An explanation of London Power Scaling?

Drew224

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Can anyone make it make sense to me? I haven't been able to find out how it works from anything they've got on their site.

Are there any amps that it won't works well with?

With a '60s Marshall circuit, is it better than putting in a PPIMV?
 

Case24

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I'll give it a go. I have a simplified version installed in my 5E3 Deluxe build. It uses a MOSFET as a heat sink to get rid of the wattage as waste heat and thereby reducing the output of the tubes and the volume of the amp without greatly altering the tone. There is a 1 meg pot attached to a small circuit board that is used to vary the amount of B+ voltage reduction sent to the MOSFET. There are 3 resistors and a zener diode on the board to reduce the current sent to the MOSFET to protect it should a power tube fail.

So basically, it is a knob you turn to reduce the amount of B+ voltage being sent to the tubes by redirecting it to a heat sink instead. This in turn reduces the volume of the amp but keeps the tone. :thumb:
 

Drew224

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So it's better than a PPIMV?
 

Case24

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So it's better than a PPIMV?
Not sure. I have no experience with one really. None of my amps have any kind of MV. All I know is I really like the power scaling.

Edit: I shouldn't say no experience. I just have nothing to compare to right now. I used to have a Traynor YCV20WR that had a gain control on each channel, kinda a master on each channel. Spent $700 and never really found the tone I was looking for. Sold it for $350.
 

Drew224

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Ah, cool.

I've heard that PPIMVs suck tone, which makes perfect sense to me, given where they are placed in a circuit.
 

Tuya Customs

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So it's better than a PPIMV?
Just different. A MV is a MV, you can mix how much preamp drive you want with volume. However power scaling is the whole circuit. So the power tubes still saturate.

Ah, cool.

I've heard that PPIMVs suck tone, which makes perfect sense to me, given where they are placed in a circuit.
Suck tone??:hmm: They do what they are meant for. If they were such tone suckers then they wouldn't be on so many amps. Also if a PPIMV is dimed then it out of the circuit.
 

Drew224

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Just different. A MV is a MV, you can mix how much preamp drive you want with volume. However power scaling is the whole circuit. So the power tubes still saturate.



Suck tone??:hmm: They do what they are meant for. If they were such tone suckers then they wouldn't be on so many amps. Also if a PPIMV is dimed then it out of the circuit.
Ah, allow me to rephrase. I've heard that they change the tone, and they're fizzy at lower settings.
 

Tuya Customs

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Ah, allow me to rephrase. I've heard that they change the tone, and they're fizzy at lower settings.
As do power scaling. You can't get nice bedroom OD out of a 60's Marshall without comprising some tone. Now a mix of the two should be pretty interesting but I don't know how that would work.
 

Lyle Caldwell

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Full Power Scaling also involves a pre-PI MV to keep the PI from breaking up when the power is scaled way down. It's a "fine tuning" adjustment - the majority of the volume reduction is handled by the power supply scaling.

The goal of Power Scaling is not to turn a 100W Marshall into a bedroom amp. It's so you can have the great sound/feel of a 100W Marshall in a small club - the realistic level is to match that of an acoustic drum set. 100W Marshalls (and really, 30W-50W amps too) are just too damn loud for most places we can play these days.

And Power Scaling is the best way to get that. A 50W Marshall sounds different than a 20W Marshall. With Power Scaling, the 50W Marshall may only be putting out 15W but the output section has a certain sound the lower wattages stock Marshalls can't match.

I mean, damn guys. I design amps, build amps, modify amps, restore vintage amps, design pedals, everything. A typical work day for me may be an Eric Johnson Strat with Kinmans through $2000 worth of pedals into a restored '58 Bassman. You want to know what my bedroom amp is?

 

Liam

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You want to know what my bedroom amp is?

:)

I use a 100 watt Marshall for pretty well all gigs at the moment. Our drummer is just a bit too loud for a 50 watt amp.

My bedroom amp isn't. I tend to practise with an unplugged electric guitar, or plug into a phrase trainer and use headphones. Amps are just too loud for home use.

Liam
 

TeleDog

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An amp is a power supply. It takes voltage and amplifies that in the preamp and then takes current and amplifies that in the power amp. All it does, that's what any tube amp will do.

A master volume is like a flood gate, it'll limit what comes out of the preamp, after that, it doesn't do crap. So, if you crank the preamp and limit it with a MV, keeping the power tubes quiet, you'll hear a harsher overdrive.

Power scaling limits what the amp as a whole can do, more or less. So, you can crank the gain stages and get good overdrive at a lower overall volume. However, if it's not properly implemented the result will be a very shallow overdrive.

For some circuits, power scaling will not offer you a very noticeable reduction in volume, but you'll hear the difference in tone. The amp will be loud, but you'll get to the overdrive sooner, less headroom. It depends on how it's designed.

If the intent of this is to find out if you can crank a 100W head in your living room at reasonable levels without tone loss, the answer is a very loud no. You can't. Remember thermodynamics in school. Tone will be lost to heat, and that's what happens, and you can't change that.
 

dwagar

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Are you sure you want to modify a 60s Marshall?
 

rocknhorse1

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Just different. A MV is a MV, you can mix how much preamp drive you want with volume. However power scaling is the whole circuit. So the power tubes still saturate.



Suck tone??:hmm: They do what they are meant for. If they were such tone suckers then they wouldn't be on so many amps. Also if a PPIMV is dimed then it out of the circuit.
Tuya, you know what happens on your Champ when you bypass the tone stack right? Same thing with a MV. Bypass that and it will sound different.
 

Tuya Customs

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Tuya, you know what happens on your Champ when you bypass the tone stack right? Same thing with a MV. Bypass that and it will sound different.
According to Randy when a PPIMV is dimed then its bypassed because its not using any signal.
 

Lyle Caldwell

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When a PPIMV is dimed the circuit is stock. It's still in the circuit because it's supposed to be in the circuit and is in fact biasing the output tubes.

It can be hard coming to the internet for information because there's so much myth and "my brother in law says" you have to wade through.
 
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rocknhorse1

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According to Randy when a PPIMV is dimed then its bypassed because its not using any signal.
I was talking a standard MV, sorry for the confusion.
As far as I know, he doesn't use a PPIMV on his amps, unless you ask for it. That is what he told me anyway.
 

Lyle Caldwell

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A properly executed MV is also transparent when dimed. It's just that there are also poorly executed MVs out there.

It's like judging German cars by a '73 Beetle.
 

Case24

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Full Power Scaling also involves a pre-PI MV to keep the PI from breaking up when the power is scaled way down. It's a "fine tuning" adjustment - the majority of the volume reduction is handled by the power supply scaling.

The goal of Power Scaling is not to turn a 100W Marshall into a bedroom amp. It's so you can have the great sound/feel of a 100W Marshall in a small club - the realistic level is to match that of an acoustic drum set. 100W Marshalls (and really, 30W-50W amps too) are just too damn loud for most places we can play these days.

And Power Scaling is the best way to get that. A 50W Marshall sounds different than a 20W Marshall. With Power Scaling, the 50W Marshall may only be putting out 15W but the output section has a certain sound the lower wattages stock Marshalls can't match.
I mean, damn guys. I design amps, build amps, modify amps, restore vintage amps, design pedals, everything. A typical work day for me may be an Eric Johnson Strat with Kinmans through $2000 worth of pedals into a restored '58 Bassman. You want to know what my bedroom amp is?

And that's what I like about it on my Deluxe; it retains the sound and feel of the Deluxe's output section when used down to about half setting. This makes the Deluxe quiter than my 5F1 when producing the tone I like to practice with. It is still putting out some volume but it is more family friendly. But it's not going to sound like a Deluxe with only 38VDC on the plates (not quite whisper quiet) which is why you can't use it to turn a 100 watt anything into a bedroom amp.
 

TeleDog

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When a PPIMV is dimed the circuit is stock. It's still in the circuit because it's supposed to be in the circuit and is in fact biasing the output tubes.

It can be hard coming to the internet for information because there's so much myth and "my brother in law says" you have to wade through.
I thought it was a friend of a friend who said.... :wow:
 

Johnny Alien

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:)
I use a 100 watt Marshall for pretty well all gigs at the moment. Our drummer is just a bit too loud for a 50 watt amp.
I play in a Ramones style punk band and our drummer hits HARD. He does not hold back. I can easily keep up with a mic'd 20 watt tube amp. I can figure out how hard your drummer has to play to be louder than a 50 watt Marshall tube amp. I am impressed.
 




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