F5 max acceptable DC offset on Inputs ? - diyAudio
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Old 19th March 2014, 12:12 PM   #1
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Default F5 max acceptable DC offset on Inputs ?

Hello,

I have a DC coupled Preamp and it has about 4mv to 1mv DC offset depending on warmup.

Is this bad for the F5 which is also DC coupled? What's the max the F5 should see. As the preamp ages, maybe the dc offset will increase...

If so should I add a series cap on the preamp outputs???

Thanks !!!!
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Old 19th March 2014, 02:25 PM   #2
Zen Mod is offline Zen Mod  Serbia
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there are numerous threads about F5 already , where you can post your questions

why starting 5 new ones in less then 12 hours ?

4mV at preamp output is nothing to worry about , especially if you check offset at F5 end regularly (once in , say , 3 months )
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Old 19th March 2014, 05:44 PM   #3
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sorry, as I asked before, what's the 'proper' way of posting.

Is it to post in the 277 page thread on the F5?

Thanks, and sorry for not behaving, I'm not familiar with this forum's best practices...

M
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Old 19th March 2014, 05:45 PM   #4
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Say things go wrong, and the preamp drifts to more then 5mv, what's the reasonable max allowed on the F5 inputs?
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Old 19th March 2014, 05:56 PM   #5
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When you open one new thread for each trivial question, instead of using an existing thread, you deprive yourself from a large audience interested in the subject, the same people who can help you. You also take away from other members, those who have been following the discussions about the F5, the chance to learn from your experience.
You got Zen Mod's attention, you will not find anyone more helpful or generous with his knowledge. I suggest you listen to his advice.
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Old 19th March 2014, 05:58 PM   #6
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Thanks for advice, I will post accordingly to the F5 thread.
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Old 1st April 2014, 03:02 PM   #7
h_a is offline h_a  Europe
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It's not about what input offset is acceptable, it's more about what is acceptable for the speakers.

Easy to calculate for you -

10mV input offset to an amp with a 10 times voltage gain will yield (additional) 100mV output offset. The 100mV are seen by the speakers then. 100mV cause a heating of 0.1^2/8=1.3mW in 8 ohm drivers.

Nothing at all to worry about.
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Old 1st April 2014, 04:22 PM   #8
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Thanks, that makes sense... The amp only drives Tweeters, but they have a crossover, so they should not get any DC,

M


Quote:
Originally Posted by h_a View Post
It's not about what input offset is acceptable, it's more about what is acceptable for the speakers.

Easy to calculate for you -

10mV input offset to an amp with a 10 times voltage gain will yield (additional) 100mV output offset. The 100mV are seen by the speakers then. 100mV cause a heating of 0.1^2/8=1.3mW in 8 ohm drivers.

Nothing at all to worry about.
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Old 2nd April 2014, 05:50 PM   #9
AndrewT is offline AndrewT  Scotland
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The capacitor isolates the tweeter from the offset of the amplifier.

If you ever go to active filtering for the treble channel, keep at least one capacitor between amplifier and tweeter.

Tweeters tend to be very sensitive.
They also tend to have very low Xmax.
A small DC offset can pull the Voice Coil way off centre and ruin performance.
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Old 7th April 2014, 04:34 AM   #10
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Default Thermal coupling the input FETs ?

Hello,

Would it be beneficial to thermal couple - using thermal epoxy - the input FETs? On the Civller board they are close together. It's an opportunity.

Thanks
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