Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

John Curl's Blowtorch preamplifier
John Curl's Blowtorch preamplifier
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
Closed Thread
 
Thread Tools Search this Thread
Old 4th June 2008, 12:29 PM   #6091
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
Hi PMA,
R5 & 11 not connected to zero volt line?
__________________
regards Andrew T.
 
Old 4th June 2008, 12:31 PM   #6092
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
John Curl's Blowtorch preamplifier
Quote:
Originally posted by AndrewT
Hi PMA,
R5 & 11 not connected to zero volt line?
No, symmetrical output. But can be connected without change of distortion.
 
Old 4th June 2008, 02:16 PM   #6093
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally posted by PMA
Yes, it changes gain, and should be chosen according to bias current.
Of course it changed the gain. And of course this circuit has relatively low distortion. This circuit is nothing but heavy NFB so there's no surprise about. This FB type also decreases both the input and output impedances by the loop gain. This makes this little circuit a transimpedance amp.

And of course it has a low noise - having such a low input impedance.

And of course it needs high Iq - the 100 ohm resistor loads the output, in parallel with the 50k "load" and it's of course the gm*100 ohm that sets the OL gain. And if you want any performance improvement by means of NFB you need some OLG, isn't it?

And of course you can lower the Iq if you increase the feedback resistor to 10k, to get the same OL gain.

It's funny how people moan about feedback but don't miss any opportunity to conveniently use it in their circuits.
 
Old 4th June 2008, 02:46 PM   #6094
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
John Curl's Blowtorch preamplifier
There is a feedback and feedback. This has nothing to do with conventional dominant-pole VFB design. 57dB and 1.7MHz BW, no slew rate limitation. This counts.

We care how it sounds, not only how it measures THD in audio band.
 
Old 4th June 2008, 02:53 PM   #6095
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
PMA, thanks for your input. I beta match to remove any significant bias. Typically, 2.5 ma and 10 ohm Re is normal. 2 x D battery powered. Re could be slightly offset to remove even harmonics. i.e. 11 ohm, 9 ohm for example. Initial even harmonic probably due to bipolar model differences in diode equation.
This is the essence of the Levinson JC-1 pre-preamp, and the SOTA headamp. Made obsolete by Vendetta in 1982.
__________________
"Condemnation without Examination is Prejudice"
 
Old 4th June 2008, 02:58 PM   #6096
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
PMA, you could eliminate the big caps by just making it truly differential with the complementary connection intact. It makes it simpler, balanced and removes the big caps. Slightly noisier though. Noise is EVERYTHING in this circuit.
__________________
"Condemnation without Examination is Prejudice"
 
Old 4th June 2008, 03:00 PM   #6097
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
For a low Z input, the single sided circuit can be driven into the emitters and the bases shorted to ground. This is the essence of the JC-1 AC, JC-1 DC, and the Ortofon phono stage.
__________________
"Condemnation without Examination is Prejudice"
 
Old 4th June 2008, 03:06 PM   #6098
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
John Curl's Blowtorch preamplifier
Thanks, John, for this further design lesson.
 
Old 4th June 2008, 03:06 PM   #6099
jan.didden is offline jan.didden  Europe
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: The great city of Turnhout, BE
Quote:
Originally posted by syn08


Of course it changed the gain. And of course this circuit has relatively low distortion. This circuit is nothing but heavy NFB so there's no surprise about. This FB type also decreases both the input and output impedances by the loop gain. This makes this little circuit a transimpedance amp.

And of course it has a low noise - having such a low input impedance.

And of course it needs high Iq - the 100 ohm resistor loads the output, in parallel with the 50k "load" and it's of course the gm*100 ohm that sets the OL gain. And if you want any performance improvement by means of NFB you need some OLG, isn't it?

And of course you can lower the Iq if you increase the feedback resistor to 10k, to get the same OL gain.

It's funny how people moan about feedback but don't miss any opportunity to conveniently use it in their circuits.

Thank you

Jan Didden
__________________
Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
 
Old 4th June 2008, 03:15 PM   #6100
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
This circuit can be OK without any feedback of any consequence. In fact, it will be even quieter. Please remember 100mV is the MAXIMUM output and usually measures about .1% DUH!. Actual operation is more like 10mV out and less. It drives other people's moving magnet phono stages directly, and will overload them if you are not careful.

IT IS A TRANSFORMER ELIMINATOR!
__________________
"Condemnation without Examination is Prejudice"
 

Closed Thread


John Curl's Blowtorch preamplifierHide 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

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 02:50 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki