donnbialik
Member
Has anyone tested this headphone amplifier? It's used pretty extensively in home audio recording, on tour and even in many pro studios.
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
PreSonus HP4 4-Channel Headphone Amplifier
- Thread starter donnbialik
- Start date
AnalogSteph
Major Contributor
Some nude pix of the older version (16V AC in) HP4 can be found in this Rock Grotto thread.
After staring at them for a while, I believe the output driver is basically an SMD version of this kind of circuit (Fig 11 c):
(This one has the wrong image)
All opamps are STMicro's MC33079D version. The SOT23 marked 2T appears to be an MMBT4403, there's another two MMBT914 diodes in the same package; I can't read what the other transistor says but it might well be 2X for the complementary MMBT4401. Emitter resistors seem to be 22 ohms - output series resistor 51 ohms as specified. I don't think the little capacitor exists. Bias resistors I can't read the value of. Power supplies I'm guessing are something like +/- 12 V.
Now 4401/4403 in SOT23 are a bit hampered in terms of thermal dissipation (I prefer SOT223 or SOT89), but they actually are pretty decent medium(ish) power transistors still. By the standards of the time, this setup would have had a decent amount of oomph. It would no doubt benefit from a small electrolytic across the diodes (perhaps some more bias in general) and replacing the silly linear volume pots by some log ones (assuming it's that easy, of course) but hey, at least they tried.
This circuitry is obviously not a match for good modern-day $99 consumer amps in output impedance, distortion or output power, but what do you expect when you're getting 4 amps for the price of one with the ability of handling +18 dBu balanced in (and a monitor output) to boot, all in what looks like a decently substantial case.
The modern version (12 V DC in) could be entirely different or just a bit; I assume it's got an internal DC/DC converter to generate its negative power rail. Presumably obtaining a decent 12V wall wart became cheaper and easier than the same for an AC transformer in the meantime. The power brick appears to be downright fancy even, with a plug-in mains cable and power switch in the DC lead.
After staring at them for a while, I believe the output driver is basically an SMD version of this kind of circuit (Fig 11 c):
https://astersart.net/amp/headphones/desigh/designing_an_opamp_headphone_amplifier.htm
Figure 11
(This one has the wrong image)
All opamps are STMicro's MC33079D version. The SOT23 marked 2T appears to be an MMBT4403, there's another two MMBT914 diodes in the same package; I can't read what the other transistor says but it might well be 2X for the complementary MMBT4401. Emitter resistors seem to be 22 ohms - output series resistor 51 ohms as specified. I don't think the little capacitor exists. Bias resistors I can't read the value of. Power supplies I'm guessing are something like +/- 12 V.
Now 4401/4403 in SOT23 are a bit hampered in terms of thermal dissipation (I prefer SOT223 or SOT89), but they actually are pretty decent medium(ish) power transistors still. By the standards of the time, this setup would have had a decent amount of oomph. It would no doubt benefit from a small electrolytic across the diodes (perhaps some more bias in general) and replacing the silly linear volume pots by some log ones (assuming it's that easy, of course) but hey, at least they tried.
This circuitry is obviously not a match for good modern-day $99 consumer amps in output impedance, distortion or output power, but what do you expect when you're getting 4 amps for the price of one with the ability of handling +18 dBu balanced in (and a monitor output) to boot, all in what looks like a decently substantial case.
The modern version (12 V DC in) could be entirely different or just a bit; I assume it's got an internal DC/DC converter to generate its negative power rail. Presumably obtaining a decent 12V wall wart became cheaper and easier than the same for an AC transformer in the meantime. The power brick appears to be downright fancy even, with a plug-in mains cable and power switch in the DC lead.
