• Disclaimer: This Vendor's Forum is a paid-for commercial area. Unlike the rest of diyAudio, the Vendor has complete control of what may or may not be posted in this forum. If you wish to discuss technical matters outside the bounds of what is permitted by the Vendor, please use the non-commercial areas of diyAudio to do so.

Fetzilla Build Documentation

Yes, MM, that's it, across Drain Source of T3.

Offset adjustment on this amp is not wonderful, but it's not bad either, and while it will drift up and down a few mV, this is not at all critical AND HAS NO IMPACT ON SOUND QUALITY WHATEVER.

Noise is more of an issue, however, I do concede that. If you can hear white noise from the speaker at distances more than 1m then there is something wrong. I did not find my FetZilla noisy at all, thought it very quiet actually. Not as quiet as the NAKSA, but damn close.

Andrew, this amp was designed to reproduce sound in a pleasing way. Does it do it for you? Do you have any comments on the sound quality, or is this a verbotten topic for fear of ridicule?

Cheers,

Hugh

Hugh,

Hope all is well,

WRT Offset, another option is to bias the IP 2sk170 with an identical 2sk170
coming off the negative rail set up as a CCS.

As such
a) your 47 ohm resistor can go directly to ground b) You can ref the IP
directly to ground without the IP coupling cap or the IP bias arrangement c)
the two devices will track each other and there will be very little offset.

WRT noise, this amp should actually be quieter than just about any amp out
there. With 47R to ground and the ~1nV / rt Hz noise figure for the 2sk170,
the two 1k resistors will dominate noise

Another thought WRT offset and noise is that with 30V or so across the IP
sk170, it will have some gate excess current causing offset drift and
possibly noise through the bias arrangement (33k /1k R).

Cascoding?

Cheers

Terry
 
Thanks Terry,

Good advice, shame the boards are all done and dusted....

The offst variation is not much more than +/-10mV, not sure why it's such a big deal, the emphasis was always on good sound and simplicity. There was an ethic between the four of us to get the component count down as low as possible, and that was achieved with good sound.

I owe you a call, sorry for being so mute. Cold, wet hibernating weather......

Cheers,

Hugh
 
Last edited:
Thanks Terry,

Good advice, shame the boards are all done and dusted....

The offst variation is not much more than +/-10mV, not sure why it's such a big deal, the emphasis was always on good sound and simplicity. There was an ethic between the four of us to get the component count down as low as possible, and that was achieved with good sound.

I owe you a call, sorry for being so mute. Cold, wet hibernating weather......

Cheers,

Hugh

Hi Hugh

+- 10mV :) that's next to nothing.

Let's speak towards the end of the week - v busy atm.

WRT weather - agreed, when is winter over????

cheers

T
 
Second channel almost ready
 

Attachments

  • DSCN4945.jpg
    DSCN4945.jpg
    338.9 KB · Views: 585
MM,

I've just checked the clearance of the rectifier leads in a stock, unstuffed FetZilla pcb.

They are tight (0.9mm) but fit just fine. The fitting is deceptive however, because the holes are slightly splayed wrt the component - you have to spread the leads before insertion.

If you ever drill double sided boards in future, always take care to check you really need to, as they are through plated, and if you do, always solder the component BOTH sides.

This is a trap for newbies.... I've been there too!

Congratulations on a good build. Now to fire it up and start the listening tests!

Hugh
 
The holes of the middle diodes on both side were realy too small the others were tight but OK.Not a big deal just dril them larger but I didn't think about the upper layer.Just did a check up and the most value thing,I've learned something that's the good part.The casing is almost ready too will post some pics later.
 
The amp is ready for use and I'm happy with the sound.I'll try to explane how it sounds not easy cause english isn't my native lanquage.First you need to know,for me everthing must be in balance.I don't like the hights are too present but when I disconnect the tweeter I need to say Hé the hights are gone.That's why I love my Blame ST from Carlos so much good bass and for me nice hights and relaxed sound.The test is done with vintage speakers the DM14 of B&W a closed cabinet with two 6,5 inch woofers and a 28mm dome tweeter.And now my Fetzilla compaired with the Blame ST even stronger dry bass regarding to that my opinion is the Fetzilla wants bigger speakers.It produces realy puchy bass.The hights are more present but very clear and crispy but cause the puchy and strong deep bass all in balance.The Fetzilla deserves good flourstanding speakers which can cope the bass of the Fetzilla.Now it's time for a high power Fetzilla,I realy like this amp too and I'm happy building it.
Hope this explaines a bit what I think about this amp.
 
For someone says he's not comfortable with English you have done bloody well......

Thanks man!!

If the bass is a bit dry and punchy, try this.

Put a 0.22R resistor between the crossover and the BASS driver on both your speakers.

This will loosen up the bass, make it sound huge, but take away some of the dryness.

Then you should have the perfect amplifier with matching speakers!!

Cheers,

Hugh
 
Hugh,I like the bass the way it is.You just can't believe the bass these DM14 produce with the Fetzilla amp.Maybe I don't use the right words but the bass is realy tight also some of the advantage of a closed speaker.Also planning to build a large speaker system,wondering how the Fetzilla behaves then.The Fetzilla is here to stay.Hugh,thanks for this amp!!
 
MM,

I seem to remember power up dump is infrasonic and around 3V. This is trivial and won't cause any issues for any driver I know about. It's a good indication that the amp is on and ready!!

A speaker delay will involve a relay. Choose very carefully - the one to use is the Amplimo, made in Nederlands, but it's expensive. This relay has two parallel contacts; one tungsten alloy, the other gold faced. The hope is this will prevent degradation of the music signal.

A 150W FetZilla would not be too difficult, requiring only three pairs to the output stage. The existing VAS stage would need revision, however, more current, and possibly a bipolar VAS transistor.

Thanks for your enthusiastic review. I would say you are about the seventh or eighth builder to report his thoughts on the sound - lots sold, but not many built, I gather.

Cheers,

Hugh
 
Hugh and everyone: Help me with my build

It's been a while and I've not finished my Fetzila due to lack of time and it did take sometimes for me to collect all needed parts.

A few day ago, I started building the amp. Yesterday, after I finished soldering everything on the PCBs. I switched on the power, I use a variac and set the (main) input voltage at half (110V)(the transformer secondary voltage is only 12V AC) to see if something go wrong and actualy something did go wrong (I shoud have used a bulb in serie with the amp as someone advised on this topic). After I turned the power on, the toroid hummed loudly and it seemed that I got a short somewhere since I saw smoke come out below the PCB, from the position I came out, It seemed to come from the metal oxide resistors which are mounted underboard, it happended to both channels.
I turned off the power immediately to prevent further damage. I guess that I did something wrong. After that I tested the fuses on PCB and they all intact.

Attached here are the pics of my PCB. Coud you please take a look at them to see if I put everything in correct order.
As you could see, in the power supply section picture. I did not mount the diodes optimally as I soldered them with the metal tab facing in instead of facing out but I only realised it after soldering them in positions. Actually, I tried to separate them and not to let their metal tab to touch each other.

Thank you in advance.
ncc
 

Attachments

  • P1010005.jpg
    P1010005.jpg
    692.5 KB · Views: 575
  • P1010007.jpg
    P1010007.jpg
    98.7 KB · Views: 544
  • P1010010.jpg
    P1010010.jpg
    812.9 KB · Views: 503