Blown Luxman (Chris??)

K-amps · 20th July 2006, 05:24 PM

I am setting up a HT for my suister and used an old luxman M-117 power amp I had lying around to drive the Front main speakers which are an old pair of B&W 801 S3's I got for her off ebay.

The M-117 is driven by a Denon 4306 receiver off the pre-outs. The Denon Receiver also has dish and cable boxes connected to it.

Here's the issue:

Low to mid volume play was fine, but as I cranked it up, the Lux shut down. I thought the amp blew, but not really...

Symptoms:

Before I uninstall her whole HT set up to open up the Luxman to check it, I was wondering if you guys have experienced anything like follows:

without RCA's connected to the input of the power amp, the amp turns on and also engages the speaker relays... tells me the OP stage is perhaps not dead. HOWEVER:

As soon as I connect the RCA cables to the poweramp, the clip indicator goes on, I hear a buzz from the power amp and the relays do not engage ( this happens regardless of speakers connected or not). I figured some hi level signal from the pre-outs of the receiver may be overloading the Lux...

As a further test I disconnected the RCA cable going to the Receiver.. so essentially all I have is an open ended cable connected to the input of the Lux power amp... Lo and behold the amp still buzzes and clipping indicator on again...with just a acble attached!

Apart from some RF oscillation, I have no clues why it is doing this. (Note without a cable attached, the amp powers on fine)... why is an open ended cable feeding a phantom signal inot the power amp???

All cables are new.

anatech · 20th July 2006, 06:29 PM

Hi Arif,
Many amps do not like a capacitive load on the input. They may become unstable. Old, high ESR decoupling caps can cause this or make the symptoms worse. In good condition, I haven't seen one of these do this.

Another consideration is our old friend .... the cable ground. I refuse to even hook it up in our house - to anything! Yoiu can try to disconnect the cable from every component in that system as a test. I'd suggest you get a ground isolation transformer for it in any event. That would be the very first thing the cable hits when it comes into the house unless there is a lightning arrestor. Then it's the next thing the cable hits. The cable could give you both hum and RF.

Make sure the Denon isn't throwing out DC on either output as a final suggestion.

-Chris

K-amps · 20th July 2006, 06:40 PM

I would put a ground insulating thingamajig if the symptom happened with the cable box connected..

Issue is there is NOTHING connected to the power amplifier except an RCA cable that goes to the amp inputs on one end and no where on the other end. i.e. open ended.

When I remove this RCA cable, the amp stabilizes i.e. Buzzing from the Mian power transformer dies away in 1.5 to 2 seconds slowly and then the relay's engage.

Why is a pice of wire causing this... well even if I connect the other end to the Denon, the same issue persists.

I checked the Denon, not throwing AC or DC. (signal absent ofcourse)

anatech · 20th July 2006, 07:52 PM

Hi Arif,
Check and / or replace the coupling caps and supply decoupling caps.

I'd say the amp is unstable and is oscillating in that condition. It's a repair now.

-Chris

K-amps · 20th July 2006, 08:27 PM

Thanks Chris, I guess I will have to do that... but how did the caps suddenly go when I crank blewed up the volume?

Surely I either blew a grounding connection or resistor or even the OP stage.

Oh yes I remember, just before bowing out, the sound suddenly went thin, i.e. without bass and then poof.

Should I check the 801's woofers for shorts?

anatech · 20th July 2006, 08:33 PM

Hi Arif,
You may possibly have bad decoupling caps on that old Luxman. I've even had Box Polyesters go open, much to my surprise.

The woofers may have gone to Valhalla. You zobel may have gone away in the amp.

Keep an open mind when crazy things happen or you'll get stuck. I am interested to know what you find out.

-Chris

K-amps · 20th July 2006, 08:54 PM

So far it may be dumped into the garbage... !!!!!

K-amps · 20th July 2006, 08:55 PM

Quote:

Originally posted by anatech
Hi Arif,
You may possibly have bad decoupling caps on that old Luxman. I've even had Box Polyesters go open, much to my surprise.

The woofers may have gone to Valhalla. You zobel may have gone away in the amp.

Keep an open mind when crazy things happen or you'll get stuck. I am interested to know what you find out.

-Chris

Decoupling caps... you mean on the input coupling cap? If I remember, it has a Elna cerafine bypassed with film type.

bluesmoke · 20th July 2006, 09:23 PM

I agree with anatech. Cable TV ground is evil.

If absolutely necessary, build a switch that will isolate both the signal and ground (a simple DPDT will do), or use a friction fit coupling near where you have it hooked up, so when un-needed you can easily disconnect.

As for solving the problem, if you can isolate & test each component separately, usually you can at least find the source of the problem. A discman makes a great feed for an amp. A leftover full range speaker great for testing speaker outputs. etc...

anatech · 20th July 2006, 09:28 PM

Hi Arif,
It's a frustrating problem, but these are good sets normally. So it's not a design fault. Something happened to the amp. Don't chuck it!

-Chris

20th July 2006, 05:24 PM	#1
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Blown Luxman (Chris??) I am setting up a HT for my suister and used an old luxman M-117 power amp I had lying around to drive the Front main speakers which are an old pair of B&W 801 S3's I got for her off ebay. The M-117 is driven by a Denon 4306 receiver off the pre-outs. The Denon Receiver also has dish and cable boxes connected to it. Here's the issue: Low to mid volume play was fine, but as I cranked it up, the Lux shut down. I thought the amp blew, but not really... Symptoms: Before I uninstall her whole HT set up to open up the Luxman to check it, I was wondering if you guys have experienced anything like follows: without RCA's connected to the input of the power amp, the amp turns on and also engages the speaker relays... tells me the OP stage is perhaps not dead. HOWEVER: As soon as I connect the RCA cables to the poweramp, the clip indicator goes on, I hear a buzz from the power amp and the relays do not engage ( this happens regardless of speakers connected or not). I figured some hi level signal from the pre-outs of the receiver may be overloading the Lux... As a further test I disconnected the RCA cable going to the Receiver.. so essentially all I have is an open ended cable connected to the input of the Lux power amp... Lo and behold the amp still buzzes and clipping indicator on again...with just a acble attached! Apart from some RF oscillation, I have no clues why it is doing this. (Note without a cable attached, the amp powers on fine)... why is an open ended cable feeding a phantom signal inot the power amp??? All cables are new.

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20th July 2006, 06:29 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Arif, Many amps do not like a capacitive load on the input. They may become unstable. Old, high ESR decoupling caps can cause this or make the symptoms worse. In good condition, I haven't seen one of these do this. Another consideration is our old friend .... the cable ground. I refuse to even hook it up in our house - to anything! Yoiu can try to disconnect the cable from every component in that system as a test. I'd suggest you get a ground isolation transformer for it in any event. That would be the very first thing the cable hits when it comes into the house unless there is a lightning arrestor. Then it's the next thing the cable hits. The cable could give you both hum and RF. Make sure the Denon isn't throwing out DC on either output as a final suggestion. -Chris

20th July 2006, 06:40 PM	#3
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	I would put a ground insulating thingamajig if the symptom happened with the cable box connected.. Issue is there is NOTHING connected to the power amplifier except an RCA cable that goes to the amp inputs on one end and no where on the other end. i.e. open ended. When I remove this RCA cable, the amp stabilizes i.e. Buzzing from the Mian power transformer dies away in 1.5 to 2 seconds slowly and then the relay's engage. Why is a pice of wire causing this... well even if I connect the other end to the Denon, the same issue persists. I checked the Denon, not throwing AC or DC. (signal absent ofcourse)

20th July 2006, 07:52 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Arif, Check and / or replace the coupling caps and supply decoupling caps. I'd say the amp is unstable and is oscillating in that condition. It's a repair now. -Chris

20th July 2006, 08:27 PM	#5
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Thanks Chris, I guess I will have to do that... but how did the caps suddenly go when I crank blewed up the volume? Surely I either blew a grounding connection or resistor or even the OP stage. Oh yes I remember, just before bowing out, the sound suddenly went thin, i.e. without bass and then poof. Should I check the 801's woofers for shorts?

20th July 2006, 08:33 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Arif, You may possibly have bad decoupling caps on that old Luxman. I've even had Box Polyesters go open, much to my surprise. The woofers may have gone to Valhalla. You zobel may have gone away in the amp. Keep an open mind when crazy things happen or you'll get stuck. I am interested to know what you find out. -Chris

20th July 2006, 08:54 PM	#7
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	So far it may be dumped into the garbage... !!!!!

20th July 2006, 09:23 PM	#9
bluesmoke diyAudio Member Join Date: Mar 2006 Location: Great White North	I agree with anatech. Cable TV ground is evil. If absolutely necessary, build a switch that will isolate both the signal and ground (a simple DPDT will do), or use a friction fit coupling near where you have it hooked up, so when un-needed you can easily disconnect. As for solving the problem, if you can isolate & test each component separately, usually you can at least find the source of the problem. A discman makes a great feed for an amp. A leftover full range speaker great for testing speaker outputs. etc...

20th July 2006, 09:28 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Arif, It's a frustrating problem, but these are good sets normally. So it's not a design fault. Something happened to the amp. Don't chuck it! -Chris

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