John Curl's Blowtorch preamplifier part II - Page 453 - 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 3rd June 2010, 03:25 AM   #4521
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
The measurements where taken at ( from felt to right ) at -40dB/V, -30dB/V and -20dB/V.
Signal noise is -77dB against 1mV when you include the peaks.
  Reply With Quote
Old 3rd June 2010, 04:52 AM   #4522
diyAudio Member
 
Terry Demol's Avatar
 
Join Date: Apr 2002
Location: *
Quote:
Originally Posted by Joachim Gerhard View Post
Allan Wright and i listened in my place to his top Tube Stage compared to one of my OPamp based preamp. Ask him. I do discrete too when i try to make the best posible but this little preamp is a lot of fun. The MC input stage in that Pramp is an INA build from two LME49990 and one ADA4627 per channel. A conventional feedback structure with the LME49990 brings not the best sound out of it. I tryed virtually everything, series feedback, shunt feedback, differential etc. and the INA topology works by far the best soundwise. I can not measure distortion in that circuit at cruising level. It is below the noise.
Joachim,

I think you have made some excellent points in all these posts. WRT INA
topology, I am assuming you mean a fully symmetrical instrumentation
topology. If you refer to Samuel Groners excellent opamp measurement pdf
it is clear that common mode distortion is a major player in opamp non
linearity and especially at higher frequencies. Using the 'INA' topology will
largely cancel this form of distortion.

WRT measurements of these pre amps , I would again do a 20kHz
measurement where CM distortions will show much clearer, a THD
versus frequency measurement and note how much it all tilts up toward
the HF. Note my post on power amp measurements.

cheers

Terry
  Reply With Quote
Old 3rd June 2010, 05:00 AM   #4523
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
The signal to noise of even the best op amps is problem, and a balanced input as you are making would ruin it for me, but I do like the IN-AMP topology for microphone inputs.
  Reply With Quote
Old 3rd June 2010, 05:24 AM   #4524
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Terry, i did that. You can see my MPP tread. Distortion in a well designed Opamp stage, be it harmonic, be it intermodulation, be it Belcher or whatever fancy test you can throw on them, is a non issue provided you do not drive it into a too demanding load and keep the voltage level resonable. My experience tells me that "magical sound" comes from carefully designed noise and distortion at a low level. Too high distortion then sounds foggy and uninformative unless a musician just wants that on the recording side.
  Reply With Quote
Old 3rd June 2010, 10:46 AM   #4525
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Quote:
Originally Posted by john curl View Post
Joachim, I do not think that any IC op amps do as well as a well designed piece of tube equipment, OR good discrete solid state electronics.
As far as IC's are concerned, today I tried your suggestion of National OP AMP as replacement for the AD797, which is very good, but too expensive, in my opinion, compared to its competition. It works fine, sounds good, and I did not measure anything higher than 3'rd harmonic. Perhaps this IS progress in IC's, I hope so.
My problem with vacuum tubes is the related coupling to and from it, that means lots of caps, and or transformers. It is these components that I worry most about.
John

There is a way out and that is to build a direct coupled valve preamplifier if you are keen , you just need of coarse some protection on the output ( I prefer a relay here).

Its surprising what they sound like without all those coupling caps.

I think you could also do an RIAA stage that could be direct coupled all the way through too.

Regards
Arthur
  Reply With Quote
Old 3rd June 2010, 10:52 AM   #4526
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Quote:
Originally Posted by Joachim Gerhard View Post
Silicon circuits, even with the latest generation of OPamps can be made to sound extremely well. When it comes to measurements it is hard to make a tube stage that has as low distortion, noise and very high bandwidth. Using discrete circuits with relatively high voltage it gets quite thin for tubes. I can see no cheap and easy compromises provided the circuit is competent and build with good parts. I whould say that it is cheaper and easiers to make a good sounding tube circuit. I know what i am talking about because i had a lot of tube amps at home with aspiration to be "The Best". I listened at length to them and i measured them as good as i could. Except a portion of harmless second harmonic and a different noise profile i could not find any magical properties in them. For me it is just another technological option. A lot what a tube can do sonically can be mimicked with single ended Fet circuit and i got particular good in building buffers that add whatever distortion and noise i like. Actually i think a lot what makes a tube sound good is adding some ( small ) extremely attractive distortion to the music. But now i am back where i should not be here.
Hello Joachim

What do you imagine a low distortion valve stage to sound like do you think it would sound like a low THD silicon stage. In both cases I am talking about designs with no coupling capacitors.
  Reply With Quote
Old 3rd June 2010, 11:27 AM   #4527
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I think ones the distortion is under -80dB, low order, exponentially falling, noise is not audible and frequency response is better then 200kHz -3db, tubes and transistors can sound surprisingly similar. Parts choice matters in silicon circuits too in my experience.
A tube poweramp with transformer output and low damping factor will always sound different from a good solid state design. In case the tube amp sounds better i asume it has some artfully designed distortion that makes the music sound better. I have no problem with that as long as i can enyoy the result and fatique does not set in.
I was told by David Salz of Wire World that there exists a tube manufacturer that sells to the State of America tube amplifiers that are extremely fast and have very low distortion, like silicon based circuits, so it can be done. Hewlett - Packard and Tectronics ( for that matter also Rhode & Schwarz and B&K ) must have known too how to design like that in the old days.
  Reply With Quote
Old 3rd June 2010, 11:38 AM   #4528
PHEONIX is offline PHEONIX  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Australia
Quote:
Originally Posted by Joachim Gerhard View Post
I think ones the distortion is under -80dB, low order, exponentially falling, noise is not audible and frequency response is better then 200kHz -3db, tubes and transistors can sound surprisingly similar. Parts choice matters in silicon circuits too in my experience.
A tube poweramp with transformer output and low damping factor will always sound different from a good solid state design. In case the tube amp sounds better i asume it has some artfully designed distortion that makes the music sound better. I have no problem with that as long as i can enyoy the result and fatique does not set in.
I was told by David Salz of Wire World that there exists a tube manufacturer that sells to the State of America tube amplifiers that are extremely fast and have very low distortion, like silicon based circuits, so it can be done. Hewlett - Packard and Tectronics ( for that matter also Rhode & Schwarz and B&K ) must have known too how to design like that in the old days.
Hello Joachim

Are you familiar with Sequoia.
  Reply With Quote
Old 3rd June 2010, 11:41 AM   #4529
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
No i am not.
  Reply With Quote
Old 3rd June 2010, 11:42 AM   #4530
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Do you mean the software ? I am familiar with Samplitute, Wavelab etc.
  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 08:40 AM.


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