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

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

John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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 28th March 2013, 04:44 PM   #37471
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
Quote:
Originally Posted by jan.didden View Post
I'd be interested in some examples here.

jan
high voltage, high power, access to bias or other 'internal' local FB loops/degen that may tweak operating point for the specific load that may not be brought out on the opamp pins. some of these things can be achieved with a mixed IC/discrete layout as well, but as a self confessed opamp lover, there are some things that you are more free to do with discrete.

you dont really feel that an opamp is always the best choice do you?

also i'm not so much talking of the limitations of the technology, moreso the limitations of available devices. an IC could be designed to do just about anything, some of the internal parts/features are difficult to match whats possible with external larger parts like very linear higher capacitance are just too large for the most part to have internally. the flexibility of discrete is hard to beat, though given access to the technology and budget it would be very cool to be able to generate custom application specific ICs. one day i'm sure, probably sooner than we think.

Last edited by qusp; 28th March 2013 at 05:02 PM.
 
Old 28th March 2013, 05:03 PM   #37472
Kindhornman is offline Kindhornman  United States
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
John Curl's Blowtorch preamplifier part II
On the Virtins Technology software package mentioned earlier they are also showing the separate external oscilloscope modules to the right of the page. Is this only a capture card application or is there something I am missing here with those? How do those interface with the software and what do they add to the picture? Humor me as I am trying to understand all of what is being said here...
 
Old 28th March 2013, 05:08 PM   #37473
jacco vermeulen is offline jacco vermeulen  Netherlands
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Quote:
Originally Posted by PMA View Post
But, the real thing
A surface mount 10-20R trimpot is smaller than a TO-92 footprint.
__________________
Why does it hurt when I Pee ? (Ay Ay Ay https://www.youtube.com/watch?v=w5fLGWrHouk)
 
Old 28th March 2013, 05:15 PM   #37474
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
John Curl's Blowtorch preamplifier part II
You might like to keep it stable with fixed resistors . Nothing is worse than trimpot wiper. Good trimpots are multiturn and big.
 
Old 28th March 2013, 05:49 PM   #37475
jacco vermeulen is offline jacco vermeulen  Netherlands
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Just mentioning what everyone on this thread knows.
(h, i'm not getting near a 270 degree cermet trimpot with a 10ft pole)

Then add a 3d FET to auto-adjust offset, Q2 is just a stinkin current source.
__________________
Why does it hurt when I Pee ? (Ay Ay Ay https://www.youtube.com/watch?v=w5fLGWrHouk)
 
Old 28th March 2013, 05:58 PM   #37476
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
PMA (or anyone that cares to answer), do you have any idea what an average amount of parasitic capacitance and inductance might be for a trimpot say 5k at HF? less than 10-20pf? we are looking to replace a trimpot for bias with some parallel SMD 0603 fixed resistors and a pair of opto isolated relays (remotely controlled with an MCU, the specific part is IXYS CPC1117N), which are LED and fet based. the Vbias is generated across a 2ma CCS on the LME49830 bias circuit.

I started worrying about unwittingly adding some less than linear lumped ciss/coss from the fets that interferes with the compensation. these elements, as well as the fet bandwidth could interfere with loop stability/phase angle.

that being said its replacing a pot, which I know has some parasitic C and L already, but its not something specified in datasheets.

the idea is to allow some optimal/smart/automated and remote bias setting wrt ambient temp/month of the year, as well as allowing the chip and power supply to start up into a lowish 100ma bias, then after a few seconds increase to 400 or 600ma for more class A and lower distortion, based on set environmental variables.

Last edited by qusp; 28th March 2013 at 06:08 PM.
 
Old 28th March 2013, 06:03 PM   #37477
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
You guys amuse me. First, why not just use a DUAL jfet and forget the matching?
__________________
"Condemnation without Examination is Prejudice"
 
Old 28th March 2013, 06:07 PM   #37478
john curl is offline john curl  United States
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
For the record, I don't layout my own designs. My associate has been doing the layouts for the last 30 years, and he is a pro in the layout business. High frequency does not bother him. I consider his efforts close to my own in value, and ALL the Parasound JC series, as well as the Vendetta Research, CTC Blowtorch, and many other products were all done by him at my insistence. He is the T in CTC.
__________________
"Condemnation without Examination is Prejudice"
 
Old 28th March 2013, 06:40 PM   #37479
coresta is offline coresta  France
diyAudio Member
 
coresta's Avatar
 
Join Date: Mar 2005
Location: Paris
Hi John,
is the published shemo of the JC-1 correct ? i tried one with aother Siliconix J-fets and couldn't reach nor high gain nor low dissipation of the Jfets ... any forgotten Kilo in the values ?! regards
 
Old 28th March 2013, 06:42 PM   #37480
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
John Curl's Blowtorch preamplifier part II
Qusp, the real issue is unstable resistance set by trimpot. Sensitive to shaking and mechanical impacts. I know what I speak about.
 

Closed Thread


John Curl's Blowtorch preamplifier part IIHide 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 01:55 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki