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Old 26th July 2014, 10:41 AM   #1
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Default Class A Follower Buffer?

Per Mr. Pass' suggestion, I am requesting info on a simple Class A follower buffer using a constant current source for bias and a filtered 19V supply like the one used for the Amp Camp Amp.

My goal was to build a TEA2025B based amp for use with my Sony MDR-V700's, but the aforementioned low-power Class A arrangement was Mr. Pass idea, and he said I should ask about it, here.

Info would be appreciated--and I love building stuff.
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Old 26th July 2014, 11:03 AM   #2
Zen Mod is offline Zen Mod  Serbia
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if you insist in using chips , instead of crappy chip amp as core , better to use bipolar supply and proper OP

then OP will take care about output offset ...... blah blah

more elegant , better sound
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Old 26th July 2014, 12:58 PM   #3
juma is offline juma  Germany
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Quote:
Originally Posted by Logistics View Post
...My goal was ...
...confusing.

Let's be more clear:
You want to drive Sony MDR-V700. Those are $50 DJ headphones, Z=24 Ω, nominal sensitivity is 107dB/mW which means that you need only 0.15V to achieve deafening sound pressure level of 107dB.
That excludes the need for voltage gain and the ugly TEA2025B should be best forgotten (it can be used only for very bad AM radio or as a monitor amp for practicing Morse code).
Class A buffer is all you need - one of the best you can build is DAO Follower but it deserves much better headphones than Sony MDR-V700. Optimal solution here would be mini F4 built with irf9620/irf610 or 2sk2013/2sj313, biased at 100-200mA, PSU +/-15V or some SE cl. A headphone buffer, like this one Click the image to open in full size. or similar
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Old 26th July 2014, 02:00 PM   #4
juma is offline juma  Germany
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If it happens that your music source is some gadget with extremely weak output and you still need gain, this circuit will provide some (about 2.5V/V), together with single ended cl. A buffer:
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File Type: gif HA-JGS+SF.gif (4.1 KB, 732 views)
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Old 27th July 2014, 12:22 AM   #5
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Logistics View Post
Per Mr. Pass' suggestion, I am requesting info on a simple Class A follower buffer using a constant current source for bias ...
If you only need very low power this shouldn't be too hard to make or too expensive.

I think somebody mentioned this already:
DIY IRF610 MOSFET Class-A Headphone Amplifier Project


If you want more power you could look here too (you could use this one at lower voltage perhaps since you don't need 7W):

SEWA - Seven Watt Amplifier
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Last edited by Bigun; 27th July 2014 at 12:25 AM.
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Old 10th August 2014, 05:16 PM   #6
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Before I pull the trigger on parts, what about the NP-100v12? Would that be a good candidate, too? I always wanted to build a tube-based amp.

-Jay
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Old 11th August 2014, 12:08 AM   #7
Ripcord is offline Ripcord  United States
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I built the NP-100v12 in to a little wooden box. It's pretty easy to make and sounds really good. I made it because I too wanted a tube type hpa. (Don't look to close because I definitely messed up a few things while making it).
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File Type: jpg NP-100v12 2.jpg (829.5 KB, 486 views)
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Old 23rd August 2014, 03:26 AM   #8
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Quote:
Originally Posted by Ripcord View Post
I built the NP-100v12 in to a little wooden box. It's pretty easy to make and sounds really good. I made it because I too wanted a tube type hpa. (Don't look to close because I definitely messed up a few things while making it).
Could you tell me which headphones you're using with it? I'm just wondering if they're comparable specs as the pages concerning the NP-100v12 don't actually mention which cans they are compatible with, IIRC.
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Old 24th August 2014, 06:03 AM   #9
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Quote:
Originally Posted by juma View Post
If it happens that your music source is some gadget with extremely weak output and you still need gain, this circuit will provide some (about 2.5V/V), together with single ended cl. A buffer:
When I actually thought about your post, I considered how many devices I may have which I would like to utilize for listening purposes, and I realized that I am probably going to need this. Thank you, very much!

(For instance, my original Playstation, which I believe has very weak output. No, I won't be using this as a quality transport, but in any case, thanks!)
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Old 25th August 2014, 03:13 PM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Logistics View Post
Per Mr. Pass' suggestion, I am requesting info on a simple Class A follower buffer using a constant current source for bias and a filtered 19V .............
This is an almost perfect description of the PASS B1.
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