Moog Music Forum

Can anyone please describe in what consists exactly the slew rate mod?
Do you have board pictures or schematics about it?

The original oscillators are a bit duller in sound then the classic minimoog or Moog Source ones.
Even slight changes do change the sound as the filter overdrive reacts very much to higher harmonics on the input. Also the resonance is sounding better with higher harmonic content.

The slew rate mod changes some capacitors and OP amps for a wider bandwide of the audio path. The exact technical details appear to be different for the slightly different analog voice boards.
Before I sent my Voyager a few years ago to Rudi Linhard, the master of the Voyager software, he instructed me to cut of a few capacitors as first aid. And this improved the sound to my taste.

(I am not a technician, so please excuse my bad technical details)

Thanks a lot, good to know that. There is little literature available on Voyager mods actually.

till wrote:The slew rate mod changes some capacitors and OP amps for a wider bandwide of the audio path.

BTW do you know how many OP amps need to be replaced? Just wondering how much invasive this is for the PCB.

Don't know more details.

till wrote:cut of a few capacitors as first aid. And this improved the sound to my taste.

Well, this sounds easy to try. Do you remember which ones you cut? At least their color/shape?

Newmoog wrote:

till wrote:cut of a few capacitors as first aid. And this improved the sound to my taste.

Well, this sounds easy to try. Do you remember which ones you cut? At least their color/shape?

As said: there are different board versions.
Can't remember details.
It was years ago.

Slew rate is an op amp spec basically, or anything really for that matter I believe, relays etc and is essentially freq. bandwidth of components. More relevant when you get into rf territory generally speaking, I guess.

Google slew rate and you'll learn more technically speaking than I know. Basically after the mod the voyager sounds brighter and to my ears doesn't change the low end at all (why would it?) having listened to lots of voyagers, modded / unmodded ones. PM for more details if you're uk based.

sauce wrote:Slew rate is an op amp spec basically, or anything really for that matter I believe, relays etc and is essentially freq. bandwidth of components. More relevant when you get into rf territory generally speaking, I guess.

Google slew rate and you'll learn more technically speaking than I know. Basically after the mod the voyager sounds brighter and to my ears doesn't change the low end at all (why would it?) having listened to lots of voyagers, modded / unmodded ones. PM for more details if you're uk based.

Yep, that is clear to me, just struggling to identify what capacitors are responsible for worsening the filter response. They must be acting as a low-pass filter somewhere in between the oscillator stage and the actual filter stage I guess.

The Voyager main PCB is so complex it's no use asking which caps are responsible without referring to a schematic or layout. Basically each stage under the control of an opamp can be made into a filter. When using fast/high bandwidth opamps, you need to incorporate a filter in order to prevent that section from self oscillating. So it's a combination of both the opamp spec and its circuit topology that give a characteristic frequency response.

latigid on wrote:The Voyager main PCB is so complex it's no use asking which caps are responsible without referring to a schematic or layout.

What he said. Also, it's a triple layer pcb I beleive, so you really should be pretty sure of what you're doing before diving in and changing IC's.

also had the slewrate mod done by rudi. still very happy with the result: more britle hights, more in the direction of minimoog model-d or better multimoog to mho
before i thought to much of a veil over the sound of the voyager.
didn't sound bad before for sure, but sound more alive/ direct/ better afterwards.
( also compared it with unmodded voyagers afcourse and multimoog and model-d )