Chill-amp II Updated on: May 17th 2016 For more than three years, I have been experimenting with 'gainclone' amplifiers. Gainclone amplifiers use opamps instead of the tubes and transistors that can be found in most amplifiers. I now present the second reincarnation of the Chill-amp concept.   Gainclone history My interest in trying something with opamps was born when I saw the raving reviews of the Gaincard of 47 Labs and the article "Op-amps are More Fun than Tubes". Soon, I found some pages describing various clones of the gaincard (called gainclones). The most interesting was a forum dedicated to making amplifiers with opamps, the Amp Chip DIY Forum. I found an interesting circuit made by Thorsten Loesch there, an inverting gainclone. With this circuit, I made my first amplifier, the Thor-amp. That amplifier sounded quite sweet and for a long time I was quite happy with the result! I found some limitations. I tried the non-inverted After a while, opamp circuit, and found it to be superior to the inverted circuit in some ways. I called it the Chill-amp. Meanwhile, on Diyaudio a gainclone rage was born, especially after the gainclone thread with beautiful casework of Peter Daniel. Finishing the second version of the Chill-amp took longer than expected due to various reasons. There are still some things to be tried out, but I think that the difference in sound over the first version is worthy of a release. The target of the Chill-amp II was to raise the bar further in performance (detail, imaging, dynamics, instrument realism etc.) while maintaining a good listenability with a wide range of material. Ultimately, I built this amplifier to enjoy all kinds of music, not to listen to some obscure audiophile labels only.   Chill-amp II compared to Chill-amp I Supply The biggest difference compare to the Chill-amp I is in the supply. The supply makes use of two transformer per channel. This way, less diodes are necessary. This improves the speed and linearity of the supply. I use STPS20H100CT dual schottky diodes. These are very practical because only two are necessary per channel. Supply decoupling I use a 1 uF capacitor very close to the opamp to reduce the supply noise and improve stability. Attenuator I now use a 50k stepped attenuator from DiyFidelity. It has 23 steps, which is more than enough for a good range in volume. The attenuator sounds great, and is very affordable. Input capacitor I use the Elna Silmic II 22 uF input capacitor. This is a very musical capacitor and sweetens up everything a tiny bit.   The schematics The circuit is very simple and consists of one power op-amp per channel with a handful of resistors and capacitors. The amp is built dual mono. The amplifier circuit The supply P1 is the stepped attenuator (50k). D1 and D2 are in one package, and so are D3 and D4.   Speakers A very important topic regarding chip amplifiers is the choice of speakers. The Chill-amp II can be best used on high efficiency speakers (>90 dB/W). Also, speakers with an impedance of 8 ohm are better suited. This amplifier is not so suitable for speakers with an impedance under 4 ohm. The Chill-amp II delivers about 40W. I currently use the Chill-amp II with Supravox 215 Signature Bicone full-range speakers in open-baffles. Very recommendable! More information will follow about these speakers...   Photos Here is a photo of the interior of the Chill-amp II: click me!. Furthermore, here you can find some photos of an earlier version of the Chill-amp II: Chill-amp II beta photos   PCB's The Chill-amp II makes use of PCBs. This done for multiple reasons. The first reason is that it makes the amplifier much easier and faster to build. It is easier to make good solder connections, especially for the ground wires! The components are mounted more rigid, thus vibrations will have less influence on the sound. Also, the two channels are more identical. Finally, the robustness is somewhat improved... (and it even looks better IMHO!) Regrettably, the PCBs and kits are not available any more. Please look for an alternative online. The supply PCB The amplifier PCB Transformers I bought a stock of block transformers to be used in the Chill-amp II. The transformers are 220 V primary, 18-0-18 V secondary, NOS from the late seventies. They are probably between 40-60 VAC; enough for a gain-clone if four are used. They sound fine. The transformers are available for only EUR 30,00 for four! I advise to pick them up directly if you are in the neighborhood (Eindhoven). I will be able to sell only about twenty transformers. Note: shipping outside the Netherlands will be quite expensive, so that is maybe not so recommendable.   Datasheets LM3875 power opamp STPS20H100CT diode   Build your own Chill-amp!!! Have a look at the Chill-amp II building manual!!! Here you can also find some additional information: DIY Chill-amp page   Links 47 Labs, the company that makes very inspiring audio designs! Amp Chip DIY forum, forum about Gainclones and non-oversampling DACs Audio-cube, page about 47 Labs and other high-end products Nick Whetstone's gainclone page Craig Frasers gainclone page Maartens gainclone page Richard Murdeys gainclone page Show the Chill-amp II building page please!!! Show the other audio projects!