The Importance of Being Biased

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

AMV8

Member
Joined 2005
Hi

In post 59 Nelson Pass stated;

5) Sound. An XA30.5 with fewer devices sounds thinner and
has less control than the larger XA amplifiers. Since we want a
"family similarity" sonically, we use more devices than absolutely
necessary

I have experienced this in power amps particularly with mosfet output stages but less so with bipolar putput stages. I have assumed it was due to the limited ability of one transistor to deliver the current needed for transients - but I am guessing. I would like to know why the improvement occurs if someone could explain.

Don
 
C

ctong

Member
Joined 2005
Nelson Pass said:



4) Current capacity. The Zen is short proof (and limited into
low impedances) by the constant current source biasing. It
simply will not deliver high currents. The XA30.5 is designed to
deliver 30, 60, 120, and 240 watts into 8, 4, 2, and 1 ohms until
the fuse blows or the thermal switch triggers.


:cool:
Click to expand...

Mr. Pass,

The XA30.5's high current capability is amazing. Does it still have the aleph current source? If yes could you explain how the modified current source delivers the high current? In the owner's manual you mentioned that the X.5 and XA.5 have similar circuits with different bias, does it mean that the X.5 series also have the aleph current source?
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
AMV8 said:
5) Sound. An XA30.5 with fewer devices sounds thinner and
has less control than the larger XA amplifiers. Since we want a
"family similarity" sonically, we use more devices than absolutely
necessary

I have experienced this in power amps particularly with mosfet output stages but less so with bipolar putput stages. I have assumed it was due to the limited ability of one transistor to deliver the current needed for transients - but I am guessing. I would like to know why the improvement occurs if someone could explain.
Click to expand...

Who knows? I do know that it is possible to overdo it, and the
sound gets very not-thin.

:cool:
 
A

Audio_se

Member
Joined 2004
Importance of temperature?

With bias also comes a higher temperature.

Are the heatsinks dimensioned just from reliability point of view?
Or is there an optimal temperature region in the transistors for best sonic performance?

If the answer already exists in another thread please give me a hint ;)
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
I don't see an optimal temperature as such. I tend to design
around standardized heat sinks, and the result is a trade-off
between power and bias, as the heat sinks usually are the
limiting factor. I inevitably seem to end up at about 55 deg C on
the heat sink.

:cool:
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
non-sparking said:
Hi there!

Referring to Post #1:

I`ve made an A30 building report on my (commercial) web site with just these relations a while ago.

http://www.audioprojekte.de/html/diy2_en.html

Combined with a lot of measuring work on the input/power devices i have reached a very low distortion figure.

Amps are sounding extremely good!

Ralf
Click to expand...

referring to KK's pcbs can be sign of ignorance or something else?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom