JFET input, MOSFET VAS, LATERAL output = Perfect!! - Page 53 - diyAudio
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Old 30th May 2011, 05:18 AM   #521
MiiB is offline MiiB  Denmark
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It mainly works at high signal levels... when you push the amplifier...the cascode prevents the higher harmonics from building up...and aids so to speak the amplifier to maintain it's character a different signal levels.
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Old 30th May 2011, 06:50 AM   #522
lineup is offline lineup  Sweden
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Quote:
Originally Posted by mikelm View Post
I never expected to see a feedback amp with a Push Pull o/p that can operate with normal loads without any compensation - truly a step forward.

p.s. does anyone know where I can buy 2sk170's or Lsk170's in europe ? the ones I have will probably only arrive in about six weeks - can't wait that long
mikelm
Mouser is a good seller of 2SK170BL.
Has got salesfuntion for UK.
Has got lower price than Farnell to order.
2sk170

This is the one to buy:
2SK170BLF Toshiba JFET
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Old 30th May 2011, 06:54 AM   #523
lineup is offline lineup  Sweden
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Quote:
Originally Posted by MiiB View Post
the BF862 part in my circuit might be even better....it's easy to get...and has less noise and twice the gain...
MiiB
It is well worth to investigate.
I know BF862 is a great JFET.
I am adding the SPICE Model of BF862 to my library.
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Last edited by lineup; 30th May 2011 at 07:16 AM.
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Old 30th May 2011, 07:15 AM   #524
lineup is offline lineup  Sweden
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Default BUILD the amplifier WITHOUT capacitance compensation

For the builders it is good with an amplifier that is stable
without compensation. There are other benefits with lower OLG.
I am happy to see
swordfishy has built an amplifier without compensation cap.
I will publish a diagram from swordfishy's latest.
With a bias of the JFET with CCS from negative rail.


Here is swordfishy's great amplifier again:

Click the image to open in full size.
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Old 30th May 2011, 07:21 AM   #525
lineup is offline lineup  Sweden
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Quote:
Originally Posted by MiiB View Post
It mainly works at high signal levels... when you push the amplifier...the cascode prevents the higher harmonics from building up...and aids so to speak the amplifier to maintain it's character a different signal levels.
I tried a Hawksford Cascode and at 1 Watt 1 kHz it even was worse data.
So you say it is at higher power the benefit comes.

On the other hand, cascoding is not necessary for good result i this amplifier.
By complicating we can make people think amplifier looks complicated.
And they buil something more simple instead.
Some other amp. Like Hiraga orr JLH.

MY saying is NO to ANY cascode of Fetzilla.

Regards
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Old 30th May 2011, 07:44 AM   #526
lineup is offline lineup  Sweden
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Quote:
Lineup,

I actually tried removing the Feedback Cap yesterday and had some pretty bad DC offset issues. Not sure if this will apply with the CCS version, but it was pretty terrible with the front bias version.
I don't know what you mean by Feedback Cap????
Bad DC Offset can sometimes indicate an OSCILLATION going on.
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Old 30th May 2011, 08:03 AM   #527
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Hi Lineup,
would you mind posting your *.asc file? I would like to poke around a bit with it.

Rüdiger
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Old 30th May 2011, 08:07 AM   #528
mikelm is offline mikelm  England
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I think regarding DC linking ( or for that matter any other variation ) it is important to make sure that the design is modified suitably so that it is re-optimized with the new element added.

With DC linking the front bias circuit is not necessary and is probably better to remove it.

I am not clear from swordfishy's remarks about DC linking whether the DC offset was terrible or the sound was terrible but I do feel fairly confidant that if it is implemented carefully and thoughtfully that it will sound better.

The main point I am making here is that it is not really valid to judge the inclusion of a particular feature unless the design has been thoughtfully adjusted to accommodate it.

I have been reading about LSK170 from LT. It seems like a better device. Can anyone think why using this would not be a good idea ?

mike
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Old 30th May 2011, 08:54 AM   #529
AKSA is offline AKSA  Australia
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Mike,

I would caution on removal of the 1000uF feedback shunt cap.

Yes, this gives DC linking, no question, but there is a problem.

The offset voltage of the output stage is divided by the gain, giving much reduced control over offset correction. The consequence of this is very loose offset control, at times quite high values, particularly as the Vgs of the IRF9610 VAS varies considerably with temperature, affecting the voltage drop across the feedback shunt resistor.

Hugh
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Old 30th May 2011, 09:37 AM   #530
mikelm is offline mikelm  England
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Quote:
Originally Posted by AKSA View Post
Mike,

I would caution on removal of the 1000uF feedback shunt cap.

Yes, this gives DC linking, no question, but there is a problem.

Hugh
I appreciate you concern Hugh but,

Every amp I built and happily used for the last 10 years has been DC linked including a version of the JLH simple class A .

Sure, there was some DC offset, but with some thought & effort it can be managed and reduced to acceptable levels as TimA has demonstrated & documented. For me the rewards are very well worth the effort needed to achieve this.

Anyway, no worries, I accept that some seem to have an aversion to taking this route but for me it is fundamental. I'm in this pursuit to aim for a sound that is natural & wonderful, and for me, this cannot be achieved with caps in the mix - perhaps a Teflon film cap would be OK and I confess that I didn't try biasing then with DC before, but electrolytics are just too much.

Susan Parker rejoices that she has no caps in her transformer linked Zero Feedback Power Amplifier but for me transformers & caps are all in exactly the same category.

Perhaps my o/p fuses won't blow and I will blow up my speakers and you can all have a laugh, but I don't mind I would buy another set still stay with DC linking.

Sorry to go on like this you don't seem to realise that I really don't like the sound of capacitors.

But I will build swordfishy's amp as a reference and am happy to hear from anyone about the best sounding 1000uF cap to use but I will be amazed if I prefer the sound because I've been here so many times before.

kind regards despite my ranting

mike

Last edited by mikelm; 30th May 2011 at 09:40 AM.
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