Quickie Battery bypass capacitors

brightcity · 2522

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Offline brightcity

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on: January 28, 2018, 02:26:41 PM
Hello all, I recently installed 3 0.47uF film capacitors on the Quickie 36v supply and both of the 1.5 V filaments.

The benefit is a sharper imaging of instruments and better low level detail.



Offline Jamier

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Reply #1 on: January 30, 2018, 08:25:41 AM
Really, seriously?

Jamie

James Robbins


Offline brightcity

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Reply #2 on: January 30, 2018, 09:56:20 AM
Yeah, it worked wonders. Increased soundstage quite considerably. I used the cheap rectangular brown ones.



Offline Paul Birkeland

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Reply #3 on: January 30, 2018, 05:12:11 PM
You should consider the impedance of the capacitors you used at audio frequencies vs the impedance of the batteries.

This is where Jamie's skepticism comes from I suspect.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Jamier

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Reply #4 on: January 31, 2018, 06:02:36 AM
Paul is giving me way too much credit with respect to my understanding of power supplies. I, like many of you, consult this forum to educate myself. My understanding of power supply capacitor function is pretty basic, but I know that two of the functions are Reservoir and filtering of AC ripple.I'm thinking that with a battery supply you don't need the caps since there is no ripple and the battery is the Resevoir. It seems to me that randomly adding caps to a Quickie supply is a recipe for disappointment.

Jamie

James Robbins


Offline Paul Joppa

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Reply #5 on: January 31, 2018, 06:26:04 AM
In stock form (no PJCCS) the signal current flows through the power supply, so any noise or nonlinearity in the battery will affect the signal.

Paul Joppa


Offline Paul Birkeland

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Reply #6 on: January 31, 2018, 06:28:40 AM
A bypass cap can be helpful if you have high frequency noise, as capacitors have some internal inductance that can make them ineffective at high frequencies.  The Quickie power supply operates at 0 Hz, so this isn't a factor.

Batteries have very, very low internal impedance.  I would expect the string of Alkaline 9V batteries in the Quickie to be under 10 Ohms at DC.  As the frequency across the power supply increases, this resistance will go down.

A 0.47uF capacitor presents 340 Ohms of impedance at 1kHz, decreasing down to about 34 Ohms at 10kHz.  If the batteries start under 10 Ohms and drop as frequencies increase, it won't be able to catch up to the battery. 

The situation is more extreme in the filaments, as a typical alkaline D cell will have 0.1 Ohms of resistance at DC, dropping with frequency.  A 0.47uF cap will become helpful at 10mHz, but since the Quickie isn't a ham radio, we don't have to be too concerned way up there.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline brightcity

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Reply #7 on: January 31, 2018, 01:54:25 PM
Oh, whoops, I just guessed it would help like the DC filament in the Stereomour II.



Offline Jamier

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Reply #8 on: February 01, 2018, 05:46:55 AM
I don't have the DC filament heater in my SIIs, but I think it uses fairly large capacitance to filter the AC ripple. I think Paul will correct me if I'm wrong about this. The Quickie is using batteries from the get-go, so no AC.

Jamie
« Last Edit: February 01, 2018, 05:34:16 PM by Jamier »

James Robbins


Offline brightcity

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Reply #9 on: February 01, 2018, 03:07:52 PM
True, there is no AC. The strange thing is that they helped make it sound better to my ears so Im going to leave them in.



Offline Jamier

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Reply #10 on: February 02, 2018, 03:31:19 PM
OK. Have at it.

Jamie

James Robbins