The point I was trying to make is that for a transformer to output 250mA at 12volts would be rated 3VA and at 24V it would be rated at 6VA which may require a larger transformer than the 2VA transformer I was asking about.
I am a total noob so maybe I am missing something.
No, your calculations are correct. I should have looked at your question more carefully. Sorry, my apologies. The quoted 250mA is a estimation and you can probably go lower than that.
The Antek AN-0124 is a 10VA toroidal and works just fine on this board (it’s tiny and looks like a toy). So parallel the primaries (for 115VAC in) which means each independent 24V secondary is 10VA/2 =5 and 5/24 = 0.21A at 24VAC. For a transformer with one primary and one secondary (24VAC) a similar 0.21A output calculates to a 5VA transformer.
A G5LE relay’s coil (12V) has a rated current draw of 33.3 mA but can handle more A 2VA 24VAC transformer (if a single secondary) should output 83 mA if there are no mains voltage fluctuations. You were correct...you’re living life on a fine edge with the 2VA transformer (but it may work). My Mean Well RS-15-24 put out 24V at 625mA (a comfortable margin).
The Antek AN-0124 is a 10VA toroidal and works just fine on this board (it’s tiny and looks like a toy). So parallel the primaries (for 115VAC in) which means each independent 24V secondary is 10VA/2 =5 and 5/24 = 0.21A at 24VAC. For a transformer with one primary and one secondary (24VAC) a similar 0.21A output calculates to a 5VA transformer.
A G5LE relay’s coil (12V) has a rated current draw of 33.3 mA but can handle more A 2VA 24VAC transformer (if a single secondary) should output 83 mA if there are no mains voltage fluctuations. You were correct...you’re living life on a fine edge with the 2VA transformer (but it may work). My Mean Well RS-15-24 put out 24V at 625mA (a comfortable margin).
Thanks! I wish I could get a tiny toroidal 10VA like that Antek but shipping to Spain is way too expensive. The European transformer companies I have found only make 20VA and up, quite a bit larger! Since it's not powering audio circuits I can probably get something from eBay, but who knows what kind of EM noise it will create in the chassis!
I created a couple projects on Mouser to help with easy ordering.
12VAC supply: Mouser Electronics
24VAC supply: Mouser Electronics
12VAC supply: Mouser Electronics
24VAC supply: Mouser Electronics
You are looking for the speaker delay board... it protects from turn on and off transients. I can't say if it will work, or not, I haven't built one yet hopefully someone else will chime in...
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TTs is correct..you want a speaker turn delay relay circuit not a soft start. If you buy it from the DIYAudio store the speaker delay and soft start boards are sold as a pair (but you can obviously use them independent of one another). I’ve used both boards in an amp build. Speaker delay works fine but needs to be driven by a small, second transformer. My only complaint about the speaker delay board is that it’s not very compact.
Cheers, Pete
I have a separate 7VA transformer to run this speaker protection board but am a little confused about how I reference this to my amplifier 0v for the DC protection to work?
Do I just power this board directly from the 7VA transformer and then take a link from the 0v in to my star ground in the amp? (star ground is connected to the PSU 0v via a CL60)
Do I just power this board directly from the 7VA transformer and then take a link from the 0v in to my star ground in the amp? (star ground is connected to the PSU 0v via a CL60)
Negative DC not triggering protection?
I just rebuilt my F5 after some big changes and thought I'd test a few things before putting it back in use.
To test the speaker protection I used a small 2x AAA battery holder and touched the negative lead to the terminal marked G (I think?) and the positive to IN1. It did what was expected and opened the relays for a few seconds.
I decided to also test negative DC, so I swapped the battery holder leads. This did nothing after several seconds.
3V seems like it should be plenty to test DC protection -- and clearly is for positive DC. I would have assumed the board would protect against negative DC. Did I assume wrong? Has anyone else tested this and found the same or different results?
If it matters, I am driving this straight from a dedicated 24V (15VA?) transformer, so I am using the onboard rectification. The G terminal is connected to one secondary and also audio/PSU ground (floating from chassis ground). The other terminal is only connected to the other secondary.
I just rebuilt my F5 after some big changes and thought I'd test a few things before putting it back in use.
To test the speaker protection I used a small 2x AAA battery holder and touched the negative lead to the terminal marked G (I think?) and the positive to IN1. It did what was expected and opened the relays for a few seconds.
I decided to also test negative DC, so I swapped the battery holder leads. This did nothing after several seconds.
3V seems like it should be plenty to test DC protection -- and clearly is for positive DC. I would have assumed the board would protect against negative DC. Did I assume wrong? Has anyone else tested this and found the same or different results?
If it matters, I am driving this straight from a dedicated 24V (15VA?) transformer, so I am using the onboard rectification. The G terminal is connected to one secondary and also audio/PSU ground (floating from chassis ground). The other terminal is only connected to the other secondary.
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If you look at the schematic, positive voltages on the speaker terminal drive the base of the sensing transistor. Negative offsets connect to the emitter of the sensing transistor and, therefore, do not have the benefit of the transistor current gain so negative offsets have to draw sufficient current through resistor connected to the collectors of the sensing transistor to turn the relay drive transistor off. It simply takes a higher offset than the positive direction.