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Phase Linear 400 speaker protection?

Oblivion321

Oblivion321

Active Member
I am picking up a series 1 in a couple of days and am looking into the dc protection board a member here sells. I found the thread last night, but cannot seem to find it again. Supposedly, this unit was serviced by a professional tech not too long ago, but don't have any other details as to what was done. Maybe I'll get lucky and won't need a total rebuild. Hey, it was really cheap and I always wanted one. Any help is appreciated. I'll take some pics of the previous work when it's actually in my hands. Thank you.
 
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Nobody? Should I post this in another forum? Anyone want to lend me a pair of speakers? Promise I won't smoke em. :beatnik::angel:
 
"No matter where you are exactly I am no where near you."

Yeah, the PL 400 was not too healthy for my speakers either, even though it did not fry out. It sounded perfectly clean when it ripped the (almost new) foam surround off of one woofer (in a small sealed cabinet) and blew the tweeters.

I have no idea where that thread is either but all the info was not here. I think White Oaks does those but there are a couple of other designs, probably available at fleabay but I have not checked.

If you actually get the manual, it says to use speaker fuses and gives the approximate values based on what the power handling is. This gives the advantage of protecting speakers that can't quite handle it all from an overzealous application of the volume control. the circuits they sell or install do not do that and you should have speakers that can handle the entire power output of the amp.

For simple protection from DC offset caused by the amp shorting out you can use speaker fuses but put large electrolytics across them. This is not cheap. you need like four 15,000 uF/100volt wired plus to plus in series. (minus to minus works just as well but the fact is you are building a 7,500uF..100volt cap). I know of no bipolars of that rating that won't cost you an arm and a leg.

There was a discussion of using a bridge rectifier and a relay, in fact I was in it. The problem there is getting a relay with sufficient current and voltage capacity that has a sensitive enough coil.

The White Oaks deal IIRC has to be installed in the amp and runs off its power supply. I can't be sure it is compatible with the original series one circuit, but it probably is.

The amp is already protected against short circuits, as long as that is working. It is just a matter of - is it ? Kinda hard to tell and the testing is not that kind, if it doesn't work that is. There are germanium transistors involved IIRC nd if you need them, switching to silicon is not all that easy. There will be resistor values to change.

I would Google for it. Here, you never know where they put it. It could be in Solid State, General, DIY. But in the meantime at least get some speaker fuses.
 
Thank you guys for your responses. I got this thing cheap and should have it in hand this weekend. I was planning on having to get it serviced and/or upgraded. I've heard a lot of good, and also the horror stories. I wasn't expecting a plug it in and crank it up unit. Ultimately I wanted something to power my 901's but don't want to turn them into charcoal either. I'm just looking into options and expenses to get it up to par even if it takes a while. I'm not a tech, but with some concentration and patience I can do some of the work myself and am looking forward to it. Supposedly it was "professionally serviced" recently, so I will take some pics of the guts post em up to get your thoughts and opinions. Any other thoughts or suggestions are welcomed and greatly appreciated.
Bruce
 
It is doubtful the PL400 could fry the 901s even if they tried. I mean shorted out. IIRC they either take 8 amp fuses or two sets of 5 amp fuses. Eight times eight is sixty four. Sixty four times eight is only five hundred twelve watts. But see that is BOTH channels.

It would have to sit there and cook in front of you, that is not likely to happen is it ?

Don't get me wrong, there are low impedance woofers that this thing will fry in milliseconds, but the 901 array is not one of them. You got A LITTLE BIT of time.

I would use 5 or 6.3 amp on them tops. Use 7s if you got the balls, go ahead. Actually you can because they are all in series and you don't blow them all, just the unlucky one. Plus the fact that 901s are nearly resistive and will not beat on an amp like that. It might bother some new AVR rated 500 watts but has a 2 amp fuse, but they are not going to beat on the ole 400. That old Man can handle it, as long as he is working properly.
 
In JURB's blurb, he wrote: "The problem there is getting a relay with sufficient current and voltage capacity that has a sensitive enough coil."
Keep in mind you can "stack" relays. Choose your sensitive coil candidate, and then use it to control a second relay with desired current and voltage capacity. You may lose microseconds in response time, but better that than failure of the protection scheme.

Posted as one who has given up Wharfedales as burnt offerings to the PL400 gods...

Chip
 
The Audiokarma member you speak of is d3imlay.
He sells complete protection relay kits for Phase 400 and 700b's.
I have installed several of them in my two 400 and 700b amps.

Bob
 
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