PSU-OPA - Opamp Supply Derived from Heater


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PSU-OPA provides a transformer-isolated +/-8Vdc supply for opamps derived from the 6Vac heater supply found in most tube amps, or use PSU-OPA to support one RLY Mechanical Relay in a ground-referenced circuit.

  • 6Vac input
  • +/-8Vdc out at 15mA
  • single 12-16Vdc oiutput at 15mA

Modern guitar amps often mix a bit of solid-state circuitry with tubes. That mix can be heavily weighted towards being a solid-state amp with a tube added or a tube amp with a solid-state circuit added. Most hobbyists build the latter, resorting to solid-state when they run out room but wish to add one more feature: an extra gain boost, an effects loop, a reverb, or to allow an upgrade of the opamp in the GMX-KIT (Transconductance Multiplier). The usual approach is to add a mains-powered auxiliary transformer, rectifier, filter and so on, along with fuses for the small power transformer (PT). Is your amp switchable between different mains voltages? If so, the aux PT for the new circuitry needs to be as well.

PSU-OPA simplifies the installation by using the heater supply - which every tube amp has - as its power source. Opamps require very little current, so a typical dual-opamp package only loads PSU-OPA lightly. Up to 21mA is available but this should be used as a drive reserve, especially in the case of a solid-state line output driver.

PSU-OPA's epoxy-potted transformer uses concentric windings to reduce radiated noise to vanishingly small levels. It can be mounted nearly anywhere inside a tube amp. Cascaded RC filters assure smooth noise-free DC power for any opamp application.

Of course, PSU-OPA can be used as a single voltage output to support a 12Vdc relay coil (RLY), or other circuitry. This is a much better option that the usual rectified heater supply, as PSU-OPA provides a fully isolated relay supply that can be grounded properly. In a cathode-biased amplifier, PSU-OPA plus two RLY can be used to select Power Scale controls in an SV2 circuit AND switch between Drive Compensation controls as well.

Kit requires assembly.

PCB size: 2.1" x 1.6" x 1"H (54 x 41x 26mm)

About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

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