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Balanced Drive 2 Transistor SE Class A Headphone Amp
Balanced Drive 2 Transistor SE Class A Headphone Amp
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Old 16th June 2019, 03:02 AM   #11
Dibya is offline Dibya
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xrk971 , the legendary class A man is back.


By the way , I am a electric guitar player , too be honest certain types of noise actually fills good . I have a modern class AB amp , which I don't hate but old germanium based Class A amp which I got from my granny sounds really amazing as if I am listening to some short of tube amp .
We shall remember that sound is subjective so only objective measuring can't explain whether a AMP sound's good or not . Probably you guys know guitar player generally prefers germanium fuzz pedal over silicon one .

Last edited by Dibya; 16th June 2019 at 03:12 AM.
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Old 16th June 2019, 03:32 AM   #12
Mark Johnson is offline Mark Johnson  United States
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Balanced Drive 2 Transistor SE Class A Headphone Amp
Hmm, ok, so the math is wrong (Zout of each balanced output is 10R) but nevertheless the sound is right (?). Then why even mention the math? It only distracts from the main message which, apparently, is: forget numbers, they do not match human perception.

What has happened here is, somebody focused upon SPICE simulated harmonic distortion without checking whether the balanced outputs were or were not balanced. Upon discovery that in fact they are not balanced, not even close, the goalposts begin to move. Ok.
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Old 16th June 2019, 05:37 AM   #13
xrk971 is offline xrk971  United States
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Balanced Drive 2 Transistor SE Class A Headphone Amp
When viewed with an OScope the signal splits very evenly with square waves:
Click the image to open in full size.

And with music:
Click the image to open in full size.
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Last edited by xrk971; 16th June 2019 at 05:40 AM.
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Old 16th June 2019, 09:04 AM   #14
00940 is offline 00940  Belgium
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I would worry less about thd or absolute balance (which doesn't matter much for headphones) than about the effect on frequency response of a highish output impedance into headphones. Some have a very uneven impedance curve.

Once you get through the trouble of having a pcb made, adding a few transistors into the mix is a very marginal effort/cost. So those EF mentioned sounds like a good idea to me.
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Old 15th July 2019, 03:58 AM   #15
dogears is offline dogears  Philippines
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aksa on a headphone amp - must be good!
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Old 28th July 2019, 02:31 PM   #16
diegomj1973 is offline diegomj1973  Argentina
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Excellent work xrk971 !!!

Why not try it with just one transistor? I think it can be equally as good as the first, only using a somewhat less components and perhaps more compact.

Best regards

Balanced Drive 2 Transistor SE Class A Headphone Amp-bd1tseha-jpg
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Old 28th July 2019, 02:39 PM   #17
Mark Johnson is offline Mark Johnson  United States
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Balanced Drive 2 Transistor SE Class A Headphone Amp
Horacio, take a close look at the "balance" of the 1-MOSFET circuit you posted. The output impedance of the top node (drain) is 150 ohms, while the output impedance of the bottom node (source) is [150 || (1/gm)] where "gm" is the transconductance of the MOSFET at the chosen bias current. I assume you'll bias it somewhere around 77mA , similar to the schematic in post #1. The impedances are not even close to balanced.
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Old 28th July 2019, 04:51 PM   #18
diegomj1973 is offline diegomj1973  Argentina
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Possibly, I should change the name of my circuit from balanced to unbalanced, or better yet, to floating . I should change the name of my circuit from amplifier to buffer, too . If someone tests it, you will find that it does not respond very differently to the one that starts this thread.
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Old 28th July 2019, 10:49 PM   #19
diegomj1973 is offline diegomj1973  Argentina
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In relation to the objective of reaching superlative parameters in the design of a stage of the sound chain, I have found a certain contradiction. This contradiction could occur when the possible response of the transducer is not integrated in its way of altering the waves that finally reach our ears, in the design objectives for the favorable treatment of electrical signals.

There are clear guidelines that should be achieved, regardless of how the transducer responds acoustically: how, for example, to avoid zero crossing distortion of the electrical signal, among some other possible ones.

An electrodynamic transducer can reach a noticeable rate of acoustic distortion, much higher in value than the rates of electrical distortion of today's designs.

With very simple measurements, one can easily find that the acoustic distortion of a transducer could reach values ​​of 2 to 3% in determined frequency and level of excitation, while that of an amplifier itself (for example) could be placed several orders of magnitude below , for the frequency and levels that the same transducer needs simultaneously with the previously mentioned values.

I have measured the distortion of a transducer fed with a practically pure fixed frequency sinewave signal. While the electrical signal had a distortion of 0.00031%, the acoustic distortion reached values ​​of 1.64%.

Balanced Drive 2 Transistor SE Class A Headphone Amp-woofer-sin-cancelaci-jpg

Then, I altered the distortion composition of the electrical signal to achieve a lower value of acoustic distortion in the transducer. The amplitude and fundamental frequency of the electrical signal was maintained, but its electrical distortion increased to no less than 2.66%, to reduce that produced by the transducer to only 0.23% !!!.

Balanced Drive 2 Transistor SE Class A Headphone Amp-se-al-cancelatoria-jpg

Balanced Drive 2 Transistor SE Class A Headphone Amp-woofer-con-cancelaci-jpg

It does not necessarily imply that maintaining that same composition and level of electrical distortion at other frequencies, there will always be a reduction of the acoustic distortion in the transducer (since its composition also varies frequency to frequency and with the different levels applied). In fact, I have measured the acoustic distortion at other frequencies, applying a similar fundamental amplitude of electric signal and similar spectral composition ratio (THD of 2.66%) and the acoustic distortion would seem to be reduced only in a limited frequency range, although in other ranges it could even be greater than that obtained with an almost pure electrical signal.

The point is to try to minimize acoustic distortion in zones of sensitive frequencies and amplitudes of the audible range, while possible increases in acoustic distortion can occur in less sensitive areas of the spectrum and level.

Something interesting to know is that electrodynamic transducers show spectral compositions with appreciable levels within the first components such as H2, H3 and, perhaps, some of the H4, provided that it is operated within its most linear area of ​​operation. Interestingly, the spectral composition of the electrical signal that could minimize acoustic distortion in the transducer contains almost the same spectral components (H2 and H3 or, at most, H2, H3 and some H4). That electric distortion profile could correspond to the typical of a single ended operating circuit.

Best regards
Attached Images
File Type: jpg Woofer sin cancelación.jpg (117.7 KB, 81 views)
File Type: jpg Señal cancelatoria.jpg (115.6 KB, 81 views)
File Type: jpg Woofer con cancelación.jpg (116.2 KB, 82 views)

Last edited by diegomj1973; 28th July 2019 at 11:05 PM.
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Old 29th July 2019, 01:33 AM   #20
xrk971 is offline xrk971  United States
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Balanced Drive 2 Transistor SE Class A Headphone Amp
Quote:
Originally Posted by Mark Johnson View Post
Horacio, take a close look at the "balance" of the 1-MOSFET circuit you posted. The output impedance of the top node (drain) is 150 ohms, while the output impedance of the bottom node (source) is [150 || (1/gm)] where "gm" is the transconductance of the MOSFET at the chosen bias current. I assume you'll bias it somewhere around 77mA , similar to the schematic in post #1. The impedances are not even close to balanced.
You know Mark, you don’t need perfectly balanced impedance on the two halves to have pretty darn good balanced output signals as anyone can see from this OScope screenshot. Also, the slight imbalance imparts a more pleasing second harmonic signature as shown in the FFT.

Balanced Drive 2 Transistor SE Class A Headphone Amp-eabc8488-72a1-4a56-9723-d312c6635f51-jpeg
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File Type: jpeg EABC8488-72A1-4A56-9723-D312C6635F51.jpeg (475.2 KB, 239 views)
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