Quick check required.

Nordic · 29th January 2006, 06:58 PM

Hey hey...

I'm very proud of myself today as I made my first PCB (a Franz valve buffer clone

)

Anyway it got me going bigtime and I ripped the guts out of the broken Tedelex amp I bought last weekend...

Now I'm going for integrated Inverted LM3886 fed by either a preamp or the the "Franz valve buffer" with a selector, furthermore it should also act as a input selector etc.... phonopre etc... everything you'd expect from an integrated amp (your wife could operate).

I didn't know PCB was that cheap, I'm prototyping real cheap using a magic marker, peroxide an pool acid, main amp boards are positioned allready and fits perfectly in old board's place (very long heatsink for STK463 chip).

Now, allthough I don't want to use the old buttons I would like to use the Display LEDs on the front to indicate source....

I came up with this solution

Is it viable? will the voltage for the LED only stay in that loop? What if I connected katode to ground instead of 0v?

Will it create noise on the input?

poobah · 29th January 2006, 07:09 PM

Nord,

You must a resistor in series to limit the current in the LED. Otherwise you will only see the LED flash one time, VERY bright.

For example... if you have 5 volts to power the LED circuit:

Voltage of circuit - Voltage of LED = Voltage of resistor

5 - 1.5 = 3.5

Now 3.5 mA is good to power an LED. So, 3.5 Volts/0.0035 Amps = 1 kOhm resistor. You can use a smaller resitor for more light.

Nordic · 29th January 2006, 08:33 PM

yeah sure, I was going to use a resistor, just left it out as my question had more to do with wheter that power loop around the led would produce the voltage down the input line its connected to... which would be bad...

Nordic · 30th January 2006, 06:16 AM

The more I look at it it looks like a voltage source over the input...
was going to use DPDT swithes to switch both signal and ground wires, think I will rater just switch signal with one, and the indicator light with the other pole.... and hope for the best with groundloops etc...

Nordic · 30th January 2006, 08:38 AM

Ok, will have to settle for 1 input less in order to make parts availablity and costs more reasonable

So now I'm looking at 3 pole 4 way for this job.
Like so.

pinkmouse · 30th January 2006, 09:05 AM

That should work fine. If you want to get more inputs, why not use a single gang switch to drive the LEDs and some 5V relays that actually do the signal routing?

zek · 30th January 2006, 09:06 AM

That is just what I did in my tube preamp many years ago, and it works.
Put some resistor 1K5 or so infront of +V (12V=) and that is it.

Nordic · 30th January 2006, 01:19 PM

Relays would mean more PCB realty, which I think is starting to run out... In fact I'm starting to think about using an extarnal 12V input for the opamps etc... As I allready have 2 traffos in the box now... and have not catered for 12V rails yet.

29th January 2006, 06:58 PM	#1
Nordic diyAudio Member Join Date: Sep 2005	Quick check required. Hey hey... I'm very proud of myself today as I made my first PCB (a Franz valve buffer clone ) Anyway it got me going bigtime and I ripped the guts out of the broken Tedelex amp I bought last weekend... Now I'm going for integrated Inverted LM3886 fed by either a preamp or the the "Franz valve buffer" with a selector, furthermore it should also act as a input selector etc.... phonopre etc... everything you'd expect from an integrated amp (your wife could operate). I didn't know PCB was that cheap, I'm prototyping real cheap using a magic marker, peroxide an pool acid, main amp boards are positioned allready and fits perfectly in old board's place (very long heatsink for STK463 chip). Now, allthough I don't want to use the old buttons I would like to use the Display LEDs on the front to indicate source.... I came up with this solution Is it viable? will the voltage for the LED only stay in that loop? What if I connected katode to ground instead of 0v? Will it create noise on the input?

30th January 2006, 09:05 AM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	That should work fine. If you want to get more inputs, why not use a single gang switch to drive the LEDs and some 5V relays that actually do the signal routing? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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29th January 2006, 07:09 PM	#2
poobah diyAudio Member Join Date: Nov 2005	Nord, You must a resistor in series to limit the current in the LED. Otherwise you will only see the LED flash one time, VERY bright. For example... if you have 5 volts to power the LED circuit: Voltage of circuit - Voltage of LED = Voltage of resistor 5 - 1.5 = 3.5 Now 3.5 mA is good to power an LED. So, 3.5 Volts/0.0035 Amps = 1 kOhm resistor. You can use a smaller resitor for more light.

29th January 2006, 08:33 PM	#3
Nordic diyAudio Member Join Date: Sep 2005	yeah sure, I was going to use a resistor, just left it out as my question had more to do with wheter that power loop around the led would produce the voltage down the input line its connected to... which would be bad...

30th January 2006, 06:16 AM	#4
Nordic diyAudio Member Join Date: Sep 2005	The more I look at it it looks like a voltage source over the input... was going to use DPDT swithes to switch both signal and ground wires, think I will rater just switch signal with one, and the indicator light with the other pole.... and hope for the best with groundloops etc...

30th January 2006, 08:38 AM	#5
Nordic diyAudio Member Join Date: Sep 2005	Ok, will have to settle for 1 input less in order to make parts availablity and costs more reasonable So now I'm looking at 3 pole 4 way for this job. Like so.

30th January 2006, 09:06 AM	#7
zek diyAudio Member Join Date: Aug 2003 Location: Belgrade, Serbia	That is just what I did in my tube preamp many years ago, and it works. Put some resistor 1K5 or so infront of +V (12V=) and that is it.

30th January 2006, 01:19 PM	#8
Nordic diyAudio Member Join Date: Sep 2005	Relays would mean more PCB realty, which I think is starting to run out... In fact I'm starting to think about using an extarnal 12V input for the opamps etc... As I allready have 2 traffos in the box now... and have not catered for 12V rails yet.

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