While surfing the web a year ago
I stumbled upon the weirdest of DIY audio cults - people sculpting
flashy amplifiers, to which they ascribed magical levels of sonic
performance, around a 'common garden' IC amplifier chip - the
type you might find in a car stereo, portable stereo, or TV. Jumping
further into the paranormal, the concept is supposedly based on
some mythical "47 Laboratory Gaincard", with mysterious
construction features like ultra-short signal paths and tiny power
supply capacitors. These beasts go by the strange name of "Gainclones".
But this made me think. Monolithic
(or single-chip) amplifiers as a rule are scoffed at by audiophiles
the world over, being considered "cheap and nasty scum of
solid state", so the question has to be asked - "can
anyone hear the difference at all"? By this I refer to the
whole untidy brawl between the audio objectivists and subjectivists,
fuelled by (apparently) unmeasurable qualities of things like
power cables having (apparently) obvious audible effects.
Amplifiers with vanishingly low
THD specs are quite common these days, so why on earth would an
IC amp with a 0.1% THD spec be treated as such a sonic holy grail?
This is kind of good, but by no means the best. To put it in perspective,
it is maybe 100 or even 1000 times worse than some high end amplifiers,
and we're not talking about the more graceful valve (tube) distortion
here, but nasty-as-it-gets class-B "transistor distortion".
Note that many people still do consider 0.1% distortion to be
beyond the limits of human hearing, double blind trials have failed
to show it is detectable, so many (cheap) audio circuits are still
designed using 0.1% as a benchmark of inaudibility - on the assumption
that going any better is merely pandering to placebo effect (or
plundering the bounty of placebo effect, depending on your point
Over the past few days however,
while developing a chip amp, I stumbled over some surprising results
that have cleared up a lot of this confusion. Read on to find
A Gainclone isn't a mythical beast,
and neither is the "47 Laboratory Gaincard" it is modelled
Laboratory Gaincard is 'just' a model of amplifier manufactured
by 47 Lab, a Japanese audiophile brand, with the usual quirky
and minimalist approach. By all accounts it is a very good little
amplifier, and while I am in no position to judge (having never
tried one), the technical basis looks sound.
A Gainclone, surprise surprise,
is a clone of the Gaincard, so it usually has these features:
In fact, Gainclone has come to
mean "any minimalist chip amp intended for high quality sound",
and their popularity has continued to grow since I first stumbled
onto their existence at the beginning of 2003.
So that's that mystery solved.
They're not that special. People (like me) have been building
chip amps for years with exactly these same features.
Hang on. This is exactly the sort
of misguided reasoning which is responsible for all the confusion.
Firstly, this would be assuming all amp chips are designed to
that magic 0.1% distortion spec mentioned above. Secondly, 0.1%
THD definitely is audible for the right signal. (Perhaps THD should
stand for "transistor" harmonic distortion rather than
total harmonic distortion?)
To cut a short story long: Back
in my university days I bought an old Discman over the internet
had the internet back then), along with Stereophile
Test CD 2. I tested this on an HP dynamic signal analyser,
one of the tests was to verify the 0.3% THD claim for track 24.
This track has a 500Hz tone distorted through a transistor amplifier,
which is very audible - the result was indeed something like 0.31%.
(I actually had remembered the figure as 0.1%. So much for memory.)
Fast forward to the present, and
I'm testing a chip for that amp development I mentioned above.
This particular chip (which I wont name) seemed to have
good enough distortion specs (0.05% from 50mW to 12W at 1kHz),
and be ideal for my application. It was fine without a load (typical
for class-AB amplifiers), but on load I was having to work hard
to get distortion at low signal levels down to the noise floor
of my analyser (about 0.001% - something I have come to expect
from a modern high quality amplifier - irrespective of whether
this level of distortion is audible or not). (More notes below
on this below) So I hooked
up a small speaker, hoping the signal would be too quiet for the
distortion to matter, but even at a few milliwatts I could hear
the distortion components I was working with - these were in the
range of 0.1% to 0.01%. After hours of experimenting with distortion-reducing
ideas I managed to get the chip working acceptably for the application
(distortion measuring below 0.006% was inaudible for the vast
majority of situations).
The Gainclone concept I had stumbled
across a year earlier had left me confused, but this latest experience
turned it into a grating inconsistency: Here I have the best amp
chip I could find (to work in the application), measuring cleaner
than many chip amps, yet it clearly remains sonically impure.
So I had the brilliant idea (it was probably 4am, any idea seems
brilliant then) to test my other "Gainclones" while
I had the distortion setup going...
Of course these aren't actual
Gainclones as I built them before I knew of the concept, but they
use much same techniques - perhaps for different reasons:
The first one is an LM1875
based amplifier I built for our main MLS tester. I never expected
much out of this chip, with a good THD+N spec of 0.015% but rapidly
rising THD at lower output levels, typical of class-B transistor
amplifiers. On specs alone, I'd put it in the same category as
the chip I was using above. In actual fact I couldn't face using
it in an audio application, and ended up putting it in a parts
drawer to be used as servo motor driver or something one day!
This circuit is made with a combination of veroboard and point
to point wiring, and is very compact. Its main function is to
play an MLS signal (essentially a square wave), but on occasions
I have routed music through it and been surprised at how good
The second amplifier is more conventional
(I actually have a few of these). It is built around a DSE K-5612
50W+50W amplifier kit based on LM3886
chips (February 1995 issue of Silicon Chip magazine). It gets
used for testing and sometimes demonstrating our speakers. I went
for these kits because they were very easy to build and modify,
and had one of the best amp chips available at the time with an
acceptable THD spec of 0.03%, and a minimum THD of 0.002% hinting
at better performance potential - plus indications on the web
that they sounded good.
(There's more info on these amplifiers
in the detailed tests section below.)
Testing the LM1875 Gainclone was
particularly easy, being part of the LAUD system used to measure
distortion. All I needed to do was hook an 8 ohm resistor and
a probe up to the amp output terminals, and do a low-level 1kHz
single tone FFT.
I was stunned (kinda was already
anyway - being 4am): The 3rd harmonic was always better than 90dB
down, typically 95dB. The 5th was always better than 100dB down,
typically -105dB = 0.0006%! (the residual of the raw LAUD analyser).
The 2nd harmonic was the one that led to the THD spec of 0.015%,
but that's ok. So:
The LM3886 amp was much the same,
but without the even harmonics (2nd and 4th), leading to the lower
THD spec, while retaining much the same potential for audio performance.
Maybe the result doesn't tell
the whole story, because these chips are set up as big power opamps
with huge amounts of negative feedback and may behave differently
on transients or high frequencies - but I'm thinking that it does
tell the whole story. There's certainly no denying the linearity
of these "Gainclone" chips.
So that's the Gainclone issue
resolved. In case you were hanging out for an executive summary,
There you have it. There's no
magic - not in my opinion anyway. Short feedback paths, small
filter capacitors and the like are interesting features but really
are just good power opamp circuit design (as I'll expand on later on). I know there are other brands
of chip which apparently work well, one day I might test some.
That's the original question answered,
but if you're interested in more details, tests and amplifier
building hints, then read on...
A day later, I got out the big
guns, and fired up a more serious notch-filter based distortion
rig which has a distortion residual for the 5th harmonic of -126dB
Summary of test conditions
details for devices under test
(also see description of these above)
notes about my distortion testing philosophy / approach
The harmonic distortion that matters
never exceeds 0.001%, which equates to a power level ten billion
times lower than the fundamental (0.001%^2 = 1E-10). This
is better than the performance of most CD players, including many
high end models.
Chip amps have always had a good
following. They may be seen as the "scum of transistor tyranny"
by some, and certainly do have their limitations compared to many
discrete designs, but most designers appreciate the advantages
that chip amps can bring:
Remember the people at National
are 'just doing their job'. They are not part-time hobbyist designers,
working with dubious quality information off the web, limited
experience, limited resources, and making subjective judgements
about everything. They dont have to arrive at good solutions
They have (or at least can have)
full understanding of and control over how every part on the chip
behaves. They have the resources to simulate everything, run prototypes,
and have the responsibly to apply an objective and thorough approach
to everything (especially these days). They either design or have
the option to alter the design of every component they use. Project
briefs like "design a superb quality high power monolithic
audio amplifier for our new range" are bound to attract audio
enthusiasts, creating an environment (or design team sub-culture)
that is naturally motivated, sonically competent, with a healthy
balance of subjective input and innovation. I've seen indications
of the same thing at Tripath, Philips and Analog Devices (from
their documentation, or talking to their designers), and I'm sure
it occurs elsewhere, so this is not a National sales pitch. When
it works, it really works, and I hope the designers at National
are pleased (if slightly amused) to see their chips gain a cult
Disclaimer: I have never built a "Gainclone"
as such, because I thought they were bizarre until I measured
the ones I had already built (that will only make sense after
reading the text above). These ideas are pulled from my general
experience, or experience with other chip amps and may be a little
bit - what's the word - "empirical". Enjoy.
Filter caps: Get supply filter caps as close to the
amp chip as possible, but keep them small because you don't want
ultra-high current pulses going into them if they're right by
the chip. If you want to use bigger caps, put some resistance
and/or inductance in series with the transformer, or use a smaller
transformer. (If you had an ultra low signal level opamp on an
input board in a piece of instrumentation, you wouldn't run a
dirty supply to a thundering great big cap hovering over the input
pins, so why do it in an audio amplifier?). Remember that highly
nonlinear audio power currents will run all the way back to any
caps you have in parallel, while pulses of current will run from
the power transformer all the way to the cap closest to the chip
(more sophisticated solutions then become obvious). But with the
PSRR of the Natsemi amp chips, why would you go to all this effort
when a bit of voltage ripple isn't going to hurt? Small 1000uF
caps close to the chip are sounding better all the time.
Bypass caps: Only play with these if you know what
you're doing (or have time to trial properly). Parasitic inductance
and low ESR can cause resonances.
Rectifier: In my opinion not a lot beats big old
bridge rectifiers. They're slow, so they don't generate a lot
of noise to start with, and can (should) always be bypassed with
fairly big capacitors and/or snubbers. I personally think fast
recovery diodes here are pointless. Use soft recovery types if
you can. If you get interference on your TV (as with the LM3886
amp described here actually - must fix it), you know something
Transformer: If everything else is right, it shouldn't
really matter. Just make sure it is not susceptible to mains-borne
interference, doesnt howl away audibly, and doesn't radiate
a magnetic field strong enough to melt metal casework next to
it. The choice is well documented.
Grounding and layout: This is "everything". If you
don't understand, do what the datasheet layout notes say, and
remember that power supply currents are highly nonlinear and all
wires are resistors. The effects usually go in this order:
Negative feedback: These chip amps are terrible for oscillation.
They're fast, so they're going to oscillate if used improperly.
Keep the negative feedback input pin node as short as possible
so it doesn't capacitively couple to anything else. Keep the other
side of the resistor close to the chip output so it doesn't pick
up inductance of the output leads (won't hurt the speaker signal,
but will hurt the negative feedback). If you look at the 47 Lab
pages, you'll see a description
of exactly the same battle with almost no mention of fringe
concepts such as "time smear".
More stability stuff: Thats not enough, they'll still
oscillate if someone on the other side of the world starts thinking
about it (the more Gaincloners there are, the bigger this problem
becomes). Use the Zobel networks as prescribed, and the output
filter thing. Put a tiny cap across the inputs of the chip if
you absolutely have to. Bypass the supplies better. Don't run
the amps at low gain. Even that's not enough and I must admit
to not really knowing what's going on. (I didn't know what oscillation
was until I tried building a chip amp from scratch, and I've designed
a few amps in my time.) If your amp is hissing, getting hot, or
making crackling noises on transients (more so than clipping),
it is probably oscillating. Some amps actually sound better like
this and 400kHz (or 22 MHz I think I measured at one point) won't
blow up your tweeters, but it's unlikely to be stable.
Miniaturisation: In general it's nowhere near as important
electrically as it is mentally. I miniaturise things mainly because
I think it is cool, or because it uses less materials, or because
clients want it. It does reduce parasitics, including nonlinear
parasitics (such as dielectric absorption, microphonics) and EMC
problems, but the benefits are almost always secondary to good
grounding and layout as described above. If you build circuits
right, size doesn't matter until you get up to UHF frequencies.
In short - it doesn't hurt to miniaturise your Gainclone, but
don't expect it to make much difference.
No mute: Looking at the circuit diagrams, the mute works
by disabling current from the input stage. Extra parts on silicon,
or unwanted signals getting in could be a problem. Really, I wouldn't
worry, but if you feel the need...
Inverted mode: Use it if you want, well documented reason
(common mode rejection). Again, I wouldn't worry because the gain
is much higher than unity so there is little common mode swing
at the inputs.
Omission of + input ground
resistor (inverted mode only):
Yes, only use one if needed for protection. It is a relic from
days when opamps had high / unpredictable bias currents. All it
does is increase noise (not that it's a problem at line levels).
Absolute polarity: Absolute polarity is very audible with
the right signals, so it is important to get the speaker wires
the right way around. Your woofers should move out when you apply
positive voltage to the amp's input (and no, this has nothing
to do with dogs for those of you chuckling along in the background).
DC offset voltage: Personally I'd leave it alone. A bit
of bias current shouldn't hurt.
Class-A bias: This is something I haven't seen applied
to Gainclones yet. You put a resistor (or choke) from one of the
supplies to the opamp output. This may or may not improve things
and generally needs an ever-expanding amount of work (including
listening tests) to get right. It makes little difference to chips
like the LM3886.
Temperature effects: Another approach I haven't seen applied
to Gainclones yet. Transistor (BJT) gain goes up as the chip gets
hotter, therefore distortion can reduce if they are kept hot.
However I've never managed to find any usable effect in a chip
Heatsink: Not as critical as most people make out, because
music doesn't have anywhere near the average power requirement
of a continuous test tone. With discrete amps you do need a good
safety margin, but these chips are very good at protecting themselves.
Soldering: A note for the inexperienced - with a
controlled temperature soldering iron (which is something you
should try to get) there should be no need to worry about soldering
heat destroying the chip. The melting point of lead based solder
is not much higher than the rated operating temperature of the
chip. Get plenty of heat in there to ensure you make a good joint.
Capacitors (in nearly all their forms) don't like to be melted,
and neither do thermal fuses in case you haven't already found
this out the hard way.
Speakers: Just a note that high impedance, inefficient speakers
can clean up "transistor" distortion very well. And
a note about speaker efficiency - you don't need high efficiency
speakers as a rule with a 50W amp. It's only 3dB less than the
"industry standard" 100W. You don't necessarily need
high efficiency speakers with a 5W amp. Try it and see. And don't
worry about blowing up your tweeters with an "underpowered"
amp, this is another myth
(it's the volume control that blows tweeters, not power amp clipping).
Output DC protection capacitors: Not that anyone does it any more, but
this is another relic from the past, when amps used to blow up
and take out the speakers. Use fuses if you're worried, 5A fast
blow protects the LM3886 (or rather the speakers) nicely. I'm
always blowing fuses for silly reasons (these are test amps, remember),
and I've never had one blow in use.
Chip selection: Don't trust the datasheet specs! They
are correct, but not necessarily relevant or useful for comparison.
I have found out the hard way!
Disclaimer: I'd prefer to avoid this section because
it's just asking for a fight, but there are a growing number of
people who are shocked when they find out that some common audio
design techniques have little or no theoretical basis, and no
objective evidence to back them up. They feel ripped off, lied
to, by the audio industry - and either turn away from it altogether,
or become rampant objectivists who prefer to spout their theoretical
beliefs rather than risk continuing a search for the truth. I'm
not saying that the concepts here are irrelevant - for example
it was only a few decades ago when the "1% distortion is
generally inaudible" rule of thumb held true. I'm just saying
"open your eyes before you open your wallet".
Wire: Definitely not an argument I want to get into here,
but you should know that the concept of sonic differences between
things like copper and silver wire is totally foreign to electronics
theory (which is the basis of amplifier design). I'm not saying
there is no difference, just that there is a massive amount of
hype around which has never been justified by measurement (either
electrical, or in objective listening trials). I do agree that
using silver wire is very cool, and if it were to impart a sound
of its own I should hope it would appear brighter, more revealing,
and a bit less "warm" than copper.
"Stored energy" and
"speed" of filter capacitors: The concepts, as usually presented, are actually
quite foreign to the field of electronics. They seem to have parallels
with the actual theoretical concepts of "stored energy"
and "speed", but not enough to justify the strange theories
and effects attributed to them. The explanations seem to have
much more to do with the perception of the sound than any technical
reason/s behind it.
Time smear: This is a meaningful defect for transmission
systems, storage systems, coding (such as MP3) and even speakers,
but it has no real meaning for amplifiers, which rarely have any
real means of storing (delaying) information to the extent needed
to justify blanket application of the word "smear".
The closest parallel with accepted theory seems to be "group
delay" or "phase shift", which is easily measurable.
Again, the audible effects may be perfectly real, but the explanation
is probably barking up the wrong tree.
Mechanical vibrations: Another contentious subject - is an amplifier's
performance affected by acoustic vibrations? Undoubtedly yes,
and severe problems with microphonics will be noticeable, but
vibration treatments and associated theories frequently drift
off into a dreamland unsupported by any actual experience. Another
word for this is "guesswork" - so be careful. A lot
of mechanical treatments seem to have less to do with vibration
and more to do with making something look cool. That can't hurt.
Resistors and capacitors: Yet another contentious subject. It is
well known that these parts are imperfect (V does not equal I
* R etc), but most resistors are near ideal for audio and this
often has very little to do with how expensive they are. Imperfections
in capacitors are more pronounced, but very few people know that
most modern electrolytic capacitors perform as well or better
in distortion tests than polyester for example. It's an area overflowing
with hype, assumption, conjecture, emotion and belief. But that
can be fun.
Non-ferrous construction: From wiring to resistors to casework,
this has a basis in reality, because magnetic effects in steel
are nonlinear and eddy current losses are therefore also nonlinear.
However, it also has a basis in "fashion". DIY designers
would benefit if it was possible to separate the two.
Burn in: This also has a basis in reality - dielectrics
of capacitors in particular can take a while for charges to "bed
down", and impurities (contamination) and stresses in semiconductors
may be relieved after a period of use, leading to lower noise
and possibly reduced distortion. But when people start talking
about burning in of wires, bang goes any sense of technical credibility
as seen by the vast majority of engineering professionals - along
with the likelihood of you returning a product that may have had
no real effect in the first place.
In closing, the effects described
above are rarely measurable in any clear sense, so the design
process often resorts to guesswork, using rough subjective evaluation
for feedback. This is better than doing nothing I guess, and represents
the application of a certain level of "art", "innovation"
and "attention to detail" which isn't a bad thing. But
you should remember that there is a huge difference between clearly
measurable harmonic distortion in an amplifier chip, and conjecture
over the sound of a short piece of silver versus copper wire.
My intention isn't to provide
a comprehensive set of links here, just some pointers to get you
Q: Can you tell me more about Gainclones or help me
out with my design?
A: No, sorry. I can't help you with your Gainclone design,
because I am not a Gainclone guru (not in the cloning the Gaincard
sense). See our services
page if you wish to inquire about my contract design services
(audio design is my job, so I can't be doing it for free).
Q: Can I have your Gainclone schematics and assembly
A: See answer above. There are plenty of designs on the
web, kits are available, and National has always been good with
their application notes. All this stuff is documented from a practical
point of view and I suggest this is your best bet. Check out our
for our range of audio products, some of which will be of interest
Q: Tell me more about your distortion test setup so
I can criticise it, or replicate it.
A: No. If you haven't got the time, tools and knowledge
to replicate these measurements yourself, don't criticise mine.
If you have a genuine question, specific suggestion, or are convinced
I am in error, please let me know.
Q: Can I have the raw test results?
A: Not at this stage sorry. I want to hang onto them because
they contain information which might be commercially sensitive
to our company (which is in the business of designing amplifiers).
If you want to copy the graphs, please link to this page or at
least credit where they came from.
Q: You use a lot of polysyllabic words. What do they
A: Check out our glossary (when it arrives).