I have had my (matched) pair of Coles 4038 for about three months in the studio now and feel confident to judge the mic and write this review that will hopefully be helpful for some of you. There are a vast number of alternatives available in the ribbon microphone market, but these are one of the classic designs and have been around for ages.
First off, these are really heavy microphones, if you plan to use them as drum overheads be prepared to get some solid stands, off the shelf K&M hardware will not cut it. At least add some heavy counterweights so that the mic will not pull down the boom or make the stand fall over. For general use it is very convenient that the angle of the head of the mic with the capsule is adjustable, to fine tune the position. The overall construction is very solid and the plastic case gives them a good home when not in use.
Initially I was looking for a more mellow alternative to my pair of Josephson C42 for drum overheads, but also as a general use stereo pair. Placed above the kit in a position of where I would normally place condenser mics in spaced pair, the 4038 yield a very full sound but certainly need EQ'ing for more modern styles. The real revelation came when trying them out on drum room, in my small / medium sized room with 35 square meter with 4m ceilings: After struggling with critical placement on both condenser and dynamic mics in my room, these guys sounded great straight away. No nasty resonant peaks and none of the usual harsh cymbals overpowering the room sound give a very pleasing and powerful representation, the tight low end can sometimes even spare you putting up an outside mic for kick drum and add a great body to toms.
In general the 4038 reproduce high frequencies beautifully but often need some lift above 10k. The low end can be a bit too much come mix time, I tend to pull offending frequencies EQ'ing straight to tape. This is not so much a problem as they take EQ well and reward you with a great punchy sound in regards to dynamics and transients that never sounds hyped or unnatural. On the other hand, I would not really describe their sound as "true to the source" but it's always very organic and never obtrusive. The 4038 sounds like no other mic in my microphone locker.
Although they are a figure of eight I find them to be rather direct sounding, without too much room sound from the rear side of the capsule. Most engineers whom I present recordings would often blind guess the mics to be at half the distance as they actually were set up. Initially a bit uncertain about being limited to the single mic pattern (as with most ribbons) I have come to take advantage of the excellent side rejection of the polar pattern, which works well in blending out unwanted spill with proper placement.
After some weeks I tried them out for acoustic guitar, here I found them to sound great pointing them at bridge about two feet away, rather than the usual 12th fret approach that has served me well with condenser mics. For a Jazz session I put them in use for grand piano as a stereo pair under the lid with fantastic results. I had mixed results with Electric Guitar, for crunchy and heavy tones I missed some definition and prefer the Beyer M160, if I want to use a ribbon. But micing up a Fender Twin gave a huge pristine clean sound with a very 3D quality. For vocals I tend to be happy with a SM7 or Neumann U types in front of the singer so I haven't done any testing yet. For now I'll keep them on drum room and will try to get another U87 for stereo overhead, which goes better with the pop / rock styles filling up my studio time.
These mics are great on a variety of sources and have a unique flavour, they tend to show a pronounced but still defined low end and are sometimes a bit too dull to be recommended as a "one mic solves it all" solution.