♫♪ My little cheap Circlophone© ♫♪ - Page 17 - 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 August 2011, 08:51 PM   #161
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Quote:
Originally Posted by Elvee View Post
Device balance in the driver (or VAS or predriver, call it what you like, it doesn't fit conventional classification, in short the lower LTP) is completely unimportant.
if matching is unimportant the I'm wondering why structure it as an LTP instead of running the emitters of both devices independently to the bottom rail ?

Quote:
Originally Posted by Elvee View Post
In the input stage, it is like any other amplifier for one thing: the offset voltage will be copied unchanged at the output, but unlike conventional amplifiers, the unbalance will not cause further degradation, the linearity will remain unaffected.
I'm still struggling with this.. I may be too stuoopid to get there quickly. The top LTP still forms an error amplifier, it has signal input and feedback signal input - I thought an LTP requires good balance for low distortion when working like this ?
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 20th August 2011, 10:37 PM   #162
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Quote:
Originally Posted by Bigun View Post
but this is Class A only though right ?
Schottky diode law (something close to square law) AB + 150mA.
I am doubtful the reality follows perfect "law", but not important...

Whats important is that the crossing glitch is smooth and gentle
enough for the main loop's gain bandwith to finish correcting the
problem. Without adding a mess of high order harmonics and IMD.
Also eases symmetry requirements for the LTP that will otherwise
have to sense these crossing errors.

You want linear class A, simply replace sense diodes with resistors.
Still be far less quiescent than old JLH with a blind current source.
I take it all the way to AB with diodes, only to show how the SRPP
current control is versatile enough to make any shape inbetween.

Any offset of the unmatched LTP is copied at only unity gain to
the output. A capacitor in the feedback loop sabotages gain for
the lowest of low frequencies. That DC offset and rumble is not
otherwise amplified by the full closed loop gain. All non-inverting
amplifiers can use this trick...

I may not have drawn that capacitor into every version of my
schematic, but you can assume it needs to be there...

Last edited by kenpeter; 20th August 2011 at 11:07 PM.
  Reply With Quote
Old 21st August 2011, 02:57 AM   #163
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
still digesting...

Kenpeter - I tried simulation of the output, without gnf, with and without schottky and although the curves changed the overall distortion wasn't necessarily better ?

Elvee - sorry if you said already, but can you explain more about what is the function of R14 attached to Q12 in your schematic (I didn't understand your earlier explanation) ? what would have to be adjusted to maintain proper operation if it were replaced with zero ohm ?
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 21st August 2011 at 03:21 AM.
  Reply With Quote
Old 21st August 2011, 05:56 AM   #164
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
I have no idea what you simulated without GNF...
Current steering alone certainly wouldn't be linear.
You changed Q1 to PNP perhaps?
  Reply With Quote
Old 21st August 2011, 06:44 AM   #165
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Hi Kenpeter, sorry, my mistake what I should have siad is that I was simulating a complementary EF output and I swapped out the emitter resistors for schottky diodes. I did see the smooth cross over curves you predicted when looking at the current flow through the outputs but I haven't tried this with the JLH.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 21st August 2011, 08:33 AM   #166
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by Bigun View Post
if matching is unimportant the I'm wondering why structure it as an LTP instead of running the emitters of both devices independently to the bottom rail ?
It could also work like that, but there are reasons in favour of the LTP.
Here are the most important:
-Common mode. Not exactly the usual one like CMRR, but the fact it doesn't convert common-mode (vertical path, ancillary control loop for current servo) into differential-mode (horizontal path, noble signal loop), but, and this is important, it transmits the common-mode to control the quiescent current.
-Symmetry: the current from one emitter has to come from the other one, and this forces a symmetry in the output, even if the devices are different.



Quote:
I'm still struggling with this.. I may be too stuoopid to get there quickly. The top LTP still forms an error amplifier, it has signal input and feedback signal input - I thought an LTP requires good balance for low distortion when working like this ?
The current flowing in the input transistors equals 1.2/R6 (or R7).
Mismatches in lower LTP will only add or subtract millivolts to the 1.2V potential, and mismatches in the input LTP will only force an output offset sufficient to rebalance the currents in the input transistors.
QED: mismatches in input or VAS transistors have no first order effect on linearity.

Quote:
Elvee - sorry if you said already, but can you explain more about what is the function of R14 attached to Q12 in your schematic (I didn't understand your earlier explanation) ? what would have to be adjusted to maintain proper operation if it were replaced with zero ohm ?
It is probably simpler to look at what would happen without R14.

If the supply voltage changes, the current in R21 changes accordingly.

Connected as a simple diode, like Q7, transistor Q12 has a dynamic resistance ~0.026/Ie, and this means that some of the supply voltage variations will be fed to Q13, the first transistor of the current servo amplifier.

This is undesirable, as it will give a poor PSRR, and create parasitic modulation effects.

By adding a B-C resistor having the same value as the dynamic resistance of the transistor, this effect cancelled for a certain range of supply voltage.

An equivalent result could be achieved by using a CCS instead of R21, and it would also make constant the load current of Q2, but it is more complicated and unnecessary:
Variations at the collector of Q2 are simply perturbations inside the current-servo loop, and are mostly rejected thanks to the loop gain.
At the level of Q12/Q13, the input signal itself is corrupted, and that's outside the loop.


For your unity gain buffer here are already two possibilities: first Unigabuf:

Quote:
Originally Posted by Elvee View Post
This unity-gain follower is an audiological UFO:

It is adjustment-free, requires no thermal compensation, has no feedback, no servo, can even work with fake or reject transistors, and yet offers low DC offset and sub-ppm linearity:
UniGaBuf, a follower cut out to be a leader
Note that a prototype has actually been built and tested, it isn't pure simulation.

And here is another idea, for a symmetrical buffer:
Attached Images
File Type: gif SymBuff.gif (35.2 KB, 666 views)
Attached Files
File Type: txt BclassIq5.asc.txt (4.3 KB, 17 views)
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 21st August 2011, 09:06 AM   #167
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Hi Elvee,

thanks for all the details of the UFO ! - I will need to study further.

Back to the circlophone - my current and incomplete understanding of this topology is a little different from your explanation of it and if correct I'm afraid that you are getting IM products. It makes me wonder if this is what you were seeing in the simulations when you commented that you don't think the sims are working properly at higher frequencies. I can't confirm this at home (iMac doesn't run LTSpice), I will have to wait til I have access to a PC during the week. What I would expect to see is 3rd harmonic and above being slightly accenuated, depending on the effectiveness of the nfb, and the sound being slightly coloured,.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 21st August 2011 at 09:09 AM.
  Reply With Quote
Old 21st August 2011, 02:31 PM   #168
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by Bigun View Post

Back to the circlophone - my current and incomplete understanding of this topology is a little different from your explanation of it and if correct I'm afraid that you are getting IM products. It makes me wonder if this is what you were seeing in the simulations when you commented that you don't think the sims are working properly at higher frequencies.
No, what I mean is that there are big discrepancies between simulated and actual, measured parameters, like power bandwidth.

IM can be produced by "simple" non-linearity mechanisms, just like harmonic distortion, and by more complex, dynamic interactions.
In the case of the Circlophone, the THD figure is good, nothing to see here, and the transient behaviour is spotless, as the oscillograms given at the beginning demonstrate.

Can you explain exactly why you think the topology could generate excess IM?
Quote:
I can't confirm this at home (iMac doesn't run LTSpice), I will have to wait til I have access to a PC during the week. What I would expect to see is 3rd harmonic and above being slightly accenuated, depending on the effectiveness of the nfb, and the sound being slightly coloured,.
Since this is a balanced, symmetrical design, odd order harmonics are predominant.
In an ideal world, there would only be odd harmonics, nothing wrong there.
Now, whether you like it or not is another story: some prefer SE amplifiers for that very reason, while others go in the opposite direction with super-symmetrical amplifiers.

But all the harmonics even or odd, have their amplitudes nicely decreasing with increasing order, thus quite healthy and normal.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 21st August 2011, 03:15 PM   #169
Bigun is online now Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Quote:
Originally Posted by Elvee View Post
Can you explain exactly why you think the topology could generate excess IM?
The LTP has a good CMRR, but only to signals presented at the differential inputs. An LTP doesn't have great PSRR and so benefits from a CCS. Note the first "C" in CCS.

You are modulating the current flow through the LTP. This turns it into a simple analogue multiplier.

The sub-circuit that measures current flow through the output devices produces a signal that is predominantly twice the frequency of the input signal and so you are modulating the LTP with a current that varies at twice the signal frequency. The differential input will be modulated by it to produce the common mode output that does what you want in terms of the output stage current, but it also outputs sum and difference side-bands. The upper side band will be at three times the signal frequency, hence 3rd harmonic.

For complex music there are many different frequencies and the modulated LTP will turn them into multiple IM products. Now you may have only low levels of IM products being generated and the gnf network will reduce them but I believe they will be there nonetheless.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 21st August 2011, 06:34 PM   #170
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Quote:
Originally Posted by Bigun View Post
The LTP has a good CMRR, but only to signals presented at the differential inputs. An LTP doesn't have great PSRR and so benefits from a CCS. Note the first "C" in CCS.

You are modulating the current flow through the LTP. This turns it into a simple analogue multiplier.

The sub-circuit that measures current flow through the output devices produces a signal that is predominantly twice the frequency of the input signal and so you are modulating the LTP with a current that varies at twice the signal frequency. The differential input will be modulated by it to produce the common mode output that does what you want in terms of the output stage current, but it also outputs sum and difference side-bands. The upper side band will be at three times the signal frequency, hence 3rd harmonic.

For complex music there are many different frequencies and the modulated LTP will turn them into multiple IM products. Now you may have only low levels of IM products being generated and the gnf network will reduce them but I believe they will be there nonetheless.
It is a shunt regulated current source. And not modulated at random.
The modulation inherently includes correction for CM and PSRR. 2nd
order harmonics so created are complimentary, and cancel at output.
A highly regulated complimentariness, with a high cancellation....

In the output, I see 2nd and 3rd down -70db, with hardly anything of
high order splatter....

---------

I have seen quadrature modulators do some amazing things for the
cancellation of undesired sidebands and/or even the fundamental...
I am not certain what was fed to I and Q to make that happen, but
was controlled by a feedback of some sort... I don't think we have
even one full Gilbert cell going on here, and you would need at least
two to play those tricks. So maybe what I've seen was irrelevant.

But I do think it is meaningful that any modulation may occur in
the LTP and/or SRPP is at 90 degree angle to the fundamental.
Not mixing random things at random angles, and with both eyes
always on the result.

--------

I don't care much for EF + Schottky, as the emitter drops are still
dominant in the equation, and a blind thermal variable. If you are
using Schottky drops as an active feedback to the spreader, now
EF or anything else is fine because the hot devices are no longer
blindly operating upon their own curve.

Last edited by kenpeter; 21st August 2011 at 07:03 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 02:42 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