temol
Well-known member
1..2..3.. let's go
First of all - its big, it's dangerous (almost 300V to power the tube) and rather expensive to build (compared to regular pedals).
1. Project, schematic, etc.
It's all available from freestompboxes. Schematic (four separate pieces) and pcb layout (Sprint Layout format).
2. Power supply.
Rotospere requires 12-13V AC power supply. It's boosted to high voltage (transformer), then rectified, etc.
Speaking about transformer - original circuit calls for step-up type transformer (15V primary, 250V secondary) but it's quite expensive. It's possible to use regular step-down trafo, in reverse. Just note - it's 15 to 250 not 15 to 230 (230 to 15), so transformation ratio is not the same.
Before even ordering the board and buiying all the components I strongly recommend breadboarding power supply section (with tube connected). Just to verify which ordinary transformer works best (unless you plan to buy original trafo). The transformer used has an influence on the value of dropping resistors, voltage, etc. It is also good to know transformer ping spacing - just in case if it does not match the original transformer. I used a 230/12V sealed transformer and had to modify the resistor values quite a bit to get 12.6V for filament and 280V for anodes. I couldn't get it exactly right but it's acceptable for now (13V filament, 260V anodes).
AC power supply: the AC voltage value from the power supply also obviously affects the voltage value after the step-up transformer.
3. Components. I suspect $100 is the minimum for parts alone, plus possible shipping. You need about 220 resistors, 30 diodes (zener, led, rectifiers), 120 capacitors, 19 chips, 25 transistors, sockets, potentiometers, etc.
4. Meticulousness. There is no room for errors in the installation of elements.. finding where you made a mistake is quite problematic. Additionally - in case of a mistake, removing the components can be very difficult or even impossible without damaging the board. All because of the plated holes and the troublesome desoldering of the components.
5. Initial setup. I could not find any info on how to set the onboard trimmers and their functions.
6. Things to pay attention to.
Unfortunately, I didn't avoid mistakes - incorrect value of one zener diode on the pcb, incorrect descriptions of 5 transistors on the PCB (BC546B instead of BC556B, which is a significant difference - PNP vs. NPN). Fortunately, I caught it during assembly, before the first start-up.
So far - the effect started right away, the LEDs flash, it make sounds, footswitches work properly.
My doubts concern the operation of the guitar/keyboard switch. Not much happens when switching. Also the rotor balance potentiometer supposedly works but I don't know if it works properly. It definitely adds a lot of bottom when turned towards LF.
Trimmers - let's say that 3 of them have a clear impact on the sound, the rest remain quite mysterious
I also have mains hum. I don't know if it's due to poor power supply filtration or lack of enclosure, or maybe because of the tube heaters...
Now I have to design the enclosure.
First of all - its big, it's dangerous (almost 300V to power the tube) and rather expensive to build (compared to regular pedals).
1. Project, schematic, etc.
It's all available from freestompboxes. Schematic (four separate pieces) and pcb layout (Sprint Layout format).
2. Power supply.
Rotospere requires 12-13V AC power supply. It's boosted to high voltage (transformer), then rectified, etc.
Speaking about transformer - original circuit calls for step-up type transformer (15V primary, 250V secondary) but it's quite expensive. It's possible to use regular step-down trafo, in reverse. Just note - it's 15 to 250 not 15 to 230 (230 to 15), so transformation ratio is not the same.
Before even ordering the board and buiying all the components I strongly recommend breadboarding power supply section (with tube connected). Just to verify which ordinary transformer works best (unless you plan to buy original trafo). The transformer used has an influence on the value of dropping resistors, voltage, etc. It is also good to know transformer ping spacing - just in case if it does not match the original transformer. I used a 230/12V sealed transformer and had to modify the resistor values quite a bit to get 12.6V for filament and 280V for anodes. I couldn't get it exactly right but it's acceptable for now (13V filament, 260V anodes).
AC power supply: the AC voltage value from the power supply also obviously affects the voltage value after the step-up transformer.
3. Components. I suspect $100 is the minimum for parts alone, plus possible shipping. You need about 220 resistors, 30 diodes (zener, led, rectifiers), 120 capacitors, 19 chips, 25 transistors, sockets, potentiometers, etc.
4. Meticulousness. There is no room for errors in the installation of elements.. finding where you made a mistake is quite problematic. Additionally - in case of a mistake, removing the components can be very difficult or even impossible without damaging the board. All because of the plated holes and the troublesome desoldering of the components.
5. Initial setup. I could not find any info on how to set the onboard trimmers and their functions.
6. Things to pay attention to.
- step-up transformer - size and voltages
- potentiometers. The original potentiometers from Rotosphere have some kind of extension that moves the whole board away from the mounting surface. With regular potentiometers, the edge of the pcb is higher than the mounting surface of the potentiometer and you have to put some washers. But then there is not much thread left for the nut.
Unfortunately, I didn't avoid mistakes - incorrect value of one zener diode on the pcb, incorrect descriptions of 5 transistors on the PCB (BC546B instead of BC556B, which is a significant difference - PNP vs. NPN). Fortunately, I caught it during assembly, before the first start-up.
So far - the effect started right away, the LEDs flash, it make sounds, footswitches work properly.
My doubts concern the operation of the guitar/keyboard switch. Not much happens when switching. Also the rotor balance potentiometer supposedly works but I don't know if it works properly. It definitely adds a lot of bottom when turned towards LF.
Trimmers - let's say that 3 of them have a clear impact on the sound, the rest remain quite mysterious
I also have mains hum. I don't know if it's due to poor power supply filtration or lack of enclosure, or maybe because of the tube heaters...
Now I have to design the enclosure.
