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Old 1st May 2010, 12:21 AM   #1
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Default Preamp and Chip Amp from same power supply

I'm building a Chip Amp based on a LM3875 (from AudioSector.com) and would like to integrate a preamp (the Death of Zen preamp from Rod Elliot's site) using the same power supply as the amp itself.

Is this a matter of making a lead off the PS board and using a couple resistors to bring the voltage to where it needs to be, or should I think about an entirely separate PS board for the preamp?

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Old 1st May 2010, 10:12 AM   #2
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A separate PS is the solution with the highest potential to sound good. A couple of resistors only is the exact opposite. Depends on your demands on sonic quality. A better approach is to add some voltage regulators. At least use some Zener diodes like Rod Elliott does in Figure 6 in his Project 115
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Old 1st May 2010, 10:29 AM   #3
Mooly is online now Mooly  United Kingdom
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If the supplies are correctly implemented there is no problem using the same supply as the main amp. If the supplies in the main amp effect the preamp then it's the implementation that's wrong, not the principle.
That means suitable regulation, perhaps simple discrete series pass and then an IC or zener shunt if the current requirements are modest.
Grounding is (very very) important too and must be correct.
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Old 1st May 2010, 02:30 PM   #4
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Ok, thanks for the input.

I want to keep this project as error-proof as possible since I'm new to building amps, so would it be a bad idea to skip the active preamp and instead go for a passive version consisting of an input selector and volume control? I've read different things about chip amps needing an active preamp, people both for and against it. The integrated amp described on the audiosector site doesn't have one, so it seems like it should be fine.

If it is recommended, do you guys have any recommendations about where I can read up on how to implement the single power supply to provide for both boards (the suitable regulation, discreet series pass, zener shunt, and the very very important grounding) as Mooly mentioned?

Many tips of the hat.
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Old 1st May 2010, 04:46 PM   #5
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Quote:
Originally Posted by fingersoccer View Post
I've read different things about chip amps needing an active preamp, people both for and against it. The integrated amp described on the audiosector site doesn't have one, so it seems like it should be fine.
A chipamp does not necessarily need a preamp. Try it without first and add the preamp later, if you are not satisfied with the result.


Quote:
Originally Posted by fingersoccer View Post
If it is recommended, do you guys have any recommendations about where I can read up on how to implement the single power supply to provide for both boards
There is a link in my previous post.
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Old 1st May 2010, 05:49 PM   #6
AndrewT is offline AndrewT  Scotland
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Yes, I agree with Pacific.
Learn how to build a simple chip power amp. Find out how you could package it once you see the size of the assemblies. Then think about the extra space needed for the selector/pre-amp stages. Finally buy a chassis to hold a power only amp or big enough for the full integrated amp.

Do the initial bit in small achievable stages.
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Old 16th August 2011, 04:26 PM   #7
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OK, what about buying a voltage regulator module from eBay (DC-DC Converter Board Voltage Regulator Stepdown Module) to regulate the voltage to the preamp? This seems like something that any idiot could figure out (which is important to an idiot such as myself), but I want to make sure I have the right idea here.
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Old 16th August 2011, 04:52 PM   #8
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by fingersoccer View Post
OK, what about buying a voltage regulator module from eBay
Quite an old thread...

Not what you want tbh

What are the voltage requirements for the preamp ?
How much current ? Preamps are usually in the 10's of milliamps at most.
Do you want to run it off the main chip amp PSU if possible ?
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Old 16th August 2011, 05:19 PM   #9
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Mooly, thanks for the quick response.
The preamp I'm planning on building is the Rod Elliot Project 37a Death of Zen Preamp. Current requirement is <10ma, voltage requirement is 15V.

I'm working on an integrated amp, so using the amplifier's power supply would be ideal. I know I need to knock the voltage down to around 15V, but I'm not entirely sure how to do so.
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Old 16th August 2011, 05:27 PM   #10
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All you need is a simple zener regulated supply for that current and voltage. It's as easy as it comes and performance is excellent.

Two 15 volt zeners, two resistors and two caps...

I can draw it for you later if no one beats me to it
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