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Old 7th March 2005, 11:56 AM   #1
Buhl is offline Buhl  Denmark
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Default Optimizing bass response in Zen 4

Having finished an "upgraded" proac 2.5 with 9500 tweeter, i have some questions on how to get the most low end control out of the zen 4 circuit. I have 4 boards, but now Im running only two, with irfp240 and 2,8 amps of bias, 750 va toroid 63000 uF for both channels.

The 2.5 clone have a hefty booming problem in my living room, so other placements should be tried, but I also feel that the low damping factor of the zen affects the booming in the lower octaves.

I have the options of finishing two more boards, and running i parallel, or running the bridged. I am very, very pleased with the level of detail and the overall sound in the midrange of the zen, and Im afraid that some of this may vanish if I start to parallel boards.

Bridging gives more power, and i have also read that people thinks it betters control, paralling boards gives option of double bias, up to 5,6 amps, and mabye a little more output power.
although more power would be nice, 30 watts i more that enough for me, as my room is about 20 square meters, and the high level of detail in the speakers and amp lets me enjoy music at lower levels than normal. I have 044 as well as 240 mosfets avaiable for use.

Is it possible to just another output fet, with just tow more resistors ??

What configuration should I go for ?

Cheers !
Hans
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Old 7th March 2005, 05:31 PM   #2
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While not very high, the DF ought to be adequate to bring
a woofer under control, however there are apparently other
qualities to bottom end performance, and the Z4 doesn't have
a lot of whatever mysterious quality it is that delivers transient
punch with real energy. I don't see it as damping factor as such,
since we've observed a number of cases where the DF measured
the same but the bottom end punch and control were very
different.

Usually more hardware (more supply, larger or paralleled devices,
etc) achieve an improvement in this area, but often at the
expense of performance in the upper end of the spectrum. If
you can bi-amp, this is an area that you can explore easily.

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Old 7th March 2005, 11:26 PM   #3
Blues is offline Blues  United States
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Hans,

Some builders including me have noticed better quality bass by increasing the input buffer bias...I have mine at about 30mA. One more thing I noticed is again better bass detail when the Drain of Q1 is at least 24V or more. Although at 2.8A bias Q1 will be about 67W dissipation...if you heatsunk well you can try it. Try also increasing your PS uF value to one that approaches the Aleph 3's or more if you can.
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Old 8th March 2005, 11:09 AM   #4
MikeW is offline MikeW  United States
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Try scaling back the feedback. I changed mine by a factor of 5. Then adjusted the gain a little. It will take a little time to get the sound you like.
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Old 8th March 2005, 05:52 PM   #5
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It's an interesting effect that adjusting the amount of
feedback will improve the bottom - often in the reverse
direction than you would imagine. Part of this is from
a higher output impedance on the amp with lower
feedback.
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Old 8th March 2005, 07:38 PM   #6
MikeW is offline MikeW  United States
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Quote:
Originally posted by Nelson Pass
While not very high, the DF ought to be adequate to bring
a woofer under control, however there are apparently other
qualities to bottom end performance, and the Z4 doesn't have
a lot of whatever mysterious quality it is that delivers transient
punch with real energy. I don't see it as damping factor as such,
since we've observed a number of cases where the DF measured
the same but the bottom end punch and control were very
different.

Usually more hardware (more supply, larger or paralleled devices,
etc) achieve an improvement in this area, but often at the
expense of performance in the upper end of the spectrum. If
you can bi-amp, this is an area that you can explore easily.

Could you look into this further? Compare a Zen to a X1000, same signal, same speakers. Square waves @25 Hz. into El-pipeO.
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Old 8th March 2005, 08:30 PM   #7
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Hmmm. Look into this further? All I have is subjective
anecdotal observations. No question that the X1000
will surpass a Zen at 1 watt, although it does measure
better, so that isn't going to be much of an illustration.

More interesting to compare like-to-like.

All other things being roughly equal, I usually observe:

Bigger hardware has better bottom end.

3rd harmonic character (PP) has a better bottom than
2nd harmonic (SE), more specifically, balanced circuits
have better bottom than single-ended.

Class A can has better bottom end than AB (back to the
bigger hardware thing).

The key word is usually and counter-examples exist.
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Old 9th March 2005, 11:49 AM   #8
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Quote:
Originally posted by Nelson Pass

3rd harmonic character (PP) has a better bottom than
2nd harmonic (SE), more specifically, balanced circuits
have better bottom than single-ended.
Hmm...

Zen has a weak bass, but I do not realize it long because the sound above midbass lets me forget it soon. The sound of Zen resembles a bulb lamp light. Meanwhile, I have Zen V2 which is X-fied. From this, I well hear the roaring RPM of Harley-Davidson, which Terminator is riding, and the upper frequency sound resembles a bit fluorescent light (however, still very good). This might be related with 2nd (Zen) and 3rd (X-Zen V2) harmonics as you say.

I did try other things to improve the bass sound of Zen. But, the best way was X-fying it.

To me, it seems that the bass sound is getting better when the size of transformer is as big as possible and when the output current supply capacity is well enough (my speaker's nominal impedance is 4 ohms). This is based on my experience with Monolithic SuperSymmetry amps. I hear very tight and deep bass sound when I do paralleling them. Meanwhile, If I do bi-amping them, I hear very detailed and transparent upper frequency sound.

Last weekend, I had a small party at my place. One Norwegian guy said that the sound from the paralleled was as good as his Electrocompaniet plus B&W system. By the way, that night, I offered too much Cognac to a young guy. He was finally drunk and fell down with my speaker.
Damaged......., not him.
Eventually, it was my fault.......
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Old 9th March 2005, 12:09 PM   #9
steenoe is offline steenoe  Denmark
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Quote:
The 2.5 clone have a hefty booming problem in my living room,
The Clone's has a reputation of beeing boomy themselfes. That could be part of it. Try and stuff the bassports with a homeknit sock or something like that, to check that out.

Steen.

Ps. I have a pair of those myself.
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Old 10th March 2005, 07:04 PM   #10
Buhl is offline Buhl  Denmark
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Hello all (especially "The One" - you are so much THE MAN for providing poor students (and others) with the possiblity to build state of the art amps !!!!!)

I agree with you nelson, that the Z4 doesn't have much of the mysterious punch and energy in the bottom octave, but I would certenly not call its bass weak, as mentioned in this tread - the bottom is indeed wery plentyfull..... OTOH, i love its midrange qualitys very, very much. I have fooled around with the hardware options the last few days, added another 47000uF cap, so now I have close to 100000uF - for two channels. I have then lowered the bias to the "original" 2.0 amps, and noticed that the sound got alot more "sleek" and correct, not as plentyfull bottom - and thus solved my problem, or at least helped some way. BUT, I have also noticed, sadly, that the "space" around the speakers have diminished, and the wonderfull midrange, that seems to pop out of nowhere with the greatest of ease, have become more harsh and troubled..... I thougth that more bias helped the amp cope with the low impedances, and thus improved the low range reprodution, now I have also learnd that is affects the other aspects of the amps audio spectrum as well.


I have increased the buffer bias, but dont know how to change the feedback or gain ??? I read from the thread that I should raise the feedback, how is this done ?? I suspect R3 @ 221K and C12 @ 5PF should be changed ?? Gain is R2 or R8 ??

I know that the 2.5 is troublesome, but I think that the problem is only occuring now, because my previous speakers vere closed system, and very weak in the low range, and thus now the plentyfull bottom in the Z4 becomes to much......

Steen: Godt træk med at sende nogle Bolcher til ham Italieneren - det er ægte indre-marked-frihandel Har prøvet at dæmpe porten, men syntes det går ud over dynamikken i mellemtone, øverste bas, måske skal jeg bare prøve at tune basporten om.......

Cheers !

Hans
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