Lar/Mar PPIMV - Transparent on a Trainwreck?

[PlinytheWelder]

I think I might try on of these PPIMV on my trainwreck build. it takes the place of the 2 220k bias feed resistors and is very
close to stock when dimed.

http://forum.metroamp.com/viewtopic.php?f=4&t=4390
[img:600:527]http://metroamp.com/wiki/images/thumb/9 ... PPI-MV.jpg[/img]

I put one in my Laney GH-100L and it certainly works as advertised. It's my opinion that what's commonly referred to as power tube
distortion, even on a trainwreck, is really just the PI stage clipping and this MV should be pretty transparent.
It really is in the Marshall style Laney I have one in.

Has anyone else tried one yet?

[tele caster]

Yes it works very well. I put one in a plexi build. Don't forget to use shielded wire.

[JamesHealey]

installing a PPIMV stops the amplifer working as it should, it sounds alright actually I've used one live a few times on a 60w Wreck based amp and it's good!

But it deffinatly doesn't allow the Power Tubes to clip first like they should in a real non-mv wreck.

[johnny riff]

Is the left side of the pots grounded or hooked to the bias supply where the 220k's where removed.If grounded where is the bais supply connected?
JR

[PlinytheWelder]

Is the left side of the pots grounded or hooked to the bias supply where the 220k's where removed.If grounded where is the bais supply connected?
JR

The bias supply is used as as a shield, which works fine in this application.

[PlinytheWelder]

installing a PPIMV stops the amplifer working as it should, it sounds alright actually I've used one live a few times on a 60w Wreck based amp and it's good!

But it deffinatly doesn't allow the Power Tubes to clip first like they should in a real non-mv wreck.

I was looking at the scope photos of a wreck that's on here somewhere and it really doesn't look like the power tubes are really distorting. It looks more like all in the PI to me...

http://home.polstra.com/amps/wreck1/scope/

This is the most transparent PPIMV that I've come across and it's effectively out of the circuit when dimed. So I think I'll give it a try along with a Hall VVR3.

[martin manning]

Is the left side of the pots grounded or hooked to the bias supply where the 220k's where removed.If grounded where is the bais supply connected?
JR

Left sides (lug 1) of the pots are connected to the bias supply. The idea here is that the 250K pot elements paralleled with the 2M2's keeps the AC load on the PI constant and looking just like the 220K bias feed resistors that were removed. The 2M2's are to protect against loss of bias if the pot wipers lose contact.

MPM

[PlinytheWelder]

Here's the schematic. It's a refinement of Ken's type 2 PPIMV.
[img:720:540]http://verosurfcam.com/Lar-Mar_PPIMV.jpg[/img]

[geetarpicker]

The problem is once you back the master down a bit, you won't really be pulling on the power supply nearly as much. Part of the wreck feel and the clean to mean potential is the power supply sagging when you really crank it. What happens with a master is the dirty tones end up having less compression, and therefore end up being too loud compared to when you back your guitar down for clean. This is because once you get things really backed off the power supply is barely stressed. Anyway, long worded way to say IMHO a master on a wreck is not nearly as good a way to go as a nice attenuator. It might not be half bad if you simply play your guitar cranked all the time. But if you really want that magical clean to mean with literally no volume change you need to run the original circuit and forget about a master. That all said some folks have reported nice clean to dirty tones when using a power scaling setup. Perhaps the power scaling devices have somewhat of a sag to them even if the voltage is scaled down?

[johnny riff]

Will this MV work on a cathode bias(Liverpool) as well?

[funkmeblue]

yes it will work. Be aware that this master effects the negative feedback loop. Would work better on a rocket

[PlinytheWelder]

The problem is once you back the master down a bit, you won't really be pulling on the power supply nearly as much. Part of the wreck feel and the clean to mean potential is the power supply sagging when you really crank it. What happens with a master is the dirty tones end up having less compression, and therefore end up being too loud compared to when you back your guitar down for clean. This is because once you get things really backed off the power supply is barely stressed. Anyway, long worded way to say IMHO a master on a wreck is not nearly as good a way to go as a nice attenuator. It might not be half bad if you simply play your guitar cranked all the time. But if you really want that magical clean to mean with literally no volume change you need to run the original circuit and forget about a master. That all said some folks have reported nice clean to dirty tones when using a power scaling setup. Perhaps the power scaling devices have somewhat of a sag to them even if the voltage is scaled down?

That makes a lot of sense, thanks Glen.
I suppose that I should build mine close to stock before modifications,
at least to get a baseline.

[johnny riff]

Is there another MV that would work better in a liverpool style amp.
What about type 3 from the TW pages.Has anyone here try that?

[paulster]

I don't think you'll find a better master than the Lar/Mar variation on an Express or Liverpool because of the reason Glen has pointed out.

Getting the power tubes working and therefore the power supply compressing by design is a fundamental part of the wreck sound.

[El_Martin]

Hi!

Liverpoools -being cathode biased- pretty much like the VVR power scaling thingy. It's easy to scale the whole amp and keep the clean to mean reactivity at different volumes.

Totally turned down you will not be too happy, though.

Ciao
Martin