TNC mic "lineage"?

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premiumdan
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ACM-100

Post by premiumdan » Mon Jan 04, 2010 10:47 am

I was hoping to find a frequency plot there, but from the looks of the Audix
plots, either of the SCX25 or SCX25A could be related to the ACM-100.
A few specs are not the same, so probably not 100% matches... Is it
possible TnC brokered a deal for a proprietary mic?

Mr Joly:
The ACM-100 is advertised as a "transistor" condenser.
Any differences with this design v/s "capacitor", x/f, non-x/f, other?
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Post by Michael_Joly » Mon Jan 04, 2010 12:30 pm

This is K67-type condenser capsule, FET (Field Effect Transistor) front end mic. The specs do not state if it uses a transformer or not. At the volume TnC was buying they would not have been offered a proprietary mic. That happens at around 15,000 units / year depending on vendor. So most likely this is a standard catalog mic sold by other importers / re-branders.

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Post by Aj » Mon Jan 04, 2010 1:25 pm

I'm wondering if the lollipop shape (and the relatively open/exposed capsule, as compared to a U87 style mic body) has something to do with it's less shrill top end.
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ACM-100 guts

Post by premiumdan » Sun Feb 12, 2012 2:12 pm

Following up with a pic of the insides.
(yeah I'm kinda slow with these things...) :shock: :wink:

Image
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Anyone ever solve the mystery of the ACM 100?

Post by Aj » Tue Oct 22, 2013 7:32 am

Arise, zombie thread... this mystery still has me stumped, so I'm bringing you back to life.

Did anyone ever figure out the lineage of these odd bird TNC ACM-100 mics? The great TNC Mic Group Buy of 2008 apparently didn't involve any custom mic designs (we've seen every other TNC mic many times over, rebranded and sold by Apex, MXL, Avantone, etc.). And very few of these ACM 100's were made for TNC, as it was the least popular mic of the entire group buy. So ACM 100 mics should have also been available rebadged from other manufacturers - in much greater quantities too.

And yet... I haven't seen any lollipop condensers like this anywhere, ever... aside from those relatively pricey Audix SCX25A piano mics.

Anyone ever solve this? Has someone ever compared the inside of those Audix piano condensers to the ACM 100? Or were these ACM 100's really one-offs made just for our little group buy? If so, why?

Sorry to dig up something so ancient (and obscure), but I wonder about this every time I throw up my pair of better-than-they-have-a-right-to-be ACM 100s.

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Post by digitaldrummer » Wed Oct 23, 2013 7:51 am

the picture of the circuit board looks exactly like the one found in the MXL 603, which with the right caps replaced (mainly the one right across the capsule), also sounded pretty good for the price.

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Post by Aj » Wed Oct 23, 2013 12:03 pm

Thanks Mike. Very intriguing... assuming that's true, then these should be easy to upgrade (I seem to remember there are 2 or 3 caps that get replaced for the biggest improvement - can't wait to try that!).

Also, didn't those MXL 603's have an issue with the capsule being recessed too far into their standard pencil-style mic body? I'm going to guess the lollipop design wouldn't have that issue.

Still - if these are modified MXL 603-style mics, this all remains quite puzzling. Why were the 603 electronics inserted into this modified lollipop design? Perhaps to fix the recessed capsule issue? And if so, why didn't any other manufacturers ever rebadge these and sell them? It seems like a great mod to an already well-respected value mic.
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Post by digitaldrummer » Wed Oct 23, 2013 1:47 pm

From what I've read the MXL 603 circuit is just a Schoeps rip-off. 8)

btw, I usually preferred a polystyrene cap across the capsule (in place of the nasty ceramic cap that usually comes stock)
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Post by jgimbel » Wed Oct 23, 2013 5:16 pm

Aj wrote:Also, didn't those MXL 603's have an issue with the capsule being recessed too far into their standard pencil-style mic body?
I'm not sure if that's something that was considered an issue with it as much as it's something that is changed to make them more like KM84s in the mods that Jolymod does. They call it "diaphragm setback coloration". So it certainly has a subtle (or maybe not) effect on the sound, but I've never thought of it as a design flaw as much as just a mic characteristic. Personally I still love my (stock) 603s. I use my KM84 pair way more often but I don't hesitate to use the 603s when the KM84s are in use.
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Post by Aj » Thu Oct 24, 2013 5:51 am

jgimbel wrote:
Aj wrote:Also, didn't those MXL 603's have an issue with the capsule being recessed too far into their standard pencil-style mic body?
I'm not sure if that's something that was considered an issue with it as much as it's something that is changed to make them more like KM84s in the mods that Jolymod does.
Good point, and these TNC ACM-100 mics seem to have the larger K67 capsules anyway (as opposed to the smaller KM84-style capsules in the MXL 603).

So the ACM-100 is indeed an odd-bird... apparently, a K67-style capsule with Schoeps-style circuitry in a compact lollipop-style housing (rather than the larger and much more common Neumann U87-style housing). Seems cool to me. Really makes me want to add the HF de-emphasis circuitry and hear what happens to the top-end. Does anyone have a good parts list for doing that? Just tried googling it, but can't find anything recent or complete.

Oh, and incidentally, those pricier Audix SCX25 piano mics also use K67-style capsules (with what appears to be a nearly identical housing/headbasket). I've scoured the net and can't find any interior pictures of those Audix mics - but I'm just dying to find out if they too share the Schoeps circuitry and also whether or not they have included the Neumann-style HF de-emphasis electronics. (If anyone has one of those mics - and can post a picture of the inside - that would be great!)

Anyway - here's a nicer hi-res picture of the ACM 100's interior (from RecordingHacks):


Image

The larger hi-res version is here.

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Post by Nate Dort » Fri Oct 25, 2013 7:08 am

The 603 is a four-transistor circuit. The original schoeps circuit was a three-transistor design. The TNC only has two based on those photos. It's still probably similar to the schoeps FET front-end though.

Or maybe it's like the two-transistor circuit in the Oktava MK012s, though that's less likely.

Either way, I'm going to guess that it's not a true balanced output, but rather impedance balanced like the Oktava.

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Post by digitaldrummer » Fri Oct 25, 2013 8:23 am

yeah, looking at the 603 again (and the larger picture of the TNC) it is different. here's a pic of the 603:

Image


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Post by Aj » Sun Oct 27, 2013 8:25 am

Thanks for catching that Nate. Man, it's a mystery wrapped in a puzzle inside an enigma with this mic. So it's a two-transistor circuit? Which means it's probably NOT just a lollipop version of all those K67/Schoeps circuit mics out there.

I'd like to try modding this mic, but I'm not sure where to start. Was hoping to find a circuit match (or near match) with a more commonly modded microphone. Does anyone know of other common K67 Chinese mics with a two transistor topology like this? And, hopefully, a schematic for it (and ideas for part swaps)?
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