Sound of Zenquito

ABO · 2004-06-10 2:07 pm

Some time ago I started a thread inquiring about Zenquito evolution. It resulted in me deciding to build one and promising to report my findings.

Well the amp is finished now. I can only compare the sound against my old amp, Elektor's IGBT-amp (nonante in French). I had hoped that Zenquito would be a worthwhile upgrade because I had read a lot of positive things about the amp, mostly in a French forum.
In comparison, Zenquito sounds less dynamic, less transparent and somewhat muddy in the midrange. And completely flat soundstage.
In another thread someone compared the sound of amps with muddy ponds and crystal clear mountain lakes. Zenquito obviously is of the former type. I'm sure it can sound good to some, but not to me. It has no special timbre of emotional engagement at all. To me it just sounds uninteresting.

In short: I don't like the amp. I really don't understand why people like this amp. I hope that someone can explain what it is he likes about the sound, I'm very interested.

Perhaps there is something wrong of course. I attached some pictures. If anyone can come up with improvements or sees any mistakes I may have made, please let me know.

ABo

ABO · 2004-06-10 2:09 pm

ABO · 2004-06-10 4:59 pm

Zen Mod · 2004-06-10 10:12 pm

& your speakers are?

ABO · 2004-06-11 7:32 am

Hi Choky,

Do you think it would matter. I compared both amps in exactly the same setup. Are there any known issues with Zenquito that makes the amp sensitive for speaker load?

Anyway here it goes:

http://home.hetnet.nl/~geenius/HATT-III.html

ABo

BTW: This experience got me thinking. In France there is a community of people who all really like this amp, just like we have a community of people, here in DIYaudio, who all just love Aleph's.

Aleph and Zenquito share some technical similarities too: fairly high THD and similar distortion spectrum. My experience with Zenquito is corresponds exactly with the remarks PMA makes about Alephs. Of course it could be I'm plain deaf or just wrong, but it seems to me that the entire Aleph/Pass thing may well be a severe case of groupthink.

Disclaimer to all Passfans: I actually never listened to an Aleph or any other Passlabs amps.

Jay · 2004-06-11 9:00 am

Even though I have never built the Zenquito, I believe that the
speaker does matter, and so is pre-amp. This amplifier reminds
me of some MOSFET amps I have ever built including the Crescendo.

What you have described was just the "signature" of MOSFET amps
running in class B and with relatively short path (amplification
stage). I have heard that this amp is only a little better than
the crescendo (but that's just somebody's opinion).

Assumming that this amp is similar with those MOSFET amps, especially
the crescendo, you need at least 8" woofer of Peerless quality, or
a floorstander. 3-way is better, may be because the amp is not good
at mid (muddy).

MOSFET usually have low transconductance. I believe this makes it
dificult to match with many speakers to get an interesting sound.

And of course, you cannot compare such amps with Alephs. May be
MOSFET is good only in class A???

Zen Mod · 2004-06-11 11:11 pm

simple amp need simple speaker

off course-meaning on highish efficiency and friendly impedance modul

till · 2004-06-11 11:46 pm

as i understand - there are speakers of a kind that need a lot of power and a lot of damping factor.

And there are speakers of a kind that makes a lot of SPL with a few Watts and do not need much damping factor.

You say aleph, Zen etc, have a lot of THD. Thats not true. You compare numbers at full load or substancial amount of Watts. I measured ZEN 4 against chipamps. The truth is the Zen, aleph etc. has very very low THD at low power, growing with power you pull out of them. The chipamps are different, THD is significantly higher than Zen at low power levels, goes to very low values for something like 10% to 100% nominal power. As my speakers for example need something about 200mW for normal listening, a Zen or Aleph is much better in THD...

fab · 2004-06-12 4:47 am

till said:
as i understand - there are speakers of a kind that need a lot of power and a lot of damping factor.

And there are speakers of a kind that makes a lot of SPL with a few Watts and do not need much damping factor.

You say aleph, Zen etc, have a lot of THD. Thats not true. You compare numbers at full load or substancial amount of Watts. I measured ZEN 4 against chipamps. The truth is the Zen, aleph etc. has very very low THD at low power, growing with power you pull out of them. The chipamps are different, THD is significantly higher than Zen at low power levels, goes to very low values for something like 10% to 100% nominal power. As my speakers for example need something about 200mW for normal listening, a Zen or Aleph is much better in THD...

The increase on THD as the power increases is an effect of lower feedback amp design (as I have experienced).
You really listen to 200mW! You must have efficient small speakers? Regarding THD criteria, you probably already know as it is mentioned a lot on this forum that it is only one of many criteria and probably not the most important.

Regards,

Fab

jam · 2004-06-12 2:43 pm

ABO,

There are a couple of ways to improve the sound of Zenquito. One is to run yhe front end off it's own bridge rectifier and possibly regulate it and the other option is to increase the bias.

Regards,
Jam

ABO · 2004-06-12 8:23 pm

Hi,

Thanks for your reactions.

Till,

I haven't read the datasheet for any power opamps, but usually the THD+N vs. power plot has a bath tub shape. In the lower power region the values is determined by noise and HD is neglectable. As output power rises the contribution of noise decreases, but HD rises. There is a optimum somewhere between in the 1-10 W region, then HD rises more than noise falls and THD+N is rising again.

At least this is my conclusion from these graphs. It seems that S/N ratio of your amp is just better than most chipamps, not HD.

Jam,

thanks for your suggestions. I did try a low-pass filter between PSU and input and VAs stages (10 ohm / 1000 uF), see picture. The sound seemed to clear up entirely. Bass seems tighter, soundstage much more transperant and less muddyness.

However there still seems to something wrong. I can't put my finger on it yet. Perhaps it's what Jocko says about current feedback: it just don't sound right.

You said you liked Zenquito. Difficult perhaps, but can you tell what is was you liked? What is the amps strongest point?

Best,

ABo

jam · 2004-06-13 4:06 am

ABO,

I have some ideas, could you e-mail privately at jsomasundram@carolina.rr.com.

Regards,
Jam

JFG67 · 2004-06-15 5:46 pm

ABO said:
Some time ago I started a thread inquiring about Zenquito evolution. It resulted in me deciding to build one and promising to report my findings.

Well the amp is finished now. I can only compare the sound against my old amp, Elektor's IGBT-amp (nonante in French). I had hoped that Zenquito would be a worthwhile upgrade because I had read a lot of positive things about the amp, mostly in a French forum.
In comparison, Zenquito sounds less dynamic, less transparent and somewhat muddy in the midrange. And completely flat soundstage.
In another thread someone compared the sound of amps with muddy ponds and crystal clear mountain lakes. Zenquito obviously is of the former type. I'm sure it can sound good to some, but not to me. It has no special timbre of emotional engagement at all. To me it just sounds uninteresting.

In short: I don't like the amp. I really don't understand why people like this amp. I hope that someone can explain what it is he likes about the sound, I'm very interested.

Perhaps there is something wrong of course. I attached some pictures. If anyone can come up with improvements or sees any mistakes I may have made, please let me know.

ABo

Bonjour

,

(nonante 90 in no French ... in Belge)

Elektor's IGBT-amp, Hexfred IRF 60W, avec l'ampli caisson de basse 240W à IGBT, techniquement les plus mauvais amplis conçus par Elektor, et ayant posés le plus de problèmes aux lecteurs français. :smash:

http://perso.wanadoo.fr/jm.plantefeve/sche.html

Etage d'entré 2SK246/2SJ103 >>>> 1 ~ 1,5 mA
Etage driver 2N3440/2N5416 >>>> 10 ~ 15mA
Etage puissance 2SK1058/2SJ162 >>>> Classe AB 110mA/Mos
Etage puissance Classe A, ajuster R driver R68 ~ R150 ohms suivant I repos ...
P classe A = ( I repos x SQR 2 ) ² x Z
Variables 470 ohms ajuste Offset et I Repos

Impédance d'entré :

>>>>> Source <1k ohms maxi >>>> potar 10k ohms >>>> 47 k ohms

... Lorsqu'on fait un ampli double mono il n'est pas souhaitable de relier les masses des prises Cinchs à la terre car l'on crer une boucle de masse bien inutile :dead:

Mosquito JFG67

http://perso.wanadoo.fr/pol.bct/JFG/Dsc02015.jpg
http://perso.wanadoo.fr/pol.bct/JFG/Dsc02013.jpg
http://perso.wanadoo.fr/pol.bct/JFG/Dsc02018.jpg

ABO · 2004-06-16 8:53 am

Finally, a reply from France!

JFG67 said:
Bonjour ,

(nonante 90 in no French ... in Belge)

Elektor's IGBT-amp, Hexfred IRF 60W, avec l'ampli caisson de basse 240W à IGBT, techniquement les plus mauvais amplis conçus par Elektor, et ayant posés le plus de problèmes aux lecteurs français.

Hmm.. I wish I could read French better, those links look like recommended reading.

Hi JFG,

According to the designers, the IGBT-amp is one of their best sounding amps! It is true however that is is notoriously unstable, both electrically and thermally.

You are also quite right about my grounding scheme. I've started another thread about that, and I think I have it sorted now:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=35973

Changing grounding scheme is an improvement. But the real bang comes from some modifications that Jam and I are working out. I can now say that, with minor effort, this amp can be great. The improvement is so big and the mods are so simple that I cannot understand why Plantefeve didn't do this himself.

JFG,

You are a real champion for Zenquito. I read a lot of your posts on the French forum. You are always helping people out with advice. Are you using the unmodified Zenquito yourself? Or did you also do some serious modding. Do you recognize some of my remarks about sound quality?

Elso Kwak · 2004-06-16 9:43 am

Re: Modifications

ABO said:
. But the real bang comes from some modifications that Jam and I are working out. I can now say that, with minor effort, this amp can be great. The improvement is so big and the mods are so simple that I cannot understand why Plantefeve didn't do this himself.

Hi ABO,
I am looking forward to the modifications Jam and you worked out!. Will these be posted? Or else could I receive some more info by email?

PMA · 2004-06-16 10:07 am

Great country flag, Elso

Upupa Epops · 2004-06-16 10:46 am

To ABO : This amp must have big distortion on high frequencies, 'cos current in VAS / driver stage is too low and OLG is low too. Only what you can do with this connection is, that you must get out driver from PCB and replace it by another type with higher Pc, which you must get on main heatsink. Certainly you must get there resistors with lower value to the emitors of VAS. But don't wait, that sound will be dramaticaly upgraded

, circuit with this concepcion is not quite correct

.

ABO · 2004-06-16 12:16 pm

Hi Epupa,

I have indeed some problem with that. Because of thermal problems (VAS transistor ran too hot) I decreased bias to 9 mA. The VAS stage by design has bias current of some 10 mA. This is low indeed. On the other hand, the input capacitance of the lateral mosfets (2sk1058/2SJ162) is also very low. Using another VAS transistor should allow for larger current. Do you have any suggestions?

Changing the VAS' emitter resistance is tricky. It increases open-loop gain and could compromise stability. The same may go for changing the transistor, because it determines the dominant pole.

Unfortunately, I don't have a scope and signal generator or any other faciltities other than my DMM. So I'm not in for real serious changes to the circuit.

Hmm, I should have kept my job as a design engineer

Upupa Epops · 2004-06-16 12:35 pm

Easy way for replacemet is MJE 340 / 350. Yes, with lower resistors rise gain, but it is,what you need - but do it without scope is it suicide

. But some of your friends have it, or no ? Input capacity of two fets is app. 1200 pF ( n ch ), respectively 1800 pF ( p ch ) and it is not so little.

ABO · 2004-06-16 1:49 pm

Hi Epupa,

I'm afraid I don't have any friends with even the slightest interest in electronics or audio. I can sometimes use some equipment of our local univeristy. But only on occasion.

I took a look at another amps:

Elektor crescendo ME: vas-bias 35 mA, inputcap of mosfets 1700 pF

Zenquito: VAS bias 10 mA, input cap. 1200 pF

Indeed VAS bias is somewhat low. OTOH, input capacitance is a more linear. At 20 kHz the reactance of 1200 pF is some 6600 ohms. This cannot be neglected at all. I think that improvement can be made here.

Now I really wished I had more facilities. I can't see myself experimenting with other transistors and emitter resistances with only a DMM. :whazzat:

I still can't understand why all those French Zenquito builders are so quiet. Come on guys, you should know. Help us out here!

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