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Untitled Document START NEW THREAD From: Date: Subject: Page 1 of 8 REPLY Top of Thread LIST Read 538 times Marshall Maniac ([email protected]) 8/11/2001 8:30 PM London Power "Power Scaling" Have any of you ever used London Power's Power Scaling Kits (http://www.londonpower.com/psmadv.htm)? They appear to let you reduce plate voltage on the output tubes from 100% down to less than 1% using a panel-mounted pot. Seems like a good alternative to a Hot Plate. I've been using a Power Brake for some time, and the idea of having nothing between the OT and the speaker (other than a cord) is very interesting to me. Thanks for any thoughts! START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST PREVIOUS LIST Read 516 times Plexinator ([email protected]) 8/11/2001 10:00 PM Re: London Power "Power Scaling" I am thinking about trying this also plexi START NEW THREAD REPLY Read 505 times From: Date: Subject: JWK ([email protected]) 8/11/2001 11:04 PM Re: London Power "Power Scaling" The power scaling kits only became available in the last couple of weeks. There are a few people around who might give you their insight as to how the actual London Power amps perform with the integral power scaling. I almost ordered a studio about a year ago, but just can't bring myself to buy any amp I can't hear for myself after the last major "burn" I experienced two years ago. In any case, I will probably get the kit for a 50 watt amp I'm dreaming up when I gather a bit more experience and knowledge. John START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 497 times SeanF ([email protected]) 8/12/2001 1:47 AM all I know is what I've heard... from two people whose ears I trust completely, and both of them rave about it. I'll probably give it a try shortly. http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 2 of 8 Read 462 times From: Ed ([email protected]) Date: Subject: 8/12/2001 6:54 AM Re: all I know is what I've heard... Please let me know how it turns out. thank you Ed START NEW THREAD From: PREVIOUS LIST Read 440 times Tone Doctor ([email protected]) Date: Subject: REPLY 8/13/2001 4:37 AM Re: London Power "Power Scaling" The Power Scaling kits are pretty new, but I have owned a London Power Session 50 amp for a year or so. It rocks, and the Power Scaling is the coolest thing in the world. As you lower the plate voltage the dynamic range of the output section is lowered. If you adjust the volume at the same time, you can use it to get the same tone as you would use at a higher SPL, just quieter. Conversely, if you leave the input volume up, and turn the Power Scale down, the thing starts to sustain like a violin. I think the separate bias controls in the kits allow you to use disparate tubes in the output stage, as well. That can be an interesting sound. TD START NEW THREAD From: PREVIOUS LIST Read 387 times Plexinator ([email protected]) Date: Subject: REPLY 8/13/2001 3:54 PM Re: London Power "Power Scaling" TOne DOctor How do you think this would sound on a 50 watt marshall plexi amp? plexi START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 270 times Tone Doctor ([email protected]) 8/14/2001 12:54 PM Re: London Power "Power Scaling" http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 3 of 8 Plexi I am planning to do a 100W JMP Marshall myself. I think it should sound great. TD START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 413 times Matthew Springer ([email protected]) 8/13/2001 4:04 PM Re: London Power "Power Scaling" Power scaling bascially is a "volume" control for the AC voltage being fed into the rectifiers. The heart of the idea is to use a dual ganged pot to reduce the secondary AC voltage into the power supply. So the answer is YES, anything derived from the main secondary PT AC windings (ie. everything but heaters pretty much) will be affected. In his most excellent books, Kevin seems to hint that he also derives the bias voltage from the secondary AC as well (as oppossed to a separate bias winding), so this voltage will also exactly scale with power scaling (but obviously, being a negative voltage, it scales "upside down"). -Matthew START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 387 times Plexinator ([email protected]) 8/13/2001 4:11 PM Re: London Power "Power Scaling" Does this effect the preamp too?? or just the power section aka power tube plates and screens? SOmething to Ponder Plexi START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 283 times Tone Doctor ([email protected]) 8/14/2001 12:52 PM Re: London Power "Power Scaling" Plexi Kevin could talk to this better than I, but I believe the voltage scaling is applied to the power tubes only. It varies the plate, screen and bias voltages in proportion. By not applying it to the preamp or PI, it allows these sections to stay "fast". TD START NEW THREAD REPLY PREVIOUS LIST http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 4 of 8 Read 417 times From: Date: Subject: Dave Rich ([email protected]) 8/13/2001 4:20 PM Re: London Power "Power Scaling" Thats all there is to it???? At low settings that would create a lot of sag. It would have to be cathode biased too I presume. Thats interesting. I would like to know more about it. START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 356 times Tone Doctor ([email protected]) 8/13/2001 6:05 PM Re: London Power "Power Scaling" It's not as simple as that. The circuit adjusts the plate voltage and the bias voltage in proportion. Power Scaling works well in both fixed and cathode biased amps. TD START NEW THREAD REPLY PREVIOUS LIST Read 275 times From: Date: Subject: KB ([email protected]) 8/14/2001 4:14 PM Re: London Power "Power Scaling" he also derives the bias voltage from the secondary AC as well (as oppossed to a separate bias winding), so this voltage will also exactly scale with power scaling (but obviously, being a negative voltage, it scales "upside down") So where does the DC come in as we all know that bias voltage can't be AC, KB. START NEW THREAD REPLY PREVIOUS LIST Read 272 times From: Date: Subject: jaysg ([email protected]) 8/14/2001 4:37 PM Re: London Power "Power Scaling" The heart of the idea is to use a dual ganged pot to reduce the secondary AC voltage into the power supply. http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 5 of 8 Should this be rephrased so no one trys a dual-ganged pot across their PT secondary? The pot must be controlling MosFet gates? START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 237 times Tone Doctor ([email protected]) 8/15/2001 12:59 AM Re: London Power "Power Scaling" There seem to be a lot of opinions about what Power Scaling is and how it works. I can tell you reading from this thread, that a lot of the opinions are just that. The reason I know what the curcuit looks like and does, is because I copied the design from my Session amp, and have used it in other amps. I really hope that any owner of a London Power amp would never think to publish schematics. Kevin is a great guy and we should support him. I can tell you from knowing the components involved, that he is charging a very reasonable price for his kits. And look at the bright side, after you buy one you won't have to think, "I wonder how he does that?" TD START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 224 times Plexinator ([email protected]) 8/15/2001 3:19 AM Re: London Power "Power Scaling" Well i will probably end up getting one for the plexi 50 watt that i am building...After i get my plexi done....i will give you guys a run down of how it sounds! I am pretty sure its gonna sound amazing because...well Kevin O'connor is a very knowledgable person...and i trust him to make a good product!! plexi START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 219 times Matthew Springer ([email protected]) 8/15/2001 4:45 PM Power Scaling (longish) Jay, Should this be rephrased so no one trys a dual-ganged pot across their PT secondary? The pot must be controlling MosFet gates? No. I'm _pretty_ sure the whole cricuit is just a big, lowish impedance, high wattage dual ganged pot right across the secondary windings and you feed the rectifiers (two for the main b+ and one http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 6 of 8 or two for the bias rail) right off the wipers. No MOSFets are involved as far as I can make out. Although I'm sure Kevin uses them elsewhere in his amps. My guess is he does something clever with diodes to ground at each bottom leg of the wiper to reduce the staic power disipated by the control. DISCLAIMER: I haven't seen any schematics either, but I have tried to grok my way through the book. If you think about it the actual power disipated by say a 10K dual ganged pot across a 300VRMS voltage source is ~ 9W total DC. They make 25W rated wire wound pots. Let's see if I can still do this... P = V * I, V = I * R, so P = I^2*R A 10K pot (we'll do one leg of the AC winding) therefore draws 30mA DC, so that disipates 30A^-3 * 10k = 9W. Assuming a diode in the bottom leg to reduce this by half (so you don't draw current when your side of the secondary winding is negative, but you've got two pots in one case so x2 = ~9W. This is strictly back of proverbial envelope so don't try this at home kids, but you might be able to get away with it withthe right pot. -Matthew START NEW THREAD From: REPLY PREVIOUS LIST Read 202 times Matthew Springer ([email protected]) Date: 8/15/2001 8:42 PM Subject: And another thing... Anybody even remotely interested in Power Scaling or amp building in general should run out and immediately buy every single book every written by Kevin O'Connor (I'm dead serious). These books are some of the finest refernce materials/textbooks on analog circuit design I've ever read and I've got a masters in EE. I think between him and RG and Randall, I've saved maybe a year of lab time. Whenever Randall writes his treatise on amp building I'll be the first in line for that one too. And I certainly don't intend to give away Kevin's secrets in this or any other forum. But I think everybody agree's that discussing generalized approaches seems to be ok, discussing actual design specifics would probably be less ok. Anybody interested in actually building a power scaling amp should certainly run out and buy his kit. Whatever design problemns we (the community) are going to encounter designing and building a collapsing B+ rail he's doubtlessly already solved in his most elegant of ways. -Matthew START NEW THREAD REPLY PREVIOUS LIST Read 192 times From: Date: Subject: MBSetzer ([email protected]) 8/15/2001 9:05 PM Re: And another thing... Well, in the research lab it is often said: *a year at the lab bench can sometimes save you more than an hour of time in the library* Mike http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document START NEW THREAD Page 7 of 8 REPLY PREVIOUS LIST Read 126 times From: Date: Subject: O'Connor ([email protected]) 8/18/2001 3:30 AM Re: And another thing... Thanks for the kind words and support! For those of you who have "grogged through the books" and actually understand it, you will know right off that Power Scaling may in fact be do-able using ganged pots, but is most certainly NOT elegant or even how I do it in my amps or kits. TUT2 presented many ways to achieve a Power Scaling result but the term was never mentioned so very few people ever connected the dots between the book and the Power Scaling Dialogue on our site. There are about 60 distinct ways to do it and endless variations of those. Every method cannot be universally applied-- although there are some that can be. The technique used in my amps has limited applicability as does that for the kits-- which is why there are three kits and likely more to come. I'm hoping to get TUT3 finished for Christmas--it will be filled with construction approaches for standard circuits and their variants, and cover grounding, noise abatement, etc, in detail. But after that, there will be three books that will shed light on what many deem cutting edge retro: "Power Scaling Tutorial", "Super Scaling Tutorial" and "Power Management Tutorial". Each covers the development of the topic area in great detail, with tonnes of schematics and tips. You can get a taste of this technology in the kits we sell, and learn a whole lot more from the upcoming books. Power Scaling does only what is claimed and it works because it only has to do one thing, It just has lots of beneficial side-effects. Have fun Kevin O'Connor START NEW THREAD From: Date: Subject: REPLY PREVIOUS LIST Read 115 times Matthew Springer ([email protected]) 8/18/2001 5:04 AM Kevin O'Connor on Kevin O'Conner So, Kevin Now that we have your attention... As a curious experimenter and engineer but also as a concerned and ethical netizen: I'm curious to know what level detail and discussion about your designs you would like to see in this and other forums. As a person who's been on quite the cutting edge of "Tube Knowledge for the Masses", you are in some ways on both sides of the intellectual property debate; trying to disseminate information without giving away the farm. I was wondering if you'd care to comment on what you consider an appropriate balance is between all of us DYING to know how you did things and also respecting the hard work you've obviously put into your designs. http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001 Untitled Document Page 8 of 8 And about the dual pots, I THOUGHT after reading _Secrets_ revealed that was the idea I got, but when I sat down to write a post supporting this idea yesterday and actually did the power dissipation calculation I realized this couldn't have been how you did it either. I also looked at your kits and relaized you'd incorporated current limiting features which means MOSFETS and zeners, not pots. (sigh) back to the books for me.... -Matthew alternate display for printing http://firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=132880 ... 8/20/2001