Group Buy TnC ACM-4 + Lundahl LL 2912 Transformer

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antichef

antichef

pornk rock
Wanted to get these up real quick (each 15 megs):

Stock ACM-4: http://recursor.net/ACM4-Stock.wav

ACM-4 with Lundahl 2912: http://recursor.net/ACM4-Lundahl.wav

and each track in a mix (mp3s are much smaller:

Stock ACM-4:


ACM-4 with Lundahl 2912:


I'll reply to this post some time later today with more details - but quickly: big treble difference! I like the 2912, but the change is so dramatic, I'm wondering if I did something wrong. I did have to dispense with the mu metal casing, because even the Lundahl didn't fit (the Edcor was way too big).

I still plan on doing a Lundahl vs Edcor comparison, but I have some newbie logistical problems (short leads on Lundahl) that I'll describe in more detail when I post again.

but here's the ACM-3 with the Edcor, so that I'm not completely empty handed (no mp3 for this one):

ACM-3 with Edcor RMX1: http://recursor.net/ACM3-Edcor.wav
 
Keep getting pulled away from the computer -- I do have a couple pictures and more to tell.

But briefly, if the leads of a transformer are too short to reach between the XLR pins and the ribbon motor (by more than an inch, I think, in the case of the ACM-3) what should I do?
 
here are some pics:

ribbonmic1-orig.jpg


and

ribbonmic2-orig.jpg


You can see that the leads on the Lundahl are just long enough to make it. Because I couldn't get it to fit inside the metal casing that held the old transformer, I pulled a cotton ball apart and put it on either side to hold it in place (is that muffling the treble? just kidding :D).

The stock transformer looked identical to the ones in the ACM-2 and ACM-3, *except* that the two input wires were both insulated. On the others, one was bare/braided. Because of this, I couldn't be sure which was which, so I just took a guess with the input wires on the Lundahl.

The ACM4 is definitely less newb-friendly than the other two when it comes to surgery. If you work on yours, be very careful with screwdrivers -- the metal is very soft. I tried to release the XLR housing by turning a flathead screw that holds it in place, but, even with the exactly correct sized screwdriver, I merely chewed up the metal. I also chewed up one of the internal philips screws. Because the XLR housing is recessed (and won't come out, due to the messed up screw), I had to reach in with my $8 soldering iron to push the delicate output leads of the Lundahl into place in the solder-filled hollow back ends of the XLR pins. Somehow I pulled it off, but I don't think I'd be so lucky if I tried it again, so I believe my tranny mods are done with this unit.

I just did pull out the internal windscreen (leaving the external grill windscreen in place) to get some treble back - this after making the recordings. It seems to help some.
 
antichef said:
Keep getting pulled away from the computer -- I do have a couple pictures and more to tell.

But briefly, if the leads of a transformer are too short to reach between the XLR pins and the ribbon motor (by more than an inch, I think, in the case of the ACM-3) what should I do?
Click to expand...
Just solder a couple of extension wires to either set coming from the transformer and cover with shrink-wrap tubing (or electrical tape.) Try to use wire of about the same gauge.
 
Antichef

I was thinking about trying to use one of the PCB mounted models like LL2913 and LL2914 because they are shielded.
http://www.kandkaudio.com/proaudio.html

K & K has the little carrier PCBs too which should make the wiring easier.

I'm actually surprised there was enough wire to reach with the 2912.

Nice job on that mod. The modded ACM 4 sounds much fuller and deeper.
 
Thanks -- I didn't even think about those models, probably because I was only thinking about fitting them into the ACM-2 and ACM-3.

Crazydoc - thanks -- I guess that's obvious, but not to me. I'll try and find some matching wire, and then get back to work.

BTW, in the mp3, the acoustic guitar is recorded with the ACM-310 (and the cheap harmonica with an old Shure Unisphere 588A)
 
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I just placed an order for the 2914 and the little PCB. I don't think it will be a problem fitting that big bastard in the mic.

I have some silver wire I scrapped out of some old military test gear to wire the transformer up with. I guess if I'm ever gonna use the stuff this would be a good time.

This is curious (from K & K audio site)...
the LL2914 uses a more traditional mu-metal (permalloy) core, which results in a more vintage tone.
Click to expand...

I wonder what exactly this means...
 
Thanks Craigmorris, that is a useful heads-up. Makes me think I might be on the right track for once ;)

antichef, I listened to your samples again when my mixer wasn't being so squirrelly about the temperature and humidity in my house. The difference is more pronounced than I originally perceived.
There is more "dimension" to the sound of the modded ACM-4. Almost like it's been taken out of a small box.

I've heard some sample recordings of the AEA R92 and the modded ACM-4 sounds similar to it. Not quite close enough to ape the R92 but almost in the ballpark.

I'm excited to get my Lundahl now!!!
 
Somnium7 said:
I just placed an order for the 2914 and the little PCB. I don't think it will be a problem fitting that big bastard in the mic.

I have some silver wire I scrapped out of some old military test gear to wire the transformer up with. I guess if I'm ever gonna use the stuff this would be a good time.

This is curious (from K & K audio site)...


I wonder what exactly this means...
Click to expand...

Did this ever happen? I'm kind of curious which transformer to go with. They're neat mics, but need something to "open them up."
 
I did it with the LL2912 (wire leads) - here's a writeup with some before/after sound samples:

http://www.recursor.net/blosxom.cgi/music/ribbonmic.writeback

It did not fit in the little mu metal casing inside the mic, so I had to remove it and put some cotton balls around it to hold it in place. I haven't had any EM interference problems, and I really like the mic.

edit: oops - this was my thread about this mic and project to begin with :o:o - anyway - time passed and I still like the mic a lot :D. Somnium7 has been back on line recently and can maybe fill us in about the other one. His skill/experience > mine, so assign weight to his posts accordingly.
 
The LL2912 would certainly be easier to work with because you don't need a PCB (hard to fit in such a tiny enclosure).

On the interference issue, in the absence of active electronics, I wouldn't think there would be the slightest possibility of interference caused by not using a shielded transformer, as the mic case itself is basically a giant faraday cage.... :)

The usual thing I've seen holding transformers in commercial mics is hot wax, IIRC, but don't ask me how they actually do that without getting the transformer too hot.
 
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