Project files: Opamp buffer for ICEpower ASX-modules

What is it?
This is the PCB design for the dual opamp-based input buffer for the ICEpower ASX-modules as described in a previous post. This can be used before ICEpower ASX-modules in SE-mode if you need to raise the gain and/or the input impedance of the modules. You can also tune the sound quality and sound signature by using different opamps (yes, it does make a difference).

How big are the boards?
Boards measure 1.975″x1.75″ (app. 50x45mm) which means they are just small enough to be made very cheaply by Itead or several other companies.

What is the status of the boards?
This board is in version 1.1. I have previously prototyped version 1.0 which had a slightly different layout and only one input capacitor footprint, otherwise they are electrically identical. At the time of posting this I have ordered prototypes of v1.1 for myself but they haven’t arrived yet.

Does it use any special/expensive/hard-to-find parts?
No. At least not unless you go completely overboard with your choice of opamps 🙂

Anything else I need to know?

  • You can omit the input caps (bridge them) if you are using a source that does not have DC offset.
  • This board is not compatible with the ASX-modules when running in bridge mode because both opamps operate in phase.
  • You can’t power the board directly from the AUX supply on the ASX-module because the voltage is too high and the supply is unregulated. Use an external regulated supply or read the ICEpower docs for instructions on how to use the AUX supply.

Download design files here

Related information:
See the links referenced in the original blogpost.
Note: Always read the “intro post” for additional important information about my designs.

EDIT 07-09-2013 – added picture of the board.



17 Responses to Project files: Opamp buffer for ICEpower ASX-modules

  1. David Quayle says:

    Hi I’m finally getting around to using the buffer, with the last project I was going to use them on I realised the Active Crossover I was using to feed the 50ASX amp which was in the same case & mm’s away had it’s own output buffer, so adding another buffer didn’t seem warranted. With the buffer design any chance of explaining a couple of things, I have tried to work it out but am not sure I’m right. I’ve also tried to do a Spice Model & vary the components with little effect:
    I’m planning on using these buffers for the Icepower ASC200 modules I have.

    What purpose is C1A & C1B serving and why 2 in parallel?
    What purpose is R1A serving?
    How do you decide what value C10A should be?
    Is installing D1A really of any value, is there a downside?

    • theslowdiyer says:

      Hi David,

      Apologies for the late reply. As I am “out and about” at the moment this is going to be a bit short 🙂

      – C1 is the input capacitor to protect the amplifier from being fed DC. If you are absolutely sure there is no DC-offset on the source you can bridge this. The only reason for having two in parallel is to offer two separate footprints (5mm and 10mm pin spacing)
      – R1A: Feeds the opamp input from a voltage divider. Normally R1A should be small compared to R2A (so there is no attenuation of the input signal)
      – C10A: Good question, I am honestly not sure. It is intended to be used as bandwidth limiting if using fast pampas. Most circuits I see use 22-47pF here so that is what I have used as well.
      – D1A: No downsides that I am aware of. The upside is probably not much, but could be worth trying. Suggested further reading is this:



  2. Claus Hollen Nielsen says:

    Why can’t I use this board with a bridged 50asx2 (btl)
    Building 2 monobloks you see.
    Maybe just build half a board?
    Great that you share your design! Thanks

    • theslowdiyer says:

      Hi Claus,

      You can use the board with a BTL-module – as long as you have a balanced source. This board isn’t capable of BAL-SE conversion as both channels are in phase, but if you do not need that then there is no problem 🙂

  3. sqwerty says:

    Any chance of a BOM for this project?

  4. tomaszrondio says:

    If output impedance of my sound card is 100Ohm is it required to have a buffer?

    • theslowdiyer says:

      No, it will not be required to use a buffer. However,you might be able to tweak the sound a bit more to your liking this way.

      • Tomasz Rondio says:

        What is output impedance of Nadja?
        Nelson Pass says that best preamp is no preamp and I believe him 🙂 I want to have as transparent gear as possible.
        Thinking about volume control of all 6 channels. Daisy chained PGA4311 or PGA2311 controlled by arduino. Makes sense?

        • theslowdiyer says:

          I assume you mean the Najda DSP board? The output impedance is not quoted and there are no schematics, but I would assume it is between 50-200 ohms which would be fine for driving the ICEpower boards directly – I am sure an email to the designer would get that confirmed quickly. The Arduino-controlled PGAs should be a solid approach to doing volume controls. There is also the 8-channel CS3318 which would give everything in one chip, but routing a board for all those channels isn’t easy 🙂

          • Tomasz Rondio says:

            I asked for Nadja bcs I read somewhere (probably that you made these buffers bcs of hight output impedance of Nadja. Nevermind 🙂 S3318 looks interesting. Audiophonics sells a kit and they even provide Arduino code. I have small knowledge about electronics so this seems to be best way to go for me. Thanks!

Leave a Reply

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

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

Google+ photo

You are commenting using your Google+ 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 )


Connecting to %s

%d bloggers like this: