Resistor wattage question

[DeadSpeaker]

Hi,
Does anyone know if 1/4 watt resistors can be used in Project 27? The schematics show that some resistors should be 1 watt or 5 watts, but most have no wattage listed. Does not listing a wattage mean that it one should use some kind of a standard? Thanks for the help.

 

[Andy L. Francis]

You mean ESP-P27?
Then the answer is yes. Use 1/4W resistors, except R16...R21 (5W).

 

[DeadSpeaker]

Yes and thanks. I suppose I can use 1/2 as well?

 

[xiphmont]

Yes and thanks. I suppose I can use 1/2 as well?

Yep.

 

[DeadSpeaker]

awesome. I have this whole thing planed out so now i'm just freaking out about the little things.

 

[Andy L. Francis]

Sorry, for R9 position 1/4W rated resistor is not enough, there 1/2W rated is needed.

 

[DeadSpeaker]

Thanks. I was going to use 1/4 watt metal film, but I found that I have quite a few 1/2w carbon films that will work. So I will not be using any 1/4w ones.

 

[cabbagerat]

Thanks. I was going to use 1/4 watt metal film, but I found that I have quite a few 1/2w carbon films that will work. So I will not be using any 1/4w ones.

Most metal films are 1%, and most carbon films are 5%. Metal films also have less excess noise, and better temperature stability. I would stick to the metal films in positions where 1/4w is enough.

 

[peranders]

Sorry, for R9 position 1/4W rated resistor is not enough, there 1/2W rated is needed.

I hate to tell you that this is not correct. Only a couple of nA will flow through this resistor. 1/4 W will certainly do.

 

[DeadSpeaker]

Thanks for the tip. I just noticed that c14 is 10uf and it is non-polar. Is it possible to use electrolytic here, and if so how would it be oriented? Thanks.

 

[peranders]

Most metal films are 1%, and most carbon films are 5%. Metal films also have less excess noise, and better temperature stability. I would stick to the metal films in positions where 1/4w is enough.

... and the are rated 0.6W

 

[peranders]

Thanks for the tip. I just noticed that c14 is 10uf and it is non-polar. Is it possible to use electrolytic here, and if so how would it be oriented? Thanks.

You have pure AC over the cap since the stage is fed from +15 V and -15 V but the AC voltage will probably be quite low so the cap will last for quite a while.

If you know your load you can calculate which cap value you'll need.

f = 1/(2*pi*R*C) where

f = where the base starts to drop
R = your load (10k or more?)
C = the cap

 

[Andy L. Francis]

I hate to tell you that this is not correct. Only a couple of nA will flow through this resistor. 1/4 W will certainly do.

Both you and me were correct!
I mean R9 on power amplifier circuit (4.7k), you mean R9 on the preamp circuit (2.2k).

At 40V +Vcc the dissipation on that resistor in the bootstrap circuit would be ~150mW. That's why I recommended 1/2W rated resistor instead of 1/4W rated.