Marshall JMP1 rack unit

[roberto]

Here in europe the price of rack units is going quite down, and some units that ten years ago were quite costy, now are absolutely cheap.

I'm currently looking for some units I had in the past, to build a rack system for triamping. The first preamp is an italian Brunetti Mille (something similar to a CAE 3+ preamp), while the second I would like to add is a JMP1.

Taking a look at the schematic:
http://www.drtube.com/schematics/marsha ... -61-04.pdf
I noticed 4053 signal,switchers http://www.ti.com/lit/ds/symlink/cd4052b.pdf
Being supplied by a -5,6 +5,6V the maximum signal will be 11,2Vpp.

At the grid of V2 (top right on the schematic) we have a maximum signal of 4,2Vpp (BR3 + D12), while V2 gives a total gain around 34, and R91 + R92 cuts out 30% of the amplitude.

But, due to the 11,2 Vpp limit, going backwards through R92+R91, it's like IC12b is starting to distort when we have around 500 mV on the grid of V2.

So the unit's distortion comes from IC12b?

[roberto]

Ok, yes, it is distorting through the 4053.
That family is well known to have a nice clip behaviour, but seems it's born more due to serendipity than a well known aspect of the engineering.