Marshal drive master mods

[littlestevie]

Hi there !

I'm just loocking for marshall DriveMaster mods, I've searched the forum but I haven't found anything...
Is there some of you who modded their Drive master (gain, tone mods..) ?

Jef

[Johan]

the first generation drivemaster was identical to the first generation Guv'nor, with the exeption of the FX-loop. so just look for Guv'nor mods...

johan

[petemoore]

I'm just loocking for marshall DriveMaster mods, I've searched the forum but I haven't found anything...
 The first thing I'd do is find a schematic of the Drive Master, and post that.
Is there some of you who modded their Drive master (gain, tone mods..) ?
 Probably, even so, the knowledge of those whove modded circuits like the Drive Master may be of greatest help, I haven't seen a thread or link to DM Mods.
 Also there is a thread called BUM [blind urge to mod], this is a great read for those soliciting for modding advice on any circuit.
 It asks questions like 'why', which are good to understand before attempting mods.
 Are you sure the pedal is the 'problem'?
 what is your DM doing that you don't like?
 What is it not doing that you'd like it to?
 IIRC the DM is a nice pedal with tone knob, lots of boost, and some distortion, perhaps by the time you've found what circuit you like best [technically mod IS a different circuit] it may not resemble a DM anymore...or...the sound you want, a DM may not be capable of producing.

[Johan]

here are the facytory schematics..
http://aronnelson.com/gallery/johan/drivemaster
http://aronnelson.com/gallery/johan/guv_nor

johan

[littlestevie]

Thank you guys !
I'll check if there is Guv'nor modds.

Are you sure the pedal is the 'problem'?

No, but I often mod my gear, I think it's a disease   
 

what is your DM doing that you don't like?

When the gain pot  is below 3 h the sound turns very bassy, and muddy, I'd like it to be more shiny

What is it not doing that you'd like it to?

Add more gain, and add highs when gain pot is turned down.
I'd like to know if people tried other op amp.

Jef

[petemoore]

When the gain pot  is below 3 h the sound turns very bassy, and muddy, I'd like it to be more shiny

Add more gain, and add highs when gain pot is turned down.
The schematics are small/dark/illegible for me, there may or may not be a mod I could pick out to get close to that, I can't find the drive pot.
  I'd like to know if people tried other op amp.
  I would bet they have, and have found out that the TL072 is a great performer, or just fine OA for the DM, or just fine, and that rather subtle 'flavor' differences, at best, are what's had with OA swaps in the DM...YMMV/IMO.
  I'll see if there's a Guv Schematic around that's brighter.
 
 

[petemoore]

  Ok there's one at GGG...
  http://www.generalguitargadgets.com/diagrams/guvnor_sc.gif
  For the Guv'nor
  R1 and C1 ... I need to do more homework...math in particular.
  I'll go read and see if I can sort this one...I'm stuck right now...altering the values of R1/C1 will change the voicing and gain range of the gain knob.
  Other caps could be re-valued for a revoiced DM sound, as well as clipping secion [the LED's] element changes, two Si diodes placed where each LED was will give a different sound without a big volume drop [the LED's should sound loudest], one Si where and Led was [one or both]...Ge's would make much different sound with volume drop. Lowering the clipping threshold with other than LED's there...I'll see if I can increase my understanding of R1/C1...

[MartyMart]

Reduce C10 and C12 to 100n or perhaps 68n ( will thin things out a little so appear brighter )
Increase the drive pot from 100k to 250k (FB loop op opamp) or stick a 100k r in series with it from
pin 2
Reduce C11 to 100p for a bit more "high grit"
Reduce C8 (off drive pot to VB) to keep more bass with drive up, or increase it for reverse.
Change one of the LED's for a 1N4148 or two in series, bit more crunch and assymetrical distortion, which
I prefer in general.

MM.

[petemoore]

  Marty Mart seems to have the answers...
  Here's what I found to read up on C1/R1, It's from GEO "technology of the Tube Screamer", notice the similarity in the TS clipping section and Guv's Gain opamp, and discussion of:
  Zi is formed by the series resistor and capacitor from the (-) input to ground. This combination is frequency selective, in that the capacitor impedance is inversely proportional to frequency. At DC, the capacitor is an open circuit; it's impedance goes down as frequency goes up. At very high frequencies, the capacitor is effectively a short circuit, and the resistor is the sole determining factor in the gain, the capacitor impedance being negliglible compared to the resistor. At the point where the capacitor impedance equals the resistor, the gain of the entire circuit begins to fall off toward a gain of one. With the stock 4.7K resistor and 0.047uF capacitor, this frequency is 720Hz. Only notes and harmonics above this point get the full gain of the distortion stage, and everything below it gets pregressively less gain - and distortion. This fact probably accounts for the lack of "muddiness" of the distortion in the TS series as bass notes are clipped least.
  I know the DM and TS are quite different, but this discussion of the TS's gain/voice of a gain selectable OA stage explains those parts.
  IIUC, a smaller value C1 = less bass gain/less mud?
  IIUC, a larger value R1 = more gain?