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gold

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Posts: 1,505 Member Since:27/01/2011

#41 [url]

Apr 16 15 3:07 PM

The most common standard is 7cm/sec @1Khz lateral (stereo). An older standard was 5cm/sec. The question is like asking what level 185nW/M should play back at. The answer is "0" but the answer is also 0 for 250 nW/M or 315 nW/M.

5cm/sec lateral is about 3db lower than 7cm/sec.

Last Edited By: gold Apr 16 15 3:12 PM. Edited 1 time.

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Hermetech Mastering

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Posts: 385 Member Since:22/02/2011

#42 [url]

May 5 15 6:24 AM

zmix wrote:

Thanks to Chuck Zwicky for bringing this test record to my attention:With frequencies up to 35kHz! [image] -dcollins

I should note that on the sleeve they recommend that you bypass the RIAA EQ when playing the ultrasonic test bands.One day soon I'll plug my cartridge directly into a mic pre and record the test LP at some PONO-graphic sample rate to see if there's anybody up there.

zmix, or anyone else, how would one go about interfacing the cartridge directly to a mic pre? I'd like to be able to do this, to have a play with different implemetaions of the RIAA curve in the digital domain. Which connections from the TT phono out would you need to connect to the balanced line in of the mic pre?

Gregg Janman, Hermetech Mastering

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mark chalecki

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Posts: 496 Member Since:04/03/2011

#43 [url]

May 6 15 2:32 PM

kinda guessing here, but wouldn't there be an impedance issue plugging directly into a mic pre, isn't the output of a mm cart something like 50k ohms?

_m

Last Edited By: mark chalecki May 6 15 2:48 PM. Edited 1 time.

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Hermetech Mastering

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Posts: 385 Member Since:22/02/2011

#47 [url]

May 8 15 6:11 AM

Thanks, crazy, I hadn't even considered that, seems obvious, I could just use a simple adaptor too! My Chandler TG2's DIs are rated 100k input impedence, and bypass the input transformers. My basic electronics knowedge of R and C is pretty poor, so please enlighten me, how would I know which values to use, and how would I add them in parallel?

Gregg Janman, Hermetech Mastering

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waltzingbear

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Posts: 1,239 Member Since:16/07/2012

#49 [url]

May 8 15 12:09 PM

generically the cartridge wants to see 47k with 200pF TOTAL load C. that means a C load minus the arm and cable capacitance. (for a MM cartridge)

YMMV depending on the cartridge.

Alan Garren
Waltzing Bear Audio

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dcollins

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Posts: 2,343 Member Since:27/01/2011

#51 [url]

May 8 15 2:14 PM

gold wrote:
Just thought I'd mention that Wayne Kirkwood has designed a kick ass phono pre. It's a swiss army knife like the M/S board. There are no PCB's yet but it's in the works. http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=423 
Why not just feed into a regular opamp input?

And if you really need a matched pair I’d bet a nickel that bipolar transistors would be slightly quieter.

Self has all kinds of stuff on this in his book, and there are Baxandall stone-tablets from Wireless World that have a lot of good info too.



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gold

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#52 [url]

May 8 15 5:14 PM

dcollins wrote:

 

Because one of the design goals was to have a balanced front end. That's why it looks somewhat like a Cohen mic pre. It turns out the balanced front end is not nearly as important having the front end on an umbillical right next to the tone arm. In the thread someone mentioned the difference in noise between this front end and a fancy Japanese bipolar is about 1dB

I've rarely had self noise of a phono pre be a problem. It's always EMI/RF type stuff.

Last Edited By: gold May 8 15 11:03 PM. Edited 1 time.

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dcollins

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#53 [url]

May 9 15 4:20 AM

a7537b3bceca4e69a4debde2d0f48729_r.jpg

gold wrote:
dcollins wrote:

 

Because one of the design goals was to have a balanced front end. That's why it looks somewhat like a Cohen mic pre. It turns out the balanced front end is not nearly as important having the front end on an umbillical right next to the tone arm. In the thread someone mentioned the difference in noise between this front end and a fancy Japanese bipolar is about 1dB

I've rarely had self noise of a phono pre be a problem. It's always EMI/RF type stuff.


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gold

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#54 [url]

May 9 15 7:31 PM

An MC lends its self to a balanced front end. A balanced front end for an MM cartridge isn't as strightforward. Along with John Roberts design there is an Analog Devices app note AN124 that has a balanced front end for an MM.

The above circuit looks closely related to AN124 if I'm not mistaken.

Last Edited By: gold May 9 15 7:40 PM. Edited 1 time.

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zmix

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#56 [url]

May 10 15 8:40 PM

dcollins wrote:
I think it’s actually a better implementation than AN124, and the balanced input stage could be replaced by a fancy bipolar opamp.

http://collinsaudio.com/Prosound_Workshop/ASP.jpg

A readable version.

Thanks for posting that.  Now that I can read it, I am a bit shocked by the use of the SSM2017... that was used in a lot of the cheaper AMEK consoles in the 1890s, especially in the early to mid 90s.
THD is  ~ 0.01%  but the noise spec is low at high gains ( 0.95nV/RtHz for gain of 1000) and high at low gains (107nV/RtHz for a gain of 1)

Surely a decent (i.e. more recent) opamp would do better than this?

EDIT: It appears someone in Carlsbad, CA has created a drop-in replacement boasting a discrete front end and a 3,000v/µs opamp

http://forum.analogconsole.com/viewtopic.php?f=22&t=1149

 

Last Edited By: zmix May 10 15 8:47 PM. Edited 3 times.

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zmix

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#57 [url]

May 10 15 8:41 PM

gold wrote:

I've rarely had self noise of a phono pre be a problem. It's always EMI/RF type stuff.
 

Not to mention the surface noise of the disk itself...

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dcollins

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#59 [url]

May 12 15 1:42 AM

zmix wrote:
dcollins wrote:
I think it’s actually a better implementation than AN124, and the balanced input stage could be replaced by a fancy bipolar opamp.

http://collinsaudio.com/Prosound_Workshop/ASP.jpg

A readable version.

Thanks for posting that.  Now that I can read it, I am a bit shocked by the use of the SSM2017... that was used in a lot of the cheaper AMEK consoles in the 1890s, especially in the early to mid 90s.
THD is  ~ 0.01%  but the noise spec is low at high gains ( 0.95nV/RtHz for gain of 1000) and high at low gains (107nV/RtHz for a gain of 1)

Surely a decent (i.e. more recent) opamp would do better than this?

EDIT: It appears someone in Carlsbad, CA has created a drop-in replacement boasting a discrete front end and a 3,000v/µs opamp

http://forum.analogconsole.com/viewtopic.php?f=22&t=1149

 
Yeah, I agree that it’s not the best possible input stage (just a modern balanced input opamp would be better) but the overall approach seems good.

I personally wouldn’t settle for anything as slow as 3,000V/us, but if it’s ok for you who am I to judge?



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drknob

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Posts: 788 Member Since:02/02/2011

#60 [url]

May 12 15 7:45 AM

dcollins wrote:

I personally wouldn’t settle for anything as slow as 3,000V/us, but if it’s ok for you who am I to judge?
 

Last time I heard anything that slow, I think it was called 'lightning'. Sounded good for about, oh, a microsecond.

Harold Kilianski

Music Industry Arts
Fanshawe College

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