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Old 13th June 2001, 12:56 PM   #11
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Default Elektor preamp

I will put up the PCB designs in the next couple of days - i will also try to put up the schematics

check back to this link in a couple of days:

http://www.winesafe.com.au/preamp.htm
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Old 13th June 2001, 01:00 PM   #12
jam is offline jam  United States
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Default Single -ended amplifier

Jason,

You are going to need a + and - 35volt rails, allowing for losses to achieve 45watts. If the amp uses mosfets this could be higher(27volt rails wont make it).
Another potential problem is that a single-ended class A amplifier has half the efficiency of one that has a complemenry output stage, further increasing current requirements. To get this all to work correctly requires a pretty large stack of batteries and caps.
Don't mean to rain on your parade but just be careful of the costs involved.
Good luck!

Jam

PS. What amplifier design are you using?

[Edited by jam on 06-13-2001 at 08:08 AM]
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Old 13th June 2001, 01:10 PM   #13
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Default Calculating Wattage

How do i calculate theoretical wattage of the class A SE amp at +- 27v rails?

I know the efficiency will be somewhere between very poor and abyssmal, but electricity is cheap and my house almost always needs heating anyway.

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Old 13th June 2001, 01:14 PM   #14
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Default Amplifier Design

The amplifier design has not previously been published - it was designed for me by a friend (a commercial amplifier designer). I will put up a schematic on my website when all things are looking shipshape.
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Old 13th June 2001, 01:17 PM   #15
jam is offline jam  United States
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Default Wattage

Jason,

Is your amp bi-polar or mosfet, and could you describe the topology?
As a rough guess I you would get about 25 to 27 watts, you have yo take into account the juncion drops of the devices used.

Jam

PS. There are more losses with mosfets because their turn on voltage is higher, which sometimes requires a higher supply rail for the front end.

[Edited by jam on 06-13-2001 at 08:24 AM]
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Old 13th June 2001, 03:48 PM   #16
mlloyd1 is offline mlloyd1  United States
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Cool Re: Elektor preamp

Smithy666:

Very nice work! What issues of Elektor was this project featured in?

Michael
mlloyd1@enteract.com

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Old 14th June 2001, 12:32 PM   #17
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Default Schematics are up...

Schematics for the preamp are up at http://www.winesafe.com.au/preamp.htm

The originals appeared in Elektor Jan/Feb 97 + updates in July/Aug 97

i will post my pcb files for the updates early next week
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Old 14th June 2001, 01:17 PM   #18
jam is offline jam  United States
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Cool Pre-Amp.

Smithy666,

Great looking circuit. I especially like the idea of buffering the volume and balance controls.

Thanks,
Jam
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Old 29th June 2001, 07:54 PM   #19
ALW is offline ALW  United Kingdom
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Default To solstice

I fail to see how a large capacitor bank helps.

The one thing I can guarantee is that as you draw current from a Lead-Acid it's terminal voltage is constantly, slowly, dropping. The rate of this drop is directly proportional to load current. Apply impulse loads and it behaves very strangely, as the chemical reaction inside the cell reacts.

This means it has a low frequency AC component to it's output, that cannot be eliminated. The capacitor bank will just result in a different profile to the load induced voltage steps. The capacitor bank cannot maintain a constant voltage, greater than that of the battery. Both will therefore drop under load.

The following image shows the FFT analysis of my own PSU, the two traces with humps are noise increases from the output capacitors on the regulators forming a resonant circuit with the regulator inductance.

The flat trace is the optimized supply.

Note that noise is at a very low level (-130dB!)

Click the image to open in full size.

Andy.

P.S. The other thing to bear in mind with battery supplies, is one needs a spare charged set, or an equally quiet supply for charging, unless one is prepared to be without music, or accept performance degradation when batteries require charging. Sounds like a lot of work for no reward
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Old 30th June 2001, 03:59 AM   #20
ppl is offline ppl  United States
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I used a Battery pack of 16 AAA's NI-MH Cells to Build My Portable Headphone Amp. During the Devolopment i noticed that Large capacitors were needed to give the Best bass reoproduction. I ended up with a bank of (4) 15,000uF per
rail. The Virtual ground is derived from using a Buffer as used in the Output Stage. In this mannor the Supply can Sink or source Current . The Ability to Have a low Impedance from the Supply is a requirement when Driving reactive loads like Transducers. Conventional single ended Regulators like the IC types used most often Do not sink Current as well as thay source so A Complimentry Type of regulator is Needed. Using Batteries and a Virtual ground Driver With Large capacitor Banks Will Both Sink and Source Current well.

Regarding Battery Supplies for High Power Loudspeaker amps Jeff Rolland has this as an option so i think there is Merit to Batteries.

Regarding the bandwidth of Typical regulators Those IC types Are Slow and Start rolling off at about 100-1KHZ. Improvement can be had with the Newer LTC fast Regs but still I Havent heared an IC regulator I like the Sound of. Morover The LM-317 & LM-337 become inductive at rather High frequencies tend to Be unstable and do inject lots of Noise.
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