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Old 15th May 2019, 11:51 AM   #1
Nico Ras is offline Nico Ras  South Africa
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Default Balanced Headphone Amplifier

The below headphone amplifier was constructed using my current amp's two channels combined into a balanced class A amp.

This configuration simulated indicates odd harmonics to be dominant and monotonic and even harmonics to be much lower but constant in character.

The bandwidth is way into the MHz region and phase remains almost entirely at zero being unconditionally stable. Harmonics shown are for 100kHz fundamental just for interest.

This is my first experience of a class A amp that sound crisp as opposed to warm.
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Last edited by Nico Ras; 15th May 2019 at 11:58 AM.
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Old 15th May 2019, 03:48 PM   #2
Mark Tillotson is offline Mark Tillotson
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DC offset might be an issue unless those 33 ohm resistors are tightly matched.
The BD140 GB product is 3MHz, so how does your sim. have gain at 10MHz?
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Old 15th May 2019, 04:18 PM   #3
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Quote:
Originally Posted by Mark Tillotson View Post
DC offset might be an issue unless those 33 ohm resistors are tightly matched.
Still although 33Ω are matched, transistors may not be, or only in a small range of temperatures, so I adhere to the idea of DC offset difficulties.
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Old 15th May 2019, 05:47 PM   #4
Nico Ras is offline Nico Ras  South Africa
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Thanks for your comments. The unit that I am fooling around with has decoupling caps and the offset is of no concern.

The attached was the schematic straight from MicroCAP10 schematic capture and models are from a reputable source. (there is a photo amp that I am trying the concept on).

I am specifically interested in the power density distribution of the odd order harmonic content compared to the even order. The flatness of both frequency and phase response is interesting.

Would you care to comment on why there is virtually no even harmonics, maybe you have some mathematical explanation that you may want to share in this regard.
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Old 15th May 2019, 06:00 PM   #5
Nico Ras is offline Nico Ras  South Africa
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Sorry, I forgot to give my dues to Hugh Dean who was instrumental to the original single ended topology. It still is my everyday listening HP amp since it was conceived in 2008, but bringing two halves together in a differential arrangement changed the audio experience completely.
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Old 15th May 2019, 06:20 PM   #6
Nico Ras is offline Nico Ras  South Africa
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Quote:
Originally Posted by Mark Tillotson View Post
DC offset might be an issue unless those 33 ohm resistors are tightly matched.
The BD140 GB product is 3MHz, so how does your sim. have gain at 10MHz?
fT= 160MHz typical as per Philips, the original manufacturer of this transistor. BD140-16 datasheet(3/8 Pages) PHILIPS | PNP power transistors
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Old 16th May 2019, 08:11 AM   #7
Nico Ras is offline Nico Ras  South Africa
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I have changed the schematic to a balanced complementary symmetry topology and found that the distortion takes on a completely different characteristic. Anyway guys, this was just sharing an idea with you nothing noteworthy really. C18 should not be there. It was an afterthought only and the sim is without it.
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Last edited by Nico Ras; 16th May 2019 at 08:16 AM.
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Old 16th May 2019, 10:41 PM   #8
Mark Tillotson is offline Mark Tillotson
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fT= 160MHz typical as per Philips, the original manufacturer of this transistor. BD140-16 datasheet(3/8 Pages) PHILIPS | PNP power transistors
Very much at odds with this datasheet which says 3MHz (but at 0.5A, not 50mA): http://download.maritex.com.pl/pdfs/sc/BD140.pdf


Perhaps the 0.5A rating is saturated switching, not linear region? Or perhaps the 160MHz figure is common-base, not common emitter?

Last edited by Mark Tillotson; 16th May 2019 at 10:45 PM.
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Old 16th May 2019, 11:12 PM   #9
Nico Ras is offline Nico Ras  South Africa
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This is all besides the point, even if this is a 1THz transistors what is your take on the harmonic distribution. Can you make any useful contribution.
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Old 16th May 2019, 11:45 PM   #10
xrk971 is offline xrk971  United States
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Balanced Headphone Amplifier
Nice work! I have made something similar with Hugh’s help. It does indeed sound very good. The harmonic distortion profile is ideal with the monotonically decreasing higher orders.

Click the image to open in full size.
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