sound disappearing

[Jakob]

Hi!

I've had this problem now for a couple of weeks. The sound in both channels disappear now and again in what seems to be a random way. It's sounds almost like a loose connection. It's not present all the time, so it's a bitch to investigate. So far it hasn't happened on high volume levels.

I have my homebrew E145+2450+2405 constellation connected to an ARC LS7 (all tubes) pre and NAD 218 power amp (SS) and the source is a Pioneer PDS-06. I've come to believe its in the electronics the error lies, but I'm not sure.

I have checked all the connections and they seem fine. This weekend I will check the networks.

How can You tell when the tubes in the preamp are worn out?

If the laser in the CD player is faulty, can it give these results?

Any input appreciated!


Regards: Jakob

[Don C]

Whenever I've had this problem before, it was either RCA jacks that get weakover time, ot switch contacts in the pre-amp. I'd start by listening to an alternate program source for a while, and see if the problem is common to another input.

[Jakob]

Today I tested with another preamp and another CD-player, but the problem is still there. Tomorrow I will try another power amp to see what happens.

[sweetliberty]

Hi Jacob
I am not familiar with the NAD power amp. I assume (as most amps have) it has a common power supply. The problem must be in the power supply for the power amp.

[Jakob]

Well, I've located the problem to the power amp. I tried another poweramp today, and the problem disappeared.

The weird thing is that it is on low volume only the problem excists. If you turn the volume up a bit it the problem disappears.

Thanks all!

[WDJ]

I've seen cases where at very low signal levels the gain controls causes this sort of a problem. My Mac 2120 has done this to me a couple of time.

Deoxit (a spray on contact cleaner) can help. I would suggest you not use WD40, as it can actually make this worse.

[grumpy]

No volume controls on 218.

I'd toggle and clean the switches on the rear panel (bal/unbal [especially],
soft clip, bridging). If persists, I'd check solder joints to/on input board.

Older NAD amps (e.g., Power Envelope 2200) had an issue with the output
relays and how they were soldered ... I have one waiting for me to fix in
my copious free time. Your's may be a completely unrelated issue, but the
symptom is similar. -grumpy

[subwoof]

In any power amplifier the entire chassis vibrates at the line frequency ( 50 or 60 HZ for you EU guys ) and this will fracture the solder connections over time.

As part of ALL overhauls in the shop, the large components on the circuit boards are re-soldered along with ALL I/O jacks and relay connections.

Since the sound does come back, there is NO damage to the amplification circuit(s) themselves and if it happens to BOTH channels, 99% of the time it's the wonderful protection circuit that is at fault - esp the relay.

Check the relay circuit components and if it uses a time-delay, REPLACE the small electrolytic caps that are around it. I can't tell you how many amplifiers come into the shop dead ( or flaky ) and only needed a 2 dollar cap replaced.

Grumpy is right - and YES, using some good de-oxit on the controls and switches is a good idea and may also be part of the problem ( you can have more than one at a time that cause the SAME result )...

SKOL



sub

[Jakob]

Thank You all!
I'll dig into my amp this weekend and see what I can find. How can I spot the output relays and the protection circuit, anybody knows???

[toddalin]

I had a similar problem with my dBx subwoofer amp. (Not actually made by the original dBX, but probably by BSR or such.) Over the years it had developed the same problem you describe that continued to get worse. I resoldered many of the joints (especially around the protection circuit) and even replaced the power caps that appeared to be leaking.

Relief was short-lived and the problem always came back worse on short order.

Eventually, I determined that the recourse was just to replace it with a Crown PSA-2XH that I picked up used for $225. (It was very rough, but cleaned up nicely.)

[Jakob]

hmmm, I really hope I don't have to buy another amp right now. I bought this just a couple of months ago since my old h/k Citation 22 gave up.

Short on money since I've just bought two 2227 frames that need reconing and the boxes for my latest project will be finished next month, the carpenter will be wanting his money, also thinking of new SL-dias for the 2450's... and yes, I'd like a DBX driverack as well...

/regards: Jakob

[Rolf]

Sometimes this "hobby", I say "way of life" demands money to fix things, wherever we have them or not. That is a fact. I had to use my credit card for not so long ago to fix one of my woofers. I hated that!

[Jakob]

That's a very good expression:" a way of life"!!!

Maybe that can help me convince my wife that I really need to bulid a pair of 4345's