How to build a 21st century protection board

[jwilhelm]

These PC board mount relays really clean up the wiring.

 

[kimschips]

It looks very nice, how big is the pcb?
How fast does it reacts in case of a short circuit?

 

[jwilhelm]

This is all mounted vertically on the backside of one of OS's modular power supply. the control board is 77 x 97mm. Terry's NTC resistor would make it neater still.

 

[still4given]

Hi Jeff,

I ordered the transformer that fits this board but looking at it it appears that it will block the mini usb plug. How do you get to it to if you need to reprogram the board?

 

[jwilhelm]

The Nano is meant to be mounted in a socket. You pull it out of circuit for programming.

 

[kimschips]

How fast does it reacts in case of a short circuit?

 

[jwilhelm]

I haven't tested this one yet, but it's the same design as the earlier boards. They are faster than a slow blow fuse.

 

[jwilhelm]

This layout makes for some really short high current wiring. I'm building twin rack mount stereo versions of Valery's's CFA-CFPx2 amps.

 

[still4given]

The Nano is meant to be mounted in a socket. You pull it out of circuit for programming.

I didn't get the memo. I soldered in the nano. Too much trouble to unsolder now. I guess I'll just use a different transformer.

 

[jwilhelm]

If you have the space, you can mount the transformer under the board and use long standoffs, or another transformer.

 

[still4given]

I have another transformer hooked up. It is 14-0vac. Seems to be working fine. The board powers up. Both LED's light. The board LED starts to blink after a while. When it powers up I read 12Vdc across the heater lugs but nothing across the inrush or power lugs. If I measure from the center pin of the RailSense terminal, I get 12Vdc at all three + terminalsl but the - sides seem to be open on the inrush and power. is the negative terminal the side that gets switched?

Thanks, Terry

 

[jwilhelm]

Yes relay switching is done on the negative side. The heater relay should become live immediately, then the inrush 30 seconds later, followed by the power relay. 3 seconds after that it should shut down and flash the led because there is no rail voltage.

 

[still4given]

Wow, 30 seconds before the inrush starts? I would think the heater would be full strength earlier than that. I'll hook up a PSU and see it it will finish.

Thanks, Terry

 

[jwilhelm]

Timing can be adjusted easily in the software, but TubSomo took almost that long to warm the tube up.

 

[LineSource]

"To Serve and Protect" .... Police matra

With the output current overload protection in place, any plans for some type of "smart bias"?

Krell VFA amps use a Plateau Bias which senses large current demands at the output and at the pre-driver, and increases bias current for a short period before testing for safe bias reductions. Krell has recently patented iBias which uses a microprocessor to control the bias algorithm for Krells new CFA amps.

 

[kimschips]

Here are the two boards together.

What is the size of the main board?
Pcb group buy?

Thanks

 

[jwilhelm]

What is the size of the main board?
Pcb group buy?

Thanks

The control board is 77 x 97mm. I haven't put any thought into a group buy. Gerbers are always available, and I usually have a couple left over test boards with minor errors to work around.

 

[jwilhelm]

"To Serve and Protect" .... Police matra

With the output current overload protection in place, any plans for some type of "smart bias"?

Krell VFA amps use a Plateau Bias which senses large current demands at the output and at the pre-driver, and increases bias current for a short period before testing for safe bias reductions. Krell has recently patented iBias which uses a microprocessor to control the bias algorithm for Krells new CFA amps.

There was some talk early in the thread about "smart bias" but nothing has become of it yet.

 

[vzaichenko]

It looks very nice, how big is the pcb?
How fast does it reacts in case of a short circuit?

It's so fast - the speaker cone doesn't even move ))

I have never really measured, but did a real life test - I have accidentally shorted the amp output to the negative rail, with the speakers connected
Scary? Just a small "click" from the speaker, the amp shut down.

Restart - no damage, it's just working again

 

[yngvejos]

I'm ordering parts for the amp control 3.5 boards.
Can I use one board for a dual mono amp? Or should I build two separate boards?
I notice that Q1, 8, 9 and 10 and I1/2 are quite expensive, can I omit ex Q8, Q10 and I1 if I have to use one board per channel?