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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Increase input impedance with LL1540?
Increase input impedance with LL1540?
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Old 8th January 2019, 06:22 PM   #11
jev is offline jev  Netherlands
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Great tip!

Indeed I just now send a mail to Connex about the input cap. I think looking at the print there is a bipolar of 10uF there. Not so nice if this is indeed the case
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Old 8th January 2019, 10:02 PM   #12
PRR is offline PRR  United States
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Quote:
Originally Posted by jev View Post
...impedance (3k6). ... cap needs to be 30uF to reach 20 hz which is my goal for the subwoofer....
30uFd into 3.6k is 1.5Hz @ -3dB, 3Hz @ -1dB, 6Hz @ -0.5dB.

_I_ would try any good 5uFd cap before I would put a transformer in there. A C and an L together form a resonance. If you do not do your math, it may be a slight slump or a huge peak. A 47uFd bipolar electrolytic or a 6uFd motor-run capacitor should do fine for a lot less cash than a transformer.
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Old 9th January 2019, 09:51 AM   #13
DF96 is offline DF96  England
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Almost any cap is going to do a better job of passing on audio unmolested than almost any transformer. I don't understand your reluctance to simply use the right cap value, or simply add a buffer.
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Old 11th January 2019, 06:49 PM   #14
jev is offline jev  Netherlands
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I plan to have the following order:
> Pre amp (ultrapath transformer coupled)
> Tube based filter with 1uF at the end
> Stepped attenuator 50K
> Opamp buffer with some gain (no cap at the end), powered by the extra 2*18V on the power amp
> Power amp (have no answer from Connext but I guess the have implemented an input cap)

So no reluctance but would prefer to use hi Q caps only and prefer low value caps

Last edited by jev; 11th January 2019 at 06:51 PM.
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Old 11th January 2019, 06:55 PM   #15
jev is offline jev  Netherlands
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Quote:
Originally Posted by PRR View Post
30uFd into 3.6k is 1.5Hz @ -3dB, 3Hz @ -1dB, 6Hz @ -0.5dB.
I used this calculator:
Coupling Capacitor Calculator by V-Cap

They say:
3db Frequency (Hz): 1.47
Optimal low frequency response (Hz): 14.74

For 20hz I would need indeed "only" 22uF:
-3db Frequency (Hz): 2.01
Optimal low frequency response (Hz): 20.10
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Old 12th January 2019, 10:32 AM   #16
DF96 is offline DF96  England
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Preferring low value caps and hearing bass are two conflicting requirements. You choose.

Faradaphobia is a horrible disease, because it forces its sufferers into taking all sort of peculiar actions to avoid the source of their pain. It is curable, but it takes a while and the occasional relapse is likely.
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Old 12th January 2019, 07:25 PM   #17
jev is offline jev  Netherlands
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Yes yes point taken :-)
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