F5 max acceptable DC offset on Inputs ?

[mfrimu]

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 !!!!

 

[Zen Mod]

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 )

 

[mfrimu]

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

 

[mfrimu]

Say things go wrong, and the preamp drifts to more then 5mv, what's the reasonable max allowed on the F5 inputs?

 

[grimberg]

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.

 

[mfrimu]

Thanks for advice, I will post accordingly to the F5 thread.

 

[h_a]

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.

 

[mfrimu]

Thanks, that makes sense... The amp only drives Tweeters, but they have a crossover, so they should not get any DC,

M

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.

 

[AndrewT]

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.

 

[mfrimu]

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

 

[Marra]

A cable tie works well.