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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 27th January 2019, 08:08 PM   #5521
martyh is online now martyh  United States
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Still working towards building the 1969 version to power 600 Ohm headphones and I have a couple of questions that hopefully someone can help me with.

Is it always better to use higher gain transistors for TR3 and TR4? I bought enough BD139-16 and BC559-C to match channels for hfe and ended up with a couple of pairs of each. These already have higher gain than the original transistors but wondering if I should use the pairs with the highest gain.

Is there any reason to choose a cap multiplier supply over a 3 pin regulator? I have some LM338K in the parts bin and it makes for an easy solution to regulation so I am leaning in that direction.

And the last is based on my very limited theoretical background… I noticed in simulations that the light loading on the outputs extended the HF knee by a considerable bit, it occurred to me that slower devices for the outputs might be usable or even desirable at those positions so I acquired some (what I hope are original) homotaxial RCA’s to try. Assuming I can get the hf extension I am looking for out of them, what is the best way to check the stability of the amplifier into the light load? I have an old 15Mhz scope and an AF generator, is there a way to excite and see HF oscillations with the equipment I have?

Thanks,
Marty
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Old 27th January 2019, 08:49 PM   #5522
grunf is offline grunf  Croatia
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Quote:
Originally Posted by nigel pearson View Post
I think DN2540 is obsolete now. A depletion type if I am right? More like a jfet or vacuum tube. Again a bipolar CCS would be interesting and what best sets standing current. BC327-40 could work. An emitter resistor almost ensures linearity and is the current setting. Most MOS FET and all bipolar are enhancement (?) devices. The CCS for them look different. Bipolar types need about 0.55 to 0.7 volts to to switch on. This means a calculated design will be very close to actual result. Other devices may spread 2 to 4 volts.

The DN2540 is still in production, in three different cases.
dn2540 Microchip MOSFET | Mouser Croatia
DN2540 is depletion type and in my case it needs Vgs of -0.8V for 30mA. This CCS I think to improving with a better mosfet with lower Vds and maybe with a cascade with FET at a lower position although DN is doing its job well.
In the past few years I've been playing a lot with CCS and I like the sound of DN2540a at higher currents.For less current I prefer FETs. The BJT CCS in the simulator has a slightly smaller distortion than the DN2540,so I'll try it one day though I know it will not be better than the DN2540.
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Old 27th January 2019, 09:35 PM   #5523
grunf is offline grunf  Croatia
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This is a collection of transistors I've tried for Tr3. There is a difference in the sound whether the scheme is with botstrap or with the CSS for Tr3. 2SC3421 I deliberately left the end because it was listed as the best replacement for 2N1711. And now I can say it's not worthy of that title.
My favorites are 2SC1941, 2SC3116, 2SD571, 2SD438, KSC2682, KSC3505 and 2SC3423. The 2SC3421 is missing the stage width, somehow it is muddy.
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Old 27th January 2019, 09:58 PM   #5524
Mark Johnson is offline Mark Johnson  United States
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JLH 10 Watt class A amplifier
Tens of thousands of DN2540's in stock and on the shelf:
click me
Part status: Active Production , according to two different distributors.

_
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Old 27th January 2019, 11:28 PM   #5525
Jonathan Bright is offline Jonathan Bright  Australia
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Hi Martyh, Re: JLH headphone amp' are you aware that he did create a dedicated headphone amp' based on the '69 power amp?
Just might save you "reinventing the wheel".
Paul Kimble has assembled a lot of his audio circuitry at the following site,
(A Paul Kemble web page - John Linsley Hood preamp designs.)
The HFN-RR amp is about a quarter of the way down the page.....its split rail too.
Its got a 'tone control' attached to the front but that's not an issue....
cheers, Jonathan
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Old 4th February 2019, 05:04 PM   #5526
fredbloggstwo is offline fredbloggstwo  United Kingdom
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Hi Folks

I was cleaning up my list of favourites and came (again) accross Stan Curtis' site. Stan appears to have a straight forward, no nonsense attitude towards amplifiers and Hi-Fi in general.

Of particular interest was his musing on various topics in various articles that can be found here:

Stan Curtis, Engineer, articles from HiFi Critic magazine

More to the point of this thread, a sort of inclination/rationale for the use of Class A amplfiers and of simple design that can be found in Stan's Safari part 3.

I have always had this notion (with nothing to substantiate it) that the minium number of amplifying elements in an audio chain is a way to reproducing a good sound - "Far too many transistors Mr Mozart" (with applogies to W. A.)

Worth a read

Happy listening

Mike
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Old 4th February 2019, 08:02 PM   #5527
grunf is offline grunf  Croatia
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Here is a new version of JLH with CCS, the first CCS formed by a pair of cascoded FETs, and the second with cascoded depletion MOSFETs. The sound is really great, so far the best improvement.
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Old 5th February 2019, 03:36 AM   #5528
Bigun is offline Bigun  Canada
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JLH 10 Watt class A amplifier
looks good!

Great to see new versions. IIRC this is similar to what is sometimes referred to as the 1996 version, which is an all BJT version with ccs so you’re in good company.
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Old Yesterday, 09:45 AM   #5529
danielwritesbac is offline danielwritesbac  United States
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Original JLH documentation that is becoming hard to find online. JLH Library
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