[drtaudio]

Why would you replace the cathode follower stage???

When I pull out my original 1966 tube manual and look up Cathode follower it states, " The use of the cathode follower permits the design of a circuit which has a high input impedance and high output voltage. The output impedance is quite low and very low distortion can be obtained and it can provide very low damping factors to inductive loads (transformers). The peak to peak signal voltage approaches 1.5 times the plate voltage if maximum power is required. This sounds like the perfect circuit to drive a microphone output transformer. The output impedance is low enough that you could remove the transformer in the 460 and put a larger output transformer in the power supply. The St Ives 6.8k to 200 ohm transformer in the Neve 1073 comes to mind or the Cinemag CM-2461. Although the smaller Cinemag CM-2480 will fit up into the bell housing of the 460. Once the capsule is upgraded to a Peluso, a selected 6072a installed, the coupling capacitor changed and the ouput transformer replaced the microphone will go head to head with microphone in the $3500 price range.

Cheers, Dave Thomas (Advanced Audio)

I believe the NADY/Carvin version uses the 3 micron plated capsules and this increases the upper midrange making the microphone even more sibilant.

Originally Posted by dale116dot7

I did the C414BULS capsule in the Apex 460, but I did a few more mods:

AKG 2072Z0005 capsule
Sowter 4935 transformer
NOS 6072 triode
Remove the cathode follower stage, change the plate resistor to 100k, and through a 1uF, 200 volt cap, feed the transformer from the plate of the one tube.
Replace a couple of the electrolytics with film capacitors.

A 12AT7 sounds pretty good if you add a 10pF capacitor from the grid to the plate. I never did like the 12AX7 in a tube mic.

Cinemag apparently has a transformer that is the correct ratio for the C12 (and other 6072 based mics) though I have not tried this transformer yet.

My mic sounded pretty good to my ears. If you are selecting a capsule, I would recommend against a capsule that requires the EQ section of a U67 or U87 - so I would not pick a capsule that comes from either of those. The Blue K47 copy would probably sound pretty good, I have not tried one of those yet. One caution is that the original capsule mount is for a 32mm capsule, and that works for my DIY'ed capsules (which are based on the Neumann M7, complete with a glued diaphragm) - they are 32mm in diameter, but most others are 34mm. I will be trying one of my M7-like capsules in my 460 in a few weeks (once I get more diaphragms).

I would avoid the Chinese 32mm capsules, they generally sound harsh to my ears. I am not sure if they can be tuned any better. Most of the sound is determined by the drilled passages, so changing much of anything except making new backplates is not likely to help the sound much. The diaphragms on my Apex 460 were not glued to a tensioning/retainer ring (as the Apex 430 diaphragms were) which means that if you take the capsule like this apart, you will not get it together properly without a brand new diaphragm.

I ordered the AKG capsule from Long and Mcquade, it was about $300.

Here is my mic lab, and this shows depositing metal on a diaphragm, tensioning a diaphragm and one possible jig used to do that:

http://www.10000cows.com/diyaudio.htm

-Dale