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★★Free JLH Hifi Headphone Amp PCB, 0.008% THD★★
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Old 3rd August 2015, 09:14 PM   #101
e_fortier is online now e_fortier  Canada
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Join Date: May 2001
Location: Eastern Canada
★★Free JLH Hifi Headphone Amp PCB, 0.008% THD★★
Glad you enjoy it, I have built their Power amp with my own components and it sound superbe !

Not sure how much more distorsion you are getting with a reduced global feedback but if it sound good don't touch it

Looking forward for the picture.

Sounds like this is your own PCB, you simply used the schematic, is this correct ?

Don't forget to comments on the slam, attack once both channel are built.

Best regards,
Eric
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Old 4th August 2015, 06:26 PM   #102
rensli is offline rensli  Estonia
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Got 2nd ready.
Fired them all up with ZOBEL networks installed (100nf, 27R) and 10R 3W Wirewound output series resistor!

With bias 200mA per channel:
First i notice, they seem to be a little slower in music "rhythm" compared to NAIM 140 amplifier Maybe its the headphones... but i like the sound this way from post 86. schematic.

Up to 35% volume:
Sound is nice, pleasant, lots of background, imaging... music notes doesnt fade or disappear when rising volume to a named point.
Piano seems almost like real, maybe a little bassline from the lower piano notes are missing... just a little..
I am comparing this to a power amplifier

Pendulum in Silico 2008 for example, drums are great ! Slam and bassline - its all there and shaking your head inside out!

From 35% volume and up:
Too many highs, they cover almost all the notes in the music.
I could listen to Psy Trance only @ that high volume, with 50-70% volume it is kicking hard, u almost can feel that its coming inside your head.

It seems that there is too much gain again?

Besides, i dont feel headphones clipping anymore... @ 80-90% volume... but its intolerable to listen, cuz of the HIGHs ruining all the party


Should i try new values or e_fortier might have better idea ?

EDIT: I later cut both Zobel networks at the same time while listening to pendulum, no difference in sound imo

Pics are taken @ first hook up:

EDIT2: Forgot to mention that there is a lot of middle tones in the music, female voices are superbe(Y)
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Last edited by rensli; 4th August 2015 at 06:33 PM.
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Old 5th August 2015, 02:29 PM   #103
e_fortier is online now e_fortier  Canada
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★★Free JLH Hifi Headphone Amp PCB, 0.008% THD★★
Strange that you have a gain increase at higher frequency, the global feedback and Zobel should prevent this.

Is your volume hardware? If yes, where is it located in the circuit and what it's value. Maybe you are creating some sort of filter at the input causing the low frequency to decrease.

Have you tried a different pair of headphone ?

Best regards,
Eric
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Old 5th August 2015, 08:06 PM   #104
rensli is offline rensli  Estonia
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Quote:
Is your volume hardware? If yes, where is it located in the circuit and what it's value. Maybe you are creating some sort of filter at the input causing the low frequency to decrease.


No, volume is software... WIN 7 mixer

Yes, You are right, its something else creating it. It does not roll off bass frequencys. high notes are just gaining too much dB.
Bass stays, actually low frequency starts to produce huge pressure on the ears... u feel the cans are vibrating hard @ full volume.. also lots of HHHHSSSS of highs and thats about it. LOL

IMPORTANT:
Hooked up a pair of 32R AKG K518-LE headphones, @ 100% volume and highs are gone

OFFTOPIC:
This headphones are bassy even without the JLH amplifier I wont suggest to buy AKG-s to anyone... as these are not comfortable for 1h+ use... or else the ears will be in much pain..

CONTINUE:
Most of the difference comes from output resistors... more resistance means less bass into ATH-AD900. Also PSU makes a huge improvement in sound.

Is it okey to use no resistor on the output ? Shorting the outputs without a resistor does not give any current increase from PSU... the output offset is too small to generate it.

Tried amps on LM317AT % LM337AT PSU. Sound is remarkably better with this setup.

EXPERIMENTS:
Well, tested few more things:
OUTPUT -> 2SC5200 or BD136, no difference. Using TIP41
Input caps -> 10uf Muse Nichicon(bright), 10uF BC128 Solid(better)
Feedback resistors(2.2k & 1k, 2.7k & 1.2k, 3k & 1.5k) no difference in music(tonal balance and so on).
Very odd feedback resistor combination gave high offset values on the amp output.
16V vs 12V per rail, nothing... 16V rails might get you oscillating amp without a Zobel(10R & Soviet 100nF huge ceramic)
160mA vs 60 mA, no difference @ 35% volume (class A operation).

HELP
Is it wise to use 3 output configurations ?:
1. with an inductor to damp highs a little, what values are suggested for headphone amplifiers ?
2. just a plain output without series resistors
3. Regular output with 4.7R series resistor ?


CONCLUSION:
Its good all around schematic and is bullet proof for human stupidy actions also(removing rail voltages, powering up without GND connection and so on). <--- dont try this without current limiter circuit !!!!
I like the sound of this amp, its relaxing, different sounding from AB class. Tested only with ATH-AD900 headphones... AKG-s are no good in quality sound (dynamics, more bass but its dull and its not kicking"i mean there is also a high frequency note with a bass note that creates a hard kick like a real speaker ).

Last edited by rensli; 5th August 2015 at 08:20 PM.
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Old 5th December 2016, 04:56 PM   #105
johngalt47 is offline johngalt47  United States
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Is there an official schematic for this amp? My kit came with 3055 / bc 550 /bc560 transistors.
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