Listen to the Op Amp´s

Can you hear the difference between Op Amp´s? Yes!
With this headphone amplifier.

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This is the basic cmoy headphone amplifier, hacked to fit many different Op Amp´s!

To explore Op Amp´s the "cmoy" headphone amplifier is a good starting point.

This project here is basically a cmoy, to fit the Op Amp challenge even the virtual ground is done with a Op Amp.  So at least 3 Op Amp´s are used here, 2 chips when a dual is used.

What is a cmoy?  It´s a headphone amplifier made by Chu Moy a.k.a. Headwize around 1998. It uses a dual Op Amp and 9V battery. There is quite a lot of documentation around from many sources, sadly some are gone but many can be found with the webarchive.

To start, here is the original cmoy:

But whats with the "listening to the Op Amp´s" you might ask? Yes they sound differently, today you could call it a equalizer pre-set, or some kind of filter. 

Here is a list of some Op Amp´s and the sound you can expect:

The PCB is made to fit SMD and THT where possible, and it can be populated in many ways. Using different or no input capacitor, changing the amplification. Even a ZIF socket can be used to make swaping the Op Amp´s simpler.

There is much more to come, PCB´s and parts are currently ordered :-)

  • pcb parcel lost

    Stephan Martin6 days ago 0 comments

    Thats a first for me, the package is lost :-(

    It is now getting manufactured again but it will be to late to complete this project in time for the Op Amp Challenge deadline.

    So meanwhile this is how the SMD and alternative THT footprints are used:

    Only R4 shows on the silkscreen, the _1 variant is hidden.

    It is a 1206 SMD Footprint in R4 and a THT Axial 1/8W D1,6mm L3,6mm with 7,62mm spacing as R4_1 combined.

    It is possible to mix SMD and THT so you can use up whatever is on hand

  • Classic 47, a DIY kit for single Op Amp´s

    Stephan Martin05/22/2023 at 18:54 0 comments

    Search online for "Classic 47 Headphone" and you will find kit´s to solder that are basically cmoy headphone amplifiers.

    As im still waiting for the PCB´s i soldered up such a kit to give it a go:

    Both Op Amp´s are already in sockets and its delivered with a set of NE5532.

    So far i have given it a quick test to confirm it works, and then tried to hear a difference against OPA604 and AD8065. But i cannot say that its a clear difference...

  • ZIF and dual or single

    Stephan Martin05/13/2023 at 19:45 0 comments

    While waiting for the PCB let´s use KiCad´s 3D view to show how the ZIF socket will look when mounted:

    The ZIF socket is stacked in the DIL socket´s, i placed some resistors too close so on this version of the PCB its not possible to solder the ZIF socket directly... This will be fixed once i have build up the first amp and therefore discovered the other hidden bugs still inside...

    It´s possible to use Dual or Single Op Amp´s, but dont use both at the same time, or maybe give that a try?

    A 28 pin ZIF socket is used, that gives 1 row spacing between the Single and Dual Op Amp´s.

    (the ZIF is not needed, inserting the Op Amp´s directly into the DIL sockets is ok. but it will not look as fancy...)

  • Bag of Parts arrived!

    Stephan Martin05/08/2023 at 10:07 0 comments

    The Parts arrived, this is a bag full of Op-Amp´s and everything else needed for the build up.

    The red item in the lower left corner is a DIL ZIF socket, with above some SOIC ZIF sockets. Like this its possible to test different OP Amp´s without soldering them in, or lets say thats the plan :-)

    Now im waiting for the PCB´s to be shipped...

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