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I am currently writing up a review for the HP-1 headphone amp, which is from the same designer as the Modulus-86 (Neurochrome). The man is a technical monster with some very impressive chops, and his headamp is possibly one of the most detailed and resolving that I've heard (and I am one of those nuts who has gone through more than his fair share of headphone gear). While I don't have first hand experience with the Mod86, I have some friends who do and they speak very highly of it. http://www.neurochrome.com/product/hp-1-ultra-high-end-headphone-amp/http://www.neurochrome.com/product/modulus-86/
Are those SMPS modules for the power supply, on the headphone amp?
I use SMPSes in my differential preamplifier (DIFF PRE 8x2), HP-1, and SMPS-86 which I used to power the LM3886DR and Modulus-86. All these circuits provide state of the art performance and have very low noise floors. The switchers perform better than most linear supplies. I do add filtering on the output of the SMPS, but that's mostly a precaution. The switching noise is spread-spectrum, thus, low in amplitude and way outside the audio band (60-70 kHz), so it's not an issue for audio circuits.On the HP-1, I went one step further and added a set of low-noise regulators to the output of the filtered switching supplies. The main reason was to get the rail voltage I wanted so I could get 3 W into 20 Ω and 3 W into 32 Ω. The post-regulators also provide a nice marketing blurb about super filtered supplies, though, the filtering isn't all that necessary from a technical standpoint.There are ways to screw up the performance by adding filtering, by the way. If the designer isn't careful, it's possible to cause some severe peaking in the combined output impedance of the filter + SMPS. It should go without saying but I'll say it anyway: I spent considerable time and effort designing the SMPS post-filter to ensure good performance across the audio band.
Good to see that folks are happy with the results - I have the boards for the Mod-86 but haven't started the build yet. I think I'll use the Modushop chassis from the diyaudio store and a PS from a Class-D-Audio amp that I had. the PS voltage is on the upper end of things, but should be ok in my application where I don't really crank it (at least I hope).
His smps is compelling. I love how thorough and accessible his explanations are.
Am I correct to assume the headamp is also a "composite amplifier" topology like Mod86?
Now about the circuit. As noted a few pages back, the HP-1 uses the OPA1612 for the differential receiver and input buffer. Input selection and gain selection is accomplished by Kemet relays with gold plated switch contacts. The headphone output stage is an LME49600 in a composite loop with an OPA1611. The composite amp has a built-in compensation network which ensures stellar performance even with heavy capacitive loads (long headphone cables). It'll drive up to 22 nF || 300 Ω. That's close to 1 km of headphone cable. That aught to do it... I have seen OPA1611+LME49600 amps from other vendors. I wonder if they noticed that it'll oscillate at load capacitances in the 100-500 pF range (common cable capacitance). You need that compensation circuit... To minimize DC on the output of the amp, an OPA2140 provides a third order DC servo for an output DC offset below 100 µV. I chose a 3rd order servo to ensure a fast settling time while not impacting the THD at 20 Hz. The servo settles in about 30 seconds. The HP-1 needs no further warm-up than that.There are no capacitors in the signal path as the HP-1 is DC coupled. Should any part of the amp or any circuitry upstream of the amp fail resulting in DC on the output, the built-in protection circuit will disable the output. Also, in the event of power supply failure where one rail collapses, the other rail will be shut off. The final feature of the protection circuit is that it provides a turn-on delay, thus, eliminating turn-on and turn-off thumps in your headphones.
Anand, thanks for your follow-up.Intuitive Audio Gamma Summit two way monitors 89db nominal 4 ohmsWish I could tell you more about the specifications but not much available online about them. I understand they like a little power and current to open up. I just recently purchased the speakers and haven't had a serious audio system in a few years. Just getting back into the hobby and trying to figure out a great amplifier for these speakers.Thanks,Nick
