Description
SV2 is now a COMPLETE Power Scale solution for 99% of cathode-biased guitar, bass or synth amps
- Precision Power Scale for cathode-bias only
- Full product name: SV2-Zh includes Voltage Clamp
- up to 700V plate (Va)
- up to 700V screen (Vs)
- Power range: 100% down to zero
- Loudness range: unusably loud to unusably quiet
- adjustable Voltage Clamp <200Vmax in/out difference
- PCB size: 2.6″ x 1.4″ 66.1 x 35.6 mm
- Built height: 1.3″ 33mm
- Controls included: Power Scale, Drive Compensation
- kit notes: 8-pages
EVERY Vox AC-series amp needs SV2 and may also require TREM
If your amp has bias-modulated tremolo, our TREM Tremolo Level Tracker is also required.
MusicMan amps with the hybrid output stage also use SV2 for Power Scaling.
SV2-Zh is part of our Precision Power Scale family using the Z-core main circuitry. SV2-Zh is very sophisticated yet fits into tight chassis spaces. Cord-wood construction allows this compact module size and requires careful assembly and soldering. For detailed assembly instructions see this thread in our forum:
https://theultimatetone.com/thread-324.html
Build time for this PCB is 2-hours. Installation time is extra.
Low-level resolution of the Power Scale sweep has been improved allowing you to precisely dial in the desired quiet level.
Screen voltage is typically just a few volts less than plate voltage, accommodated by the stock values in SV2-Zh. Changing one resistor allows Vs to be far less than Va, in amplifiers using a voltage-doubler supplier, or where a large resistance ties Vs to Va with a corresponding large voltage difference. A few Vox models are like this. SV2-Zh kit notes explain how to calculate this resistor value.
When power is dialed down, the supply voltage will rise. The built-in Voltage Clamp will maintain a constant voltage to the non-scaled circuits to help maintain tone consistency from loud to quiet, and also provides clean power to those low-level audio circuits. EVERY production cathode-biased amp requires both circuit sections for a proper Power Scale solution, so SV2-Zh is a complete Power Scale solution for all cathode-biased amps without bias-modulated tremolo.
Some cathode-biased Fender and Vox amplifiers have grid-modulated tremolo and will require SV2+TREM. See the bundle page for this offering at a small discount.
A Drive Compensation pot is provided. Using DriveComp and Power Scale together maintains a given tone, while setting them differently provides four different operating modes for the amp. If the amp has a master volume that regulates ALL sounds of the amp, then the MV can perform the DriveComp function. Depending on the amplifier’s circuit, there is a single-knob solution as described in our forum: https://theultimatetone.com/thread-270.html Most Vox amps can take advantage of this option where the MV is replaced by the combined-function control.
SV2-Zh uses small, non-critical pots, allowing easy placement of these components on a crowded front panel. Those supplied are 16mm and mount on individual PCBs to make wire connections easy. Kit notes include schematic, expanded board layout, and wiring instructions. Components use precise values and should be sorted prior to assembly. The connection points within the amplifier are common to all tube power amps and are shown schematically. For the pre-assembled kit, London Power has discounted our hourly rate by 20%. London Power is not responsible for any damage caused by misinterpretation of the kit notes
Available configurations:
SV2-COMP: Includes PCB, components, pots, kit notes; assembly required; installation required
SV2-BLT: PCB comes pre-assembled; includes kit notes; installation required
Note that the Built Kit will cover assembly of TREM as well, if TREM is on your order.
If your amp is <450V with screen and plate supported by a single supply node, and cathode-biased ONLY, see SV84. VCK is required.
For more information about Power Scaling Kits, see also:
Who can install Power Scaling for you?
Licensed Power Scaling Builders and Installers
