Thermistor removal from crossover rebuild?

[CliffR52]

Yes, and this would be the best thing to do now that we have sourced an Australian supplier of the C955 PTC.

Hi.

Don't know what happened but the schematics are no longer there.

What's the plan?

thanks

Cliff

 

[AllenB]

Cliff, you have capacitors and have decided to replace the electrolytics. I've noticed some concern about resistance to go with them. Capacitors have a small value of parasitic resistance that appears in series with the capacitance.

Equivalent series resistance - Wikipedia

When this resistance is enough to cause a difference in the crossover, and when you replace with another capacitor that has a different value of resistance you can get a change in the crossover. It is usually quite small. This change may account for some of the reports of different sound in certain circuits, hence this explanation.

In your case, if it turns out your treble is too loud you could experiment with series resistance. e.g. between the capacitor and the tweeter (and/or between the other capacitor and the mid).

 

[Galu]

...the schematics are no longer there. What's the plan?

Stick to the original crossover layout as per your drawing.

AllenB has verified that your circuit is OK, so go ahead and replace the capacitors and the PTC thermistor.

If you like the end result, then well and good. Job done!

If the mid/high frequencies sound too bright, then return here for advice on fitting the series resistors that AllenB mentions.

 

[CliffR52]

Stick to the original crossover layout as per your drawing.

AllenB has verified that your circuit is OK, so go ahead and replace the capacitors and the PTC thermistor.

If you like the end result, then well and good. Job done!

If the mid/high frequencies sound too bright, then return here for advice on fitting the series resistors that AllenB mentions.

Thanks.

I'll be ordering the PTC thermistor from the supplier you referred me too.

To maximise my shopping list I thought I'd order some resistors while at it.

For tuning purposes and for having such such parts on hand for future typical upgrades what values do you recommend (ohms)?

 

[Galu]

A batch of 1.0 ohm, 5/10W ceramic resistors would be handy for your fine tuning purposes in that they can be wired in parallel to give a smaller resistance or wired in series to give a larger resistance.

If you wish to pad out the order, a selection of resistors between 1.0 and 10 ohm would be good to have in hand for future projects.

 

[CliffR52]

Cliff, you have capacitors and have decided to replace the electrolytics. I've noticed some concern about resistance to go with them. Capacitors have a small value of parasitic resistance that appears in series with the capacitance.

Equivalent series resistance - Wikipedia

When this resistance is enough to cause a difference in the crossover, and when you replace with another capacitor that has a different value of resistance you can get a change in the crossover. It is usually quite small. This change may account for some of the reports of different sound in certain circuits, hence this explanation.

In your case, if it turns out your treble is too loud you could experiment with series resistance. e.g. between the capacitor and the tweeter (and/or between the other capacitor and the mid).

Thanks Allen.

Have had many distractions and find re reading posts makes things clearer.

You mentioned replacing electrolytic with film caps may yield a variation(mostly small) in resistance.

Do polypropylene caps (vs electrolytic) mostly result in lower resistance?
Would adding small value resisters in series between cap and driver reduce overly bright or loud tweeters/mid range speakers?

Would adding resistors in parallel increase brightness or loudness of tweeters/mid range speakers?

 

[AllenB]

Do polypropylene caps (vs electrolytic) mostly result in lower resistance?

It usually goes this way. Also, specifications are available for parts. Also, this effect can be measured, or you can just use you ears.

Would adding small value resisters in series between cap and driver reduce overly bright or loud tweeters/mid range speakers?

Yes, even in a general sense. With much added resistance the effect can vary with frequency where the impedance also varies. One way to reduce this effect is to attenuate using both series and parallel resistance.

 

[JMFahey]

Sorry about that.
I'm all over the job.
My mother was hospitalized and not doing too well.
Haven't had a lot of sleep over the last week or two.

Dear Cliff, hope all goes well with your Mom

 

[AllenB]

I'm sorry Cliff. Best regards to your mother.

 

[CliffR52]

thanks guys.

she's doing ok at the moment but had some critical moments.

been playing havoc with my projects

hardly any decent periods to devote to getting things done

scary when i have multiple projects in varying states of build with parts all over the place

had visions of forgetting what goes where and was starting to lose it

but nothing would be getting off the ground (for my sound projects) without your input

value = priceless

thanks

 

[CliffR52]

With much added resistance the effect can vary with frequency where the impedance also varies. One way to reduce this effect is to attenuate using both series and parallel resistance.

That's very interesting.

So to overcome brightness or overly loud highs/mids would I add a resistor in series and listen for changes, but if brightness continues at given frequencies, add a similar value resistor in parallel.

Is that what you're instructing?

What ohm values would you incrementally try when doing adjustments?

thanks

Cliff

 

[AllenB]

Say you have an 8 ohm resistor in parallel with a speaker which is (nominally) 8 ohms as well. That's four ohms total. Put a four ohm resistor in series to make a total of 8 ohms again. Now the signal Voltage is divided and the speaker gets half.

From here if you reduce the series resistance you should increase the parallel resistance and vice versa to maintain a balance of 8 ohms (not that you must stay at 8 ohms, but it keeps the crossover frequency).