Fully Integrated HiFi Studio Monitor

Studio Monitor and PCB

Have you ever wanted to build a high quality audio crossover and amplifier? [Rouslan] has put a lot of thought into making his dual amplifier studio monitor both high quality and simple to build.

With a concise schematic, a meaningful block diagram, and simulation results to boot, his well-written post has everything you need to build self-powered bi-amped speakers based on the LM4766 from Texas Instruments. It is great to see simulations which verify the functionality of the circuit, this can go a long way when working with complicated analog filters and audio circuitry. For those of you who do not have access to PSPICE (an expensive professional simulation tool), [Rouslan] uses LTspice from Linear Technology. TINA-TI from Texas Instruments is another great free alternative.

Additionally, [Rouslan] goes over the typical issues one has with a bi-amplifier studio monitor, such as phase misalignment and turn-on pop, and then provides a solution. Note that his project is powered by 20VAC, which requires an external transformer to convert the 120VAC in the wall to 20VAC. Be careful with high voltages! In the future, adding a high quality voltage regulator will most likely increase the performance.

His post finishes up with a very clean circuit board, which he ordered from OSH Park. With such a complete design, there is nothing keeping you from building your own. Go out and put that old speaker sitting in your basement to good use!

If you don’t have an old speaker sitting around, check out these very cool DIY speakers.


  1. David says:

    1. He forgot the Zobel networks.

    2. Audio amplifiers don’t benefit from regulated power supplies – see Doug Self’s book.

  2. tekkieneet says:

    Might want to watch out for ceramic caps in the audio and/or feedback path.

    Certain classes (2 & 3) of ceramic caps are known to have piezoelectric effects. Probably last thing you want inside a speaker as it can pick up vibrations . See here: http://product.tdk.com/capacitor/mlcc/en/faq/faq00031.html

    If you must use ceramic caps for the audio path, stick with C0G/NPO in Class I and you’ll get low temperature coefficient, low dielectric loss and stable over voltage. There are also film caps for higher values and they are available in SMT form.

    Not as much of an issue for decoupling.

    Note PSRR. That tells you how sensitive of the analog part of the power supply with respect to frequency.

  3. tekkieneet says:

    and the usual metal film vs carbon film resistors on thermal noise…

  4. Paul Smithe the great says:

    The zoble network is required for amplifier stability. Saying that loudspeakers with short leads are inductive to quite high frequencies and therefore this network can (dependent on amplifier) be as simple as a resistor and capacitor in series from the output to ground. This is the network I use on my similar chip amplifiers with no problems.

  5. Fallen says:

    I love making active monitors. They let you implement LR4 filters, which have a roll-off of 24dB, and sum to 0dB at the crossover point. Unlike typical butterworth filters, that have a 3dB bump at the crossover point. You can invert the phase of the tweeter to attenuate it 3dB and flatten it out, but now your phase response is messed up. That and a steeper rolloff will help your tweeters mechanical power handling (you can cross lower). <3 fully active monitors.

  6. Mike Lu says:

    If he uses one of those hybrid digital amplifier chips from TI, he could dispense with the heatsink altogether. Not to mention loads more efficiency.

  7. technotepad says:

    I have made this hack also to a pair gut old speakers. The link to schematic and PCB for DIY can befound here: http://techmind.dk/elektronik/aktiv-hojtaler-hack/

  8. uri says:

    Give them 10 more minutes until his board is available from China on eBay.

  9. Per Jensen says:

    I’m not at all fond of using the IEC C30-plug on the back for less-that mains voltage – that will end in a bang sooner or later when someone plugs the wrong cord into it…

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Get every new post delivered to your Inbox.

Join 96,687 other followers