Parasound JC-1 - Standby during playback?

Thanks, I was aware of the multiple turn-on delays. Apparently increasing the time delay can largely address the matter of turn-on thumps from upstream components.

Essential
No, but I have had turn on "thumps" when turning on the JC2/JC1 if I power it up cold from the AC plug. That is even if the JC2 runs its delay mute, I find that the mute time is not long enough to prevent these thumps through the JC1s.

When I measured the output of the JC2 to see the source, I found the DC levels were not quite zero (25 mV DC was enough to hear through the power amps). They did go down to 0.01 mV after a few more seconds, however. It appears that the DC servo control opamps in the JC2 take a bit of time to zero out after a cold power up, and need ten or twenty more seconds than Parasound programmed in to the mute delay.

So now I apply AC power to the JC2 and wait 30 or 40 seconds before I power the JC1/JC2 combo up and no thumps.

Most folks don't realize this, but the JC1 actually has three consecutive turn on delays. The first one is adjustable with the pot on the rear panel. The second one connects the main power to charge the large PS caps, and the third one unmutes the output connections to the speakers. In older JC1s, the delay times on the second and third delays can be shortened considerably due to bad electrolytic caps and poor zener diode voltages. So when you turn on a JC1, you should hear one click after the main delay, then a second one about 5-10 sec later, then a third one (and music) after another 5-10 sec.

I ended up re-building my timing boards to restore these delays. Each are important as they allow circuit stabilization to occur over the proper time period.

Dhl, have you experienced the phenomenon described by Shsohis? I do not use the 12V trigger feature but have seen such behavior due to upstream components which in fact may put one or both amps into protection mode briefly. Your suggestion of adjusting the turn-on delay is a good one.

You can set the JC1s up so that they have a staggered turn on cycle. You do this by adjusting the turn on delay control at the back of the amp. Even if they get simultaneous 12 V turn on signals, they will power up after different delays. You should not need staggered 12 V turn on signals. I do this with my JC2 powering up both my JC1s. Same 12V siganl from the preamp, but I have the delay set differently on each JC1.

I am not sure what using the 12V turn on signal would have to do with DC coming from the pre-amp. They are completely different issues. DC on the audio input to the amp triggers a fault condition which puts the amp in a protection mode. Unless the implication is that the JC1s are powering up before the DC levels on the preamp settle to zero. In that case use the longer delay settings on the JC1.

I bought a pair of walwart 12V power supplies for he JC-1. I have set them power up in such a way that one lags the other by about 12 secs.

Meanwhile, I have started with the recommended powering-on sequence - so far so good. I need to monitor for a longer period of time. Pray this works. Will come back with an update - positive one I hope! Thanks all!

It's possible that when both amps are turned on the same time, the line voltage may drop due to high inrush current and cause the amps to go into standby. You can try turning on one amp at a time see if the problem goes away.

Shsohis, if you're turning on the JC 1s via the 12V trigger rather than manually, it's certainly possible a bit of DC could be coming from the Nagra preamp. The amps should be turned on last and turned off first, and when turning on allow time for the preamp to stabilize before turning on the amps. The turntable power supply should be turned on before or at about the same time as the preamp.

Please let us know how this works out for you.

I would, simply as a troubleshooting action, place the JC-1s in Manual, just long enough to verify that they are/are not being erroneously triggered off by the preamp.

Of course during the testing, be sure to manually turn the amps on and off in the proper order as to avoid a possible big THUMP into your speakers.

Good Luck!

To Rayooo: I'm using a pair of 12V trigger to turn on the amps and the selection on the rear panel is correct.

To Essentialaudio:

Outlet 1-> Shunyata Cyclop-> Parasound JC-1s
Outlet 2-> Shunyata Cyclop-> Nagra PL-L, TT motor power supply, CDP

Of course, Outlets 1 & 2 are from the same power point.

Turning on sequence: Nagra PL-L -> Parasound JC-1 -> Turntable Power Supply

So, it might be a problem with the preamp or the power-on sequence?

Are you sure they are not in the "Audio Signal" mode where they turn on, and off, based on audio input?
Make sure the switch on the rear left panel is in "manual"

More information on your system (components and line conditioning) could be helpful...

Rather than this being due to voltage sag, I would suspect a bit of DC coming from your preamp is causing the amps to go into protection.

Always power on your front end components before the amplifiers and power down in the reverse order.

Parasound Halo dealer.