Lateral F4/BA

buzzforb · 6th October 2011, 09:52 PM

What are the benefits of using laterals in a buffer like he above. I have one set of boards wired up with IRF fets and was considering putting 2sk1058/sj162 in the other. I don't have test equipment so the only measurements i will have are my two ears and the space between, which seems expansive these days. I have read that they are more stable and don't necessarily require Rs. While i know this may help with noise, what does it do to linearity and distortion.

Nelson Pass · 6th October 2011, 11:24 PM

They may not measure better, but I'll bet they sound great.

hitsware · 12:07 AM

> I have read that they are more stable and don't necessarily require Rs.

Yes.
They need no degrading temperature compensations.
BUT ! ...................... AND ............. !
They are stable @ ~ 0.10 Amp rather than ~ 1.00 Amp (as IRF type parts)

> While i know this may help with noise, what does it do to linearity and distortion.

It helps because of the simplicity of being able to ignor temperature
(to a sensible extent)

buzzforb · 7th October 2011, 12:03 AM

Might as well try, right. Hope to try Fairchild parts as well. I want to wire my F4 boards with a switch between the FE and the buffer so that it can function as both F4 and BA output. I have a few questions though. In the F4, C3 and C4 serve as bootstrap caps for FE, but in BA output, these are grounded and bootstrap resistors are dropped. Will it affect the performance of the BA version if wired like F4 with bootstrap resistor and cap in place and wired to output. Also, in F4 there are two smaller electrolytics on FE but on BA there is 1 larger cap. Once again, will performance be affected if i use the two smaller caps. To use as standard F4, i need both, so should I just increase or leave alone?

buzzforb · 7th October 2011, 10:53 AM

I have been reading about driving lateral outputs and have found somethingt that i had a question on. Many folks use different gate resistors for the N and P channel parts as a way of trying to balance the different gate capacitances of the devices. Some even use smaller caps to accomplish the smae task. I have not seen Nelson do this on any of his push pull outputs and was wondering about the importance. Most of these suggestions come from the BJT Uber low THD chasers and I don't necessarily subscribe to the Massive OLG/Low THD school of though.

buzzforb · 7th October 2011, 03:28 PM

Looking at datasheet, is it optimal to try to bias the transistor into the linear region of the input capacitiance? Above 3V, looks very linear and would get me into a similar bias setting to standard F4. Am i right in how I am looking at this. Also, small Rs may be helpful, but i will try without. ANy comments welcomed.

flg · 7th October 2011, 04:34 PM

Ussually the linear region of FET C does not even begin to start until about 20Vds

I'm not sure but I think a mismatch of characteristics of N-P will give you 2nd Harmonics. Not so bad

buzzforb · 04:57 PM

check out datasheet and see what you think. 3Vgs @10Vds and up is about 2A and is in the linear C range.

generg · 20th October 2011, 06:04 PM

Quote:

Originally Posted by Nelson Pass

They may not measure better, but I'll bet they sound great.

I tried them in my crippled F4 and they have a sweet sound compared to the FQA......

buzzforb · 20th October 2011, 06:08 PM

Generg, you are busy. Sweet but sloppy, or just sweet. Will be matching this weekend. I have one crippled F4 ready, the other will get the newly matched Lateral. SO you have heard the FQA, what do you think?
Nelson or anybody, what role does the gm of a fet play when using it as a buffer like F4. Doesn't it mainly affect the output impedance

6th October 2011, 09:52 PM	#1
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	Lateral F4/BA What are the benefits of using laterals in a buffer like he above. I have one set of boards wired up with IRF fets and was considering putting 2sk1058/sj162 in the other. I don't have test equipment so the only measurements i will have are my two ears and the space between, which seems expansive these days. I have read that they are more stable and don't necessarily require Rs. While i know this may help with noise, what does it do to linearity and distortion.

6th October 2011, 11:56 PM	#3
hitsware diyAudio Member Join Date: Mar 2002	> I have read that they are more stable and don't necessarily require Rs. Yes. They need no degrading temperature compensations. BUT ! ...................... AND ............. ! They are stable @ ~ 0.10 Amp rather than ~ 1.00 Amp (as IRF type parts) > While i know this may help with noise, what does it do to linearity and distortion. It helps because of the simplicity of being able to ignor temperature (to a sensible extent) __________________ http://www.youtube.com/watch?v=xZmfCYr8mwA Last edited by hitsware; 7th October 2011 at 12:07 AM.

7th October 2011, 04:34 PM	#7
flg diyAudio Member Join Date: Jul 2005 Location: North East	Ussually the linear region of FET C does not even begin to start until about 20Vds I'm not sure but I think a mismatch of characteristics of N-P will give you 2nd Harmonics. Not so bad __________________ “Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.” Dr. Seuss

7th October 2011, 04:37 PM	#8
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	check out datasheet and see what you think. 3Vgs @10Vds and up is about 2A and is in the linear C range. Last edited by buzzforb; 7th October 2011 at 04:57 PM.

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6th October 2011, 11:24 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	They may not measure better, but I'll bet they sound great.

7th October 2011, 12:03 AM	#4
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	Might as well try, right. Hope to try Fairchild parts as well. I want to wire my F4 boards with a switch between the FE and the buffer so that it can function as both F4 and BA output. I have a few questions though. In the F4, C3 and C4 serve as bootstrap caps for FE, but in BA output, these are grounded and bootstrap resistors are dropped. Will it affect the performance of the BA version if wired like F4 with bootstrap resistor and cap in place and wired to output. Also, in F4 there are two smaller electrolytics on FE but on BA there is 1 larger cap. Once again, will performance be affected if i use the two smaller caps. To use as standard F4, i need both, so should I just increase or leave alone?

7th October 2011, 10:53 AM	#5
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	I have been reading about driving lateral outputs and have found somethingt that i had a question on. Many folks use different gate resistors for the N and P channel parts as a way of trying to balance the different gate capacitances of the devices. Some even use smaller caps to accomplish the smae task. I have not seen Nelson do this on any of his push pull outputs and was wondering about the importance. Most of these suggestions come from the BJT Uber low THD chasers and I don't necessarily subscribe to the Massive OLG/Low THD school of though.

7th October 2011, 03:28 PM	#6
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	Looking at datasheet, is it optimal to try to bias the transistor into the linear region of the input capacitiance? Above 3V, looks very linear and would get me into a similar bias setting to standard F4. Am i right in how I am looking at this. Also, small Rs may be helpful, but i will try without. ANy comments welcomed.

20th October 2011, 06:08 PM	#10
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	Generg, you are busy. Sweet but sloppy, or just sweet. Will be matching this weekend. I have one crippled F4 ready, the other will get the newly matched Lateral. SO you have heard the FQA, what do you think? Nelson or anybody, what role does the gm of a fet play when using it as a buffer like F4. Doesn't it mainly affect the output impedance

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