Marshall power scaling? (Origin series etc)

[Carl M]

Does anyone know how Marshall's power scaling is working? I had a London Power power scaling kit installed in my Lead 50s (1987) and it's a bit of a nightmare to balance the power scaling pot with the drive compansation pot (or pots).

But the way Marshall do it with just a three way switch in the case of the Origin, it's so easy and convenient and it seems to sound and work better than other power scaling methods. I'd love to see the same power switching fitted in Super Leads or Lead 50s.

So, does anyone here know anything about how Marshall is doing it?

 

[junk notes]

Mojave Peacemaker, Reeves, or Stephenson, and Suhr has his take. Pete Thorn has a video demonstrating Badger volume settings for scaled down tones and how to achieve them. When it was new, that video helped me in understanding that circuit for my Badger.
I do not think that Marshall is interested in power scaling for now, and would be more prudent to reissue the PB-100 at this point and with the popularity of the Studio Series SV circuit, players would show interest.

 

[junk notes]

For now, Marshall is doing it right offering dual voltage amps like the Studio Series 5/20 watts.
That seems like a big hit with the customer base.
I often see posts with members that mix up dual voltage transformer amps with vrtual variac amps droppping plate voltage..

edit type-o fixed Thanks @PelliX

 

[Carl M]

I do not think that Marshall is interested in power scaling for now,

Well Marshall are producing several products and have produced several products in the past with variable output power.

- Both the now discontinued YJM100 and AFB100 had power scaling.
- The Origin series has three stepped power scaling. (My Origin 20H can be set to 20, 3 and 0.5w)
- The DSL series have a half power setting on several model, but DSL1 can be switched between 1w and 0.1w.

The Studio series seems to have a different arrangement, where the power switch switches between pentode and triode to alter the maximum output power. (My Studio Vintage can be switched between 20w in pentode mode and 5w and triod mode.) This isn't power scaling because it actually changes tube type to reduce the power, unlike how the Origin series does it which seem to maintain the EL34s in pentode mode and instead are feeding the output devices with lower volumes.

The arrangment used in the Origin series is really cleaver and i am interested in learning how it works. Perhaps this can be applied to bigger Marshall or perhaps we can expect future Super Leads and Lead 50s variants to feature a three way power switch to make them easier to use in smaller venues, in studio and at home. I would probably order one straight away if they launched one...

Anyway it's encouraging that Marshall is bringing out products like the Studio series and the Origin series which are more usable than our old vintage Marshalls which most of us rarely can use to their full potential, because most of us don't play at football arenas that often...

 

[fitz288]

The arrangment used in the Origin series is really cleaver and i am interested in learning how it works.

I read somewhere that it's a transformer voltage thing, as opposed to a pentode/triode thing.
Not sure exactly how it works, or if could be a retrofit into an existing non-power scaling amp, if that's what you're getting at.
I have both the O20H & DSL20HR and only use them on 20w.
IMHO, they get their best tones when they're cookin'.

 

[Carl M]

I read somewhere that it's a transformer voltage thing, as opposed to a pentode/triode thing.
Not sure exactly how it works, or if could be a retrofit into an existing non-power scaling amp, if that's what you're getting at..

I am really just interested in learning more about how the Origin series switchable output power is working. The technology could probably be applied to bigger classic amp if one just understands how it works. But I would probably rather buy a new Lead 50 or Super Lead with this feature if Marshall would release such a version of the classics. I should have bought a YJM100 when they were still available, but I didn't...

 

[Carl M]

I have both the O20H & DSL20HR and only use them on 20w.
IMHO, they get their best tones when they're cookin'.

A friend of my recorded his Origin 20 at all the three power settings and normalized the volume levels to make them sound equally load and they the three power settings (20w, 3w and 0.5w) sounded surprisingly similar and since I bought my Origin 20 specifically to get a 0,5w EL34 Marshall to use at very low volume for composing in the next room and to use for silent tracking with acoustic drums I will really only use it in the 0.5 w mode. I have other Marshalls which can do the "loud" thing...

 

[PelliX]

For now, Marshall is doing it right offering dual voltage amps like the Studio Series 5/20 volts.

You mean Watts, and it's not quite that simple. I'm pretty sure the Low setting is more than 5W, and yes, I'm aware of the log curve, W vs dB ratio, etc.

I read somewhere that it's a transformer voltage thing, as opposed to a pentode/triode thing.

That might have been me. I can't speak for any other amps in the series, but the SC20 drops voltage on the output section for the power reduction. I was expecting triode/pentode, but no.

OP: Maybe check the Official Origin 20 thread (have a search on the forum). I'm pretty sure someone outlined more about the innards over there. I don't have one, so I've never been particularly interested. Yet.

 

[MarshallDog]

Does anyone know how Marshall's power scaling is working? I had a London Power power scaling kit installed in my Lead 50s (1987) and it's a bit of a nightmare to balance the power scaling pot with the drive compansation pot (or pots).

But the way Marshall do it with just a three way switch in the case of the Origin, it's so easy and convenient and it seems to sound and work better than other power scaling methods. I'd love to see the same power switching fitted in Super Leads or Lead 50s.

So, does anyone here know anything about how Marshall is doing it?

The comments you make in regards to the London Power Scaling mod are very interesting to me. Why, I have the LPS mod on a 74 NMV MKII 2204 and love it but then again it does not have a gain/master volume knob! I just set the LPS and use the volume knob as desired. If I want a cleaner tone at higher volumes I lower the LPS knob, mine works flawlessly. Sorry to hear yours does not!

 

[Ivan H]

I haven't owned, or been inside of an Origin amp, but from talking with a buddy who has owned an Origin 50, & also another buddy who modified it for him, I "believe" that Marshall simply lowers the screen grid potential (+ voltage) for the two lower power settings, thus making the power tubes run less efficiently. I'll try catching up with the guy who modified the amp (mainly pre-amp circuitry & associated HT rail voltage dropping/decoupling resistor values) to ask more on how Marshall are dropping the screen potential. Cheers

 

[junk notes]

Well Marshall are producing several products and have produced several products in the past with variable output power.

YJM100 and AFB100

Yes, familiar with the amps and the YJM, and was just pointing out in those same words, but pointing out that they are not interested "for now", focusing their attention on the Studio Series. IOW, there is no dialog happening in the office. If you have seen or have heard something brewing, then please post!

 

[junk notes]

You mean Watts, and it's not quite that simple. I'm pretty sure the Low setting is more than 5W, and yes, I'm aware of the log curve, W vs dB ratio, etc.

doh! watts, not volts! yes lol ..sorry 'bout that. Thanks

 

[Carl M]

The comments you make in regards to the London Power Scaling mod are very interesting to me. Why, I have the LPS mod on a 74 NMV MKII 2204 and love it but the again it does not have a gain/ master volume knob! I just set the LPS and use the volume knob as desired. If I want a cleaner tone at higher volumes I lower the LPS knob, mine works flawlessly. Sorry to hear yours does not!

Thank you for your input. I assume that if your amp has no master volume and was built in 1974, then it's a 1987 and not a 2204, which is the master volume mode which was intrduced a year or two later.

In that case then the amp I had a London Power PS kit installed in is very similar to yours, because it's a replica built using 1987 drawings dated 1968.

The London Power kits has two pots one which will reduce the voltage in the power amp and another one which they call "Drive Compensation" which is there to lower the signal to the power amp, because if you scale down the volume then the input from the preamp section will be too high and then you will get too much distortion from the power amp compared to the preamp when comparing to a non-scaled amp.

The problem is the London Power's drive compensation is just a master volume control very similar to the one in a Marshall 2203 or 2204 which is not very popular in Super Leads or Lead 50w (1987) for a good reason. All master volume controls have their advantages and disadvantages. I didn't like the stock "drive compensation" in my 1987 clone, but instead of replacing it I added a second master volume a PPIMV type 2 (Lar/Mar) Having two masters at different parts of the amp doing less work each was an improvement and then I had a third masted fitted inside the phase inverter and having three was better again, but it was a nightmare to find the right balance between the power scaling pot and the three master. As a result I never move any of the four pots...

If I understand you right you only have one pot (power scaling) and no drive compensation (i.e. master). That is very interesting because the problem you have with drive compensations and masters in a 1987 or 1959 Marshall is that the master volume itself isn't great. But the way you do it is that the channel volumes are your drive compensation. Why didn't I think of that? That sounds like a good idea. I didn't consider bypassing the drive compensation and just use the volume control.

Many thanks. This sounds like a very good way of power scaling a 1987 (Lead) or a 1959 (Super Lead)

 

[Carl M]

I haven't owned, or been inside of an Origin amp, but from talking with a buddy who has owned an Origin 50, & also another buddy who modified it for him, I "believe" that Marshall simply lowers the screen grid potential (+ voltage) for the two lower power settings, thus making the power tubes run less efficiently. I'll try catching up with the guy who modified the amp (mainly pre-amp circuitry & associated HT rail voltage dropping/decoupling resistor values) to ask more on how Marshall are dropping the screen potential. Cheers

Yes, I assume that they are dropping the the voltage powering the power tubes, but because you control it with a three way switch. They also need to bring down the signal hitting the power tubes to prevent them from distorting like crazy when you drop the voltage in the power amp and I assume that this is what some of the relays are for because they need to lower the signal from the the preamp when dropping the voltage power in the output devices.

It would be very interesting if you can ask the guy who modified your buddys Origin.

 

[Carl M]

Yes, familiar with the amps and the YJM, and was just pointing out in those same words, but pointing out that they are not interested "for now", focusing their attention on the Studio Series. IOW, there is no dialog happening in the office. If you have seen or have heard something brewing, then please post!

No, I don't know anything about Marshall's plans but the power switching in the Origin series seems to be to good to not use in the UK made higher end models.

The Studio series seems to be completed and I would assume the Marshall R&D are working on something else and since both the Studio Series and the Origin series are new then perhaps next up is something higher up in the range...

 

[Gene Ballzz]

At least a couple former employees/designers from Marshall have confirmed (on this website and/or others) that the Studio Series, ORIGIN 20 & 50 Series, Astoria and I believe latest iterations of DSL20, 40 and 100 do not use Pentode Triode switching for the lower wattage settings. I believe the previous 25, 40 and 100 DSL versions did though! For that matter, the DSL 1 & 5 are already dual triode powered, so.....?
Just Rememberin'
Gene

 

[Carl M]

At least a couple former employees/designers from Marshall have confirmed (on this website and/or others) that the Studio Series, ORIGIN 20 & 50 Series, Astoria and I believe latest iterations of DSL20, 40 and 100 do not use Pentode Triode switching for the lower wattage settings.

Thanks. Interesting. I was under the impression that the Studio series had a pentode/triode switch to reduce the output power.

 

[junk notes]

At least a couple former employees/designers from Marshall have confirmed (on this website and/or others) that the Studio Series, ORIGIN 20 & 50 Series, Astoria and I believe latest iterations of DSL20, 40 and 100 do not use Pentode Triode switching for the lower wattage settings. I believe the previous 25, 40 and 100 DSL versions did though! For that matter, the DSL 1 & 5 are already dual triode powered, so.....?
Just Rememberin'
Gene

I appreciated this tidbit of info.

_
(with the SV/SC this new-to-me, I am trying getting acquainted with the Studio Series circuit, and wrapping my electrons around self-biasing. so..
Just Learnin', gettin' a schoolin'.)

 

[sunflower]

_Steve kindly posted his voltage survey around 5w/20w modes on SV20.

Studio Vintage SV20 mods (and SC20 too)

I wrote them down if you need them. I’m interested to see them, if you don’t mind looking them out, thanks :)

www.marshallforum.com

It seems like marshall lower PI plate voltage and power tubes plate/screen voltages to reduce power on SV20.