i have Boomtube EX, which have two TA2024 chips with 2x40w power. can join or not leh? thanks.

cheers,
wps

You're always welcome JC. With or without the boomtubes

Y.C.,
I have a feeling that 1K is too low, so I took a look at my LED, a clear blue which should be having the same current requirements with WHITE LED (I have tested).
I am using a 10K resistor, 1/4W (brown,black,orange) as the current limiter. It's a balance between dim and too bright as I do not want it to be a glaring distraction at night
I believe it should work in your set up too, plus minus a few K if you wish to adjust the brightness... Hope this helps in time for tomorrow's session!

Can someone bring along another pair of speakers just in case? My Heybrook HB2s are not very efficient (that's why I want to try them with the TA2024, my TA2022 works fine with them) and it would not be very nice to listen to 3 hours of clipping in the unlikely(?) scenario that the TA2024 can't drive them.....

Junchoon, yes, you are most welcome to out t/t session. What about you bringing along your T/T and phono stage?
Pardon me for my 'wild' suggestion; just brush it off as a joke unless you actually do not mind bringing them.

Jazzy, thank you so much for sharing your configuration on the LED bulb with me.
I had originally wanted to install a faint blue bulb to my T-amp but some shops in JP ran out of stock so I bought a faint green for a mere 30 sen instead. Subsequently when new stocks arrived, I was told that blue coloured bulb is more expensive at RM1.50 each so I held back.
I did not know the amperage of the bulb and was told the smallest size is of 3V and I shall need 1K ohm resistor so I duly picked one up for 10 sen. I wired up the LED bulb parallel to my T-amp board without use of any fuse to it. Out of curiosity, if the amperage of bulb is 20mA and from the online calculator provided by bsl last night, the answer obtained is 450 ohm and when rounded to its nearest value of 470 ohm or for that matter 1K ohm is already sufficient, so why 10K ohm? Unless my LED bulb is actually of 100mA/200mA.
But I will buy a 10K ohm resistor and new faint blue (I also do not want it to be too bright) LED bulb to try out.

March, okay, I shall bring along my tiny Q Acoustic 1010. I also do have the 3" single cone (paper) JVC loudspeakers in my office.

Guys, kindly do response by indicating whether you are coming or otherwise so could plan accordingly.



This post has been edited by Y.C.: Oct 24 2008, 03:28 PM

Y.C.,
Not at all. I have a few spares LEDs(blue, white, orange too) and several values of current limiting resistors. If you need any, just give me a 'holler'

Yes those blue LEDs are kinda expensive.. the cheapest I got was RM1.30
Why 10K? Good question! I blew 2 LEDs before I got it right.. Learning the hard way..

I am definitely coming..

I think it's just the usual reject(?) quality stuff from JP. I bought a pair of white LEDs for car 12 volt operation. One blew after a a few weeks....the other one's still working fine after months of use - same power supply, a 12 volt SLA.

Once or twice I do suffer too with regards to 'quality' issues.. that's why I sometimes buy stuffs from JP more than one in quantity eventhough I need only one.. just incase JP= Jamban Products..

Jazzy,
TQVM the offer but I will pick up the LED bulbs from JP as I also need the 10K ohm resistor.

You are bringing along your 100K ohm passive pre-amp to our session?

So far, the confirmed attendees are Jazzy, March, Junchoon, Y.C., Y.C.'s colleague, Xtorm (he has some family matter to attend to but will try to come). As for the rests, no feedback yet.

Y.C.,
You're most welcome. Get extra for 'spares' just in case..
Yes.. Will bring my 100K passive. It's a 10K actually but a quick swap with a 100K pot is no big deal..

thanks for welcoming me to the tt...

but i don't have turntable nor phono stage, must have mistaken with someone else

i might bring along some LPs for Jazzy to record, heehee

the Boomtube EX has two bass modules and speakers. but RCA connection lah from amp to speakers like most computer speakers.

cheers,
wps

Ok lah guy to make it more clear....here is the attendance list for 'The First LYDN T-amp TT Session 2008'



1. Y.C (Host)

2. Jazzy

3. Junchoon

4. Y.C.'s colleague

5. Xtorm (50-50 attendance)

6.

7.

8.

9.

10.



Guys....fill up the list for the convenient of the host so that he can provide as much as drink possible....!

Junchoon, hehehe......since you are bringing some LPs (as in long play and records, right?) for Jazzy to record, I thought you must be having a turntable and phono stage at home...

Gabanyayaya, I did not see your name on your list; you not coming? And you left out March05 who has confirmed he is coming.

Oh.....a thousand apologies Mr. Y.C.....


The Participation

1. Y.C (Host)

2. Jazzy

3. Junchoon

4. Y.C.'s colleague

5. Xtorm (50-50 attendance)

6. March05

7. gabanyayaya

8.

9.

10.

Come fill up a list...!

Hmmm... this thread is so quiet even on a Friday night?

This is purely an academic exercise (understanding the underlying theory)
Let us revisit the subject of LED (light emitting diodes) and the required value for its resistor. A LED needs a resistor connected in series to it to limit the current passing through else it will be killed instantly like what happened in my case.

Ohm's Law: V = I x R,
hence value of resistor, R = V / I, where:
V = voltage across the resistor (VS - VL in this case)
I = the current through the resistor
So R = (Vs - Vl) / I, where:
Vs = supply voltage
Vl = LED voltage (I goggled that most LEDs are with average value of 2V with exception of 4V for blue and white LEDs)
I = LED current (20mA), this must be less than the max permitted; for use as pilot lamp / status indicator application, the required current is only between 5 to 6mA

We must choose the nearest greater standard value of resistor if the calculated value is unavailable, so that the current will be a little lesser. We may also opt to choose an even greater resistor value to reduce the current so as to dim the brightness of the LED.
In my case, the supply voltage Vs = 12V, and I have a green LED (assume Vl = 2V), requiring a current I = 20mA = 0.020A.
R = (12V - 2V) / 0.02A = 500 , so I should choose 680 (the nearest greater value) but I have chosen 1000 yet my green LED was still killed.

So question here is exactly how high has the supply voltage surged during powering up? Anyone wish to comment?
Let us revive this thread again.

Friday night.. too quiet lah!

Calculation wise, there's nothing wrong with it.. putting it to work.. well we know the story Sorry Y.C. If only I knew the answers...

Jazzy,
I'm curious and hence opened the subject for comments by those who might know. There could have been something that I have missed out hence practical could not equal to theory here. I already got the practical solution from you, ie. use a 10KΩ resistor. This is merely for academic purposes.

This post has been edited by Y.C.: Oct 25 2008, 12:14 AM

Y.C.,
Yes I know. I actually measured the voltage across the LED, which reads 2.8VDC! Which means that the current limiting/voltage drop resistor is CORRECT!
Why doesn't the formula reflect this?
In my setup, using the formula; with 13.4VDC supply voltage and 2.8V LED forward voltage, the LED forward current is 1mA! Maybe 20 or 30mA LED current is not the correct figure?

I think we may have missed something.. I have been doing some reading, found something but not conclusive.. needs further 'digging'..
Anyway, just completed re-assembling a 100K 'passive' preamp.. finished testing and it sounded 'not bad' I'd say!
14 hours to go!

I've a strange feeling, those JP led's are likely of poor specifications and quality. It likely won't withstand more than 10mA current and at 1.7 to 2.2VDC. In this case the calculation with 20mA (about maximum safe value for standard LED) and fitting the suggested resistor will fry the LED. One safe method of determining the resistor value is to buy a multi turn precision trimmer of 2kohm value and connect in series to the LED. Set at maximum and then apply the voltage. Turn slowly to reduce the resistance while monitoring the brightness. Once the desired brightness is determined, measure the trim pot and obtain the nearest resistor matching the previous measurement.

I guess this is the price you pay for 'cheap' things... although they are really not that cheap!

I use my variable voltage PSU and a bunch of resistors to get the required/correct current limiting resistors..

Again, a 1mA forward current for my blue LED? Heck, as long as it works..