Marantz amp question (Transformer).

DaRkF0g said:
Can someone PLEASE explain to me why if I use 3 330ohm resistors they dont get hot, but of i use a single 1/2 watt 1K ohm resistor it gets burning hot? I dont understand why if you put 3 resistors in series they stay cool (wouldnt alot of current still be flowing through the first resistor?!)
Click to expand...

every component in a series circuit gets the same amount of current, in this case 20ma. it is the voltage drop that makes the resistor hot, not the current flowing through it. by having 3 resistors, they each only have to drop 1/3 the voltage, thus staying 3 times cooler. welcome to electronics 101.

DaRkF0g said:
And if I DO use a 100ohm resistor in a chain of 7 would it get too hot??
Click to expand...
i would say no, as it only has to drop ~1 volt at 20ma. that is .02 watts, an order of magnitude less then .25 watt (1/4 watt resistor)
 
Thank you very much shadow! :)

Ok I rethought the LED plan up (who knows I may get around to this tomorrow :p )

Heres what I came up with:

I have a 8.5"X~2.5" area of numbers to fill with the light from the LED's. The way I figure it I can place the LED's 1 1/4" apart from each other. By doing this I will be able to use 8 LED's in that area.
Now I have those 2 little meters that I still need to light. I can squeeze 2 led's each in those things.

So that would mean I would have a chain of 7 and another chain of 5.

For the chain of 7 I can use a 100ohm resistor, and for the chain of 5 would I still use the 3 330 ohm resistors (I dont want to have that heat problem again)?

Sound about right? Ill reuse that cap and rectifier and I should be in business!

How does that plan sound? (I always love how I go back and plan this stuff AFTER the project is finished! :D
 
You could also try sanding down the ends of the LED so they're opaque, this spreads out the light more.

More resistors = more surface area, so the cooling is better. Also, get a multimeter and make sure what the rectified voltage is. If you use two chains, you would halve the resistor value since you need to pass twice as much current. But, that resistor will see the same voltage drop with twice the current. Since the resistors you are now using seem to be working fine, I would use a second set of resistors on the second chain to spread out the heat.
 
DaRkF0g said:
So that would mean I would have a chain of 7 and another chain of 5.

For the chain of 7 I can use a 100ohm resistor, and for the chain of 5 would I still use the 3 330 ohm resistors (I dont want to have that heat problem again)?
Click to expand...

Based on some guestimates, I would say that the resistor is dropping several volts (my guess is at least 10) and will need a bigger value. I would try at least 330 ohms and maybe two 330s in series on the 7 LED string. Either that or try two strings of 6 with 660-1000 ohms each.
 
Fenris_Ulf said:
Based on some guestimates, I would say that the resistor is dropping several volts (my guess is at least 10) and will need a bigger value. I would try at least 330 ohms and maybe two 330s in series on the 7 LED string. Either that or try two strings of 6 with 660-1000 ohms each.
Click to expand...
Well, I went ahead and tried that and had no success. Its all in the massive amount of energy I have to dissipate. Way too much for a few resistors to handle.

So I called a friend of mine up who REALLY knows all about electronics, and I explained to him what I was trying to do.

He said that I would better off running the LED's in parallel (have 1 resistor per LED). He also recommended that I should use 3.3k 1/2watt resistors. Does that sound about right?

Now If I DO run parallel would I be limited to 7 led's (23.1V) because my supply is 24V?? This is what I STILL dont understand. How can you have like 15 LED's on a source that is only providing 20V, for example??? Is that even possible??

Let me hear some ideas, this project is on hold for now until I get some good answers ;)
 
DaRkF0g said:
Well, I went ahead and tried that and had no success. Its all in the massive amount of energy I have to dissipate. Way too much for a few resistors to handle.

So I called a friend of mine up who REALLY knows all about electronics, and I explained to him what I was trying to do.

He said that I would better off running the LED's in parallel (have 1 resistor per LED). He also recommended that I should use 3.3k 1/2watt resistors. Does that sound about right?

Now If I DO run parallel would I be limited to 7 led's (23.1V) because my supply is 24V?? This is what I STILL dont understand. How can you have like 15 LED's on a source that is only providing 20V, for example??? Is that even possible??

Let me hear some ideas, this project is on hold for now until I get some good answers ;)
Click to expand...

This might work, but it's not as efficient. The resistor(s) have to have to drop the excess voltage. If you have 30v - 3.3v then each is dropping 27v. With a 3300 ohm resistor, the amperage is 8ma and the resistor dissipates .22w. If the LEDs are in series, the voltage drop across the resistors is less and therefore the power (and heat) dissipated is less.

6 LEDs in series is a drop of 19.8v. This means that the resistor has to drop 10.2v. At 8-12ma, the corresponding resistance would be 850 to 1275 ohms. The resistor would only have to drop about .08 to .12 watts. Several quarter watt resistors in series (for example three 330 ohm resistors) would only have to handle a few hundreths of a watt each.
 
Fenris_Ulf said:
This might work, but it's not as efficient. The resistor(s) have to have to drop the excess voltage. If you have 30v - 3.3v then each is dropping 27v. With a 3300 ohm resistor, the amperage is 8ma and the resistor dissipates .22w. If the LEDs are in series, the voltage drop across the resistors is less and therefore the power (and heat) dissipated is less.

6 LEDs in series is a drop of 19.8v. This means that the resistor has to drop 10.2v. At 8-12ma, the corresponding resistance would be 850 to 1275 ohms. The resistor would only have to drop about .08 to .12 watts. Several quarter watt resistors in series (for example three 330 ohm resistors) would only have to handle a few hundreths of a watt each.
Click to expand...
But apparently this does NOT work! I tried the three 330's and they were all burning hot! I have no idea why either.

Oh and one more thing, somewhat off topic. When I take a multimeter and measture the current coming off the transformer it measures 24VAC and then I switch it to DC and it measured 18V. Now the multimeter is working properly; like if I measured the 12V rail on my computer it would read 12vdc, and if I switched it to AC I worldnt get anything. Any idea why it would do this (and this is a Fluke meter that I was testing this with, not my POS radiocrap one.

ALSO I was screwing around and I took the black probe from the multimeter and shoved it into the groung plug on a will outlet and I took the red probe and touched the casing of the amp and I got 81VAC. Is that even possible?
 
Yes it's possible. A voltage meter reads potential difference, which is the difference in voltage between any 2 points. Your wall outlet, in theory is 111 volts, assuming your transformer puts out 30. The meter sees the 111 from the wall, and it also sees the 30 from the transformer. 111 volts minus 30 volts is 81 volts. That’s the potential difference.
 
Allright thanks for explaining that to me, now I just need to figure these resistors out!
 
I'm thinking of a way to help you with that also. I haven't stumbled across anything yet, but what I would do is use an external transformer. One that outputs whatever voltage you need in direct current. I would also put a jack in the back of the amp to plug the external source into. From there, run wires to the LEDs. But that would require extra wires, more mess, etc.
 
I was originally going to use that as my solution, but a transformer is too bulky to fit inside the amp, and I know resistors can solve my problem. Its just getting them setup correctly so they dont get so hot.
 
Yeah, those specs are good, but Radio Shack put the wrong image on the page. If you can find a few with those specifications, go for it! :)
 
Well I finally have some damn success! :)

I found a 100 ohm TEN WATT resistor laying around so I decided to solder it up and try it out.

Well, I didnt have 8 SED's but rather REALLY bright LED's. I think the 100 ohm needs another friend, but RadioShack is closed now so I will have to wait until tomorrow.

I decided to go with the array idea (not parallel) its just too much trouble at this point to change everything around.

The 10watt did get warm, but no-where near hot. The blinding LED's took a little hit, the last one in the array was getting pretty hot, a definant sign that I need a little more resistance. LED calculator that I used said I needed ~210ohms(1/2 watts go figure!) so I am thinking of putting 2 100 ohm and a 50 ohm in the picture; all of which will be rated at 10 watt of course. It takes up alot of room on my PCB but hell if it works thats all I care about.

I still need like 4 more LED's in there for other meters that need to be lit, but I am thinking of maybe using a lower voltage source for this. Ill just have to poke around with my multimeter to see what I can stir up :)


Ill keep you guys posted as I go along :)


Oh yeah, and as for the array its cool to see how the voltage drops along it, bu the last LED I have like 5V. Its a little too much, but again a higher value resistor should fix that.
 
DaRkF0g, do us a favor and measure what the DC voltage is across the capacitor. Without the DC voltage there, this is all random guessing.
 
Is it OK for me to ask you a very dumb question now?

Why are so dead set on using LEDs that you had to order? :confused:

All it took was a few of the fuse type incandesent bulbs I linked you to in the first reply...some board mounted fuse clips and a couple of chunks of Perfboard.
There would have been no messing with rectifiers, capacitors, oversized resistors, different layouts and all of the other stuff you have went through to get the same exact results <insert evil smiley>
 
*Stabs Mr. X with a hot soldering iron*

:p Just kidding!

Anyway yeah Icould have taken that route, but why not just to the rest of the way and put 1 more resistor in and call it a day. :)
 
DaRkF0g said:
But apparently this does NOT work! I tried the three 330's and they were all burning hot! I have no idea why either.
Click to expand...

in series, 7 LEDs would draw a total of ~25ma. 25ma at 30v = .75 watt. that is why your 1/4 watt resistor is heating up! it is pulling 3 times more power then it is designed for. 2x 660 ohm 1 watt resistors in parallal would give you ~330 ohms, with only .35 watt going thrugh each one. this is your best bet.

DaRkF0g said:
I found a 100 ohm TEN WATT resistor laying around so I decided to solder it up and try it out.
Click to expand...
or that works, lol

Mister X said:
All it took was a few of the fuse type incandesent bulbs
Click to expand...
Oh comon... modding != to incandecent bulbs :rolleyes
 
Hello again shadow,

Thanks for explaining that to me. The reason I went with 10 watt was because radioshack doesnt sell 1 watt (Only 1/4, 1/2, and 10). I know I can order them but its not worth the wait.

At the same time I was not sure if 1 watt would be able to handle it (now I know it could) as the 10 watt was getting warm, I can only imagine that 1 watt would be hotter.

Ill post back later when I get the 2nd 100 ohm resistor(accompanied with pics of cource :) )!
 
Mister X said:
There would have been no messing with rectifiers, capacitors, oversized resistors, different layouts and all of the other stuff you have went through to get the same exact results <insert evil smiley>
Click to expand...
Oh and by the way this whole project has really boosted my knowledge in electronics. Now I can apply my LED knowldge to other appications as well :)
 
Mister X said:
There would have been no messing with rectifiers, capacitors, oversized resistors, different layouts and all of the other stuff you have went through to get the same exact results <insert evil smiley>
Click to expand...
DaRkF0g said:
Oh and by the way this whole project has really boosted my knowledge in electronics. Now I can apply my LED knowldge to other appications as well :)
Click to expand...
Another approach would have been to locate and tap into the low voltage dc supply, saving the need for building another filtered supply dedicated towards illumination led's. Sometimes it is helpful to learn to use what is already available as well.

And I've just got to say, without poking (too much) fun at ya, that
DaRkF0g said:
PS. That transformer is the STRANGEST transformer I have ever come across. The LED's flicker like they are on 60 hz or something!
Click to expand...
is one of the more entertaining quotes I've come across in a while ;-) But hey, we all gotta start somewhere, I'm happy to see you gaining experience along the way.
 
agent420 said:
And I've just got to say, without poking (too much) fun at ya, that
is one of the more entertaining quotes I've come across in a while ;-) But hey, we all gotta start somewhere, I'm happy to see you gaining experience along the way.
Click to expand...
The only reson I said that is because is was the first time that I had come across a AC to AC transformer. I was used to working with AC to DC transformers. I guess its just the shear size that boggled my mind :p
 
DaRkF0g said:
The only reson I said that is because is was the first time that I had come across a AC to AC transformer. I was used to working with AC to DC transformers. I guess its just the shear size that boggled my mind :p
Click to expand...
:p . ALL transformers are AC to AC, otherwise it wouldent work! Anything with AC->DC has a rectifyer somewhere hidden
 
:eek: Ok I understand now!

So all it is doing is essentially doing is lowering the voltage for the circuitry?
 
yep, a transformer can step down or step up (or theoreticly step the same) AC voltage only. if you put DC thrugh a transformer it becomes a resistor.
 
DaRkF0g said:
The only reson I said that is because is was the first time that I had come across a AC to AC transformer. I was used to working with AC to DC transformers. I guess its just the shear size that boggled my mind :p
Click to expand...

;-) (Added to list)

I'm guessing your experience has been with "Wall Warts"

An another note, hang on to that Marantz! It's a classic and they just don't make'm like that anymore (at least affordably). Current day amps can claim globs of power, but in my own biased opinion those older discrete amps have something special. Plus, it's soooo retro. There may even come a time when you develope a preference to the original style warm incandescent lamps over the cold modern leds. (gasp!)

theshadow27 said:
yep, a transformer can step down or step up (or theoreticly step the same) AC voltage only. if you put DC thrugh a transformer it becomes a resistor.
Click to expand...
Or an inductor
 
agent420 said:
;-) (Added to list)

I'm guessing your experience has been with "Wall Warts"
Click to expand...
Yep

agent420 said:
An another note, hang on to that Marantz! It's a classic and they just don't make'm like that anymore (at least affordably). Current day amps can claim globs of power, but in my own biased opinion those older discrete amps have something special. Plus, it's soooo retro. There may even come a time when you develope a preference to the original style warm incandescent lamps over the cold modern leds. (gasp!)

Or an inductor
Click to expand...
Thanks for further explaining that to me. I had a feeling that may have been what the transformers purpose was, but I want entirely sure.

Trust me, this amp isnt going anywhere :p

Hey if I dont like the LED's I can always go incandescent, nothing is not reversible with this project :)
 
Well it looks like I FINALLY got it, but Im not going to speak too soon :)

Anyway, it took 12 LED's(Plus the ones I burnt up (yeah thats about 18 more :p )), 3 100ohm 10 watt resistors, 1000uF cap, a rectifier, and alot of time and patience.

So heres how it turned out. They still arent mounted up but I aimed them in the approximate direction:

amp_final.JPG



And the circuitry (So many things I dont need there but what the hey, it works)
power_final.JPG


Ill cleanup the board a little once I get a new soldering iron. My RadioShack one finally died (RIP I think not! :p )
(Went with a weller one if anyone cares ($50 ebay :) )
 
I know this is late but I think....I have that amp just sitting in my basement. I will try and check when I get back in town incase you need anything in the future.
 
O M G,

I FINALLY impressed Mr. X.

I am noting this moment right here and now :p

I am glad the way it came out too. The extra LED's did make a big difference. It also helps not to aim the beam directly at the numbers, if you aim them down then it helps blend the light together.

I still have to light those VU meters, but I am going to tap into a different part of the amps power system for that (only need to light 4 led's)
 
Looks good. Well done for persisting and learning about electronics along the way.
 
Thanks Ill post pics when I get it all together :)

Still have to figure out how to rig the PCB up though.
 
DaRkF0g said:
I am glad the way it came out too. The extra LED's did make a big difference. It also helps not to aim the beam directly at the numbers, if you aim them down then it helps blend the light together.
Click to expand...
Just looking at the picture again, I thought to myself:

"Hm, I wonder if a system of mirror(s) would make the LED light more uniform..."

I bet you could put a mirror (or 3-5) in there at *certain* angles to improve the dispersion of the LED light (not directly at the numbers, but just a little extra indirect light). As always, even the plastic mirrors would work (does'nt have to be a glass backing). Then again, looking at the pics, its hard for me to see if there would be enough room..

But... still something to consider. (In my mind, I have a little plastic/mirror box that the LED's are in that encloses the display (the LEDs are inside the box. Again, fooling around with the angles will probably yield diffrent lighting styles).

(if this is a repeat of what someone else said, whoops)

~Hope this helps, and congratulations! It came out very good!
 
Yeah I was thinking on that, how I could even the light out a bit.

As for mirrors:

A: I dont think that would help spread the light out
and
B: Theres about a 1 3/4" in there to work, theres no way that someone with hands as big as mine could ever work in there :p

I was thinking of maybe painting the inside white??? Its a tan color right now

On second thought that plastic is EXTREMELY brittle so I would be better off not touching it!
 
Ah, if space is tight, then that's not going to work out too good.

Here is a pictorial sketch of what I would try to do.
LED.gif

(Note: I have the LED vertical, but you could do many sorts of combinations).

I would do it eaither with 3 plain (flat) mirrors, or try for a concave/convex one that stretched the whole lenght like this almost.
If using the 3 mirros, just use a little hot glue, and presto ^_^.

Plain mirros that size usually run about 0.50$ to 2$ us each.

I will say though, that the mirrors Would add more light and dispersion to the display, that's for sure.

Oh well, it still looks very PIMP!!! I love the brushed metal look, and the color just sets it apart. Too bad it did'nt have one of those sick ossciliscopes for a visual eq ^_^!!!!! Boy, I want to see one of those in person some day.

~Keep us posted
 
You must log in or register to reply here.
Back
Top