Mod for marshall 50W 1986 Bass

[frusciante89]

Hi guys,
I've built a Marshall 1986 Bass 50W last year... I love the clean tone I can get out of it, however, I'm not able to get any crunchiness at acceptable volumes - lots of headroom... I tried to implement the Lar Mar PPIMV mod, but to me it sounds too harsh and not "creamy" enough... yesterday I was at Guitar Center and I tried a Friedman SmallBox: it blew my mind, totally... so warm, so creamy at bedroom level... NOW: I am eager to hotrod my 50w in order to try to achieve that heavenly experienced with the Friedman: do you guys have suggestion?
By the way, these are the few of the pics of my build: http://forum.metroamp.com/viewtopic.php?f=7&t=42874

[Littlewyan]

I'm guessing it doesn't sound as harsh when cranked without the Master Volume?

Try different valves, particularly the Phase Inverter as this will be providing most of the distortion when you use the Master Volume. If the amp sounds harsh when cranked normally then tweaking is needed elsewhere.

[Phil_S]

50W is going to be loud. Maybe so loud you can't crank it to 10.

Try pointing your speaker at a fairly dead wall or corner, maybe hang a blanket on it or put a couple of big pillows there. You may find you can get an acceptable sound by changing how you think about using the equipment rather than changing the equipment. You might also go for a less efficient speaker.

Another thing to keep in mind is that you'll need to go from 50W to 5W to cut the perceived volume in half. Most "bedroom" amps are in the range of 1/2W to about 2W. Getting your 50W Marshall to be like that probably isn't going to happen.

[Smokebreak]

Just put a normal master between the treble pot wiper and PI cap.

[Littlewyan]

If he does that he'll lose a LOT of distortion. Trust me, been there, done that, its pants. I actually took a different approach though, I had a 1987xl head with the effects loop and stuck a volume control pedal (pot in a box pretty much) in the effects loop. Wasn't until I got my attenuator that I realised just how much distortion and tone I was missing out on. O all those wasted times at rehearsals and gigs!

[Smokebreak]

Sure, there are sacrifices with most all MV setups. This just happens to be the one I personally prefer with Marshalls.
I'm not sure I'd say a LOT of distortion loss though. Compared to a cranked amp with the outputs cookin? Sure. I've had great experiences with the master in that spot. Even in plexis.

[frusciante89]

and what do you guys think about Steve's "one wire mod"? http://home.comcast.net/~mamp17/Misc%20 ... 0Info.html

[Littlewyan]

I thought the standard Randy Rhoad's one wire mod sounded kinda cool when I tried it but wasn't really for me. Cranked it was way too much distortion. Very harsh.

[John_P_WI]

Nothing really special about the small box, build a JCM 800 with a large 1st stage plate load resistor, 2k7 cathode resistors on both 1st and 2nd stage bypassed with 0.68 u caps, 820r 3rd stage // 22 u. Add snubber caps and grid stoppers to taste... Fairly standard Friedman, conventional master after the tone stack. Again, just a tweaked JCM 800....

[frusciante89]

Nothing really special about the small box, build a JCM 800 with a large 1st stage plate load resistor, 2k7 cathode resistors on both 1st and 2nd stage bypassed with 0.68 u caps, 820r 3rd stage // 22 u. Add snubber caps and grid stoppers to taste... Fairly standard Friedman, conventional master after the tone stack. Again, just a tweaked JCM 800....

Could I get close by modding my 1986?

[Smokebreak]

Totally! Steal a triode of the input stage and cascade it into the plexi channel, using the values John suggested. Put that added stage on a switch.

I just read the description and it says the gain channel is a bit different from the brown eye, more vintagey and midrangey. That tells me instead of the usual 68K/68K Jose split after the 1st stage, it's probably more like an 800 , with a larger peaker over the 470K going to the pot . Try 1n or 2n.
Also, looks like there are 2 gain pots. One after the first stage and one after the second. Look up "Jose mod" for the basic idea. You can get fancy and use relays and 2 MV if you like for the switching, like that amp does.

[Reeltarded]

The same guy with the one-wire mod has other layouts.

Use 2204 layout. I build only high input. Screw the low input. Don't change your output section values. Use what's already in there.

This is not a SB50, but it's a Dave-ish amp.

Split the cathodes on V1 for 2k7/.68u per stage. The input stage gets a 220k plate. The mixer from the second stage to the third is 470/470 with 500p over the signal side. The third stage is 1k bypassed with a 330u you took off the shared cathode from the mod to V1.

The slope resistor is a 47k.

Turn that PPIMV to ten and never use it, ever ever unless you using it above 7 and balancing it with the simple master. Yay. gunk gunk gunk I like NFB.

Add resonance. Add resonance! You need to add resonance. It's all about that bass.

It basically sounds like Gary Moore just before he became a complete pussy with all that blues crap.

haha

[Gaz]

There's a Small Box discussion and schematic at the SLOclone forums. But, I'll save you the trouble... it's the bright channel of a Jose mod with a few snubbers to make it less fizzy.

[Smokebreak]

Ah I see. So 100k/68k divider with no pot after 1st stage

[Gaz]

Yeah, all this mods put the gain pot after the 2nd stage, and in "hairy brown eye" mode, the gain pot is after the 3rd stage! You have a less control of the gain that way, but the tone is consistent....ly butt rock.