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Old 11th June 2012, 12:59 PM   #61
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Originally Posted by AKSA View Post
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
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Old 11th June 2012, 01:29 PM   #62
AKSA is offline AKSA  Australia
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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
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Last edited by AKSA; 11th June 2012 at 01:31 PM.
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Old 11th June 2012, 02:02 PM   #63
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Originally Posted by AKSA View Post
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
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Old 12th June 2012, 06:18 AM   #64
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Second channel almost ready
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Old 12th June 2012, 09:03 AM   #65
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Good work, MM, nearly there!!

Hugh
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Old 13th June 2012, 06:46 PM   #66
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Having a problem, LED1 and 2 don't light,possible to set bias no problem there.Can't set the bootstrap voltage not higher than 19-20Volts.Must sa I did power up the the first time without the fuses installed
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Old 13th June 2012, 07:19 PM   #67
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Update :
Had to dril the holes of the middle rectifier diodes on both sides cause they were to small and the middle leg of D1A didn't make connection with the upper layer so a bit solder on the top side problem solved.Me Happy again

Last edited by meanman1964; 13th June 2012 at 07:35 PM.
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Old 14th June 2012, 12:03 AM   #68
AKSA is offline AKSA  Australia
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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
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Old 14th June 2012, 06:15 AM   #69
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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.
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Old 17th June 2012, 08:18 AM   #70
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Custom made case,only needs a new rear panel.When the casing is totaly completed I will post some pics from the inside and rearside.
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Last edited by meanman1964; 17th June 2012 at 08:24 AM.
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