Yet another relay attenuator - Page 4

jleaman · 22nd January 2006, 06:10 PM

Quote:

Originally posted by jwb
Jos, that looks very nice! How sounds it?

My regret with my first attenuator is that I used 1/4W resistors. I should have used 2W resistors, or Dale, or some other kind of low noise, like you did.

I really appreciate that you share your source code. Thanks a lot.

Why would you want to use bigger resistors ? Why not smaller.. makes no sence to use bigger ones for signal.

jwb · 22nd January 2006, 06:47 PM

The predominant noise in metal film resistors is "contact noise". Higher power ratings have lower contact noise for a given construction and current. A 2W metal film resistor will always have less noise than a 1/4W resistor from the same manufacturer. The contact noise is related to the geometry and the type of material. Better materials (Dale, for example) has less noise. Larger geometries (higher power ratings) also have less noise.

Secondarily, for any given device the thermal noise (Johnson noise) is proportional to temperature. Since a power resistor will be cooler, it will naturally have lower noise.

Thermal noise is also proportional to resistance, which is why you never want a 1M resistor in your audio equipment.

In general, for low noise, use the highest practical power rating, the lowest resistance, and keep currents to a minimum. Lately I've been using all Dale RN65 series.

Jos v E · 22nd January 2006, 11:14 PM

I agree with jwb about the resistors. Unfortunately I cannot say that I am experienced with direct listening tests on many different resistor types. However it is clear to me that the 1W Vishay/Beyslag metalfilm that I mostly use, sounds really better than the typical small (1/4W) metalfilm.

Jos

EC8010 · 22nd January 2006, 11:43 PM

Quote:

Originally posted by jwb
Thermal noise is also proportional to resistance, which is why you never want a 1M resistor in your audio equipment.

As one who has 1M resistors strewn with gay abandon, I think that statement wants qualifying. You wouldn't want a 1M resistor in series with your signal. If it's in parallel, it's shunted by a much lower resistance and is irrelevant. Phew!

samoloko · 21st July 2010, 07:17 AM

jwb

would you please post again details of schematic from first post
I need the same steps and 20 K Input volume attenuator

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22nd January 2006, 06:47 PM	#32
jwb diyAudio Member Join Date: Mar 2002 Location: San Francisco, USA	The predominant noise in metal film resistors is "contact noise". Higher power ratings have lower contact noise for a given construction and current. A 2W metal film resistor will always have less noise than a 1/4W resistor from the same manufacturer. The contact noise is related to the geometry and the type of material. Better materials (Dale, for example) has less noise. Larger geometries (higher power ratings) also have less noise. Secondarily, for any given device the thermal noise (Johnson noise) is proportional to temperature. Since a power resistor will be cooler, it will naturally have lower noise. Thermal noise is also proportional to resistance, which is why you never want a 1M resistor in your audio equipment. In general, for low noise, use the highest practical power rating, the lowest resistance, and keep currents to a minimum. Lately I've been using all Dale RN65 series.

22nd January 2006, 11:14 PM	#33
Jos v E diyAudio Member Join Date: Aug 2003 Location: Eindhoven	I agree with jwb about the resistors. Unfortunately I cannot say that I am experienced with direct listening tests on many different resistor types. However it is clear to me that the 1W Vishay/Beyslag metalfilm that I mostly use, sounds really better than the typical small (1/4W) metalfilm. Jos

21st July 2010, 07:17 AM	#35
samoloko diyAudio Member Join Date: Jun 2006	jwb would you please post again details of schematic from first post I need the same steps and 20 K Input volume attenuator

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