Pass ONO or XONO PCB???

[amhlee]

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]

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]

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]

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]

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]

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]

you don't have bleeder resistor at that side ?

 

[Marra]

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]

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

 

[Marra]

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.

 

[amhlee]

Your 10Uf cap must be leaking...... :O

 

[Marra]

Your 10Uf cap must be leaking...... :O

It looks that way. Strange that they should all go together and only after a few months use!!
I there a way to test them?

 

[d to the g]

use an LCR meter?

Also, for what those boards, a decent case, and parts cost you could buy a used stock ono. Sometimes it does not pay to diy.

 

[Marra]

use an LCR meter?

Also, for what those boards, a decent case, and parts cost you could buy a used stock ono. Sometimes it does not pay to diy.

Your probably right. I have a lot invested in this build so need to get it sorted.Trawling through the threads there appears to be a couple of things to try so fingers crossed otherwise I might need to seek proffesional help[ for me or the amp?]

 

[blue lander]

It's definitely an expensive build. I think my project is going to come in around $250-$300 since I didn't buy a case or boards or power supplies and I'm only building the unbalanced half. Parts alone for just unbalanced MM came to about $140.

 

[blue lander]

I finished the second channel but, of course, it doesn't work. All the values look good (other than getting 1.3v across R53), but I have to turn the volume all the way up before I can faintly hear any music.

 

[dot]

For the three boards, parts and pair of transformers I’m into it for about $550 US. I will make my own cases and maybe swap in some boutique caps. This is just a fraction of what the cartridge cost. The last that I checked a guy could buy a used Xono off A’gon for around $1900.

 

[h_a]

I find the voltages unstable while the unit warms up or without operating in an enclosure.

Pretty normal due to the small currents, thermal coefficients and high gains, nothing to worry about. Simply keep the lid closed

There are ways to adjust the DC-offset by trimming the gain resistor of the 2nd stage, but, as you already know, during warm-up or without the lid the whole thing is floating quite a bit, so this adjustment would not be perfectly stable anyway. That's why there are the 10uF caps.

Hannes

 

[Marra]

I finished the second channel but, of course, it doesn't work. All the values look good (other than getting 1.3v across R53), but I have to turn the volume all the way up before I can faintly hear any music.

Have you tried changing R5 from its original value of 6k8 to 15k. This makes a small differance to the voltage drop across R53 & R67 and in my build lowered the dc offset fluctuation on the outputs by a lot. Details here.

http://www.diyaudio.com/forums/pass-labs/10326-aleph-ono-project-pcb-group-buy.html

 

[blue lander]

I'll give that a try, thanks.