Any value to replacing feedback loop resistors?

[sweetbeats]

I've wondered about this for awhile...I'm talking about replacing resistors in opamp feedback loops in 20+ year-old audio gear.

 

[Dr ZEE]

no.

************

 

[sweetbeats]

ZEE...I think you're going to single-handedly keep me from doing a bunch of stoopid stuff...

 

[Dr ZEE]

I had a conversation with a guy about restoring some older electronic musical instruments and gear and he proudly mentioned that where ever he can, while fixing, he always 'upgrades' a unit/instrument with military-grade components that are exclusively made in USA. I had nothing to say (to reply, that is) to that

I myself often choose parts just for their cool look. Heh heh. I like colors and shines and strange looking "devices" , so my "advice" or opinion should be taken with caution (!).

I still think you need to get yourself a set of breadboard/power supply, some function generator, scope (if you still din't )...so you can put together quickly a circuit and experiment something and see for yourself. Just do it already Stop relying on opinions of "experts" and their fairy tales... ( <<<< click!) huh huh

 

[sweetbeats]

My favorite color is green...I really like those green Nichicon ES series MUSE caps...

I have a so-so condition Tascam MX-80 that only partially works and has been scaveneged for parts...sad little thing but could be a good thing to frankenstein and try different things on...I did end up getting a scop. Pick it up today. Its a reportedly fully functional Tek 455 with a pair of probes for $70.

Heheh...fairy tales...

 

[dgatwood]

Theoretically, some types of resistors do produce higher levels of noise than others.

http://www.aikenamps.com/ResistorNoise.htm

Short form: wirewound resistors are lower noise than film, which are lower noise than carbon. Within the family of carbon resistors, the larger the wattage of the resistor, the lower the noise.

Is it worth doing? Probably not. But there's certainly nothing wrong with experimenting with it.

 

[mshilarious]

You probably don't want a wirewound resistor in a feedback loop as they can be inductive. That's a potential oscillator. Also, the current in a typical opamp feedback loop should be very small, so I don't think there is a big concern with noise.

Whatever thermal noise you get from the series resistor will be shunted along with the signal, so the noise addition will be small. Note that amplifier circuits tend to have lower equivalent input noise at higher gain, partially for that reason.

 

[dgatwood]

You probably don't want a wirewound resistor in a feedback loop as they can be inductive. That's a potential oscillator.

Good point. I forgot to mention that.

 

[Minion]

Another reason you don"t want Wirewound Inductive resistors is they have a different resistance as different frequencies and could conceivably be a dead short at audio frequencies which doesn"t bode well for setting Gain in an audio amp ....

 

[dgatwood]

Another reason you don"t want Wirewound Inductive resistors is they have a different resistance as different frequencies and could conceivably be a dead short at audio frequencies which doesn"t bode well for setting Gain in an audio amp ....

Uh, you have that completely backwards. A wirewound resistor is only usable at audio frequencies (DC to about 50 kHz). Beyond that, you may start to have problems due to the resonant frequency of the wire.