Audiophilepure

Specifically, I was interested in trying out the 7N7 and 7AF7 loctals, 6SN7 near-equivalents via adapters, albeit with a loss in overall gain. Note that I only replaced V1 and V2, the gain stage tubes, leaving the cathode follower (V3) alone. In particular, the 7AF7 worked extremely well for the end result I was after; namely, textural sweetness galore. It wasn’t as focused or tight in the bass as the CV181, but it nicely vitalized textures when partnering solid-state designs. Neutrality or warmth—both are possible with the right 6SN7. And that is the important point about tube rolling: It allows the end user to voice the LA4 to match a particular system or sonic preference. 

It would seem that David Shaw has cracked the code for preamp excellence. His classic recipe includes a 6SN7 gain stage, a tube buffer, and a tube-rectified power supply. This combination, together with excellent engineering and parts selection, makes the Icon Audio LA4 Signature into a formidable line preamp. This is one preamp I could live with happily ever after. 

https://www.stereophile.com/content/topping-pre90-line-preamplifier

I bought three Pre90s. In principle, the volume on all three Pre90s can be controlled with a single carefully aimed remote control and monitored via the numbers on the front-panel display. But I tried that approach with the Benchmark LA4 and found it a less-than-ideal solution. It’s not ideal because the volume can easily get out of synch among the three preamps, and we already know that the Pre90’s remote control is finicky.

With the Benchmark preamplifiers, I improved things by buying an IR receiver/splitter on the internet for about $20. This little box accepts a tiny, wired IR sensor as input and has four tiny, wired IR transmitters as outputs. I attached one transmitter to the IR sensor on each of the three Benchmark LA4s. It’s a bit of a kludge, but it worked. I intend to try the same thing with the Topping preamps.