TPA3255 - all about DIY, Discussion, Design etc

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#5,307
Hey sorry I missed the fine point about your SE drive on one end.

Perhaps you could use something similar to my two transistor balanced output drive and then use both inputs

xrk971

Thread 'Balanced Drive 2 Transistor SE Class A Headphone Amp'

Hugh Dean (AKSA) showed me a pretty cool circuit a few years ago, but it was only recently made public in this thread. It is beautifully elegant with only 2 actives, but worked like a charm. Very useful for making balanced (two identical outputs with 180deg phase) from a single ended input. Orginally, Hugh designed it as a live driver, but I played with the circuit and added a bigger TO220 output transistor and boosted the bias current. What I ended up with was a beautifully simple, elegant and great sounding amp for balanced drive headphones as low as 40ohms impedance...

I used BJTs but probably can be done with MOSFETs. Idea is to use the drive above and below an output device for opposing drive voltages out.

1736553847557.png


Scope output shows very even balanced split.

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#5,308
xrk971 said:
I used BJTs but probably can be done with MOSFETs. Idea is to use the drive above and below an output device for opposing drive voltages out.
Click to expand...
Yes, the old Paraphase/Concertina phase splitter is a great performer. Also acts as an 1:1+1 transformer. This is how it could be used as a SE to BAL stage for the TPA3255. If +/-24V was available a 2SK170 would work fine without any 8-legged critters in the signal chain.

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#5,310
xrk971 said:
Hey sorry I missed the fine point about your SE drive on one end.
Click to expand...
The question was actually about how to deal with the unused INPUT_B/OUT_B.
Got some indications from bunny and then got it verified from the guys at Ti.
Direct input from the DSP and via a simple buffer for the 60Hz filter into the SE.
The two cascaded 60Hz filters forms a 2nd LR.

1736620247811.png
 
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#5,316
You can compare it with a transistor or MOSfet amp where you double the number of output transistors. Sometimes you can hear an improved bass without changing anything else, as you basically half the output impedance. First found out about this with some modular amps, completely identical, except for the output devices. They where rated at 100, 200 and 300 Watt. All powered with the same supply (voltage), larger versions had harder impact in bass on the same speaker. It also fellt like better control of the bass driver.
The effect may vary with different speakers.
 
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