Aleph 2 Power resistors = V2/R

[macka]

Has anyone tried or using 2 watt metal film power resistors in their Aleph 2 project?

I am thinking about this and tossing up whether to use plain 5 watt ceramic wire wound or go for 2 watt power film resistors.

My sums suggest the power disipation will be 0.50 watts per resistor where V 2sq / R where V=voltage = 0.50 volts R = 1.00 ohm (A=0.50 amps) ie 6 x 0.50 amps = 3 amps bias current.

Alternatively if more power is needed 2.2 ohm and 1.8 ohm (0.99 ohms) could be placed in parrellel for 4 watts due to temperature drift.

Please forgive me if my sums are wrong.

If this correct then I could use obtainable Philips metal film resistors in 2 watt ratings from Farnel!

This assumes of course metal film resistors be preferable over standard ceramic cased wire wound versions?

All comments and opinions are most welcome.

regards

macka

[UrSv]

As far as I can tell calculation would be that you have 1*0.5*0.5 W (R*I*I) per resistor which is 0.25 W which then gives some room for using 2 W metal oxide at 1R and not think more about it. I would go for it. If you do not feel comfortable with that 2 0R47 in series works as well giving 4 W maximum pwer handling for the resistors.

/UrSv

[Jmertz]

I have also looked into this issue and in my opinion 2W will be just fine. If it helps any, I emailed NP to ask the same question and he agrees that 2W is plenty.

Jake

[Jmertz]

Also, I am using 3W metal films for my Aleph2

[promitheus]

for 0,5 A bias for each fet 2-3 watts resistors are ok. I will use 3 watt ones.

[Jakeh]

Anyone who needs power resistors, I have spare Caddock MP816 1R resistors - from memory they're about 2 or 3W without a heatsink, and 15W with. £1.25 each.

Cheers Jake

[Salmacis]

I guess a lot of people use Caddock power resistors for the 0.47 and 1.0 ohm resistors, but has anyone tried either Vishay RS5, RS2B or Mills ‘MRB’ Series?

The Mills MRB series are non inductive, but does it matter?
How much do the power resistors actually influence sound quality?

Thx and regards

Axel

[BrianGT]

If you look at the Aleph 2 in the PassDIY gallery by Wayne Sankey. instead of using 6 - .47 ohm resistors, he used 7 .5 ohm RS2B Vishay resistors.

He seems to have no problems, and I have planned to go the same route. The RS2B resistors are 3W and work fine for the .47. He used the RS5 for the 1 ohm resistors, also with no problems. If you wanted, you could use 2 RS2B 2 ohm resistors in place of the 1 ohm resistors, as suggested by some people in earlier discussions.

--
Brian
gte619j@prism.gatech.edu

[Peter Daniel]

Another good choice for .47ohm resistors would be one Caddock MP-930 .10ohm 30W resistor.

[HarryHaller]

Yes the 0.47 power resistors are in the signal path and act as degeneration for the output fets and have an influence on the open loop linearity on the amp. Using a good resistor here will have sonic benefits. The Mills MRA-5 non inductive wire wounds have an excellent reputation for this type application and would be on my short list. I use two Dale 1 ohm 1 watt wire wounds SMTs in parallel in my modified Aleph 3 and they sound great. Surplus shoppers look for 1% wire wounds. CaddockMP-820s would also be excellent. There are some real sonic differences in small value wire wounds.

H.H.