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HE-500, LCD2, D5000, DT770, SR80, on a speaker amp (Emotiva mini-X A-100) Project - Page 200

post #2986 of 3639
I currently have no resistors installed. With volume set to noon or higher and no music playing, I hear a hum. Sounds similar to the ground loop from my cable. I installed a filter between the cable an cable box that took care of that problem.

I don't have any issues needing SPL attenuation.

Would a pair of resistors between the speaker taps and headphone jacks knock out the hum? If so, what type and Ohms should I use?

Otherwise, I'm very happy with the sound.

Thanks
post #2987 of 3639
Quote:
Originally Posted by bluemonkeyflyer View Post

I currently have no resistors installed. With volume set to noon or higher and no music playing, I hear a hum. Sounds similar to the ground loop from my cable. I installed a filter between the cable an cable box that took care of that problem.

I don't have any issues needing SPL attenuation.

Would a pair of resistors between the speaker taps and headphone jacks knock out the hum? If so, what type and Ohms should I use?

Otherwise, I'm very happy with the sound.

Thanks

 

I'm not sure if resistors would fix your problem, but if you want to try using series resistors, you can figure out the ohm value to use with this formula.

Output power in watts = ((20* headphone impedance)/( resistor impedance + headphone impedance))^2  / headphone impedance. 

Instead of trying to solve that thing algebraically, I'd suggest plugging in your headphone impedance and then graphing the function using something like fooplot (free website). 

Robrob has some more in-depth formulas for other types of resistor networks that give you SPL attenuation instead of just output power. 

 


Edited by manbear - 1/10/14 at 10:01am
post #2988 of 3639

Use the right side of the graphic. 110 ohm resistors on the two + headphone wires will give you 12dB of attenuation which is about the minimum I'd recommend anyone start with, so 100 to 200 ohm 3 watt resistors is my recommendation. One resistor attenuation like this is usually fine for solid state amps but for any tube amp I'd recommend you go with the left side of the graphic's two resistor network to match the amp's expected speaker load.


Edited by robrob - 1/10/14 at 2:01pm
post #2989 of 3639
Quote:
Originally Posted by manbear View Post

I'm not sure if resistors would fix your problem, but if you want to try using series resistors, you can figure out the ohm value to use with this formula.


Output power in watts = ((20* headphone impedance)/( resistor impedance + headphone impedance))^2  / headphone impedance. 


Instead of trying to solve that thing algebraically, I'd suggest plugging in your headphone impedance and then graphing the function using something like fooplot (free website). 


Robrob has some more in-depth formulas for other types of resistor networks that give you SPL attenuation instead of just output power. 


 

Quote:
Originally Posted by robrob View Post



Use the right side of the graphic. 110 ohm resistors on the two + headphone wires will give you 12dB of attenuation which is about the minimum I'd recommend anyone start with, so 100 to 200 ohm 3 watt resistors is my recommendation. One resistor attenuation like this is usually fine for solid state amps but for any tube amp I'd recommend you go with the left side of the graphic's two resistor network to match the amp's expected speaker load.

As headphone impedance increases, should the Resistor impedance increase or decrease?

So, I simply splice the appropriate Resistors between the speaker taps and the headphone jack?

Thanks, Guys
post #2990 of 3639

I bought this amp a few weeks ago from Emotiva directly and the price was $169.  I see it's back up to $219 again... sale over...for now.

post #2991 of 3639
Quote:
Originally Posted by bluemonkeyflyer View Post

As headphone impedance increases, should the Resistor impedance increase or decrease?

So, I simply splice the appropriate Resistors between the speaker taps and the headphone jack?

Thanks, Guys

The headphone impedance has very little effect on the one or two resistor setups in the graphic so just ignore it.

 

Insert the resistors in the left + and right + headphone wires any way you care to do it.

post #2992 of 3639
Quote:
Originally Posted by robrob View Post

The headphone impedance has very little effect on the one or two resistor setups in the graphic so just ignore it.

Insert the resistors in the left + and right + headphone wires any way you care to do it.

O.K. Many thanks.
post #2993 of 3639

Step bits and a super 1950's drill dress always make for a lovely saturday evening.

 

LL

post #2994 of 3639
Quote:
Originally Posted by hemipowered007 View Post
 

Step bits and a super 1950's drill dress always make for a lovely saturday evening.

 

LL


Beautiful work!  Enjoy.

post #2995 of 3639
You koiloco, are the reason me and a few others now have this simple solution. I thank you sir, more people need to do this mod. If ya have the tools, its very very simple. I believe I spent maybe 45 minutes all together, case open to case closed. Again, thanks for the idea.
post #2996 of 3639
Quote:
Originally Posted by hemipowered007 View Post

You koiloco, are the reason me and a few others now have this simple solution. I thank you sir, more people need to do this mod. If ya have the tools, its very very simple. I believe I spent maybe 45 minutes all together, case open to case closed. Again, thanks for the idea.

Then I will have to thank the OP, M-13 and a few others to carry on the hype train so that I could be annoyed enough to try this little amp out. :D  For the part $ and how long it takes if you have the tools, it's silly not to mod this amp.  I am glad it worked out for you as it did for me.  :beerchug:

post #2997 of 3639
Hype train indeed
post #2998 of 3639

The best part, is that we all are using koiloco's jack :p

 

Installed 150ohm resistors to mine today. Bye bye noise floor.

post #2999 of 3639
Why dont you share your resistor install process with us sir. I need to create something for my magnums.
post #3000 of 3639

I should have taken a picture of it, but all we did was cut the wire ahead of the spade connector (on both the right and left positive leads) and solder on a 150ohm resistor in series to each lead. All covered up with heat shrink.

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