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

Solid State Talk all about solid state amplification.

feedforward vbe compensation in class-A
feedforward vbe compensation in class-A
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 22nd June 2004, 06:53 PM   #11
Nelson Pass is offline Nelson Pass  United States
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
feedforward vbe compensation in class-A
No way you're going to need that much voltage.
  Reply With Quote
Old 22nd June 2004, 07:07 PM   #12
HDTVman is offline HDTVman  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Chicago area
He must have instant deftness as a goal. 1 watt into headphones is very dangerous to the phones and your hearing 30 milliwatts is loud.

later BZ
__________________
What ever makes the tunes flow
  Reply With Quote
Old 23rd June 2004, 02:45 AM   #13
tifojo is offline tifojo  United States
diyAudio Member
 
Join Date: Jun 2004
Location: pasadena
I'm not planning on sitting around listening to sine waves at 126 dB. the point is, you don't need that much power continuously, but you need it to be available at low distortion for the transients. not for all music, but a big orchestra is probably at least that loud at full blast.

anyway, what's the point of having a 16 bit recording if you can only squeeze 14 bits worth out of your amplifier?

also, remember that the ears' sensitivity (and risk of damage) is highly frequency dependent. I remember reading once that 1/3 of the power in an orchestra comes from the bass drum...maybe that's exaggeration, but the basic point is that huge bass transients do exist in real life, and that none of the amplifiers most of us have ever listened to are capable of properly reproducing them. in fact, having an overpowered amplifier makes it safer for your ears, since less of the bass gets up-converted to more damaging frequencies.

plenty of people drive themselves deaf with the $.20 op amp in their walkman...

and to cope with the risk that something fails, I will of course have some protection system. I plan on actually calculating the real power delivered to the load using a current-sense resistor and analog multiplier, and shutting down the amp at a continuous power dissipation well below one watt. simple current limiting is no good, since headphones come in such a wide range of impedances. even if deafness were my goal, I wouldn't want to break my headphones!
  Reply With Quote
Old 23rd June 2004, 09:04 AM   #14
tifojo is offline tifojo  United States
diyAudio Member
 
Join Date: Jun 2004
Location: pasadena
oh, and i guess i should point out, there are probably precious few recordings for which this amplifier will have any advantage... the first couple least significant bits are probably noise anyway, and with the "level war" going on in popular music, serious dynamic range conpression is the norm.

but my feeling is, I want to design a headphone amp only once in my life, and whatever new recording technology comes along, I want it to be up to the challenge...at least power-wise.
  Reply With Quote
Old 23rd June 2004, 09:55 AM   #15
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
I think it would be a great idea to test these headphones with a standard amplifier, your favorite music, your usual listening levels and a peak detector so you can get a precise figure of the required peak output voltage
  Reply With Quote
Old 23rd June 2004, 10:33 AM   #16
padamiecki is offline padamiecki  Poland
diyAudio Member
 
Join Date: Mar 2004
Location: Krakow
Like my colleaguess I suggest to use a simple project, please concern a single bjt with a ccs as re as an emmiter follower (EF) that is steering direct from a cd player. 2Vrms from a cd is enough to drive 300 ohm through a EF?

Because the bjts like to have a large nfb maybe is it better to use a real re, not ccs, which will give 100% nfb? You will loose some damping factor which in case of 300 ohm do not seems to be important?

Probably it would be very hard to build an amp like you want and the result might be not worth of your efforts.

And please do not be afraid of the 2nd harmonic at -60dB: I hope that you will not hear it! Similar like nobody does! The worst are high order odd harmonics (5, 7, 9, 11.....) which even at -120 dB are very dangerous for making the sound unpleasant, sharp, metallic, etc...

In the end I recommend a use of a single mosfet DC coupled loaded by ccs in source follower mode. I doubt if is there something better and simpler?
__________________
regards, Pawel
  Reply With Quote
Old 23rd June 2004, 11:53 AM   #17
sreten is offline sreten  United Kingdom
R.I.P.
 
Join Date: Nov 2003
Location: Brighton UK
Hmm.......

Its a long time since I've read such tortured logic to complicate
what is essentially a very simple design problem by adding in
engineering terms non-sensible requirements.

Having said that its perfectly feasible to connect 300 ohm head
phones across a power amplifier, and there are class A power
amplifiers dersignsespecially converted for headphone use,
with much reduced standing current in the output stage.

The musings on dynamic range are risible. If a high voltage
swing amplifier is being used and you are not using its swing
much you are simply compromising signal to noise, which will
be improved by using an attentuator at the output, basically
the "old-fashioned" amplifier headphone socket method.

Concern for dynamic range is fine, inconsistent logic isn't.
IMO 106dB maximum with an inaudible noise floor is better
than 126dB maximum with an all too audible noise floor.

Concerns for transients that simply don't exist on most
recordings is also fairly pointless. The very nature of
setting CD "average" levels means they will be limited,
except for the few brave souls allowing high peak to
average levels on CD, but this by definition means
average resolution is a lot less than 16 bits.

sreten.
  Reply With Quote
Old 23rd June 2004, 01:27 PM   #18
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Hearing loss and (by reading between the lines) estimates of dynamic range requirements for "natural" sound level reproduction are covered in this article:

http://headwize.com/articles/hearing_art.htm

while I’m not noticing any obvious clipping with op amp drive capable of 8 Vrms into my HD600 I don’t find the assertion of higher peak power requirement totally unreasonable – higher power (= more than standard op amp Vswing) does seem to be a differentiating feature of high end amps designed for 300 Ohm headphones


Your output stage ramblings seem to show a lack of understanding of the Vbe distortion cancellation of a class A push-pull complementary emitter follower stage – a very basic audio output circuit – as a discrete buffer many here and at the headphone forums make a fetish of the “diamond buffer” implementation of a complementary emitter follower

stabilizing bias for a low power class A stage is simpler than for high power class AB output but there are still many choices and subtleties

Gilmore certainly agrees with the high peak power requirement and has several class A output designs, his latest:

http://www5.head-fi.org/forums/showt...t=71705&page=1

For all things headphone related you should cruise the content of both of these sites
  Reply With Quote
Old 23rd June 2004, 03:56 PM   #19
tifojo is offline tifojo  United States
diyAudio Member
 
Join Date: Jun 2004
Location: pasadena
hmmm...

Quote:
Your output stage ramblings seem to show a lack of understanding of the Vbe distortion cancellation of a class A push-pull complementary emitter follower stage – a very basic audio output circuit – as a discrete buffer many here and at the headphone forums make a fetish of the “diamond buffer” implementation of a complementary emitter follower
your offensive tone is sick, but THANK YOU.

just because I haven't ever designed an output stage, I'm not worthy of any respect? I consider output stages boring grunge, and I'd rather never have to build a power amp in my life, but whatever.

anyway, I don't have a book lying around that covers these things, so perhaps you could recommend one? I'm really sick of trying to find anything useful about power amps on google.

and what, if people had just read my original post and replied to that rather than dragging me around a tree over the voltage headroom I wanted, maybe I wouldn't end up having to ramble off?
  Reply With Quote
Old 23rd June 2004, 05:11 PM   #20
tifojo is offline tifojo  United States
diyAudio Member
 
Join Date: Jun 2004
Location: pasadena
Quote:
Because the bjts like to have a large nfb maybe is it better to use a real re, not ccs, which will give 100% nfb? You will loose some damping factor which in case of 300 ohm do not seems to be important?
for sure, you're absolutely right. but I want to try the current source too just to compare, and as long as the current source is there along with the current-sense resistor for the protection system, why not try subtracting it? it will be fun just to see.

maybe I'm going overboard on the protection system...I just don't have good specs on the thermal handling characteristics of the headphones, so I'll want to play it safe. the protection system is going to double the parts count anyway...
  Reply With Quote

Reply


feedforward vbe compensation in class-AHide 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tube Amp Compensation Q atiq19 Tubes / Valves 60 9th January 2009 07:18 AM
TubeCad Feedforward Shunt Regulator jayme Tubes / Valves 1 5th May 2007 02:55 PM
Dual voice coil for feedforward? Mr Evil Multi-Way 0 17th April 2005 03:02 PM
cascode compensation? mikek Solid State 4 10th October 2004 11:14 PM
Error feedforward - need help please. Circlotron Solid State 9 3rd June 2003 05:55 PM


New To Site? Need Help?

All times are GMT. The time now is 06:38 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki