If you happen to be a fan of Popol Vuh, you are more likely to have albums like Hosianna Mantra (1972), Seligpreisung (1973), Einsjager & Siebenjager (1974), etc. You know that Florian Fricke tended to use piano as his main instrument, and no electronic instruments were used by any other band member. So it's a huge shock that Popol Vuh started off as an electronic group, with Florian Fricke on the Moog III modular synth! This was before he underwent a religious conversion in 1972 (both Christianity and Hinduism, which I'm certain didn't settle well with many people of either faith), and for some weird reason or another, caused him to ditch all electronics for non-electronic instruments. Around 1975, Fricke apparently sold his Moog to Klaus Schulze, figuring Schulze would have far greater use of it than he ever would after '72 (which is obviously true, I do see a picture of a Moog in the gatefold of Schulze's 1976 album Moondawn, and it looked like the one Fricke once had).
On a side note: it's interesting to note around the same time, a group from Norway was calling themselves Popol Vuh and managed two albums under that name (self-entitled 1972 debut and 1973's Quiche Maya, so if you buy those albums, be aware, they are not Florian Fricke's Popol Vuh), but both the Norwegian and German groups found out about each other, and by 1975, the Norwegian group's name was changed to Popol Ace to avoid confusion (but still continued releasing albums, this time under their new name, until 1978, while the German group kept releasing albums right up until Fricke's death in 2001).
In their early electronic phase, Popol Vuh managed two albums, In der Gärten Pharaos (1972) and this one, Affenstunde, which is their debut. This debut album was originally released on the Liberty label, and was allegedly the very first ever Moog album by a German act. The group, aside from Fricke, of course, consisted of Frank Fiedler for additional synthesizer and Holger Trülzsch on percussion. Uncredited, apparently, is Bettina Fricke (not sure of her relation to Florian) on additional percussion (she is credited to production) (back cover shows her playing tabla, she had that hippie look, complete with headband, something Glenn Cornick of Jethro Tull also worn around that time).
If you know only their post-1972 albums, be prepared for a shock! This is electronic, this is experimental, this is sorta like their version of Tangerine Dream's Zeit (and in fact, Fricke did make an appearance on Zeit). The opening cut, "Ich Mache Einen Spiegel" is a three part piece, consisting of lots of electronic effects and droning ("Dream Part 4"), then the group goes in percussion overdrive ("Dream Part 5"), before settling down to something more mellow ("Dream Part 49"). Noticing that these movements were not called "Dream Part 1, Part 2", etc. probably meant these were simply excerpts from extended sessions, and so they likely spliced what they felt was worth putting on album. The next, and final cut is the title track. Once again, you get treated with lots of electronic effects, sounds of trains and traffic (which you can't be sure is the real thing or from the Moog), before the droning starts and the band starts exploring electronic raga (without sitar). Here the synth keeps a sustained note, while the rest jams on percussion and other electronic sounds.
Popol Vuh is a case of an artist who drastically changed their sound in their career, meaning fans of one phase might not like their other phase (this is even more of a shocking change than when Tangerine Dream moved to Virgin Records and started recording actual electronic albums, since Popol Vuh went the opposite way, for a more organic approach). But Affenstunde is a great place to explore the roots of Popol Vuh, it's little like anything they did after 1972, but comes recommended to all adventurous electronic music fans!