Hi Grey,
Thanks for all your fine technical input. For better readability, could you put an extra space after each of your paragraphs? It's like drinking from a fire hose for my tired old eyes with all the text lines run together.
Thanks, Chuck Hansen
Thanks for all your fine technical input. For better readability, could you put an extra space after each of your paragraphs? It's like drinking from a fire hose for my tired old eyes with all the text lines run together.
Thanks, Chuck Hansen
john curl said:
My comparison was of someone else's vinyl setup to 15ips 1/2 track masters made for the BSO. The point was only in my, just my very own anecdotal world, the inherent quality of the recording was not destroyed by being broadcast over FM radio. What I listen to makes me happy, certainly happy enough to use my time and energy elsewhere. My CD's of LP's, again to me, capture enough of the "vinyl" experience that more would be diminishing returns.
Most of the classic vinyl around has gone through a generation of tape, so are you trying to say the transfer to vinyl has improved the sound? By this I mean things like RCA LSC's and Mercurys, there must be people here who treasure some of these.
I have a bunch of boxed Sheffield's, do you want them? I can't stand the performances in general, that's another story and another personal opinion.
Enough of this boring side show, what I was talking about last week was CAPACITIVE feedback. Why has no one tried it? I have, it works. 17 years age I was working with the Navy folks in MD on some sonar spook stuff, and got the idea. People have tried pots and variable transformers, but I have not seen anyone publish a variable capacitor amplifier. By this I mean an op-amp (inverter) with GNF (capacitive conventional feedback) so maybe it does not apply here. DC biasing is a side issue that can be dealt with. The reason, noise, you can make a conventional line stage for instance, that has 1nV RTI noise at all gain settings even 6dB.
Scott, I regret that you feel that this is a 'boring side show'. NO, I don't think that ADDED processing or distortion makes better sound in general. However, a good analog master tape will transfer to vinyl with LESS LOSS (subjectively) than if it is transfered to CD. Wilson audio has proven this often enough.
Sheffield recordings have often been criticized over the years for their musical content. However, they provide a 'test track' of high quality sound to really try to see what a sound system can do, subjectively. If, for example, you are moved by Thelma Houston in 'Don't Misunderstand' on one of the Sheffield records, then your audio system is up to hi end standards. Unfortunately, the CD is usually not as 'moving' or even the tape produced version, compared to the direct disc.
If you have real direct disc versions and not tape copies put on vinyl, then you could get some real money for your Sheffield records on E-bay. You might want to think about that, before sending them to me. I will accept them gladly.
Sheffield recordings have often been criticized over the years for their musical content. However, they provide a 'test track' of high quality sound to really try to see what a sound system can do, subjectively. If, for example, you are moved by Thelma Houston in 'Don't Misunderstand' on one of the Sheffield records, then your audio system is up to hi end standards. Unfortunately, the CD is usually not as 'moving' or even the tape produced version, compared to the direct disc.
If you have real direct disc versions and not tape copies put on vinyl, then you could get some real money for your Sheffield records on E-bay. You might want to think about that, before sending them to me. I will accept them gladly.
I meant the discussion about what I choose to spend on my LP setup. I don't discuss personal financial choices in public, it only makes some people feel bad.john curl said:
As for the other stuff, one point that is not so clear is that some folks made up their minds about what 'can' and 'can't' work based on those 30 yr. old experiences with those components you now denigrate. There are now IC's with low noise thousands of volts per microsecond slew rate and unmeasurable amounts of any of those 'distortions' that people like to talk about. Some articles, as timely as they were in the 70's simply are no longer relevant. You can say "an op-amp with feedback can never work for high-end" all you want, but the evidence remains a long string of anecdotal shaggy dog stories.
BTW Charles, after reading further I realized that Sony article was using the same Primo EM-21/3 electret capsule that Nakamichi used in their line of 'prosumer' mikes. I might be wrong but there are to many exact coincidences. This is what I have been using myself. This is a nice, plentiful on the used market, mike.
Scott, for the record, capacitive feedback is not 'new'. Nor is the concept of capacitive dividers. Almost every commercial microphone, Neuman (your favorite) Shoeps, AKG, etc have a little switch on the side that reduces the capsule level to prevent 'overload' They do this with a capacitor across the element that acts like a capacitive divider. The problem with this is that it creates lots of 2'nd harmonic distortion.
This is because the MOVING capacitor (microphone element) is changing in value with its vibration. While this is OK and linear with a very high resistive load, and is the way that the capacitor microphone transfers charge into voltage, it is NOT good to load it with a significant capacitive load, as this causes distortion at higher levels of SPL.
If you will only look at a typical B&K microphone preamp, you will find that the resistors loading the microphone are BOOTSRAPPED (positive feedback) with some care, in order to REDUCE the PASSIVE capacitance inherent in any design.
The technique of using capacitive feedback will add some passive capacitance to the equation. How much, I am not sure, and maybe it is not important enough to cause significant distortion. However, B&K thinks it is important to REDUCE the passive cap load by any means possible. Erling taught me this, himself, please don't take it for granted.
This is because the MOVING capacitor (microphone element) is changing in value with its vibration. While this is OK and linear with a very high resistive load, and is the way that the capacitor microphone transfers charge into voltage, it is NOT good to load it with a significant capacitive load, as this causes distortion at higher levels of SPL.
If you will only look at a typical B&K microphone preamp, you will find that the resistors loading the microphone are BOOTSRAPPED (positive feedback) with some care, in order to REDUCE the PASSIVE capacitance inherent in any design.
The technique of using capacitive feedback will add some passive capacitance to the equation. How much, I am not sure, and maybe it is not important enough to cause significant distortion. However, B&K thinks it is important to REDUCE the passive cap load by any means possible. Erling taught me this, himself, please don't take it for granted.
Scott, I am not AGAINST op amps, I have 100's of op amps, maybe 1000's in my office right now. I have UA709's that are 42 years old. Interested?
At this time, I am making two phono preamps on similar principles. One is discrete, all fet, and the other is IC's, in fact designed with YOUR AD797 in the front end. Why? Because it is considered one of the finest IC's on the market. Too bad that it is excessively priced.
Now what do I gain or lose between these two designs?
Well, the IC version will sell at 1/10 the price or so of the discrete unit.
The discrete unit will be all open loop, without op amps.
The IC version will use your IC with feedback, with a second dual fet input op amp.
The discrete version will be about 12 dB quieter. This is because your IC and a 50 ohm resistor will set the noise floor. I don't dare go lower than 50 ohms, because of excess output loading of
this IC if I do, or early overload.
What will really matter is the SOUND QUALITY.
IF I can make the JC-3 phono stage as good, subjectively, as the VR-3 then my work is done and IC's can rule the roost from now on. Let's see what happens.
I know that Dick Sequerra uses your AD797 and loves it, BUT he does not use it in a conventional way. You should really try to find out what he is doing, as his approach is brilliant! His approach will really give my best efforts something to compare to.
At this time, I am making two phono preamps on similar principles. One is discrete, all fet, and the other is IC's, in fact designed with YOUR AD797 in the front end. Why? Because it is considered one of the finest IC's on the market. Too bad that it is excessively priced.
Now what do I gain or lose between these two designs?
Well, the IC version will sell at 1/10 the price or so of the discrete unit.
The discrete unit will be all open loop, without op amps.
The IC version will use your IC with feedback, with a second dual fet input op amp.
The discrete version will be about 12 dB quieter. This is because your IC and a 50 ohm resistor will set the noise floor. I don't dare go lower than 50 ohms, because of excess output loading of
this IC if I do, or early overload.
What will really matter is the SOUND QUALITY.
IF I can make the JC-3 phono stage as good, subjectively, as the VR-3 then my work is done and IC's can rule the roost from now on. Let's see what happens.
I know that Dick Sequerra uses your AD797 and loves it, BUT he does not use it in a conventional way. You should really try to find out what he is doing, as his approach is brilliant! His approach will really give my best efforts something to compare to.
Would you consider to try OPA211? I probably would. But delivery times are bloody 
, I amp expected to get them end of August.
, I amp expected to get them end of August.
Oh also (FWIW), Tim de Paravicini gave a talk at ETF06 which included some interesting uses of capacitive feedback for tubed mike preamps. Pretty similar to what you're talking about.
SY said:
You mean someone else has "Da Crusher"? If they're not from Milwaukee they don't count. Otherwise I'll switch to The Fabulous Moolah. BTW I found out that Killer Kowalski lives only a couple of miles from me, small world.
Who's that ? I'm stumped.
john curl said:
Wait for some pictures, you still don't get it. Think Peter Baxandall and reciprocity and driving the capsule into a virtual ground, i.e. a short circuit. It has absolutely nothing to do with bootstrapping or the standard attenuator pad.
"For instance, with a -20 dB attenuation pad on the microphone, the AKG C414's can handle up to 160 dB with less than 0.5 percent Total Harmonic Distortion [THD]. " OUCH!" I thought second harmonic was caused by the one sided nature of most mikes in the same fashion as a Magnepan speaker. The dual diaphram ones should be symetrical i.e. thirds?
I never claimed it was new, I just claimed that the IC busness has gotten to the point that it might deserve another look. The phantom power spec doesn't allow for 70's era low noise op-amps in the head. We can now do 2nV on 1.5mA with lots of slew rate and rail to rail too.
Sennheiser makes mikes that put the capsule in an RF bridge. They are very highly regarded and resist moisture (also expensive).
Take two (ideal) capacitors C and charge one of them to V. Short them together and the charge is conserved so you have V/2. Where did 1/2 the energy go? (E = 1/2C*V^2).
The 'physics' answer needs no equations.
chascode said:
Your point is a valid one, but...
I'm an author (not that you'd know it from my output recently--the combination of kids and that JFET group buy I got myself into have clobbered my writing time) and "real" writing uses a tab to show the start of a new paragraph. Unfortunately this site, for reasons that are unclear to me, refuses to acknowledge tabs. In fact this site is unkind to nearly all whitespace characters. I'd be happy to use tabs, but can't and using a space between paragraphs qualifies as a bad habit--one I would rather not form. Please feel free to take the tab issue up with the management. I will back you if you do so. It's just plain dumb not to allow them.
Besides, adding blank lines makes posts look longer than they are. I am often (justly) accused of making lengthy posts. I see no reason to make them longer than they are. I did, grudgingly, use spaced paragraphs in beginning posts of the GR-25 thread, but it's not something I do lightly.
John,
While I'm on the subject of writing, it might help if you were to address the posts that you intend for a specific person to that person. In the present case, it would have saved much confusion on my part if I'd known you were writing to Scott.
It's difficult to format things for online consumption, as there's no generally accepted way to go from speaking to one person to the group at large, then back to one person again. If we were all sitting around a table, we'd generally turn to face the person we were speaking to, but that's not an option online. All the physical cues that we take for granted in person are lost. In fifty years there might be a consensus regarding the grammar and etiquette required, but for now there's little guidance.
It's not helped by the lack of tabs (hint, hint...I don't know who's in charge of such things [Dan?] but it would be nice to have tabs).
Grey
I read good things about the newest National specialized audio op-amp LM4562 (dual) and LM49710 (single) at under $2.00. http://www.national.com/pf/LM/LM4562.html
Anyone try these, any comments?
Anyone try these, any comments?
Sorry SY, I get it now.
John - last sale on eBay of that Amanda McBroom LP was for $7.50, Harry James - $5.00 original D to D versions.
John - last sale on eBay of that Amanda McBroom LP was for $7.50, Harry James - $5.00 original D to D versions.
Reference without comment:
''Reduction of Non-Linear Distortion in Condenser Microphones by Using Negative Load Capacitance" , BY ERLING FREDERIKSEN, BRUEL AND KJAER TECHNICAL REVIEW, 1996, pp. 18-27.
Anyone have access to a copy?
''Reduction of Non-Linear Distortion in Condenser Microphones by Using Negative Load Capacitance" , BY ERLING FREDERIKSEN, BRUEL AND KJAER TECHNICAL REVIEW, 1996, pp. 18-27.
Anyone have access to a copy?
john curl said:
Which library caries these? I noticed that B&K has been chasing numbers lately. They have a mike with a spec of .008% distortion at 134dB SPL, applications list includes homeland security!!??
John, my application is nature recording at <80dB SPL where almost any capsule is < .01%. I'm trying to help some DIY'ers save money, I'm doing it gratis. My circuit has no effect on the distortion inherent in the capsule plus or minus. I have built it, measured it, and listened to it. I thought the technique was interesting in that you can get a traditional op-amp with GNF circuit that has low noise at low closed-loop gains (no resistor noise).
john curl said:
I have this one -
Frederiksen, E., Eirby, N. and Mathiasen, H.: Prepolarized Condenser Microphones for Measurement Purposes. Bruel Kjaer Technical Review, 1979, pp. 3 - 26.
I have the issue.
The article is free for registration only. It covers low frequency distortion at huge SPL's. The graphs show a pretty narrow sweet spot.
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