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View Full Version : Anybody put a Master volume on a plexi Marshall?


skhan007
07-22-2009, 06:28 PM
I'm talking re-issue here, not messing with a vintage one. Right now I'm running my 50 watt with the Ultimate Attenuator and it's OK, I guess. Part of me thinks that I might be better with a master vol.

I'm curious if this is an easy/reversible mod (I've seen Marshalls with a master vol knob in place of one of the two speaker outs).

Either that or sell my plexi for something Marshall-like with a master.

phsyconoodler
07-22-2009, 06:34 PM
You can install a post-phase inverter master volume and get seriously nice tones.It requires a dual 1meg pot and a couple of caps and resistors.
Look up 'lamars master volume mod'.
Killer nice tones,likely better than your attenuator.

RussB
07-22-2009, 07:13 PM
Lar-Mar PPIMV

I put one on my Plexi clone, and it works great.

rob2001
07-22-2009, 07:16 PM
Marshall pretty much did it with the JMP 2203's/2204's and the JCM 800's.

sliberty
07-22-2009, 07:30 PM
A MV on a Plexi will work fine, but I'd suggest a VVR instead:

http://www.hallamplification.com/main.html?src=%2F#2,2

HipKitty
07-22-2009, 08:43 PM
yes, quite a few...all ppimv's. You do lose some of the Presence control depending on where the mv is set.

frankencat
07-22-2009, 08:44 PM
Yeah, TopHat. :D

skhan007
07-22-2009, 10:14 PM
A MV on a Plexi will work fine, but I'd suggest a VVR instead:

http://www.hallamplification.com/main.html?src=%2F#2,2



Oh man, that's an economical fix!! I had no idea a VVR was available for fixed-biased amps. I thought that technology was for cathode-biased amps! Hall's page states it's only 5 wires to hook up. This may be something I can handle and maybe I should pull my amp from the emporium before someone buys it!:)

I read up on the PPIV-MV and about 1/2 the guys like it and others said that it doesn't do well. At least it's a reversible mod if I go that route.

phsyconoodler
07-22-2009, 10:32 PM
The Lar-Mar master is fabulous.And VVR works best with master volume anyway.

stump
07-23-2009, 08:28 AM
LAR/MAR user here. Works great and is easy to install.

paolojm
07-23-2009, 11:05 AM
Done a few, and by far the LarMar is better for both tone and reliability.

FrankieSixxxgun
07-23-2009, 02:03 PM
Yup, put a Lar/Mar in my Metro 50 watter. Works excellent and sounds better than my Hot Plate.

scott1568
07-23-2009, 09:41 PM
The Lar-Mar master is fabulous.And VVR works best with master volume anyway.

Can someone tell me what Lar-Mar master is and VVR? Sounds interesting.


thanks

scott1568
07-23-2009, 09:48 PM
The Lar-Mar master is fabulous.And VVR works best with master volume anyway.

Can someone tell me what Lar-Mar master is and VVR? Sounds interesting.


thanks

phsyconoodler
07-24-2009, 11:26 AM
The Lar-Mar master is a dual ganged pot that is basically the same as the old Trainwreck PPIMV but has a couple of 2.2meg resistors added.
VVR is 'variable voltage regulation'. It is a circuit that can be added to an amp to lower internal voltages so you can turn the overall volume down to even whisper quiet levels and still have nice tone.They sound better than any attenuator IMHO,and they are actually easier on tubes.
You will have to do some of your own legwork to find a schematic or layout for these items,as they have been around for quite a while now.

skhan007
07-24-2009, 12:45 PM
OK guys, thanks for your feedback on my question!

Is it safe to say that many of you think it's better to keep & mod my reissue Marshall plexi rather than selling it for a similar amp that has a master vol? I was thinking one of the clones/boutiques would serve me well (e.g. Twister F3, Matchless, Bad Cat, etc.). I know they're not "MARSHALL" but a good plexi approximation can be found at lower wattage and lower volumes.

FrankieSixxxgun
07-24-2009, 01:29 PM
OK guys, thanks for your feedback on my question!

Is it safe to say that many of you think it's better to keep & mod my reissue Marshall plexi rather than selling it for a similar amp that has a master vol? I was thinking one of the clones/boutiques would serve me well (e.g. Twister F3, Matchless, Bad Cat, etc.). I know they're not "MARSHALL" but a good plexi approximation can be found at lower wattage and lower volumes.

It's a no brainer. A Lar/Mar will cost you $8. How much is selling that Plexi and buying some boutrique thing gonna cost?

scott1568
07-24-2009, 01:59 PM
[QUOTE=phsyconoodler;6480352]
VVR is 'variable voltage regulation'. It is a circuit that can be added to an amp to lower internal voltages so you can turn the overall volume down to even whisper quiet levels and still have nice tone.QUOTE]


Is this another name for power scaling?

thanks

ripoffriffs
07-24-2009, 11:50 PM
Here's another website that does power scaling for existing amps: http://www.skipzcircuits.com/index.html

Also, Uncle Albert's in Indy can install PPMV in your plexi.

Roe
07-25-2009, 06:41 PM
use a double 250k pot http://metroamp.com/wiki/index.php/Lar/Mar_PPI-MV

skhan007
07-26-2009, 06:14 PM
Thanks guys. I currently use a vari-watt (power scaling) in my 18 watt Marshall clone, so I'm very familiar with/and like power scaling.

I did get some advice that it's better to sell and get something else than to mod. I'm actually still thinking that modding might be a safe bet.

Let me run this by you cats: I love the sound of KT66's, so I could throw a pair in my plexi, re-bias properly, and then get the VVR put in (or the PPIV-MV for that matter). That should sound great and suit my needs well. Do you guys know of any correction/fix for that "hair trigger" volume on the high treble channel? You know, it goes from nothing to full-on in your face gain by the time it's on 2. Is there a way to smooth that out so I get some range with that High Treble volume (without taking out the bright cap)?

RussB
07-26-2009, 08:47 PM
Thanks guys. I currently use a vari-watt (power scaling) in my 18 watt Marshall clone, so I'm very familiar with/and like power scaling.

I did get some advice that it's better to sell and get something else than to mod. I'm actually still thinking that modding might be a safe bet.

Let me run this by you cats: I love the sound of KT66's, so I could throw a pair in my plexi, re-bias properly, and then get the VVR put in (or the PPIV-MV for that matter). That should sound great and suit my needs well. Do you guys know of any correction/fix for that "hair trigger" volume on the high treble channel? You know, it goes from nothing to full-on in your face gain by the time it's on 2. Is there a way to smooth that out so I get some range with that High Treble volume (without taking out the bright cap)?


You can have KT6's installed, but the bias supply will need a different value resistor to get the KT66's in their prober range.

You can change the value of the bright cap to a "smaller" cap (100pf to 250pf) That will make it less dramatic.

What I did was to put the bright cap on a push/pull pot. That way I can have my cake and eat it too.

It's the Sprague "Black Beauty" wired up to the pot on the left.

http://img.photobucket.com/albums/v432/RussBert/6M45/2-24-09001.jpg

skhan007
07-27-2009, 03:39 PM
You can install a post-phase inverter master volume and get seriously nice tones.It requires a dual 1meg pot and a couple of caps and resistors.
Look up 'lamars master volume mod'.
Killer nice tones,likely better than your attenuator.

Lar-Mar PPIMV

I put one on my Plexi clone, and it works great.

The Lar-Mar master is fabulous.And VVR works best with master volume anyway.

LAR/MAR user here. Works great and is easy to install.

Done a few, and by far the LarMar is better for both tone and reliability.

Yup, put a Lar/Mar in my Metro 50 watter. Works excellent and sounds better than my Hot Plate.

It's a no brainer. A Lar/Mar will cost you $8. How much is selling that Plexi and buying some boutrique thing gonna cost?

This is great info here. Can the Lar-Mar mod be done on a PCB plexi? Seems easy enough on a PTP amp, but my Plexi is a PCB.

Roe
07-27-2009, 04:31 PM
yes, it can be done on a pcb. just remove the two 220k resistors and put in a pot

jay42
07-28-2009, 04:36 PM
Do you guys know of any correction/fix for that "hair trigger" volume on the high treble channel? You know, it goes from nothing to full-on in your face gain by the time it's on 2.The first thing to do is to verify that there's actually a difference between the bright and normal channels, though it sounds like you're focusing on the channel you use. Next, verify that the pot is not linear, and is an audio/logarithmic taper pot. Assuming it's audio taper and you still want it to react slower, put a 500K ohm 1/2W (carbon film) resistor in line right before the Bright channel pot.

I don't know how the RIs are wired. If the pot is soldered directly to a printed circuit board, it would create a bit of a challenge.

skhan007
07-28-2009, 07:15 PM
Thanks Jay. Here's a photo of the RI 1987x 50 watt. From the schematic I saw on-line, the vol pots are audio taper. If I put in a 500 k Ohm resistor, would one end of the resistor go to ground and the other on one of those lugs (sorry for being a novice in this dept.).
http://i69.photobucket.com/albums/i57/skhan007/DSC_0005-4.jpg

Also- I think I'm going to try KT66's in there an bias up to the proper range. 65% * 25 watts/465 plate Volts DC = about 35 mA.

RussB
07-28-2009, 07:32 PM
Also- I think I'm going to try KT66's in there an bias up to the proper range. 65% * 25 watts/465 plate Volts DC = about 35 mA.



You can have KT66's installed, but the bias supply will need a different value resistor to get the KT66's in their proper bias range.



...

skhan007
07-28-2009, 07:53 PM
OK, with the KT66's, I now see what you mean. I just put in my KT66's and took a reading with my bias probe and my lowest mA draw is 60 mA. That's as low as it'll go with the KT66's, so there is obviously the need to change resistor values (which is something I don't know how to do).

jay42
07-28-2009, 08:25 PM
Thanks Jay. Here's a photo of the RI 1987x 50 watt. From the schematic I saw on-line, the vol pots are audio taper. If I put in a 500 k Ohm resistor, would one end of the resistor go to ground and the other on one of those lugsUsing that picture, disconnect the red wire on the rightmost lug. Solder one end of the resistor to that lug and the other end to the red wire. Easy.

skhan007
07-29-2009, 11:53 AM
Using that picture, disconnect the red wire on the rightmost lug. Solder one end of the resistor to that lug and the other end to the red wire. Easy.

Thanks Jay! Yes, I think I can handle that mod! Can I get that 500k Ohm carbon film resistor from Radio Shack or is that something I need to order from an amp parts store/website?

off topic, but an good time to ask this: are all modern Marshalls made this way? The reissue plexi models (non PTP) in my experience seem to be very well made amps. Yet, I tend to think of Marshall build quality as C grade. Perhaps because of comments about the other models.

Yes, unless it's a "handwired" series amp, they will be PCB. I think the amp is very well made, however some of the parts have been weak. For example, on my amp, the amp tech had to replace the screen grid resistors on V4 & V5 and they turned out to be cheap plastic looking things.

jay42
07-29-2009, 12:09 PM
Can I get that 500k Ohm carbon film resistor from Radio Shack or is that something I need to order from an amp parts store/website?Perhaps. RS doesn't have great selection, however, that's a value they might have. Shipping from mouser or digi-key would be sort of ridiculous for one resistor. Look for amp & stereo repair places and electronics surplus stores if RS fails you.

skhan007
07-29-2009, 02:37 PM
Perhaps. RS doesn't have great selection, however, that's a value they might have. Shipping from mouser or digi-key would be sort of ridiculous for one resistor. Look for amp & stereo repair places and electronics surplus stores if RS fails you.

Thanks Jay. I found some 470K 1/2 watt carbon film resistors at Radio Shack. This will be my $0.99 mod. I'll wire her up tonight and give her a test drive and report back!:rockin

skhan007
07-30-2009, 09:34 AM
Using that picture, disconnect the red wire on the rightmost lug. Solder one end of the resistor to that lug and the other end to the red wire. Easy.

I did the Jay-mod to my High Treble volume last night. Seems to be a slight improvement! I now have a bit of range between nothing and full gain. Before, it used to just "jump" into mucho gain, and now there's a bit of medium-gain tone before it jumps. Thanks for the tip on the $0.99 mod!