Burning Amp 2016

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
J

jrubins

Member
Joined 2009
Bob Cordell said:
Some folks expressed interest in seeing the slides from my Burning Amp 2016 presentation of the Hafler DH220C revamp using a full-complementary JFET input stage with a floating tail. It is a powerpoint file, and, unfortunately, it is over 7 MB, even zipped (zip compression of ppt files is negligible). I don't know of any easy way to post it here. Please email me if you would like a copy.



Cheers,

Bob
Click to expand...


You should be able to "save as" or "print to" pdf, which is much more portable :)



Sent from my iPhone using Tapatalk
 
D

delange

Member
Joined 2012
Bob Cordell said:
Some folks expressed interest in seeing the slides from my Burning Amp 2016 presentation of the Hafler DH220C revamp using a full-complementary JFET input stage with a floating tail. It is a powerpoint file, and, unfortunately, it is over 7 MB, even zipped (zip compression of ppt files is negligible). I don't know of any easy way to post it here. Please email me if you would like a copy.

Cheers,
Bob
Click to expand...

Dropbox is an easy way to share files.
 
B

Bob Cordell

Member
Joined 2006
cordellaudio.com
AndrewT said:
Thank you for all your efforts to get these posted.
You used 489 and 689 dual jFETs.
Can k170/j74 be substituted? or k389/j109?
What performance would deteriorate with this substitution?
Click to expand...

In principal, these substitutions can be made in this architecture with appropriate changes to some passive component values, especially the tail resistor. However, there is little benefit unless you already have those parts hanging around (most are no longer available). A key issue is that you really want dual monolithic matched pairs for the P and N JFETs. The hassle of matching and changing component values is probably not worth it. Although the parts you mention have somewhat lower voltage noise, the net reduction in noise by use of these larger-area JFETs is not great, since there are other contributors to noise. Moreover, with the LSK489/LSJ689, the amplifier already achieves very low noise for a power amplifier. The larger-die JFETs, like the k389, also have much higher capacitance.

Cheers,
Bob
 
A

AndrewT

R.I.P.
Joined 2004
Bob Cordell said:
In principal, these substitutions can be made in this architecture with appropriate changes to some passive component values, especially the tail resistor. However, there is little benefit unless you already have those parts hanging around (most are no longer available). A key issue is that you really want dual monolithic matched pairs for the P and N JFETs. The hassle of matching and changing component values is probably not worth it. Although the parts you mention have somewhat lower voltage noise, the net reduction in noise by use of these larger-area JFETs is not great, since there are other contributors to noise. Moreover, with the LSK489/LSJ689, the amplifier already achieves very low noise for a power amplifier. The larger-die JFETs, like the k389, also have much higher capacitance.

Cheers,
Bob
Click to expand...
Thanks for that.
I already have matched pairs of k170a, b and bl and matched pairs of j74bl. I don't have j74a so am stuck with using the higher Idss grade.

I think I am interpreting your reply to mean there should be no deterioration in performance if I make that current change. Instead of 4mA what do you suggest? 5mA, 6mA? or to a lower current?
 
Last edited:
B

Bob Cordell

Member
Joined 2006
cordellaudio.com
AndrewT said:
Thanks for that.
I already have matched pairs of k170b and bl and matched pairs of j74bl.
I think I am interpreting your reply to mean there should be no deterioration in performance if I make that current change. Instead of 4mA what do you suggest? 5mA, 6mA? or to a lower current?
Click to expand...

Although the larger die devices can be optimally operated at higher tail current, the safest thing to do is to adjust the new tail resistor to achieve the same tail current as before. A smaller value for the gm-equalizing degeneration resistors might be appropriate due to the larger overall gm of the stages (the larger die devices produce somewhat higher gm for a given operating current), but I'm not sure by how much.

Cheers,
Bob
 
A

AndrewT

R.I.P.
Joined 2004
Bob Cordell said:
Although the larger die devices can be optimally operated at higher tail current, the safest thing to do is to adjust the new tail resistor to achieve the same tail current as before. A smaller value for the gm-equalizing degeneration resistors might be appropriate due to the larger overall gm of the stages (the larger die devices produce somewhat higher gm for a given operating current), but I'm not sure by how much.

Cheers,
Bob
Click to expand...
OK, I understand.
This could end up going into a set of Sugden P128 which uses 2pr of LatFETs.
EUVL posted info for j74 Pch degen that I have saved.
 
Variac

Variac

diyAudio Editor
Joined 2001
BurningAmp.org
Paid Member
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom