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I'm all attracted to minimalism. Not as strange as it may sound since I'm just like most other tube lovers building my amplifiers and other designs with just a few components. The slogan "less is more" is quite popular nowadays. As we all know, most consumer equipment is stuffed with electronic components (not always high-end) and sometimes it is difficult to speak about an amplifier when most of the components seem to be intended to support the user interface functions. Most AV-receivers are more an embedded computers than something else.
Apart from this, most of these functions are not necessary to appreciate it's sonic performance anyway and they may distract you from the really important part: The musical experience.
In other areas the are : Older young people, successful in life buy themselves a Harley motorcycle. Harleys may strictly technically spoken not be the best motorcycles, and they're certainly not full of LED,s, computers, gadgets etc. (Honda Gold Wing) etc. But the driver feels in contact with his technology and the driving experience is more intense. In my opinion, the same is true for tube amplifiers and other minimalist designs: More focus on the things that are important, and use of very good components to realize the goals.
On this page the introduction and my search for the right chip and design. On the second page you will find the actual GainPre construction.
On another page in the DIY section you will find the description of my first OpAmp project, the GeenKloon. The GeenKloon is one of the reincarnations of the gainclone or the 4706 Gaincard amplifier of 47-laboratories.
These designs are based on a very minimalist component selection, although strictly speaking an OpAmp can not be seriously described as "one single component". OK, it has only 5 pins (5 pins used, it has 11) but it is in itself a complete amplifier excluding housing, power supply and proper rectification. Of course there are people that claim that by definition a transistor based device, especially if making use of highly integrated circuits cannot sound well. Please let's step over these prejudices and try to make the best sounding IC pre amp ...
After making the gainclone I thought that it would be a good thing to make a matching phono preamplifier. After all, not all of my favorite sources do have an output level of 2 Volts. For a moment I thought that 47-laboratories had not thought about this, but I was wrong. There is a 4712 Phonocube which matches the gaincard. Kimura San's had the following design goals in mind:
Therefore, I have decided that sooner or later I'll have to build my own version of the Phonocube based on an OpAmp. I do not know whether I'll be able to find my own "cheapo"alternative for the design criteria found above but we'll see and I'm determined to try.
Also for my project I have to describe a few goals which will prevent from letting it run out of hand later (especially cost and time).
OK, my first activity was to visit the site of National Semiconductors and search for OpAmps which might be useful for someone building a phono amplifier. There are far more OpAmps than I had ever imagined but in order to make a shortlist I did a search for "phono" in the database of Application Notes. This reduced the list of results considerably and resulted in amongst others in the LM318, LM380 and LM833. The LM380 was not suitable for the project as it contains a power amplifier, but the last one seemed to have better properties.
There are many more OpAmps that offer similar or even better performance than the LM-833, but this one contained hints and tips for creating phono amplifiers which allowed me to make the schematics above. Fortunately, the formulas given in the application notes of the LM-833 are applicable to other OpAmps as well. In any case one needs an OpAmps with high-gain because a phono equaliser -whether for MM or MC cartridges- amplifies between 30 and 75dB.
Still, most of these OpAmps do not have the specifications I'm looking for in a new phono amp. Especially offset voltage etc. needs to be very low and better slewrate etc. As I will use the device to amplify very low voltages of MC phono cartridges I might as well match the requirements with better OpAmps. Some others that seem to have better characteristics are:
Especially the LT-1037 seems to be very useful for phono applications. Unfortunately I have no experience with high-precision opAmps and therefore no idea how this OpAmp will behave in my equaliser. Also, costs of some OpAmps are outrageous and I find it difficult to relate their price to sonic performance. On the other hand, high-precision opamps are in general more expensive than Power Opamps used in Gainclones.
The Power Supply of the GainClone can also be used for the phono amp, at least that is what happens in the original Gaincard/PhonoCube setup where the Power Humpty is shared between these devices. In this case, sharing of the power supply seems a convenient solutions as well, be it that most Opamps need a lower supply voltage.
In the original Gaincard/Phonocube setup, the Humpty Dumpty may or may not be loaded with only one or two devices at the same time, 47-labs does advise separate power supplies for optimum performance. However, for cost saving purposes (especially if one is charged $2,200 for an original Power Humpty), there is nothing wrong in sharing one power supply between two devices. Should the sonic performance be satisfactory then I can always add more power to the setup.
It becomes time to build my own phono equaliser. In the spirit of he GainClone designs I will try to use as little components as possible yet to let it make music. Since it will be relatively easy to swap components at a later stage, I do not worry too much about exotic components.
Given the costs of High-Precisison OpAmps I will probably first build a simple prototype which I can upgrade at a later stage. However, I need to find at least a version that can deal with input voltage levels of MC cartridges in order to be useful.
Below you will find a table with a RIAA amplifier setup which is based on the Application Notes of the LM833 and that will allow building both an MM phono pre with 30dB amplification as well as a MC phono pre with 71dB amplification. But I doubt whether the LM833 is suitable for making an amplifier for input levels of 1mV or less.
| # | Comp |
AN-val |
71dB | Description |
| 1 | V1, V2 | Dual high-gain OpAmp | ||
| 2 | R0 | 499 | 510 | Determines Av1 amplification of first stage |
| 3 |
R1 |
80.6k |
150k |
Part of the 50, 500Hz RIAA filter |
| 4 | R2 | 8.45k | 16k | Part of the 50, 500Hz RIAA filter |
| 5 | R3 | 2.37k | 2.4k | Part of the High filter R3,C3,R6 |
| 6 | R4 | 2k | 1k | Value is free, but determines together with R5 amplification Av2 of second stage |
| 7 | R5 | 4.3k | 160k | The relation between R5 over R4 determines the amplification Av2 of the second stage |
| 8 | R6 | 54.9k | 43k | Part of the High-filter R3,C3,R6 |
| 9 | C0 | 200uF | 220uF | Decoupling DC |
| 10 | C1 | 39nF | 22nF | NF filter |
| 11 | Cp | ?? | ?? | (parallel to input, not used) |
| 12 | C3 | 0.033uF | 33nF | Part of the High-filter R3,C3,R6 |
| 13 | C4 | 2uF | 1uF | Audio Coupling capacitor |
| 14 | Ri | 47k | 1k | Impedance of 47K (MM), can be left out for MC |
The values above result in the following schematics for the phono amplifier:
This is a very minimalist design, and I'm curious whether it will produce any sound at all. I expect to need a few more components in order to get the thing working the way I want. The power supply of most OpAmps need to stay under 35 Volts, something that's nearly impossible when using the powersupply of the GeenKloon. Apart from that, for this type of application we need more buffering in the power supply. After all, the OpAmps used here and the signal level coming from the turntable is different from that used in a power amp such as the LM3875.
The datasheets of the AD797 (and most others) specify a power supply of +/- 5 to about +/ 15V. As gainclones need almost double this voltage level I have decided not to use the GeenKloon power supply in this stage. Later we'll see.
Of-course we need a handful of other components before being able to make the GeenKloon such as:
On the following pages more information on the 4712 Phonocube, Gainclones and the original 4706 Gaincard can be found:
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