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Old 5th September 2012, 06:20 PM   #18381
Puffin is offline Puffin  United Kingdom
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Quote:
Originally Posted by mcd99uk View Post
Experiment conducted. It seems, Ray, you were correct. I have learnt something. I tried making a single turn loop of different sizes using the scope leads and could see a difference in noise measurement. Conclusion there is still noise but not as much as I thought.

While I was at it I decided to complete the component changes detailed on your PDF. Now I'm ready to start creating and adding regulators. Was thinking that the DAC should get 4 LT317 based regs and the Opamps get 2 LT317 + 2 LT337 based regs as well. The rest of the CD player will get LM317 regs.
Just remembered that I built one of these (see schematic) just to see if I could. Have never used it ad had forgotten about it. Have tested it with 12v and it drops it nicely to 5.5v. However if you take your power for the regs from C814 (I think from memory) it only gives just over 10v, fine for a 7805, but not for this application. I suspect that with a change of resistor it could be made to fit.

Click the image to open in full size.

The schematic says min of 9v, so will try a 9v battery to see what output is.
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Old 5th September 2012, 07:10 PM   #18382
6h5c is offline 6h5c  Netherlands
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Originally Posted by Puffin View Post
What you have to realise is that I am now blind and stupid through years of solder sniffing Now I know why I could not get a reading off the resistors (even when off the board) using 20k setting!!!

Ah well.....more regs to go

Rob.
Yes, that's because it's a very low value

Quote:
Originally Posted by Puffin View Post
Stupid question/quote time: I thought that the resistor was dropping the voltage from 12v to 5v?
No, the whole thing is running on 5V. The resistors are in series with the 5V supply to each IC, dropping only very little voltage because their value is so low, and the current is not very high.

The resistor + the capacitor behind it act as a low-pass RC-filter that blocks HF noise and thus provides some separation of the various circuits. The resistor also acts as a fuse, it is a special non-flammable type that will burn out in case of a defective IC without setting the player on fire .

Ray
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Old 5th September 2012, 07:16 PM   #18383
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Quote:
Originally Posted by Puffin View Post
Just remembered that I built one of these (see schematic) just to see if I could. Have never used it ad had forgotten about it. Have tested it with 12v and it drops it nicely to 5.5v. However if you take your power for the regs from C814 (I think from memory) it only gives just over 10v, fine for a 7805, but not for this application. I suspect that with a change of resistor it could be made to fit.

Click the image to open in full size.

The schematic says min of 9v, so will try a 9v battery to see what output is.
I see, the output of 5.5V is too high actually. That's because the output voltage is set by the LEDs, and in practise they give almost 4V the two, instead of 3.8V. Changing the resistor won't help, but using one red and one green LED will

If it says 'minimum 9V' at the input, why do you think it won't work on the 10V from C813?

Ray
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Old 5th September 2012, 07:17 PM   #18384
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Originally Posted by 6h5c View Post
Yes, that's because it's a very low value



No, the whole thing is running on 5V. The resistors are in series with the 5V supply to each IC, dropping only very little voltage because their value is so low, and the current is not very high.

The resistor + the capacitor behind it act as a low-pass RC-filter that blocks HF noise and thus provides some separation of the various circuits. The resistor also acts as a fuse, it is a special non-flammable type that will burn out in case of a defective IC without setting the player on fire .

Ray
Thanks very much for the info and sharing your knowledge.

Rob.
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Old 5th September 2012, 07:18 PM   #18385
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You're welcome!
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Old 5th September 2012, 07:19 PM   #18386
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I see, the output of 5.5V is too high actually. That's because the output voltage is set by the LEDs, and in practise they give almost 4V the two, instead of 3.8V. Changing the resistor won't help, but using one red and one green LED will

If it says 'minimum 9V' at the input, why do you think it won't work on the 10V from C813?

Ray
Once again thanks for your reply. I had assumed that as I had 5.5v from 12v I would get less output from 10v.
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Old 5th September 2012, 07:45 PM   #18387
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Noooo..... the circuit is a regulator, not something that just drops some voltage .

It's not like a resistor, that drops a fixed amount of voltage, depending on the current that runs through it, and the value of the resistor itself. That is called Ohm's Law, and it is V = I x R for a fixed value resistor.

The regulator circuit, on the other hand, holds the output voltage constant, independent of the input voltage or the load current. It compares the output voltage to a fixed reference voltage, and regulates the output voltage back to the desired value if the load or input voltage changes.

The reference voltage is usually an internal source, like an integrated zener. With the 7805 for example, the output voltage is pre-set to a fixed value and it's ready to use. The LM317 has an adjust pin, which gives access to some of the internals of the IC and that allows you to set the output voltage yourself. Usually this is done by two resistors, but you can also use an external zener, or some LED's to set the output voltage.

So, in short, if you connect this circuit to any voltage from 9V to 35V, it will give 5V output. Great, eh?

Ray
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Old 5th September 2012, 08:00 PM   #18388
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Mega!

You know so much, can we get married?

By the way, would 5.5v be too much for the 63? I will change to a red led if neccessary.

Rob.
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Old 5th September 2012, 08:29 PM   #18389
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Oh, yes, no problem, i'm not married yet! Sounds good, Rob and Ray. But only on the forum, ok?

5.5V is a bit too high for most IC's, it is the maximum supply voltage for some types. It's better to go for a 5V nominal voltage, that way there wil be some room for component tolerances.

The problem with using LEDs is that you have to find the right combination to get the desired output voltage. You need about 3.75V across the LEDs for a 5V output. A red LED has a 1.6V drop, a green one 2V, a yellow one 2.2V. But it can vary a little between brands and the current through them is also a factor of influence. So you can tweak the 220 ohm a little to get what you want.

Ray
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Old 5th September 2012, 08:34 PM   #18390
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Ok, thanks.

Rob.
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