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Old 1st July 2011, 08:28 PM   #141
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Default Two versions now built ..

Hi guys

Busy week and have done LOTS of work this week on the boards, I have now build and tested two versions ..
  1. JHL Chinese Version
  2. JLH MkI Version

Lots of testing done with some very disappointing results, I have a very busy weekend of writing up todo ..
More soon

Miles

JLH MkI version from here
Attached Images
File Type: jpg JHL and JLH MkI.jpg (361.5 KB, 1019 views)

Last edited by MilesCampbell; 1st July 2011 at 08:34 PM. Reason: Forgot to add the picture
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Old 2nd July 2011, 08:39 AM   #142
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Default Testing the power supply on the PCB

Back on post #129 the board was assembled to the power supply stage and required testing.

The stage requires a good quality DVM, but a passive meter can be used at this stage.

Picture List
  1. Transformer Calculations
  2. Voltage Regulator pinouts

AC Test Points Assuming 12Volt Tx
  1. Set the meter to AC V
  2. AC (Left screw terminal) to GND= 13VAC
  3. GND to AC (Right screw terminal) = 13VAC
  4. AC (Left screw terminal) to AC (Right screw terminal) = 26VAC

DC Test Points
  1. Set the meter for DC V
  2. GND to 1N4007 (7912 Side of the PCB) bottom legs = -17VDC
  3. GND to 1N4007 (7812 Side of the PCB) bottom legs = 17VDC

Using the attached datasheet for the correct pintout, which is read as if the device number is facing you.
The device is highlighted in yellow TO-220 style case. Note the subtle difference in pinout!
Always keep the NEGATIVE or BLACK lead of the meter to GND therefore using the Positive or RED lead for the measurements.

7812 Test Points
  1. Set the meter for DC V
  2. Left Leg = 17VDC
  3. Centre Leg = 0VDC
  4. Right Leg = 12VDC

7912 Test Points
  1. Set the meter for DC V
  2. Left Leg = 0VDC
  3. Centre Leg = 17VDC
  4. Right Leg = 12VDC

Tips
  1. Don't forget to change the DVM from AC to DC for the second set of measurements.
  2. Take the time to satisfy yourself that the values are correct

To Done List
  1. Will Alps Blue Velvet fit the PCB ? - It will not physically fit on the PCB, it is just too big ..
  2. Is an output protection module required ?
  3. What is a sensible transformer specification ? - 12 - 0 - 12 VAC at 25VA (Bigger VA number rather than smaller) See below
  4. Draw a logical and simple schematic

Next time, we finish the build of the PCB and start making noise ..
Hope this is helpful
Miles


DVM = Digital Volt Meter
Tx = Transformer
Attached Images
File Type: jpg JLH HA SbS - TX Spec.jpg (216.8 KB, 960 views)
File Type: jpg JLH HA SBS Build - 20b Pin out VReg.jpg (134.8 KB, 858 views)

Last edited by MilesCampbell; 2nd July 2011 at 08:51 AM. Reason: Amended TX Spec
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Old 2nd July 2011, 08:42 PM   #143
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Default Updated To Done List

To Done List
  1. Is an output protection module required ?
  2. Draw a logical and simple schematic
  3. Are larger heatsinks required ?
  4. Reduced the gain of the amplifier for a 2Vrms input rather than the older 0.707Vrms standard?

Have I forgotten anything else ?
More in the morning ...
Miles
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Old 3rd July 2011, 01:04 PM   #144
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Default Final Build Stages

During the final stages of assembly it is very important these components are inserted in the correct orientation ! Transistors and electrolytic capacitors suffer catastrophic failure in power the wrong way around ..

Picture List
  1. Input Connector and input transistor 2N2222 2 off
  2. Transistors - 2N2907 4 off
  3. Capacitors 2200uF - Post Regulator Smoothing 4 off
  4. Output Connectors
  5. Output Transistors TIP41 mounted on their heatsinks
  6. Output Transistors assemblies mounted on the PCB
  7. Potentiometer

Comments
  1. The 2N2222 and the 2N2907 are not interchangeable and must go in their correct positions and orientation. Looking from the top the device is in the shape of a D. On the PCB there is also a D shape and these flat sides allow the device to be inserted correctly.
  2. There is a slight misalignment between pins of the output transistor and the heatsink alignment holes on the PCB. The TIP41 pins are not quite straight when all is complete.
  3. The 2200uF capacitors are marked on one side with a minus sign and a shorter leg. The PCB is marked with a smile and this is the negative leg. Failure to insert any electrolytic capacitor with the correct polarity can lead to CATASTROPHIC consequences.

Tips
  1. Inserting the 2N2222 and the 2N2907 can be quite tricky and the legs will break if flexed tooo much.. I would suggest that the first and third legs are bent slightly out and the device then inserted with the bottom 5 to 7mm from the board.
  2. Can I suggest that the output transistors are mounted onto the heatsinks with the screws LOOSE... Insert on to the PCB and solder the middle pin of the device first, then check to see if the assembly is mounted square and flat to the PCB. Now solder the other legs of the transistor and the heatsink. Finally tighten the screw on the heatsink.
  3. The large power supply smoothing capacitors are another component which it can be easy to leave a gap between to the PCB. Again solder one leg and check that the component is tight to the PCB retouch the joint if necessary and then solder the other leg.

Now we are ready to power the board and finally test ...
Miles

Last edited by MilesCampbell; 3rd July 2011 at 01:11 PM.
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Old 3rd July 2011, 02:50 PM   #145
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Default Testing the completed board

I have tried to make this testing phase simple and painless, with all of the testing done with a DVM.
Some measurements are taken With Reference to Ground WRG Using the black test probe connected to the GND terminal of the AC input connector.

Before the board is powered a load should be applied across the output terminals, in my case 100ohm resistor at 1 watt. Please don't use your best headphones at this stage, if something is wrong this could be a VERY expensive mistake.

I have assumed that the board is on the bench with the AC connector at the top as shown in the picture.

Picture List
  1. Test rig Two Avo 8's measuring the AC current into the board.
  2. AC Input connector
  3. Pinout of the voltage regulators
  4. 5.1 Ohm resistors
  5. Zener Diodes
  6. Finally the Output Connector

AC Test Points
  1. With the meter set to AC volts
  2. AC input connector WRG approx 13V at each AC input
  3. AC input connector approx 26V at between each AC input
  4. Voltage Regulator output pins WRG - a few millivolts
  5. Output Terminal connector of each channel WRG less then 5mV

DC Test Points
  1. With the meter now set to DC Volts
  2. Right side 1N4001 bottom pin WRG 17V DC
  3. Left side 1N4001 bottom pin WRG -17V DC
  4. Output pin 7912 WRG -12V DC
  5. Output pin 7812 WRG 12V DC
  6. Across the 5.1ohm resistor 0.6V DC (Red test probe top and black test probe bottom)
  7. Across the zener diode 3V DC (Black test probe top and red test probe bottom)

If all of the above measurements are correct, the heatsinks of the devices should start to warm up.. After about 5 mins a finger placed on top will feel heat. Both voltage regulators have over temperature, short circuit and over current shut down if anything is seriously wrong.

If all the above conditions are met the final stage of setup can be completed below.

Setup
The variable resistor is a 10 turn version which removes the DC offset at the output. With the DVM connected to the output connector with variable resistor should be turned until the offset is removed..

Comments
Please note : A limitation of this design is that the DC offset will vary over time and due to heat. 50mV = 0.05V is quite acceptable

At this point is VERY tempting to plug your best headphones in and kick back with your favourite CD .. Please don't .. Can I suggest that the board is now soak tested for at least 6 to 10 HOURS to allow any suspect components to fail .. If a semiconductor or electrolytic capacitor is to fail it will happen in the early period or end of a product life cycle.

Check the DC offset value once again and now FINALLY kick back and listen to your hard work ...

Next I will look at some AC testing of the board..
I hope this has been helpful
Miles

DVM = Digital Voltmeter
Attached Images
File Type: jpg Testing - 1 Test Rig.jpg (96.6 KB, 258 views)
File Type: jpg JLH HA SBS Build - 19 AC in.jpg (188.4 KB, 248 views)
File Type: jpg JLH HA SBS Build - 20b Pin out VReg.jpg (134.8 KB, 138 views)
File Type: jpg JLH HA SBS Build - 12 5R1.jpg (189.8 KB, 129 views)
File Type: jpg JLH HA SBS Build - 04 Zener Diodes.jpg (205.1 KB, 114 views)
File Type: jpg JLH HA SBS Build - 26 Output Connectors.jpg (163.2 KB, 130 views)
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Old 3rd July 2011, 04:03 PM   #146
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Default AC Testing

Below are a series of waveforms to test the design under ideal conditions by applying an impulse to the input, in this case a square wave and the output is displayed on an oscilloscope. The oscilloscope has two channels CH1 and CH2 which have the same functionality. The X10 (Times 10 or multiplied by 10) versions show an expanded X axis of the graph to quickly show the effective rise time of the amplifier.

Picture list
  1. 100Hz Square wave
  2. 100Hz Square wave X10
  3. 1kHz Square wave
  4. 1kHz Square wave X10
  5. 10kHz Square wave
  6. 10kHz Square wave X10

In the following tests CH1 (Top of the screen) displays the input waveform from the signal generator and CH2 (Bottom of the screen) displays the output of the amplifier. In a perfect world both signal should look the same and the rise time of each signal should match.

Testing the board
A square wave of the following frequencies is applied to the board and the output recorded.
  1. 100Hz
  2. 1HKz
  3. 10kHz

On the right hand side of each picture there are a number of measurements taken by the scope which are helpful to understand what is happening..
  1. The first is the frequency in Hz of the input signal
  2. The second is the rise time of the orignal signal on Channel 1 CH1
  3. The third is the rise time of the output of the amplifier on Channel 2 CH2


Comments
There are 6 pictures, 3 sets of two for the following frequencies
  1. 100Hz Picture 1 and 2
  2. 1HKz Picture 3 and 4
  3. 10kHz Picture 5 and 6

Conclusion

The sharp increase in rise time and the X10 pictures clearly show the reactance of the amplifier rapidly increasing as the frequency increases, in effect reducing the high frequency performance.

So this Chinese version of the JLH design will sound dull and a bit lifeless ..

It must be strongly emphasised that the original design was capable of much better performance than this implementation. So the next job is now convert this board to the original JLH shown in circuit 1 here.


Please note : My waveform generator was made a technical college many years ago and had the latest 8038 device at the centre of the design.. Many years have passed and it can be seen that the square output at low frequencies is not very good at all, so a new version is required..

Picture list
  1. 100Hz Square wave
  2. 100Hz Square wave X10
  3. 1kHz Square wave
  4. 1kHz Square wave X10
  5. 10kHz Square wave
  6. 10kHz Square wave X10
Attached Images
File Type: jpg Testing - 2a 100Hz.jpg (100.7 KB, 158 views)
File Type: jpg Testing - 2b 100Hz x10.jpg (100.0 KB, 90 views)
File Type: jpg Testing - 3a 1kHz.jpg (100.4 KB, 79 views)
File Type: jpg Testing - 3b 1kHz x10.jpg (96.2 KB, 70 views)
File Type: jpg Testing - 4a 10kHz.jpg (102.4 KB, 73 views)
File Type: jpg Testing - 4b 10kHz x10.jpg (98.5 KB, 81 views)
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Old 4th July 2011, 07:06 AM   #147
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Default JHL In Summary

PCB Issues
  1. C23, C24 : Are shown on both the schematic and the PCB with incorrect polarity
  2. The left and right swap sides on the PCB - the input connector is logically labelled L - G - R, however the LEFT channel is on the RIGHT side of the PCB and the RIGHT channel is on the LEFT side of the PCB!
  3. The ground track for both outputs is a VERY poor layout
Component Issues
  1. C9, C10 : 33nF However the supplied value is 0.1uf
  2. C13, C14 : 1uF Are supplied as 0.47uF
  3. C15, C16 : 330pF Is a ceramic capacitor which will perform poorly in this function
  4. C1, C2 - C23, C24 : Would benefit from having high quality components
By design the original JLH version was inherently stable at RF frequency a number of components are not required
C5, C6 - C19, C21 - C17, C18

The zener diode stated on the schematic diagram 2V7 = 2.7V The supplied value is 3V0 = 3V

The zero ohms links supplied are of poor quality and have a value of 0.4 to 1 ohm

In Summary
C23, C24 Require inserting with the correct polarity

There is also another layout issue around the input of each channel with regard to space C13, C14 - C15, C16 It seems a small ceramic capacitor of 330pF has been used to allow a fit next to the MUCH larger 0.47uf which by design should be a 1uF again would be larger still.

Some of the above issues with the PCB cannot be resolved and have to be put down to experience.

In an attempt to make the best of the current PCB and components available another two versions will be built
  1. JLH Original using the circuit 1 from here - Done and Tested
  2. JHL Simplified with correct component values - This month July 2011

To Done List
  1. JHL Simplified with correct component values - This month
  2. Is an output protection module required ? - This month
  3. Draw a logical and simple schematic - When the circuit is finalised
  4. Reduced the gain of the amplifier for a 2Vrms input rather than the older 0.707Vrms standard
  5. Are larger heatsinks required ? - Due to the reduction in gain this may not be an issue
Attached Images
File Type: jpg JHL HA SbS PCB - Combined Layers.jpg (465.8 KB, 244 views)
Attached Files
File Type: pdf JHL Headphone Amp MKI Schematic.pdf (48.5 KB, 311 views)
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Old 4th July 2011, 08:12 AM   #148
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Default Mistake on last post

Quote:
Originally Posted by MilesCampbell View Post
PCB Issues
JLH Original using the circuit 1 from here - Done and Tested
The link should point to here

Thanks
Miles
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Old 5th July 2011, 03:49 AM   #149
jambul is offline jambul  Belgium
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Default Thanks for your hard work

Hi miles,

thanks for your hard work on the board, i'll be waiting for you to convert the Chinese JHL to the original one

regards

denis
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Old 5th July 2011, 07:11 AM   #150
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Hello Denis

I'm on the case, I will try and write up this week ..

Thanks for your message
Miles
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