I just don't understand why these THT designs are still a thing. SMD parts are so much better. You can get 0805 SMD thin film resistors with 0,01% tolerance for the same price as 1% THT metal film resistor.
And you can get very high quality acrylic and PPS SMD film capacitors with 2% these days.
Well, I prefer full SMD design myself and I also hand solder them on 4-layer boards, no problem at all and don't have to cut those extra wires after soldering.

But THT design has its benefits too so it is more a matter of preference than anything else. I can of course say that fighting RF and other types of disturbances is easier with SMD but you can do it with THT as well if you know what you are doing. It is the board layout that is the most important detail.
You are right about the PPS caps. The 2 % series is exactly what I'm using in my RIAA eq part. But 0.01 % thin film SMD resistors are
very expensive. I don't think you really meant 0.01 % but rather 0.1 % which I'm using in all the amplifier sections? They are still quite expensive and cost more than typical 1 % metal film THT resistors.
There are two factors that decide how accurate your RIAA eq is:
- Circuit design. Wrongly calculated or inaccurate component values due to price reduction throw the eq accuracy immediately off.
- Parts tolerance. Even with 2 % caps and 0.1 % resistors, the RIAA curve can be off by several tenths of dB.
Obviously
@Michael Fidler has succeeded in both design and parts selection. It is simply impressive how well this amplifier performs and RIAA curve is practically flawless even with 1 % resistors (I bet they are hand picked). My own amp that is full SMD construction and has switching PSU reaches very similar performance but if I wanted to make it significanty better than this one it would be really hard, regardless of SMD construction or number of board layers.
I just took a look at Michael's web site and was delighted to notice that his design philosophy matches my own in most cases. There are some differences too but perhaps I should start a thread of my own sometimes when I have time to avoid any more OT.