[atbglenn]

I opened up my Little Dot 2++ and noticed that the two large blue resistors are discoloring. I think they are getting too hot. I took pictures along with my Little Dot 2+ which doesn't have this problem. I wonder if this is a design problem..

To see my pictures go to: http://glennsoffen.googlepages.com/mystereo

Let me know what you think

 

[jamato8]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif I opened up my Little Dot 2++ and noticed that the two large blue resistors are discoloring. I think they are getting too hot. I took pictures along with my Little Dot 2+ which doesn't have this problem. I wonder if this is a design problem.. To see my pictures go to: http://glennsoffen.googlepages.com/mystereo Let me know what you think

That is not abnormal for resistors that are in a spot where they are going to dissipate heat depending upon wattage requirements. A resistor puts off heat by necessity so it is going to get warm, hot or very hot. It may or may not discolor. I normally use about 5 times the needed rating. I feel they sound better and there is a larger surface area to get rid of the heat. The resistor there looks to be a 1 or 2 watt. I didn't read the bands.

 

[penguindude]

Wow, interesting. Although i wonder why it's only the center part that's discoloring...

How long have u been running your Ld2++?

 

[atbglenn]

Quote:

Originally Posted by penguindude /img/forum/go_quote.gif Wow, interesting. Although i wonder why it's only the center part that's discoloring... How long have u been running your Ld2++?

I'd say about 30 hours total. Around 5 hours a day

 

[penguindude]

i wouldnt worry too much about it. Usually resistors can operate in a temp of more than 100 degree Celsius.

 

[feifan]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif I opened up my Little Dot 2++ and noticed that the two large blue resistors are discoloring. I think they are getting too hot. I took pictures along with my Little Dot 2+ which doesn't have this problem. I wonder if this is a design problem.. To see my pictures go to: http://glennsoffen.googlepages.com/mystereo Let me know what you think

Hmm. Found the exact discoloration pattern on my 2++. I also found discoloration on two of the four 2+ resistors -- the ones closest to the front. The ones in back are clear. I have about 50 hrs on each. Those responding feel they're benign so I guess there's no need for concern.

 

[atbglenn]

Today I ran my little dot 2++ with the bottom cover removed and measured the resistors with my Fluke Inferred Thermometer . Both resistors are running at around 90 degrees C after 10 minutes of use. I think I'm going to change these resistors to a higher wattage rating and keep them spaced away from the circuit board.

 

[rain_uk]

My LD2 (not 2+) had discolored resistors and it didnt cause any problems...I guess its part of the 'burn in'

 

[penguindude]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif Today I ran my little dot 2++ with the bottom cover removed and measured the resistors with my Fluke Inferred Thermometer . Both resistors are running at around 90 degrees C after 10 minutes of use. I think I'm going to change these resistors to a higher wattage rating and keep them spaced away from the circuit board.

Wow, what happens if the resistors get overheated?

 

[atbglenn]

Quote:

Originally Posted by penguindude /img/forum/go_quote.gif Wow, what happens if the resistors get overheated?

Possibly burn out or worse. Since these amps are NOT UL or otherwise approved , I wound not leave them unattended. I wish the designer would comment here.

 

[KT88]

If the resistors get to hot they'll increse their ohm value, this will decrease the voltage that will go to the tube, and will have an influence on sound. This is in what happened in most amps that suffer from this problem.

yet, as atbglenn daid, in this case it could be diffrent. I would replace the resistors if I had such an amp. A audiophile grade resistor should be able to handle at least 3 times the watt's it will see in normal use.

 

[jirams]

These will be screen feed and/or cathode resistors and normally do run hot. The type used here will discolour slightly.

If you are technically up to it, measure the voltage drop across them and using Ohms law work out the power being dissipated in them and report back here - otherwise put the lid back on the amp and forget about it.

P = ExE/R ie. Power dissipated = Voltage drop squared divided by resistor value. The resistor value is colour coded in the bands around the body - The resistors look like Red Red Black Black which would be 220 ohms but hard to be positive from image.

P in Watts - Voltage drop in Volts - Resistor value in Ohms
Search net for Resistor colour code

NB. The wattage rating of the resistor is a function of its construction and size

"Here endeth the lesson"

 

[jirams]

Quote:

Originally Posted by KT88 /img/forum/go_quote.gif If the resistors get to hot they'll increse their ohm value, this will decrease the voltage that will go to the tube, and will have an influence on sound. This is in what happened in most amps that suffer from this problem. yet, as atbglenn daid, in this case it could be diffrent. I would replace the resistors if I had such an amp. A audiophile grade resistor should be able to handle at least 3 times the watt's it will see in normal use.

Take my advice and leave alone - these resistors are bias resistors and are not directly in signal path - audiophile grade screen feed or cathode resistors is nonsense.

 

[jamato8]

I am afraid I can not agree with you. Have you ever bypassed a cathode resistor with a 220 to 400uf cap? There is a change to the sound and often the mids become better. Anything that affects the electron flow is in the signal path, just like the AC music signal that rides on the DC that gets to the output transformer or decoupling cap. Everything has and effect on the sound.

I would use a good 5 watt, if it is getting too hot of a noninductive type. I have used noninductive wire wound with good success and have even used 20 watt so the heat is better dissipated.

 

[jirams]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif I am afraid I can not agree with you. Have you ever bypassed a cathode resistor with a 220 to 400uf cap? There is a change to the sound and often the mids become better. Anything that affects the electron flow is in the signal path, just like the AC music signal that rides on the DC that gets to the output transformer or decoupling cap. Everything has and effect on the sound. I would use a good 5 watt, if it is getting too hot of a noninductive type. I have used noninductive wire wound with good success and have even used 20 watt so the heat is better dissipated.

A designer chooses to bypass the signal component at the cathode by use of a cathode bypass capacitor - it is not added as a an additional component later to improve the sound quality. Doing so prevents the AC component of the cathode current from affecting the cathode voltage developed accross the cathode bias resistor and causing a feedback vector. From the signal point of view the capacitor 'quality' will have much more effect than the resistor.