My "audiophile" LM3886 approach - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 1st April 2005, 02:53 PM   #21
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Quote:
Originally posted by macboy
This is the most original design that I have ever seen on this forum. This forum needs more innovation like this; the last thing that we got excited about was putting a freakin' snubber in the power supply (like nobody has ever done that before).

Quite an interesting and original topology. Yes we need more of that on this forum.

On the other hand implementing something so simple as the snubbers with such a great positive effect on the overall sound (using bigger PS caps) deserves getting exited about. I think the goal should be a good quality reproduction and as far as I'm concerned, the simple the topology the better. One thing I don't want to see is unnecessary stuff thrown in an amp just to make the circuit look sophisticated (this is not the case with the amp discussed in this thread).

Bottom line, if a resistor placed in a right place improves the performance of the amp as much as adding a preamp, then I'm exited about the implementation of the resistor more than by the implementation of the preamp.


Good work Mauro! And your English is fine too. Keep on talking!

Greg
  Reply With Quote
Old 2nd April 2005, 11:35 AM   #22
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Quote:
Originally posted by maupenas
Hi Andypairo,

The LM318 choice it's extremely determinant (for my). I have tested various OP-amp (NE5534, OP27, TL081, TL071 ecc...), but the audio performance (compareted a class A amplifier) are superior.
An other motivation is that the slew-rate of this OPAMP is suited to this application (or all final amplifier device )
Ok. Did you try the well regarded OPA627 and similar from BB?

Quote:
I am not able to explain shortly the theme of the topology ( in English ).
I understand Italian quite well
I can help yopu with the translation if you want but I think that you are clear enough.

Quote:
In brief, say that this type of amplifiers "feelses" the load that in minimum departs comes to be part of the feedback network, on account of the presence of the bridge in exit (or an other high impedance current driver).
[/B]
I've done too much programming lately... must give a look at my electronics books...

Quote:
No tuning problem (for you, and this schematic).
The recommendation it's a good bypass and short length of
a input network on LM3886 . I have built all the circuit a 100*160mm card, (as in the photo), and abundant stagnated all power copper track.
If have a oscillations problem, increase C33,C34 on 110 or 120 pF.
If to is not enough, added C31,c32 sperimentaly, (1- 3,3 pF).

ciao

Mauro Penasa [/B]
So another project on queue....
Where do you live? I'd like to hear the baby singin'

Cheers

Andrea
__________________
I don't believe in audiophile components - except when I can get them at frugal-phile(tm) prices
  Reply With Quote
Old 2nd April 2005, 12:41 PM   #23
Giaime is offline Giaime  Italy
diyAudio Member
 
Giaime's Avatar
 
Join Date: Oct 2004
Send a message via MSN to Giaime
Good! See.... italians just do it better...


(in Gainclones at least)


If my beliefs are confirmed, this is gonna be the most advanced and good sounding LM3886 implementation. Let's hope it sounds well... and it's not so dependant on expensive op amps!

Ciao a tutti e buona fortuna... Continuate così!
  Reply With Quote
Old 2nd April 2005, 01:08 PM   #24
diyAudio Member
 
Join Date: May 2005
Location: TN
I believe that will like you so as it is. Nothing forbids to try other solutions, but my suggestion is to do it if dispose of suitable tools.
I not have tested OPA627.

I have led by departs JLH 69 and other "clones" for this, but the tastes are taste.

The theoretical treatment do it only if like you the result.


Ciao

Mauro Penasa
  Reply With Quote
Old 4th April 2005, 04:35 PM   #25
diyAudio Member
 
Join Date: Jun 2004
Location: Alpes
Hello Maupenas,

Can you provide basic principles of your speaker protection circuit?

Regards,
Yoghourt
__________________
Dzharis: raaaaaah lovelyyyy!
  Reply With Quote
Old 5th April 2005, 12:38 PM   #26
diyAudio Member
 
Join Date: May 2005
Location: TN
The Voltage +VRL it's about +24V.
At start up C12 it' s discharge and determined (with R14 charge current) the ON-time delay. At VB Q1 >1,2V the darlington (Q1&Q2) close the Output relay.
If at Ampli out it's present a positive tension with time- costant > several mS (integrated on C19-R42 or R41) and Voltage > 2V (about),
Q3 discharge C12 and Relay are Open. If the status return at 0VDC, C12 are recharge with delay.
If a negative tension are present at ampli out, C12 it's discarge (from R44 or R43 and Q1 base potential are about 0V (or some negative mV) so, Relay it's off.
The Low value of C13 disable immediately the relay on power off state.

Ciao

Mauro
  Reply With Quote
Old 5th April 2005, 03:32 PM   #27
GregGC is offline GregGC  Canada
diyAudio Member
 
Join Date: Oct 2003
Location: Toronto
Quote:
Originally posted by maupenas
The Voltage +VRL it's about +24V.
At start up C12 it' s discharge and determined (with R14 charge current) the ON-time delay. At VB Q1 >1,2V the darlington (Q1&Q2) close the Output relay.
If at Ampli out it's present a positive tension with time- costant > several mS (integrated on C19-R42 or R41) and Voltage > 2V (about),
Q3 discharge C12 and Relay are Open. If the status return at 0VDC, C12 are recharge with delay.
If a negative tension are present at ampli out, C12 it's discarge (from R44 or R43 and Q1 base potential are about 0V (or some negative mV) so, Relay it's off.
The Low value of C13 disable immediately the relay on power off state.

Ciao

Mauro

Mauro,

The time constant for the negative DC-ON seam kind of high to me. R44xC12=82kx100u=8.2sec. I know the actual reaction time is shorter but still looks quite slow. I may be missing something of course.

Greg
  Reply With Quote
Old 6th April 2005, 10:58 AM   #28
diyAudio Member
 
Join Date: May 2005
Location: TN
Hi, Greg

Your observation is near, but...

My description is a lot of fast, and non exact (sorry). With the components used in the circuit the threshold of intervention is +5,5VDC @ 0 , 5 sec. and -5, 5V @ 2 sec. The motive is that C12 discharge of 0,3V to stop the relay. Naturally modifying R44 R43 R42 R43 gets the constant and the threshold that is prefered.
Affair remembers that the speed of various intervention to the increase of the tension, and if an ending is spoiled usually in exit there are about tens of volt. In this conditions the intervention becomes < 0,5 sec. even on the negative thing.
Obviously this circuit not doesn't want be an absolute reference, and it is in my scheme because much compacts ( all the circuit is on a 100160mm card ). In the use daily paper has not given never problems and the breakdowns of the prototypes have not damaged never my loudspeakers.

Ciao

Mauro
  Reply With Quote
Old 6th April 2005, 12:54 PM   #29
diyAudio Member
 
Join Date: Dec 2004
Location: gran sasso
Mauro,

I'm highly intrigued by your design, and would like to understand a bit better.
All designs are a kind of compromise. So there are strong / weak points in all. While I was thinking of it, some weak points came to my mind. If you don't mind, I would list them, so you can tell the reasons behind your tradeoffs.

You are right when saying that the feedback loop impedance characteristics are important for an opamp design. This is where the original Gaincard concentrates, also. It is using low impedance & very short feedback loop. It's impedance seen by the -pin is ~ 600 ohm. The +pin, in an optimal case, when driven by an external pre, or a Cd output, is supposed to see a dynamic impedance of a couple of hundreds ohm, also. So I would say, it is quite balanced for both the inputs. The low impedance input & feedback network is decreasing the input capacitance effects, the input bias current effects. It is decreasing the feedback loop phase shifts to a possible minimum.

The common mode signal showing up at the input is ~30 dB below the output signal level, which is not a small advantage.

In your design the impedance seen by the input pins is precisely equal, 5 kohm for each input. But ~ 8 times higher, than in case of the Gaincard. So the input capacitance & bias current & phase shifts are worse ~ 8 times.

The Common mode signal present at the inputs is half of the output signal! that's 24 dB worse than the Gaincard case!

What I wanted to say with this is that the LM3886 has to work harder in your setup. So it distorts more than in a gaincard case, though this will be compensated for by the extra open loop gain added by the lm318.

The LM 318 is a fast opamp, but then for stability, you have to slow it down, quite heavily. [A side note: you say it's important to have a high slew rate opamp here, though it's output swing is strongly limited, only a few tens of millivolts - though I understand what you want to say here - an opamp's slew rate is determined by it's INPUT circuitry, and we need a fast diff. amp. Hm, I see, though the output voltage is low, the output current for the LM318 is not so low - and its output impedance is open loop for low frequencies ]
So I suppose that the overall speed of the full circuit is lower than that of the Gaincard alone, again.

What you gained in the process is that the open loop overall gain is much higher, so after global feedback you have less distortion;
The output current is buffered from the input diff. amplifier which provides the error signal;
It is possible to use an input opamp with very good input characteristics.
The final product is a high feedback, low distortion, low output impedance voltage amplifier with ~ 30 dB gain.
It seems to me that this is quite against the tendencies presently followed - which is giving up some gain thus lowering the feedback & extending the open loop gain bandwidth, as much as possible.

What I don't see is how this internally applied current buffer would help more, then a common unity gain buffer, or a buffer with some gain?

Ciao, George
  Reply With Quote
Old 6th April 2005, 04:40 PM   #30
diyAudio Member
 
Join Date: May 2005
Location: TN
Hi,Joseph K
your questions are complex, but not don't want give too complex answers.
Gather the things.

Thing is this circuit:

LM3886 is a power bridge Voltage/current.
The fact that with the acquisition values has a behaviour similar to a "Voltage Gain Amplifier"
not change the dynamics of operation, that is different.
the parameters of project are:

Iout = ( R55*Vin)/( R5*R3) ( Vin is the U1 exit ).*

Rout= R3*(R6/%error) ( R6=R55=R5=R8 and %error = tolerance value among the res.)*

With the values of the circuit, and R6 R55 R5 R8 = 1 % matching,the impedance of exit of the bridge is about 1 ohms
and it develops 100 A/V ( then the pilotage is little ).

LM318 it's the drive to the bridge and checks the differential tensions.

This circuit it may consider a variation of " dumping current " ( current power & control voltage ).
to the test, this topology is a lot of effective to check the crossover distorsions that increase when decreasing load )
across the global neg. feedback ( and sound it's good ).

The motive for which have chosen a double invert. is in the greater stability of the 2 OPamp
in this configuration, primarily on account of the exploitation of the input capacity.

LM318: Excellent integrator/comparator ( see the datasheets ). probably the better thing, to this price,
if it comes used with this technique of the signal on the " ground virtual " (-IN).
Other choices: Theoretically ( and practically ) are able use other OPamp to low noise and better DC chars.
To depart the final audio evaluation ( I love LM318 "valve" sound ),
has to consider a suitable high frequency gain margin, and phase, to maintain
stable all. This circuit is the result of a serious long of experiments, among the like some on
techniques of feedforward one's own about to this OPamp (not used).
Then there is the fact that the 100A/V value has been definite only after different technical tests and of listening.
Initially ( and even you praies if want try, is enough lead till 0,1ohm on R3) this value are very smaller.
Besides there is the fact that the loss of profit of IC1 high frequency does works hard of more U1.

Close gain loop, ecc feedback...: closing the ring all is born...
Personally I am not afflicted by paranoias on the negative feedback. How to all the things it can be good or bad. in my case this is rather tall, but
the particular configuration me allows to use it to reduce the distorsion without altering the acustics performances
that to like me, and the margin of drive of U1 helps me to me defend from IMD problem.

Conclusions: a 50W/8ohm Amply, 0,002% THD medium all band (the FFT show traces of the distorsion of the generator, that to 10Khz is 0,0040 %), sound good.

Ciao

Mauro

*National Semi. Applications
  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 05:12 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