• Transparency
• Micro-detail
• Harmonics
• Soundstage (Depth – Width)
• Speed and Dynamics

• Obviously, Cables.
• RCA or XLR Jacks, Binding posts.
• Solders,
• Internal wires,
• Capacitors
• Resistors
• Tube sockets
• Tubes / Transistors

At the very basic level, the conductivity is ultimately important. If, one of these elements are of lower quality than the others, the total performance would be the performance of the lowest performing component.

There are hundreds of brands out there. Lets consider

Resistors: NOS versions, carbon resistors, metal-oxide ones and tantalum resistors. All have a different performance. Metal-oxides almost always sound slightly metallic. Carbon ones are warm slightly colored. Tantalums – the new productions, which are slightly magnetic, are neutral but not natural, the NOS tantalums are very natural, neutral and organic.  My preference is towards using the NOS tantalums. They are claimed to have a zero-magnetic property as well.

Solders: There are tens of different solders in the market. Some claim to have the highest silver within them. This, by itself, does not prove a more natural sound. Mostly, the performance is brighter than  usual, again, losing the low-level impact. My preference is towards using solders with silver and gold together.
For low-budget systems, any upgrade is advised to  be made with a cheaper version of solder, with a silver level not exceeding 2.5%.

Capacitors: A higher-quality capacitor is a necessity for any system. Capacitors and internal wires would bring the highest impact in terms of sonic improvement.

Power Capacitors

On the power section of each unit, there exists the power capacitors. Almost all the time, if you take the cover off your unit, you would see the cheap electrolytics usually manufactured by thousands in the FarEast. Unfortunately, these power units usually have a very high ESR value (internal resistance of the capacitor) and this is a true degradation in the purity of the powerline. The result is usually low dynamics, uncontrolled bass and absence of the 'lower body' in sonics. If the chassis does not have sufficient space, bypassing the powercapacitor with a bipolar capacitor 1% of the powercapacitor value (usually stated in uF) would certainly decrease the ESR value and improve the sonic performance. The best electrolytic to date is BlackGate which are considered NOS as of today, since the Japanese manufacturing no longer continues. They are very fast. natural sounding and have incredible dynamics.   Even better than Blackgate capacitors is a new  generation power capacitor, which is called FilmFolio power capacitors.  These capacitors are the best in every criteria.  The ESR value are the lowest and the realism is at its best.

Signal Capacitors

As the name implies, the quality of Signal Capacitor is very critical in determining the sonic signature. In very pure signal paths, it is very possible to hear tremendous changes in sonics, especially if one upgrades a standard signal capacitor to an exotic one.  For instance, my preference is towards Silver Gold Oil type of capacitors and stack foil capacitors. I personally prefer the Silver Gold Oil capacitors within the pre-amp and power amp stage, and the combination of stack foil and Silver Gold Oil capacitors in the crossover level. Of course, this is my personal preference in the Ultra-High End. An audiophile may also bypass the original capacitor with another (preferably better) capacitor 1% of the value and still get an improvement. But, this would only give a 'glimpse' of the bypass capacitor sonically. Changing the capacitor with a better capacitor would certainly have huge improvements and significantly  contribute to the purity principle.

Internal Wires: A higher-quality internal wire is a necessity for any system. Capacitors and internal wires together would bring the highest impact in terms of sonic improvement. When we mention the signal path, the actual path that the signal travels is through the internal wires of device.  Serious manufacturers usually prefers to use low capacitance internal wires in devices.  Interestingly, few - very few of the manufacturers have sonically verified cables within their devices. By sonically verified, I mean very pure copper, silver or alloys, manufactured under tight tolerances - just like a high quality interconnect or a speaker cable. Even from very expensive preamplifiers and poweramplifiers, I have frequently came across 'Low Capacitance Microphone Cables'.  A standard RadioShack grade wire is the biggest block against purity and the ultimate supporter of Harmonic Distortion. In any upgrade, a lower capacitance, inductance and resistance of a cable is very - very important. After that stage, on the low-level signal, choosing the correct AWG is crucial on choosing the internal wire.  A lower AWG than necessary would eliminate the bass performance and all instruments will start to sound thin and without the required 'body'. In summary, choosing a high purity wire with the correct AWG would be a significant improvement.

Pure silver wires, may sound bright, with extended highs and less significant lows. Pure Copper may have more 'body', but lower resolution. The source of silver and copper is very important in the sonic signature. Usually, alloys may be very convenient solutions in internal wires.

Jacks and Binding posts and tube sockets: When the signal transfer from the male socket to female jacks, a high quality plating and a short signal path in the R CA socket decreases the resistance, and significantly improves the sound properties.

Again, changing a stock RCA or XLR male/female socket with a higher quality one is a sure improvement.

Gold Plated Sockets/Binding Posts: A minimum 20 micron Gold plating with a high quality polish: Warm, natural sound. 

Silver Plated Sockets/Binding Posts: Similar to internal wires, may sound bright, with extended highs and less significant lows.

Multiple Plated Sockets/Binding Posts: Multiple plating such as Palladium over Gold, Palladium over Silver  or Rhodium over Silver usually may give incredible sonic results in ultra-high end parameters.

Tubes: To be posted very soon...