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Old 28th December 2011, 03:54 PM   #2181
shaan is offline shaan  India
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Board Plan done. Added Iq control pot.
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Old 28th December 2011, 05:17 PM   #2182
Mooly is online now Mooly  United Kingdom
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I'll be interested to know what you think to the sound quality. I suspect it will be excellent.
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Old 28th December 2011, 05:29 PM   #2183
shaan is offline shaan  India
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I hope...

currently soldering.
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Old 28th December 2011, 07:47 PM   #2184
EUVL is offline EUVL  Europe
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You might wish to consider changing all BJTs to FETs and not just the output devices.
You could actually end up with a much simpler circuit.


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Old 29th December 2011, 03:35 AM   #2185
shaan is offline shaan  India
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Nah... I'm not experienced enough to do that. Eventually it may happen. I had tried it once in the past, irf9610 as input. Measured awful, sounded dreadful. I had done something wrong. It was an all vertical FET amp. Now I am into the Laterals, the old dudes.
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Old 29th December 2011, 06:26 PM   #2186
shaan is offline shaan  India
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Amplifier is running fine at stable 1.5A bias. Turn on is silent. But a loud transient at turn off. What is causing this? Help please.
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Old 29th December 2011, 06:41 PM   #2187
AndrewT is offline AndrewT  Scotland
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The output capacitor is sitting with a half supply voltage charge across it's plates.
At turn off that charge passes quickly through the speaker voice coil producing that burp/bang/whatever.
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Old 30th December 2011, 12:06 AM   #2188
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Our JLH is DC biased. There's no burp at both on or off when the offset is adjusted to zeor. I think for DC coupling design zero (or near zero) offset should also be set to avoid burp.
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Old 30th December 2011, 02:25 AM   #2189
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Unity gain CFP in the feedback path can automagically cancel DC offset.
May look like LTP, but actually not. CFP'd feedback has overwhelmingly
more transconductance than the input transistor, but at only unity gain.
So, a deliberately unbalanced (except for DC offset) pair. Remains JLH
style single ended feedback gain path (without the JLH DC problem)...
Might also now technically fall into the category of folded cascodes?
Both DC offsetting transistors also forced equal collector current and
voltage, with no precise adjustments needed to make them equal.

No caps involved this way, maybe no thumps? Theoretically... Possibly...
Well, there's still a big cap in my bootstrap path, so maybe not...

I call this style a shunt tail pair. Could be made a balanced shunt tail,
but in this case works better (prevents loss of 1/2 loop gain) and fewer
parts to leave it very simple and AC gains extremely unbalanced...

Don't mind the current steering and CFP MOSFETs in this drawing.
BJT's as you might normally use for JLH still work. R3 & R13 would
be about 330R if all BJTs were to be used.

The proposed shunt tail offset fix and shunt reg'd bias of SR-JLH2011
is one less transistor than JLH2005's series reg'd currents for similar
and/or superior functions! Shunt reg'd output classes are easily flexed.
No problem to rig a front panel switch with many options...
Enriched A, Linear A, Square Law A, AB + CCS, all easily defined.
And furthermore: Does not care if output transistors match...

All this, ONE LESS TRANSISTOR than 2005 version. Count em'...
Shunt regulated current sources is the magic.
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Old 30th December 2011, 06:24 AM   #2190
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by shaan View Post
Amplifier is running fine at stable 1.5A bias. Turn on is silent. But a loud transient at turn off. What is causing this? Help please.
I suspect it's because of the servo and the fact the amp is single ended. I'm surprised switch on is silent though tbh.

As the rails finally collapse the output will swing over to one or other rail as the servo becomes unable to maintain biasing. There are time constants involved too.

Just thinking out loud but I see you eliminated the "feedback return electroylitic " making the whole amp DC coupled apart from the input coupling cap. I tried to do this on my amp (which is a very similar topoloy) but found the compromises in doing that and still being able to get the DC biasing and wanted AC peformance unacceptable. And I use a 6 second speaker delay on power up together with an instant off (within a few 10's of milliseconds of AC power being removed). The instant off isn't so important as the PSU caps power the amp for quite some time.

What is the normal steady state DC voltage at the output of your TL072 ?
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