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GeenKloon?
(=NoClone?)
The following pages are available:
You might wonder what this project is all about. Some time ago a new forum started in the Netherlands, the "High- End forum of AudioCube. The forum is owned and moderated by two audio/Hifi enthusiasts who intended to start a community through this portal.
On the site I read how the forum owners also import Hifi equipment that otherwise would not reach the Dutch market, for example because manufacturers do not have a local distributor or because their products are simply unknown to the public. As part of their hobby and without profit intentions, they therefore import such equipment themselves and do all the work such as customs duties, VAT, warranty and all other paperwork . Hmm, I like my job but I also like to be paid for serious work and at least I would like to be compensated for my efforts. Therefore I can hardly believe we're talking community work here ... but .. O well, it's their "business".
But
that's not the reason for my interest in the GainCard, it is the minimalistic
approach which makes this design interesting. The amplifier, the 4700 GainCard
for example consists of two separate boxes that are kept together by the front
faceplate. Inside is a bare minimum of 9 components and an attenuator and some
connectors on the back. The most important component inside is the power opamp,
an amplifier-on-a-chip, and it delivers 25 or 50 Watts (depending on the model).
Should you think that a power supply is bundeld with the amplifier, you're wrong: The power supply is an aluminium cylinder called 4700 power Humpty. Inside is a transformer, a rectifier and maybe a few small capacitors.
Both the power supply and the amplifier unit are apparently made of quality materials and components. But still, €1800 for the amp and €2200 for the power supply is a lot of money for these components. Even if you like myself like the design and the looks, it's still expensive for an object of art. (images copied from official Sakamura Systems site)
Since copying the Gaincard showed promising results, lot's of people worlwide are building their own version of the GainClone. Of course it will never be or sound the same as the original, but if that's your problem you should buy one. However, building your own copy is challenging, not for the looks but for the musical capabilities.
Still, the original GainCard is not document extensively and there is little known about the insides of the small boxes. therefore we have to rely on reviews of components, interviews with the manufacturer and experiences of other GainClone enthusiasts. Normally, such a reverse engineering process would be nearly impossible, but because the GainCard is composed of just a few (9) components it pays to try anyway since there is only a limited amount of variables.
At the time of writing this page for the first time, I did not have any experience with the GainCard and it's sound, so strictly spoken I was not even copying the original butI built my own amp (more or less). And I don't care, after all it's a hobby and I might accept the invitation of AudioCube to compare my clone with the original. And should the 4706 Gaincard win I still don't care, after all my GeenKloon cost me about $200 and the original is still around $3000, there should be a difference to justify the pricepoint. It would be a bad day for 47labs if mine sounded better right?
Meanwhile, more people start building their own clone and the overall feedback is positive.... (read the thread "Wie bouwt de mooiste Gainclone?" on hear.nl)
The
schematics of a Gainclone amplifier are very simpel. On the website of National.com
the datasheets of for example the LM1875
and the LM3875 can be
found in PDF format without problems. And in these datasheets the basic amplifier
schema's and several options for the Gainclone can be found. Of course there
are still lots of options left to the reader to tweak his/her own design.
There are two ways of connecting the poweramps to their powersupply: By means of a symmetrical power V- and V+ or the "single supply". The symmetrical setup is the easiest one to build (maybe with exception of the power supply itself) and this one must also be the one used by Kimura San (the single supply design would probably bring the number of components in the Gaincard above the 9 mentioned).
On his GainClone page, Craig uses a different component numbering scheme and since the numbering of the LM1875 and LM3875 differ anyway, I will adopt Craigs numbering here in the table and the figures.
What are the minimum requirements for building a GainClone yourself. First of all you have to make a choice for the type of Power Opamp that will be used. This choice is essential as it determines the output power (should match your speakers) and other options such as mute. Some Power Opamps are available in different types of housing with 5 or 11 pins etc. this determines the layout of some key components (such as the feedback loop) inside the amplifier.
On the internet, several others have written down their story,
and therefore I decided to stay close to both the datasheet and the design of
some others. These people give good advice for your GainClone as well: Do not
use chips with mute functions (their sound is impacted), do not use a stereo
model etc. etc.
Common models that are often used are the LM-1875 and the LM-3875 of National and I more or less decided to start with one of these chips for two reasons:
The original Gaincard only has a total of 9 components. 8 of them are capacitors and resistors. The following list describes the components for a typical GainClone and this list may be the basis for your own GainClone. The component numbering used is the same as used on the Gainclone homepage of Craig Fraser:
|
Craig's number |
LM1875 |
LM1875 |
LM3875 sheet |
LM3875 Value |
Description |
| R1 | R3 | 1K | Ri | 1K | gain |
| R2 | R4 | 20K | Rf1 | 20K | gain |
| R3 | R5 | 1 Ohm | ??? | 1 | zobel |
| R4 | R2 | 22K | R1N | 10 K | input imp |
|
C1 |
C2 | 22 uF | Ci | 22 uF | |
| C2 | C5 | 0.22 uF | ??? | ??? | zobel |
| C3 | C6 | 100 uF | Cs | ??? | stabilisation |
| C4 | C7 | 100 uF | Cs | ??? | stabilisation |
| C5 | C4 | 0.1 uF | n.a. | bypass of elco | |
| C6 | C3 | 0.1 uF | n.a. | bypass of elco | |
| C7 | C1 | 2.2 uF | n.a. | Coupling Cap | |
Rows in Bold are considered mandatory components in the literature. Including the power Opamp itself this brings us to 9 components per channel. This is the amount mentioned in the several articles on the web. Apart from these 9 core components we need more to build a GainClone amplifies such as:
Housing: The original is a dual-mono concept with two small boxes (one for each channel) connected through the thick aluminium faceplate.
Finally there is still one important component missing in this picture:
The power supply of the GainCard, the power Humpty, is simple when we must believe reviews and articles on the Gaincard. And since the proposed Power Opamps have an excellent power rejection, non regulated -30 and +30Volts DC power is basically all we need to keep the Opamp happy. Therefore we need:
Kimura San apparently decided not to build a bulky power supply with lots of buffering but instead make use of fast components in combination with a sufficiently large transformer for the power supply.
Just like Kimura San, the designer of the original GainCard I will try to use as little components as possible but an acceptable soundscape has priority. I do not worry too much about the exact choice of components and will use good but not too exotic components. After all it is relatively easy to swap components at a later stage should this enhance the GeenKloon significantly.
I want to begin using the LM3875 for my GeenKloon, and although some people use SMD type resistors because of their (in principle) shorter signal path (I cannot imagine this to make any difference). The original Gaincard uses a feedback circuit of 9mm, and for hardwiring and shortest signal path with the LM3875 a SMD resistor is nonsense. Instead I plan to use quality metalfilm resistors (0.6W, 1%) and low esr capacitors (Philips, maybe Black gates in a later stage). This is my component list:
|
GainClone |
LM3875 |
LM3875 |
Description |
| R1 | Ri | 1K | gain, metalfilm 1% |
| R2 | Rf | 20K | gain, metalfilm 1% |
| R3 | n.a. | 1 Ohm | zobel, against oscillation |
| R4 | n.a. | 22K | input impedance |
|
C1 |
Ci | 22 uF | Decoupling C for-Dc/Gnd |
| C2 | n.a. | 0.22 uF | zobel, against oscillation |
| C3 | Cs | 1000 uF | stabilisation |
| C4 | Cs | 1000 uF | stabilisation |
My plans were to use the GeenKloon as a power-amp at first, and after successful testing and an acceptance test by my wife invest time and money in pre-amp components such as attenuator etc. But, as a 12-step switch and some resistors turned out to be really cheap and cost me just half an hour to turn innto an 12-step attenuator I decided in the last days to build an integrated amp.
Instead I decided to leave out the power switch for the moment because the OpAmp does not care about power switch-on and switch-off current.
For the power supply I think that an Amplimo/Plitron model of 225VA will be the best value for the bucks. This transformer delivers 2 times 22Volts AC which after the rectifier will result in -30, 0 and +30 Volts DC. For the 25 Watts version of the Gaincard Mr. Junji Kimura uses 1000 uF and for the 50W version he uses 2200uF. As far as I know the Power Humpty is equal in this case so I expect the differences to be in the amplifier boxes only. As a result, I have chosen a value of 1000uF for both the V- and V+ pin. (And C3 and C4 will therefore not be 100uF but 1000uF).
The 1000uF value makes the design of the power supply very simple. the only thing we need is a transformer and 4 diodes. Of course you can add your own favorite components too, such as voltage stabilisators, additional caps etc. but strictly spoken these are superfluous and not necessary. The original transformer in the 4700 power Humpty is of a type that is not easy to obtain (170 VA according to web sources) and therefore I decided to use a slightly oversized Plitron type (225 VA).
On the following pages more information on GainClone design and the original (47 labs) can be found:
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© Maarten@Platenspeler.com, November 2002, 2005