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fredmarantz
09-28-2003, 08:02 AM
Hello!

Is it normal that this amplifier (JBL sa-600) causes driver excursions when I turn it on or off. I have seen this phenomenon on some HK-receivers as well. I don't like it, but it seems that nothing harmful happens. My spearkers are jbl 4333A - should be rugged enough to take it?

Some good comments are appreciated.

many regards

Freddy

Ananda
10-31-2007, 02:07 AM
Dear Freddy,
I am uaing a JBL SA600 for the last 20 years. I am using JBL Lancer 99 speakers. This speaker excrusion is due to non availability of speaker protection. But any good speaker will handle it.

Regards,
Ananda.


Hello!

Is it normal that this amplifier (JBL sa-600) causes driver excursions when I turn it on or off. I have seen this phenomenon on some HK-receivers as well. I don't like it, but it seems that nothing harmful happens. My spearkers are jbl 4333A - should be rugged enough to take it?

Some good comments are appreciated.

many regards

Freddy

Jan Daugaard
11-01-2007, 02:41 AM
I have sent you a PM (you have to log in to see it).

hjames
11-01-2007, 08:44 AM
Before it went off for repairs, my old 6260 amp would sometimes thump loudly on power up.

I found out it helped to turn on the preamp and any sources first.
I also helped to turn the Amp volume all the way down before powering it up.

SMKSoundPro
11-01-2007, 03:14 PM
I always turn of the power amps first!
Then I wait for the soup can capacitors in the power supply to wane.
Then I turn off the preamp and all of the processing gear, eq and such, as a group.

When powering on...Preamps and processing gear first.
Thek power amps last.

I am using Yamaha P2200's for my workshop rig with the L200b's and my double 2245 cabinet crossed over at 80hz. It sounds great in my shop!

Once, I didn't wait long enough for the power amps to recede, and turned off the preamp stuff and BLAMO! The 136 woofer jumped and barked and let me know how unhappy they were with me!

Just be careful when using "pro" amps!

Scott.

BMWCCA
11-01-2007, 03:58 PM
Umm, the SA600 in the original post in this thread is an integrated amp. Makes it kind of hard to turn on the pre-amp without the amp. :blink:

hjames
11-01-2007, 04:01 PM
Umm, the SA600 in the original post in this thread is an integrated amp. Makes it kind of hard to turn on the pre-amp without the amp. :blink:


Are you saying power on (or power-Down) thump is normal with that model?

Even so, turning the volume all the way down should help.

Otherwise, I'd think someone needs to have a look at it (power supply filtering and such)!

subwoof
11-01-2007, 07:44 PM
Many early solid state amplifiers had this issue and in reality the only way to prevent this is to construct an external relay bank that disconnects speakers at turn off and connects them WITH a delay upon power up.

This way an entire system can be remotely controlled or powered up with a single switch.

With vintage monitor components reaching unreal prices for repair ( and in some cases parts are NLA ) this is good insurance and practice.

Crown ( and a few others ) used a CMOS switch ( chip ) in between the input opamp and the power section ( IE: the PS200/400 and the consumer versions PL3,4 ) that prevented the preamp section from causing this and it does work well for their designs.

The older "D" series used a couple of capacitive tricks to do the same BUT with the inevitable degrading of electrolytics with age and the tolerance factor ( +/- 20% ) it wasn't enough protection for critical monitoring use. Stories abound of these crowns whistling and squealing on turn-off and a mod is required to correct this. I have done this mod to hundreds but some amps just refuse to get with the program.

The JBL/UREI lines used high current mechanical relays for the speaker leads and this gives the additional DC protection if needed in case a major output stage malfunction happens that does NOT blow a fuse ( usually a SINGLE output transistor shorts C-E ).

poof.

sub