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December 05, 2019, 04:50:35 AM

Author Topic: Parafeed Output Cap Value  (Read 411 times)

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Offline kritpoon

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Parafeed Output Cap Value
« on: October 02, 2018, 08:34:45 PM »
Hi All,

If I were to change the values of the Parafeed output cap from the stock 3.3uf to 2.2uf, theoratically speaking the -3db lower frequency roll off will be move higher by a few Hz? I remeber reading on the forum somewhere that PJ stated 2.5uf is the best value which using the capacitor half above or below 2.5uf is OK.

I will be using my 8" fullrange BLH speaker which start to roll off at about 80Hz anyway and wondering if I'll be hearing less of the lower bass region with 2.2uf instead of the stock 3.3uf value for output capacitor. Thank you.

Krit.

Online Paul Joppa

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Re: Parafeed Output Cap Value
« Reply #1 on: October 03, 2018, 02:15:09 AM »
It's a compromise, so as always "it depends..."  :^)

The bass extension goes as the squre root of the capacitance, so the rough estimate is sqrt(3.3/2.5) or about 15%. But the minimum load impedance is higher, so there will be slightly greater maximum output in the deep bass region, and slightly lower distortion at the same levels. And if there is a bass resonance in the speaker system, it will interact differently with the amp.

The "optimmum" region is  fairlyf lat so differences will be subtle
Paul Joppa

Offline kritpoon

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Re: Parafeed Output Cap Value
« Reply #2 on: October 03, 2018, 06:06:36 AM »
Paul, thank you so much for the information. When you mean "sqrt(3.3/2.5) or about 15%", please correct me if I am wrong (I am very new at these things) the rated frequency response at the lower end 20Hz is +15% meaning it will be rated @ 23Hz?

"And if there is a bass resonance in the speaker system, it will interact differently with the amp." Can you kindly elaborate on that some more? I do have some problem with my fullrange BLH speaker with pretty bad bass resonance at around 100Hz-500Hz making the mid bass sound muddy and boomy. 

I think I am going to try the 2.2uf value since @ 2.2uf the Cap costs about 30% less than the 3.3uF and the size of the cap is much smaller (I am looking at Jupiter Copper Foil at this position). Some $$$ saving is nice, I can get some other cool upgrades for my Stereomour II. :-)

Offline Doc B.

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Re: Parafeed Output Cap Value
« Reply #3 on: October 03, 2018, 06:24:13 AM »
100-500 Hz resonance is going to be something that needs to be fixed in the speaker or in its room position, not the amp. The parafeed cap size is going to have most effect much lower than that. If I had to guess I would say you might need to decouple the driver from the cabinet. A Fix kit might also help.
Dan "Doc B." Schmalle
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Offline kritpoon

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Re: Parafeed Output Cap Value
« Reply #4 on: October 10, 2018, 09:46:35 PM »
100-500 Hz resonance is going to be something that needs to be fixed in the speaker or in its room position, not the amp. The parafeed cap size is going to have most effect much lower than that. If I had to guess I would say you might need to decouple the driver from the cabinet. A Fix kit might also help.

I agreed DOC, the problem is with the speaker itself. Thanks for the suggestion about decoupling, I'll try that. In the mean time, I use some damping material (foam sheets) damping the mouth of the horn toward the inside and up the horn path which helps to dampend the resonace around that area quite a bit.