Hi all 🙂
I'm thinking of building a nice, simple SE headphone amplifier. Op amp driving a single NPN BJT with LM317 current source. I have a bunch of TIP31 and TIP32 in my parts bin, but will be ordering parts soon. Is there a better choice of currently-manufactured transistor than the TIP31C?
Thank you!
I'm thinking of building a nice, simple SE headphone amplifier. Op amp driving a single NPN BJT with LM317 current source. I have a bunch of TIP31 and TIP32 in my parts bin, but will be ordering parts soon. Is there a better choice of currently-manufactured transistor than the TIP31C?
Thank you!
If your design performs as it should using the TIP devices then why look further?
If they are limiting your design requirements then that is when you need to look for alternatives.
If they are limiting your design requirements then that is when you need to look for alternatives.
That will be the next step 😀. I'll need to determine what changes must be made to the circuit.
I haven't built it yet, was just wondering if there was a better alternative while I'm putting a parts order together 🙂. For example, the 2SC5171 is famous but hard to find.
MJE171 is broadly similar but with much higher fT (50 MHz). Earle Eaton's headphone amplifier from the '90s used the MJE243, a higher voltage, somewhat higher current part with somewhat less beta and fT (but also much lower Vce,sat) that's still available as well. Both TO-225 (TO-126) case rather than TO-220.
I imagine that in an SE buffer at >100 mA even the TIP31 would do quite well, though the others would do far better in a push-pull AB scenario and are likely to require less feedback (pole splitting) capacitance on the opamp.
MOSFET buffers have a reputation of being fairly foolproof (a few hundred ohms worth of gate stopper and that's it), which isn't necessarily the case with BJT followers that may tend to oscillate when confronted with capacitive loading. Usually nothing that some capacitive feedback for the opamp, a base stopper resistor and a Zobel couldn't fix, but still. Voltage drop is different, of course.
I imagine that in an SE buffer at >100 mA even the TIP31 would do quite well, though the others would do far better in a push-pull AB scenario and are likely to require less feedback (pole splitting) capacitance on the opamp.
MOSFET buffers have a reputation of being fairly foolproof (a few hundred ohms worth of gate stopper and that's it), which isn't necessarily the case with BJT followers that may tend to oscillate when confronted with capacitive loading. Usually nothing that some capacitive feedback for the opamp, a base stopper resistor and a Zobel couldn't fix, but still. Voltage drop is different, of course.
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As drivers I found fairchild TIP31c/32c limiting high frequency performance (top octave solo piano) in a 50 W amp. As compared to RCA 40409/40410 on the other channel. (you can't buy the latter anymore).
On semi MJE15028/15029 were entirely satisfactory in the same circuit. 10 times the Ft. Drove MJ15003 equivalents.
As output transistors MJ15003 are 4 mhz Ft and TIP31 are 3 mhz, TIP31c/32c might do all right as output transistors at low currents for a headphone amp. Do the experiment.
On semi MJE15028/15029 were entirely satisfactory in the same circuit. 10 times the Ft. Drove MJ15003 equivalents.
As output transistors MJ15003 are 4 mhz Ft and TIP31 are 3 mhz, TIP31c/32c might do all right as output transistors at low currents for a headphone amp. Do the experiment.
What headphone impedance? You don't need 24v power to drive 32 Ohms and you don't need 100s of mA to drive 600 Ohms
Thank you for the information everyone 🙂. I've got a lot of time on my hands at the moment so will experiment.
Several different models across the impedance range, including HE-6s
Several different models across the impedance range, including HE-6s