John Curl's Blowtorch preamplifier part II - Page 3301 - 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 19th January 2013, 07:40 PM   #33001
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Both MX-R and XA160 are power amps. But the 7th concept is universally valid, right?

If he wants to design based on a single figure, it is fine, but if he repeatedly blames other designs like AD797 based on this and untrue arguing (apples x oranges, distortion magnification), then it is just unfair.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html

Last edited by PMA; 19th January 2013 at 07:44 PM.
  Reply With Quote
Old 19th January 2013, 07:52 PM   #33002
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
I am blaming 'somewhat starved' IC amps, that use lots of negative feedback to 'linearize' them. It is the FEEDBACK that I worry the most about.
Look everybody, including PMA, use what you want, and please don't bother me about it.
The Blowtorch preamp has not been built for the last 5 years, and will never be built again. Please find your own audio 'nirvana', you don't have to scold me for your audio choices, and if you don't believe in my design philosophy, make your own! '-)
  Reply With Quote
Old 19th January 2013, 07:54 PM   #33003
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by SY View Post
So why did you start off with the positive rail, then lurch over to the negative rail when it was demonstrated that the noise consequence with your 1968 chip was something less than the white noise left over from the Big Bang?





Your unit conversions are creative to say the least. And I see you went up another octave while you were at it. In any case, the impedance of a cheap (under a dollar in onesy-twoseys from Digikey, not 1968 vintage) 10,000 uF/25V aluminum electrolytic is under 50mohm. I'll let you work the numbers from there- can't wait to see what you come up with.

There are more productive horses to flog than this one, Ed.
SY

I am on a cell phone and the typos and auto spell drive me nuts

I thought I had posted the noise with 10000 uF of filtering. It shows a clear rise of rectifier noise in the upper midrange lower treble.

Now where did you get your 120 mV from?

The best power supply I posted was -120 dB re 1V.

I have been doing a lot of power supply measurements. From the same manufacturer there can be a great variance in performance. This was a bit of a surprise as expectations were for the usual extremely consistent quality.

I also used the AD 797 as an example because it has fairly good PSSR.

Now would you like to show your measurements of PSSR on a few different preamplifier designs? As you probably know in a real build you can approach the opamp limits but the rest of the circuit degrades it

Now how many tangents do you want to divert the issues to?

I started with the FFT of a simple power supply and so far no is willing to publicly even venture a guess as to the load.
  Reply With Quote
Old 19th January 2013, 07:57 PM   #33004
gpapag is offline gpapag  Greece
diyAudio Member
 
gpapag's Avatar
 
Join Date: Nov 2002
Location: Athens-Greece
Quote:
Originally Posted by SY View Post
Ed's use of 1968 components for examples, so even my numbers were enormously higher noise than you get from modern ICs.
Some amateurish measurements with 1968 components
White trace is the Big Bang noise ((loop-back signal of the cardís other channel)
PSU RC multistage filtering
The spectrum emitted from the nearby power x-former can be picked up by the "clean DC" wires past the regulator and swamp anything else.

George
__________________
["Second Law is a bitch." - SY] ["The Road To Heaven:Specify the performance & accept the design. The Road To Hell:Specify the design & accept the performance"-Bruno Putzeys]
  Reply With Quote
Old 19th January 2013, 08:04 PM   #33005
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by PMA View Post
Both MX-R and XA160 are power amps. But the 7th concept is universally valid, right?

If he wants to design based on a single figure, it is fine, but if he repeatedly blames other designs like AD797 based on this and untrue arguing (apples x oranges, distortion magnification), then it is just unfair.
Pavel

It is an interesting question if the distortion weighting is the same for an amplifier as for a preamp. As the preamp is followed by a power amplifier it may be more important.

Now why JC prefers the sound of discrete designs to monolithic is an open question. As he leans to a single figure of merit, such explanations would follow. Now I suspect you and I would do the measurements at the actual operating point so see. Others will just argue aimlessly.
  Reply With Quote
Old 19th January 2013, 08:04 PM   #33006
Waly is offline Waly  United Kingdom
diyAudio Member
 
Waly's Avatar
 
Join Date: Jan 2011
Location: London
Quote:
Originally Posted by simon7000 View Post
Now you may consider less than 100db S/N adequate. But as it is not masked by signal, others may find it a problem, particularly when it drops below 80.
Not to mention when it drops below 60, or even worse, 40.
  Reply With Quote
Old 19th January 2013, 08:07 PM   #33007
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by gpapag View Post
Some amateurish measurements with 1968 components
White trace is the Big Bang noise ((loop-back signal of the cardís other channel)
PSU RC multistage filtering
The spectrum emitted from the nearby power x-former can be picked up by the "clean DC" wires past the regulator and swamp anything else.

George
Thanks George

It was a bit fatiguing with all the noise from the paper results crowd.


ES
  Reply With Quote
Old 19th January 2013, 08:17 PM   #33008
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by RNMarsh View Post
JC has said he belivevs there is more to better audio performance than only those numbers. There are other numbers and there are affects of materials, grounding, pcb artwork/layout and loading and interfacing etc etc etc. .... There is plenty to discusss besides comparing numbers only. Attention to a LOT of details makes a better product. At this point in the maturity of analog audio design - its all in the details.
Thanks for this Mr. Marsh. YOu are entirely right.

Lets look at these details on the original JC2, the one with AD797 that was caned by the reviewers. JC was kind enough to share the circuit with us. It may give us a clue to JC's design philosophy.

The AD797 is used as a MM & MC preamp. It is entirely inappropriate for this purpose. The surrounding circuit degrades the usual Lo Z MC cartridge noise by at least 10dB. There is a similar degradation for MM cartridges but due to the choice of AD797.

AD797 is appropriate for only one type of rare MC cartridge but then the gain structure is completely wrong.

So here is a Golden Pinnae device, supposedly supa dupa matched with its 2 settings and getting them ALL wrong.

JC, did you do ANY calculations for noise? Did you MEASURE the noise? If you did, did you decide these figures weren't bad enough to upset your illustrious moniker on the front panel?

You may also like to compare the decoupling on JC2 with the recommendations on the datasheet. JC2's naive decoupling is likely to result in instability which will be difficult to see but will almost certainly result in poorer THD and intermodulation under certain signal conditions.

Without looking at the PCB and wiring details, its difficult to be sure .. but the schematic suggests inadequate attention and poor understanding of earthing for low noise & distortion.

All in all, JC2 Mk1 is the type of circuit produced by someone who failed Electronics 101 .. but believes a $zillion price tag, using Golden Pinnae parts without considering if they are appropriate (AD797) and a 'hand carved by virgins from solid Unobtainium' front panel guarantees sales.

To his credit, JC did change the AD797 for even more 'hand carved by virgins from solid Unobtainium' parts .. hopefully more appropriate for their role.
______________

JC, as for your pontificating on THD harmonics in class A, you really need to read Baxandall. Unlike you, he calculates AND measures it to confirm his theories.
______________
Attached Files
File Type: pdf phono.pdf (64.3 KB, 62 views)
  Reply With Quote
Old 19th January 2013, 08:58 PM   #33009
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
kgrlee,
Now I await a reply to what you just wrote not from John but from Scott who can answer if what you just stated he is in agreement with.

Ps. I would still like to hear how you make a bad cd sound like anything but. I just put on an early transfer of a Doors album and I must say it sounds like crap.... Put on a Manhattan Transfer album and it was night and day. Anyone who says that all cds sound good with the correct equipment must not have a bad cd in the bunch. I know in this particular instance that the vinyl Doors album would just blow out the cd version, no comparison. I'll take the clicks and scratches over horrid cd sound any day. I guess that cd will make a nice coaster.
  Reply With Quote
Old 19th January 2013, 09:00 PM   #33010
gpapag is offline gpapag  Greece
diyAudio Member
 
gpapag's Avatar
 
Join Date: Nov 2002
Location: Athens-Greece
Quote:
Originally Posted by simon7000 View Post
Thanks George
It was a bit fatiguing with all the noise from the paper results crowd.
ES
Paper results (e.g. ICs with better specs) are one thing to consider and implementation (layout, component orientation ect) is another.
I wrote above of the x-former emitted noise.
Attached are some spectrums from a sensing coil output, which was placed close to the x-former that was feeding the bridge/smoothing/regulator PCB.
I was recording the signal picked up while moving the coil, starting closest to the x-former and moving toward the circuit inch by inch.

George
>Edit: 1 inch, 2 inches, 3 inches, 4 inches, 6 inches
Attached Images
File Type: png 1in Spectrum.png (10.5 KB, 156 views)
File Type: png 2in Spectrum.png (10.2 KB, 152 views)
File Type: png 3in Spectrum.png (9.2 KB, 152 views)
File Type: png 4in Spectrum.png (8.4 KB, 152 views)
File Type: png 6 Spectrum.png (7.4 KB, 150 views)
__________________
["Second Law is a bitch." - SY] ["The Road To Heaven:Specify the performance & accept the design. The Road To Hell:Specify the design & accept the performance"-Bruno Putzeys]

Last edited by gpapag; 19th January 2013 at 09:05 PM.
  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



New To Site? Need Help?

All times are GMT. The time now is 10:06 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