UDNeSS, or You don't need Semisouth's

[Gerrit Kroesen]

Question for Patrick: if I have a PSU like Nelson Pass suggested in his F5T paper, with 40.000 uF connected to each rail after the R of the CRC, and that PSU is connected with 2.5 mm2 wires of 15 cm, would I still have to put 10,000 uF closer to the amp pcb? Or would the psu caps suffice?

 

[EUVL]

I cannot tell, you have to try.
15cm should be OK, But I use HF litz wires.
https://www.ebay.de/itm/304154052959


Patrick

 

[totaltech]

Hi,
Thanks Patrick for such a great project. I have had boards for a while, and about to build two pairs.
By any chance has anyone got any OPA604's that could sell me and ship to Australia? High voltage op amps seem to be unavailable at the moment!

Thanks in advance.

Cheers

Rob

 

[EUVL]

You don't need the servo.
Build the amp without first.
Can always add later.


Patrick

 

[totaltech]

You don't need the servo.
Build the amp without first.
Can always add later.


Patrick

Thanks Patrick,
Is this true even if using fairchild output mosfets?

Cheers

Rob

 

[EUVL]

Yes

 

[totaltech]

G'Day Patrick,
Sorry another question if I may, When matching Q2 and Q3 2sk209's (4 per channel), does it matter even if each side is matched, the VGS @ 3mA is different on each channel?

Cheers

Rob

 

[EUVL]

No. Only need to match per channel.

 

[viltsone]

@EUVL If I like to use 2SK1530 (have 4 of them) or 2SK3497 instead of FQA9P25 what changes I need to make in UDNeS Cas V1 THD.asc?
What would be better replacement for KSC1845?
Do I need to match these 2SK1530 in this scheme?

 

[EUVL]

FQA9P25 is a P-channel MOSFET. All those you mentioned are N-MOSFETs.
To use those, build the J2 at the Pass forum, not this here.

And I do not think I used the KSC1845 anywhere in this circuit.
Are you sure you are in the right thread ?


Patrick

 

[viltsone]

I am sorry that I mixed up P-channel MOSFET and N-channel. In this post you are sharing a LTSpice scheme. https://www.diyaudio.com/community/...t-need-semisouths.343164/page-17#post-6655510
In this scheme is also Q1 - KSC1845.
If I like to use 2SJ618 or 2SJ201 then what changes are needed in this scheme and in this following scheme? https://www.diyaudio.com/community/threads/udness-or-you-dont-need-semisouths.343164/post-6832584
Have anybody tested this scheme and have built it amp?

 

[EUVL]

In this scheme is also Q1 - KSC1845.

KSC1845 is an active device with plenty of voltage headroom.
Very easy to get. So why replace ?

If I like to use 2SJ618 or 2SJ201 then what changes are needed in this scheme and in this following scheme?

They are both obsolete devices, so I shall not spend any time figuring out how to apply them here.
It is not what this circuit is meant for,
And I will certainly not publish any unproven schematics using them.

You are of course most welcome to run your own simulation using those devices.
In real life, you need to apply thermal compensation for the large positive tempco of the 2SJ618.
In addition, you need to change the values of the source resistors and the gate biasing resistor because of different Vgs ad Yfs.


Success,
Patrick

 

[EUVL]

And for anyone interested in this, the FQA9P25 is end of life, but still available at Mouser (>11000 pcs in stock).
So time to get lifetime stock.

Patrick

 

[viltsone]

KSC1845 is an active device with plenty of voltage headroom.
Very easy to get. So why replace ?

KSC1845 is in my opinion a little bit noisy and there are maybe better replacements for using in audio circuit? I read that BC550 is also good to use. What are your thoughts about that? Do I need to change some resistors to use BC550?

 

[EUVL]

BC550 is not an active part.
Not intend to use obsolete components in this circuit.


Patrick

 

[mbrennwa]

Well, the BC550 is a transistor, which surely is an active part. In contrast, for example, resistors are passive parts. Maybe you meant to say that BC550 is not produced anymore, but there are still plenty of these parts around.

 

[EUVL]

Active at Mouser / DK means that it is not obsolete.
Now clear ?

Again, UDNeSS was designed not to use ANY obsolete parts.
It does not matter what you can still get from ebay or diy store or what not.
Everything posted in this circuit, you can get from Mouser / DK with no NOS premium.


Patrick

 

[totaltech]

G'Day from Australia!
When matching mosfets of the UDNESS @ 1.4A how close do you get the Vgs?

Thanks in advance

Rob

 

[EUVL]

Circuit still works without matching.
So it depends on how well you want equal current sharing, and channel matching.
If I have enough devices, then 3mV Vgs.
So let's say 10mV.

But you need a large pool to match from.



Patrick

 

[totaltech]

Thanks Patrick!