Marshall Drive Master - Advice/suggestion/help needed

[arma61]

Hi

I've build a Marshall Drive Master according to this schematic

http://users.sa.chariot.net.au/~gmarts/pix/a_mdm.gif

it works fine except for the following

-with gain pot at Max it start howling, a sort of a note inbetween Eb and F
-with both Level and Gain pots at 0, I can hear a sort of noise, like a roar/wroom, Yoga's Ommmmh  ! very low in frequency

anybody has experience with it. I searched the forum but very few infos on it.

Also I need also some suggestions

on the attached schematic, on the right side
there's a resitor with no value and ".0039uF cap instead?" any ideas on the resistor value and what it or a cap does ?
there's a cap with .22uF and three  , again any ideas on this ?

Thanks vm m8s for help, if needed I can post voltages, again searching I didn't find any to compare with mine though.

Armando

[Johan]

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=3812&g2_serialNumber=2

your howlin and aooooom is probably the result of feedback through the layout. try moving cables around..

j

[arma61]

thx Johan for reply and the schematic,

I'll try to move cables tonight and see what happen,

I've drawn my own pcb layout, could also this cause this issues ? (never had problem like this in the past though),
At the moment the only "unusual" thing I did are

- used 3 trims instead of the 3 tone pots.
- used some electro. caps (.22) instead of poly/ceramic ones
- +/-/in/out cables are bundled together (just thinking this is bad  , as I neved did it before! )

About the schematic you linked, I can see that the big difference is that most of the connections on the schem I have tied to Vref, are tied to gound on the original schematic. Could this also causing the howling and aoooom, or any other issue?

I really dig the sound I can get (at the moment) out of it !

thx m8
Armando

[petemoore]

  About the schematic you linked, I can see that the big difference is that most of the connections on the schem I have tied to Vref, are tied to gound on the original schematic.
  Could this also causing the howling and aoooom, or any other issue?
  Yupp, Grounds and Vrefs need to be correct too, they could cause various types of problems.

[arma61]

thx guys got it working  , "all wolves killed "      and no more Yoga's aooommm       

just tied to ground all of the Vrefs, and it works! only the tone pots seem working a little bit less then when I have them tied to Vref.

Anyway I'm going now for a new layout from the schematic posted by johan, I hope I can read all the exact values!, though there are not big difference.

Thanks again m8s
Armando

[Johan]

cool...please note that the drivemaster is nearly identical to the first generation Guv'nor (sans fx-loop), so there are allready plenty of layouts out there...I think you find layouts at both GGG and tonepad...

j

[arma61]

Thx Johan, yes I know them, I've used their own layout sometime or based my own on their , but you know sometime DIY is making you so addicted that you want to do everything yourself !!