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Quanghao Audio Design Quanghao Audio Design is a producer of DIY Audiophile Kits and PCB boards, selected from many listening tests!

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Old 20th February 2010, 01:45 PM   #11
pred is offline pred  Switzerland
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Just a small question did you put some grid stoppers on tubes, since I do not see them in schematics, and D3a are known to oscilate easy?
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Old 20th February 2010, 03:52 PM   #12
audiodesign is offline audiodesign  Italy
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In these last 2 years I have design many circuit with the D3a and I never seen problem of oscillation without grid stop resistor.

Other tubes give me these problems like the 5842 and 6C45.

I consider this tube perfect for these points:

1) only one brand so always the same neutral good sound
2) low distortion for large swing (see measurement on my PF2007 amp.)
3) no oscillation
4) no microphonic
5) high gain about 70
6) low internal resistance in triode connection near 2Kohm
7) low cost about 10-12$
8) easy to find on german Ebay shop
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Old 20th February 2010, 06:44 PM   #13
pred is offline pred  Switzerland
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OK I would prefer it be there but if you have experience otherwise I am ok with it. I know the tube, have some of them on my small stock.

I know you simulated it and measured it but could not never understand how you found 16pF at the input of the second stage is so low. From the datasheet I see we have like 2pF and with miller and gain of 70 it should be more like 140pF. Would you please explain where I am wrong?

Pred

PS
Price at German ebayers is much higer now. They found people in HIFI like them so it is now more like 25-35...

PPS
I still wanna PCBs
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Old 21st February 2010, 01:08 AM   #14
apelizzo is offline apelizzo  Australia
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Quote:
Originally Posted by audiodesign View Post
I have some my friends interested to build this easy and good phono preamplifier so if we will arrive to 50 persons the price should be only 50$ each including shipping cost.

This project use D3a easy to find on Ebay germany shop at 10-12$ each.

The sound depend by the passive components used.
I'm interested. Please reserve a set for me too.
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Old 21st February 2010, 04:35 AM   #15
anilva is offline anilva  India
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I am interested too.

Thanks.
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Old 21st February 2010, 08:15 PM   #16
webby is offline webby  United Kingdom
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Hi,
I am also interested if it is suitable, how much gain will it have compared to my CA 640p? The 640 specification is Gain @ 1kHz = 55dB,Nominal output 300mV,Sensitivity for 0.5mV nominal output.
The this is enough for my 0.5mV at33prg cart.
Thanks
Ian
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Old 22nd February 2010, 10:48 AM   #17
quanghao is offline quanghao  Viet Nam
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more image Phono D3a
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File Type: jpg Phono-4-5.jpg (380.7 KB, 1877 views)
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Old 22nd February 2010, 01:26 PM   #18
audiodesign is offline audiodesign  Italy
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Ian,
This phono preampl. is good for any type of MM and for MC high output cartridge.

In a measurement I have on output 1.24Vrms with 3mV input and this mean 52.3dB.

Is you have low output MC cartridge it is necessary an input step/up transformer.
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Old 22nd February 2010, 09:24 PM   #19
guglielmope is offline guglielmope  Italy
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OLD THREAD Hi-end phono preamplifier by Andrea Ciuffoli
I'm also interested to buy one board.
Thanks
Guglielmo
Italy
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Old 23rd February 2010, 04:28 PM   #20
wushuliu is offline wushuliu  United States
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1 set for me as well, please.
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