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 Post subject: Re: Hi from Atlanta
PostPosted: 03 Sep 2008, 02:56 
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Joined: 29 Jul 2008, 08:12
Posts: 182
Location: Wiltshire, UK
Hi Bill.

It's good to see you here. I'm a very new DIYer so I'm sure you may be answering some of my many questions later on.

I look forward to reading about your future projects.

Kind regards, John. Salisbury, UK


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 Post subject: Noob from Boston
PostPosted: 14 Sep 2008, 15:29 
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Joined: 10 Sep 2008, 19:54
Posts: 22
Location: Boston
Hi all.

I'm a Junior computer engineering student at Boston University, looking to get my electrical chops up. I found the site looking for a way to build myself an amp for my home theatre setup. I'm a somewhat miserly nerd who really appreciates a good quality piece of electronics, and I love movies, music, and videogames. Until recently, i've been very happy with my creative gigaworks system, but this summer it bit the bucket.

I've had a class in circuit theory, and I've been a tinkerer since I was a little kid, but I think I'll need some guidance on where to start here. I've never attempted a 120 VAC project and I'm a little intimidated about plugging something that I built into the wall. I have a small multi-tester and a soldering iron, and I've done some small personal projects including replacing an op-amp in a small 2.1 system which has temporarily replaced my surround but in looking for a good quality replacement on a tight budget I decided that the best way for me to be sure I was making the right choice would be to be in total control.

My computer system is home-built, the shelf for my TV and my consoles is made out of plywood, drywall screws and 2x4s, and I think it would be quite a cool project to build myself an amp for my surround system.

I have an external decoder (the Creative DTS-100) which outputs 8 channels of discrete surround, and I have the 5 sattelites and the sub from my gigaworks, all I need is a set of analog amps to put out the signal.

I like what i've seen of the DIY projects on this site, and what I've seen elsewhere, but I'd feel a lot better having someone to hold my hand through the process of choosing a kit (or designing my own custom device) and putting it together.

I guess it would be appropriate to put forth some questions:

1. I know numbers and specs can be decieving. And it seems that the most important (RMS) can be the most decieving. The gigaworks S700 boasted a total 560 Watt RMS for the whole system (90 watts per sattelite and 110 for the sub) and as far as volume was concerned they were totally satisfactory. I know the "efficiency" of the drivers comes into play, and obviously the resistance of the speakers themselves will affect the output of the circuit. But from what I understand not all 500W systems are created equal and I've never really been able to get a thorough answer as to why.

2. What are the safety procedures for working with 120 volts? If the circuit is grounded am I safe from shock? What levels of current are *really* dangerous? If i short a circuit with my hand behind a 5 amp fuse am I in danger?

I'm going to go do some research into how vacuum tubes and chip amps work, and will probably come back with more, but any nudges in the right direction would be appreciated. I look forward to this project and I hope to learn a bit from the experts :)


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 Post subject: Re: Noob from Boston
PostPosted: 14 Sep 2008, 23:10 
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Joined: 28 May 2008, 21:53
Posts: 4530
Location: Winnipeg, CANADA
Hi sconeman,

I went the Civil route and my only course was first year electrical science.

WRT safety, it does not take all that much current to be lethal.
http://en.wikipedia.org/wiki/Electric_shock
A fuse is going to protect the circuitry, not you. The ground is there to keep a conductive chassis from going hot. Always be very carefully when checking equipment that is live. Also, it is best to start with projects other than tubes until you are comfortable.

For your first question, the RMS is often instantaneous peak power. Take apart the old system. Then look at the fuse. We know P=IV. So for 560W at 120V, you would be looking at a min 5 or 6A fuse. My bet is was not that large. Anyway, you might be able to salvage some it and get a decent transformer or heat sink from the dead unit.

It sounds like all you will need 6 channels. Chips, Class T and for the sub Class D are good choices. There are a lt of kits out there that are suitable for the beginner.

Did you have any idea on where you wanted to go first? A kit is a good place to start.

Welcome to the forum.

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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 Post subject: Re: Noob from Boston
PostPosted: 15 Sep 2008, 09:22 
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Joined: 10 Sep 2008, 19:54
Posts: 22
Location: Boston
Thanks for the reply.

I'd like to get started, is where I'd like to go first! :)

I think I probably can salvage some good stuff from the dead unit. It is a 6A fuse (slow-blow? what exactly does that mean anyway?) I know it uses a BASH amp for the sub, and from what I've read those are choice components. My guess is that the issues it was having were in the power circuit (since that is where the sparks came from when I opened it up, hence my safety concerns).

What exactly do Class T and Class D mean? I'll go ahead and look that up on wikipedia, but maybe an explanation from a real person will make more sense :) What kits would you reccommend? If I can find the part numbers from the more important components I already have (is a solid-state amp just based around a large op-amp?) can people here help me design a circuit around those?

More specifically, does it behoove me to put high-pass/low-pass filters in the unit for separation of sub/satellite channels? I presume that since the signals are discrete I won't have to set a cut-off frequency for the sub electronically but will I lose performance in the highs if they also have the low-frequency signal (if, for example, I wire the device to take a stereo input for my ipod...)

So i guess first I'll try to find out what components I already have and report back. Should I continue the thread here or should I start a new thread elsewhere?


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 Post subject: Re: Noob from Boston
PostPosted: 15 Sep 2008, 10:41 
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Joined: 28 May 2008, 21:53
Posts: 4530
Location: Winnipeg, CANADA
Bash amps are good. Start a new thread and post some photos of the parts you can salvage. Look at what you have on hand before you pick a kit to go with.

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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 Post subject: Hi Noob Here
PostPosted: 14 Oct 2008, 13:08 
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Joined: 14 Oct 2008, 12:46
Posts: 1
Hello everyone im new to the forums and speaker building to be exact. I was just wondering how do you go about learning about all the different components in speakers and how to build crossovers etc. I really wanna start building my own speakers. So if someone could point me in the right direction that would be great.


thanks


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 Post subject: Re: Hi Noob Here
PostPosted: 14 Oct 2008, 13:38 
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Joined: 26 Aug 2008, 20:57
Posts: 415
Location: Atlanta
Crossover design is something of a black-art. Personally I would suggest just building a pair of single driver full-range for a first project and then delving into the dark-side if you feel it necessary.

There are programs out there that will help you with crossover design but the problem is still the amount of experimenting required to get it "just right".

I would suggest if you seriously want to build crossovers to acquire yourself a parts bin of various capacitor, resistor and coil values so you can experiment. They do not have to be expensive parts...just something to use until you get it right and then you can purchase the higher quality parts when you do the final build. If you don't do this you could end up spending hundreds of dollars on a crossover or just settling because you don't want to pay the price to buy different parts.

As far as basics:

Capacitor- Simple 6dB/octave high pass filter.
Coil-Simple 6dB/octave low pass filter.

1st order-

6db/octave filter using a cap on the high pass and a coil on the lowpass

2nd order-

12dB/octave filter using a cap and coil on each:

High pass:

---C----(+)
-------L
---------(-)

Low pass:

----L----(+)
-------C
----------(-)

It then gets further complicated.


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 Post subject: Re: Hi Noob Here
PostPosted: 14 Oct 2008, 19:31 
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Joined: 28 May 2008, 21:53
Posts: 4530
Location: Winnipeg, CANADA
Hi Drummer, welcome to the forum.

The wikipedia is a reasonable place to start:
http://en.wikipedia.org/wiki/Audio_crossover
That will give you the basics and there are a ton of links to follow if you want to get more detail.

Cheers,
Gio

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 29 Oct 2008, 08:39 
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Joined: 29 Oct 2008, 08:33
Posts: 1
Location: Brasil
I had informations the people here is more educated, less snobish and more friendly... reason why i am here.

be happy guys.

I am from Brasil Northeast.

57 years old folk

bye

Carlos


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PostPosted: 29 Oct 2008, 08:58 
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Joined: 06 Jun 2008, 20:12
Posts: 971
Location: Houston, TX
Hi Carlos and welcome to DIYAUDIOPROJECTS :)
Glad to have you here. We do not have a discrete expert here and it will be nice to have your ideas and advice to learn from.
Many chip builders here but it seems that our most active members are tube enthusiasts.
I love tubes to, but the voltage gives me a scare right now.
Thanks for stopping by. Hope you plan to stay.
Ri

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