So just how "good" can a chip amp be ? - Page 8 - 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 27th March 2010, 04:43 PM   #71
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
Quote:
Originally Posted by a.wayne View Post
I wantie , wantie want ....... tell me more , interesting it current limits very early and yet can still drive a 1 ohm load, anymore details , i know off topic , but i'm very interested and would like to take a look and yes the ribbons will need a lot more than 50 watts, i currently pop 10 amps fuses ( speaker side) from time to time, when i do get carried away with the sound ...

Couldn't you parallel enuff chips to increase the power ? I know 7 amps would not be enuff i had to go to a 10 amp from a 8 amp fuse to stop blowing the fuses.

Hello the tube,

Well that would be "people " who can't evaluate what they hear so they have to see . A double blind test would not have made a difference, I can hear the difference between amplifiers, et al .
There are ways to parallel the amps but I have not perfected any particular circuit. Please recall I use the chip amp in a composite amplifier circuit which causes different behavior than just the chip alone. 2 in parallel should give more current for sure- maybe as much as double. Which might be enough for you. What is the resistance of the ribbon?

I agree on the double blind test having done a lot of those and not blinded test also. There are lots of people who cannot select a particular amplifiers sound without seeing the amp first and yet quite a few people that can tell from a different room which amp it is never even seeing the speakers or the operator. I happen to be the later and know plenty of both kinds of listeners.

The logical error of generalization says taking something which applies to a group and then applying that generalization to a specific person. This is not a valid action which is what "tube" has done.
__________________
What the other guy said----Standing on the shoulders of giants.
New avatar- no more little array
  Reply With Quote
Old 27th March 2010, 04:58 PM   #72
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
Quote:
Originally Posted by analog_sa View Post
I can certainly see that more OLG and more feedback translates into lower harmonic distortion. Does this in any way correlate to better sound? THD is pretty low in chip amps anyway. Are you eager to follow into the footsteps of Jap designers from the seventies?

Damping factor? Can you give a numerical example? Are you using superconductors for your speaker cables?

As far as the current goes i have no objection to the datasheet rating but why do these amps fail completely with some speakers? SPike protection?
I have two sets of speakers which play with less stress, more dynamics and better bass when powered from a 15W tube amp than a 68W chipamp with a monster PS.
Jap designers generally follow what was done by the founder here in that era and not the other way around.

I do use terminated 8 ohm impedance speaker cables which have been shown to be more satisfactory for many reasons including damping.

Yes I agree the 3886 by itself is a decent amp but not what I would call anything like high end class with a Goldman or FM acoustics and is quite variable in performance. For my style of testing the 3886 is not all that stable requiring an RC and an inductor on the output to stabilize it so outright oscillation does not occur. Any amp that requires this kind of band-aid to be stable is unpredictable in sound from all my experience. The composite amp version does not need band-aids and one thing for sure bass is a rock and plays with the best bass amps there are by all others accounts. So we do agree about the sound and the composite amp is the solution providing sound and bench results much better than the 3886 alone.

Several have ask and will be firing one of these little guys up for measuring low power specifications soon. If anyone wants me to measure any particular spec on the composite 3886 amp let me know exactly what you want and I will add it to the test list and post the results when complete.
__________________
What the other guy said----Standing on the shoulders of giants.
New avatar- no more little array
  Reply With Quote
Old 27th March 2010, 10:21 PM   #73
diyAudio Member
 
Join Date: May 2008
Quote:
Originally Posted by a.wayne View Post
i currently pop 10 amps fuses ( speaker side) from time to time,
Quote:
Originally posted at http://www.tradebingo.com/1pekingroa...e&orderby=desc post #147
The Maggies have been designed to feature a purely resistive and ruler straight impedance curve so theoretically speaking at least, the impedance does not drop, like many other dynamic speakers do, on either end of the frequency spectrum. The thing that goes wrong is the speaker frame. It is not strong enough to withstand the shrinkage inflicted by the grille cloth (our diehard planar freak, thekong, had his T4 stripped naked and he has never had the same problem). As a result, the frame becomes bent from both sides, thereby lifting the magnets away from the Mylar film where the “voice coil” lies. Magnetic field reduces dramatically over distance and hence what we may have is a near short-circuit when situation gets real worse.

Since the Mylar (the mid and bass panel) is reluctant to take 98% of the load, the ribbon, being a separate entity hooked via the crossover, has to suffer to take all the power imposed. When bass becomes inevitably lean as a result of the warping, people tend to turn the volume up further, making the situation even worse. This explains why old Maggies tend to burn their ribbons or fuses frequently.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 27th March 2010, 11:45 PM   #74
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
the 2 main technical reasons I see to be suspicious of chip amps are;
with the output devices and the input diff pair on the same Si there is thermal coupling which can give distortion with large signals
and for efficiency sake they use relatively low bias Class AB output stages so nonlinearities near crossover should be expected to cause distortion at low signal levels

composite amplification with a quality audio input op amp with feedback wrapped around the chip amp can pretty much eliminate any thermal and low loop gain/psrr distortion concerns, if you can successfully manage the compensation challenge

the crossover distortions can be reduced by biasing the output stage with a "crossover displacement" ccs of several hundred mA or by paralleling 2 chip amps with a Voffset and small current sharing output R to get Class A push-pull (or "heavy" AB) bias to assure low level linearity

combining both techniques should result in hard to measure distortion performance, if RFI/EMI rectification/breakthru is prevented with good RF design and filtering there is little reason to believe audio frequency performance could be meaningfully audibly bettered by any technology within the I,V limitations of the chip amps used - at least if your goal is truly "high fidelity", "wire with gain" vs a "musical" amp with "euphonic distortions"

Last edited by jcx; 28th March 2010 at 12:09 AM.
  Reply With Quote
Old 28th March 2010, 06:22 AM   #75
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
i had the same idea of using 8 to 16 lm3886's or lm4780's in a parallel and/or BPA configuration to direct drive some diy ribbons.
I had gotten 5 lm4780 samples from N.S. before they even hit the market and was going to get 5 more just for that purpose,sadly i never did anything with them yet.
I'm still considering the project for my esl's with dipole subs.
the design requires an amp that can handle a 1ohm load and still swing 30v to 40v.
16 of them in a BPA should be able to come close.
These are some maxium estimated figures and not definite as they won't be running that level 24/7 but the 1 ohm figures are relisitic and I was considering a composite configuration for stability and lower distortion.
I'm also planning a micro minnie apogee dueta replica for my desktop computer speakers as i have the real ones to model from.
Just turning up the heat on some back burner projects as I've got a whole lot more! jer
  Reply With Quote
Old 28th March 2010, 07:00 AM   #76
diyAudio Member
 
Join Date: May 2008
Quote:
Originally Posted by jcx View Post
the 2 main technical reasons I see to be suspicious of chip amps are;
with the output devices and the input diff pair on the same Si there is thermal coupling which can give distortion with large signals
and for efficiency sake they use relatively low bias Class AB output stages so nonlinearities near crossover should be expected to cause distortion at low signal levels
Quote:
Originally Posted by jcx View Post
combining both techniques should result in hard to measure distortion performance,
At large signals human hearing becomes less sensitive to distortions. At low levels distortions will be masked by ambient noise or be unperceivable even if they are easy to measure.

Are you sure that your techniques won't only trade certain distortions for others instead of reducing them?

Two parallel chipamps with DC offset and small current sharing output R give push-pull class A? All I would expect, are hot chipamps and resistors.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)

Last edited by pacificblue; 28th March 2010 at 07:03 AM.
  Reply With Quote
Old 28th March 2010, 08:47 AM   #77
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Quote:
Originally Posted by jcx View Post
the 2 main technical reasons I see to be suspicious of chip amps are;
with the output devices and the input diff pair on the same Si there is thermal coupling which can give distortion with large signals
What distortion mechanisms are caused by temperature? The ones I've seen has been caused by non-optimal bias due to too low temperature.

There are ways - with proper layout - to ensure that thermal gradients won't impact the input pair. Or it will impact the two sides of the input pair equally, thus, show up as common mode -- suppressed by the input pair. Furthermore, the thermal system bandwidth is incredibly low (on the order of mHz) so any variation in temperature caused by the output pair is not likely to be linked to the signal frequency, hence, won't show up as a distortion product.

~Tom
  Reply With Quote
Old 28th March 2010, 05:49 PM   #78
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
actually there can be several thermal effects - the symetric/quad diff pair layout does greatly reduce Vos modulation effect, but Hfe of all of the transistors are temperature sensitive, VAS and Output will have gain modulation – look for Bob Pease “output modulation” article

thermal time constants in the Si chip are much faster than the package-heatsink and can be in the low audio range

looking at SMTE or other low+high frequency IMD with heavy loads usually reveals likely thermal caused errors

some additional power related errors can come from the shared supply pins with the output devices heavy currents giving ps common impedance coupling to the earlier amplification circuitry

using a lower noise input op amp in a separately supplied, physically separated package, closing a outer feedback loop around the power chip amp avoids multiple error mechanisms

the classic "bad high feedback" amplifier perception may date from 70's amps boasting low % THD - with full scale output, but under-biased outputs may have given large % distortion at lower, common listening levels
Today designers with as diverse opinions as Bob Cordell, John Curl and Nelson Pass (Pass goes Class A mostly now days) here are proposing very high output device bias in discrete amps - 100s of mA - why wouldn't we try that with chip amps as well? Dr Geddes - of the GedLee distortion metric advocates testing amps for nonlinearity at very low levels

Class A output stage bias does avoid several distortion mechanisms, in exchange for efficiency - even Douglas Self agrees - the question is only whether the trade off is "worth it"

I have biased "chip amps" (LM6172, TPA6120, LT1210) into full Class A for headphone amp use

this sim shows the push-pull bais principle:

Click the image to open in full size.

from:
AD8397-class A? - Page 2 - Head-Fi: Covering Headphones, Earphones and Portable Audio

I know these techniques can reduce measurable distortion to -160 dB (indirect IMD test, extra gain and long averaging) with my op amp circuits driving 32 Ohm loads, similar results shoud be available to power chip amp builders

I don't know if these techniques are "necessary" - but the effects they address are real and the solutions I propose do reduce these distortions in the output rather than just "rearrange" them

Last edited by jcx; 28th March 2010 at 06:03 PM.
  Reply With Quote
Old 28th March 2010, 06:49 PM   #79
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by pacificblue View Post

Quote:
Originally Posted by a.wayne View Post
i currently pop 10 amps fuses ( speaker side) from time to time,
Quote:


Originally posted at http://www.tradebingo.com/1pekingroa...e&orderby=desc post #147
The Maggies have been designed to feature a purely resistive and ruler straight impedance curve so theoretically speaking at least, the impedance does not drop, like many other dynamic speakers do, on either end of the frequency spectrum. The thing that goes wrong is the speaker frame. It is not strong enough to withstand the shrinkage inflicted by the grille cloth (our diehard planar freak, thekong, had his T4 stripped naked and he has never had the same problem). As a result, the frame becomes bent from both sides, thereby lifting the magnets away from the Mylar film where the “voice coil” lies. Magnetic field reduces dramatically over distance and hence what we may have is a near short-circuit when situation gets real worse.

Since the Mylar (the mid and bass panel) is reluctant to take 98% of the load, the ribbon, being a separate entity hooked via the crossover, has to suffer to take all the power imposed. When bass becomes inevitably lean as a result of the warping, people tend to turn the volume up further, making the situation even worse. This explains why old Maggies tend to burn their ribbons or fuses frequently.





.

Not for me , i don't have maggies , I had listened to a Pr of maggies! I'm running a direct drive 3 way ribbon 1.2 z min and do pop 10 amp speaker fuses when listening spirited ...
  Reply With Quote
Old 28th March 2010, 07:22 PM   #80
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
Quote:
Originally Posted by jcx View Post
actually there can be several thermal effects - the symetric/quad diff pair layout does greatly reduce Vos modulation effect, but Hfe of all of the transistors are temperature sensitive, VAS and Output will have gain modulation – look for Bob Pease “output modulation” article

thermal time constants in the Si chip are much faster than the package-heatsink and can be in the low audio range

looking at SMTE or other low+high frequency IMD with heavy loads usually reveals likely thermal caused errors

some additional power related errors can come from the shared supply pins with the output devices heavy currents giving ps common impedance coupling to the earlier amplification circuitry

using a lower noise input op amp in a separately supplied, physically separated package, closing a outer feedback loop around the power chip amp avoids multiple error mechanisms

the classic "bad high feedback" amplifier perception may date from 70's amps boasting low % THD - with full scale output, but under-biased outputs may have given large % distortion at lower, common listening levels
Today designers with as diverse opinions as Bob Cordell, John Curl and Nelson Pass (Pass goes Class A mostly now days) here are proposing very high output device bias in discrete amps - 100s of mA - why wouldn't we try that with chip amps as well? Dr Geddes - of the GedLee distortion metric advocates testing amps for nonlinearity at very low levels

Class A output stage bias does avoid several distortion mechanisms, in exchange for efficiency - even Douglas Self agrees - the question is only whether the trade off is "worth it"

I have biased "chip amps" (LM6172, TPA6120, LT1210) into full Class A for headphone amp use

this sim shows the push-pull bais principle:

Click the image to open in full size.

from:
AD8397-class A? - Page 2 - Head-Fi: Covering Headphones, Earphones and Portable Audio

I know these techniques can reduce measurable distortion to -160 dB (indirect IMD test, extra gain and long averaging) with my op amp circuits driving 32 Ohm loads, similar results shoud be available to power chip amp builders

I don't know if these techniques are "necessary" - but the effects they address are real and the solutions I propose do reduce these distortions in the output rather than just "rearrange" them
SO has anyone tried a class-a lm3886's or lm4780's chip amp
  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
"Mr. ED" Non-Inverting monobloc chip amp group buy. Russ White Group Buys 25 1st May 2010 08:14 PM
"toy" Chip amp Fast1one Swap Meet 0 5th October 2007 11:01 PM
The "Cheap, but good" rectifier & diode thread. Spasticteapot Parts 8 21st March 2006 02:44 AM
Is this "el cheapo" Velleman100wRMS kit good enough for a subwoofer amp? Spasticteapot Solid State 5 17th March 2006 09:09 AM
Hybrid "SE Tube Amp Sound Style" Chip Amp idea ThorstenL Chip Amps 24 7th February 2003 06:41 AM


New To Site? Need Help?

All times are GMT. The time now is 09:47 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