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Old 2nd March 2001, 01:32 PM   #11
diyAudio Member
Join Date: Feb 2001
Location: Czech republic
I have only one simple question.
What speakers do you have? I mean, what impedance and
sensitivity these speakers have or what brand. Because
I have also built the Zen and I think that my speakers
aren't quite suitable for that amplifier.
Thanx DooShan
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Old 2nd March 2001, 04:45 PM   #12
awj is offline awj
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Join Date: Feb 2001
Location: US
Default speakers

I did a lot of research on speakers after i built zen. speakers selection depends on your listening style and of course your budget. being a diyer, my budget is limited. what i find in speakers within my budget is: the more efficient a speaker, the more terrible it sounds (ex: new klipsch product lines). it is true that efficient speakers (>95db) will sound louder, but if you don't need a concert hall like sound in your home, you can still live with less efficient one.
after reviewing many speakers, i narrowed them down to dynaudio and kef (both bookshelf types). the final decision is kef rdm2 monitor. it has 6 ohms impedance and 91db efficiency. it sounds excellent especially for mid and high. bass is a little bit weak due to zen's low damping factor and low impedance, but I am not a big fan of thunder bass anyway.
I managed to tighten the bass by implementing pass' zen revisited. setting bias current = 3A improves damping factor.
if you really need a good and efficient diy speaker, check the stright8 (www.bottlehead.com). some people say it is a very good speaker for se amps, but it definitely is out of my budget.

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Old 2nd March 2001, 06:00 PM   #13
byu is offline byu  Canada
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Join Date: Feb 2001
Location: Toronto, Canada
Default speaker

I do not think the quality of the speaker is in any way related to efficiency, actually the Zen requires a relatively high efficient speaker. I constructed a pair of Ariel 6 ( 93db ) last year and it sounds great with my 8 Watt SOZ. I think high efficieny speaker may have an advantage since it requires less wattage to produce the same level of sound. Lower power output from the Amp means lower distortion.

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Old 5th March 2001, 07:51 AM   #14
diyAudio Member
Join Date: Feb 2001
Location: Lublin/Poland
As for the speakers.
I use 8Ohm speakers from Bose. I cannot tell you what
efficiency they have. They are ~10yrs old and I bought
them 2nd hand. They are of a traditional design, no
direction reflecion principle (or whatever they call it).
I do not think any of the problems I experienced was
due to the speakers. I do not play and do not intend
to play my music loud. Actually, Zen is quite loud for me.
And yes, I have enough bass.

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Old 23rd March 2001, 04:24 PM   #15
diyAudio Member
Join Date: Feb 2001
Location: Lublin/Poland
So now the clipping in the BOZ is gone.
I adjusted the voltage at the drain of the mosfet
as you have suggested. It helped (in 99%).
Since I do not need that much gain I lowered
the valued of R104 down to 820Ohm (now it is ok in
the remaining 1%).

Then I turned my attention to ZEN. I had the original
circuit. I have upgraded to the Return of Zen.
(with R10 1kOhm, P1 25kOhm and R8 47kOhm and R11 6.2kOhm
instead of 3.3 as by NP). It playes better now, but
when I remove R11 I get the impression of more intimacy,
more dramatic sound. I know that feedback vs. no feedback
is subject to a huge debate. (Ok, I did not remove all the
I am listening to really huge distortions and enjoying them? Or do you think I really get some improvement?

The bad news is (in the low feedback case) that the Zen starts to clip when listened at higher positions of the BOZ's volume pot. To me it is not a big problem, because it is loud enough way before
it clips.

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Old 24th March 2001, 02:42 AM   #16
rljones is offline rljones  United States
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Join Date: Mar 2001
Location: california
Default low feedback/distortions


I originally constructed a Zen amp using only N-channel mosfets. What I found, and only by using a distortion analyzer and a scope, was that unless there was about the same level of feedback applied as NP recommended, the frequency response was 5 dB down at 20 kHz. Feedback is necessary to get a decent response out to around 50 kHz. Of course, the more feedback, the less overall gain the amp has, but that is a definite trade-off with only a single stage.

The other problem with the Zen design is that the input source dramatically affects the frequency response. In fact, with some sources you could hear, and measure, the rise and fall in the upper harmonics: that is the input modulates the amp in a non-linear fashion. (This may not be a problem if the amp is matched with a NP mosfet preamp, as the single mosfet preamp effectively behaves as an input stage for the output mosfet in the Zen.) This non-linear response probably occurs because there is nothing to isolate the input from interacting with the feedback. I ended up adding another stage, and finally, after putzing around with various input stages, I scrapped the circuitry and built an Aleph style amplifier.

This isn't the thread to continue with the Aleph story, but I did modify the NP design and wound up with an amp that has 10 times less distortion, a freq. response to 200 kHz, and between 5 to 10 times greater S/N ratio (around -102 dB) than a stock Aleph. I've also simulated the design and optimized the IV control portions of the circuit so it can better deliver current into 4 and even 2 ohm loads, albeit with slightly more current and heat dissipation. I made a 4x7 inch circuit board that holds everything, including the power supply and up to 4 pairs of output mosfets: just plug in a transformer and the input and output jacks. If anyone is interested I can provide more details.
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Old 2nd April 2001, 08:14 AM   #17
Koy is offline Koy  Czech Republic
diyAudio Member
Join Date: Jan 2001
Location: Zlin
Default Re: low feedback/distortions

Would you be so kind to send me more details about you construction. I made some simulations of Hoffmanns ampamp like Alpeh 3)- the results were very bad - THD about 2%. So I am interested in your results ( NP declares THD less then 0.2%, for Alpeh 3). Are you better?? Koy

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Old 2nd April 2001, 08:16 AM   #18
Koy is offline Koy  Czech Republic
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Join Date: Jan 2001
Location: Zlin
Default Re: low feedback/distortions

I am sorry, my reply is for rljones. I made a mistake.
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Old 2nd April 2001, 09:56 AM   #19
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Join Date: Feb 2001
Location: London UK
Default aleph

I'd be very interested to hear more about your 'aleph', rl. I'm currently dithering about what poweramps to build, and the points you have addressed are exactly the ones that I have marked down as the 'cons' of an aleph.

Please, new thread!
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Old 31st October 2001, 08:26 AM   #20
bawang is offline bawang  Malaysia
diyAudio Member
Join Date: Oct 2001
Location: Malaysia
I read with interest all the comments on the BOZ preamp. Surprising none of you list noise (humming @ 50/60Hz and buzzing @ 100/120Hz) as a problem. See my posting in the other Bride of Zen category on this problem.

Putting the volume control at the input in my case resulted in circuit (oscillation?) at the extreme settings of the pot when coupled to the Leach Amp. Even when it's not oscillating, hum/buzz level is extremely high, measuring at least 50mV at the power amp output.

Nelson Pass suggested that I increase the gate resistance from 100 ohms to 1,000 ohms. This helped a bit, no more oscillation but still the high level hum/buzz problem........ Moving the pot to the output solved this problem.

Supposing the BOZ has a gain of 8 (18dB) and clips at an output level of 10V, the maximum input level must not exceed 1.25V; which any CD player will exceed. Again, Nelson's suggestion is to attenuate the input. I might try to lower the gain as stated in this forum.
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