Marshall - Drivemaster  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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borislavgajic
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Post by borislavgajic »

enjoy......not bad sounding........good with superhardon in front of it.........
:thumbsup
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Post by Dirk_Hendrik »

Looking at that Bottom/jack board... and how similar it looks to the jackboard of my Bluesbreaker when it was given to me.... This might be handy (3 pages long!)

http://www.dirk-hendrik.com/temp/bluesb ... mboard.pdf

furthermore:
This schematic contains errors. Could you verify if the potvalues are correct?:
Image
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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borislavgajic
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Post by borislavgajic »

here you go Dirk :thumbsup
100k....gain
9.42k...bass
9.49k...mid
8.83k...treb
16.48k...vol

measured vith pots all the vay up......and connected to pcb
so it seems like that schem have ok values.

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andregarcia57
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Post by andregarcia57 »

hello ....
I'm looking through google many different schematics of Marhsall drivemaster
Has anyone had any oiriginal can help me find schematic true?

this is below correct? ]
C8 is actually on bias and not on the ground?
thanks....
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7line
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Post by 7line »

it is correct schematic. all values right
but c8 must be on the ground
resistors in bias are two 47k
drivemaster.jpg

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Post by Bernardduur »

For some more fun!!

A Marshall Drivemaster; almost identical to the Guv'nor. Only difference is the absence of an FX loop, the filter cap of the ref voltage is 100u (instead of 10u) and there is a 1M resistor added to the output of the effect

Enjoy!
Marshall - Drivemaster2.jpg
'No more....... loud music.......'
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Post by nooneknows »

Reviving this old thread...

I've just bought a Drivemaster, good external condition, it seems nobobody touched inside BUT it doesn't work properly, in fact the sound bypassed AND the effected sound, both seem like they're muffled, like there would be a tone control dimed.

That leads me to think the drivemaster isn't a true bypass pedal, not really an issue but I really don't know what kind of problem could it has, I'd like to hear a clear bypassed signal.
A defective switch? A defective jack? I followed the input and output traces with a tester and it seems they're good, at least until the first cap.
Maybe a defective cap? I can't see on the input or output cap going to ground that can make a low pass filter like this

Any help would be appreciated
thank you
Marcello

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Post by MoonWatcher »

nooneknows wrote:it doesn't work properly, in fact the sound bypassed AND the effected sound, both seem like they're muffled, like there would be a tone control dimed.

That leads me to think the drivemaster isn't a true bypass pedal, not really an issue but I really don't know what kind of problem could it has, I'd like to hear a clear bypassed signal.

A defective switch? A defective jack? I followed the input and output traces with a tester and it seems they're good, at least until the first cap.
It's not true bypass like with a 3pdt footswitch, because it only uses a dpdt (I have a Drivemaster, too).

The way the switch is wired, it shunts the signal path in between the op amp stages to ground when in non-effect mode. So it's very likely a problem with the switch. My Drivemaster needed the switch replaced when I got it (used).

Many of the schematics for making a DIY clone of those Marshall pedals eliminate a resistor and capacitor, halving the value of the cap, and doubling the value of the resistor. You will see a 100n cap and a 10k resistor in the clone schematics, but the actual Marshall pedals will have two 220n caps and two 4k7 resistors. 1/2 of the switch either connects the status LED to ground (to light up), or connects to where the two 4k7 resistors join, to mute the effect path signal straight to ground.

If you trace from the input jack, you should find that it connects to both the 10n input cap and a terminal of the footswitch.

So simply by removing the switch, you should be able to verify that it's faulty - you could temporarily hardwire it for bypass or effect path operation.

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Post by nooneknows »

Thank you very much MoonWatcher, I'll double check the switch first following your advices

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Post by Ice-9 »

The Drivemaster is exactly the same topology as the better sounding original Guv'nor pedal, all that needs doing to convert the drivemaster to the guv is a few value changes. Well worth doing.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by MoonWatcher »

Ice-9 wrote:The Drivemaster is exactly the same topology as the better sounding original Guv'nor pedal, all that needs doing to convert the drivemaster to the guv is a few value changes. Well worth doing.
Actually, there's so many new pedals that use the Guv'nor as the basis that it kind of makes sense to add some of those tweaks to the Drivemaster/Guv'nor as well. Someone here mentioned using different values of pots for the tone circuits, and I played around with that - it was very good sounding. You could go from 10k up to just 25k, or maybe even 50k. I don't think all three pots necessarily will benefit much from being changed, but they are easy enough to swap out.

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Post by nooneknows »

Update: it wasn't the switch, I changed with no results, it took a bit to find it but in the end it was the malfunctioning opamp. I replaced it with a TL072CN I had at home, now it works without problem. (It was the first time I encounterd a defective opamp in a pedal indeed, it's always a matter of old solders or supply issues).
I have to still to test it in band situation but it seems really promising

thank you!

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Post by nooneknows »

Ok, tried it, I don't like it :lol:

The sound it's very marshally but it's dull, I had to cranck the gain and/or the treble, otherwise it seemed muffled and dull. The only usable position is in front of my TImmy, to boost it, that way it opens up a bit, but my Ts9 or my hardwire cm2 works way better that way.

I double checked it and the solders seems original, no trace of modding apart from mine to fix it, so I think it's the way it has to sound. I suppose it works better with transistor amps.

Anyone with same feeling? Any tested mod to make it more usable at lower gain? (the idea of changing the tone pots to have a guv'nor seems a bit expensive and I think it doesn't change so much the pedal character, but I'm open to your ideas)

thank you

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Post by phatt »

C3 is 4n7,,,,Try 15nF or just add a 10nF. That should bring some balance to the tone circuit.
Phil.

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Post by phatt »

I had some time to kill ,,,so
Just to give an idea of how a simple mod might change the outcome I thought a picture might help.
Now I don't own this unit but I've designed and built a fair bit of gear and you tend to develop an eye for what works. :wink:

FWIW, This is what I would do;
Just add a 10nF cap across C3 will make the treble more guitar friendly.
If the bass is still too strong then double the value of R2
Maybe un-solder just one end of R2 and add another 1k5 in series.
Be careful not to over heat the copper pads as some older pcbs will delaminate if over heated. :slap:

Just a point worth note;
Hanging passive tone circuits off the end of dirtbox circuits seems to be common but a buffer would be a wise addition.
There is already only ~8Db difference in tone shape ability and it totally relies on a short cable to a very high Z input for the next stage.
If your cable is long and input Z of next circuit is lowish then the tone shaping ability suffers even more loss. (Instant tone suck) :whappen:

Remember this tone setup like most Passive tone circuits also suffer insertion loss so a 1 volt swing at the input is reduced to about 300mV ,, with no buffer it's a gamble. [smilie=a_hrm.gif]
Phil.
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Post by nooneknows »

Thank you very much for your help Phatt, I'll try the mod as soon as possibile!

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Post by Renegadrian »

For the record

Updated schem (right, c8 is to ground) and vero. Didnt put led res on vero but it's easily doable
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Post by Lithium_Grim »

Thanks! Ok, nitpicking... The IC pin 8 (V+) and 4 (v-) are missing in the schematic, but I guess that anyone building it already knows how to connect a dual opamp :)
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