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?
Thanks!
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?
Thanks!
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
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.
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.
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.
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.
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.
There is a link in my previous post.
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.
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.
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.
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 ?
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.
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.
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 🙂
Two 15 volt zeners, two resistors and two caps...
I can draw it for you later if no one beats me to it 🙂
Mooly, I WOULD SHAKE YOUR HAND RIGHT NOW IF I COULD. I've seen schematics of zener regulated supplies, but they seem fairly project-specific and I don't know how to calculate what values I would need for the components.
Here's the circuit.
The two zener diodes determine the rails so that's two 15 volt zeners for -/+15 volts.
The resistors are calculated as follows...
Supply =30 volts (substitute what yours actually is). We call that Vsupply
So each resistor has to drop Vsupply minus Vzener. So that's 30-15=15 volts. That's the voltage that appears across each resistor.
If we choose a low wattage zener, say a 0.5 watt then the maximum zener current allowed is I=W/V which is 0.5/15 giving 33 milliamps.
So the lowest value resistor we can use (allowing for the supply to be safe wuith no load) is R=V/I which is 15/0.033 giving 454 ohms. Play safe and choose next highest common value which is 470 ohms.
Resistor wattage is W=V squared/R which is (15*15)/470 giving 0.478 watts. A 0.6 watt metal film would be fine or a 1 watt carbon.
Your preamp uses about 10milliamps. Lets play safe and say it uses 20milliamps. That means that of those 33 milliamps flowing in each zener, whatever the preamp wants will come out of that. So if it did use 20ma that still leaves 13ma for the zener which is perfect. As long as there is a couple of milliamps for the zener the supply is regulated. If the preamp drew more than 33 milliamps then we would have to rescale things.
The caps are around 10 to 100uf 25 volts... not critical.
The two zener diodes determine the rails so that's two 15 volt zeners for -/+15 volts.
The resistors are calculated as follows...
Supply =30 volts (substitute what yours actually is). We call that Vsupply
So each resistor has to drop Vsupply minus Vzener. So that's 30-15=15 volts. That's the voltage that appears across each resistor.
If we choose a low wattage zener, say a 0.5 watt then the maximum zener current allowed is I=W/V which is 0.5/15 giving 33 milliamps.
So the lowest value resistor we can use (allowing for the supply to be safe wuith no load) is R=V/I which is 15/0.033 giving 454 ohms. Play safe and choose next highest common value which is 470 ohms.
Resistor wattage is W=V squared/R which is (15*15)/470 giving 0.478 watts. A 0.6 watt metal film would be fine or a 1 watt carbon.
Your preamp uses about 10milliamps. Lets play safe and say it uses 20milliamps. That means that of those 33 milliamps flowing in each zener, whatever the preamp wants will come out of that. So if it did use 20ma that still leaves 13ma for the zener which is perfect. As long as there is a couple of milliamps for the zener the supply is regulated. If the preamp drew more than 33 milliamps then we would have to rescale things.
The caps are around 10 to 100uf 25 volts... not critical.
Attachments
Mooly's circuit should be good enough.
I am taking +15/-15V (for buffers/preamp) from +35/-35V (for chip power amp) using a portion of Rod Elliot's Power Supply for Preamps after passing through Pre-Regulator
I am taking +15/-15V (for buffers/preamp) from +35/-35V (for chip power amp) using a portion of Rod Elliot's Power Supply for Preamps after passing through Pre-Regulator
To back up Mooly's idea, i have also implemented this zener circuit into my own project without fault. The idea of pre-amp, a few board members made suggestion i wouldn't need one for my chip amp, maybe true that, but i did anyway and found i was able to gain a few more cleaner db's out my project.
rick
rick
You could consider adding a RC or LC filter after the zeners, to suppress any noise still present and stabilize the supply a little bit more.
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