TLM67 modification to dual output

[emrr]

What to do with a spare TLM67 electronics set? Make a dual output microphone, so you can choose the pattern later, or use it as a stereo microphone (this is the same pattern as mid-side with an omni mid). A little cypherin’ led to the hookup scheme, and a bench test gave proof of performance. It’s a tight fit, requires getting different M3 standoffs for the amp boards, and wiring the new 5 pin XLR to the output boards.

You get dual output with F8 pattern selection. If you go to cardioid or omni, you get those out the front output, and nothing on the rear output. Look to the Lewitt LCT-640-TS or Sennheiser MKH 800 Twin manuals for an explanation of usage.

HPF and -10 work on the front only.   Set to omni, use -10 switch, reverse polarity, and use reverse side to get wide cardioid through the front output. Use the HPF to change the off-axis response in the lows only.

Recording session tests this weekend, I may start with it over a drum kit for stereo OH.

before:

[emrr]

This thing works great as a stereo mic, much better than i expected. Stoked.

[Nick Sevilla]

Nice job!

Will you sell plans to mod them, or???

[emrr]

Thanks Nick! Clearly you've got have a second set of electronics to work with. Sennheiser will sell you the parts but they aren't cheap, so used market is a better source. Outside of that, if you look at the U67 and/or U87AI schematic to understand the pin connections, it's pretty easy to sort out; things you no longer need, and things you will need. The output boards to the new XLR is the toughest part, and getting those boards off the original XLR is also tricky. I tore one pad off the PCB doing it, and had to mend it with a wire scrap.

[emrr]

This is what you get using it as a stereo mic in this situation, at about 5 feet. Direct into a battery powered Tascam DR-701D.

https://www.dropbox.com/s/klhydwxjf4vyu ... 8.mp3?dl=0

[jimjazzdad]

Thanks for sharing the photos and description. Nice job on the modification but I personally wouldn't consider it a stereo mic in any normal sense of 'stereo'. Sure it has totally independent outputs from the two diaphragms of the capsule, but it is still only one capsule with two outputs 180 degrees apart. This is useful as it allows you to blend the two signals in post to create an infinite number of patterns from omni through figure 8, but it does not yield a 'stereo' signal in any accepted sense of the word. For a stereo mic, you need two capsules in some accepted configuration: XY, MS, NOS, ORTF, etc. Some designs - e.g. Pearl DS 70 - provide separate feeds from the front and rear diaphragms, like your mod, but there are still two separate capsules oriented at 90 degrees to each other. However, if you find it useful...great.

[emrr]

Jim! This is the same pattern created by mid side with an omni center. Look it up! In fact several of the Pearl dual output mics describe such stereo usage. I'm guessing you didn't listen to the sample. One could argue it's not 'exactly' like MS with an an omni M in that there's no typical on-axis treble response in the center, and that is where I'm most surprised with the result. It's probably a bit more like using a ribbon for mid and a condenser for side, but the center treble content works better than I imagined.

At any rate, not intended as my main usage.

Thanks for sharing the photos and description. Nice job on the modification but I personally wouldn't consider it a stereo mic in any normal sense of 'stereo'. Sure it has totally independent outputs from the two diaphragms of the capsule, but it is still only one capsule with two outputs 180 degrees apart. This is useful as it allows you to blend the two signals in post to create an infinite number of patterns from omni through figure 8, but it does not yield a 'stereo' signal in any accepted sense of the word. For a stereo mic, you need two capsules in some accepted configuration: XY, MS, NOS, ORTF, etc. Some designs - e.g. Pearl DS 70 - provide separate feeds from the front and rear diaphragms, like your mod, but there are still two separate capsules oriented at 90 degrees to each other. However, if you find it useful...great.

[jimjazzdad]

I'm guessing you didn't listen to the sample. One could argue it's not 'exactly' like MS with an an omni M in that there's no typical on-axis treble response in the center, and that is where I'm most surprised with the result. It's probably a bit more like using a ribbon for mid and a condenser for side, but the center treble content works better than I imagined.

Doug, I did listen to the sample, but just on cans jacked to my laptop. It has nice tonality, as I would expect with a Neumann mic, but I could not detect a lot of stereo image - but it wasn't exactly mono either. I do a lot of MS orchestral recordings, either Fig 8 + cards (even wide cards), or crossed Fig 8s and I am used to almost pinpoint accuracy with regard to the stereo image. I almost never use Fig 8 + Omni mid as I seldom get what I am looking for in this configuration. No doubt I am biased when listening to your sample. I think it would probably work OK as a drum OH mic. Anyway, I really enjoyed the DIY show and tell and I didn't intend any criticism of the final product...I was just being a bit of a pedant I guess.

[emrr]

I could not detect a lot of stereo image - but it wasn't exactly mono either.

You probably couldn't tell the other mic pair in front of it is a MS MKH30/MKH800Twin set. Pretty similar imaging on this source at this distance.

Anyway, this was a test to see what would happen while using others for tracking, no placement tweaked at all.

[Magnetic Services]

Pay the haters no mind - this is a really cool mod and we thank you for sharing!

You could buy up used TLMs, write up the instructions and sell it as a kit!

[winky dinglehoffer]

On my headphones I found the stereo imaging pretty impressive. Very cool idea for a mic mod.