Resistors & doubts ;(

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Hi,

For the resistors (except the 0.47 and 1 ohm) of my Aleph5 I bought 0.4 watt BCC metalfilm resistors.

But they are so small (less then 4 mm)!! Will they stand the heat??? I probably will want to increase the bias a bit.

datasheet

(clickable image)
An externally hosted image should be here but it was not working when we last tested it.


My other question. For the 0.47 and 1 ohm power resistors I have these Vishay RTO-20 resistors. But the are 5%. Will this impact the sound of the amp in a negative way?????

I first ordered Caddock MP816 (1%) but the shop couldn't deliver them (had to buy 50 pieces). The exchange between the Caddocks an Vishays was done by the shop themself, only sending me a small mail (not even stating the type of Vishays). Although I like the owner of the shop, I'm not really happy with this. Of course the difference in price was refunded (and put into other parts).

I just wish I had discovered Welborn labs sooner, I would have bought everything there.

Since I was planning to make my Aleph very good, this worries me a bit.
I have invested a lot af money in all the other parts so far (more than a 1000 euro)
For instance 4 of these babies
An externally hosted image should be here but it was not working when we last tested it.

(I don't mean Rickie :) )

Hope you can tell me if my worries are justified of if its only in the mind ;)

Ronald
 
The 0,4W is good for the circuit, even with increased bias.

For the source resistors, 5% is not good :eek:
Not to worry though. What you need to do is to match the 5% the same way as you matched the output mosfets.
-> Send a known amount of current (0,5A-1A or thereabout), and note the voltage drop across the resistor. This I would do even with 1% resistors.. It is essential that the resistors match as much as possible, so that the outputfets share the load equally. This has more to do with reliability than sonics.

-You can easily get 1% tolerance from 5% parts this way;)
 
This is not difficult!

I use an old psu (wall-wart or what you call it) from my pc-sub (2A, 15VDC) and two 47R 17W resistors in paralell. Then you put your mosfet or resistor in series and measure VGS or V (=U) across the part. I take the measurment after 5 seconds. Measure the voltage across the two 47R, and you know the current, I. Then it's a simple R=U/I for your source resistors;)
 
Thank you mr Pass. Still, I will try to measure them.

As for the little BCC ants ;) . Try reading the colour code on these thingies (I have -5 lenses! :bigeyes: ).

But now I'm worried again. What is the worst that can happen if one of the liitle resistors on the PCB gets fried? :flame:
Can that result in a unduly death of my mosfets?? :scratch: :dunno: :dead:
 
Edit. Btw according to the datasheet (see PDF abopve) the 0.4 watt is for 40 degrees celcius ambiant temperature. At 60 degrees C (more typical for an Aleph) it is only 0.3 watt. Is this bad?
(My PCBs will be attached perdendicular to the heatsinks, at 2 or 3 cm distance minimum, so for most resistors the distance wil be greater)

(couldn't edit the above message anymore)
 
Nelson Pass said:
I wouldn't worry about the 5% on the Vishays, even if they
were really 5%. More likely they are 1% or better.

As to the .4 watt BCCs, they look awfully tiny....

:bigeyes:
I say, avoid them if you don't have space problems. They are so easy to fire up. Normal 0.6 W is "normal" for me. They have the same size as 0.25 W carbon, 2.5 x 6.5 mm

0.6 watts is VERY hot in these small resistors and 0.4 watts is equally hot in these even smaller types.

I calculate for max 0.3-0.4 watts into 0.6 watts resistors.
 
Maybe they're a little wimpy :eek:

I always use Firstronics RM0207S in all my projects, they're rated 0,6W @70'C 1% +- 50ppm/'C, -55 - 155'C. Still I believe you could use 0,4W, but considering that 0,6W parts costs nearly nothing, why take the chance? Mr Pass is most likely correct that the Vishays are more like 1%, but it wouldn't hurt to check (you'll atleast sleep better at night;) ) I measured my Caddock MP930 (1%), and they where even tighter in tolerance:nod:
 

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