Hi all,
I'm in the last few stages of building a pair of Doz amp modules and I've a question about the output caps. Death of Zen - A new Class-A power amp
Firstly, how is the value of 4700uF for the output cap determined? And what difference would altering it make to the amp?
Secondly, I have a few 20uF MKT caps about; would they suffice?
Cheers to all that take the time to answer a newbie question!
I'm in the last few stages of building a pair of Doz amp modules and I've a question about the output caps. Death of Zen - A new Class-A power amp
Firstly, how is the value of 4700uF for the output cap determined? And what difference would altering it make to the amp?
Secondly, I have a few 20uF MKT caps about; would they suffice?
Cheers to all that take the time to answer a newbie question!
DOZ capacitor
The size of the output capacitor (in conjunction with the speaker impedence) will affect the frequency bandwidth coming out of the amplifier. If you look in your speakers you will most likely see that there are already one or two low value capacitors in the crossover network there to filter the high frequencies over to the mid and/or high units - using a low value capacitor on the output of your amplifier will have much the same effect, hence the schematic specifying a much larger output capacitor value.
If you're only using the DOZ to drive a tweeter in an active crossover set up then you have less to worry about.
The size of the output capacitor (in conjunction with the speaker impedence) will affect the frequency bandwidth coming out of the amplifier. If you look in your speakers you will most likely see that there are already one or two low value capacitors in the crossover network there to filter the high frequencies over to the mid and/or high units - using a low value capacitor on the output of your amplifier will have much the same effect, hence the schematic specifying a much larger output capacitor value.
If you're only using the DOZ to drive a tweeter in an active crossover set up then you have less to worry about.
See this calculator: Coupling Capacitor Calculator by V-Cap You can play with the values and see the effect on frequency response.
A coupling capacitor in combination with your load acts as a high pass filter. In the case of your 20uF caps, you would chop off a huge chunk of the frequency response, starting at around 900Hz. You may be able to halve the 4700uF cap or thereabouts if you only use 8 ohm speakers, but that would be about it if you wish to build a circuit with the same performance as Elliot's.
It's an AC-coupled design. If you want a DC-coupled JLH amp, you might look at the 1996 variant.
A coupling capacitor in combination with your load acts as a high pass filter. In the case of your 20uF caps, you would chop off a huge chunk of the frequency response, starting at around 900Hz. You may be able to halve the 4700uF cap or thereabouts if you only use 8 ohm speakers, but that would be about it if you wish to build a circuit with the same performance as Elliot's.
It's an AC-coupled design. If you want a DC-coupled JLH amp, you might look at the 1996 variant.
There's a fellow named "Shaan" who has built a bunch of JLH designs and the DoZ in both AC- and DC-coupled versions, IIRC. You might look at his (recent) thread on Death of Zen if you get a chance: http://www.diyaudio.com/forums/solid-state/208076-death-zen-15-watt-power-amplifier.html
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