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Old 13th May 2004, 09:04 AM   #1
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Default ok, i'll try and make it simple.

i can not see any other power supply on that schematic. the only supply is 12vac which feeds straight to the tube. someone on the forum built one of these. . . had the 12ax7 burn out after a couple of months they said. the amp runs like this;

input>latching push button switch channel select> 2 seperate identical channels with gain, level, 3 band eq, etc> master post gain> tda7294v poweramp chip > 100w 8ohm marshall MG4x12 angled cabinet ok?

So I was just looking for a safer way to use valves, because maplin siad it could be used as a low voltage pre-amp???? (the ecc83 on the www.maplin.co.uk website) And to know where I could get transformers to go from 220v to whatever I will need to run the valves, 300VAC? and to ask what +-10 to 42vcc meant, which is the rating for the poweramp chip. Is that DC 10 to 42 volts?
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Old 13th May 2004, 11:33 AM   #2
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OK, it's fairly clear what you want to do- and I'm going to tell you not to do it. Tube amp design and construction is hazardous, it involves voltages (and sometimes parts) that are potentially lethal. From the nature of your questions, you've got close to zero experience. Nothing wrong with that, that's how we all start. But zero experience + hazardous circuits + no supervision = great hazard to life and limb.

If you want a tube preamp, go buy a tube preamp. In the meantime, start learning about electronics playing with chips and transistors. Once you've got the basics of design, construction, and (most of all) safety, once you've burned up your share of small, inexpensive parts, then you'll be ready to tackle this.
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Old 13th May 2004, 06:35 PM   #3
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Default I'm not as naive as you think. . . Well not quite. . .

I'm not completely unkowing.
I've been using Electronics since I was six, When I began modifying my laptop. . . The fun way. . . I've virtually built a laptop out of a 1994 amiga, I cant source a screen but thats it (If you're wondering, I dont mean plugging connectors in, I mean via soldering iron.) I know all about safety, I know all about the hazards, I was intending on isolating the guitar circuit from the amp using opto-isolators if possible, use a circuit breaker at all times, earth all metal surfaces, you name it, I wasnt going to use it until I had a wireless system so that i could completely seperate myself from the amp by 6 feet or so, I was just wondering about voltages because Half the amps I've looked at ran on 12 volts AC, The Stack-in-a-box by www.piai.com or something, and 10 odd homebuilt projects off the net. here we go www.piai.com/siabsch.pdf And proof that the damn thing runs on 12Volts. I try not to talk crap. I always check it out first, which is WHY im asking for help on the forum? So theres no need to give an overstated opinion of my naivity. And I told you. They dont sell What I'm looking for!

Which is this:
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Old 13th May 2004, 06:37 PM   #4
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Default P.S.

I take it you dont know what "+-10 to 42vcc" means then? Which was what I asked. I didnt think that was an unreasonable question. Please dont reply with an opinion, just answer my question, I beg of you.
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Old 13th May 2004, 07:18 PM   #5
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Hi,

Quote:
I take it you dont know what "+-10 to 42vcc" means then?
It could mean crete a crete which is French for peak to peak.

Without further context it's just guesswork anyway.....

Cheers,
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Old 13th May 2004, 07:35 PM   #6
SY is offline SY  United States
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Quote:
It could mean crete a crete which is French for peak to peak.
More likely the allowable supply voltages for the amp chip.
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Old 13th May 2004, 09:53 PM   #7
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Default Right, got ya. . .

So, does the little
+
-

symbol next to it mean that it's DC? or AC? Or something completely different? Thankyou for keeping it simple guys
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Old 13th May 2004, 09:57 PM   #8
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If it's a power opamp, it probably has a positive and a negative supply, both of which are DC. This is probably telling you that you can run the chip off of +/-10V (that is, +10V on the +ve supply and -10V on the -ve supply) through +/-40V (likewise, +40V on the +ve supply and -40V on the -ve supply).

Without seeing the datasheet for the chip, this is a guess.
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Old 13th May 2004, 09:58 PM   #9
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Here's the datasheet:

http://www.datasheetcatalog.com/data...TDA7294V.shtml

You should be able to get most of your answers from here.
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Old 13th May 2004, 10:04 PM   #10
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Quote:
I'm not completely unkowing.
Can you be specific about every circuit you are interested in adapting (manu, model #)? I'm sure I'm not alone in not wanting to spend intellectual effort on a rather ambiguous request which will most probably be transformed in midstream due to its unformed initial nature, resulting in a waste of my time.
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