AR-LST's fizzle at low volume

[Guest red55]

I've had this pesky problem with my AR-LST's for a few years now. I don't know why I didn't mention it in this forum earlier. At lower volumes they're inclined to fizzle or cut out altogether. This is in no way predictable, mind you. They might be fine for 30 mins and suddenly one will go dead. I can turn the volume up temporarily to bring back the sound, and then sometimes they'll be fine again at low volume, or sometimes the problem will re-emerge immediately. Often this happens to one speaker and not the other.

They're powered by an accuphase P-300 which ought to be plenty powerful right? I know that LST's are power-hungry. I haven't been able to test them with another amp yet. The thing is, other speakers play just fine with this amp, and the amp was serviced recently.

The LST's have fuses in back. Could these be needing replacement? What are those fuses for anyway??

Anyway, advice would be much appreciated. They play flawlessly at louder volumes, but I like to listen to music casually while I read sometimes, and this is the exact volume that causes trouble.

[KlausDK]

Hi

I have had a similar problem on one of my LST's, I even tried replacing a midrange driver, because I thought it was bad, until I realised it was all of them.

I ended up concluding it was bad contacts on the level switch on the front. I clicked it back and forward through all the positions a few times to clean the contact surfaces and the problem disappeared.

BRgds Klaus

[Mexicomike]

Sounds to me like they are totally fried and just this side of kindling. But I'll take them off your hands; I need some large paperweights! I'll give you 20 bucks and pay the shipping.

I can't recall from the adds (I have never seen an LST though I lusted after them in the early 70's), Do the LST's have pots like the lessor classic AR's? Seems like I remember they had position-type switches rather than constantly variable pots. But, in either case, it might be worth taking a look at the pots/switches and cleaning them. The pots on my 3a's were completely unworkable but a good cleaning and lubing with dielectric grease put them in like-new operational condition. The pots on mine would cut in/out, acting a lot like you are describing at various volume levels.

[dynaco_dan]

Sounds to me like they are totally fried and just this side of kindling. But I'll take them off your hands; I need some large paperweights! I'll give you 20 bucks and pay the shipping.

I can't recall from the adds (I have never seen an LST though I lusted after them in the early 70's), Do the LST's have pots like the lessor classic AR's? Seems like I remember they had position-type switches rather than constantly variable pots. But, in either case, it might be worth taking a look at the pots/switches and cleaning them. The pots on my 3a's were completely unworkable but a good cleaning and lubing with dielectric grease put them in like-new operational condition. The pots on mine would cut in/out, acting a lot like you are describing at various volume levels.

Hi there;

For your information, AR used a Mallory switch for the early AR-LST's.

If you go to the library and download the AR-LST manual, you will see the Mallory part number listed in the drawing.

This switch had open wafers and contacts.

Later on AR switched to a more sealed and more expensive switch by a different U.S. manufacturer.

Mallory may have discontinued their switches, or worse, AR found they had problems with installing them, or later field problems, which we have no field notes on, yet.

To lubricate, use DeOxit or equal, the contacts of the Mallory switch, this would require only accessing the interior contacts, the switches would not need removing.

Access is via removing the woofer, in this case of the crossover installed via this opening.

Those of you with the earliest version of AR-LST's, the crossover was mounted on the rear panel and bolted to the cabinet from the enclosures rear.

You cannot just undo the shaft nuts and spray down the shaft, as I have read on ebay, for the pots.

The later switch, I believe, is sealed but I cannot remember further.

If it is sealed, there may still be a way of still lubricating them without cutting all of the leads and soaking them in a DeOxit solution.

Going back to the original issue of, no or low volume, I would be certain the the pre-amp level controls are cleaned first.

[Guest matty g]

I've had this pesky problem with my AR-LST's for a few years now. I don't know why I didn't mention it in this forum earlier. At lower volumes they're inclined to fizzle or cut out altogether. This is in no way predictable, mind you. They might be fine for 30 mins and suddenly one will go dead. I can turn the volume up temporarily to bring back the sound, and then sometimes they'll be fine again at low volume, or sometimes the problem will re-emerge immediately. Often this happens to one speaker and not the other.

They're powered by an accuphase P-300 which ought to be plenty powerful right? I know that LST's are power-hungry. I haven't been able to test them with another amp yet. The thing is, other speakers play just fine with this amp, and the amp was serviced recently.

The LST's have fuses in back. Could these be needing replacement? What are those fuses for anyway??

Anyway, advice would be much appreciated. They play flawlessly at louder volumes, but I like to listen to music casually while I read sometimes, and this is the exact volume that causes trouble.

Hi -

I recently went through the exact same thing with my rig. I also blamed the speakers at first because the volume control and other signal path switches on my preamp had no effect on the fizzle and drop out. It was so intermittent that it stopped doing it when I hooked up another speaker to that channel by luck, and then started when I reconnected the original speaker (which really threw me off the path). After months of changing wires, interconnects, speaker swaps and so forth I finally found the culprit. Turns out it was the delay relay in the preamp (the relay that holds back the signal for 10 seconds or so when the preamp is powered up). That was a hard one to find, because it happened so rarely that it was nearly untraceable. If you have swapped out the speakers and it still does it on that channel you might try lightly tapping on the delay relay to see if it comes back in - it worked on my Tandberg!

Matt

p.s. - Of course that's just to troubleshoot the relay. If tapping it does bring the channel back, the relay cover must be removed (not always easy to do) and the contacts sprayed or redressed. Good luck!

[Guest red55]

Many thanks for the thoughtful responses.

The pre-amp is certainly not the problem, as the issue remains when I plug my ipod directly into the power amplifier.

I suppose I'll undertake more dramatic surgery if necessary, but later today I'll try giving those front switches a few good turns and hope that helps.

I'll report back. In the meantime I'm more than happy to continue receiving advice if its out there.

[Guest george w]

I've had this pesky problem with my AR-LST's for a few years now. I don't know why I didn't mention it in this forum earlier. At lower volumes they're inclined to fizzle or cut out altogether. This is in no way predictable, mind you. They might be fine for 30 mins and suddenly one will go dead. I can turn the volume up temporarily to bring back the sound, and then sometimes they'll be fine again at low volume, or sometimes the problem will re-emerge immediately. Often this happens to one speaker and not the other.

They're powered by an accuphase P-300 which ought to be plenty powerful right? I know that LST's are power-hungry. I haven't been able to test them with another amp yet. The thing is, other speakers play just fine with this amp, and the amp was serviced recently.

The LST's have fuses in back. Could these be needing replacement? What are those fuses for anyway??

Anyway, advice would be much appreciated. They play flawlessly at louder volumes, but I like to listen to music casually while I read sometimes, and this is the exact volume that causes trouble.

Try cleaning the fuse holder clips and make sure they're still tight. If that doesn't help then change out the fuses with a new pair and use FNM 2 1/2's. These are specific time delay fuses and protect the entire speaker from excessive long term power inputs. By the way, the Accuphase is no where near powerful enough if you tend to listen a higher volumes.

The fuses and the spectral balance switch contacts are about the only things that could cause the speaker to 'fizzle out" at low levels. Try rotating the SB switch the next time this occurs. Position 2 is the position to start out with.

[dynaco_dan]

>Try cleaning the fuse holder clips and make sure they're still tight.

Good idea, both they and the fuse caps oxidize real easy.

>If that doesn't help then change out the fuses with a new pair and use >FNM 2 1/2's.

ABSOLUTELY NOT!!!!!

The AR-LST was and is rated as using a FNM 2 amp fuse.

My suggestion is to, perhaps downsize a little, in consideration of the aging of the drivers and rarety of the drivers, should they blow.

>These are specific time delay fuses and protect the entire speaker >from excessive long term power inputs.

Not quite, the woofer is the primary benefactor and cause of the fuse blowing, the mids and tweeters, less so.

The mids and tweeters should have had there own slow or even better yet, fast blow fuseholders, as well.

By the way, the Accuphase is no where near powerful enough if you tend to listen a higher volumes.

The fuses and the spectral balance switch contacts are about the only things that could cause the speaker to 'fizzle out" at low levels. Try rotating the SB switch the next time this occurs. Position 2 is the position to start out with.

When one or the other FNM fuse of a AR-LST blows, there still is a reduced input to the drivers.

I believe that the original design of the circuit did not jump out to sales department at AR, until after a few expensive warantee repairs, that were maybe only blown fuses.

After paying round trip shipping and service labour at the warantee depots, they were well aware of the potential problem.

The AR-LST literature later included advice to check for a blown fuse, as there will be still, at a much reduced level nonetheless, musical output.

A quick jumper test with a short across the speaker fuse will show this as a possible problem or not.

Check all speaker wire connections, input lines and existing fuses for continuity.

Reverse left and right speaker wires at the amp.

Also as a caution, when removing or installing a fuse in the AR-LST and perhaps AR-LST/2 and others that had fuse clips attached to the crossover boards and were soldered down.

Pull or push the fuses straignt onto or off of the clips, soldering them down has caused them to become brittle and they will break off in the solder puddle, if a little too much off-center pressure is applied.

They should not have been soldered but machined screwed to the boards.

[Diamonds&Rust]

They're powered by an accuphase P-300 which ought to be plenty powerful right?

200w/channel into 4 ohms should be plenty - and that amplifier...well, I'm jealous. I've heard LSTs play really well on a lot less.

What a great piece of equipment. I haven't seen one of those since 1980, but I've thought about picking a used one up several times. Built like a tank.

Have you had any work done on it?

[dynaco_dan]

Many thanks for the thoughtful responses.

The pre-amp is certainly not the problem, as the issue remains when I plug my ipod directly into the power amplifier.

I suppose I'll undertake more dramatic surgery if necessary, but later today I'll try giving those front switches a few good turns and hope that helps.

I'll report back. In the meantime I'm more than happy to continue receiving advice if its out there.

Hi there;

I went back and re-read the opening paragraph of this topic.

If, by using the Ipod it still happens, I lean towards the amplifier now as having a problem.

Does the amplifier have it's own volume controls?

If so, turn them many times, back and forth, to clean them temporarily.

Have you reversed the speaker cables yet to confirm this thought or not?

Reverse them, channel for channel, at the amp, not the speakers.

I am assuming that you already have confirmed the connections at the, pre-amp, amp and speakers are solid.

Also use DeOxit on the banana plugs and all other connections, EXCEPT, the power cord.