[jamont]

I've got the heatsinks mounted and I'm setting the bias now. I'm wondering about the opamp bias measurement, shouldn't we be measuring the voltage across R5 rather than R7?

 

[morsel]

Quote:

I'm wondering about the opamp bias measurement, shouldn't we be measuring the voltage across R5 rather than R7?

Yes, use R5. You just found a typo in amb's documentation.

 

[amb]

Quote:

Originally Posted by morsel Yes, use R5. You just found a typo in amb's documentation.

Oops, thanks for catching that.

Now fixed.

 

[jamont]

Here's the board on the desktop, coming to thermal equlibrium for the final bias checks:

Next step will be to hook up temporary input/output jacks for testing.

Eventually it will wind up in a custom Pars-metal case (I hope), but that's a ways off.

 

[Magsy]

Quote:

Originally Posted by jamont Here's the board on the desktop, coming to thermal equlibrium for the final bias checks: Next step will be to hook up temporary input/output jacks for testing. Eventually it will wind up in a custom Pars-metal case (I hope), but that's a ways off.

Ohh I'm jealous, hope my board has arrived by the time I get home

 

[steinchen]

Quote:

Originally Posted by Magsy Ohh I'm jealous, hope my board has arrived by the time I get home

we have to wait a further week due to custom process time etc, I'm afraid :/

 

[jamont]

I've hooked up in and out for testing. The offset is 1.6 mV on one channel, less than 1 mV on the others. I'm not really concerned about the 1.6 mV, but I'd like to get it under 1 mV like the others - any suggestions?

I took a quick look on the scope and the square wave response is outstanding, the best I've seen on a DIY amp, no question. There is not a hint of overshoot. At the highest frequency of my dipy function generator (150kHz), the leading edge is becoming just slightly rounded (I'm using the 33pf caps). Great stability and bandwith, excellent engineering job on this!

With AKG K501's and AT A900's, the sound is excellent, as expected. I'll leave detailed listening rewiews to those more qualified, but this appears to me to be a potential PPA killer.

 

[amb]

Hi jamont, congratulations!

1.6mV DC offset is very low and there is no need to worry about it. Short of swapping opamps there is really nothing you could do to reduce it further.

As you state your amp is already a superb performer. If for some reason you want to make the square wave even more "square" in the ultrasonics, see the notes on the my parts list web page about further optimizing the value of the L and R channels' compensation caps based on the opamp you're using and the voltage gain.

Happy listening!

 

[jamont]

Quote:

Originally Posted by amb 1.6mV DC offset is very low and there is no need to worry about it. Short of swapping opamps there is really nothing you could do to reduce it further. As you state your amp is already a superb performer. If for some reason you want to make the square wave even more "square" in the ultrasonics, see the notes on the my parts list web page about further optimizing the value of the L and R channels' compensation caps based on the opamp you're using and the voltage gain.

Thanks for your comments! I'm impressed by all the work you did tweaking C1 for different opamps, but I think I'll leave it as is unless I find a need for a low power RF amplifier

 

[Ic3Floe]

Quote:

Originally Posted by n_maher jamont, And idea what the total parts cost was? I know that there are a bunch of us waiting to see how much this is going to hurt. Thx, Nate

I second that request. Total bill was how many "bones?"

 

[thrice]

Here we go:

I don't think my iPod Earbuds have ever sounded so good

 

[individual6891]

Looking good thrice

 

[amb]

Coolness thrice. Another M³ is born!

 

[n_maher]

I have an excel spreadsheet of one possible configuration of an MMM with bass boost. I'd love to have someone check it before putting it up for public consumption. It's pretty basic but it does hot link you to all the parts and sources everything from either or AMB or Mouser (minus the case, knobs and ins/outs).

PM me if you're up for the task, also it'd make a good starting point for someone looking to compare configurations and costs and I'm happy to give it to whoever wants it.

Nate

 

[amb]

Quote:

Originally Posted by n_maher (excel spreadsheet) PM me if you're up for the task, also it'd make a good starting point for someone looking to compare configurations and costs and I'm happy to give it to whoever wants it.

I can have a look. Send it to me.