A Baby Zen V2

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Joined 2002
A Baby ZV2...?

Having no measurement tool, I mathematically estimated the ac current ratio between R1 and R13/14 of ZV2 (of 30V dc-supply). I got 55.2941%. I did this just for a DIYer¡¯s fun.

By the way, I am stepping back to reduce the bias current from 2 to 1.32A. It is mainly to lower the heatsink temperature. The work for this would be easy by applying 0.5 ohms for all of R1, R13 and R14. Sure, it is a must that I should get back to the 50% ac current ratio, either by replacing R15 with 700 ohms or by replacing R6 with 3.3k ohms.

Meanwhile, I have the following questions.

This tweak must be worsening the distortion character. Is it however OK if I stay within 8W output, for a 4-ohm speaker?
If no, what could be menimum bias current for the (A) to be practical?
Which is better, replacing R15 or R6?

Your advice before I kick my ... would much appreciate.

Disabled Account
Joined 2002
Thanks Mr Pass for the advice on R16.
Attached is inner side of my baby ZV4 in case anybody comes in and calls for open discussions.

ZV4 is the summit of Zen variations. Relatively, my baby has a low profile. Nevertheless, the baby is now launched, and on sea trial with a passive pre. I have a plan to post the sea trial results in 10 days.



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Disabled Account
Joined 2002

The baby is still on the sea trial.

By the way, the circuit is somewhat modified. I re-checked data of IRFP150,
estimated the C(gs) and C(Miller), and got the total C(in) of about 3000 pF.
C(stray) is however ignored. With this high C(in), I wanted the upper critical
frequency beyond about 60 kHz in normal listening. The modification was
a result of this thinking.

I presume the max output power of 15W+15W. If I stay within 10W+10W,
I would not need to think about the distortion much.

I¡¯m continuing my listening trial with TV providing 0.5Vrms output, DVD/CD player
of 2Vrms and tuner of 2Vrms. So far this baby works really better than expected.
Tho I am wondering if this circuit has no technical defects¡¦

Any advice, comment or question¡¦?

In a few days, I¡¯d like to come back with about the sound.



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Disabled Account
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Conclusion is made with the baby attached below.
  • The maximum output power is low.
  • The heatsink temperature is low. According to the measurement, it is 41.1 degC at the room temperature of 25.5 degC. (230mmx250mmx65mm of 18 fins per channel)
  • The asymmetric Class A character of Zen might be a bit diminished due to the reduced bias.
  • However, the naturalness of the sound, as in other Zens, remains the same.
  • Detailed sound is distinctive, but somewhat dry. I think the dry sound could be improved by using the active preamp, e.g. BOZ.
  • The overall musical impression is to my satisfaction.
Thank you for your reading.


The above is with 4-ohm 92dB Ariel speaker. I increased R16 from 700 to 1k ohms to soften the bass a little bit. If I increase R16, it also helps speaker quietness on idling condition.


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Disabled Account
Joined 2002
Thank you for the advice, Mr Nelson Pass.
If I replace the 150¡¯s with 140¡¯s or 044¡¯s, I¡¯ll come back.

One thing is missed in the above conclusion.
The R19 of 2.7k is sized to scale down the output level.
The full output could be achieved, with R19 of 1.5k
when the input is 2 Vrms.


Disabled Account
Joined 2002
To whom interested

For me, the best sound performance is finally achieved with 1.5K of R16--i.e. when the AC current through R0 is 30% of the current going through the parallel R14 and 15.

The texture of BEETOVEN SYMPHONIE No5, Wiener Philharmoniker, Carlos Kleiber, was very nice. Also other music¡¯s...

As you might already know well, we could find our sound by tweaking this resistor value not only with the baby, but also with ZV2 and V4. It's another fun... I'm sure it.
Disabled Account
Joined 2002

I have a plan to make my baby Zen balanced, with a transformer of 24V(6.2A)+24V(6.2A).
Sure, I need you help.

  1. Is the circuit acceptable?
  2. Any room for improvement?
  3. The balanced operation might convert the asymmetric Class A character of the unbalanced Zen
    to symmetric character. In this case, the naturalness of the sound would be lost?
    Instead, the dynamism of the sound would be a gain?[/list=1]
    Your advice would much appreciate. ;)



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Disabled Account
Joined 2002
Hi Micke

  • I need few powers, not big.
  • My wish is gaining the purer sound from the simpler circuit.
    (I carry my backpack, HAGLOFS LIM series made in Sweden.
    I'm sure you know what LIM stands for.)
  • Since I have no idea how to produce the PCB, I should do p2p wiring.
  • I look forward to easier repair and modification.
  • I feel more fun when I make the difference from the others.
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