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Author Topic: Crack output cap as preamp  (Read 4172 times)

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Offline Ritchie

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Re: Crack output cap as preamp
« Reply #15 on: October 12, 2013, 04:19:39 AM »
Thanks guys, this was educational for me, I have always built pre amps with small output caps as I was using tube power amps with high input impedance, so I never paid much attention to the output resistor as it was usually 1M.
I now realize the difference with a very large output cap.
I have a soft start timer circuit which I can use to have the preamp output shorted for 30 seconds on start up.
Would this be an option to allow me to use a much higher resistor such as 1M?

Thanks
Ritchie
Ritchie M.

crack/speedball as preamp,linn lp12 w/radikal/keel/urika phono, linn majik 4100 active monoblocks,linn majik isobarik speakers(active).

Offline Ritchie

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Re: Crack output cap as preamp
« Reply #16 on: October 12, 2013, 04:30:26 AM »
When calculating with a 5K resistor my -3db ends up around 2.7 hz, that should be fine?

Ritchie M.

crack/speedball as preamp,linn lp12 w/radikal/keel/urika phono, linn majik 4100 active monoblocks,linn majik isobarik speakers(active).

Offline Grainger49

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Re: Crack output cap as preamp
« Reply #17 on: October 13, 2013, 06:15:53 AM »
Ritchie,

I couldn't remember what it was that bothered me about this thread.  I have it now.

It is a good design parameter for first order 3dB down point of 0.2 Hz, flat at 20 Hz.  But...  You and I live in the real world.  Neither my speakers nor my room could produce a flat 20 Hz.  It is extraordinary for a speaker to be FLAT at 20 Hz.  It would take a distance from your woofer to the "back" wall of 56.266 feet for a full wave to emit from the woofer before reflecting.  This doesn't even go into the lack of 20 Hz notes in 99.99% of recorded music.

What I am saying is that the reason you will hear no ill effects from a smaller capacitor. Give one 22uF a try, then parallel in the other.  You are likely not to hear a bass improvement with two in parallel.  However, you might get some smearing of the image with two in parallel.  (I did when doing a cap comparison in my Eros)

Offline Ritchie

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Re: Crack output cap as preamp
« Reply #18 on: October 13, 2013, 02:19:12 PM »
I will definitely give that a try as I would much prefer just the single cap also.
I have found paralleling caps to create a bit of smearing but usually with different values as they have different time constants.
One is better than two or more, but I have always been under the assumption to only parallel with equal value caps.
I agree, we tend to over design to ease the audio nervosa.

Thanks Grainger,
Ritchie
Ritchie M.

crack/speedball as preamp,linn lp12 w/radikal/keel/urika phono, linn majik 4100 active monoblocks,linn majik isobarik speakers(active).

4krow

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Re: Crack output cap as preamp
« Reply #19 on: October 13, 2013, 02:28:33 PM »
 G,

  I know that I am side stepping a bit here, but regardless of that, I am curious about something. Maybe I don't recall correctly, but wasn't there a time when Multi-cap made a capacitor that had an internal bypass capacitor? Maybe I just dreamed it.

Offline Ritchie

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Re: Crack output cap as preamp
« Reply #20 on: October 13, 2013, 02:37:15 PM »
I believe they still do. Haven't tried one in a long time though, maybe they have some manufacturing voodoo!
Ritchie M.

crack/speedball as preamp,linn lp12 w/radikal/keel/urika phono, linn majik 4100 active monoblocks,linn majik isobarik speakers(active).

Offline Grainger49

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Re: Crack output cap as preamp
« Reply #21 on: October 14, 2013, 12:44:24 AM »
Greg,

I agree.  Yet, still, I didn't like the parallel 0.22uF KK Teflon caps as much as a single 0.22uF.  The design value was 0.47 for that flat 20 Hz.  Still, it just didn't sound as coherent.