Sound Quality Vs. Measurements - Page 290 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th February 2012, 11:07 AM   #2891
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Thorsten, in general, how do you feel about an LT1115 active eq circuit, but with a gain set to a lower value, followed by another ciruit, op amp or discrete, which could run off greater voltage rails, and which would bring the output of the first stage to its full nominal value?

Have the LT do the eq part and deliver say 25 mV of linear signal, subsequently amplified times 4?

Wouldn't this help increase the LT's overload point by quite a bit, thus avoiding the problem of relatively low power rails of +/-15V?
  Reply With Quote
Old 28th February 2012, 12:02 PM   #2892
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by dvv View Post
Thorsten, in general, how do you feel about an LT1115 active eq circuit, but with a gain set to a lower value, followed by another ciruit, op amp or discrete, which could run off greater voltage rails, and which would bring the output of the first stage to its full nominal value?
This would in practical terms not be constructive.

To lower gain would mean to either reduce the RIAA Network Impedance which would in turn increase the loading on the output, or to increase the foot resistor in the divider, which in turn would increase the noise.

There is an optimum solution there somewhere and for standard values of the EQ Capacitors it happens the one I suggest.

At best reducing the gain of the circuit will reduce THD at the cost of noise, which seems a poor trade-off.

Anyway, the LT1115 for example has (relatively) poor common mode and output linearity, so it likes to work into relatively high impedance loads (relative to 600 Ohm) and with low input levels. Hence it is ideal for our application, even if the circuit appears to simple to be good.

Quote:
Originally Posted by dvv View Post
Wouldn't this help increase the LT's overload point by quite a bit, thus avoiding the problem of relatively low power rails of +/-15V?
We do not have any overload margin problems with the 15V rails and active EQ, they only happen with passive EQ.

For active EQ, 60dB Gain and +/-15V rails and 0.5mV @ 5cm/S we get 500mV Peak at "0dB" so we have around 28dB Overload Margin for all frequencies on the output of the phono stage that produce an equal 500mV peak.

So if gain is set correctly there is no overload margin issue. Incidentally the same applies to the MM version.

For passive EQ we must either compromise overload margin or noise over optimum solutions.

Ciao T
  Reply With Quote
Old 28th February 2012, 12:21 PM   #2893
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by dvv View Post
Thorsten, I never claimed this to be anywhere near optimal - but I do say that I have seen and heard at least 15 versions of that schematic, all of which did a good job and in fact did sound better than most other run-off-the-mill fare.
The overload margin is really not that bad, though it won't have the stunningly good numbers of a tube circuit.

The concern is really the first gain stage, since following the EQ, the high frequencies are attenuated, and the output of a cartridge at low frequencies is... low. You've got a gain of 45, so if we assume that the opamp can swing 13V peak with the 15V supply, that's 9.3VRMS. Divide by the stage gain and the input overloads at something like 200mV. That's 32dB above rated cartridge output for most MMs (5mV). Now certainly cartridges output more than their rating when hitting ticks and pops, but 20-25mV is about the most you're likely to see. So the overload margin is not state-of-the-art, but probably good enough.

On topic, my own subjective and unsupported experience is that phono stages with high overload margins make poor records more listenable. How high is high? That's a different question, but I think that 200mV is good enough.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 28th February 2012, 01:07 PM   #2894
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
I seem to remember a Pioneer integrated amp, a long, long time ago, in another galaxy ... which had +/- 53V rails, or some such very high number. I remember thinking that was enough to do 100W/8 Ohms.

I also seem to remember reading somewhere, really a long a time ago, that "crackle" and "pop" on LP records could get as much as 200 mV to the input stage. Under normal conditions, for MM cartridges, that would be 20...30 mV.
  Reply With Quote
Old 28th February 2012, 01:33 PM   #2895
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Several people have published data on maximum signal levels from cartridges. That hasn't stopped me from designing my own preamp to have far larger overload margins than it would appear are necessary.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 28th February 2012, 02:42 PM   #2896
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by bcarso View Post
There's a boy to watch . We were both a little puzzled about some of the claims that there might be some sort of "thermodynamic" limit to such reduction with paralleling. He moved more quickly than I (which is not saying much ) to disprove this empirically. IIRC he's using 220nH in each gate lead.
Sam and I are good buddies That comment might have come from me and it got slightly misconstrued. I think it was MTS instruments (they make giant counterweights to put on top of skyscrapers for active damping) that found for low frequency noise in air there seemed to be a point where the heat flow from the increased power started to increase the 0.1 - 10Hz noise to counteract device paralleling.

They used strain gages to sense building flex and I guess the natural freqency of a 100 story tower is well below a Hz.
__________________
"This logos holds always but humans always prove unable to understand it, both before hearing it and when they have first heard it."
  Reply With Quote
Old 28th February 2012, 03:19 PM   #2897
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by scott wurcer View Post
Sam and I are good buddies That comment might have come from me and it got slightly misconstrued. I think it was MTS instruments (they make giant counterweights to put on top of skyscrapers for active damping) that found for low frequency noise in air there seemed to be a point where the heat flow from the increased power started to increase the 0.1 - 10Hz noise to counteract device paralleling.

They used strain gages to sense building flex and I guess the natural freqency of a 100 story tower is well below a Hz.
If it had its origin with you, that wasn't attributed. Where I saw it was in the pages of Jan's bookzine, in connection with others' phono preamp pieces. About the limits to noise performance, it was a speculation with arm-waving mostly, and in one case provoked a LTE from me (about that and many other issues in the particular article, which was something of a tutorial) and one from Burkhard Vogel, who, as is his wont, filled several pages with equations I still was unable to persuade the original author that using a resistor for feedback around an inverting amplifier did not lower its current noise, and I was advised to do a simulation

The skyscraper thing reminds me of the story about Tesla, which I suspect is a very old urban legend, about his determining some natural resonance of a building and installing a little stimulator in it, which according to legend was about to cause the structure to collapse before he turned it off.

If I wanted to bring a structure down, I'd just arrange to rent out my upstairs neighbors in the apartment here At least they don't play music --- perhaps they are stomping around with iPods or the ilk.
  Reply With Quote
Old 28th February 2012, 03:39 PM   #2898
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by DF96 View Post
Sorry, I forgot that there is another quite different circuit also called a Norton amp. Clever people should only be allowed to invent one circuit each! [snip]
Those are two different clever Nortons. The one after whom the current-differencing amps are named (but certainly not their inventor) was Edward Lawry Norton, 1898-1983.
  Reply With Quote
Old 28th February 2012, 03:52 PM   #2899
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by bcarso View Post
Those are two different clever Nortons. The one after whom the current-differencing amps are named (but certainly not their inventor) was Edward Lawry Norton, 1898-1983.
I remember Norton Commander. And Norton Antivirus.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 28th February 2012, 03:55 PM   #2900
dvv is offline dvv  Serbia
diyAudio Member
 
Join Date: Sep 2004
Location: Belgrade, Serbia
Quote:
Originally Posted by bcarso View Post
...

The skyscraper thing reminds me of the story about Tesla, which I suspect is a very old urban legend, about his determining some natural resonance of a building and installing a little stimulator in it, which according to legend was about to cause the structure to collapse before he turned it off.
I believe this effect is called sympathetic vibrations. If memory serves, the idea is that if you can get the natural resonance of a building to coincide with external vibrations, they would multiply and the amplitude would be quite destructive.

Quote:
If I wanted to bring a structure down, I'd just arrange to rent out my upstairs neighbors in the apartment here At least they don't play music --- perhaps they are stomping around with iPods or the ilk.
Brad, you want to get them before they multiply.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quality Control differences = variations in sound quality? KT Class D 3 4th June 2014 12:02 AM
Sound Card for Measurements Marik Solid State 2 2nd January 2012 08:59 PM
Sound Card Recommendations (For Audio Measurements) dchisholm Equipment & Tools 5 16th July 2011 09:40 AM
How to protect sound card during amp measurements? okapi Everything Else 13 2nd September 2008 03:06 PM
Sound cards - test and measurements jackinnj Everything Else 2 5th July 2003 03:02 PM


New To Site? Need Help?

All times are GMT. The time now is 04:37 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2