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Old 25th June 2011, 09:19 AM   #131
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Default Almost there...

I've checked the PSU, and got 12v and -12v to within a sufficient tiny margin. I'm using a 15-0-15v AC 30VA transformer, as I had it to hand, for a pre-regulator voltage of +/- 22v DC.
I've populated the board fully, and attached a 270R 2w resistor to each output for testing. The board has been gone over three times with a magnifying glass, and potentially dodgy joints redone.
So, I'm ready to fire up.
I'm guessing the pots are for DC offset, and should be adjusted for lowest output, then readjusted a few times during the first few hours of running. I'll start with them in the middle position, and adjust from there.
Fingers crossed! (Makes it difficult to handle meter probes though..)

Steve
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Old 25th June 2011, 01:26 PM   #132
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Quote:
Originally Posted by fj12centauro View Post
Hello
I have just finished and tested my headphone amp with my HD600 ' after controls of course), it works fine but the level is too high.
where are the resistors to change to reduce the gain?
Thanks
You need to increase the value of R5 (470R) to reduce gain I have 2K2 in place which is good for my Senheiser cans HD 565s.
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Old 25th June 2011, 07:02 PM   #133
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Default I seem to build very S L O W L Y ..

Hello all

Sorry for the delay but I seem to build and document very slowly..

Picture List
  1. R17, R18 470 ohm resistor
  2. Composite board image highlighting C23, C24

fj12centauro
I have to admit using TIP41 in the output stage my assumption was there may not be enough gain! Which type of source are you all driving from ?

hotiron
Thanks very much I will try that. On the Chinese Version it's R17 and R18 that can be found in the first picture below..

All
Attention must be draw to C23, C24 it has been highlighted on the composite image attached. The PCB and the schematic both show it the incorrect polarity!! Electrolytic capacitors are very sensitive to incorrect polarity so can I suggest this is replaced and a new one is insert with the corrected the polarity ..

This week I will try and catch up with you guys and get the testing done.
Hope this helps
Miles
Attached Images
File Type: jpg JLH HA SBS Build - 06 470.jpg (201.6 KB, 859 views)
File Type: jpg JHL HA SbS PCB - Combined Layers.jpg (465.8 KB, 854 views)

Last edited by MilesCampbell; 25th June 2011 at 07:05 PM. Reason: See italic, change of wording
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Old 25th June 2011, 10:19 PM   #134
hotiron is offline hotiron  Scotland
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Sorry bout that Miles I was referring to the JLH schematic.

The Class-A Amplifier Site - JLH Headphone Amplifiers
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Old 26th June 2011, 08:47 AM   #135
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Default This is a VERY good point ...

Quote:
Originally Posted by hotiron View Post
Sorry bout that Miles I was referring to the JLH schematic.

The Class-A Amplifier Site - JLH Headphone Amplifiers
Hotiron, this is a VERY good point you have mentioned

Quite frankly the provided schematic is AWFUL and the part numbering is all over the place and it's on the list to be redone. This is the first build of 4 different types, and is a learning exercise for me with a bunch of new toys and a subject which I have messed with since being a young lad moving then onto my first degree ..

Please keep the comments coming, they are really helpful ..

Thank you
Miles
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Old 26th June 2011, 05:05 PM   #136
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Talking Modify the gain

Hotiron : Thanks, for your answer, i'm going to try some different value.

MilesCampbell: I use a Marantz CD6000 with discrete Opa Moon in the output
Very good sound!
it's a very good idea to post you build

Other questions:
Is someone replace the original potentiometer with an ALPS Blue Velvet?

I'm looking on ebay for a output protection, what are you think about?
Because i pull on my JLH, after ten minutes i plug my headphones and the offset don't move, the value is around 3 millivolts.
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Old 26th June 2011, 07:19 PM   #137
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Default More great questions

Quote:
Originally Posted by fj12centauro View Post
MilesCampbell: I use a Marantz CD6000 with discrete Opa Moon in the output
Very good sound!
it's a very good idea to post you build

Other questions:
Is someone replace the original potentiometer with an ALPS Blue Velvet?

I'm looking on ebay for a output protection, what are you think about?
Because i pull on my JLH, after ten minutes i plug my headphones and the offset don't move, the value is around 3 millivolts.
Very nice CD player setup

Good idea to change potentiometer, for the next build attempt to change to Alps Blue Velvet.
I will put one on the next order.

Protection and offset : Can I will answer by the end of the week ?

Steve : Did you manage to get the offset to zero ?

Great conversation guys,
thanks Miles
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Old 26th June 2011, 08:00 PM   #138
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Question output protection

Yes of course , i'll be wait, i'm a little afraid because i don't want destroyed my precious headphones.
I just see that my transformer is very hot, it's make 20VA, perhaps it's too small. what are the power of you transformer?
The problem of the offset is when the temperature goes up, the offset goes down.
Perhaps the right and cheaper way will be to have only one big heatsink for the four TIP, what are you think about?
Excuse me for my bad english, but you're know that frenchies only talk french
best regards from a french biker with a modest 600 Transalp
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Old 26th June 2011, 08:20 PM   #139
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Default Re: Offset

I need to grab a couple of 100uf and get them fitted first... I compared the original JLH schematic and the JHL version, and as you say the cap is the wrong way round. Damn. Never mind..
If I get the unit running, I have a 50K alps blue I salvaged from an old dead CD player. I might use that. Let's walk before running first
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Old 27th June 2011, 06:29 AM   #140
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fj12centauro : Your english is very good, don't worry can I suggest writing lots of words similar to what you mean in (brackets) and we can help .. The heatsink that are used on this PCB can be stacked or replaced with a taller version, I'll find a picture ...

badgerboy : I'm very interested in the fit of the Alps on the pcb

General Note : Can I strongly suggest that a CHEAP pair of headphones is used at this stage for testing ..

To Done List
  1. Will Alps Blue Velvet fit the PCB ?
  2. Is an output protection module required ?
  3. What is a sensible transformer specification ?
  4. Draw a logical and simple schematic

This week should see the finish of the power supply testing and the SbS build.

Thank you for all your comments, keep them coming ..
Miles

Last edited by MilesCampbell; 27th June 2011 at 06:35 AM.
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