Pass ONO or XONO PCB??? - Page 3

amhlee · 12th March 2011, 12:28 AM

Quote:

Originally Posted by Marra

Took the top off my Xono built with Ralf Stens pcb's to check the bias setting. I reset to 0.35v it had drifted a bit; when I checked the dc offset it was fluctuating wildly; +- 100mv plus on both sides of the 10uf output caps and could not be adjusted much with the trimmers. Is this something to be concered about? Any advice/pointers as to what to check would be much appreciated. TIA.

It is a little bit high , are you using 2sk389 or 2sk170 ? Look like it is the matching of the transistor.

Marra · 12th March 2011, 03:59 AM

Quote:

Originally Posted by amhlee

It is a little bit high , are you using 2sk389 or 2sk170 ? Look like it is the matching of the transistor.

I am using 2sk389.

dot · 12th March 2011, 01:57 PM

At the risk of stating the obvious, I find the voltages unstable while the unit warms up or without operating in an enclosure. Thermal instability.(?) That said I have found the Sten xono clone boards to be the best sounding phono preamp I have heard. It bested the phono section of a Spectral DMC20. (Just my opinion, mileage may very.)
Cheers, Glenn

Marra · 12th March 2011, 02:17 PM

Quote:

Originally Posted by dot

At the risk of stating the obvious, I find the voltages unstable while the unit warms up or without operating in an enclosure. Thermal instability.(?) That said I have found the Sten xono clone boards to be the best sounding phono preamp I have heard. It bested the phono section of a Spectral DMC20. (Just my opinion, mileage may very.)
Cheers, Glenn

Thanks Glen; yes I realise that things do not settle down for quite a while with this phono stage. It has been out of use for some months what with one thing and another so I thought I'd better check things again before connecting it back in my system and for some reason the output offset won't settle. Other voltages check out .
I must agree this is one fine sounding phono amp; I used it for some months last year before the system had to be disconnected.

amhlee · 14th March 2011, 01:43 AM

Look like that some the transistors/ resistor are not well match. But it does not really matter as there are caps in the output to filter out. Pass does not design this as 0mv out, Mine has a full matching set on both transistor and resistor, I am able to achieve 10 mv output.

Marra · 14th March 2011, 02:51 AM

Quote:

Originally Posted by amhlee

Look like that some the transistors/ resistor are not well match. But it does not really matter as there are caps in the output to filter out. Pass does not design this as 0mv out, Mine has a full matching set on both transistor and resistor, I am able to achieve 10 mv output.

Unfortunately these readings are on the output side of the 10uf caps

Zen Mod · 14th March 2011, 06:21 AM

you don't have bleeder resistor at that side ?

Marra · 14th March 2011, 09:57 AM

Quote:

Originally Posted by Zen Mod

you don't have bleeder resistor at that side ?

No its not that there is a 100k resistor to ground after the capacitors.

Zen Mod · 14th March 2011, 10:04 AM

if you have bleeders at output cap's side , then something is wrong either with your DMM or your caps

Marra · 14th March 2011, 11:46 AM

Quote:

Originally Posted by Zen Mod

if you have bleeders at output cap's side , then something is wrong either with your DMM or your caps

I'll try a different DMM before taking things apart.

14th March 2011, 06:21 AM	#27
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	you don't have bleeder resistor at that side ? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb

14th March 2011, 10:04 AM	#29
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	if you have bleeders at output cap's side , then something is wrong either with your DMM or your caps __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb

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12th March 2011, 01:57 PM	#23
dot diyAudio Member Join Date: Oct 2005	At the risk of stating the obvious, I find the voltages unstable while the unit warms up or without operating in an enclosure. Thermal instability.(?) That said I have found the Sten xono clone boards to be the best sounding phono preamp I have heard. It bested the phono section of a Spectral DMC20. (Just my opinion, mileage may very.) Cheers, Glenn

14th March 2011, 01:43 AM	#25
amhlee diyAudio Member Join Date: Feb 2007 Location: Hong Kong	Look like that some the transistors/ resistor are not well match. But it does not really matter as there are caps in the output to filter out. Pass does not design this as 0mv out, Mine has a full matching set on both transistor and resistor, I am able to achieve 10 mv output.