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Old 12th May 2008, 11:10 PM   #51
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Some input: a possible open loop input stage with 44dB gain, simed dist. less than 0.001% with nice harmonic spread and balanced of course. The MAT-Q's are actually from that corporation.

Rüdiger
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Old 13th May 2008, 02:36 AM   #52
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Peranders, thanks for posting that link to Dennis Colin's phono-amp - excellent article.

I liked his intrinsic fidelity test methodology.
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Old 13th May 2008, 03:41 AM   #53
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Rüdiger,
bearing in mind the current circumstances, not that bad...
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Old 13th May 2008, 09:20 AM   #54
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From GRollins

' . . . the choice of active EQ invokes the same gain loss as passive EQ--roughly 20dB at 1kHz. That's inherent in the RIAA curve. Headroom problems are a function of circuit design and are easily avoided.'

Please explain quantitively - I don't understand th e gain loss at 1KHz of 20dB.
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Old 13th May 2008, 10:21 AM   #55
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Disregard this

You have different headrooms for different topologies. This can be studied in LTSpice very easily.

What Mr. Rollins means is different gains when he writes "gain loss".
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Old 13th May 2008, 10:22 AM   #56
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Active equalisation, 2 opamp blocks, first with 20dB linear gain. About 60dB at 1kHz. This will be built soon.
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Old 23rd May 2008, 03:13 AM   #57
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Default Phoenix Systems P-100 phono preamp

This preamp built in the late 1980s (one of the absolute best I have ever heard) used a combination of passive and active EQ. The cartridge was buffered by a JFET, which had a capacitor across its source and drain to provide the (passive) RIAA roll off above 1 kHz. Then he used a second opamp stage with active eq for the boost that happens below 1 kHz. Finally, he rolled off things below 20 Hz for infrasonic protection.

This combination sounded better then ANY other I have heard, including any purely active or purely passive EQ circuit. Low Noise, dead accurate RIAA eq. and a sound that blew any CD player away.

I wish I still had one (Though I found one for sale online for 100 dollars).

http://cgi.audiogon.com/cgi-bin/cl.p...hon&1215724261

This was the last product that John Roberts designed and marketed before he went to work for Peavey as their chief design engineer.

Phoenix Systems used to market audio kits in Popular Electronics in the '70s and '80s.
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Old 23rd May 2008, 03:28 AM   #58
Bonsai is offline Bonsai  Taiwan
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My post #54 was done 'tongue-in-cheek'


Rudiger, nice design - .001 simmed distortion. Put a bit of GNF around that thing and you'd easily get to 100ppb!

I see a lot of designs with JFET's but my concern is over matching and availability (P-chan seems to be the main issue).

I have been looking at Dennis Collins cct again and really like the tradeoffs he has made wrt to overload and noise. I'm wondering however if one of the stages could be eliminated (3rd one) for the same/similar performance. Also, the new Natsemi LME49713 looks like it might do a better job here than the existing op-amp. I need to look into it a bit more and do some sims.
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Old 23rd May 2008, 03:31 AM   #59
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dpuopolo, do you have a circuit?
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Old 23rd May 2008, 03:37 AM   #60
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Default I don't

I don't but I'll try to get hold of JR and see if he can FAX me one.
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