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Old 31st January 2007, 01:28 AM   #1
fab is offline fab  Canada
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Default Lateral mosfet w Normal or Diamond buffer?

Hi to all

This time I would like to get your opinion on the differences between the Normal emitter follower buffer and the Diamond buffer to drive a Lateral Mosfet power output stage.

I will attached 2 amp schematics:
- one with Normal buffer
- other with Diamond buffer (same one as APEX PA52 device)

Except for the buffer to drive the output stage the rest of the amp is the same. According to the basic measurements I do with Microcap 6 simulator I can not see really the differences between both topologies.

For the diamond buffer, the low VGS off the output lateral mosfets, makes me use a simple VR for bias current (but with regulated supply) instead of the Vbe multiplier. Maybe I could use a low VGSoff lateral mosfet for this but I think that I would need to select especially low VGS off devices for that purpose...

I have read some other threads on the diamond buffers but thy use a current source in place of Q17 and Q46...

first the Normal buffer...

Please comment.
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Old 31st January 2007, 01:29 AM   #2
fab is offline fab  Canada
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Default Now the Diamond Buffer version

...Diamond Buffer version
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Old 31st January 2007, 01:36 AM   #3
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Maybe there is little difference, but you could adjust R130/R131 and R40/R42 in your second schematic assymetrically (smps-styled) to prevent any current spikes in output mosfets at fast slew or transient.
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Old 31st January 2007, 02:53 AM   #4
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Quote:
Originally posted by darkfenriz
Maybe there is little difference, but you could adjust R130/R131 and R40/R42 in your second schematic assymetrically (smps-styled) to prevent any current spikes in output mosfets at fast slew or transient.
Can you explain your reasoning or what criteria to use to adjust assymetrically these resistors?
Are you talking about cross conduction issue?

If there is little difference why APEX selling its Amplifier IC PA52(A) at such a high price? or is it the rest of its circuit or the overall?
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Old 31st January 2007, 02:30 PM   #5
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Yes, I mean cross conduction at transients. Aside from better discharging of gates and probably lower cross-conduction and slightly higher slew rate I don't know why diamond output should be pricier.
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Old 1st February 2007, 12:44 AM   #6
fab is offline fab  Canada
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Quote:
Originally posted by darkfenriz
Maybe there is little difference, but you could adjust R130/R131 and R40/R42 in your second schematic assymetrically (smps-styled) to prevent any current spikes in output mosfets at fast slew or transient.

Quote:
Originally posted by darkfenriz
Yes, I mean cross conduction at transients. Aside from better discharging of gates and probably lower cross-conduction and slightly higher slew rate I don't know why diamond output should be pricier.
Darkfenriz,

I am not following you here. First you say that the second schematics (diamond buffer) may have cross conduction but secondly you say that the diamond buffer is better for lower cross conduction...
Also, what do you suggest as resistor values for R130/R131 and R40/R42?
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Old 1st February 2007, 02:03 AM   #7
fab is offline fab  Canada
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Default New version 3B

Hi I have modified the diamond buffer as per http://www.elecdesign.com/Globals/Pl...tent/2800.html

The drawback is that for power amp with bias adjust I need 2 pots (VR1 and VR2)...

Any comments compared to previous 1A version (same diamond as APEX 52A)?
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Old 9th February 2007, 10:05 AM   #8
lineup is offline lineup  Sweden
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Default Re: Lateral mosfet w Normal or Diamond buffer?

Quote:
Originally posted by fab

Lateral mosfet w Normal or Diamond buffer?

This time I would like to get your opinion on the differences between the Normal emitter follower buffer and the Diamond buffer to drive a Lateral Mosfet power output stage.

I will attached 2 amp schematics:
- one with Normal buffer
- other with Diamond buffer (same one as APEX PA52 device)

---------------
Please comment.

Good question you put here, fab.
Same question can be asked for Bipolar Output stages.


I have began to use more and more Diamond!
I my simulations ... with great results, in compare to 'normal' Darlington outputs.

This is because of super results, when I did my clone of AD797 hifi Op-Amp:
See details in:
AD797 Clone people! Who can make a better one.
AD797 Clone people! Who can make a better one.
... and when I did my follow up, with 'an improved' Hifi Op-Amp
also using Diamond Output, like AD797:
New JFET Hifi Op-Amp release!
New JFET Hifi Op-Amp release!

======================================


If this way of output stage, Diamond, works in preamps and Op-Amps
of course it will work great in some Power Amplifier applications, too.
And so it does.
There are people that have done excellent power amps this way before!

My thought:
- diamond output stage, with 2 drivers and 2 output power transistors
can not beat the gain of a triple darlington. Like in Leach Super Amp, for example.
But in some amplifiers we do not need as much gain.
And here I can not see any drawback using Diamond.
Not when compared to a usual 'Double Darlington' output. ( 2drivers + 2 output T )


Here are my current testings, fab
See Attachment Circuit.
I am designing a Class A amplifier with 100 Watt idle supply.
+/- 25 VDC and 2.0 Ampere current.

Results are very promising.
My first verson here, 1.0, is simulated with MJ15024/25.

I will try 'the better' MJL21193/94 and MJL3281A/1302A.
I have no doubt my figures will be improved. Those better devices usually lowers THD figures considerably!
I have no doubt!


Regards, lineup
Lineup Audio Lab
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Old 10th February 2007, 12:29 AM   #9
fab is offline fab  Canada
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Quote:
Originally posted by lineup
...
My thought:
- diamond output stage, with 2 drivers and 2 output power transistors
can not beat the gain of a triple darlington. Like in Leach Super Amp, for example.
But in some amplifiers we do not need as much gain.
And here I can not see any drawback using Diamond.
Not when compared to a usual 'Double Darlington' output. ( 2drivers + 2 output T )
[/B]
What about diamond buffer at 20 ma and a pair or more of lateral mosfet power transistors?...

Quote:
Originally posted by lineup

Here are my current testings, fab
See Attachment Circuit.
I am designing a Class A amplifier with 100 Watt idle supply.
+/- 25 VDC and 2.0 Ampere current.

Results are very promising.
My first verson here, 1.0, is simulated with MJ15024/25.

I will try 'the better' MJL21193/94 and MJL3281A/1302A.
I have no doubt my figures will be improved. Those better devices usually lowers THD figures considerably!
I have no doubt!
[/B]
Thanks lineup it is good to know that some peoples are interested in the diamond buffer...
You may have notice that the diamond buffer before the output transistors I am using is the same one as APEX (my revision 1A circuit) and not the Walt Jung one with current source(same as yours). It would be intersting to compare both diamond variations...

Your circuit looks quite interesting. I like jfet too for performance but they are always complicated to match or even get the proper IDSS current compared to bjt where only HFE parameter is used for optimization. I found that the "low memory" input stage with bjt I used is very linear too (simulation and real measurements too).

Please keep us informed of your simulation and prototype results.

On my side I have a version (based on my revision 1A circuit) on breadboard powered by only 28 Vdc with limited current. THD is about 0.1 % in 16 ohms which is high for me but I think this is a breadboard/power supply/grounding scheme problem. I am working out a pcb layout in paralel. I plan to maybe connect a more higher current capability power supply at 40 Vddc to see if my current bias for each stage is sufficient....
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Old 10th February 2007, 01:00 AM   #10
lineup is offline lineup  Sweden
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Quote:
Originally posted by fab


What about diamond buffer at 20 ma and a pair or more of lateral mosfet power transistors?...

Thanks lineup it is good to know that some peoples are interested in the diamond buffer...
Please keep us informed of your simulation and prototype results.
---------------------------------

On my side I have a version (based on my revision 1A circuit) on breadboard
powered by only 28 Vdc with limited current.
THD is about 0.1 % in 16 ohms which is high for me but I think this is a breadboard/power supply/grounding scheme problem.

I am working out a pcb layout in paralel.
I plan to maybe connect a more higher current capability power supply at 40 Vddc
to see if my current bias for each stage is sufficient....

I don't know how you think 'diamond buff + lateral' would be setup ..
-----------------------------------------

Actually I was a bit wrong, that you can not use
Diamond at 3 stages, to match triple darlington gais.
You just make, driver a sziklai pair. Or make output use sziklai config.
But this is only if we need high gain and low load, burdon, onto VAS stage.
-----------------------------------------

Your 0.1% breadboard might be something! With some tweaking.

Here I quote Hugh AKSA Dean:
'An acceptable level of distortion for my power amplifiers is THD 0.05% or less.'

And what I know, there is no valid listening tests
proving that humans can hear lower distortions, than 0.1% THD.
So I say, AKSA is well in line with reality here

------------------------------------------

You may have a look at my latest Diamond Follower, 500mA Class A.
I designed it today and did virtual simulation tests to refine it.

In the Pass Labs GRollins topic:
MOSFET follower headphone amplifier
MOSFET follower headphone amplifier

In my own HUMBLE Opinion:

Post #44 is the most interesting and innovative in that Topic, so far
... MOSFET single device followers, there are 20 by the dozen around already


Regards
lineup
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