HeadAmp Pico Slim Portable Amp Review

img 2377IMG 2377 HeadAmp Pico Slim Portable Amp Review

I have been enjoying the original Pico for over three years now and it’s a great portable amp which I have no plans of ending our relationship any time soon. Knowing first hand the overall quality that Justin Wilson, owner of HeadAmp Audio Electronics, puts into HeadAmp products I decided to sign up early for the Pico Slim to reduce the size of my portable amp and see if going with a digital potentiometer would make a difference for me. So I became interested to sign up to the pre-order and  received it about 11 months later, I have been using it now for a few months (5/14/09 received 04-19-2010). Sure that seems like a long time to most people but in the beginning this was a concept that moved to a prototype and finally went into production, so this long wait time should not be the case with normal orders, but I have to say that this might be my last venture with pre-orders.

Contrary to what others have written, I like the overall performance of the original Pico more to my liking, although there is a size difference but not a problem for me and the channel matching difference may not be as good on paper but very difficult to notice a difference unless you listen at extremely low levels. Without further delay let’s discuss the Pico Slim.

Included items

The Slim portable amp, pleather case, the AC charger and user manual. The USB cable is optional and only used to charge from a PC USB port. I would like to briefly mention that the case is designed so that it can be used while the interconnect cable is connect, unlike the original Pico pleather bag. Although since then HeadAmp has also released a similar case for the original Pico.

Manufactures Specifications

  • Device Type: Solid State
  • Battery Type: 1-Cell Lithium-Polymer
  • Battery Life: ~60 hours per charge
  • Recharge Time: 3 hours
  • Frequency Response: 20Hz-20KHz +/- 0.1dB
  • Signal-to-Noise Ratio: >100dB
  • Total Harmonic Distortion: 0.003%
  • Stereo Crosstalk: >85dB @ 1KHz
  • Gain: up to 2x/6dB
  • Input Impedance: 10K ohms
  • Output Impedance: less than 1 ohm
  • Output Voltage: 4V peak-to-peak, 1.4Vrms
  • Output Power: 0.35Wrms w/ 32 ohm load
  • Inputs/Outputs: 1x 3.5mm input,  1x 3.5mm headphone out
  • Chassis Dimensions: 3.15 (L) x 1.55 (W) x 0.37 (H) inches

I will get the draw backs out of the way so we can discuss her better side, which are not issues with the original Pico. First there is an issue of an approximate 40 to 60db thump or pop to the iem’s when you first turn her on and one less powerful when powering her off. If you are aware of this it may not be a big deal because you can insert your iem’s after powering up, although better for your hearing, still not good for the drivers. Without being 100% sure, I believe this can cause long term damaging effects to sensitive armatures that come in high end iem’s or customs.

Going with my belief I immediately wrote both Ultimate Ears and Knowles Electronics to inquire about possible armature damage and tolerances. I did receive a reply from UE but did not expect one from Knowles as the tolerance might be proprietary information to their customer and I certainly did not receive a reply from them. Rather than try to reword or shorten what UE wrote me back, I decided to quote the majority of their response here:

“Asking a question like this is like asking a doctor…”hey will my knee give out if I take a ball-peen hammer and give it a little smack every morning”…There is no good answer to a question like that….except, “why??”

In the case of any speaker driver this type of thing is not good and should be avoided….even with the most expensive meier-sound drivers in $8,000.00 wedges, it is the responsibility of the system operator to sequence power and signal devices such that pops do not occur….pops are really a voltage transient when there is energy stored in a circuit component…it’s a dv/dt event like an arc. An impulse of energy is released when it finds a path to exit through …

So for a large PA system, we always turn the signal devices (in this case an iPod etc) on first and let any transients bleed out and reach a steady state then we turn on the power amps and then the reverse order when shutting down … “

That said, one can buy an in-line volume control to minimize this harmful effect but for the price one pays for this portable amp this is unacceptable.

The second issue I have is the useable range for listening on the potentiometer is small, the first ¼ turn is completely inaudible. For example, picture the face of a clock instead of the face of the potentiometer knob and the line on it can be the only hand on the clock. When you turn the knob, moving the line from zero or say 6 o’clock to 9 o’clock the sound is not audible. Depending on the impedance of the headphones you use, you can actually begin to hear the sound of music on or just after 9 o’clock faintly. I’m sure it varies for different individuals, but using my ue11s the real sweat spot ranges from 11 o’clock to 1 or 1:30 and honestly you wouldn’t want to go louder unless you are driving higher impedance headphones. This amounts to quite a small range of the 255 steps advertised, sure I didn’t expect to get all 255 steps, but this equates to around 53.13 steps that work for me. If you are curious about how I determined this: 255/12 = 21.25 steps for my imaginary 11 o’clock to 12 and another 31.88 steps till my 1:30 mark. That said, when you are listening in this sweet spot the amp does performs admirably and both channels do match very well at lower listening levels.

The last and final issue I have with the Slim is the hissing that starts after the sweet spot, around 2:00 o’clock, which becomes progressively louder the higher you turn the volume up. Although the hiss does not seem to be a problem with or without sound in the sweet spot (described above), it’s either inaudible or it’s just not there. While the music is in pause, the hiss can be a little more noticeable, although as I said above when in the sweet spot the amp performs fine. By the way this hissing is not an issue with the original Pico in either low or high gain at similar volume levels that I’ve noticed.

Build Quality

Obvious from the pictures, the Slim is notably small and thin with a very sleek look and professional build quality like its predecessor it’s excellent in this department. The size makes it great for portable use for those that do not like bulky products to carry on the go. As mentioned the slim is noticeably smaller and thin compared to her older sister the original Pico, as the Slim is actually similar in size to the iPod Nano (dimensions above). Both the original and Slim Pico share that “built like a tank” quality when compared to most other portable amps and a very good design, although their similarities end there.

Available in brushed aluminum or glossy black finish at the time of this writing, the housing is made from aluminum with a very sturdy/strong feeling to it, unlike the plastic cases or thin aluminum found on other portable amps. Skimping on their build quality does not seem to be the case with any of the HeadAmp products that I have seen tested or own. I did read about a few customers that noted a few small scratches on their new amp but I do not believe this to be the norm and knowing Justin if this issue was common he would just replace the amp in question or have it fixed. It’s hard to say that the Slim looks are not impressive, but impressive looks don’t make a portable amp perform any better and although it does have its advantages, it comes with it’s draw backs that are not an issue with the original Pico.

Front & Rear Panels

Front Panel, viewed left to right: Illuminated on/off power switch, 3.5mm headphone out and the volume potentiometer knob.

Rear Panel viewed left to right: 3.5mm female input jack, charging led and the Amphenol Micro-USB jack (this is the new standard and not the Mini-B connector).


The amp is housed with a digital potentiometer using the typical analog adjustment knob which makes for very precise adjustments although the knob may appear a bit small for large fingered users, it’s still great for quick easy volume adjustments. Continuing with the internals, the coupling caps are Niobium Oxide and PPS film, from my understanding and based on what I read these capacitors are better suited for portable audio-coupling circuits because they are more stable over time and temperature with the ability to withstand harsh environments such as heat and vibration, while providing low ac ripple, supposedly delivering clear, noiseless filtering but whether it’s them or the digital potentiometer there is hiss outside of the sweet spot. Also important to note is that the gain changes as you turn the volume knob because it’s a variable gain amplifier.

The attenuation is impressive; allowing you to make very minor steps in volume adjustments to a very low precise level if desired. You can listen as low as you wish and the channel matching is very accurate but hard to tell the difference when comparing to other good analog potentiometers, I myself find the original Pico hard to differentiate in this department, it really is a great amp compared to what the “latest flavor of the month club” believes. Rest assured that even if you can not note the difference a good digital potentiometer is more accurate at low listening levels.

Battery life

Stated to be 60 hours at the time of the prototype and in the finished specifications is more than acceptable. Although when I spoke with Justin at the time of testing it, he told me that he was getting close to 70 hours, so after my test surpassed 50 hours I stopped testing and opted for more listening, honestly over 50 hours battery life is more than respectable.


I’m sure everyone wants me to discuss my opinions about its sound quality, nothing wrong here; I believe it does what it’s supposed to do well. I’m not going to get into sound quality as I don’t feel it colors the sound and I honestly can’t say that it improves treble, midrange or bass as others have written. Rather I believe that these factors depend on the iem’s you use and if you use EQ or not. However if run in her sweet spot it can remove the unwanted hiss produced by digital audio players often heard from low impedance, sensitive iem’s and allow you more flexibility with precise volume adjustments to very low levels.


In my opinion HeadAmp did a very good job with design, build quality and sound reproduction eliminating hiss heard from sensitive low impedance iem’s without any noise within the sweet spot. On the down side, it’s a very expensive amp for what she does, it hisses outside the sweet spot for me, which means it may hiss for others who prefer listening at higher volumes. She seems to scratch easy as her predecessor, but this isn’t a deal breaker.

Normally I do not have a problem recommending HeadAmp products but in this case, what more can I say, she’s a beautiful work of craftsmanship at an expensive price. So it’s your call if you need a small thin amp that has great channel matching at very low listening levels and removes the hiss from low impedance overly sensitive iem’s or custom monitors she might be right for you.


  • Noiseless while in the sweet spot
  • Great build quality and very solid
  • Channel matching very good at low listening levels
  • Small size
  • Useable amp case
  • Warranty


  • Expensive
  • Thump or pop to armatures/drivers on power up
  • Hissing above the sweet spot
  • Not enough available listening steps (first ¼ turn is completely inaudible)
  • Scratches easily and finger print magnet without case
  • Long wait time from order date
  • The Amphenol Micro-USB cable is extra accessory (not included)

MSRP: $399.00 plus shipping – For further info, see HeadAmp


Billy Bob on October 11, 2010 4:20 PM

holy crap thats expensive

tds01 on October 11, 2010 5:03 PM

Great review my friend. Now you may have just added ANOTHER sweet piece of tech I’ll need to add to my “Must Have” list. Especially since this is sized to pair wonderfully w/my Cowon J3.

tbdbitl on October 11, 2010 11:06 PM

12/7/09 to 04-19-2010 is not 17 months. It is only 4 months.

Ramón Garcia-Lavin on October 12, 2010 12:43 PM

Thank you for pointing out, apologies I must have had a brain fart, became interested on 5/14/09 but the pre-order didn’t register till 12/7/09 and my order was received 4/19/10 so it was around 11 months from the start. Regardless it was a long time and I have fixed the review, thanks again …

GreatDane on October 12, 2010 12:05 AM

Very nice and professional review. I’m a bit disappointed that the charge light on my Slim is defective but it seems to charge fine. Justin says send her back but I’m afraid of “The Wait”lol

Ramón Garcia-Lavin on October 12, 2010 1:16 PM

Thank you for the comments on the review, personally I would either send it back or ask for the part to replace it yourself, heck you already waited a long time, whats a few more weeks.

Ross Seymour on October 12, 2010 2:51 PM

Quite a contrast to the Arrow review. These amps seem to be in the same league, but reading between the lines, the Arrow is the better value. Funny there’s no comparison.

Justin on October 12, 2010 3:31 PM

?? probably a soldering issue on the charging LED. Just send it to me so I can fix it already.

lestatar on October 12, 2010 5:26 PM

Nice work Ray! As you know I have no need/interest in this kind of thing ATM, but one never knows, especially as I hang around ABi more and more. lol

However, the single most troubling thing I read in the entire review was the on/off “thump”.

I assume this kind of thing is abnormal for amps of this type? I would be very very leery of this…

Great pics and writeup!

Chris C. on October 12, 2010 9:21 PM

Nice write up. But for $400, this thing should NOT thump OR hiss, period. AND they don’t even include the needed mini-cable? That’s just wrong. I could find nothing in your review that could justify it’s selling price to me.

Justin on October 13, 2010 2:02 AM


The hiss he is referring to is a slight hiss if you turn the volume all the way up, and even then you need a very sensitive IEM to hear it. This is normal because all digital volume controls are going to have some added noise, but its worth it and is not audible at any kind of listening level.

There is a thump at turn-on due to the type of design, which can be avoided by plugging in the headphones after turning it on. There is click/pop suppression circuitry available but tends to add 10x the distortion of the whole amp.

Third, a Micro-B USB cable is NOT required. A universal DC Adapter is included for charging. You can also charge from a PC, with the cable.

Ramón Garcia-Lavin on October 13, 2010 1:15 PM

“There is a thump at turn-on due to the type of design, which can be avoided by plugging in the headphones after turning it on.”

Of all the amps I’ve tested in this caliber making your connections and then turning on the amp there has never been a harmful pop/thump, including the original Pico. I have tested your method and as illogical/unorthodox as this method sounds it significantly reduces the pop/thump to the point which I do not believe would causes damage to armatures, thanks for the input. Although based on my findings, I would definitely include a warning in the instructions as without doing it, it is highly possible that armature damage may occur.

Chef on October 13, 2010 3:11 AM

Sounds like a piece of crap… How can you defend this product? A good amp does not hiss period. It doesn’t cost this much either…

You say that the UEs or whatever hiss when you use them with normal devices… I hesitate to say it, but maybe that is also a major flaw with the UEs? Is there any reason their impedance must be that absurdly low that they require a special amp?

I don’t know! Sounds like a lot of money to spend on things that don’t work, especially when there are more cost effective alternatives.

Ray on October 13, 2010 10:31 AM

I’ve designed IEM drivers and UE is correct; it’s not a good idea to regularly smack them with a high level impulse. The drivers are tested for high level voltage and gravity impulses but not on such repeat events.
If damaged you’ll get high levels of second harmonics or intermod buzzes. Is it worth the risk??

Justin on October 13, 2010 12:07 PM

Because I make it? Anyway, the sensitivity of some of the top IEMs is so absurdly high that the SNR required for no audible noise is beyond the specs of any digital volume control on the market, unless the amplifier has no gain at all. If Ramon goes and looks at other amplifiers on the market w/ digital volume controls, plugs in his UEs and turns the volume all the way up, he’s going to hear a small amount of hiss as well. I suspect the reason they are so sensitive is because they use (or originally used) drivers that were intended for use in hearing aids so in the interest of low power consumption & high volume they were made to be very sensitive.

Ray on October 13, 2010 4:45 PM

Justin, if you cannot get a mid band volume setting for yout IEM tell enough people and manufacturers will go out of business.
If you get a comfortable IEM setting but the amp produces an uncomfortable impulse on turn-on/off doesn’t that suggest that the amp needs a couple of extra components?
I have no involvement with any of the companies here and these comments also apply to moving coil drivers.

Justin on October 13, 2010 6:05 PM


There are IEMs that are not ridiculously sensitive. They are also not as popular. The sensitivity of the most popular custom IEMs ranges from 119 to 125dB/mW. The ones Ramon is using are at the very top of that sensitivity. As for turn-on noise, any kind of relay-based muting would be the most transparent however no relay is even close to fitting in something of this size. Option #2 would be using FET analog switches on the headphone out for muting. The problem is this method will probably add 10x as much distortion under heavy loads as the whole amp. So if it bothers someone I would just recommend plugging in the headphones after it is turned-on.

Ramón Garcia-Lavin on October 13, 2010 8:16 PM

This review is not about the UE-11’s, it’s about the Pico Slim that was designed and promoted to work with overly sensitive iem’s and customs. Their sensitivity is 119dB @ 1mw with an impedance of 18 Ohms at 1kHz, the UE-11’s don’t hiss with every source, just some portable players. BTW if you are interested in reading my opinions on them please look at my UE11 Review or even my UE11 One Year Later write up, sure they’re overly expensive but preform very good.

Chris C. on October 13, 2010 9:09 PM

I dunno…
“I’m sure everyone wants me to discuss my opinions about its sound quality, nothing wrong here; I believe it does what it’s supposed to do well. I’m not going to get into sound quality as I don’t feel it colors the sound and I honestly can’t say that it improves treble, midrange or bass as others have written.”
Add to that the weird gain taper on the pot, and having to dial into a certain sweet spot to avoid hiss…

I think I could live without this $400 bauble.

Tjames on October 16, 2010 2:27 AM

Enjoyed reading the review, it doesn’t seem all that bad of an amp from the read, albeit too expensive for what it does. I read the owners post on headfi, what a joke! Sure is strange posting that to someone who’s purchased (or did he give them to you for testing/review?) 2 of his amps. BTW posts like that, trolls and all the snake oil sales men backed by the owner is why I’ve never join forums :p

Ramón Garcia-Lavin on October 17, 2010 3:40 PM

No he didn’t give either one to me; I stood in line like everyone else and paid for both portable amps. Although I would welcome either loaned or free equipment from manufactures to evaluate and review.

Jim McGory on October 21, 2010 12:59 AM

Hey Ramon:

Good reading…I am trying to educate my self on this stuff. Going to Africa and want a nice amp to help my ipod and Sennheiser 450 PXC. Any recommendations for $200 to $300? Thanks.

Ramón Garcia-Lavin on October 21, 2010 2:24 PM

In your price range I would look at the arrow, dfkt did a review on it here and if I recall correctly it’s around $265.00 or EURO 199.

Aardvark on October 31, 2010 7:40 PM

Great Review Ray. Very interesting but the functional issues with the pops and hissing would put me off this one. How did it fare with driving full sized cans? Anyhow, well done mate on making the front page.

Ramón Garcia-Lavin on November 1, 2010 9:01 PM

Aardvark, the pop isn’t an issue when you power up first and then plug headphones into it. The hiss is only outside of normal listening range, if you turn it up that much it would hurt with customs on and isn’t an issue with high impedance phones. It fairs well with full sized cans but was designed for portability and overly sensitive iem’s, so I’d say there’s better options for full sized cans. For example the original Pico better works great with my hd650s. BTW thanks for the comments.

Anon on July 1, 2012 5:21 AM

I have the pico slim, there is no hiss at any audible listening level, there simply is none. I’ve never heard a hiss and quite frankly listening to anything higher than perhaps 2-3 on the dial would probably be too painful so I’ve never felt the need to do that. There is a pop when powering on the amp, there is no pop when powering it down. Also, this amp does indeed increase the quality of the bass mids and treble, quite substantially. This is a bad review and I advise anyone reading this to try the amp for themselves.

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