sonic effect of resistors

[John Roman]

Fresh off my efforts to experiment with my EFP3 I've learned change is not always good. I'm not all that satisfied with the sound of the Tung Sol 6SN7GTB  output tubes and will be reinstalling the 9 pin sockets soon. I've listened to them for about 40 hours and have discovered their tone to lack the detail found with the RFT 12AU7's. Before I change up I'm going to roll in some Sylvania black plate chrome tops. I tried them for a short while at first and changed quickly to the Tung Sol's. They need a more extended listen to be fair. I think I'll also leave the Goldpoint changes in place for now. They use the Nichrome thin film resistors which brings me to my question. How is it  that resistors have a sonic effect. I realize that anything in the signal path can have a "signature" but resistors? Similar in some respects to capacitors?  The existing series padding resistors on the EFP3 are 33k metal film. If I change these padding resistors to say Vishay or Dueland  will there be an sonic change? Or are they simply and only for level control? Are the stock padding resistors Tantalum? I'm getting carried away here. What are your thoughts on the signal path components, including wire, and how they effect sonic quality?  Is the signal path just about transparency such that the choices made reflect individual taste only?  Thanks!

[mchurch]

Hi John;

I am not an expert in electronics or physics but from experience and research I have learned that it is important to pay attention to resistors as we do to Caps although probably not equally. On the advice of a friend of mine I started to upgrade my resistors whenever the opportunity arose. For example any time a cap replacement was made I took the opportunity to upgrade resistors as well. In every case there was a sonic difference, some good and some so so. Once or twice the effect was downright bad, but an easy fix. There are as many resistor upgrades as there are caps. I used to think that resistance was not critical and for example 10ohms was 10 ohms even if one was achieve by placing two 5 ohm in series, boy was I off on that. I believe the sonic effects are a function of the resistors capability to convert the signal to heat. Some seem to do it better than others.

Whenever I change CAPs or resistors I always play the unit as stock till the tubes have time to burn in. That way I am used to it and can realize the changes made buy substitution. Iknow that in other critical applications only certain resistors are speced out. An example being radar and sonar systems and certain avionics gear.

I have used Vishay, Mundorf, Craddock with great success. The Vishay I used are not the standard Vishay - Dale from Mouser I use the Vishay from Parts Connextion. I am not saying that they are the be all and end all but I had changed my padding resistors before I changed to a DACT 20K pot and I perceived a more detailed sound which seemed to be un-affected by the DACT addition. Now I am just evaluating the padding resistor values before changing to a new selector switch from DACT as well.

Hopefully some of the resident experts can shed some more light on the effect of resistors for us. As Doc said in the other thread the fun of this is learning by experimentation and from others.

Cheers,

Mike

[Grainger49]

It seems that every component¹ in the audio path makes a difference.  My standard thought on Capacitors is that they are like spicing.  Some like curry, some like saffron.  Every one's taste is individual so it is hard to guarantee that a component I like someone else will like. 

Resistors by their properties are semi-conductors. The current through a resistor may take an odd path.  Wire wound and some trimmed film resistors have inductance that changes the sound.  The same thing goes for capacitors, they change the sound in an opposite direction. 

IMO part of this is that the current and voltage waves get out of phase as they pass through so called passive components.  It is explained at the top of the page here:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html

¹  Connectors, wire, resistors, capacitors, tubes, contacts on a switch... the list goes on.

[John Roman]

Thanks Mike and Grainger,
The audio education continues, my thanks for the insight. So now I'm going to look closer at upgrading the signal path components . I will attempt to do them one at a time and resist my nature to change everything at once. Now to define the signal path precisely and determine a logical progression of change.

[VoltSecond]

I like to have 25 ppm/C or better resistors in the gain stages.  Lately I've been using the CMF55 resistor from Vishay.  ( I've also had some good luck with the Vishay PTF56 resistor. )

"http://www.vishay.com/docs/31018/cmfind.pdf"  <-- Low noise, low voltage coefficient, 25ppm/C and affordable.

Cautions when using any resistor:
Don't run the resistor higher than its rated voltage. Many resistors are only good to 200V. So don't use them with 300V on them.

Don't run the resistors too hot.  I don't like to run them hotter than 1/2 their 70C rating in normal operation. I also try to stay less than rated power during power up and during a short on the output of the amp.  Remember, "rated power" for a resistor assumes the part next to it is running cool and isn't a tube or another resistor being pushed to its limits.

Note: Dale and Vishay make all grades of resistors from cheap "well at least its a resistor" to expensive "That's really that good.".

Presently, I don't care for the sound of inexpensive carbon film resistors.