Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Quickie => Topic started by: coca on November 29, 2013, 06:16:03 AM

Title: Coupling Cap Size for Quickie
Post by: coca on November 29, 2013, 06:16:03 AM

The size of the coupling cap for the Quickie is 2.2uf: Is there a range in size above that, that can be used in the quickie circuit?

Bernie.

Title: Re: Coupling Cap Size for Quickie
Post by: Paul Birkeland on November 29, 2013, 09:05:23 AM

It depends a bit on the input impedance(s) of what you're driving.  1uF-10uF is fairly common.

Title: Re: Coupling Cap Size for Quickie
Post by: Paul Joppa on November 29, 2013, 09:10:30 AM

Larger values are OK; the plate is at a positive voltage less than 36v, so electrolytics will work as well. If you have a couple 100,000uF 60v caps lying around, give them a try! (Give it a day or two for the startup transient to die out, though  :^)

Here is a table of approximate minimum values, based on -1dB at 20Hz, as a function of the load impedance (input impedance of amplifier which is driven by the preamp):

Load   uF
10K     1.5
15K     1.0
25K     0.6
50K     0.3
100K   0.15

However, one possible source of hum is minimized by using values greater than 1.0uF in Quickie, or 0.5uF for Quickie with PJCCS, Reduction, or Eros.

Title: Re: Coupling Cap Size for Quickie
Post by: coca on November 29, 2013, 09:13:35 AM

Thanks guys. That information is very helpful.

Bernie.