Janssen
In store brand used by California, USA based hi-fi & electronics chain store CAL Stereo in the 1970's, mostly loudspeakers, unsure who was the OEM supplier.

Jed L. Hacker
USA based gentleman that had formerly been a partner in Soundstring, but started making his own line of high end cables and interconnects in 2009 under the Dynastrand name, then based in Palmdale, California. The company's products were high end, with the average product price being 500+ USD, but compared to Mr Hacker's previous company this was five to ten times less then what Soundstring had been charging which lead some USA audiophile sites to review the Dynastrand products as "bargain basement" products, comically enough (AFAIK Mr Hacker's products newer got any print press reviews).

The operation was shut down in 2011 and in the latter half of 2012 the product line and trademark was sold to David Chaffey, who has since re-started the manufacture of the cables.
Resources: -- A review of the Dynastrand Dynasty and Emperor loudspeaker cable & interconnect from Positive Feedback Online (2009).

Jelmax
Japanese company founded in 1978 by inventor Kazuo Ishi but he had invented and patented a new type of electrolytic capacitor where the electron flow between cathode and anode is improved by the addition of graphite particles to the electrolyte. This gives the capacitor inherently a much lower self-noise than with a normal cap, higher possible operating frequencies and the working life is extended to 25+ years since there is less loss of electrolyte due to heating etc.

The addition of graphite brings some problems with it though, construction is more difficult since the real care has to be taken in doping the electrolyte otherwise it will short which meant that these capacitors were more expensive that standard electrolytic caps and in some configurations much more so. This meant that the market for the devices was pretty much limited to on one hand high end communications equipment that needed the improved frequency operating range that these caps offered and on the other high end audio products where the improved self-noise characteristics did in some cases bring quite extraordinary benefits.

Jelmax initially worked with a smaller subcontractor to manufacture the devices and sold them under their own Black Gate trademark but in 1988 managed to get a manufacturing contract with Rubycon that meant an improved supply and prices alongside top notch quality. While the capacitors gained a cult following initially amongst a small sector of amplifier manufacturers they did not really enter the vision of the DIY enthusiast until the advent of the Internet and even then they were controversial since they were very expensive and only performed well in certain types of circuits, but in reality similar specialist capacitors like oil filled ones are even more expensive and when the Black Gates worked they showed large performance gains.

The non-polarised variants of the Black Caps were also sold in some countries as Super E-Caps up until the late 90's or so, but in 2005 it was announced that production would cease since Rubycon no longer considered the quantities involved to be high enough to be profitable, production closed down in 2006 and the company was closed in 2007 after all existing stocks had been depleted and their website appears to have been cybersquatted.

A number of electronics parts retailers still have some of their products in stock in the summer of 2010, in particular lower capacitance values but bigger values useful for amplifier outputs or power supplies are all long gone.

Jennings Research Inc.
Loudspeaker manufacturer based in Los Angeles, California, USA and founded in March 1975 by Tom Jennings that had been the head of marketing for JBL in the late 60’s and early 70’s. Initial product line was called “Contrara Group” was introduced that summer and the company made quite a splash initially with an advertising campaign in national magazines such as Popular science and the New Yorker and these appear to have sold well since they do turn up for sale quite often, the company introduced a line of amplifiers the next year, but they appear to have been in production for only a couple of years.

Jin Qian Li
Chinese trading company active in the 1990's, sold professional audio products such as amplifiers and karaoke machines under the JQN brand, these were all sourced from local OEM's. The company merged with pro-audio manufacturers Yuantian and Liangyin to form Guang Zhou HuiYing Electronics in 2002.

JMI
Loudspeaker manufacturer based in Vancouver, British Columbia, Canada, some of their bigger models were well liked at the time and one or 2 models are still sought after by local collectors. Timeline is not known but in 1972 they had one fairly small model out that appears to have been known as just the "JMI loudspeaker" but later on they had a number of models and the brand was by then known as JMI Mercer, seem to have disappeared before 1980 but that is not known for certain either.

Joemeek See --> Fletcher ElectroAcoustics (1995 to 2002 - UK - Signal processors & microphones) — Joeaudio Ltd. (2002/2003 - UK - Signal processors)

John Gallas
A gentleman based in Los Angeles, California, USA that manufactured acoustic bass traps under the Acoustic Solutions brand between ca. 1992 and 2002. This was just a part time operation, but we think Mr. Gallas’s main profession was teaching at college or university level and that he has since retired. The traps were small cylindral things that were supposed to go into the corners behind the speakers and not in front as most are, and were slightly unusual in that they really only worked with low bass and thus only worked in some rooms, but where they did work they were better than standard bass traps, at the time anyway. They were also quite expensive at 750 USD per pair in 1996.

John M. Moffat
USA based gentleman better known in the audio industry as Mike Moffat, and is probably best remembered as the founder of Mike Moffat Labs (Angstrom) in the 90's and Theta Digital in the 1980's. After the demise of MMF in 1999 he sprang back in 2000, this time as a sole trader but selling products under the Theatris brand from his base in Simi Valley, California.

The main, or possibly only product he offered was the convergencethree (one word, also known as C3), a device that Mr. Moffat described as a "DVD Transport/Super Computer" and was marketed as a high end DVD player that was capable of putting out an upscaled HDTV signal in addition to offering some rudimentary DVD server capability, both of which were features that DVD players could not offer at the time.

The C3 had a somewhat mixed reception in the marketplace, many people saw the unit as nothing more than a HTPC running the somewhat flaky Windows 98 operating system on mid-range computer hardware sporting an outrageous of RRP of USD 6500, owners on the other hand, in particular those with very large HD screens or projectors where chuffed with the hardware and maintained that if offered the best picture quality available on the market at the time but much less happy with the service and upgrades offered

The system was a bit hyped up with sentences like "Theatris happens to be the largest single advancement of DVD playback technology since the inception of the digital disc. " in retrospect probably somewhat over the top, there were promises of software updates and in 2001 Mr. Moffat announced that he was working on a replacement software system based around Linux , but no updates were delivered to customers, neither the new system or updates to the existing Windows based software and in 2002 the Theatris product line disappeared from view altogether. Mr. Moffat was last seen partnering with Jason Stoddard making DAC's, headphone amps and the like.

JQN See --> Jin Qian Li

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