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Old 26th January 2012, 04:57 AM   #1
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Default Beginner amplifier project

Does any one have and schematics they recommend for a nice beginner project? Preferably something that revolves around an LM386 or TL072.
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Old 26th January 2012, 09:42 PM   #2
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For the LM386 you can use national's circuits, see page 5 of the datasheet.
Easy, cheap and fun to build, and also works well on a breadboard so you can goof around with components to see what does what.

Have fun!

http://www.ti.com/lit/ds/symlink/lm386.pdf
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Old 26th January 2012, 09:42 PM   #3
! is offline !  United States
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Suppose for a moment that you like what you end up building and find a use for it. What would be useful to build? TL072 by itself is just a low power opamp. It will do a terrible job of driving headphones and not much else except in an input or filter stage of another amp.

LM386, kind of dinky thing too which has its purposes but you could build a significantly more powerful amp at minimal extra expense and complexity.

So the question is how many watts into what speaker load (or what general purpose is the same), and at what general price range for just the amp without considering the case, connectors and other hardware?

I suppose a beginner project would be better if safer, if dealing with power rail voltages under about 30V rail to rail and using an AC-DC wall wart (unregulated power adapter brick) or batteries for power so you aren't dealing with exposed high voltage mains AC power yet.

Do you have any spare parts you'd like to use to speed up the build or cut costs? Any spare power bricks rated higher than 12VDC? Even if not, how about an 11W/ch stereo chipamp based on LM4752? That's enough power for driving reasonably efficient computer speakers to unlistenably loud levels (if seated nearby) with minimal external part count and expense.

Here's the datasheet for that, http://www.ti.com/lit/ds/symlink/lm4752.pdf

if you just build the whole "System Application Circuit" as-is on page 7 and powered it with an unregulated 12VDC/1A power brick it should bring more satisfaction than LM386 would but at only 12VDC (a little higher in use) it would lie between LM386 and it's 11W rated output power. Costs about $2 more than LM386 though and will need a small heatsink. Digikey is out of the through-hole version but Mouser has some, Mouser Electronics - Electronic Component Distributor LM4752

Last edited by !; 26th January 2012 at 09:45 PM.
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Old 28th January 2012, 03:54 AM   #4
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Probably should of given a little more background. I just finished a dual rail p/s +15vdc and -15vdc. I also made a 20vdc adjustable p/s and am looking for another easy project. I have a few different 6ohm speakers that i will be using.
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Old 28th January 2012, 04:01 AM   #5
djoffe is offline djoffe  United States
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You could buy a set of the upgrade boards for the old Dynaco stereo 120, but add your own 72 volt regulated supply. These boards are based on LM3886's. You can order the super heat sinks (super is a relative word, in comparison with the stock Dynaco heat sinks).

Even if you decide that's not your cup of tea, you may find other valuable information here:

Update My Dynaco

And yes...it's my web site...my apologies in advance for the shameless plug!
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Old 28th January 2012, 04:25 AM   #6
GloBug is offline GloBug  Canada
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Whats the voltage of the Dynaco power transformer?
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Old 28th January 2012, 01:22 PM   #7
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someone could work with an outline of a preamp tones. Thanks in advance. from Colombia nandoball30 ...hjbd7621@hotmail.com
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Old 28th January 2012, 02:38 PM   #8
djoffe is offline djoffe  United States
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The Dynaco power transformer has a chip side voltage rating of about 66 Volts RMS. That makes a lightly loaded peak voltage of about 94 volts on the input to the regulator. The regulator drops about 22 volts to product 72 volts DC that feeds the amplifier modules.
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Old 28th January 2012, 03:15 PM   #9
GloBug is offline GloBug  Canada
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Sorry for thread jacking. The reason I ask is I have been restoring an old Bryston, finding reliable transistors and the rest of my parts at one place with one payment method is tricky blah blah blah. Anyhow so now I am thinking of replacing the amplifier boards with something newer, etc along the lines of your conversion.

The transformers I have are 70V center tapped (Possibly 77vct) I figured this to be to high for the more traditional gainclone voltage.

I have started looking at other chips etc, although if I could use some LM3886 etc it would be great.

The transformers ares decent, each are labeled 250VA, although the bottom of the amplifier read 960VA, either way they are decent.

This is the really old 3B so I think the gainclone would sound better.

I need to do something high powered to take advantage of the iron etc. I have or I will have to get the transistors etc and restore it like I have been doing.

A gainclone conversion would cost less compared to replacing 8 transistors wit decent ones. I actually only need 2, but ideally I would replace all 8 with similar manufacture date etc.

I noticed they have some 3 channel chips and in the block diagram it looks like internally the op amps get their voltage in series with one another. lol it would be handy to do that with separate chips.
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Old 28th January 2012, 03:23 PM   #10
djoffe is offline djoffe  United States
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What is the unregulated DC (lightly loaded) voltage out of your transformers?
Also...does the amp have two transformers, and is it set up as one for each channel?
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