Speaker Protection in Parasound Monoblocks JC1

[raj691]

My Stereo setup includes Rose 150B as streamer and preamp running via parasound JC1 monoblocks feeding Monitor Audio Platinum 300 tower speakers
2 days back I was listening to this setup for about 30 minutes. Midway I restarted my Rose150 B while the amps were already powered up.
I heard a spike in the speakers with small blast. The bass driver coils in both the speakers burnt. There are 2 base drivers in each speaker so 4 base drivers were damaged.
The problem more likely emanated from Rose 150b as it is unlikely that 2 independent amplifiers will develop same problem at the same time.
I can rule out the power supply issue as the system is being fed from a 5KVA APC UPS.
Has any one faced similar issue. What checks I need to perform before I restart my system

I also want to know if Parasound Jc1 monoblocks have speaker protection circuit or this is something I will have to mod.

I changed the speakers and the system works ok. So at present the damage is only to the drivers.

Any help will be appreciated.
PS - I am attaching pictures of smoke from speaker port and a speaker with burnt coil

 

[mbhangui]

It seems to me that your monoblocks don't have a volume control. So it is always at full gain. While restarting your streamer, it could have given a short burst of noise which would have been at full voltage. In such a case speaker protection in the amp wouldn't have helped.

In such a case where the amp is at full volume, have the volume in your downstream equipment at 0 when restarting. If you have a multimeter, connect your multimeter to one of the RCA output of your streamer and restart it to see if there is a spike. Repeat the test for the other channel. Also check if your RCA output of your streamer has any DC voltage.

 

[square_wave]

Ideally a new age preamp / digital front end like the hifirose should default to a low volume level when they are restarted. If not, that is quite a crime!

 

[bornfi]

Sorry to hear about this.

No matter how good a source equipment is, it always generates a pulse when switched on and off so the rule of thumb is that whenever you have to restart your system, switch on the power amp as very last equipment and, while switching off your system, follow the reverse order.

Speaker protection comes into play when + and - terminals are shorted accidentally. In this case your amp saw the pulse from Hifirose as a signal and amplified it to the max that your speakers could not handle.

 

[mbhangui]

Are you using the XLR output from the streamer? It can be as high as 5v. According to this post the streamer does seem to have a thump when coming out of standby.

As per this post, the output on the xlr pre out can be as high as 6.2v

I didn’t try it, but I wonder if lowering the balanced output voltage levels would reduce the SNAP sound level if not eliminate it. The RS150B has a default 6.5V using the XLR balanced outputs. The RCA jacks are 2.2V. You can adjust those levels in the INPUT/OUTPUT settings are the RS150B.

Given that loud sound, I would shut off the amps first to protect the speakers until a resolution is found.

https://community.roseaudio.kr/t/rs150b-standby-mode-snap-pop-noise-balanced-pre-out/3033/10

 

[mbhangui]

Ideally a new age preamp / digital front end like the hifirose should default to a low volume level when they are restarted. If not, that is quite a crime!

The problem with many of the streamers are that the volume control is software based. So during shutdown it has to save the volume level somewhere. When the streamer starts, the software has to read the earlier saved volume level and apply it ASAP. Any ineffiency during the boot up can delay the applying of the lower volume level. Even the raspberry PI devices which uses ALSA has to call what is known as alsa-restore to restore the hardware state of the DAC connected to the PI. Some DACs have hardware volume control and the state is saved in the EEPROM. Such DACS will restore the volume level before the OS on the device becomes functional after boot up and such DACs will be safe to be used before a power amp without a volume control. The Hifi Rose 150b is an expensive streamer. I guess it would have taken care of such cases, but it looks like the glitch happened during startup, which makes me suspect the implementation of volume level restoration. I hope the OP manages to get the driver re-coiled or get 4 new drivers. What has happend is tragic to say the least. Just hope that the speakers are back on feet again. Next time the OP will have to be careful or implement a preamp with a hardware volume control. One cannot trust software 100%. It is that .001 % where a tragedy can occur.

I have a similar issue with one of my DAC which doesn't have a hardware volume control. The output on the XLR is high as 4v. If I shutdown my streamer while the music is playing and restart the streamer, it will start the music playback exactly from the point it was shutdown. So I have implemented a cheap hardware based volume control after the dac using this device. So regardless of the software setting of volume control, this device linked below tames the volume down.

Amazon.in

For those who are technically inclined, this is what happens on any Linux device during shutdown to store the DAC state

alsactl --file asound.state store

And this is how the volume level gets restored during bootup

alsactl --file asound.state restore

During bootup when the OS is running many initialization commands in an ordered sequence. The volume will be full till the above command gets called. Hence the danger that any noise from the DAC can be sent to the AMP at full volume. This is the reason why software volume control can never be trusted.

 

[raj691]

Dear Members
Thank you very much for your advice

1. Yes, Rose and amps are connected via balanced XLR cables
2. I will be careful to power and stabilize Rose 150 before switching on the Amps
3. Can I implement a speaker protection circuit in the amps to prevent such an occurrence?

Guardian-86

The Guardian-86 is a high-end solid state speaker protection circuit board module for use in audiophile audio amplifiers. The Guardian-86 uses MOSFETs instead of relays to protect your speakers resulting in better performance and better protection of your speakers.

neurochrome.com

4. I have an Analogue Anthem STR preamp which can be added to make rose only a streamer + DAC. But this adds another hop in the process.

Any inputs are welcome