I just purchased a Gemini from a forum user and it is set to arrive next week. I read all 11 pages of comments and elsewhere online and it seems that the most popular tubes are NOS 6DJ8s, of which I have many varieties including Telefunken E88CCs, and 12BH7s, of which I only have the Electro-Harmonix version coming with the amp. Could those familiar with this tube please weigh in with their favorite 12BH7? There are many NOS manufacturers of them including Amperex, GE, Sylvania, RCA, CBS Hytron, Raytheon (perhaps a relabeled CBS?), and Matsushita.
All I can say is running HifiMan Susvaras on the Gemini powered by a Topping Centaurus DAC leaves me not missing anything from a Bakoon Amp-13R (retail $6K US but no longer in production).
It drives them with authority and nuance - really great listen.
Yah, they're amazing. Have be running them in the Gemini ever since they arrived. I think they are burned in now.
The stock tubes are amazing for clarity. I did an a/b comparison, volume matched between dac > amp, vs dac > gemini > amp with stock tubes. They sound virtually identical. This is great if I want a headphone amp, but I also purchased the gemini for its tube-ness.
Enter the 12BH7 cryotone, which supposedly imparts mostly even order harmonics and were a mainstay of many a McInstosh tube amp.
It provides the extra smooth tube-goodness that the stock tubes do not which pairs magically with those cheap TPA-chip Aiyima and Fosi audio amps which tend to have a thinner, colder, neutral presentation and makes the combo sound much closer to an expensive solid state that uses Mosfets.
It thinks its preference though. When you go from extreme clarity (stock tubes) to warmer/smoother tube - initially you may feel the tube sound is muddy, veiled or lacking the leading note edges. However, for longer listening, its I realized I preferred the more euphonic, nature of the tubi sound, the dimensionality of the notes allows you to just enjoy the music.
The extreme clarity/detail of the stock tubes stands out in an A/B but I guess I've grown sensitive to the edges and sibilance in during longer listening.
I initially found the Gold Lion 6922s more muddy/veiled than the stock tubes, but now may go back and re-test them to see if I feel the same way I feel about the 12BH7s.
Yah, they're amazing. Have be running them in the Gemini ever since they arrived. I think they are burned in now.
The stock tubes are amazing for clarity. I did an a/b comparison, volume matched between dac > amp, vs dac > gemini > amp with stock tubes. They sound virtually identical. This is great if I want a headphone amp, but I also purchased the gemini for its tube-ness.
Enter the 12BH7 cryotone, which supposedly imparts mostly even order harmonics and were a mainstay of many a McInstosh tube amp.
It provides the extra smooth tube-goodness that the stock tubes do not which pairs magically with those cheap TPA-chip Aiyima and Fosi audio amps which tend to have a thinner, colder, neutral presentation and makes the combo sound much closer to an expensive solid state that uses Mosfets.
It thinks its preference though. When you go from extreme clarity (stock tubes) to warmer/smoother tube - initially you may feel the tube sound is muddy, veiled or lacking the leading note edges. However, for longer listening, its I realized I preferred the more euphonic, nature of the tubi sound, the dimensionality of the notes allows you to just enjoy the music.
The extreme clarity/detail of the stock tubes stands out in an A/B but I guess I've grown sensitive to the edges and sibilance in during longer listening.
I initially found the Gold Lion 6922s more muddy/veiled than the stock tubes, but now may go back and re-test them to see if I feel the same way I feel about the 12BH7s.
Thanks. I am planning to buy a Gemini soon. I already have an Amperex Bugle Boy 6DJ8 to play with. A high quality 12BH7 will probably be the only other tube I plan to buy.
The Gemini will be used as a HPA, a preamp for my desktop RSL amp and a preamp for a Ragnarok 2 in my main system. Three tubes should be enough for me to find an enjoyable tube sound for each.
I bought a used Sparkos Labs Gemini amp and tried it using my JM Audio Editions XTC-Closed 2.5 phones shown in the picture. And man, this is a great-sounding amp, especially at the $1000 retail price. Rolling in a NOS Amperex 6DJ8 tube brought it to an even higher level of sound. No, it doesn't have the speed, detail, transparency, and spaciousness of my Benchmark HPA4 amp, especially when struggling to drive my RAAL SR-1B phones with their transformer interface, but the midrange is absolutely gorgeous with a lot of midrange body, immediacy, and good bass with dynamic and planar magnetic phones.
I wanted to post results of my Sparkos Gemini amp using some NOS tubes I had, all of which made a shocking difference in sound over the new production Electro-Harmonix 6922 and 12BH7 tubes that came with the amp.
6922: I tried some 70s Amperex, 1965 Mullard, and 1960s Telefunken E88CC tubes I had. The stock E-H 6922 wasn't bad but the three NOS tubes brought the sound to an entirely new level. I liked the Amperex and Telefunken tubes best, vastly increasing the speed, detail, transparency, and spaciousness that I love. No, not like my Benchmark HPA4 solid-state amp with its vanishingly low distortion, but the Gemini has has more midrange body, warmth, and bass weight that works well with my RAAL SR-1B ribbon phones. I would posit that NOS tubes are an absolute must with the Gemini.
12BH7: The new production E-H 12BH7 is not too impressive, giving what I would call a soft and subdued sound. Dynamics were reigned-in, detail was weak, and there was little bass or treble to speak of. My term for these tubes is bleah. I then tried a 50s CBS Hytron 12BH7 with black plates and D-getter, and the sound was absolutely transformed in every way. They were on the side of upfront sound, not as spacious as the better 6922 tubes but music had a weight to it with gorgeous midrange body and a much more punchy and extended bass, even with my bass-shy but massively detailed SR-1B. The only argument would be which presentation you prefer when comparing NOS 6922 and 12BH7 tubes.
I still think the Gemini is a great-sounding amp, especially for its price.
Good stuff. To improve on the stock tube is impressive. I just placed an order for the Cryotone 6922s to see how they fair against the stock tube.
After living with this amp for a while, I appreciate hearing the tube differences. The stock electro is definitely more resolving than my other tubes, gold lion 6922, cryotone 12bh7, but they serve their purpose too.
I'm constantly swapping DACs and I find the stock tube pairs nicely with R2R dacs and the other tubes work great with more neutral, delta-sigma dacs. Balance each other out depending on my preferences and the sonic signature of my speakers.
I have a pair of unobtanium 1950s CBS/Raytheon 7729 D-getter tubes, an instrument-grade 12AX7 that I have been contemplating trying out in the Gemini. I guess my reservation is that the 7729/12AX7 has so much gain but it might be interesting. The earlier 7729 made by CBS Hytron is vastly superior to the later GE-made 7729 and is by far the best 12AX7 variant I have heard including the hideously expensive Telefunken ECC803S that is transparent and detailed but IMO lacks the tone and midrange body of the 7729. You can identify a GE-made 7729 through the little etched dots in the glass.
I have a pair of unobtanium 1950s CBS/Raytheon 7729 D-getter tubes, an instrument-grade 12AX7 that I have been contemplating trying out in the Gemini. I guess my reservation is that the 7729/12AX7 has so much gain but it might be interesting. The earlier 7729 made by CBS Hytron is vastly superior to the later GE-made 7729 and is by far the best 12AX7 variant I have heard including the hideously expensive Telefunken ECC803S that is transparent and detailed but IMO lacks the tone and midrange body of the 7729. You can identify a GE-made 7729 through the little etched dots in the glass.
One possibility (perhaps inexact) would be to use the 7729 with jumper #2 set to 'Type 2' -- and to have jumper #3 set to '-15dB'. This might 'offset' the extra gain of 7729.
I set my Gemini for minimum gain and rolled in my 1950s Raytheon black plate D-getter 7729 (instrument grade 12AX7 variant) and the resultant sound was the best yet. Music was supremely detailed and textured but not at the expense of transparency and spaciousness, and immediacy was off the charts. I am glad I bought these 7729s back in the day before they pretty much disappeared forever. My volume control, even on the lowest gain was at about 8:30 but I was still able to make small adjustments in volume.
Just FYI, a little history on these tubes. I believe CBS Hytron was the original manufacturer starting in the mid-1950s but some like mine were labeled Raytheon. In 1960 the getter was changed to an O-getter, of which I have a pair. The sound with the O-getter was similar but not quite as good, at least on my pair. Then in 1961 CBS and Raytheon sourced these tubes from GE that can be identified by some vertical etched dots in the glass, but unfortunately the sound was nowhere as good as the earlier CBS/Raytheon versions and is merely ordinary. So the earlier desirable versions are exceedingly rare and expensive but show up occasionally on eBay.
Anyway, probably too much information, but if you want, IMO, the best-sounding 12AX7 I would proffer the earlier 7729, along with the Telefunken ECC803S and the even more rare original Genelex B759, not the current reissue tube, the original of which I have never heard but are reportedly terrific. All these tubes are stupid-expensive these days but might be worth investigating.
• I do have a pair of Raytheon 7729 from April, 1960. Before one of those goes into Gemini, a little change of tube personnel.
• Enter Raytheon JAN-5751: a 12AX7 with 70x gain, straight black plates, the fabled 'windmill' getter holder. Jumper #1: 'Type 2'; Jumper #2: 'in, low' bias; Jumper #3: '0dB'.
• After 30 minutes of low-level music playing, time for .
Via Neumann NDH-30, fantastic tonal balance, extended frequency range, palpable, sculpted soundfield. Impact and dynamic range are thrilling! No 'hot' signal induced compression or distortion. Pure waves, pure sound! Raytheon JAN-5751 will be in Gemini residence for a w-h-i-l-e !!
After a 'local' home move, and after a few headphone amplifier / headphone pairings upon settling in, it became time to break out Gemini. With a 'new old stock' Telefunken ECC801S and with ZMF Verite Open, the sound is magnificent: delicate, detailed, emotive, forceful.
Saw this older post and it caught my attention. I just picked up a Gemini today in the classifieds and I'm waiting for ZMF November Verite Open to come in. So seeing this here has me eagerly waiting until I can try the combo myself.
Got my Gemini delivered today. A quick listen to Radio Paradise using the stock tube with Focal Clear OG was awesome. I need to take time for comparing to other amps but first impressions are very favorable. Thanks to all for their reviews of the Gemini.
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