Aleph-X builder's thread. - Page 15

SGregory · 5th March 2004, 02:48 AM

Forgive me for not bookmarking the post and linking it here, but I was not thinking when I saw it. And I havn't been able to find it again. I can't remeber what I used for search topic.

In my searching, I have found that there has been quite a bit of discusson about increasing the bias. I also saw a short post contemplating why Nelson originally chose the 400 ohms of the load resistor. Paraphrasing the comment from I believe Mr Thurgard, '400 ohms seems to give the maximum amount of gain for a given bias to achieve proper bias on the gain devices' he went on to say something well beyond my ability to understand that lowering the value of the load resistor and increasing the bias is exceeded by the change in transconductance.

If that is true, then the 400ohm would be close to optimal for the characteristics of the devices used in this circuit.

Could anybody with a more fundemental grasp on this help to clarify?

Thanks
Scott.

Brian Donaldson · 5th March 2004, 02:49 AM

After you see the prices, you may not be so eager to overkill the heatsinks by much.

hifiZen · 5th March 2004, 12:34 PM

Quote:

Originally posted by moe29
... Of course this means they're not mounted
back to back during testing...

Hmm. Not to put a fly in the ointment, but they really ought to mounted together if you can manage it... junction temperature affects a MOSFET's behaviour, so you need to be sure they're at exactly the same temp when you do the matching. This is the reason they're mounted back to back on the PCB - the tight thermal coupling keeps the die temperatures very close, and their Vgs drift matched as closely as possible during operation.

You can also do as Grey says, and swap Q2 and Q11 around to take advantage of their Vgs mismatch...

moe29 · 5th March 2004, 01:44 PM

i took a day off from working on the circuit, and i think i'll try
swapping them around, with back to back mounting today.
That seems to be the reasonable approach, as apposed to let's
get it done as fast as possible!

Coulomb · 8th March 2004, 03:10 PM

Can anybody explain the difference between K/W used in the AXE spreadsheet and C/W used by Extrusion manufacturers?

Is it Kelvin/Watt?

I know C/W is Celsius/Watt.

How do I convert from one to the other?

Regards

Anthony

Netlist · 8th March 2004, 03:17 PM

1°C = 1°K
°K starts at -273.15°C
http://www.2spi.com/spitemp.html

UrSv · 8th March 2004, 03:18 PM

It's the same with respect to the heatsink data.

Coulomb · 8th March 2004, 05:04 PM

Thanks Guy's

Coulomb · 8th March 2004, 07:15 PM

For those of us in the Frozen North (Canada) check out this thread if you thinking of buying some Heat Sinks.

Regards

Anthony

http://www.diyaudio.com/forums/showt...193#post344193

Mark A. Gulbrandsen · 9th March 2004, 03:33 AM

Ahhh, The things we do when we get tired... I mistakenly posted this under the Electronics and parts heading......

So I',m moving it to where it belongs.....

I'm about to run up my first X board on the variac and was wondering whats the proper procedure for setting the input pair current source adjustment???

Thanks,
Mark

5th March 2004, 02:48 AM	#141
SGregory Tubie Noobie diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Incresaed Bias on the Diff Pair. Forgive me for not bookmarking the post and linking it here, but I was not thinking when I saw it. And I havn't been able to find it again. I can't remeber what I used for search topic. In my searching, I have found that there has been quite a bit of discusson about increasing the bias. I also saw a short post contemplating why Nelson originally chose the 400 ohms of the load resistor. Paraphrasing the comment from I believe Mr Thurgard, '400 ohms seems to give the maximum amount of gain for a given bias to achieve proper bias on the gain devices' he went on to say something well beyond my ability to understand that lowering the value of the load resistor and increasing the bias is exceeded by the change in transconductance. If that is true, then the 400ohm would be close to optimal for the characteristics of the devices used in this circuit. Could anybody with a more fundemental grasp on this help to clarify? Thanks Scott.

8th March 2004, 03:18 PM	#147
UrSv diyAudio Member Join Date: Jan 2002 Location: Sweden	It's the same with respect to the heatsink data. __________________ UrSv Those who say it can't be done should not stop those who are doing it.

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5th March 2004, 02:49 AM	#142
Brian Donaldson diyAudio Member Join Date: Jan 2003 Location: Texas, Love it or leave it	After you see the prices, you may not be so eager to overkill the heatsinks by much.

5th March 2004, 01:44 PM	#144
moe29 diyAudio Member Join Date: Dec 2002 Location: Florida	i took a day off from working on the circuit, and i think i'll try swapping them around, with back to back mounting today. That seems to be the reasonable approach, as apposed to let's get it done as fast as possible!

8th March 2004, 03:10 PM	#145
Coulomb diyAudio Member Join Date: Jul 2002 Location: Ancaster, Ontario	Can anybody explain the difference between K/W used in the AXE spreadsheet and C/W used by Extrusion manufacturers? Is it Kelvin/Watt? I know C/W is Celsius/Watt. How do I convert from one to the other? Regards Anthony

8th March 2004, 03:17 PM	#146
Netlist diyAudio Moderator Join Date: Jan 2003	1°C = 1°K °K starts at -273.15°C http://www.2spi.com/spitemp.html

8th March 2004, 05:04 PM	#148
Coulomb diyAudio Member Join Date: Jul 2002 Location: Ancaster, Ontario	Thanks Guy's

8th March 2004, 07:15 PM	#149
Coulomb diyAudio Member Join Date: Jul 2002 Location: Ancaster, Ontario	For those of us in the Frozen North (Canada) check out this thread if you thinking of buying some Heat Sinks. Regards Anthony http://www.diyaudio.com/forums/showt...193#post344193

9th March 2004, 03:33 AM	#150
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Ahhh, The things we do when we get tired... I mistakenly posted this under the Electronics and parts heading...... So I',m moving it to where it belongs..... I'm about to run up my first X board on the variac and was wondering whats the proper procedure for setting the input pair current source adjustment??? Thanks, Mark

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