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Old 30th March 2011, 10:57 PM   #111
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Quote:
Originally Posted by hotiron View Post
Hi Miles, I just had a look at Alongs new board on ebay, and could not believe he had changed the input caps to foils and then bypassed with a ceramic.
My experience with eBay DIY audio vendors is most of them seem out to make a quick buck chasing whatever is trendy. They turn out "designs" as quickly, and as cheaply, as they possibly can.

They often throw a few impressive high profile parts on their boards so they look good in the pics. And they nearly always hype some trendy design, chip, or part in the main description (like "JLH Class A...").

When you really look at what they're selling, or make the right measurements, they often fall far short. So I'm not surprised you found foil caps bypassed with ceramics. Odds are 95% of the people buying them have no way to properly measure they even work right. And, based on what I've seen, I suspect some of the eBay vendors selling them don't either (or they don't care).

I'm fairly convinced most of them don't really know what they're doing. They just copy other designs and source the cheapest possible parts that look halfway decent. Their "audiophile capacitors", for example, are usually either fake clones or some unheard of Chinese brand.

I've measured several such DIY PCBs/Kits/assembled boards and they nearly always have one or more serious problems. I've traced the poor performance to substandard parts and things like an input ground tied to a high current output ground track.

I feel sorry for the names and reputations of JLH, Nelson Pass, and all the others who've had their designs knocked off and end up in cheap clone form on eBay. I'd rather see the same vendors take the best public designs, use proven published PCB layouts, and offer just the raw PCBs. If they're going to offer kits, they should include higher quality parts. In my opinion, that would yield much better results.
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Last edited by RocketScientist; 30th March 2011 at 11:07 PM.
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Old 3rd April 2011, 06:53 AM   #112
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Hello All

Thank you all for your very helpful comments

I have brought a number of these latter "JHL" boards to prototype with and will post a build very soon. One as original JLH and one as supplied. Would it be good manners to start a new thread or continue with this one as there will be a slight change in topic ?

Miles
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Old 4th April 2011, 07:28 PM   #113
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Miles: Ashok started this thread, but to me it sounds completely relevant for you to discuss your JLH headphone amp project here. (Especially as this thread is moving at a manageable pace while admirably staying on topic!)
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Old 15th June 2011, 07:17 AM   #114
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Default Step by step - JLH Headphone Amp build

This will be a step by step build of the JHL Class A headphone available on ebay from this seller. The service was excellent, the delivery was very quick and the combined postage was a bargain - 4 off JHL kits and 1 off USB DAC assembled.

These kits are a copy of the John Linsley Hood Class A headphone amplifiers that can be found documented here here This is a brilliant website for anything class A and JLH. These designs originally appeared in various Hi-Fi magazines and Wireless World through the 1980's.

The design methodology presented is not the most upto date thinking, but something I have always wanted to build. A well documented starting point if you will.

The plan is to make a number of these to compare the results
  1. As supplied
  2. JLH Circuit I
  3. JLH Circuit II

Picture List
  1. The kit as supplied
  2. PCB Silk screen layer (Top)
  3. PCB Copper Side (Bottom)

Comments : The PCB is of good quality, the layout has a number of issues with a number of wire and zero ohm links in very unfortunate places.

In Summary : I think this is a GREAT kit for less than 15GBP but as will be shown there are a number of small issues to overcome in the build.

Miles
Attached Images
File Type: jpg JLH HA SBS Start - 1.jpg (170.3 KB, 1103 views)
File Type: jpg JLH HA SBS Start - 2.jpg (346.0 KB, 1078 views)
File Type: jpg JLH HA SBS Start - 3.jpg (185.2 KB, 912 views)
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Old 15th June 2011, 08:29 AM   #115
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Default Step by Step - JLH Headphone Amp build

The build order shown below has a number of advantages
  1. Allows the board to be built in component size order
  2. Prevents confusion with very similar looking compenents
  3. Testing of the power supply
  4. Cleaning of the residue flux before the pot is added to the board, this prevents contamination of the vulnerable wiper and track.

Build Order
  1. Wire links
  2. Zero Ohm Links
  3. Small Signal Diodes
  4. Zener Diodes
  5. Rectifier Diodes
  6. Resistors
  7. LED
  8. Capacitors upto 100uF
  9. Vin Connector
  10. Voltage Regulators
  11. Capacitors - Smoothing 2200uf 4off (Pre-Regulator)
  12. Apply power supply to board and test output of voltage regulators
  13. Variable Resistors - Turned fully anti-clockwise
  14. Input Connector
  15. 2N2222 x 2 off
  16. 2N2907 x 4 off
  17. Capacitors - Smoothing 2200uf 4off (Post-Regulator)
  18. Output terminals
  19. Output Transistors and Heatsinks
  20. Removed flux from the board
  21. Potentiometer - Volume Control

The photographs showing the build step by step will be posted shortly

Miles
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Old 15th June 2011, 01:05 PM   #116
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Thumbs up Just what I need!

Looking forward to the build, Miles. I got one this lunchtime in the post, and a distinct lack of schematic or instructions is a bit of a problem for me. This is my first serious kit, so we'll see how it goes!
Steve
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Old 15th June 2011, 02:32 PM   #117
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Default Step 1 and 2 : Wire and 0 ohm links

Pictures List
  1. Wire links
  2. Zero ohm links

Comments
  1. The zero links provided when measured were 0.5ohms so tinned copper wire was used
  2. I missed a link on the board, in the lower centre, pleased don't make the same mistake.

Tips
  1. To get the wire links straight S-T-R-E-C-H the tinned copper wire, hold one end in the vice and the other end in a pair of pliers .. Be careful at some point it will snap and you are left with very straight links.
  2. Bend the link to the correct size, place in the board. Then turn the board over to solder the link, holding it place with the reel of solder.
Attached Images
File Type: jpg JLH HA SBS Build - 01 Wire links.jpg (197.5 KB, 858 views)
File Type: jpg JLH HA SBS Build - 02 0 ohms links.jpg (197.5 KB, 832 views)
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Old 15th June 2011, 02:45 PM   #118
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Default Step 3 and 4 : Small signal diodes

Picture List
  1. 1N4148 - 4 off
  2. 3V Zener Diodes - 2 off

Comments
  1. BEWARE The 1N4148 and zener diodes look ALMOST the same!
  2. The 1N4148 is marked in very small letter "4148"
  3. The zener diode is marked C3V0 (The circuit diagram requires a 2.7V zener diode)
  4. The are 4 off 1N4148 in the kit and only 2 C3V0
  5. Both the 1N4148 and the zener diodes have a right and wrong way to be insterted in the board
  6. Both types of diodes have a dark colour strip or ring this should be matched to the marking on the PCB.

Tip : The easy way to achieve crisp bends in the diode legs is to use, small snipe nose pliers
Attached Images
File Type: jpg JLH HA SBS Build - 03 1N4148.jpg (193.9 KB, 308 views)
File Type: jpg JLH HA SBS Build - 04 Zener Diodes.jpg (205.1 KB, 223 views)
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Old 15th June 2011, 03:50 PM   #119
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Quote:
Originally Posted by badgerboy View Post
Looking forward to the build, Miles. I got one this lunchtime in the post, and a distinct lack of schematic or instructions is a bit of a problem for me. This is my first serious kit, so we'll see how it goes!
Steve
Hello Steve

One of my outstanding jobs is to re-draw the schematic, but the original is attached .. Hope that helps

Please let me know how you are finding the SbS, I will do my best to help if you get stuck ...

Thanks
Miles

SbS = Step by Step ..
Attached Files
File Type: pdf JHL Headphone Amp MKI Schematic.pdf (48.5 KB, 357 views)
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Old 15th June 2011, 04:38 PM   #120
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Default Step 5 and 6 Resistors and rectifier diodes

I have made a mistake in the original build order in post 115 step 5 and 6 have swapped places. Please be assured this makes no difference to your build, it was just a typing error.

Picture List
  1. Resistors 4k7 ohms - 8 off
  2. Resistors 470 ohms - 2 off
  3. Resistors 1k ohms - 4 off
  4. Resistors 100 ohms - 2 off
  5. Resistors 22 ohms - 2 off
  6. Resistors 2R2 ohms - 2 off
  7. Resistors 2k2 ohms - 3 off
  8. Resistors 5R1 ohms - 2 off

Comments
  1. The resistor colour codes can be very confusing when they are seperated by powers of 10 eg : 2R2 or 22 or 220 or 2k2
  2. Just to be clear 2R2 and 2.2 ohms are the same value therefore 5R1 and 5.1 ohms are also the same value.
  3. CHECK and DOUBLE CHECK - The particular resistors in these kits seem to have very little difference in the RED BROWN and BLACK band colours.

Tip
  1. To prevent confusion with the resistor values I measure each strip with a DVM
  2. These are then laid out on a piece of paper on which all the values are written.
  3. Each value is only CUT from the strip when it required

Note to self : Next time for the resistors apply the resistor value to each picture with Photoshop!
Attached Images
File Type: jpg JLH HA SBS Build - 05 4k7.jpg (212.1 KB, 196 views)
File Type: jpg JLH HA SBS Build - 06 470.jpg (201.6 KB, 131 views)
File Type: jpg JLH HA SBS Build - 07 1k.jpg (202.8 KB, 101 views)
File Type: jpg JLH HA SBS Build - 08 100.jpg (193.7 KB, 90 views)
File Type: jpg JLH HA SBS Build - 09 22.jpg (197.5 KB, 78 views)
File Type: jpg JLH HA SBS Build - 10 2R2.jpg (211.1 KB, 80 views)
File Type: jpg JLH HA SBS Build - 11 2k2.jpg (199.7 KB, 78 views)
File Type: jpg JLH HA SBS Build - 12 5R1.jpg (189.8 KB, 104 views)
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