A DIY Beauty: Pete Millett's Butte Headphone Amp

Pete Millett's Butte DIY Headphone Amp (<$200)
Ok, ok, so it's not a whole lot to look at but that's one of the things that makes me like it. And I really like it a lot.

Disclaimer: I'm a long time admirer and occasional collaborator with Pete Millett. I will build just about anything that he designs because I've never been disappointed with the end product. That said if he laid an egg I certainly wouldn't give him a pass just because he's a nice guy. If anything it raises the bar and makes me expect more from him.

The Butte (pronounced "byoot") was originally released in 2011 as a commercial product from Apex Audio. Apex, for those that don't know, is the dynamic duo of Pete and Todd Green; their products are sold at Todd the Vinyl Junkie. This combination has produced some truly epic results including the spectacularly sounding and priced, Pinnacle. The Butte was decidedly on the other end of the spectrum and having finished its commercial run, is now available as a DIY project with essentially the same circuit converted to thru-hole components for ease of assembly and with a few alternate parts to lower the build cost.

PCB's are able to be ordered from Pete's ebay store and you can buy the professional-grade chassis that I used there as well. You are of course free to case it up in whatever you choose, one of the great joys (and pains) of DIY. Parts are readily available from the common vendors (DigiKey, Mouser, etc.) and here's where we get to one of the best parts about the DIY Butte. It's cheap. Mind-boggling cheap. All in, with the enclosure, board, parts and some shipping you're out less than $200.

And Pete has gone to great lengths to make the whole process painless. He's put together a very detailed build guide, sells the hard to get bits (PCB and chassis) and even has a one-click shopping cart at Mouser to buy the remainder of the parts. Pretty awesome if you ask me.

PeteMillett_Butte_Photo_BoardTop

So how was it to build? Refreshingly easy. The last thing that I built was a highly complicated tube-based amplifier complete with a power supply that can kill you and many, many nights of point to point wiring permutations. So when I got to sit down with a small box of parts, a single PCB and have it all up and running in less than 2hrs it was very satisfying. As mentioned above Pete has put together a detailed and comprehensive build manual and as such even the newbiest-newb should have no issue with building one of these. The only true challenge is if you elect to install the two surface-mount parts that offer a slight reduction in overall distortion. Having built many surface-mount projects this wasn't an issue for me but if you haven't done much (or any) of that, I'd steer clear. The difference, per Pete, is debatably audible.

Once past that stage is all pretty much plug and play and if you order using Pete's link with Mouser your parts bags will even come labeled to match the PCB. It's little things like this that make it such an approachable project. Assuming that, like me, you know and understand just how hard it is to hand craft a professional looking chassis, and you select the one from Pete's Ebay store there isn't much left to say about the build. Slide the board into the chassis, install the Panels as directed by the manual (there is a little subtlety involved) and you're done.

PeteMillett_Butte_Photo_BoardBottom

Well then, how was the amp to live with day to day? To my ears the answer is pretty darn outstanding. The numbers back that up, so let's start with a of few of those from the commercial product page.

Max output leven into 150 ohms @ 1kHz: 7.2V RMS / 20V P-P / 340mW
Max output level into 33 ohms @ 1kHz: 5.0V RMS / 14V P-P / 750mW
Peak output current: 200mA
Output impedance: 3 ohms
THD+N 1V 1kHz 150 ohms: 0.003%
THD+N 1V 1kHz 33 ohms: 0.005%
FR: 20-20kHz +/- 0.1dB
FR: -3dB DC - 240kHz
Noise 400Hz - 30kHz: 30uV
Max gain 1kHz: 20dB
Dimensions: 4.3" W x 5.3" D x 2" H

One important thing to note from those specs, this amp has a lot of gain, which is to say, it goes all the way to 11. This has its good and bad points. On the one hand, if you're feeding it with a low ouput source or driving hungry headphones you'll appreciate the beef. On the other hand, if you're using a higher output source and/or easy to drive headphones you may be left with a somewhat limited range of volume adjustment. I tried the amp with everything from HD800s, LCD-2s, Grado SR-100s and even a few sets of CIEMs and I was always able to find a way to use the amp comfortably. The CIEMs presented the biggest challenge and revealed that the amp does have a slight amount of hiss. It wasn't anything that was objectionable while listening to music, but it is there. Hey, that's why you have more than one amp, right?

PeteMillett_Butte_Photo_RearPanel

And this is a desktop amp, not a portable, so for most this will really be a non-issue. That's where the really good news starts to hit. Yes, it's a tidy utilitarian package if you elect to use the stock chassis, but if you want fancy all you have to do is design your own. Make no mistake the amp has some great features too, my personal favorite being a front panel switch to change between the two rear panel inputs. Oh, and those two inputs are a combination of one set of RCAs and an 1/8" jack. So whether you've got an iPod, CD player, or both, you're covered. Why many manufacturers still make desktop products with only one input boggles my mind. My next favorite—a front panel power switch. Hallelujah!

But let's get back to how it actually performs and sounds. The Butte is a wonderfully neutral amplifier, having natural but impactful bass and an extended but not harsh top end. Really, I found nothing to nit-pick about even if I ignored the bargain basement build price. My favorite combo, and one that I spent hours listening to, was feeding the Butte quality source material and driving the HD800s. Generally speaking I've not really found the HD800s to be all that enjoyable off of low output impedance amplifiers but for whatever reason they seemed to click with the Butte. There was plenty of fatigue-free detail and nice amounts of slam from the low end. I never once found myself wishing that I'd hooked up something else.

Bottom line—Park this little guy next to products costing several multiples of its build price and I doubt it'll do anything but than impress. Sure, some of the higher-end amplifiers that I own are capable of rendering more detail but you'd be adding another zero to the cost of the Butte to get there. So, if you're thinking about dipping your toes into the pool of DIY headphone amps I don't think there's a stronger recommendation that I can give for where to start. Skip the typical, throw-away type projects and invest a little bit more into something that is likely to be infinitely more useful and enjoyable. Highly recommended!

COMMENTS
Three Toes of Fury's picture

This project intrigues me! Ive been longing to break out the old soldering iron for a while. Its clear that Pete put alot of thought into ensuring that this project is doable and organized and well laid out. Your hands on review and thoughts on the sound are the icing on the cake.

Thanks!

Peace .n. Living in Stereo

3ToF

kongmw's picture

Fantastic. It's going to be my next project!

xnor's picture

Basically a OPA552 cmoy with an input select, but why the high gain? 11x right?

n_maher's picture
I'd say there's enough to differentiate this from the typical "Cmoy" that your comparison isn't warranted. On your second point, i.e. high gain, I agree, I'm generally a fan of much lower gain. I hope to speak with Pete about the possibility of suggesting some alternate resistor values which may allow for this to be tweaked although I am unqualified to figure out if there might be stability or offset issues. Still, as I said in the review this wasn't an issue for me and I'm not exactly known for cranking it up.
xnor's picture

Well, it basically seems to be a volume pot in front of an opamp, that's a cmoy for me.
The main difference from typical cmoys is the power supply. Same design as the O2 AC power section.

John Grandberg's picture
That turns a lot of amps into CMOYs doesn't it? Also, why are we not instead calling it a Grado RA-1 at heart? That thing predated the CMOY by at least several years.
xnor's picture

Well, only the "volume pot in front of an op-amp that directly drives the headphone" amps. Now you can call it that instead of a cmoy, but the latter is well known and quite an abbreviation.

I don't think Grado published their design like Chu Moy did. His design(s) actually included other features such as a gain switch (the Butte could use one too!), battery or AC supplies, balanced inputs .. heck, even a limiter.

Smiling Kev's picture

1. Too advanced for someone ( me!) completely new to DIY audio?
2. Too much gain when all my headphones (e.g., Shure 1540 and V-Moda XS) and IEMs (e.g., Shure 215 and Etymotic ER4PT) are very easy to drive either without amplification via my IOS portables or wth a low gain setting on the Schiit Magni 2/Modi 2 amp that handles the output from my NAD CD player for "serious" listening?

I want to have fun trying something new, but without setting my hair or house on fire in the process - or ending up with a finished product that really won't be very useful for me. I'll welcome any suggestions!

Thanks,
Kev

zobel's picture

This is without batteries, also available with batteries installed;

http://www.amazon.com/Objective2-Headphone-Amp-AC-batteries/dp/B00SZALHL...

Made in USA. This is not a kit, but this amp is available as a kit, here; http://www.headnhifi.com/o2-kit-full for even less, Better specs. No hiss. Portable or desktop. switchable gain, ALPS pot.

I bought the assembled version from "Mayflower Electronics for GoodCans by Listening Station" (at Amazon), and really like it. More than enough power. Uber clean. My Sennheiser HD600 never sounded better!

n_maher's picture
The project, coupled with the documentation and access to typically hard to find parts that Pete is offering, makes this totally beginner friendly even if you're new to DIY audio. I've got an email into to Pete to see if it is as easy as the schematic implies (changing two resistors). I pulled the data sheet tonight and the OPA552 is supposed to be ok down to a gain of 5 which would be a welcome change in my book. Thanks for your comments and feedback.
Smiling Kev's picture

I really appreciate your help. Once we clear out our summer visitors - after the July 4th weekend - I'll order all the materials and documentation and give it a try. It looks like a really enjoyable project!

Thanks again!
Kev

n_maher's picture
I spoke with Pete last night and gain can certainly be adjusted. I'm going to try to experiment with lowering gain as close to 5 as I can get it with parts that I should have on hand and I'll certainly report back. Pete also said that one could easily substitute the OPA551 which is unity (1) gain stable if so desired. There would be some reduction in performance with that change, hard to tell how much just from a datasheet. :)
MASantos's picture

Well, taking into account that it has a regulated power supply instead of batteries and that (using the CCS)it can be biased into class A a low bias, it's quite different from the cmoy.

Seth195208's picture

No Schiit?

xnor's picture

How is power up/down behavior with headphones connected? Any popping sounds?

zobel's picture

to answer that question.

n_maher's picture
I can't say that I noticed anything objectionable but I've also gotten into the habit (based on usage of CIEMs) of not having headphones plugged in when I power up an amp. I'll experiment with this and provide an update.
n_maher's picture
There's definitely a little pop at power on but with the full-sized headphones I tried it with it's nothing I'd consider objectionable. Just a small "woosh" at power off
xnor's picture

Okay, I'm surprised its not worse because the on/off switch is before the supply capacitors and regulators, so if they (dis)charge unevenly you could get DC at the output for quite a while.

One more thing on the gain: it really should be lowered. This amp could output over 20mV DC on its own plus the amplified (11x!) DC from the source, which should again be audible if you plug a headphone in.

n_maher's picture
Maybe I'm misunderstanding you or missing something when you refer to the position (in the schematic sense) of the power switch but this is a common, if not nearly universal, way of configuring a power switch on amplifiers both large and small. Can you think of an example where the switch is not positioned as you describe? I looked at 5 or 6 different schematics and don't see anything notably different. But for what it's worth I've checked the DC offset under normal operating circumstances and it's as near 0 as any other amplifier I've used, which is to say that on my Fluke it measures as less than 1mV. If an opportunity presents itself, like when I change the gain resistors, I'll try to measure the transient DC offset on the power up/down cycle but I have no reason to believe that other amplifiers that don't have cap-coupled outputs. One other point, if your source has significant (read: basically any) DC offset you have a whole different set of considerations to ponder when choosing an amplifier. It doesn't really matter if your gain is anything other than unity and the DC could cause you other issues even if it is a low-gain setup. At least that's my 2¢ on the situation.
xnor's picture

There are certainly other designs out there and it is not just the switch position that matters, but I won't go into details now. O2 is probably the most easiest example.

The DC measurement seems odd. OPA552 has a Vos of 1mV to 3mV max, multiply that by 11x gain for a ballpark figure.

Hands's picture

Just built one of these myself. However, instead of using the included voltage regulators and opamps, I got discrete alternatives from Sparkos Labs. Andrew was nice enough to give me a bundle deal on them and increased the max output current on the opamps he sent me as well. They work out quite nicely and can be dropped right in without further modification. I am not using the CCS section. You will want a nice heatsink for the discrete regulators (they get rather toasty with heatsinks even), and it took me some weird angling of them to fit them in the case. But it runs nicely and sounds great! Plenty of slam and "meat on the bones," nice tone, smooth, decently detailed for the price.

My only complaint is that the stock gain with this configuration and my DAC is way, way too much! Bad to the point where I had terrible channel imbalance from the volume pot until basically all of my headphones were about to explode. Thankfully, those Sparkos opamps are stable down to gains of 1 (or so Andrew told me), so I set it to something around 1. Happy camper now! Still tons of headroom, a lot more volume play, easy to get around the imbalance. Here is what Pete Millett said to me about changing the gain for those curious:

"Yes, the gain is 11 if built with the stock resistor values. That is pretty high for many headphones and sources.

You can change the gain by changing the resistors at R6 and R9. You’ll get a gain of to 5.7 by changing R6 and R9 from 1k to 470 ohms – the gain (of the right channel, for example) is 1 + (R6/R7), and R7 is 100 ohms.

To go lower than a gain of 5, you would also need to change the opamps from the OPA552 to the OPA551, or the circuit will be unstable. Then you can make the gain, for example, 2 by changing R6 and R9 to 100 ohms if you use the OPA551.

Unsoldering the resistors can be difficult. The easiest way to do it is to sacrifice them, and cut them loose by snipping the wires very close to the resistor body, then using tweezers or a needle-nose plier remove the remaining pieces of wire while heating the joint with the soldering iron. You can use solder wick to remove the solder to install the new resistors.

You can also leave the original resistors there and “piggyback” another resistor across them to lower the resistance (and so the gain). For example, if you add another 1k resistor in parallel with the existing one, the resistance becomes 500 ohms, and the gain 6. This is easiest to do on the back side of the PCB.

Lowering the gain will help the channel imbalance. The volume control pots are notoriously bad at very low settings."

niaomer's picture

Mini Review

Background
DIY Butte (with stock parts and 5.7 gain) 2-3 hr burned in
Tested with LCD2.2 (non-fazor),
Butte listening at about 10 o'clock position with LCD2
Source - Sabre ESS9018K2M DAC from DIYinHK

Butte vs O2
Butte sounded more open, it has better instrument separation than O2.
Butte seems to be on the warmer side and it sounded more comfortable to me. The details are there in both amps but I could feel more of the ambience with the Butte.

Butte vs Beta22 (2 boards)
Beta22 sounded a bit open, but the highs are much softer or rolled off. A bit too soft for me, it made the Butte sounded more detailed. You could also see it another way. But tonality wise, they are very close. I would say Butte sounded closer to Beta22 than O2. Yet the footprint of Butte is much smaller than my 2-chassis-with-massive-heatsinked Beta22.

Good stuff indeed. I'm gonna use it in my office to pair it with my future-to-be PM3! HAHAHAHA!

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