from octopart FQA28N15 is still available and we can buy them with more peace of mind :
I'm hoping to get some input on my F5m project, which in time I hope to offer as a kit. Block diagram is below and full schematic is attached.
PCB layout is next. I'll start a new thread when I've got a prototype to share, or if this ends up being distracting from the main topic.
- Two 24V, 2.5A SMPS are used on each channel for the supply rails (monoblocks).
- There's enough board space for filtering, so I've added Mark Johnson's AmyAlice SMSP filter to V+ and V-
- Switches rated for this DC voltage and current are hard to find and get expensive quickly, so I've opted to use MOSFETs to do the heavy lifting and the physical button will be switching 9V created by an always on DC/DC converter.
- All the protection modes of the power supplies result in that supply turning off it's output, so I added a basic undervoltage monitor (using zener diodes) that will switch off both supplies (via optocouplers) if either drops out.
- Will this be sufficient protection for the amp and speaker? Is a solid state output relay a better solution?
- A fan keeps the heatsink cool, so I need a way to turn the amp off in case of fan failure. I'm using the fan's tachometer output to drive a pair of charge pumps to turn on the supply rail power switches. As a bonus, since the charge pumps are AC coupled, they can be referenced to the source of each FET. This allows N-channel parts to be used on both rails, which are cheaper and have lower on resistance than the available P-ch options.
PCB layout is next. I'll start a new thread when I've got a prototype to share, or if this ends up being distracting from the main topic.
Attachments
I am building two stereo amps based on the F5M circuit. I'm planning to use these to try biamping my speakers (open baffle planar magnetic line arrays). I decided to design my own PCBs to add a few extra features.
In addition to Papa Pass's elegant circuit, I have added a line input transformer for balanced inputs which is relay-switched with the RCA input, a DC servo circuit, a speaker protection circuit with delayed turn-on, and additional local decoupling on the power supply rails.
I wanted the protection circuit and DC servo since I'll be connecting directly to the tweeters with no inline blocking cap so I wanted to make sure DC offset remains very low.
The amp is built using the SFP soft-start into an Antek 400VA 20V transformer which feeds a SLB power supply. I designed another PCB which includes an additional 60,000uF of capacitance for each channel, separately connected to the SLB through some 0R1 resistors.
I've currently got the bias set to around 1.3A (23V rails) and the heat sink temp next to the MOSFETs is around 52C.
In addition to Papa Pass's elegant circuit, I have added a line input transformer for balanced inputs which is relay-switched with the RCA input, a DC servo circuit, a speaker protection circuit with delayed turn-on, and additional local decoupling on the power supply rails.
I wanted the protection circuit and DC servo since I'll be connecting directly to the tweeters with no inline blocking cap so I wanted to make sure DC offset remains very low.
The amp is built using the SFP soft-start into an Antek 400VA 20V transformer which feeds a SLB power supply. I designed another PCB which includes an additional 60,000uF of capacitance for each channel, separately connected to the SLB through some 0R1 resistors.
I've currently got the bias set to around 1.3A (23V rails) and the heat sink temp next to the MOSFETs is around 52C.
@Vunce ,
I'm using RC filters (500R, 100uF) from the main rails into +/- 12V regulators (LT3045, LT3094) for power to a LT1007 op amp. The amp output is filtered through a 1M into 2.2uF cap. I have diodes across the op amp inputs to limit the maximum input. The output of the op amp connects to the jfet sources through a 1K resistor. I have a jumper on this connection so that I can set the bias before the servo circuit is connected.
I'm using RC filters (500R, 100uF) from the main rails into +/- 12V regulators (LT3045, LT3094) for power to a LT1007 op amp. The amp output is filtered through a 1M into 2.2uF cap. I have diodes across the op amp inputs to limit the maximum input. The output of the op amp connects to the jfet sources through a 1K resistor. I have a jumper on this connection so that I can set the bias before the servo circuit is connected.