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2Bak 22nd November 2002 07:20 AM

Zen 4 power
Zen 4
According to the article with 2 amp bias, approximately 25 watts/8 ohm...

What could I expect as output/8 ohm with 1,3 amp bias? 20 watts?
Could I lower bias even further? Which values must R0 and R16 have, for say 15 watts output? How much wattage would a 15 watt Zen 4 dissipate?


From the Zen 4 article:

[....This circuit was designed to idle at 2 amps, which is more than it actually needs to achieve the 25 watt into 8 ohm figure desired. R0 and R1 together form a .33 ohm resistor, and if you leave R1 out, the bias figure drops to 1.3 amps. With both R0 and R1 and a 50 Volt rail, the amplifier will dissipate 100 watts, and with R1 removed, the circuit dissipates 67 watts at idle....]

jh6you 22nd November 2002 08:09 AM

Hi 2Bak

The one and only could give you the one and exactly.

In case..., why not this way?
1 amp (0.66R) with R16 of 220R,
then, 1.32 amp (0.5R) with R16 of 900R,
then, 2 amp (0.33R) with R16 of 1K5.

Stop where you get the sound and the heat of the sink.

By the way, how is your nice BOSOZ working?


wuffwaff 22nd November 2002 08:14 AM


(1.3 x 2)^2/2 x 8 = 27 Watts with 50% ac- current gain.

There´s even a graph that shows power versus distortion at 1.3A bias in the last Zen article.

For 15 watts into 8ohms you need about 0.95A of bias but you need to adjust the resistors for bias and ac-current gain. Just insert trimmers and set the right values by measuring bias and ac-current gain. The put resistors with the appropriate value.

Power consumption will be about bias x supply voltage.


2Bak 26th November 2002 08:10 AM

I figured I would use two Caddock MP915 0.2 R in series and leave out R1, thus having a 0.4 R resistor. And 1K for R16.

JH, my preamp is doing fine :yinyang:

2Bak 26th November 2002 10:56 AM

just one more q:
is it important (for sound quality) that R0, R1, R10, R20, R14 and R15 are metal film types (metal oxid)?
Did anyone use simple ceramic power resistors?

jh6you 26th November 2002 01:06 PM

I normally use ceramic encased wire wound power resistors. They have shapes of white square.

You will find intersting comment about ceramic resistors here:


2Bak 11th December 2002 05:51 AM

One more question: Is there any particular reason why R14 and R15 are paralleled 0,47R except that the same part was used in R0?
I was planning to use one 0,2 R resistor for both (Caddock MP915, 15 watt). That would be just fine, wouldn't it?

vpharris 11th December 2002 06:16 AM

I think that the value is probably somewhat important. The amp will work ok with 0.2R, but those resistors are used to sense the current to the load, and the voltage across them is fed back to the current source to vary it accordingly. So if you want to use a different value, probably something in the current source should be adjusted also. Two are used to get the power handling, since they are only 3W each. I think they were chosen for ready availability.

You'll be ok with 15W, but probably want to get the value to be 0.235R.

See Zen Var 2 article, page 3.

jh6you 11th December 2002 06:49 AM


I think 0.2R 15W OK. And later if you feel the bass is weak,
reduce the size of R16 down less than 1K. Go ahead and enjoy.


SvErD 11th December 2002 07:57 AM

Where is the best place to get those Xicon resistors? They don't seem to have any distributors outside USA/Canada. What type available in Europe would be good?


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