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Extremely simple amplifier (4 transistors) with low THD.
Extremely simple amplifier (4 transistors) with low THD.
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Old 20th September 2019, 04:49 PM   #21
banat is offline banat  Serbia
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Quote:
Originally Posted by xrk971 View Post
Yes, but JLH did not have push pull output.

One thing I noticed with this amp that is unique: despite having output coupling cap, there is a slight 500mV DC offset due to the connection from the base of the PNP to the output after the cap.

This offset is not a good thing as voice coil will heat up a bit.
JLH A-class amp is also with push pull output ,

to avoid that output DC offset bias network need to be slightly modified by adding one more cap(C6) and one more resistor (R10),

this simple amp will sonicaly outperform many other solid state amps for sure because of his very specific THD spectrum .
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Old 20th September 2019, 05:33 PM   #22
xrk971 is offline xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
Quote:
Originally Posted by banat View Post
JLH A-class amp is also with push pull output
That's strange as I thought that the JLH 1969 had two NPN's for output? I guess I should have said complementary push-pull.

http://www.keith-snook.info/wireless...ier%20-%20.pdf

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Last edited by xrk971; 20th September 2019 at 05:42 PM.
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Old 20th September 2019, 07:31 PM   #23
Renbrant is offline Renbrant  Brazil
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That's the test results:
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File Type: png Frequency Response.png (54.9 KB, 309 views)
File Type: png Gain and distorsion.png (54.7 KB, 309 views)
File Type: png IDM x Power.png (54.8 KB, 306 views)
File Type: jpg THD+N x Frequency.jpg (314.5 KB, 42 views)
File Type: png THD+N X W 15v.png (59.6 KB, 37 views)
File Type: png Inpedance x Frequency.png (47.6 KB, 29 views)
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Old 20th September 2019, 07:35 PM   #24
Renbrant is offline Renbrant  Brazil
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Default Output wave format from 1.65W to 5.23W:

In this test, I was increasing the input in 1dBV steps, from -12 to -6dBV.
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File Type: png 1.65W.png (141.2 KB, 41 views)
File Type: png 2.07W.png (143.9 KB, 34 views)
File Type: png 2.59W.png (146.9 KB, 27 views)
File Type: png 3.24W.png (128.1 KB, 27 views)
File Type: png 4.03W.png (151.1 KB, 25 views)
File Type: png 5.23W.png (151.3 KB, 34 views)
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Old 20th September 2019, 07:58 PM   #25
thiagomogi is offline thiagomogi  Brazil
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maybe this is safer than UNO?
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Old 20th September 2019, 09:00 PM   #26
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by thiagomogi View Post
maybe this is safer than UNO?
It's a Philips/Valvo/MBLE/Mullard/RTC/Elcoma etc. app note, so safe and problem-free like the proverbial Volvo (or a Japanese car, if you prefer)
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Old 20th September 2019, 09:04 PM   #27
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Renbrant View Post
That's the test results:
Results are quite decent, and typical of such an amplifier.
More problematic are the simplifications, like dispensing with emitter resistors: they look like a good idea, until you run into real problems
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Old 21st September 2019, 01:54 AM   #28
Ian Finch is online now Ian Finch  Australia
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I wonder if there would be much to gain by fitting more suitable types of power transistor to such ~15W amplifiers as this Philips design. In other words, if we already have something like FJPF5200/1943 or even D44H11/45H11 which are often classed as audio transistors?
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Old 21st September 2019, 03:03 AM   #29
gannaji is offline gannaji  India
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Last edited by gannaji; 21st September 2019 at 03:09 AM.
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Old 21st September 2019, 12:13 PM   #30
anti is offline anti  Slovakia
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Quote:
Originally Posted by Ian Finch View Post
...
or even D44H11/45H11 which are often classed as audio transistors?
...
I have built some amps with these, even a minified JLH'69 - these are a little faster than originally specced devices, so there must be some compensation added. Otherwise probably good for something up to 10-something watts of class-AB...

But the above "black devil" amp is a good example of german enginierung: how to squeeze 50W out of a topology initially layed out for ~5W amps ...

If 'Mericans were at it, we would probably look at some double-digit-transistor topology ...
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