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)
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
(I don't mean Rickie 🙂 )
Hope you can tell me if my worries are justified of if its only in the mind 😉
Ronald
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 😱
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😉
For the source resistors, 5% is not good 😱
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😉
I'm afraid I didn't match the mosfets myself 
Can't I just measure the Vishays with my Fluke 111 multimeter?
Oeps checked the specs. resolution 0.1 ohm, so guess not
Can't I just measure the Vishays with my Fluke 111 multimeter?
Oeps checked the specs. resolution 0.1 ohm, so guess not
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😉
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😉
Still If I decided to replace them with the 1% Caddocks MP816, would it be sufficient to only replace the twelve 1 ohm resistors and leave the eight 0.47 ohms 5% Vishays, or are these just as important?
So if I first try to match the 1 ohm resistors, how do I group them? In 2 sets of 6 resistors for left and right channel, or maybe also within each channel two sets of 3??
What if one channel has about 0.95 ohm and the other channel around 1.05 ohm??
What if one channel has about 0.95 ohm and the other channel around 1.05 ohm??
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....
were really 5%. More likely they are 1% or better.
As to the .4 watt BCCs, they look awfully tiny....
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! ).
But now I'm worried again. What is the worst that can happen if one of the liitle resistors on the PCB gets fried?
Can that result in a unduly death of my mosfets??
As for the little BCC ants 😉 . Try reading the colour code on these thingies (I have -5 lenses!
). But now I'm worried again. What is the worst that can happen if one of the liitle resistors on the PCB gets fried?
Can that result in a unduly death of my mosfets??
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)
(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)
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 mmNelson 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....
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 😱
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
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
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