Tube Mic PSU Upgrade Service

You'll find the common Chinese-made power supply within most of the sub-$2000 tube mics on the market, e.g.:

• Avantone CV-12
• BadAax T11A
• Apex 460
• older Telefunken RFT series mics (AK-47, AR-51, CU-29, M16)

We have seen numerous problems with this design:

• The B+ rail is unregulated, which means the sound of the mic could change as wall voltage naturally drifts. (It is not uncommon for utility AC to vary by 10% over the course of a day.)
• The B+ rail voltage is often too high. Many of these mics use capsules designed for 60V polarization voltage. The mic circuit uses one-half of the B+ rail to polarize the capsule. But the B+ rail often runs at 140V or higher, leading to the capsule seeing 70V (or more). This limits the mic's SPL ceiling and headroom.
• The F+ or heater voltage is often too high. The 6072 and related 12A_7 family of tubes should see 6.3V max on the heater (assuming the two heater elements are wired in parallel, which is typically the case). Most mic designers lower heater voltage to 6.1V, which gives equivalent performance while potentially extending the life of the tube. Given that microphone-grade tubes of this type are less common and more expensive than ever before, the benefit of extending tube life is impossible to ignore. We've seen Chinese PSUs that send 6.6-6.9V to the tube heater, which will likely shorten the tube's life.
• The noise filtering in these units is adequate but not excellent.
• Parts quality is low, as is the metallurgy of the wires and connectors, all of which compromises signal integrity.

Rather than try to correct all of these shortcomings by modifying the stock power supply circuit, we developed a new circuit entirely. The benefits include:

• Fully regulated B+ and F+ rails, with trimmer adjustments to allow fine tuning.
• Noise filtering is excellent.
• Oversized heatsinks on active elements ensure long life.
• Soft-start heater voltage (4 second ramp) eliminates power-on current surge, to extend tube life.
• Front-panel XLR connectors are upgraded to Neutrik.

How it works

Reserve your upgrade by ordering the service from this page. Then ship your power supply to us. See the notes about that process here. We will contact you with the expected upgrade timeline (typically four business days) and return shipping date once we've received your PSU.

Compatibility

If your PSU looks different from the one pictured on this page, contact us first to determine compatibility. 

If your PSU is a typical Chinese style (such as pictured on this page) but is dead, this upgrade would repair it in most cases. The exceptions are: if your power transformer is dead, or if the pattern control is broken. The upgrade would not fix either issue, although we could likely repair either at an additional cost.

Costs

Included in the purchase of this PSU upgrade service: build and installation of our VPS circuit into your compatible PSU shell, wiring, burn-in, and testing. All parts and labor for the build and installation are included. Return shipping in the United States is not included, but would be added during the check-out process. You would ship your PSU to us so that we can perform the upgrade.

Optional accessories

We recommend upgrading the 7-pin cable to our Gotham GAC7/Neutrik cable, which we terminate and condition in-house.