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Is it normal "not" to have any turn on thump?
Is it normal "not" to have any turn on thump?
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Old 4th September 2002, 01:39 AM   #1
Duo is offline Duo  Canada
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Default Is it normal "not" to have any turn on thump?

I recently built a 600watt 4ohm amplifier with a 5kva power supply. When I turn it on, the lights quickly dim out like I expect, but I hear absolutely nothing, just utter silence, and there's no hiss even right close to my speaker. I know the amp is working fine cause I've loaded it down to 1.3ohms and run at about 1100watts no problem at all. It get's hot but that's to be expected... All I wonder about is, "Is it normal for a simple project amp to be so good that it stabilizes instantly and has no DC offset whatsoever, even just biased with a voltage divider/diode network???
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Old 4th September 2002, 01:43 AM   #2
jwb is offline jwb  United States
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What is the design of the amp? If it was a balanced and bridged design I would not expect any turn-on thump at all. Or perhaps you have simply done all the right things
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Old 4th September 2002, 02:52 AM   #3
Lisandro_P is offline Lisandro_P  Argentina
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Well, no, it's not normal for *most* amps, but some desings have negligible turn-on and off transients. If yours is one of them, congratulations! cool:
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Old 4th September 2002, 03:04 AM   #4
Peter Daniel is offline Peter Daniel  Canada
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Is it normal "not" to have any turn on thump? Send a message via AIM to Peter Daniel
One amp that has absolutely no turn on thump is A75.
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Old 4th September 2002, 03:33 AM   #5
roddyama is offline roddyama  United States
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Hi Duo

Quote:
When I turn it on, the lights quickly dim out like I expect...
I hope you not talking about your house lights dimming!

That would be some current draw.
Rodd Yamas***a
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Old 4th September 2002, 03:40 AM   #6
Samuel Jayaraj is offline Samuel Jayaraj  India
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Duo,

Congratulations! Fantastic job.

My experience is that most amplifiers behave differently at switch on, with different power supplies. If you were to have a totally different power supply for the amp that you describe, it could show some turn on thump. It depends on the variables at play and the intensity of the thump tends to vary.

By the way, which circuit did you use. Is it your own design or some well known design, modified. Especially, the loading down to 1.3 ohms sounds very interesting (read, intriguing). If you don't mind, could you please provide some details here. Thanks.
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Old 4th September 2002, 04:14 AM   #7
Duo is offline Duo  Canada
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Roddyama: yes, it dims all the lights on it's circuit, the pwr supply is 5kva so it takes a lot to get the transformer going. Also, when running into 1.3 ohms, it could almost shut the lights off if I had enough speakers to put on it.

Samuel Jayaraj: I will provide some more info when I can draw I diagram on the computer. The amp right now is just a big buffer with out much for a VAS stage. I hard wired it with 10 gauge solid copper wire so there is minimal current loss and you can't accidentaly bend the wires out of place without pliers. The design is very much similar in the output stage to ESP project 3A, But the rest is my own ideas. I never thought the amp would be so stable into such heavy loads, especiall since the supply voltage is 160volts rail to rail and it's my first amp! however, It has excellent sonic quality and I plan to make lots of documentation on it soon so keep your eye on here.
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Old 4th September 2002, 09:45 PM   #8
skaara is offline skaara  Slovenia
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Post a scheme..
I think its normal to have no turn on thump if it works...
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Old 5th September 2002, 01:40 AM   #9
Duo is offline Duo  Canada
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Well... not nessecarily, rarely you'll find an amp that stabilizes instantaneously upon application of power. You can usually hear some kind of little blurp or tick when you turn it on, but mine is silent. Once in a while, I can turn it on and it might make a very very quiet blip noise but it's not even an 8th of a second long and you can barely hear it even if it does make a bit of noise.

by the way guys, I remember the numbers on the transistors I used for output now. The main O/T's operate in push pull and use 3 each of B688 and D718, operating with compound pair drivers. Today I ran the amp steady into 2ohms for about an hour with about 35volts output and got enough undistorted volume to make the garage door visibly shake and the lights flash quite a bit. It was actually, believe it or not, too loud for me to sit right in front of the speakers, I had to stand off to the side or outside of the garage or I just couldn't handle it.
I'm amazed I've gotten these specific transistors to handle a two ohm load through steady music using power supply rails of +-80 volts... What do you guys think about this? Do you think these particular transistors should normally handle this in this kind of design???
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Old 5th September 2002, 01:42 AM   #10
Duo is offline Duo  Canada
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Hey roddyama, what's that picture in your avatar of? I can't figure out wether it's a pilot in a plane, or a racecar driver or what... What's the guy doing?
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