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Topic: loud pop on power up of Session |
jim milewski
From:
stowe, vermont
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Posted 17 Oct 2004 4:38 pm |
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| I get a very loud pop, when powering up the 400, how would you go about finding the source? I know it's either the positive or negative rail getting through to the output to speaker |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 17 Oct 2004 5:13 pm
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I think they all do that to some degree. All 3 that I've had did it.
Brad Sarno
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jim milewski
From:
stowe, vermont
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Posted 17 Oct 2004 5:59 pm
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| Brad, the other two 400's have a slight pop, this is very loud, with a crackle as well, my concern is for the speaker, also on turning the amp off it does the same, but not quite as loud |
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Blake Hawkins
From:
Florida
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Posted 18 Oct 2004 2:27 am
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Jim,
I have a Nashville 400 which started doing the same thing about a year ago.
Loud pop on power up, and strange noises on power down.
I replaced the power supply filter caps on both the +/- 52 volt and +/- 15 volt circuits.
That cured the problem on my amp. I still get the normal pop.
On the NV 400 the pop is caused by the initial charging of the filter cap on the +55 volt rail.
There are several old threads on the Forum about it.
Blake |
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 18 Oct 2004 4:37 am
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| Jim, Has this amp been in storage for a while without being turned on? Filter caps tend to dry out, without regular use. You may get lucky if you leave the amp turned on for several days. This sometimes heals the capacitors. I have actually done this with success on other electronic equipment. If this doesn't fix it, I agree that you should have those caps replaced.........JD |
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Ray Minich
From:
Bradford, Pa. Frozen Tundra
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Posted 18 Oct 2004 10:08 am
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| John D., If I could add something here without appearing a smart a$$, modern filter caps don't necessarily "dry out", the just get leaky, some real leaky, when they haven't been used for a while. Running them at rated DC voltage for a while "re-forms" them, hopefully reducing the leakage current to acceptable levels. When this doesn't work it's time for surgery. [This message was edited by Ray Minich on 18 October 2004 at 11:08 AM.] |
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jim milewski
From:
stowe, vermont
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Posted 18 Oct 2004 11:02 am
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| yes, it was in storage, when i got it, it had hay in the speaker box, I picked up the caps today. On the scope there was minimal ac ripple on the DC voltages so i figured the caps were ok, maybe there is more to caps than what the eyes see, another thing I had a blown output transistor (PNP) and replaced it with a generic 3055, so there is an oddball (correct polarity) transistor in there, another thing, Peavey output transistors base and emmiter are not soldered, but a male/female fit, seems I heard some people solder these for a more sure connection |
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Ray Minich
From:
Bradford, Pa. Frozen Tundra
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Posted 18 Oct 2004 11:12 am
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| I am not an advocate of power transistor sockets. |
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Shaan Shirazi
From:
Austin, TX, USA
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Posted 18 Oct 2004 12:33 pm
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On my Vegas 400 the volume of the pop is directly related to how high the pre and post gain knobs are turned up when you flip the switch.
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The Pickin' Paniolo
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 18 Oct 2004 3:55 pm
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Ray, I have added a quote here which I got from "eopinions". It explains that capacitors DO DRY OUT. The liquid electrolyte turns to gas.
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"Capacitor life will vary on the quality of products used in the manufacturing as well as the heat of the system. Given a good material and low temperature, capacitors can be expected to last up to 32,000 hours of service. With some of the poor quality electrolyte, life expectancy has been reported to be as low as 200 hours! Not too great for an expensive component in your PC. Add some heat to this and it will go even quicker…
Capacitor electrolyte is important in the transfer of electrons, and therefore the utility of the capacitor. Electrolyte will dry out over time naturally, although sealing the system does help this somewhat. Excess heat on the system will accelerate drying out of the electrolyte and thus conversion of the liquid to a gas. As most people are aware, gaseous materials take up much, much more space than liquid. For instance:
1 cubic foot of water (or any other liquid, for that matter), in liquid form, contains 7.48 gallons of that material.
If you heat up the water to the point that it turns into steam (212 degree F, saturated), 1 lb of water now occupies 27 cu. ft. of volume!
That means that your original 1 cubic foot of water now occupies:
7.48 Gallons * 8.34 lb/gallon *27 cu. ft./lb = 1,684 cu. ft.
Why is this important? It explains the failure mode for the capacitors. Granted, each capacitor holds a very small amount of electrolyte, but as you can see when the electrolyte evaporates in the sealed system, the volume expands drastically, causing a failure(bulge or pop)."
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Mark Herrick
From:
Bakersfield, CA
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Posted 20 Oct 2004 2:10 pm
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I just posted this in another thread as well.
What Shaan said. Try turning down the reverb control also. This works on my Nashville 400. I turn down the Pre Gain and the Reverb controls before powering up or down and that diminishes the "pop" considerably.
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