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

Headphone Systems Everything to do with Headphones

Different headphone amps
Different headphone amps
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 September 2020, 10:06 PM   #21
duncan2 is offline duncan2  United Kingdom
diyAudio Member
 
Join Date: Mar 2013
Location: Scotland.
Yes the LM4562 has got impressive figures but those types didn't impress D.Self .
I see what the rejection values are for it but that wouldn't stop me fitting PSU suppression components to it, I am a "belts & braces" man , it comes down to -- does it sound good to ME -- and that is the ultimate test not a THD meter reading of over 100db.
  Reply With Quote
Old 28th September 2020, 08:39 PM   #22
Antoinel is offline Antoinel  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Different headphone amps
Thanks duncan2 for your post. I fully agree with you.

The application understudy is a test method for PSRR. The attached schematic shows:

1. LM308 [U2] is the application understudy. It generate two out of phase output signals; namely Vout [VSA] and Vout [CSA].

2. The signal Vout [CSA] is a "disturbance" on both rails of +/-15 V PSU. It has magnitude and phase.

3. This disturbance causes a change in [U2's] Vout [VSA]; per the definition of PSRR; but I can't measure it at this location.

4. This same disturbance is seperately imposed on the rails of an independent LM308 [U1]. It is idle. The LTSpice model shows an emerging output voltage [Vout PSRR]. It has amplitude and phase. This method is fully applicable to a dual [or true twin] OpAmp like NE5532.

5. 20 Log {Vout [VSA]} divided by {Vout [PSRR]} is a calculated PSRR at 10 KHz. The resultant value is 60 dB.

6. The two signals in point 5 are in phase; but with a phase shift per LTSPice.

7. But suppose the two signals in point 6 are in-phase. This creates or is an internally-induced positive feedback. A possible cause of oscillation if excessive; but maybe beneficial in its abscence if low or moderate.

NB.
Vout [VSA] and Vout [CSA] are correlated and out of phase. They are a balanced pair of outputs which are suitable to drive bridge amps.

Best
Anton
Attached Images
File Type: png Mono uAmp PSRR.png (36.7 KB, 127 views)
  Reply With Quote
Old 4th October 2020, 05:03 PM   #23
Antoinel is offline Antoinel  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Different headphone amps
Default A Simply-Balanced Stereo Headphone Amp

The attached image shows the prototype's schematic for one channel and its Spice model; which runs smoothly.

Please note the following:

1. This HA has independent +/- 12 to 15 V PSUs. Their regulation in my application is not needed. This PSUs' independence favourably affects channel separation.

2. The stereo phones are independent of each other. They do not share a common/ground. Please recall I had cut the plug on my Grado Labs [SR80] and separated their leads. This favourably affects one's preferred perception of H2; do you like +H2 or -H2? Reversing the leads of each phone will give the opportunity to sample H2.

3. The stereo proto HA uses two NE5532s. One per channel. Sounds superb.

4. I have another application for the idle twin OpAmp in each channel .

5. Spice model says one can increase the value of the balancing resistors [330 Ohms shown] to 10 K each. More output power goes to the phone.

6. The OpAmp inverts phase. Gives one the opportunity to balance volume level between L and R phones. This is done by slight changes in the unity gain of one [say L ch] relative to that of [R ch].

7. The OpAmps can also be operated non-inverting without problem.

Best
Anton
Attached Images
File Type: png OpAmp Balanced HA.png (37.3 KB, 115 views)
  Reply With Quote
Old 14th October 2020, 03:19 PM   #24
Antoinel is offline Antoinel  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Different headphone amps
The OpAmp power rails did not have decoupling caps [e.g. 0.1uF] in my last posted schematic. They suppress high frequency oscillations [>100 KHz.]

The attached schematic is an LTSpice model which shows the effect of one decoupling cap [0.1uF] at Vo [current source]. The sampling frequency is 10KHz instead of 1 KHz. The resultant behaviour is a low pass filter for/at the power rails

1. Vout [current source] is reduced in amplitude relative to that at Vo [voltage source].

2. Vo [current source] is phase-shifted relative to Vo [voltage source].

One may get away with lower-valued decouple caps.

I used the learnings todate on a 75 W/ch [8 Ohm] discrete power amp module by Radio Shack [STA-2000D]; vintage 1979. I have its schematic. Here's the experiment and subjective outcome.

1. It retained the decouple caps [0.11 uF] at its power rails [+/-45 V] to ground. Without them, the amp oscillates. May remind of the residual oscillation at the output of Class D; high enough to be irrelevant.

2. Cut the PCB around electrolytic caps [100 uF] connecting Vo[current source] to ground. They'll bypass power to ground!.

3. The amp is stable, no trace of oscilation, and it idles a +/- 70 mA.

An 8 loudspeaker [Karlson] was connected as shown in the attached schematic. It sounded great, loud and clear.

The take-away messages are:

1. Adaptable to low power discrete OpAmps.

2. Scalable for high power integrated amps e.g. LM3886.

3. Audio signals on the power rails constitute a possible added global feedback [- or +] to the stages preceding the power output stage. Granted their circuits ingest this feedback.

Best
Anton
Attached Images
File Type: png OpAmp Balanced HA plus.png (41.1 KB, 84 views)
  Reply With Quote
Old 25th October 2020, 08:25 PM   #25
Antoinel is offline Antoinel  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Pennsylvania
Different headphone amps
Default Simple Operational-Headphone Amp

The attached schematic is for the subject discrete prototype.

Notables are:

1. Fully satisfactory sound. Does not hum, buzz or whistle.

2. The elements enclosed with rectangles are essential for stability against oscillation.

3. Avoided using constant current sources [CCS], and active loads [AL]. The power output [Vout-] is fully available as additional possible global feedback to all of the amp.

4. Disconnect the 47 pF cap to run its Spice model. Its harmonics look great.

It can be upgraded with the traditional [CCS] for the input diff amp, and with an [AL] for the last voltage amp instead of its 4.7K. But it works fine without these established enhancements.

Best
Anton
Attached Images
File Type: png Operational HA.png (49.6 KB, 35 views)
  Reply to this post

Reply


Different headphone ampsHide 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
headphone amps for use with mobile laplace Headphone Systems 5 27th December 2016 04:11 PM
Popularity of 2A3/45 headphone amps daysman Headphone Systems 7 26th September 2016 09:08 PM
FS : 2x headphone amps pinnocchio Swap Meet 16 30th January 2015 04:03 AM
headphone amps vs headphone inputs? awangotango Headphone Systems 7 13th October 2012 01:36 AM
DIY headphone amps - Gilmore? seroxatmad Headphone Systems 1 26th December 2006 05:33 PM


New To Site? Need Help?

All times are GMT. The time now is 05:26 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki