Laney LC15 Marshall Mod!

   Here is the Laney LC15 combo. It' s nice little 15W tube combo with one channel and a bright switch. It has a 10" speaker, 3 band EQ, Volume, Gain controls. A friend of mine turned the lc15 combo to a head and then he asked me if we could modify the circuit of the amp.
  So what's wrong with this amp? Well, not much but the competition is now fierce in the tube amp world. The lc15 doesn't have an Fx loop, it doesn't have 2 channels, no reverb and no stand-by switch. The fx loop is a feature that we should definitely add if we are to modify this amp. (The LC15R model has reverb plus an fx loop...).
  But what about the qualities of the LC15 amp? To start with, the LC15 shares almost the same preamp circuit with the mighty JCM800 Marshall 2203 amp! That's amazing and you can tell that there is something "marshall-ish" in the lc15 when you press the bright switch or turn the gain all the way up! You get a smooth and creamy classic overdrive. The differences between the jcm800 and the lc15 preamp are minor and so I decided to make it sound like a true Marshall!
  The Marshall mod is easy but it needs some skills as some if the components of the lc15 are SMD(surface mounted tiny bits...).
  First I replaced C3 and C4 with a C=22nF capacitor. This capacitor could be a 10nF for less bass and a smoother overdrive. Then, I soldered two 470pF capacitors, one across the legs of the R7 resistor and one across the legs of the R11. This gives you a bright boost.
  The final step of the jcm mod is to replace the R10 cathode resistor of Valve1 with a 4kOhm(=4000ohm) resistor. You can use a 4700ohm or even a 3,3k=3300ohm one(3,3k for more gain). The JCM800 preamp is now ready! Just turn up the gain and listen to the overdrive!

 The original Laney LC15 schematic:
http://www.freeinfosociety.com/electronics/schematics/audio/laneylc15.pdf

 The JCM 800 Master Vol. schematic: (open in new tab for full size pic)

The modified laney lc/jcm schematic:

Fx loop mod:
  To add an fx loop to this (or any) little combo you need two stereo jacks, a 100k resistor and a 100nF capacitor. The fx send and return jacks will be mounted on the amp chassis.
  The circuit is simple enough and it is placed between the master volume and the phase inverted tube stage in the signal chain. I just placed a 100nF capacitor before the send jack and replaced the R18 resistor with a 100kOhm one.
   See the original schematic: (open in new tab)

 And the here's schematic with the fx loop added:

Note: the Lc15 can be found used in various shops, sites and eBay but if you want something new, check out the newest laney tube amps such as this 12R model with 12" speaker and classic British circuitry.

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