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Old 17th February 2012, 02:00 PM   #181
xslavic is offline xslavic  Moldova
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Default hi

all of them 4k7 to 10k
it worked for me,and the caps next to 1UF should be 220uF ,and no noise
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Old 17th February 2012, 02:07 PM   #182
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Aha, thank you
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Old 21st February 2012, 12:47 PM   #183
xslavic is offline xslavic  Moldova
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Click the image to open in full size.

finally made it
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Old 21st February 2012, 08:03 PM   #184
hotiron is offline hotiron  Scotland
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Well done. Thats a neat case. Post some more pics Please.
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Old 25th February 2012, 02:34 PM   #185
JustFJ is offline JustFJ  United States
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Default Convert from JHL(chinnese version) to JLH(orig. version)

Hi Folks,

I built JHL kit(Chinnese version from Ebay) n then i converted them to JLH(original version), after i tested the amp, stil, i don't like the soundquality of the amp(the top highs/treble rolled off and the bass is weak) so i did some mods again
- VR1 10K to 100K Potensiometer
- Bypassed the C1 1uF
- Desoldered R1 47K, R3 10K, C1 100uF, D1(zener diode)
- Replaced C3 220pF with Resistor 10K,
- Replaced R5 470ohm to 1K,
then i tested them and like the improvement
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Old 25th February 2012, 10:39 PM   #186
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'scuse me, but your mod makes just about zero sense to me. You now have a considerable output DC offset, roundabout +1.8 V or so. Not something I'd call particularly acceptable. And using a 100k pot will, if anything, only increase noise and distortion.

How did you come to the conclusion of "the top highs/treble rolled off and the bass is weak"? What did you compare the amp to, with what kind of headphones? Have you carried out a basic frequency response test (using e.g. soundcard + RMAA)?

Assuming it is equipped and working correctly, the JLH amp built according to the first schematic should have none of the deficiencies you describe.
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Old 26th February 2012, 10:27 AM   #187
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Hi there,
I'd like to know if measuring the dc offset with and without load, you see any differences.
because I measure around 30 mv of difference.
My sensation is that DC offset is unstable, and I have some problems to fix it

I changed some components:
C13 = 1,5uF instead of 1uF
R19= 10 K instead of 220K ((no technical choice, only for components availability )
VR3= 2,2 K instead of 10K (idem)
C15 = 47pF instead of 220pF
In this way I extended the range of frequency from 5Hz to 22KHz flat, could it be the cause of my problem?

Thank you in advance
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Old 26th February 2012, 03:35 PM   #188
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Assuming you have adjusted DC offset to 0+/- 10 mV when the amplifier is warmed up, there should be no significant influence of loading on it. I've simulated with all kinds of transistors, there never was anything more than 1..3 mV of difference to be observed. There shouldn't be one either, since your load connects two nodes at virtually the same potential.

How stable are your supplies?

BTW, try finding a larger-value resistor for R19, otherwise power supply rejection at higher volume settings will suffer.
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Old 26th February 2012, 05:29 PM   #189
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Quote:
Originally Posted by sgrossklass View Post
How stable are your supplies?
.
I changed psu stage with LM 317/337 instead of 7812/7912.
maybe cause of improvvisation wired could generated instable voltage, but don't seem me if I see the multimeter.
http://ubuntuone.com/1nISGLbzDGSr0JKlJTzKrG
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Old 29th February 2012, 08:50 PM   #190
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I replace the original power supply stage (7812/7912).
Now I measure the same offset. However this it instable and sensible at the change of temperature.
Do you suggest me, give up the offset control and put a filter condenser in output?
If you agree, which value?
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