ADK TC Mod Service

ADK made several mics in its TC series: the TC-251, TC-67, and presumably the TC-47 and TC-49. These were Cardioid-only tube mics that shipped in a giant suitcase with shockmount, power supply, pop filter, and 7-pin cable.

We have developed an upgrade service to address a few of what we see as the weak points in what are otherwise nicely designed microphones:

• The stock 12AX7 tube has very high gain and very high distortion, giving the mics limited headroom for moderate to loud sources. We replace the tube with one that reduces the mic's output level by 6dB (which helps prevent clipping the preamp on moderate-volume sources), and lowers harmonic distortion by up to 20dB.
• We replace the output capacitor (an electrolytic) with a high-grade film capacitor, which provides cleaner, more cohesive sound. Given that electrolytic capacitors tend to fail more frequently than film capacitors, this upgrade also reduces the likelihood of a future mic failure.
• We replace the input capacitor, which appears to be a generic metallized film type, with a polypropylene and copper foil capacitor. We ensure that the solder joints on this component do not touch the surface of the PCB, which appears to be a common problem with factory built mics. PCB contact in this high-impedance joint can cause signal degradation.
• We fix an over-voltage problem in the power supply, to prevent burning up the tube prematurely. We upgrade two of the filter capacitors in the PSU also, using our bespoke Black Gate style electrolytics.
• The power supply retains dangerously high voltage for several days after being unplugged, because there is no drain path for the filter capacitors in the power supply. We correct this issue by adding bleeder resistors to the B+ circuit, so that the filter capacitors drain their stored charge within a few minutes after power is switched off. 

The circuit in these mics is capable of good performance; it is linear over a wide frequency range. We think the sensitivity and distortion are too high, and some of the components appear to have been selected to conserve cost rather than to maximize audio fidelity; otherwise, these mics are solidly designed and built, and worth the effort to upgrade.

Compatibility

This mod is for ADK's fixed-Cardioid TC series tube mics only.

Limitations

We do not recommend this upgrade if your mic is broken. We cannot guarantee that this mod would repair a defective mic. 

One exception to the above: if your TC-251 cuts out during vocal recording, we can replace the capsule, which almost certainly fixes the cut-out problem. This service would be invoiced as a separate charge from the circuit upgrade.

How it works

After you buy this service, see our Service Policies page for instructions on packing and shipping your mic. Be sure to print the Service Request form linked from that page. Indicate your choice of capsule on the Service Request form's comments area.

We would need the mic and power supply. We do not recommend shipping the entire TC series suitcase, due to the hassle of finding a suitably enormous shipping carton. Instead, pack the power supply in 1-2 inches of styrofoam at the bottom of a box, then wrap the mic in 6-10 feet of 5/16-inch bubble wrap. Pack the mic on top of the power supply. Insure the shipment for replacement cost ($800-$1000).

The typical turnaround time is 5 business days. We can provide more detailed turnaround time estimates after you purchase the service.

Costs

The mod service includes the parts, installation labor, and testing. Return shipping charges (domestic US only) are included for the microphone and power supply; if you send the entire TC suitcase, we would invoice you for additional return shipping fees.

Recommended Add-on

The stock 7-pin cable included with the mic is typical of Chinese-made audio cables: questionable metallurgy, low-quality connectors, hit-or-miss assembly. We suggest upgrading to the MicParts 7-pin cable, which we terminate in-house. We source genuine Gotham GAC7 from Switzerland. We use Neutrik connectors. We assemble and test the cables in California, and subject each one to a 72-hour burn-in using a proprietary cable cooker to condition the dielectric material within the cable.

Availability

This mod service is open to US residents only.

(Residents of other countries might find that it costs less to purchase a finished microphone.)