Fender Super Twin.

Totally off topic, but...

First, I didn't know anyone (else) in Australia knew who NRBQ are, and second, I met those guys on the ferry to Martha's Vineyard (Massachusetts, USA) around 1996 or so. The band I was playing in was headed to the island for a gig and so was NRBQ.
Joey Spampinato and Terry Adams had filthy hangovers and the ferry ride was pretty rough. Despite feeling like crap, they hung out and chatted just the same.
I nearly forgot about that. Thanks for the memory, and sorry for the hijack!

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Originally Posted by DrNomis_44

I did a quick calculation to determine what value resistor I needed to use to limit the current flowing in each led, standard 3 or 5 mm leds can safely run with a maximum of about 20mA flowing through them, any higher than that and you risk destroying the led, and they can actually explode if there's too much current flowing through them, so I deliberately chose to limit the current to about 10mA for each led, the value of the current limiting resistors worked-out to be 330 Ohms, I used three 330 Ohm 1W Metal Film resistors, and they seem to do the job fine, but I'm definitely going to swap the blue led's 330 Ohm current limiting resistor for a higher-value one to tame the brightness, but that's a job for tomorrow.

When a led explodes, it gives-off a very pungent smell, how do I know?, I've had first-hand experience with it.


As a side-note, my pedal board is all up and running again, ready for gigging or recording.

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I think I ended up using 2.4k for the blue LED in the buffer. I normally just put the LED in a breadboard and try resistor values until the brightness looks about right. This is only around 2 or 3mA running off 9v but the brightness looked good.

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Originally Posted by jugglindan

I think I ended up using 2.4k for the blue LED in the buffer. I normally just put the LED in a breadboard and try resistor values until the brightness looks about right. This is only around 2 or 3mA running off 9v but the brightness looked good.

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I've used a resistor value as high as 47k for a blue led running on a +15V DC supply, and it was still pretty bright,I did a quick calculation and found that a 3k3 resistor will limit the current to 1mA on a +4.8V DC supply for a Blue led, I used 1.5V for the forward-voltage of a Led in my calculation.


I used the following formula to calculate the resistor value:



R=Vs-Vf/I


R= Resistance.

Vs= Supply Voltage.

Vf= Forward-biased Voltage of the Led (typically about 1.5V for standard 3mm and 5mm Leds).

I= Led Forward-Biased Current.


Although, some 3mm and 5mm Blue leds have a Forward-Biased Voltage as high as 3V.

Same Ohm's law calculation that I use. I measure each LED with a DMM to get the forward voltage, since mine are quite variable. I measured my last blue LED at Vf=2.5, and my red at 1.8. So that gives me 2.7mA with the 2k4 CLR. Not much current but it still feels bright.

I like having a low current draw because I use a common power supply that is only rated to 2A. Although that's an awful lot of analog pedals needed to max it out, the digital pedals I have draw a couple of hundred mA rather than the 40 to 50 mA of the analog pedals. I find it hard to believe some of the numbers in The Power List. For example, they claim a TS-808 draws just 7.5mA. Even with a high CLR, just the indicator LED is half of that total.

Edit: I should make a modified power cable so I can measure current draw directly, just to satisfy my curiosity. I am particularly interested in the differences between bypassed and active.

Update:


I have just swapped-out the blue led's 330 Ohm current-limiting resistor for a 3k3, doing that seems to have done the trick with regards to taming the brightness so I'm happy with it now.


Here's a pic of the modded Super Twin footswitch pedal, with all three indicator leds working:

Attachment 35551


If the EQ is switched-on, the green led lights.

If the Volume Boost is switched-on, the blue led lights.

If the Distortion is switched-on, the red led lights.


You can switch on or off any combination of the three functions.

Very cool doc

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Originally Posted by Andy40

Very cool doc

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Cheers mate, not only is it cool, it's also very practical as well and saves a lot of headaches, I always like coming-up with practical solutions to problems, and sometimes the simplest solutions can often be the most effective ones.

Good work doc

I'm going to be heading out to a mate's place to do some demo recording in his home studio this afternoon, I'm going to be taking my Fender Super Twin amp, plus my pedal board, three guitars and a bass, and some other bits of gear with me, my mate has a Quad Box I can use with the Super Twin, should be lots of fun.

Jealous. Have fun