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01-23-2026, 01:39 PM
Precision Power Scale part-deux
Hi Guys
Surprisingly, the first two Power Scale kit circuit forms we released were "precision" circuits. The basic circuit used the mil-spec pot that could sustain the B+ of most guitar and bass amps, and this controlled the mosfet directly. At the top end of the pot sweep there is just the Vgs loss of the mosfet; at the bottom end there is a non-zero point to keep the mosfet conducting. Again, the mosfet output is Vgs lower than the pot wiper voltage and could go to zero with random mosfet samples.
The first form is what we now refer to as "Classic-PS", which was copied by many. The second form is the "Super Budget" type (SB), described in TUT4 and TUT6, and was the first release of DC Power Scaling kits. Many techs and amp builders still use this and we supply PCBs for them.
The SD form used in my amps for many years was tuned by ear with respect to how the pot sweep works at the quiet end. For my particular power amp circuit, the point where the audio goes to zero is not where the supply goes to zero, and from recent feedback from installers, it is higher than for more common amp circuits. This latter detail means that the programmable "quiet" voltages for the circuits described in post-1 may be too high for many players, and that the idealised goal of achieving zero output voltage is not without merit.
With the kits of the recent years, there is a compromise of "where to put the dead spot" in the pot sweep. In some installations there will be no dead spot because the voltages in the amp and all of the parameter tolerances in the SVn, SVn-D and SVn-M36 circuit achieve a synchronicity. Otherwise, there may be a dead spot at the loud end or the quiet end of the pot sweep. The top end dead spot is only of concern for players who typically run their amp flat out and want to turn it down just a little bit. The lack of loudness change for the first part of the pot sweep is then disappointing. For most players who are trying to achieve bedroom SPLs, a dead spot at the quiet end is more of an issue.
If you have an issue with an SV installation, let me know and we can optimise some of the circuit values for the supply voltage in your amp. Or let us know when you order.
The latest circuit I have has no dead spots (SVn-Zh). As soon as the pot is moved from full-CW the voltage is dropping and it gets to zero exactly at the full-CCW position. For installers who think the present kit circuit is wonky, they would undoubtedly find this new one to be totally bizarre
Hi Guys
Surprisingly, the first two Power Scale kit circuit forms we released were "precision" circuits. The basic circuit used the mil-spec pot that could sustain the B+ of most guitar and bass amps, and this controlled the mosfet directly. At the top end of the pot sweep there is just the Vgs loss of the mosfet; at the bottom end there is a non-zero point to keep the mosfet conducting. Again, the mosfet output is Vgs lower than the pot wiper voltage and could go to zero with random mosfet samples.
The first form is what we now refer to as "Classic-PS", which was copied by many. The second form is the "Super Budget" type (SB), described in TUT4 and TUT6, and was the first release of DC Power Scaling kits. Many techs and amp builders still use this and we supply PCBs for them.
The SD form used in my amps for many years was tuned by ear with respect to how the pot sweep works at the quiet end. For my particular power amp circuit, the point where the audio goes to zero is not where the supply goes to zero, and from recent feedback from installers, it is higher than for more common amp circuits. This latter detail means that the programmable "quiet" voltages for the circuits described in post-1 may be too high for many players, and that the idealised goal of achieving zero output voltage is not without merit.
With the kits of the recent years, there is a compromise of "where to put the dead spot" in the pot sweep. In some installations there will be no dead spot because the voltages in the amp and all of the parameter tolerances in the SVn, SVn-D and SVn-M36 circuit achieve a synchronicity. Otherwise, there may be a dead spot at the loud end or the quiet end of the pot sweep. The top end dead spot is only of concern for players who typically run their amp flat out and want to turn it down just a little bit. The lack of loudness change for the first part of the pot sweep is then disappointing. For most players who are trying to achieve bedroom SPLs, a dead spot at the quiet end is more of an issue.
If you have an issue with an SV installation, let me know and we can optimise some of the circuit values for the supply voltage in your amp. Or let us know when you order.
The latest circuit I have has no dead spots (SVn-Zh). As soon as the pot is moved from full-CW the voltage is dropping and it gets to zero exactly at the full-CCW position. For installers who think the present kit circuit is wonky, they would undoubtedly find this new one to be totally bizarre
