Death of Zen (Audio Amplifier) Questions

I am wanting to build the Death of Zen class A audio amp from Elliott Sound Products. Here is the circuit. I have a few questions:

• For all of the capacitors, what should the voltage rating be? I don't want to break them down from a high voltage source.

• What should the value of C3 be? Somebody HERE used a 4700µf 35V in parallel with a 10µF polypropylene. Is the polypropylene required?

• As a voltage source, I hooked a big transformer through a bridge rectifier through a 30,000 µF, 50 V capacitor and got 36 volts and 34.2 under a 1.33 A load, and 28 VAC from just the output of the transformer. Is this an OK source or do I need a choke for more filtering?

For the 2 12v Zeners I will be using, how much current should they be rated for? Is 500 mA enough?

For all of the capacitors, what should the voltage rating be?

There are no really big capacitors in the circuit, so don't worry too much about price difference. 35V voltage rating is too low, you don't want your components used at their maximum. I believe the next commonly available voltage is 63V, but I guess you can use anything above 40V.

Is the polypropylene required?

No the polypropylene is not required. It is probably used because it has better performance for higher frequencies. Electrolytic capacitors have a relatively high parasitic series induction and by connecting a smaller polypropylene cap in parallel you get best of both worlds. The electrolytic capacitor is big and cheap, the polypropylene has better specs for higher frequencies but is relatively expensive.

through a bridge rectifier

If you are sure that the voltage is not exceeding the 35V, why don't you try it? You're going to hear a hum from the mains, 100 or 120Hz, depending on where you live. It is a great way to learn. Sometimes a voltage regulator fails and you'll recognize the sound and know immediately what a problem with an amp is.

Best though is to get a series regulator to stabilize the power supply. Now this can be a bit tricky because:

1. power supply ripple: On your oscilloscope, check the lowest voltage from your power supply under maximum load. You'll recognize the 100/120Hz ripple, you want the minimum voltage to ground.
2. drop out voltage: A series regulator requires a minimum voltage across in- and output of the regulator. If you use an integrated regulator, check the datasheet for this parameter. You'll have to subtract this value from the value found under 1.
3. maximum current: Check the datasheet of the regulator if it can supply the maximum current that you need
4. cooling: Calculate how much power is dissipated in the series regulator and use a proper sink to keep. Good practice is to keep sink temperature below 70 or 80 degrees Celsius. But you'll have to carefully calculate how large the heatsink for the regulators (and the output power transistors!) need to be. That is worth a question on its own though. ( https://www.youtube.com/watch?v=8ruFVmxf0zs )

EDIT: What should the value of C3 be?

I missed the capacitor sizing question and I initially understood the mentioned parallel caps were a given. I personally think 4Hz (as @Andy calculates) lower cut off is really, really low. 20Hz is already pretty low for a audio project like this. I'd personally calculate with 4 ohm for the speaker impedance though. With these numbers C3 could easily be halved to 2200uF. @Andy's formula is easy enough to experiment with the values you have lying around. Cost and physical size are the important factors here. Also as mentioned before, I agree with @rawbrawb that the parallel polypropylene is a bit overdone for a project like this, but hey, if cost of the cap is not an issue it is nice to experiment with and form an opinion of your own.

• I have a few 2200µF 35v caps laying around so if I could use those instead it would save me a bit – skyler Oct 15 '13 at 21:12

What should the value of C3 be?

The bigger C3 is the better bass resonse you'll get. Without going into the dynamic resistances of your speaker, if you assume it's a dead-load of 8 ohms resistive you can use the following equation: -

$F = \dfrac{1}{2\pi R C}$ where R is 8 and C = 4700uF (say).

This means $F = \dfrac{1}{2\pi \times 8\times 4700 \times 10^{-6}} = 4.23$Hz

This realistically means it has a really low bass response - 4.23Hz is the frequency at which the capacitor is starting to block low frequencies and the signal level will be at approximately 70% of that at say 100Hz.

For all of the capacitors, what should the voltage rating be?

If you can get 50V capacitors these will do the job.

The 0R1 resistor should probably be rated at about 2W so take care on this.

If you find you do get some hum coming through an inductor may help else follow jippie's advice.

Speaking specifically to the capacitor type. There is a known effect with certain capacitors called Dielectric Absorption (DA for short) in which the capacitor has a short term memory effect. This arises through charge trapping (and other mechanisms) in the dielectric material of the capacitor and is a well know effect to be watchful for in precision circuits. You can sort of consider DA to be like battery in parallel to the capacitor that replays the past changes in voltage - at very low levels. Polarized capacitors like tantalum's with many allotypes and grain boundaries in the material are prime candidates for this.

However, it is unlikely that you will notice these effects in this circuit. But in some areas (especially audio it seems) known effects are exploited/exaggerated to drive sales. That might be what is driving the selection of those types of capacitors in that circuit. Do a double blind experiment to be sure you can tell the difference.