MV for Marshall Plexi
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The Lar/Mar is cool and very stable for the amp, it doesn't sound great at bedroom levels but just past half way is a good balance of tone, drive and reasonable volume, at least on my 1987x. I just did not like all the PI distortion it induces and can get mushy depending on how your filtering and voltages are set, mine were both on the low side. I ended up modding the whole front end to 2204 specs with Dave Friedman's MV wiring.
SpiderWars
Well-known member
LarMar is a PPIMV (post phase inverter mv). Jose is not. Never tried a Jose but in those amps any PPIMV (that I know of) will really only tame the volume and still sound great. You can run it at bedroom volumes but it won't sound as good. But when wound up a bit it will be the classic, cranked amp tone because it's still the phase inverter that is distorting a lot.
Since the Jose is pre phase inverter it's more about preamp distortion (the phase inverter won't distort until the amp is very loud). The preamp circuit is typically modded to give the extra gain. They are a different feel and tone. I don't know how a Jose sounds in an otherwise stock amp. I assume it's just the 1M MV pot and the zeners but I'm not sure.
Since the Jose is pre phase inverter it's more about preamp distortion (the phase inverter won't distort until the amp is very loud). The preamp circuit is typically modded to give the extra gain. They are a different feel and tone. I don't know how a Jose sounds in an otherwise stock amp. I assume it's just the 1M MV pot and the zeners but I'm not sure.
Rick Lee
Well-known member
I didn't do it on my 1959SLP, but it was modded when I got it. I took it to my tech to have him look it over and, frankly, clean up the amateurish job. He said it's a PRE PIMV, and because of that, the loop he (my tech) then added sounds just amazing. I had a Bray-modded 1987x with a factory loop that sounded like ass because the added gain stage just overloaded it (the loop). My 1959SLP absolutely nails the Fair Warning album tone. It's a real one trick pony, but it does that one trick amazingly well.
On my '69 100w Plexi clone build my tech added a sort of variac knob in the back. Those Merren trannies just put out so much power, it was unusable and would blow out my speakers if I turned it up enough to get a little breakup. Now I can turn the power down to get some more breakup with the vol. I and II knobs. But I just use this amp as a pedal platform now. It really has the mojo, but not much gain.
On my '69 100w Plexi clone build my tech added a sort of variac knob in the back. Those Merren trannies just put out so much power, it was unusable and would blow out my speakers if I turned it up enough to get a little breakup. Now I can turn the power down to get some more breakup with the vol. I and II knobs. But I just use this amp as a pedal platform now. It really has the mojo, but not much gain.
fusedbrain
Well-known member
I've got a Lar/Mar in my 1987x and it sounds really good. Far better than the amp wide open into a Rockcrusher I tried.
When I first installed it in the stock amp, I was a little underwhelmed, but as the mv is in the negative feedback loop, it dramatically affects the presence and feel of the amp. To me, the secret to the Lar/Mar is to pick a master vol setting on the amp that will be in the ballpark for most of its use, and then adjust the negative feedback resistor and the power supply filtering to get the amp dialed in. My amp doesn't sound great at bedroom level, but I set it up for typical rehearsal volume with a drummer and it kills now. I usually have the channels jumped with the normal channel on 4 and the bright channel about 7-8, and I can use the amp in just about any situation without volume issues. YMMV
When I first installed it in the stock amp, I was a little underwhelmed, but as the mv is in the negative feedback loop, it dramatically affects the presence and feel of the amp. To me, the secret to the Lar/Mar is to pick a master vol setting on the amp that will be in the ballpark for most of its use, and then adjust the negative feedback resistor and the power supply filtering to get the amp dialed in. My amp doesn't sound great at bedroom level, but I set it up for typical rehearsal volume with a drummer and it kills now. I usually have the channels jumped with the normal channel on 4 and the bright channel about 7-8, and I can use the amp in just about any situation without volume issues. YMMV
boost
New member
Not looking for bedroom levels, just looking for a good cranked plexi sound that I can dial back and use in a band situation without having the soundguy or band members jump down my throat. Going with any kind of external attenuation (no matter how good they sound) is not an option. Want to keep the setup as simple as possible.
A
Anonymous
Guest
LarMar PPIMV is what you want.boost":6yebqhky said:
Steve
fusedbrain
Well-known member
boost":2wgrrusa said:
Yup!! Lar / Mar is the solution!
Just to expand on my earlier post a little, the Lar / Mar LOWERS the amount of negative feedback as it's turned down, so in my 1987x, I lowered the NFB resistor to 68k from the stock 100k to compensate for this ( you could also just move the NFB wire from the 8ohm tap to the 16 ohm tap and get a similar result.). I run the MV @ about half and it was a little ratty sounding with the 100k in there.
For the filters, I left the 50x50 on the mains, but lowered the screens to 16x16 to get it to give up the goods a little sooner, and I went with 32x32 in the pre-amp. Now I get killer plexi-style tones at reasonable volumes and I can use the amp anywhere without any hassles.
I also took out the 4700pf bright cap and put in a 3 way bright switch with 470pf-off-4700pf. To me, it makes the amp a little more flexible, but YMMV with this.
Get the Lar / Mar in there and see how it sits with the volume you want to use and go from there. All the other stuff is simple tweaking. You might end up liking the amp with no other tweaks at all.
psychodave
Well-known member
Jose by a mile. Then add some 5 or 10 volt zeners across the pot on a switch for added gain (if wanted). The PPIV master sounds good, but the presence, treble, mid and bass knobs don't do much at very low volumes.
V2a
Active member
LarMar is easy and sounds good (although, like all Post-PI MVs, it interferes with NFB, presence, etc). It does replace the 'bias resistors' (grid leaks) for the power tubes, which really isn't the best option. Other Post-PI MVs leave the stock bias resistors in place and add in a pot to vary the drive signal. I like these better on paper, but the LarMar is so easy to install.
For a good alternative to the LarMar, do a Googly image search for 'PPIMV Bruce Collins'. Here is a current link to an image:
http://music-electronics-forum.com/atta ... emoved.jpg
And if you want a good master but don't need the extra (low-volume) gain/distortion from the PI, then check out Kevin O'Connor's 'London Power' MV: http://www.londonpower.com/amp-mods/lon ... ter-volume
Hint: a dual-master (LPMV and LarMar) set up KILLS!!
For a good alternative to the LarMar, do a Googly image search for 'PPIMV Bruce Collins'. Here is a current link to an image:
http://music-electronics-forum.com/atta ... emoved.jpg
And if you want a good master but don't need the extra (low-volume) gain/distortion from the PI, then check out Kevin O'Connor's 'London Power' MV: http://www.londonpower.com/amp-mods/lon ... ter-volume
Hint: a dual-master (LPMV and LarMar) set up KILLS!!