The 'hi-end' pre based on Carlosfm/PMA & Listen results of 21 types OPA as headphone - diyAudio
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Old 9th June 2004, 08:19 AM   #1
X.G. is offline X.G.  China
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Talking The 'hi-end' pre based on Carlosfm/PMA & Listen results of 21 types OPA as headphone

I recently build a pre amp based on the title 'High-end preamp for my GC',and thanks a lot,Carlosfm and PMA!

Interrupting byrepair the Tektronix 2213 oscilloscope ,I stoped all diy projects include the pre amp 2 weeks ago().But my friend AEON had finished before.

The pre/headphone amp PCB is designed by AEON initially,then modified in my advice.The PSU is LM317/337 standard application,the main circuit is OPA627+BUF634T.

AEON used the Holco resister and other ordinary good-quality components,and rise the amp gain to 9 in order to headphone amp.His eadphones are AKG K1000 and sennheiser HD600.Afer listening a week,he told me that the DIY headphone amp sounds very very good,is the best solid state one of the over 20 headphone amps include tube amps he made .

The other Chinese friend in remote region which build the pre amp in the same PCB using ordinary component,told me that the sound of it is the same level of his friend's low price Mark Levinson pre amp made in 90's.BTW I am receiving the CA3127E from him for repair my tek-2213 scope.

Are these enough to prove it hi-end,Carlosfm?

Next step,AEON continued to listen his headphone amp by exchanging the OPA and keep BUF634T.

He have 6 types of sigle OPA in hands,AD797、OPA627、OPA637、OPA604、UPC741(matal package)、5534(ceramic package).I have other 14 types of sigle OPAs,in my shoes-box like Elso K,including RC741、LM301A(ceramic package)、LM308AN、LF351、LT1028、OP07、OP27、OP37 、AD711、AD811、four types of NE5534 made by Signetics,Texas,JRC.

The offset-voltage of the headphone amp is 0.3mV or lower with opa627,lt1028,op37,op27,op07,741,and 3-10mV with other OPAs.

Listening these OPAs with BUF634T was very hard work.In two weeks,AEON get the below Listen results:

1.The king select is LT1028.The sounds of it is modern,clear,faster,very good dynamic,very much details,but a little uncomfortable in AKG K1000 because of too much details.If it has better in low freq,would be more ideal.

2.The queen select is LM301A(ceramic package).The sounds of it is another type,comfortable,soft,relax,natural,most warm.Its offset voltage is 10mV.

3.the prince select is OPA637,OPA627.The sounds of them are the same type of LT1028,but LT1028 is better except vocals.The OPA637 is very close to the OPA627 and better.

4.the princess select is AD797.Don't show its super quility,but still is much better than the others except above.

5.the other single OPA sounds just good,not very good.

Otherwise:
1.RC741/UPC741 sound Very special,very warm like the colour of yellow('like the sunshine in the winter',AEON said),and very slow,harsh in/lack of high freq——Very special select!
2.The 5534 of ceramic package is better than the plastic package.But all sounds of them is slow,not clear.

During the listening,the result of AD797 mostly disappointed him ,causing it is his most favourite OPA,and even got the excellent sounds in I/V circuit. The OP07,OP23,OP37 disappointed him too,sounds too harsh,too cool.The LM301A made him very surprise,but not to me,because of I knew somebody which has much experiece in DIY audio love it.Another OPA made him surprise is 741.

Although I spent 2 hours to write/type the letters above ,Sorry for my poor English.

Cheers

X.G.


BTW:Cause AEON had 'robbed' my lm301A's ,I 'stolen' his pictures show here.
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Old 9th June 2004, 08:24 AM   #2
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The encloxe(?) of the headphone apm
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Old 9th June 2004, 08:33 AM   #3
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The PCB of the per/headphone amp
Click the image to open in full size.

and the 21 types of single OPAs except 5534
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Old 9th June 2004, 08:34 AM   #4
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the 5 types of 5534
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Old 9th June 2004, 08:36 AM   #5
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the king select
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Old 9th June 2004, 08:39 AM   #6
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The queen select

BTW: the LM301A is soldered with 6pF mica cap to prevent osi.
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Old 9th June 2004, 08:42 AM   #7
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The very special select
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Old 9th June 2004, 09:17 AM   #8
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Some of opamps, which you tested, are not unity gain stable ( for example AD 797 ), so in this connection MUST to oscilate and results will be not correct !
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Old 9th June 2004, 09:45 AM   #9
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Thanks for reponse.

All listening tests set at the gain of 9,not unity gain.

The gain of the pre amp is 2.5,I will attention.

X.G.
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Old 9th June 2004, 10:02 AM   #10
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Default Re: The 'hi-end' pre based on Carlosfm/PMA & Listen results of 21 types OPA as headphone

Quote:
Originally posted by X.G.
Are these enough to prove it hi-end,Carlosfm?
I thought I was mad, but thanks for another confirmation that I'm (still) healthy and my ears are working fine.
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