Avalon U5 Freq/Phase Curves

[amplexus]

Just for fun. Slow day in the shop and I'm pulling apart my studio's DI/mic PSU cart, and i wanted to see how flat the tiny transformers in those Radial SGI Rx units really were (Turns out pretty good when loaded). Then i thought... why not see how the U5 does. Then i thought... why not trace the Tone curves and see how close they are to what Avalon publishes. Unsurprisingly close, but the phase response is interesting to see.

Anyhow, here they are. Ignore the little dips and pops up top I think that's noise in my test setup.

Tone bypassed. Pretty impressive, basically ruler flat response. Phase shift is a little wonky below 100Hz.


And then the tone curves. In order, 1 through 6. Phase shift predictably goes right to ****.

 

[rsasgtr]

I compared your frequency responses with LTSpice simulations I made based on an archived Avalon U5 EQ, and superimposed them on your images. They are pretty close.

Some minor adjustments were made to account for the tolerances of components. They are marked by using expressions e.g. 100k*.95. The only major difference (vs the linked schematic) is the change of C6 from 22n to 50n (47n+6%).

 

[pucho812]

Not to spoil anyone’s fun but the tone card uses a resistor network. as part of it all

 

[rsasgtr]

Not to spoil anyone’s fun but the tone card uses a resistor network. as part of it all

Ah yes, the MDP1603104G. I presume they are the ones marked as RN? in the schematics.

There is an old thread on freestompboxes with some pictures of the PCBs, but it seems that the tracing did not progress very far. It also seems they are missing pictures of the two small PCBs from the enclosure side. I was wondering if you could maybe spoil that part