems sound wonderful in a great room and amazing gear in a poor room sound meh. 
Everything matters absolutely but the rooms acoustics make it all possible.  

The front end records,or digital is where  your music starts ,you can’t makeup downstream any shortcomings,therefor it better be optimumbefore going to the preamp section.

@audioman58 , yes I think everyone would agree that mastering matters.

It's virtually impossible to make poorly mastered records sound good - no matter what the size of your endless  audio money pit may be. 

We also happen to be fortunate to be living in a time when the gap between budget and high-end amplification and digital sources/converters/cables is almost indistinguishable too. 

What are we left with then?

Loudspeakers and vinyl playback. 

No one would argue that budget and high-end speakers and decks can be confused in any listening tests.

Even today's constantly improved entry level Rega/Pro-Ject decks (or any sub $500 loudspeaker you can think of for that matter) still leave considerable room for future upgrading. 

This hobby is far from dead, and we haven't even begun talking about Tube amps.

https://youtu.be/vCk12xzivp8

Which is the most important part of a stereo system?

I wish someone had clearly told me the answer at the start of my trip in audio...That would had spare me money and time...


The most important part of a stereo system is not any of the electronic components, turntable, dac, computer, amplifier, speakers....( For sure choose them with care but after that forget them, dont upgrade, and begins the thinking process with what you owns)


The most important part of a stereo system is invisible to the eyes but very audible to the ears...


The most important part of a stereo system is these 3 embeddings for any stereo system whatsoever :


1-The mechanical environment of each electronic component (vibrations-resonances controls)

2-The electrical grid of the room and of the house

3a-the "passive" room treatment with materials absorbant and reflective ones
3b-the "active" acoustical space modifications with reflectors, Helmholtz resonators, Schumann generators,etc

(An important remark: Room treatment with absorbant or reflective materials and non conventional acoustical space modifications with Schumann modified generators and controls with Helmholtz resonators or different resonators and reflectors are not the same thing. We must not confuse room treatment with acoustical space modifications.)

This is what I learned, a good electronic component will work like any other good electronic component, and the upgrading of one will never rival with these three embeddings right implementation; absolutely no comparison in increasing S.Q. with an upgrade of any electronic component...

Embedding a system is the way....The Tao of audio....

Dont buy anything before thinking about that and experimenting....

The good news is that it is possible to afford Hi-Fi at low cost, buying used, vintage or simply low cost good components... I know I did that...It is also possible to create homemade low cost solutions for all of these 3 embeddings...I know I did precisely that... 

The most important is the embeddings not the brand name of the electronic components at all ( for sure we all have our likings but it is only anecdotal interest, because they are plenty of very good electronic components)...

In simple word, your ear is the only true guru in audio and you must seriously listen to him ...

My best...



" My ear know more than me" Groucho Marx