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DLH Amplifier: The trilogy with PLH and JLH amps
DLH Amplifier: The trilogy with PLH and JLH amps
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Old 1st June 2018, 12:05 PM   #511
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by diegomj1973 View Post

The small original DLH (with a single pair of mosfets) has a huge virtue to exploit that is its own wide open-loop bandwidth (almost impossible to achieve with other well-known configurations, such as the classic 3-stage: LTP , VAS and EF).
It is not true. The classic 3-stage: LTP , VAS and EF (Blameless topology acording Douglash Self) is easy to have wide open-loop bandwidth using two pole compensation (TPC) or transitional miller compensation (TMC) or the other variations of two pole compensation, like which Dadod's discover.

Other topology such symmetry LTP input can use two pole compensation, too.
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Old 1st June 2018, 02:22 PM   #512
diegomj1973 is online now diegomj1973  Argentina
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Quote:
Originally Posted by kokoriantz View Post
diegomj1973 have a look Errata and Power Buffers
Have you seen the date on which the blog was published?
Sin título1.jpg

I find that curiously striking ...

A lot of water has passed under the bridge since the DLH was presented ...

I do not discredit his blog, but he presents many of his schemes based on familiar circuits. I do not see anything new or innovative and, frankly, I do not think that many of their schemes have been physically implemented or tested. From a drawing of a circuital scheme to reality there is a long way and, many times, reality is very raw and daunting for every designer ...

Quote:
Originally Posted by Bigun View Post
Broskie is often reinventing things that others have done before, adding a little spice and a great dialogue to go with which makes his blog one of the best ever for audio. Broskie has published on some similar circuits a few years back. Hugh Dean published a Rush Cascode + BJT output buffer a few years before that, buried somewhere in somebody else's thread. Nothing new under the sun is what I learned after I reinvented all sorts of stuff shortly after starting into this hobby myself

To my eyes diegomji1973's amplifier design is one of the more interesting variations and I really like the adjustability of the harmonic profile - not just a great learning tool but allow the amplifier to be more flexible in use.
Many thanks!!!

Quote:
Originally Posted by bimo View Post
It is not true. The classic 3-stage: LTP , VAS and EF (Blameless topology acording Douglash Self) is easy to have wide open-loop bandwidth using two pole compensation (TPC) or transitional miller compensation (TMC) or the other variations of two pole compensation, like which Dadod's discover.

Other topology such symmetry LTP input can use two pole compensation, too.
DLH OLG and CLG.jpg

It would be interesting to show us if with similar complexity of scheme you would reach or exceed that parameter. You would need, at least, one more active element and a handful of passive components (crossing your fingers where nothing oscillates )

Best regards

Last edited by diegomj1973; 1st June 2018 at 02:38 PM.
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Old 1st June 2018, 02:55 PM   #513
anti is online now anti  Slovakia
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The Achilles heel of your design is the limited output swing (and the practical consequences of it).

Offtopic, I was able to squeeze 11Vp-p output at 12V supply into 6 Ohm (resistive load so no real bragging rights here...) with a modified JLH69 topology (am not publishing it) built with pedestrian euro components (BC/BD transistors etc) at cca 400mA bias. IOW; "almost" R2R ...
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Old 1st June 2018, 03:11 PM   #514
diegomj1973 is online now diegomj1973  Argentina
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Quote:
Originally Posted by anti View Post
The Achilles heel of your design is the limited output swing (and the practical consequences of it)
The DLH does not have an Achilles heel ... it has a lot of them !!!

To mention just one of the many : the shift of the DC offset with the temperature and its way of trying to correct it. Although for this defect there would be others possibles solutions: capacitive coupling to the speaker using a simple polarity power supply or running two units in bridge mode with direct output coupling.

Best regards

Last edited by diegomj1973; 1st June 2018 at 03:39 PM.
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Old 2nd June 2018, 06:12 AM   #515
kokoriantz is offline kokoriantz  Lebanon
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Default offset drift remedy

Bias the input transistor with current rather than voltage . It needs to decrease as it heats up due to rise of beta and decrease of mosfet's bias voltage. The ntc mounted on the heat sink can do it . If the input transistor has a heat sink hence less beta increase it gives less variation .
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Old 2nd June 2018, 09:44 PM   #516
diegomj1973 is online now diegomj1973  Argentina
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Thank you very much kokoriantz for your contribution! Any compensation attempt should counteract the voltage variation of the base-emitter junctions of the two bipolar transistors. The idea is that as the two joints heat up, the polarization potential of the base of the BC550C becomes less negative.

Best regards
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Old 2nd June 2018, 11:29 PM   #517
diegomj1973 is online now diegomj1973  Argentina
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In the above text, should be BC560C instead BC550C. Sorry for my error.
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Old 4th June 2018, 12:08 AM   #518
Bigun is offline Bigun  Canada
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DLH Amplifier: The trilogy with PLH and JLH amps
for me, because I could never accept the thinking of controlling current into base (as it relies on non-linear and rather inconsistent Hfe) I design with voltages and in all cases I can remember it's not difficult to insert a diode (or few) somewhere in the base circuit and put the diode and transistor into thermal contact. You can model it in LTSPice too, varying the temperature and watch to ensure temperature coefficient of idle current is negative and temperature coefficient of dc offset is relatively small.

for this amplifier you'll likely need more than 1 diode to match the temp.co for the dc-offset. In my TGM8 amplifier I used a single transistor wired up as a Vbe multiplier. It worked well although it takes more parts and you may prefer to keep it simple with a string of diodes type of approach. For my design, I fancied it up with a zener diode to create a steady fixed voltage off the negative rail so I didn't have to care too much about the rail voltage - you likely don't need that refinement. The Vbe multiplier is Q2 in the attached diagram and VR1 adjusts for the dc-offset (you'll need multi-turn or else split it into a variable + fixed resistors in series for more control).

There's many ways to skin this cat and you may find a different way that fits to the aesthetic you want.
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Last edited by Bigun; 4th June 2018 at 12:18 AM.
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Old 5th June 2018, 12:23 AM   #519
diegomj1973 is online now diegomj1973  Argentina
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Thank you very much Bigun for your contribution !!! I agree with you.

The DLH with the compensation implemented with two bipolar transistors similar to those of the input circuit works very well and under very similar concept to which you have kindly exposed. In fact, that compensation was successfully tested by xrk971 and, probably, by others. In simulation, that compensation has also behaved well.

Best regards

Horacio
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Old 5th June 2018, 09:19 AM   #520
xrk971 is offline xrk971  United States
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DLH Amplifier: The trilogy with PLH and JLH amps
I just built TimS's amp, which in some ways reminds me of the DLH but it uses all JFETs on the front end. It has self-balancing DC offset. Tracks at 5mV hot or cold. The DC offset is controlled by matched J3 and J4 and identical R78/79.
Click the image to open in full size.

My build here:
Simple High Performing Headphone Amp
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