WOPL 400 Rev. A pops on power up

[Vynuladikt]

Old 400 WOPL Rev. A control board. It used to be silent on power up or down. Now it has a pretty loud pop on power up. Seems to be equal on both channels. What should I be looking for? I'm thinking a cap has possibly failed, but a little direction from the knowledgeable could save me a lot of time.

 

[Gibsonian]

No DC protection circuit installed in your unit?

 

[wattsabundant]

At turn on, the amplifier have to stabilize. During the process which takes a few hundred milliseconds, the amplifier dumps DC into the speaker. Not 80 volts, but a significant amount. Once everything is stable there is no (less than 50 millivolts) of DC offset on the output. My relay board does not directly solve the offset problem. Instead, It delays connecting the amp to the speaker for a short time. A similar event occurs when the amp sis turned off. When the main capacitors discharge, the amp becomes unstable and dumps the remaining DC into the speaker. Depending on the amp it can be a small thump, or a louder pop. The relay board instantly disconnects the speaker so it doesn't see the DC.

A White Oak driver board is as stable as it gets. But it can't totally eliminate the pop, thump, surge or whatever term seems to apply. If this is a new condition there is a possible problem withe the board or outputs. Check the DC offset per the W/O directions.

 

[Vynuladikt]

You are correct Gibsonian, no dc protection. I should probably do that, but this is a new occurrence, although I have made some changes in configuration and connections. I'll look for offset problems Don, could be from the preamp as well I guess.

 

[Gibsonian]

Ok, makes sense. If you get a DCP installed, there will never be a turn on or off noise. Pure silence unless you turn off your preamp first, or turn it on last! With no DCP I always had some type of on or off noise, it is normal.

 

[Gepetto]

Ok, makes sense. If you get a DCP installed, there will never be a turn on or off noise. Pure silence unless you turn off your preamp first, or turn it on last! With no DCP I always had some type of on or off noise, it is normal.

Depends on the pre that you use. I use the Acurus and there is no noise regardless of the order that things are turned on or off.

 

[Gibsonian]

Depends on the pre that you use. I use the Acurus and there is no noise regardless of the order that things are turned on or off.

That's weird. I use Acurus L10 and it makes noise when started last. The only preamp I've ever owned that didn't is a CJ tube pre but it has a timed mute circuit responsible for this.

 

[Gepetto]

The RL-11 mutes for a brief time after power on and then unmutes...

 

[George S.]

My Acurus L10 is "on" anytime it's plugged in. The manual states this is to keep the circuitry at optimum operating temp. Turning from off to on, the LED comes on and audio unmutes. Turn to mute to answer the phone or change source.
No popping noise on mine when going through off, on, or mute. Haven't tried plugging or unplugging it with it "on".
Mine pretty much sits under the work bench as a test standard. Very little use in the system except for a few real world comparison sessions.
How much of the circuitry is always energized I haven't investigated, but it's a very simple design since it's lacking the remote feature. Perhaps the so called power switch just makes or breaks the signal circuit, don't know.

 

[laatsch55]

The Coherence pretty much does what it wants....just so happens it's the same thing I would do...

 

[mlucitt]

Old 400 WOPL Rev. A control board.

Does your Rev A Control Board have (4) diodes soldered on the back side?

 

[WOPL Sniffer]

The Coherence pretty much does what it wants....just so happens it's the same thing I would do...

HUH?

 

[laatsch55]

HUH?

It does all the good stuff....

 

[Vynuladikt]

Does your Rev A Control Board have (4) diodes soldered on the back side?

I'll have to look, I don't remember.

 

[mlucitt]

I'll have to look, I don't remember.

The Rev A boards needed two 1N4001 (or equivalent) diodes in opposite directions across both C6L and C6R.
That prevented the "Latch-up" problem and may be related to the problem you are having.

 

[laatsch55]

1N4148's

 

[Billboard]

My order is
Power On:
Pre-amp, then WOPL 700B (with DC protect) second

Power off
WOPL 700B, then preamp

If I power on 700B before preamp I definitely get a turn on thump from the pre.

If you are running a Phase Linear power amp get a DC protect board installed.

 

[marcok]

I had this issue with PL 400 ( stock ) and Infinity RS iii B .
Issue : thump at power up .
Solution : insert a 510 Ohm 5 W resistor between the two connector of the speaker .
It works . Try it . It's easy and unexpansive .
This " mod " comes from PL 400 service manual .
Ciao
Marco

 

[Vynuladikt]

Thanks all for the suggestions. I haven't had a chance to pull it from the rack yet and it seems to be louder now than just recently so I need to address it. Yes, DCP should be the best correction, but I also wonder why it just started doing this after running silent for many years.
Still one of, if not THE best amps I've heard or owned.