Installing Power Switch on Phase Linear 400 Power Amp

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EWalter

Active member
Joined
Sep 25, 2018
Messages
34
Location
Nashville
Hey all,

I’m thinking about installing a power switch on a phase linear 400 power amp. Right now it’s live when you plug it in which seems like a bit of a safety hazard. Plus I’d like to have the ability to easily turn it off, rather than climbing behind the rack and pulling the plug.

I’m concerned that it may not be as simple as other power switches since the speakers are likely to pop horrendously when I cut power. I thought I’d reach out to the community for some direction on this one. I feel like there’s probably a relay system on most amps that cuts audio before cutting power or something?

Thanks for the help!

Manual for the PL400 is below:
http://thecarversite.com/manuals/mandir/Phase%20400%20owner%20manual.pdf
 
> climbing behind the rack and pulling the plug. I’m concerned that it may ...pop horrendously when I cut power.

No different than yanking the plug.

I agree about not molesting a PL400 which has not yet failed.

Yes, most recent amplifiers have a relay, but this fails in odd ways, and is not simple to retrofit. I do not recall the PL400 having a "bad" thump at power-yank.
 
PRR said:
> climbing behind the rack and pulling the plug. I’m concerned that it may ...pop horrendously when I cut power.

No different than yanking the plug.
Understood. That’s why I was considering  the relay system. Currently I turn the vol down before unplugging.

I have eyed some rack-mounted power strips with on/off switches on the front. Maybe that’s just the way to go...

Thanks guys.
 
If the transient is only a problem when turning off, use a switched power strip, and get a 120VAC powered relay for the speakers. Power that relay from the same switched outlet strip.

Back in the early '70s I rolled my own DIY power amp and used a mains powered relay for the speakers. I had a 3 position power switch from an old WE tube PS. The first on position had an R in series to reduce turn on current spikes from charging a massive PS, the second on position shorted across the series resistor and sent power to the speaker relay... Silent turn on and off....  ;D

If you don't have a turn on problem, just powering a speaker relay from the same switched outlet strip will accomplish your goal, without devaluing that old soldier that probably has more nostalgic value than it deserves.

JR
 
EWalter said:
....I’m thinking about installing a power switch on a phase linear 400 power amp..... since the speakers are likely to pop horrendously when I cut power. ...

The simplest and elegant solution IMO would be placing two DPST switches (picture) to the bottom plate close to the front panel of the amp if you have one unit free space below the amp. One on left side is used for power on and second one on right side for connecting the outputs of the amp to the speakers terminal.

 

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David Kulka said:
I wouldn't use such a small switch for either the power or the speaker outputs. It looks way under-rated for that amount of power.

So, 16A/250V and 20A/125V AC isn't enough?
 
moamps said:
So, 16A/250V and 20A/125V AC isn't enough?
You'd think so, right? So did Peavey, with their CS-800 power switch of similar ratings.

But apparently, they had enough failures in the field, where they made a design change early on, so that the power switch has small current and just turned on a triac to do the heavy lifting, problem solved.

Granted, the PL-400 has a little wimpy power transformer VS the industrial-welding-machine-worthy transformer in a CS-800. so that will buy you some time before failure.

Gene
 
Gene Pink said:
.....CS-800 power switch of similar ratings....just turned on a triac to do the heavy lifting.....
I would not comment here Peavey's sub optimal designs...
industrial-welding-machine-worthy transformer
..nor welding machines...
so that will buy you some time before failure
but will repeat that  I believe the switch I proposed would work well in PL400 amplifier.  PL400 uses too small (and slow EI type) power transformer followed by small capacitor banks, so I don't see that arcing would be significant problem. Using this switch for speakers switching is also fine, especially because the switching  occurs when the amplifier isn't on full power.

Btw, you or Mr. Kulka didn't react on JR's proposal of using a power strip with a switch which is usually rated equally as switch I proposed.  Why? You should think about that. 10 or 16A is a usual rate of a single power outlet over here, so the switches are rated for this current. I don't know what's the maximum current allowed from single outlet in USA, but believe it isn't higher than 20A.



 
moamps said:
I would not comment here Peavey's sub optimal designs.....
Thank you
nor welding machines...but will repeat that  I believe the switch I proposed would work well in PL400 amplifier.  PL400 uses too small (and slow EI type) power transformer followed by small capacitor banks, so I don't see that arcing would be significant problem. Using this switch for speakers switching is also fine, especially because the switching  occurs when the amplifier isn't on full power.

Btw, you or Mr. Kulka didn't react on JR's proposal of using a power strip with a switch which is usually rated equally as switch I proposed.  Why? You should think about that. 10 or 16A is a usual rate of a single power outlet over here, so the switches are rated for this current. I don't know what's the maximum current allowed from single outlet in USA, but believe it isn't higher than 20A.
Those are continuous ratings likely based on heat rise at plug/outlet contacts, peak mains currents can transiently be much higher (especially if charging large PS capacitors at turn on).

I stand by my original advice... searching the WWW shows aftermarket speaker relay mod kits, but it seems a lot of effort for an old, modest power, amplifier.

JR

PS: I won't bore you with even more stories about power amp switches.
 
Get one of these "remote" power strips. Like they used to sell for desktop PC's. Turns all stuff on the power strip on when you turn on the preamp, or whatever other device you choose...
 
US/Can power strips are nominal 15A. (There are 20A versions, with a different plug, not normally used in residences.)

The $7 ones fail a LOT. Mostly in the blade-clip, but also the switches.

The $30 ones are a better bet, though I have seen some die.

FWIW: a later PL400 did have a front switch, and it looks a lot like the one in #5 here.
 
PRR said:
US/Can power strips are nominal 15A. (There are 20A versions, with a different plug, not normally used in residences.)

The $7 ones fail a LOT. Mostly in the blade-clip, but also the switches.

The $30 ones are a better bet, though I have seen some die.

FWIW: a later PL400 did have a front switch, and it looks a lot like the one in #5 here.
A common failure mode for cheap power strips is leaky protection devices... the good news is they are so cheap you can replace them without missing a rent payment (or just clip out the MOVs).

JR
 
Sansui transistors,

and the first solid state amp i have seen with output transformers! 

kind of. they are auto transformers for impedance matching.

boss would not let me take them apart as he needs the 4 grand right now.
 

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moamps said:
So, 16A/250V and 20A/125V AC isn't enough?

Is the actual switch in that photo really rated at 16 amps? It sure doesn't look like a 16 amp switch to me. But even if it's rated (or claimed, depending on how much we trust the manufacturer) the construction looks very wimpy and I wouldn't use it for any sort of high power application. Inrush current at turn on can be very high for a power amp or power supply -- that combined with a plastic body switch that I think I could almost crush with one hand is a bad combination.

Most power amps use power switches with much more robust construction and still, it's not unusual for them to fail over time.

A heavier duty switch toggle will just couple a little bit more and it's easier to drill a round hole.

I think that using an AC strip to switch power would be fine, if there's no issue with thumps or pops when switching on and off. (Preferably one with a good quality power switch. :) )
 
I scavenged an old QSC amp and it has a similar rated and puny looking switch.....

Can someone explain what they do in their amp to allow for this???? ??? ??? Schematic attached

amplificador-qsc-900-usa-para-checar-canal-1-noda-audio-D_NQ_NP_765019-MLM28421586422_102018-F.jpg
 

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scott2000 said:
I scavenged an old QSC amp and it has a similar rated and puny looking switch.....

Can someone explain what they do in their amp to allow for this???? ??? ??? Schematic attached
They may use an inrush current limiter.

JR
 
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