question about sound in Zen4

[Buhl]

Hi There
I finished my zen V4 (still waiting for the rigth cabinet housing...) some months ago, and have listened to it since with great joy.
But - i find the treble range / higt frequencies to somewhat rather dull - compared to other amps and on different speakers. I finished a Gainclone some weaks ago, and had to install a variable resistor on the tweeter so lower the level compared to the zen.

Otherwise the zen is wonderfull, varm, round and still clear - despite of the missing treble. Very pleasing and powerfull to listen to. Since i finished it, I have mooved the 221 ohm gate resistor on to the mosfet (IRF240), cause I have "Fets on a wire", and raised the bias to 2,8 amp - witch made the sound more varm and powerfull, but somewhat softened the bass ?

10000 uf output cap is bypassed vith 3,3 uF Vishay/roederstein polypropylene. I have a 4,7 Kohm potmeter in the input, and drive it directley from a Cambridge DAC 3 with xlr-Rca cables, so i have 5,2 volts on the input of the amp.

Anybody have an idea of what migth be wrong - or should the Zen 4 just sound dull ??

Cheers !

Hans

[till]

I can´t say this about my Zen V4. You should make some measurement.

[Nelson Pass]

I have not found the Z4 dull, but perhaps by comparison your
gainclones are bright. Best to get a frequency response curve
of the amp to see if there is something wrong.

[Stabist]

I've done few modifications in mine Zen v4 last weekend - I've replaced all 220uF caps (Jamicon --> Elna RJH) and all nonpolar caps were before Wima MKS and now are Wima MKP - but also - the output cap is now bypassed by 1uF (before 10uF) and on the input (after irf9610) there is 3,3uF (before 10uF) ...

The sound became more detailed and got more high tones (I have Focal speakers - and the highs can be real bastar... - so I'm still deciding shall I experiment more and put let's say 3,3uF also to bypass output cap)

And a question for mr. Nelson:
original Zen had two paralel 2200uF caps on the output; but later versions have 10.000uF ... But can I use 4700 or 6800uF in my case without bigger fear or not??

[Buhl]

I have had the chance to compare my Zen 4 to not only a gainclone, but also a 100 watt Vitus poweramp (around 25000 USD - http://www.vitusaudio.com )and a new accuphase integrated at around 4000$
I should say that the owner of the Accuphase got envyous when he heard my zen4 - the accuphase had better bass controll in the very lowest register, and more highs/treble, but was far outperformed in midrange, and we both liked the warm, and relaxed sound of the zen compared to the accu. The Vitus was harder to beat - but it is also a state of the absolute art product....the zen still did not look ashamed in its company - it did not have the control and power reserves, but it had the charme
(of course im highly BIASed - around 2,8 amps...hehe

Nelson - I cannot get a frequency curve, since i don't own a signal generator - i only have a "radioshack" voltage meter. I remember that you write in the Zen4 article, that the IRF044 is the preferred part - the 240 should not have this much less treble ? Can it be that i have the fets on 6-8 inches of wire, though the gate resistor is at the FET ?

I will try to bypass capacitors after the 3310 transistor with roederstein, and hope this works.

Thank you all for taking the time to reply me !

Cheers !
Hans

[till]

I cannot get a frequency curve, since i don't own a signal generator

what about a computer and a soundcard?

[nobody special]

I have found the gainclone that I built to be overly bright. Even my wife noticed, and she usually doesn't.

[Buhl]

I followed the advice earlier in ths thread, and added some Viahay/ Roederstein 0,22uF Polypropylene capacitors to the C2, witch before was an bipolar electrolytic. Also put a 3,3 uf of same type on the psu electrolyt. Now theres much more timbre sound - and more crisp upper midrange - I'm very satisfied !

Thanx to those who took the time to answer my posts, and to nelson for taking the time to make this great design available !

By the way, has anyone tried to bridge the Z4 - how is the sound/bottom end control? how about paralling zen channels - can that be done just by wiring the input and output in parallel? what should be expected soundwise form paralleling channels ?

Cheers !
Hans

[Panelhead]

Originally posted by Buhl
I followed the advice earlier in ths thread, and added some Viahay/ Roederstein 0,22uF Polypropylene capacitors to the C2, witch before was an bipolar electrolytic. Also put a 3,3 uf of same type on the psu electrolyt. Now theres much more timbre sound - and more crisp upper midrange - I'm very satisfied !

Thanx to those who took the time to answer my posts, and to nelson for taking the time to make this great design available !

By the way, has anyone tried to bridge the Z4 - how is the sound/bottom end control? how about paralling zen channels - can that be done just by wiring the input and output in parallel? what should be expected soundwise form paralleling channels ?

Cheers !
Hans

Hans,
Two small tweaks I did in mine, were to parallel a 2.2KOhm 2 watt resistor across the 4.75K in the line going to the buffer (3310). Bumping up the bias through the buffer helps across the board.
Also, try lowering the input impedance a little. Go down from 47K to 22K or so. This may add just a little crispness to the top end.
One last tweak, change the cap coupling the buffer to the 044. Try a 50v 10 ufd, N series BG. I boulght 6, and all measured 10.5 - 10.8 ufd. I think the little N series BG is cleaner than most plastic film caps in this application.

George

[Buhl]

Hi George !
Thnx for the tweaks - I'm off to the shop after resistors first thing in the morning. Is there no thermal problem with bumping up the BIAS on the 3310, or is it in the nitty-gritty-small department, and nothing to worry about ?

About the Black Gates - they are electrolytics, rigth ? how should i mount them, with the + or - facing the 3310 ?

Thnx again for sharing theese ideas and tweaks !

Cheers!
Hans