![[-]](https://theultimatetone.com/images/collapse.png "[-]")
02-25-2026, 01:38 PM
Hi Guys
It seems I was too enthusiastic with my board ordering - haha.
The SVn-M36 boards worked okay but I forgot a trace for the bias regulator on SV1-M36, which caused some inconvenience to a couple of installers. While those were being sorted out, I had already ordered boards for the SVn-Zh described above. The Zh has an ideal sweep from full B+ down to zero regardless of the B+ value. Its design range for input voltage is 200V up to 700V, so it accommodates every guitar or bass amp on the market.
I was mistaken in my statement that Zh has no dead spots. The fact the output voltage can go to zero volts means there is a dead spot of the Power Scale pot sweep at the quiet end. Between the arrival of the M36 boards and of the Zh boards, I had feedback from some installers that lead to a modification of the Zh to the Zp - hopefully the ultimate in Precision Power Scaling.
The SVn-Zp has the same sweep of voltage that the Zh has, BUT there is a built-in user adjustment to fine tune the "audible transition" from silence to sound and vice versa. The AT trimmer lets the player set the loudness at the PS=0 end of the Power Scale panel pot. So now we have a Power Scale circuit that is not voltage sensitive nor are there dead spots in the sweep of the pot. If a player just wants a bit of loudness reduction from maximum power, he can have it. If he wants to have better resolution of control at the quiet end, he has it.
With the previous Power Scaling kits one can add a "build out" resistor in series with the PS-0 end of the Power Scale control to eliminate the dead sweep at low loudness. Values up to 33k are useful. Set PS to zero and add 33k in the PS-0 wire to the PCB. Have a listen to how loud this is with your specific amp. If it is too loud, change the 33k to a smaller value, or parallel it with a second resistor to achieve the same effect. In this test, you could use a pot to vary the build-out resistance while playing through the amp, and then measure the portion of the pot used and install a fixed resistor.
Over the recent years, I have been tweaking the values around the pot to try to optimise the sweep. A big problem with that approach is that the mosfet at the input to the circuit, fed from the PS wiper, has variable gate threshold voltage requirements from unit to unit, making the circuit sensitive to B+ (Zh and Zp use a different input device that is far more consistent and predictable). Thanks to Steve Ward, I was reminded of the idea of simply adding a resistor in series with the bottom of the Power Scale control, exactly as was done in Classic-PS and the SB-series kits. It's funny how your thought process can take a direction that slowly limits you, blinding you from seeing that a solution exists right at the beginning of that path. Well, the light came in.
It seems I was too enthusiastic with my board ordering - haha.
The SVn-M36 boards worked okay but I forgot a trace for the bias regulator on SV1-M36, which caused some inconvenience to a couple of installers. While those were being sorted out, I had already ordered boards for the SVn-Zh described above. The Zh has an ideal sweep from full B+ down to zero regardless of the B+ value. Its design range for input voltage is 200V up to 700V, so it accommodates every guitar or bass amp on the market.
I was mistaken in my statement that Zh has no dead spots. The fact the output voltage can go to zero volts means there is a dead spot of the Power Scale pot sweep at the quiet end. Between the arrival of the M36 boards and of the Zh boards, I had feedback from some installers that lead to a modification of the Zh to the Zp - hopefully the ultimate in Precision Power Scaling.
The SVn-Zp has the same sweep of voltage that the Zh has, BUT there is a built-in user adjustment to fine tune the "audible transition" from silence to sound and vice versa. The AT trimmer lets the player set the loudness at the PS=0 end of the Power Scale panel pot. So now we have a Power Scale circuit that is not voltage sensitive nor are there dead spots in the sweep of the pot. If a player just wants a bit of loudness reduction from maximum power, he can have it. If he wants to have better resolution of control at the quiet end, he has it.
With the previous Power Scaling kits one can add a "build out" resistor in series with the PS-0 end of the Power Scale control to eliminate the dead sweep at low loudness. Values up to 33k are useful. Set PS to zero and add 33k in the PS-0 wire to the PCB. Have a listen to how loud this is with your specific amp. If it is too loud, change the 33k to a smaller value, or parallel it with a second resistor to achieve the same effect. In this test, you could use a pot to vary the build-out resistance while playing through the amp, and then measure the portion of the pot used and install a fixed resistor.
Over the recent years, I have been tweaking the values around the pot to try to optimise the sweep. A big problem with that approach is that the mosfet at the input to the circuit, fed from the PS wiper, has variable gate threshold voltage requirements from unit to unit, making the circuit sensitive to B+ (Zh and Zp use a different input device that is far more consistent and predictable). Thanks to Steve Ward, I was reminded of the idea of simply adding a resistor in series with the bottom of the Power Scale control, exactly as was done in Classic-PS and the SB-series kits. It's funny how your thought process can take a direction that slowly limits you, blinding you from seeing that a solution exists right at the beginning of that path. Well, the light came in.
