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Noisy shut down with Class D Audio CDA 254 bridged to mono

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Posted on June 22, 2016 at 15:43:56
islandmandan
Audiophile

Posts: 30
Location: Whidbey Island
Joined: February 17, 2005
 Need help diagnosing noisy shut down with Class D Audio mono-bridged CDA 254 amp.

I am in fear of destroying my Hard Edge converted Tannoy HPD 315 drivers with the excessive noise (loud thump) generated at shut down. I have contacted Tom Ross, and not heard back from him. The amp has two CDA 254 modules, using a common transformer and power supply.

Would any of you have an idea as to the cause, and how to eliminate it? Any help would be gratefully accepted.

Thank you,
Dan

 

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The AC power switch is causing the problem IMO, posted on June 22, 2016 at 20:48:34
Smelly_Socks
 The power switch is a bit faulty. So it is arcing when you flip it. The arc transmits a RFI pulse, which, somehow is being picked up by the amplifier and zapping your speakers.

A capacitor may be somewhere around that switch to curb such impulses, and it may have died (if this is a new problem.)

 

As Smelly asked, is this something new or amp has always thumped your speakers? (n/t), posted on June 23, 2016 at 07:28:16
FenderLover
 mt

 

RE: Noisy shut down with Class D Audio CDA 254 bridged to mono, posted on June 23, 2016 at 08:15:39
Hornlover
Manufacturer

Posts: 2529
Joined: March 8, 2002
 Maybe ask Class D Audio? Why are you using so much power on those Tannoy drivers? They dont need anywhere near 500W. Use the amp in standard 2 channel mode, with 125W channel, and you should still have buckets of headroom.

 

RE: Noisy shut down with Class D Audio CDA 254 bridged to mono, posted on June 23, 2016 at 08:59:54
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 Are you turning off the power amp first, then the preamp?

ET
ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

Give Tom some time..., posted on June 23, 2016 at 12:47:17
Dman
Audiophile

Posts: 7211
Location: Kansas
Joined: January 28, 2001
 He's usually a pretty busy guy, to my understanding! I had MANY questions before and after the purchase of my SDS-254L amp, and if he took more than two or three days, he was VERY apologetic about it.

Since the Class D modules in the amp (at least in the SDS-series) do NOT pass a signal (auto mute in the circuit) until the power supply rails are "up" or once they get below a certain V, I don't think it would be the power switch (Then again, on the OTHER side of my rig, my trusty old SWR Stereo 800 subwoofer amp ONLY thumps when turned in stereo mode, and NOT when bridged). Go figure.

Does the thump happen with a signal source (preamp, CD, etc) connected but not playing? Try turning the level attenuators all the way down? Disconnect inputs to the amp? Try anything!

Also, as "Smelly" has suggested, is this problem something NEW, or has the amp done this from day one (in that regard, is the amp still under warranty)?

I hope that Tom responds soon!

Good luck!


Dman
Analog Junkie

 

RE: Give Tom some time..., posted on June 23, 2016 at 13:45:18
islandmandan
Audiophile

Posts: 30
Location: Whidbey Island
Joined: February 17, 2005
 Thanks Guys for your responses. I've determined that most of the thumping noise is coming from one of my subwoofers, a DIY effort with 12" Eminence driver, and plate amp. I tried the shut down after turning the sub off, and the noise is very much reduced.

In answer to the question regarding 500 Wpc and my Tannoys, since it was easy to do, and cost so little, I thought I'd try it. I found the sound is something I haven't heard before from the HPD 315's, effortless in character, with a fullness, or completeness in each note, and a faster, or quicker, response time.

I know what you are saying about power. I don't listen particularly loud, and I pay attention to how the speakers are reacting to what I am feeding them. I can't afford to replace any drivers, not at the prices being charged these days for replacements, not to mention trying to get the Hard Edge conversion done nowadays.

By the way, my other amp, which I use for special occasions, is an SET 300B with EML 300B XLS tubes. The Class D amps were bought out of curiosity, and to save hours on expensive output tubes, and, to my surprise, sound very, very good.

Thanks and regards,
Dan

 

RE: Noisy shut down with Class D Audio CDA 254 bridged to mono, posted on June 23, 2016 at 16:26:21
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 Turn preamp on first and let warm up. Then turn the amps on.

Turn off amps first then the preamp.

 

Does the SW have a sub-sonic filter in its circuit? (n/t), posted on June 23, 2016 at 18:06:58
FenderLover
 mt

 

RE: Does the SW have a sub-sonic filter in its circuit? (n/t), posted on June 23, 2016 at 18:59:18
islandmandan
Audiophile

Posts: 30
Location: Whidbey Island
Joined: February 17, 2005
 No, FenderLover, it does not.

 

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