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Old 21st May 2003, 09:28 PM   #1
Electrons are yellow and more is better!
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Default Message to all korean guys - help wanted - I'm bad in the korean language

Can any korean speaking member here help me to get in contact with the guy below? It's very hard to read korean if you don't know the language. I'll appreciate any help.

http://www.headphoneamp.co.kr/bbs/vi...esc=asc&no=188
Quote:
Originally posted by sijosae
Hyun-Joon Rho is a one of the best DIYers in our Korean site. His works are REALLY excellant. There are so many pics of his nice amps in our gallery.
http://www.has.pe.kr

BTW: I have experimented with my QRV-05, a pure current feedback headphone amp. It's incredible fast. > 1 MHz power bandwidth! It's based on QRV-03 but I have removed the opamp and feed the whole thing from a cascoded daimond buffer. I have also a real Wilson current mirror (4 transistors).

Anybody who has experience of classical current feedback amps (symmetrical)?
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Old 21st May 2003, 09:43 PM   #2
Netlist is offline Netlist  Belgium
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I didn't try, because I can't find how to do it, but could "Google.translate" solve a bit of your problem?

/Hugo
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Old 22nd May 2003, 12:52 AM   #3
dhaen is offline dhaen  Europe
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Per-anders,

Why not try posting on the "foreigner-question and answer" forum at that site:



http://www.headphoneamp.co.kr/bbs/zb...sn1=&divpage=0

Just an idea

Cheers,
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Old 22nd May 2003, 03:23 AM   #4
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Quote:
Originally posted by peranders

any help
Hoping this translation meets his meaning...


Once I visited home page of Per-Anders Sjostrom, to have a look around PCBs of voltage regulators. Then, I found a headphone amp, QRV-03, by chance. This project was very attractive to me as I had been interested in QRV-01 and QRV-02.

I was not satisfied with just looking at the circuit decided as my priority no.1 DIY project. Accordingly, I made it and tuned it. I had to work late for days. To see the performance, I first tried one test channel because I thought that the circuit seemed to have areas might-be troublesome, and I made analysis and tuning. I satisfied with its performance and with the sound so that I immediately started production of the PCB.

An interesting thing was that it was possible to minimize the output DC. According to the multi-tester, DC appeared as 0.2 – 0.6 mV on both left and right sides. The values did not change even after 2 hours. These values measured when there were music signals. With no music signal, the values were measured as 0.1 mV. The output current was adjusted when the amp reached to high temperature, and it was set with 30 mA.

Meanwhile, a care must have been in the adjustment of the input current (voltage). The input current was to be adjusted towards the applied op amp. I made the adjustment through tests. The present one is adjusted for OP07 among others. I tried four op amps: OP07, OP27, LF356 and LF351. The original +/-18V was changed to +/-12V and few equivalent components were also introduced. The applied transistors were BC550, BC560, 2N2219 and 2N2905.



If you go to the "Foreigner Q&A" corner, you could talk to him.

JH
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Old 22nd May 2003, 10:19 AM   #5
Electrons are yellow and more is better!
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Many thanks for the translation. I can't figure out how I use this Foreigner Q&A ??

Could you jh6you, help me to get in direct contact with Hyun-Joon Rho?

I'm a little bit confused by his "tuning" because it's more or less identical even the not tested compensation parts "optional" in the schematics. The 22 pF and 220R were only guesses.

Still, the design works and my new one "without the opamp" is exciting I'll hope I will make a pcb later on.

Does anyone has strong opinions about current feedback?
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Old 22nd May 2003, 12:18 PM   #6
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Quote:
Originally posted by peranders

help me to get in direct contact with Hyun-Joon Rho?

Try hwmj0024@empal.com

I translated the first part only. If I have time, I will try for other parts too.

JH
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Old 22nd May 2003, 12:22 PM   #7
Electrons are yellow and more is better!
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Quote:
Originally posted by jh6you


Try hwmj0024@empal.com

I translated the first part only. If I have time, I will try for other parts too.

JH
Thanks for the email!
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