I came across an old preamp review (Nov 29, 2010) by Stereophile and noticed the same names were used for their preamp offerings then as tubes4hifi (VTA) uses today.
SP9, SP14, SP15
Were these companies related at one point?
Here is the article on the SP14
https://www.stereophile.com/content/audio-research-sp14-preamplifier
SP9, SP14, SP15
Were these companies related at one point?
Here is the article on the SP14
https://www.stereophile.com/content/audio-research-sp14-preamplifier