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Old 29th July 2004, 06:27 PM   #51
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Thanks for clarification!

Stephan
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Old 29th July 2004, 11:24 PM   #52
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Guys, you can give to Bobolix any questions about phono preamps - in this thematic he knows absolutely ALL and I claim it quite seriously .
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Old 30th July 2004, 05:34 AM   #53
dimitri is offline dimitri  United States
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>> In fact, the lowpass of 75 us is created by complete circuit consisting of R8, R9, C6, C7. The purpose of such complicated circuit is to achieve similar DC resistance "seen by" both non-inverting and inverting input of the following opamp and same time achieve low AC impedance of the low-pass, so that the noise introduced by the input current noise of the opamp would be reduced as well as the thermal voltage noise generated by the total resistance in the lowpass (R8 || R9).

Sorry Bohumil, I will interfere
1) yes, dc "seen by" both non-inverting and inverting input will be around 47k
2) > achieve low AC impedance of the low-pass - the output impedance of low-pass will be R8 4k7 with gradual decrease at hf. How R9 C7 will lower this? (R8 || R9) is only 10% reduction.
3) > the input current noise and thermal voltage noise - again, (R8 || R9) - 10% reduction is negligible.
4) dc shift of the input amp, worst case 5mV*28=140mV, will be presented at the output
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Old 28th November 2006, 01:06 PM   #54
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Quote:
Originally posted by Upupa Epops
Guys, who will send me email, I will send him original schematic of Actidamp Mk II, not copy by Project. Questions ( if will be ) I can explain later.

it is me again,
please send me a sch if possible
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regards, Pawel
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Old 28th November 2006, 03:04 PM   #55
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Later, now I'm not at home, OK ?
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Old 29th November 2006, 02:59 AM   #56
bobolix is offline bobolix  Czech Republic
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Hi boys,

don't forget it is a construction about 20 years old. I learned something since then and now I'd make it different - frankly said, I did it so, but it has been made by an order and therefore it is a subject of the "bussiness secret". Though, I can say, the dc-servo path needs to be modified slightly at least ...
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Old 22nd December 2006, 12:17 PM   #57
Ludwik is offline Ludwik  Poland
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Please find attached circuit diagram from one of the Polish magazine "Radioelektronik" No 10/1991
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File Type: gif actidamp2_small.gif (59.5 KB, 1581 views)
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Old 22nd December 2006, 12:17 PM   #58
Ludwik is offline Ludwik  Poland
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...and the PCB layout.
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File Type: gif actidamp2pcb_small.gif (54.3 KB, 1349 views)
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Old 22nd December 2006, 04:07 PM   #59
bobolix is offline bobolix  Czech Republic
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Default BTW...

... the Actidamp was made as an optimization for the MM pickup regarding noise. Recently the MCs are assumed to be the best usually and the Actidamp need not to be the optimum solution. E.g., the linear pre-preamp could be made as balanced using some of ICs determined for mic preamps - INA217 e.g. I've made even a fully symmetrical phono preamp, i.e. with completely symmetrical signal path including the equalization circs, but probably it will never be published.
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Old 26th December 2006, 10:13 AM   #60
mzperx is offline mzperx  Hungary
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I would share my symmetrical input version (with INA217). It was made on request of my friend. He his very happy with that...
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