Some years ago I built the DCB1 buffer for myself. Some time later I built another one for a friend from the same kit that sachu888 made available. The difference in the later build was I used a balanced cable made of tinned copper as internal signal wiring because that cable was what I had at the time. It sounded very different from my DCB1. It had a sense of air around the instruments and voices, especially percussion, making the highs more delicate and open. I rewired my DCB1 buffer and reproduced exactly what I heard in the DCB1 built for my friend. All my buffer, phono preamp and power amp builds from that day uses this particular balanced cable. For those interested this balanced cable is Helusound AES DMX cable, a 110 Ohm AES/EBU digital cable. Some may scream, "Sacrilege!" but it sounds what it sounds.
It has never occurred to me that tinned copper wire could possibly sound good as internal power cabling inside an amp until recently when a new amp I built sounded hard edged across the entire sound spectrum despite many hours of burn in. I had used silver plated copper wires, 1.5 sqmm cross section for all internal power and speaker wiring in this amp. Especially irritating to my ears was the midbass bump. So I decided to change the internal wiring to tinned copper. First I changed all the wirings related to the speaker output (amp boards to amp binding posts) and speaker cabling inside. The new sound that the amp produced was much more agreeable to my ears. There was no more midbass bump. In its place was a deeper bass (of course limited to what my small speakers can reproduce). The mids sounded good like before (the silver plated wires didn't harm the mids). The highs had good extension but it lacked sweetness and can sometimes sound etched. In fact I heard many new nuances and details in familiar music, but it always had a sense of being in a hurry. The tinned copper wire changed the character of the highs the most, making the sound unforced, effortless and airy. Hearing the positive changes I changed all the power wirings inside the amp to tinned copper. With this the entire wiring inside the new amp is now tinned copper.
To extend things further, I thought if tinned copper sounds good inside the amp, how would it sound as speaker cable? The problem is the tinned copper wire I got is fairly thin, and I couldn't find anything thicker in the local market. The shop said it is "23/36" wire. I haven't figured out the equivalent in AWG but by the looks of it, it seems to be about 20 AWG. Since the silver plated copper wire I had used is 18 gauge, I had to double every run to make it 18 gauge. This turned out to be a lot of work because the tinned copper wire has soft PVC insulation that immediately unravels after a pair is twisted together to double it. My solution was to twist together tightly, stretch it tightly and use a heatgun to heat up the PVC insulation uniformly and then allow it to cool down while being tightly stretched. I wanted the speaker cable to be at least 16 gauge (though I have successfully used 18 gauge transformer wire as speaker cable in the past). Twisting a pair 18 gauge to get 16 gauge was too much work so my plan got stalled till I decided to ask Prem for advice. He asked me to consider Belden 9497 which has a bit of a cult following among a section of audiophiles (especially Japanese audiophiles). I had read about this cable and filed it away in my mental storage as yet another exotica like the Western Electric WE16 cable. On a lark I called Kiran Sales in Lamington Road and asked for any Belden speaker cable made of tinned copper. Luckily they had Belden 8471 which is 16 gauge. I plugged this cable into my chain this evening and it is already sounding very promising, especially the bass weight and texture.
The point of this long-winded post is to consider tinned copper as internal and external wiring instead of chasing the purest copper that we can get. They are cheap (Belden 8471 is just Rs 90 per meter, and the 23/36 patch wire I bought is just Rs 15/m), they won't oxidise --- tinned copper wires are usually used in applications where copper oxidation can be catastrophic (like electrical wirings on boats), and they sound damned good (at least they do my ears!).