♫♪ My little cheap Circlophone© ♫♪ - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 20th July 2011, 05:20 PM   #111
Elvee is online now Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by kenpeter View Post
Wasn't ever stable till I axed one stage of drivers.
But then I had to flip the whole front upsidedown.
Had no idea what I was doing, random experiment.

Stability still goes bannanas whenever it clips.
Recovery from clipping here is just plain awfull.
I would soft clip this with Zeners across R11.

One 2n3055 gets an assist from base current, the
other dumps base current into the negative rail.
So the collector currents will never be symmetrical.
Took me a while to realize I should stop obsessing
for a perfect current balance, not posssible...
Stability aspects of this topology are somewhat disconcerting: you can't use the old recipes applicable to traditional topologies.
The schemes and values I arrived at are largely based on trial and errors, most of them on the physical circuit because the sim is not quite reliable for dynamic aspects.

In addition, I've noticed on your "nothing to see" design that the current sensing via the schottky's seems to generate or at least facilitate some instabilities: I had to add an emitter degeneration resistor on the sensing transistors to achieve complete stability with a 1µs timestep.
  Reply With Quote
Old 21st July 2011, 02:44 PM   #112
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Both loops stable now.
Also ditched a resistor only needed in MOSFET version.
Distortion reasonably low, considering 2N3055 at 750mA crossing.
And 165mA of that bias is always on, bypassing both Schottkys.

I am assuming "circlo" refers to how the bias servo returns full
circle, to regulate the tail CCS? My second loop compensation
loosens the harsh grip it has upon this at higher frequencies.

Things get weird if common and differential loops roll too close
same corner frequency, easily avoided. Resistors in series with
caps take gains down without rolling the phase too much, and
FT somewhere I havn't determined where (probably 2N3055?)
does final roll.

The 15R's could be parallel 33R's to enhance BOM monotony.
47pF = parallel 100pF, 1N4148 = diode strapped BC546B,
22K = series 10K's, etc... Too many different parts always
a shopping nightmare.
Attached Images
File Type: gif cerklowhatchmahoozit.gif (22.8 KB, 774 views)
Attached Files
File Type: txt cerklowhatchmahoozit.asc.txt (6.4 KB, 29 views)

Last edited by kenpeter; 21st July 2011 at 03:14 PM.
  Reply With Quote
Old 22nd July 2011, 09:03 AM   #113
Elvee is online now Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by kenpeter View Post
Both loops stable now.
Also ditched a resistor only needed in MOSFET version.
Distortion reasonably low, considering 2N3055 at 750mA crossing.
And 165mA of that bias is always on, bypassing both Schottkys.

I am assuming "circlo" refers to how the bias servo returns full
circle, to regulate the tail CCS? My second loop compensation
loosens the harsh grip it has upon this at higher frequencies.
It looks pretty stable, even without the CM compensation network.

It remains almost perfectly behaved, even when clipping.

The schottky's as current sensors give a very nice crossing.
Have you tried it in reality?
Is it thermally manageable?
Attached Images
File Type: gif Cerklo.GIF (63.8 KB, 762 views)
  Reply With Quote
Old 22nd July 2011, 01:21 PM   #114
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Schottkys are selected for overkill sized TO220 package.
But due low voltage drop, rarely dissipate more than 1W.
Current sensors should be ambient temp, NOT thermally
bonded to outputs. OK to thermally bond diode to diode,
we want crossing curves to behave as a matched pair.

Q8 should be thermally bonded to same sink as outputs,
I think then you have an ideal situation for locking into
equilibrium between operating current and temperature.
As Q8 gets hot, all other quiescent currents decrease.
If Q8 itself runs away, the amp safely shuts down...

Last edited by kenpeter; 22nd July 2011 at 01:41 PM.
  Reply With Quote
Old 23rd July 2011, 07:08 AM   #115
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Current (especially the minimum) in each 2N3055 a little more equal.

I don't have any flash of inspiration how fix the remaining imbalance.
What do do about current from base to emitter of the upper 2N3055?
Attached Images
File Type: gif BlamefulDucks.gif (26.9 KB, 709 views)
  Reply With Quote
Old 25th July 2011, 07:08 AM   #116
Elvee is online now Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by kenpeter View Post
Current (especially the minimum) in each 2N3055 a little more equal.

I don't have any flash of inspiration how fix the remaining imbalance.
What do do about current from base to emitter of the upper 2N3055?
This imbalance isn't bugging me anymore: at the beginning of my experimentations with circlo output stages (= same sex devices but not quasi), I tried to find ways to balance the currents better, but with experience I've found there is little to be gained, quite the opposite.
Now, I happily live with it. It may be intellectually disturbing, but the real impact is very limited.

I think I'll give a try to the schottky sensors one of these days, to see what it's really worth in practice.

I am not sure coupling Q8 to the OP transistors is the best option: coupling it to the diodes might be a valid option too.
  Reply With Quote
Old 25th July 2011, 08:16 AM   #117
diyAudio Member
 
Join Date: Mar 2004
Location: Krakow
Unhappy ?

Quote:
Originally Posted by kenpeter View Post
Both loops stable now...
Hi Kenpeter,
in my simulator b2spice
at 19V pp output @8 ohm
I have heavy oscillations of the sine wave,
I used different shottkys (10tq045)
might this cause the oscillations?
__________________
regards, Pawel
  Reply With Quote
Old 25th July 2011, 08:19 PM   #118
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Schottkys should only be affecting shape of the crossover region.
Diodes doing nothing significant at 19V that could initiate oscillation.

I prefer to worry that cascode Q9 might be a positive feedback
into the Miller of Q5? Perhaps attenuate higher frequencies from
reaching the base of Q9 would help. Ferrite bead, or low pass?
I'm just guessing, not able to run a sim right now. Can you copy
and paste a model for your Schottky?
  Reply With Quote
Old 26th July 2011, 07:11 AM   #119
diyAudio Member
 
Join Date: Mar 2004
Location: Krakow
Quote:
Originally Posted by kenpeter View Post
... Can you copy
and paste a model for your Schottky?
here it goes
.model 10tq045 D is = 9.81804e-08 rs = 0.00739225 n = 0.993075 tt = 0 cjo = 1.42434e-09 vj = 1.5 m = 0.479175 eg = 0.6 xti = 0.5 kf = 0 af = 1 fc = 0.5 bv = 45 ibv = 0.0001
and look of sinewave close from clipping,
upper part oscillates strong
but lower soft...
Attached Images
File Type: jpg Obraz1.jpg (105.1 KB, 625 views)
__________________
regards, Pawel
  Reply With Quote
Old 26th July 2011, 03:24 PM   #120
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
I got to think about this...
Problem is LTP transistors dip into shut-off at high frequency, near rolloff.
Probably because in/out error seen at the comparator becomes too great.
Increasing output bias into pure Class A cures it, but not fix I am wanting.

I am not seeing any big problem your shottky .model, it changes quiescent
slightly, but easy to bring back into alignment. I have 12R where I previously
drew 33R, and 12R straight to ground on the base of the cascode transistor.
No longer driven to follow output and provide equal LTP collector voltages,
but still provides for equal LTP collector dissipation.

Mind you: Only seeing problems at 96KHz and up, 48K and down all look OK.
And only at signal levels near the boundary of true clipping. But I don't think
we should be cutting any transistors off at any frequency considered to be
"inside the envelope".

Last edited by kenpeter; 26th July 2011 at 03:31 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Need help with OB design - cheap, cheap, cheap djn Multi-Way 38 30th May 2010 06:26 AM
Scosche SPL meter: Cheap find with potential, or cheap junk? theAnonymous1 Everything Else 5 11th October 2006 03:40 AM
Alpine cda-9831 vs. 9833 vs. 9835 cbecker33 Car Audio 3 10th December 2004 12:47 PM


New To Site? Need Help?

All times are GMT. The time now is 12:57 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