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Look ma! No Tube

FAR FET 47 *Updated*

APEX 480 mic

The APEX 480 FET microphone can be made to sound fantastic with some careful electronic component changes and a new K47 capsule

Update 2013

Since we first started modding the APEX 480 back in 2011, we have revised what we do with this nice little micrphone.

We have found there is no need to change the multi-pattern front end. The real problem has been getting the power supply for the capsule up into the 60 volt range. Turns out that is easily done by replacing the regulator zener diode on the power supply board. So no need for all the exotic changes I used to do. We still do the preamp component upgrades to improve the transparency of the sound. But now we don't fool around with the stock capsule and ONLY use a K47 capsule.

We spent a fair bit of time working on the APEX 480 and we can do a lot to improve this mic but even out the box the internal electronics are very good.

The circuit uses a 2SK170 low noise Field Effect Transistor (FET) coupled to a low noise PNP transistor in an emitter follower (EF) configuration. The EF stage drives a transformer to give things that vintage sound. The amp is flat +/- 0.5 dB form 30Hz to 30KHz! And the distortion levels are very low as well.

Stock 480 preamp response, showing flat from 20Hz to 30Khz

APEX 480 internal Preamp response Stock

APEX 480 stock preamp distortion showing less than .2% 2nd harmonic distortion.

For those of you keeping score with the tube mics, you can see that the solid state preamp shows very much lower 2nd harmonic distortion; far below a tube mic, but below 1K look at how the nasty 3rd Harmonic distortion rears its ugly head. Nevertheless, the stock 480 is nice little circuit. Straight through, two transistor, with no negative feedback.


Keep the Original Capsule?

Like all the APEX line mics, acoustically the response of the the stock APEX 480 can vary greatly. Below you can see twographs of real APEX 480s out of the box.

Not only is the stock capsule a K67 design, which you can see needs some high end EQ, but some capsules have a really poor low end response.

APEX 480 Acoustic ResponseA good APEX 480 stock response at 0.5 metres from the source
Graph showing a real APEX 480 stock capsule with now low end responseA very bad APEX 480 capsule response at 0.5 metres from the source


A FET 47 Cannot Use a K67 capsule

Even if the 32mm capsules were consistently good we cannot use them. To be true to the original principals of the FET 47, we must use a no EQ, no negative feedback preamp and therefore we have no choice but to throw away the stock capsule. We must use a capsule designed for a flat preamp.


Enter the K47 Capsule

RK 47 microphone capsule photo


The only real solution is to replace the capsule with K47 style capsule. Below is the published response of the Neumann FET 47.

Neumann FET 47 response showing mid-range lift similar to the the RK47 capsuleNote the ± 2dB lines around the response. This shows the real world variations that are possible with a Neumann FET 47. This means that at any place on the graph, one K47 could be +2dB while another is -2dB, a difference of 4 dB!

Fortunately we have a moderately priced solution in the Peluso K47 but we also have a lower priced option for the budget conscious that still gives you the K47 sound.

We have found a supplier of low price K47 capsule that performs like a champ. To be very honest for the price point we see great attention to detail and a backplate hole pattern that is a very good reproduction of the K47 capsule.

Typical RK47 capsule response, showing mid-range lift

You can see the response in the critical mid-range is a pretty good replica of the Neumann K47, giving that characteristic 2 to 3 dB lift in that sensitive auditory range. The low-mid-range is also down 1 to 2 dB like the Neumann K47 as well.

The low end in our graph is showing some proximity effect. This is because we test a .5 metres, whereas Neuman would test under an-echoic conditions at a 1 Metre distance from the sound source.

And Here's the Real Article

An below is the plot of a real Neumann K47 that we measured here in our lab. This plot is from a modded tube mic, but the response of tube preamp was about the same as the APEX480. The capsule was something over 10 years old and originally came from a Neumann FET 47.

Real Neumann K47 response measured by FAR shows real similarities to the RK47 capsule

What else do we do?

On top of replacing the capsule, we replace the two input caps with polystryene units. We replace all the tantulum caps with nichicon electrolytics. We also raise the capsule polarization voltage to 55 volts for more sensitivity and we increase the current through the 2nd stage output transistor to give the mic 3 dB more headroom.

All that to say...

If you need a good sounding FET 47 style microphone send us a note at: