Modifying Powersupply

KnightofAwesome · 28th May 2010, 10:48 PM

Hey all,

Since communication between me and Bora has slowed to a mysterious halt, I assume that I will need to ask my questions here for the time being.

I need plenty of help to get though my lack of knowledge of electronic theory.

I need to make sure that the out put with be +/- 36volts, and I'm unsure what alterations i will need to make in order to achieve this. Also what kind of transformer would i need to get this...

I also want to add some sort of LED to show that the power-supply is on.

I also don't know anything about selecting a proper 24volt relay, or choosing the values for that relay... (Talking about the two resistors with an asterisk and the capacitor)

I would also like, if possible, to have a +/-12volt rail for a "lightspeed"

Sorry for all the questions,
Kurtis

PS. the attachments go in-order from left to right
1. My assumed calculations, as well as a thyristor that i think would work
2. Board layout, beta stage, plenty of scale problems
3. original unchanged schematic

bob91343 · 29th May 2010, 02:56 AM

I don't really get it. You can get any voltage by scaling the transformer output voltage. The relay is overkill for a soft start; there are other ways. A simple lamp connected across any transformer winding will indicate power on. If you insist on using an LED just compute the required series resistor, and run it from a dc output.

I don't know what a lightspeed is. How much current do you need for it? That is all important regarding what sort of circuit you need to obtain the 12V.

KnightofAwesome · 29th May 2010, 03:53 AM

This is a lightspeed: DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

Regards,
Kurtis

amc184 · 29th May 2010, 04:58 AM

Both of the supplies in the attached pictures are totally inappropriate for a Lightspeed passive preamp. All the Lightspeed needs is a low power single supply.

I you are inexperienced with electronics, I would use a 'wall wart' power supply Use one outputting around 10 to 20VDC, and use the LM7805 circuit in the link you posted. You should be able to find one lying around, from an old computer router or similar.

bob91343 · 29th May 2010, 05:45 AM

You can use a simple divider or transistor regulator off the positive supply to get the voltage you need. Frankly, after reading the hype on lightspeed, I am not impressed with its design. It's too complicated and draws too much current.

But who am I to interfere with a legend, which this seems to have become.

amc184 · 29th May 2010, 06:04 AM

Sorry, I missed the bit about you adding the supply for the Lightspeed to the PSUs you posted. I assume you're building some sort of integrated amp.

The simple circuit I've attached will work, you only need a single 5VDC supply for the Lightspeed.

Don't use the board layout you posted, it's a shocker. Do a bit more research on how PCBs are best laid out before you attempt something like that.

KnightofAwesome · 29th May 2010, 07:23 PM

Quote:

Originally Posted by amc184

Sorry, I missed the bit about you adding the supply for the Lightspeed to the PSUs you posted. I assume you're building some sort of integrated amp.

The simple circuit I've attached will work, you only need a single 5VDC supply for the Lightspeed.

Don't use the board layout you posted, it's a shocker. Do a bit more research on how PCBs are best laid out before you attempt something like that.

I don't think you've attached anything to your post.

I'm not making anykind of integrated amp, I'm currently making Carlos's Blame ST

I'll spend some time researching PCB's too

amc184 · 29th May 2010, 11:47 PM

Here's the picture I meant to attach. If it's not an integrated amp, what's the +/- 36V for?

Don't take note of any of the numbers on the diagram below, they don't indicate pinout.

bob91343 · 29th May 2010, 11:51 PM

That regulator circuit is only good for very low load current, as the 31 Volts across it can cook the chip if the current is high enough. I was thinking to offer that but didn't try to calculate the required load current, or even verify that the chip can handle that high an input voltage. A series resistor at its input might be a good idea.

amc184 · 29th May 2010, 11:56 PM

It is within the rating of a LM7805T, but not by much. As long as it is heatsinked well it should be fine. The current load doesn't look to be an issue, just the voltage drop.

29th May 2010, 03:53 AM	#3
KnightofAwesome diyAudio Member Join Date: Mar 2010 Location: Vancouver	Thank's for your help so far This is a lightspeed: DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers) Regards, Kurtis

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29th May 2010, 02:56 AM	#2
bob91343 diyAudio Member Join Date: Mar 2010	I don't really get it. You can get any voltage by scaling the transformer output voltage. The relay is overkill for a soft start; there are other ways. A simple lamp connected across any transformer winding will indicate power on. If you insist on using an LED just compute the required series resistor, and run it from a dc output. I don't know what a lightspeed is. How much current do you need for it? That is all important regarding what sort of circuit you need to obtain the 12V.

29th May 2010, 04:58 AM	#4
amc184 diyAudio Member Join Date: May 2007 Location: Christchurch	Both of the supplies in the attached pictures are totally inappropriate for a Lightspeed passive preamp. All the Lightspeed needs is a low power single supply. I you are inexperienced with electronics, I would use a 'wall wart' power supply Use one outputting around 10 to 20VDC, and use the LM7805 circuit in the link you posted. You should be able to find one lying around, from an old computer router or similar.

29th May 2010, 05:45 AM	#5
bob91343 diyAudio Member Join Date: Mar 2010	You can use a simple divider or transistor regulator off the positive supply to get the voltage you need. Frankly, after reading the hype on lightspeed, I am not impressed with its design. It's too complicated and draws too much current. But who am I to interfere with a legend, which this seems to have become.

29th May 2010, 06:04 AM	#6
amc184 diyAudio Member Join Date: May 2007 Location: Christchurch	Sorry, I missed the bit about you adding the supply for the Lightspeed to the PSUs you posted. I assume you're building some sort of integrated amp. The simple circuit I've attached will work, you only need a single 5VDC supply for the Lightspeed. Don't use the board layout you posted, it's a shocker. Do a bit more research on how PCBs are best laid out before you attempt something like that.

29th May 2010, 11:51 PM	#9
bob91343 diyAudio Member Join Date: Mar 2010	That regulator circuit is only good for very low load current, as the 31 Volts across it can cook the chip if the current is high enough. I was thinking to offer that but didn't try to calculate the required load current, or even verify that the chip can handle that high an input voltage. A series resistor at its input might be a good idea.

29th May 2010, 11:56 PM	#10
amc184 diyAudio Member Join Date: May 2007 Location: Christchurch	It is within the rating of a LM7805T, but not by much. As long as it is heatsinked well it should be fine. The current load doesn't look to be an issue, just the voltage drop.

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