Question about Dynacomp to Ross conversions. Hoping Analogman might jump in.

[skiraly017]

I've seen Dynacomp to Ross conversion mods list but I'm curious. If you go by the Tonepad schematic which covers both, I think there ends up only being two or three resistors you could change in a stock Dynacomp to match a Ross without modifying the PCB. I understand you can swap out the transistors as well but is that all there is to that mod? Could a couple of resistors really make that much difference? Thanks.

[R O Tiree]

...and a few caps...

[jacobyjd]

check out the tonepad.com project page--that should answer any questions you have about conversion...or even switching between the two.

[analogmike]

My ears were burning!

The main deviation of the ross is the added capacitors for stabilization. They make a subtle difference. the right transistors also make a subtle difference. I really like the metal can IC chip a lot lately too. have fun!

[skiraly017]

I think the point of my question was misunderstood. I can see the differences between the two on the Tonepad layout. My question was regarding the changes to a stock MXR Dynacomp...that it seems only two resistors can be changed without modifying the existing PCB which is why I was curious how people can claim to offer Ross mods to an off the shelf Dynacomp.

[ppatchmods]

IIRC there are a couple caps to that mod. To me, it's not that it is the exact specs of the ross, but it sounds very similar to the original. It does make the comp sound smoother.

[Mark Hammer]

I think the point of my question was misunderstood. I can see the differences between the two on the Tonepad layout. My question was regarding the changes to a stock MXR Dynacomp...that it seems only two resistors can be changed without modifying the existing PCB which is why I was curious how people can claim to offer Ross mods to an off the shelf Dynacomp.

A fair question: how do you replace one resistor with 2 and a cap, if there are no pads allotted for it?  The use of two resistors in a "standing arch" configuration to replace one has a long history.  If memory serves, I think my EHX Y-Triggered Filter uses that trick to achieve a resistance likely available in 1% values with 5% tolerance off-the-shelf components.  EHX, and surely others, also used add-on parts tacked onto the copper side.  So, knowing nothing about the layout of assorted Dynacomp issues, it IS possible to stuff the added parts in without requiring the additional pads.  How neatly would depend on the board layout, the size of parts used, and the skill of the replacer.

And, as Mike points out, the changes are principally to smooth the power provided to the assorted points in the circuit.  You will note that the replacement resistors are essentially equal to the original value, divided in two, with a cap to ground at their halfway point.  There is nothing really magical about their exact individual values as long as the total resistance is similar.  One can always recalculate the cap value to achieve the same rolloff - the RC network functions like a lowpass filter on the power line.

If you look at JC Maillet's viva analog site, you'll see his "hi fi" mods intended to improve sonic quality in a standard-issue Dynacomp.  One of them involves conversion from full-wave to half-wave rectification, so as to remove a diode path that might potentially introduce unintended clipping from the output.  Although JC suggests the full-to-half converson does not result in any audible deterioration, let us simply suggest that the Ross mods to the Dynacomp might prove even more helpful in a Dynacomp altered in this way.  That's not a criticism of JC's mods.  Rather, the sonic purity of the output signal is a joint result of all sources of ripple and clipping.  Use of the Ross changes decreases ripple in the supply.  Use of the full-to-half-wave conversion theoretically increases ripple in the envelope control signal fed to the 3080, as it reduces potential diode clipping in the Dynacomp output.

[R.G.]

... "hi fi" mods intended to improve sonic quality in a standard-issue Dynacomp.  One of them involves conversion from full-wave to half-wave rectification, so as to remove a diode path that might potentially introduce unintended clipping from the output. 

It's potentially more useful to add a second emitter follower to buffer the signal from the output of the OTA, not forcing a single transistor to serve as phase inverter, diode driver, and signal output buffer all at the same time. A little resistor isolation between the two transistors (the old, all-purpose one and the new output-only follower) might also help.