August 23rd, 2009

Audio Amplifier with TDA2050

Audio Amplifier with TDA2050

Thomas Bethe built an audio hi-fi amplifier using two TDA2050 integrated chips. I haven’t seen these chips used in projects in a while, because it’s pretty known that TDA2030, TDA2040, TDA2050 chip family is not the best so to say. I remember some years ago, a local factory was building hi-fi amps using these chips and how often i needed to replace the destroyed TDA’s. Their Pentawatt package is not very good. These ICs are more suitable for TV sound amplification, radios, applications in which they drive some small full range speaker.

The speakers Thomas wants to use with his amplifier are a pair of Klipsch RB-51, which are pretty small and well behaved. In the TDA2050 datasheet it is proudly stated that the small chip can deliver 32 Watts RMS into 8 ohms with 10% THD. At this level of distortion those Watts are actually WHATS?! From graphs we can see it can actually deliver about 18W into 8 ohms and stay in the hi-fi area of 0.1% THD.

The schematic used is the split power supply version from the datasheet with an additional feature, headphone output. Thomas used a MKP capacitor at the input of the amplifier circuit. Although it’s always best to use high quality components, i wonder if any differences can be noticed with the TDA. The construction is pretty simple, just a few external components are needed but as the author says the layout is very important in reducing noise. So follow the advices he points in his article.

The amplifier is connected to +/- 25V supply rails, therefore it is not recommended for this amp to be used with 4 ohms loads. If you have low impedance speakers use +/-18V supply. Thomas’ power supply seems to me an overkill but i guess it does the job. If you plan on building this amp yourself screen the power supply and avoid crossing the wires carrying audio signal above power supply.

As far as how it sounds Thomas seems to be happy, even calls it a “mini gainclone”. To me the TDA’s don’t stand at the same level with National Semiconductor LM chips but it’s purely subjective opinion. Anyways anything you build by yourself is ten times better than what you find in the market for the same price as your investment so happy soldering.

Audio Amplifier with TDA2050: [Via][Link]

August 21st, 2009

Hi-Fi Tube Amplifier

Hi-Fi Tube Amplifier

Here is a project for music lovers. Although electronic tube or valve era is long passed, these devices are still used in high quality audio applications. It is true that you won’t wont find them in every home because their regarded as obsolete or too exotic. Guitar players are the ones who know and appreciate their sound as many famous guitarists use tube amps to drive their instruments. Stereo amplifiers built with tubes for hi-fi applications are still being made today and their cost can be pretty high as these amps are though to deliver high quality sound.

The reason tubes have a specific sound has to do in my opinion with the fact that tube distortion is mainly second order which is more music-friendly than the 3rd order distortion that solid state devices have. Some say this is because in tubes you control the flow of electrons and only electrons carry your information unlike transistors.

Depending on their output stage configuration tube amps can be single ended ( using only one tube working in class A) or push-pull ( like with transistor using two tubes working either class A or class AB). Because of the high output impedance of tubes they need an impedance transformer to drive the speakers. This is also the reason of their low damping factor which in combination with their usually low power output makes these amps suitable for certain types of speakers. From my experience you will need speakers with big woofers and very efficient (high SPL per watt). Also i have found that single ended amplifiers ( in class A of course) with high anode voltages applied are best when tube-like sound is desired.

Returning to the project at hand, it is a push-pull design using 6v6 pentodes connected as triodes. If you get an ultralinear output transformer you can use the 6v6 as pentodes.  The input stage using a 5965 double triode is as simple as it gets. It amplifies the signal in order to attack the final stage and provides phase inversion necessary for push-pull. The power supply uses semiconductor rectification which i find a bad thing for a tube project. There are tube diodes available for this task.

As with most audio high fidelity projects  the quality of the sound is in strong relation with the quality of the build. If you do this project just for fun then you will be happy with it just working, if you build it to experience tube sound you should take greater care at layout and components you use. Using multiple transformers is a bad thing as they introduce noise. Using one transformer with many output voltages is alot better. And screening of the transformers is a must. In the project link you will find many advices on how to build it even though the builder didn’t follow all of them.

Another thing, and a reason that keeps many diy-ers away from tubes, is that you will be dealing with high voltages. Be very careful with that. And to close this presentation with another advice don’t use it to amplify your iPod.

Hi-Fi Tube Amplifier: [Via][Link]

LM3886 2×68 Watt Amplifier Full Project

LM3886 268 Watt Amplifier Full Project description:
In this application, we are building a gaincard like amplifier. This application type is named gainclone in audio world. To take a satisfactory audio response, we are adding a Linkwitz equaliser to the feedback line and adding bass compensation also. We are using LM3886 which is the revised version of its brother LM3875. Briefly features of LM3886 are:

  • Maximum Output Power: 68W RMS – 108W Peak
  • THD: %0.03 at 60W
  • SNR: 110dB at 60 W – 92.5dB at 1W
  • PSRR: 120dB
  • Protection Circuitries: DC/AC Short circuit protection and thermal protection
  • Output Class: Conjugate AB-A

These are the parameters of the LM3886 that we are interested in. Honestly this values are much more better than many of HI-FI amplifiers sold in the market. Especially it is hard to find 110dB signal to noise ratio. And another property is, when there is no input, this amplifier is quite like a dead. It is nearly impossible to hear any noise when you stick your ear to the speakers. Read the rest of this project at project page.
LM3886 268 Watt Amplifier Full Project: [Via][PCB, layout, connection diagram files]

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