About EPA on YJM100

[Mats A]

I A-B´d my YJM using the EPA and my Marshall Power Brake not using the booster on the amp. When playing using the EPA you get very little distortion too little for my taste (I use a Les Paul with PAF´s). But when using the Power Brake i get much more distortion. I know the Power Brake takes away dynamics from the tone but it doesn´t add distortion anyway. Makes me wonder how well the EPA really works.
Is it as good as the London Power Scaling?

[surfnorthwest]

The way it works I understand is it lowers the voltage on the output tubes prior to the output transformer. So basically you would loose some distortion because you are not cooking the tubes as hard. Attenuators take down the voltage after the transformer.

I understand the allure of things like the new EPA, power scaling, and attenuators, I hate all of it. Over the past two years I owned two amps that had the power scaling, one was London Power Scaling and the other was Vari-Watt. I tried to like it but my ears hear everything. I am just unwilling to sacrifice any tone or dynamics because my amp is to fucking loud. There are so many good low wattage amps on the market today where you don't need this.

That is the reason I canceled the YJM order and went with the 25 Fargen Olde 800. That amp has a Master Volume which works great at 25 watts so I am able to get very hard driven tones at reasonable volumes. I love the YJM, as you know it is monster of an amp, its just didn't make sense for my studio. I guess you have to give a little to get a little with the EPA.

[Mats A]

When using the EPA i need to use a clean booster to get a playble tone for me anyway. Using the Power Brake i get a tone that´s got enough distortion for me to play with without a booster. Think you get more treble with the EPA also. It´s a bit like a PPIMV but better since these tend to give a fizzy tone when turned down much.

-- Sun Oct 30, 2011 2:05 am --

The way it works I understand is it lowers the voltage on the output tubes prior to the output transformer. So basically you would loose some distortion because you are not cooking the tubes as hard. Attenuators take down the voltage after the transformer.

I understand the allure of things like the new EPA, power scaling, and attenuators, I hate all of it. Over the past two years I owned two amps that had the power scaling, one was London Power Scaling and the other was Vari-Watt. I tried to like it but my ears hear everything. I am just unwilling to sacrifice any tone or dynamics because my amp is to fucking loud. There are so many good low wattage amps on the market today where you don't need this.

That is the reason I canceled the YJM order and went with the 25 Fargen Olde 800. That amp has a Master Volume which works great at 25 watts so I am able to get very hard driven tones at reasonable volumes. I love the YJM, as you know it is monster of an amp, its just didn't make sense for my studio. I guess you have to give a little to get a little with the EPA.

Surf does your Fargen amp have London Power Scaling? Is this any better than Marshalls?

[big dooley]

the EPA affects screen voltage, the bias and the negative feedbackloop from the amps output, back to the phase inverter...
having less distortion with EPA vs powerbrake may be due to the fact, that the transformers still have an easy job to do as they don't have to pass on large amounts of current, which causes internal voltages to sag down more, in turn causing LESS headroom

[Wildone]

the EPA affects screen voltage, the bias and the negative feedbackloop from the amps output, back to the phase inverter...
having less distortion with EPA vs powerbrake may be due to the fact, that the transformers still have an easy job to do as they don't have to pass on large amounts of current, which causes internal voltages to sag down more, in turn causing LESS headroom

Good explaination. From demos I have heard the EPA works very well.

[big dooley]

from what i can tell with the AFD100 it's great...
although i like it, that the AFD has a master volume... i like to turn the master a bit down... the YJM doesn't have a master

i've never used an attenuator, so i can't compare both to eachother though

[Mats A]

The AFD is a high gain amp where as the YJM is not. Output distortion has less affect on the tone on high gain amps. Think the AFD would sound good even without the EPA.

[big dooley]

The AFD is a high gain amp where as the YJM is not. Output distortion has less affect on the tone on high gain amps. Think the AFD woulsd sound good even without the EPA.

true, it does... but the extra compression of the 6550's on a diet with the EPA gives it a nice touch... like to try EL34's as the 6550's are hard to get into breakup

[Mats A]

I´ve had EL34´s in mine for some time now. Think i like it better with 6550´s since i think that maybe it sounds a bit thinner or has less bottom with EL34´s.

[Piemonte]

Yes I was surprised how little distortion there is with the EPA, with a Les Paul if I dig in I can get to break up a bit.

Thanks to Dooley my power sagging problem seems to have gone but I struggling to enjoy the amp. I'm no YJM fan but I love the the sound of old Marshalls and I thought this would do the trick with EPA at any volume, in my opinion it doesn't.
I just can't get rid of the treble rasping sound when I use the EPA.
I find also the boost has too much treble. I'm using vintage 30s and was wondering if greenbacks maybe a better option with a view to reduce the high treble content of the amp and lack of distortion ( with boost off).

I think in conclusion I would be better off with a master volume JMP amp however I really did not want to buy an old amp in case of problems.

I think I'm going to sell mine.

Thanks again Dooley for all your help.

[big dooley]

Yes I was surprised how little distortion there is with the EPA, with a Les Paul if I dig in I can get to break up a bit.

Thanks to Dooley my power sagging problem seems to have gone but I struggling to enjoy the amp. I'm no YJM fan but I love the the sound of old Marshalls and I thought this would do the trick with EPA at any volume, in my opinion it doesn't.
I just can't get rid of the treble rasping sound when I use the EPA.
I find also the boost has too much treble. I'm using vintage 30s and was wondering if greenbacks maybe a better option with a view to reduce the high treble content of the amp and lack of distortion ( with boost off).

I think in conclusion I would be better off with a master volume JMP amp however I really did not want to buy an old amp in case of problems.

I think I'm going to sell mine.

Thanks again Dooley for all your help.

i've had a similar thing going on when i dime the mastervolume of the AFD... i alway back it off a little and everything is cool...
somehow i think that with the YJM and AFD the phase inverter distorts more in comparison to the powertubes, then a regular marshall... poweramp distortion is not only powertubes breaking up, the phase inverter distorting plays as much if not a bigger role into the whole thing of poweramp breakup... (not for nothing, the VM has a post phase inverter master volume...)
the YJM however doesn't have a mastervolume, that can tame the distortion of the PI, which means that the amp is behaving the same as a mastervolume fully dimed
there are certain things you can try out... the simplest thing would be a volumepedal in the loop... voila... you've obtained yourself a mastervolume...
another thing you can try is to put a lower gain tube in the PI position... a 5751 may be a good place to start as it is similar to a 12AX7 but has 70% of available gain compared to the 12AX7...
if that's not enough, you can try a 12AT7... these tubes can drive the powertubes hard, as it's able to let trough a lot of current (almost 10 times more then the 12AX7), but the tube itself won't break up that easily
try it out... i wouldn't sell it that early... once you'll regret it...

[Mats A]

I use a clean booster in front of my YJM and that does the trick for me. But you get a bit more treble than with the EPA and volume dimed.

[pleximaster]

Yes I was surprised how little distortion there is with the EPA, with a Les Paul if I dig in I can get to break up a bit.

Thanks to Dooley my power sagging problem seems to have gone but I struggling to enjoy the amp. I'm no YJM fan but I love the the sound of old Marshalls and I thought this would do the trick with EPA at any volume, in my opinion it doesn't.
I just can't get rid of the treble rasping sound when I use the EPA.
I find also the boost has too much treble. I'm using vintage 30s and was wondering if greenbacks maybe a better option with a view to reduce the high treble content of the amp and lack of distortion ( with boost off).

I think in conclusion I would be better off with a master volume JMP amp however I really did not want to buy an old amp in case of problems.

I think I'm going to sell mine.

Thanks again Dooley for all your help.

This is not my experience with the YJM, of cause you don´t get 100 percent the same sound as diming the thing, there is also distortion coming from the output transformer itself and it also vocices the sound differently depending on how hard it is pushed. Thats one reson to why different OT sound different. I use vintage Les Pauls and strats (rather low output) Most of my PAF are below 8k and the vintage strats PU are often around 5,5k. I think my YJM delivers a good amount of gain and great sustain (comparing it with my vintage plexis and 4-holers metalface as reference) of cause a tad less as you maxing the EPA. Original plexis are not very gainy originally, superbass are really hard to push, so called vintage "gainmonsters" are best found in the 71-73 area but they all differ a bit, and they aren´t that gainy. Many vintage amps are however tweaked in some way to give more gain then they originally did. The never plexi reissues have more gain than these metalface "gainmonsters" to begin with and if you use them as reference you might think it low gain (I personally don´t own a reissue now but I have done so in the past I would say that YJM and reissue plexis are rather similar). So using the EPA hard you loose some gain but you are actually getting gainsetting more representative of an original plexi. However the YJM offers so many ways of compansating for "lack" of gain with the boost the effect loop and the use of infront pedals (the way most old recodings from the 70s and 80s done with plexis have had some thing added in the chain) that it truly is a working system with a plexi and EPA.

I only tried the YJM through 4x12s. I got the best sound so far using vintage 20watter greenbacks. Sounds great with the old 25 watter greenbacks as well though. I haven´t tried 30 Watt greenbacks with bass cones yet but it might be a good "umpf" adding factor to the treble effect at volume.

best regard
plexi

[aristotle]

Adding to the datapoints (or confusion...) here is my $0.02. When I'm dialed way way back on EPA, it means that I'm at home. I don't mind compensating for lack of gain by using the boost (or a pedal in front for that matter...though I don't tend to do that at home...) and any change in brightness can be dialed back ahead of time to taste. I'm just not worried about real-time changes when I'm practicing at home. Second, to my ear, speaker choice seems to be particularly important at low volumes. My favorite for low volume use is an open back cabinet with a pair of celestion blues (can't go more than 30 watts in this configuration though...) Next favorite for low-volume for my tastes is 1960AHW, but I don't haul that back home just for noodling around. For combinations of EPA and max power settings of...say...20 watts or more, to me, it's a complete non-issue. Practically speaking, for me, it's an exceedingly useful setup even for reasonably (20watt) low volume use at least in live applications. Full disclosure though....I don't need super high gain. I just want plexi-like breakup at a variety of overall volumes. For that, for me, it's great.

[Cardinal Synne]

I think it sounds more vintage if you turn the tone controls right down. It send sounds more like my 77 super lead. I think the tone controls on modern marshalls sound different to the old ones. I also think that the preamp voltage is much higher in new amps, whereas the old plexis sound more soft and less brittle. I recently had the voltage increased in my old plexi and it made it sound modern so am reversing it.