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Soft starts and DC protection

Some time ago I built a pair of 100w Class A (Pass F5t) each having two 350VA trans...one for each rail a total of 700VA. Without NTC, at power up they would take out the house RCD...every time. At first I thought there was something wrong with the amp build but I knew it was OK as on the bench supply during the build all was well and measured great. I dropped in a Avondale soft start SSM. Click, Click, as the relays where energised all seamed well ....BUT. I still had a power up issue. About a 50% chance of success on power ups on both amps before knocking out the RCD. (Which is a 'B' 16amp rating). Should be OK?.

So I dropped in a CL60 on each transformer primary (in series with the 0-115 0-115).... I've had no issues since and have even removed the SSM on both amps.

Moving on, I had the same issue last year with the new NCC300 voyager, 540va for the outputs and a further 100va per amp.. Non-starter every time. So, SSM implemented and again a 50% chance of power up success before it would take out the house RCD.

So I dropped a couple of CL60's in the primaries of the 540va's. Again I've had no issues since....In fact I would say the transformer's run quieter. I don't mean sonically but mechanically....(the gentle hum) And there is NO sonic detriment using a NTC in this application.

I now have a 'C' type RCD which I have yet to fit....
 
To the OP,
A soft start module will reduce the effect of inrush current but it does not stop the switch on thump, a speaker protection module does and protects your speakers from DC
Alan
 
Ideally you need both, a long soft start can actually make switch on thump worse - some amplifiers have a stability problem at low supply voltage and should have had an under voltage lockout circuit.
 
337alant said:
To the OP,
A soft start module will reduce the effect of inrush current but it does not stop the switch on thump, a speaker protection module does and protects your speakers from DC
Alan
Click to expand...

Indeed:- I had a full range driver (£500) go pop at switch on last year (no speaker protection module fitted at the time) and took out the output devices. A £20 Velleman K4700 would of saved it. Need less to say, all my amps now have one fitted.....
 
I found someone with a K4700 in the US, and they indicated it was the K4700U variant for the 110VAC North American market. Unfortunately it came with the 220VAC transformer, part 2060012M on Velleman's site. My Voyagers have the boards with the proper transformer, and the part number is the same with a 110 tacked on the end. I can't find it anywhere on the Velleman site, and a company rep thinks it's out of stock.

There are a few alternatives from ebay, which look similar except for the relays:
Should I just go for one of those, or try to fudge something to get the K4700 working? I suppose I could use a little 2:1 transformer, but that seems like overkill.
 
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The UPC 1237 is supposed to be a good device, I have a couple of those songle ones but havent got round to trying them yet
The Vellemans have pretty weak relays and one has already failed on my voyagers so I will be replacing mine

The only thing I have reservations about is if these songle relays are genuine for the price of the overall boards ?

Alan
 
That's a good point. I suppose one could replace the Songles with "real ones", just in case.

Is a Songle better than an Omron? I've noticed fans on both sides.

FYI, I've gotten confirmation that there are no replacement transformers available for that Velleman unit.
 
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