300v Non-linear Power Supply- Noiseless (SAFE) design??? - Page 1
Forum section: electronics / projects

author: TomJPartin
author_rank: Newbie
timestamp: January 23, 2023, 02:51:02 pm
content: Hello, all- Long time fan of EEVBlog on YouTube. First post here on the forum.First off, I'm what Dave might call a "midnight engineer". Not exactly a beginner, but certainly not sporting an EE degree. Lifelong musician, got into electronics by building tube amps when I was a young warthog. Almost finished an associate's in EET, but life got in the way.I'm working on a design for a small, lightweight, all-tube guitar amplifier. And by small and lightweight, I mean challenging the traditional form factor to the extreme, to go absolutely as small and lightweight as possible. This of course suggests nixing the large iron power transformer...So, that leaves one with a non-linear alternative. Looks like I need either a CW multiplier, or one HELL of a boost converter.Dave has been taking me to school on SMPS design on YT, (Thanks, Dave!) But I still haven't found a reasonable way to achieve a 300-400vdc output, let alone stable, let alone with low noise for an audio circuit... I've just been smoking parts. Hard to find jellybean stuff rated for these kinds of voltages. Not to mention I'm not a fan of there being NO galvanic isolation on most of these circuits I've tried breadboarding. That's something I want to incorporate into the final design, for sure.Worth mentioning, I'm in the US, and the design will be for 120v. So, I don't have a lot of volts from the wall to start with, compared to other spots in the world. This presents a challenge as well.I haven't tried the CW multiplier yet, simply because I know it won't support much of a load at all before sagging the rail horribly. And, I'd probably have to pot the damn thing in epoxy to prevent arcing between stages. But I may dig out a bunch of caps and diodes and give it a whirl- who knows? A couple of EL84s in push-pull won't draw much anyway... Exact figures escape me. On the order of 75 mA MAX for both tubes, I think?Small, stable, noiseless, 300-400vdc output. (meaning anywhere in that range, not necessarily adjustable) These are the basic criteria for this design.ANY and ALL suggestions or advice from you fine folks is greatly appreciated. Thanks a lot!!-TJP***EDIT***Okay. So, looking at the datasheet on the EL84, it stipulates a maximum anode voltage of 300v. Goody! I don't have to go quite so high. (most big bottle tubes run on 300-500v in an audio circuit) I edited the subject line to reflect this as well.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 23, 2023, 02:55:48 pm
content: Sorry I'm gonna be frank, with this voltage and related dangers, i would suggest to buy such a psuBut you have some schematics on the web, tube based psu .... the problem will be the transformer ....And other members will say it can / could be dangerous ... yada yada security warning done300-400vdc at which current, pls be more specific and sorry there is no noiseless psu loll, but low or / very low ripple could be attained .... but already made products are better in a way

author: TomJPartin
author_rank: Newbie
timestamp: January 23, 2023, 03:00:58 pm
content: Thanks for the reply! Worth mentioning, I have plenty of experience safely working with much higher voltages than this. No worries about playing safely. 😌 Current requirements are somewhere between 50-75 mA for the pair of tubes. (25-35mA each) Sorry, I couldn't pull the datasheet while typing out the post, it just deleted my text everytime

author: Marco
author_rank: Super Contributor
timestamp: January 23, 2023, 04:44:27 pm
content: A multiplier at mains frequency is not actually light weight, because the capacitors have to be huge to keep ripple down. Also no isolation of course, so the ground plane can easily go live if the socket isn't wired correctly or you have reversible mains plugs.The friendly neighbourhood Chinese have 300V switching power supplies for tubes ready to go, ya know?https://nl.aliexpress.com/item/1005001814771782.htmlhttps://nl.aliexpress.com/item/1005003516795631.html

author: TimNJ
author_rank: Super Contributor
timestamp: January 23, 2023, 05:18:47 pm
content: If your main focus is making the amp, and don't care so much about designing a power supply, buy one of those Aliexpress power supplies. If I was going that route, I'd probably stress test it thoroughly and check some component temperatures to make sure it will be reasonably reliable. You could always replace the (presumably) crap-tastic caps with some better stuff.If you are interested in designing the power supply, a flyback topology design is probably the most logical. You probably want to design to accommodate around 20W for the heaters and 50W for the B+. There are many suitable control ICs which can be used. You can use a generic old-school PWM IC like UC384x, or a newer more specific flyback IC like NCP1342. (Just as examples.) Many of the newer ICs support various "modified" flyback topologies like "valley-switching" or "quasi-resonant", which allow higher levels of efficiency.The most important aspect of designing an AC-DC power supply is the construction of the transformer. It is most important in two respects: Proper functioning of the power supply and safety of the end user.It is not *that* hard to design a safe transformer, but to the novice, there are a lot of areas to be ignorant about. And, if you're not careful you (or somebody else) can get seriously hurt.Some topics to search and dive into:1. Creepage and clearance2. Hi-pot testing2. Triple insulated wire3. Margin tape4. NEMA/UL Insulation class/system (e.g. Class B or F)4. IEC62368-1, IEC60950-1, IEC61558 (read these, if you can get them)

author: Bud
author_rank: Super Contributor
timestamp: January 23, 2023, 05:54:33 pm
content: Take a look at the article in Silicon Chip magazinehttps://archive.org/details/silicon_chip-2003_11/page/24/mode/2upIt has among other things a +260V switching power supply and DIY details including construction of the transformer.Amazingly, all the transformer parts (beside the wire itself) are still available on Digikey.

author: TomJPartin
author_rank: Newbie
timestamp: January 23, 2023, 05:57:28 pm
content: These replies are incredibly helpful... Thanks!!! And yeah, I suppose I could buy a power supply for the prototype to prove the concept. But I certainly want to optimize the psu specifically for use with this amplifier and its features. I understand there's no such thing as a truly noiseless design, I mean noiseless enough for an audio circuit. Switching noise is very unpleasant to the guitarist... I will take a look at the chips you suggested!!I have a little bit of experience winding transformers at home, but only for signal and impedance matching. Never tried to design a power tranny- wouldn't know where to start in the world of smps. Ferrite core? Air core? How small could I go with the core and the gauge of the windings per the switching frequency? These are the questions I would have... along with how to build the whole thing to be safe and idiot-proof. The end goal (pipe dream) is a production model, once I can prove the concept. So user safety and professional build quality are of paramount importance to me, for sure; one reason I dislike the idea of buying an AliBaba supply. Any good references or reading material on smps/flyback transformer design? Thanks again so much you guys are awesome 🙏🙏🙏

author: TomJPartin
author_rank: Newbie
timestamp: January 23, 2023, 05:58:04 pm
content: Quote from: Bud on January 23, 2023, 05:54:33 pmPerfect, thanks!!!

author: Bud
author_rank: Super Contributor
timestamp: January 23, 2023, 06:08:32 pm
content: If you want to design your own, I think the PS in this article is a good way to learn and experiment, as the transformer is not tiny and you can always adjust number of turns or add new windings for other voltages, great way to experiment. But I'd recommend first doing some readings to understand that topology (seems it is often being referenced as 'tapped inductor boost converter'). I found this application note useful (sure many others are out there):https://pdfserv.maximintegrated.com/en/an/AN1109.pdf

author: TimNJ
author_rank: Super Contributor
timestamp: January 23, 2023, 07:34:12 pm
content: Quote from: TomJPartin on January 23, 2023, 05:57:28 pmFundamentals of Power Electronics, Maksimović & Erickson -- Good coverage of theory and includes useful approaches to help you make initial sizing decisions/calculations. I've used the design equations/approaches many times to good successTransformer and Inductor Design Handbook, McLyman -- Lot of discussion on practical design, explanation of loss mechanisms, etc.Soft Ferrites Properties and Applications, Snelling -- Deep dive on ferrite materials, many interesting graphs/figures, probably less directly useful for a novice thoughRegarding your questions, most of the time, it's more than just picking a core and calculating turns. If you are really interested in this, pick up some of the above reading and I think you will start to see some of the complexity involved. It's not rocket science, just maybe more than meets the eye. At some point, you'll learn juuust enough to be dangerous (like me).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 23, 2023, 08:12:09 pm
content: As a beginner, definitely don't touch anything mains related. It's enough voltage to give a nasty zap if nothing else, and kill if you're really unlucky / have preconditions / etc. (The same applies to the B+ output, of course.) Electrically, it's mostly nominal, but occasionally sports transients of several kV at low impedance (surge) that will blow up anything not designed for it. Also high frequency noise/transients (mainly due to nearby activity: contacts opening, ESD, etc.) that can cause malfunction and damage to susceptible circuits. And other users in the area frown upon emission of noise up the mains network -- SMPS need to be well filtered, and isolation becomes much more challenging with that constraint: you need more than just any transformer, the transformer itself, its characteristics are part of the noise/filter system.The next best thing then, is run everything at a nice and modest 12 or 24V DC say (which can double as heater supply), using an off-the-shelf approved supply, and build a non-isolated DC-DC converter. For 300V, you want flyback, or at least two stage (cascaded) boost.Overall, I think I'd be surprised if you end up saving space over an iron transformer, using off-the-shelf parts (and whatever bespoke converter you find/make). It's definitely possible, but it will take work -- repeated attempts selecting suitable components, perfecting the circuit, and cramming it all together. Manage expectations, and budget your time and money for multiple attempts.Incidentally, there is a way to reduce the output transformer as well. But it's not easy:https://davidberning.com/technologyTim

author: TimNJ
author_rank: Super Contributor
timestamp: January 23, 2023, 09:25:42 pm
content: Quote from: T3sl4co1l on January 23, 2023, 08:12:09 pmGenerally agree, though you can get 100 - 150W+ (without a fan) in a 2" x 4" x 2" open-frame footprint pretty easily. Seems like a 100VA toroidal transformer is also about 4" (OD) x 2" (H). Caps and rectifiers will take some space, yes, though honestly not that much.I made a "low-profile" (chassis) tube amp a while ago, and I distributed the bulk capacitance across the board with some long of these long, small diameter caps (brown ones below). Not that it would take that much space to clump them together in one spot either.Quote from: T3sl4co1l on January 23, 2023, 08:12:09 pmThat's cool. I wonder, does nano-crystalline have any promise as a replacement for iron-core output transformers? High flux density, broadband material, with much higher permeability than silicon steel.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 23, 2023, 09:43:11 pm
content: Quote from: TimNJ on January 23, 2023, 09:25:42 pmNot really -- Bmax is about the same (or less maybe?), so it's limited by LF cutoff at full power. You can get much more small-signal bandwidth, but not power bandwidth. And HF losses are mostly irrelevant because Brms is inversely proportional to frequency. If you don't need the low end, you can save weight either way (as many guitar amps do, in contrast to bass guitar, or hifi).Maybe as a substitute for permalloy, for audio (signal) isolation transformers?Cute ampTim

author: jonpaul
author_rank: Super Contributor
timestamp: January 24, 2023, 02:09:42 pm
content: Wrong terminologyNon linear is usually for log curve eg uLaw A law ADC or for microwave/VHF harmonic gens like certain diodes and parametric amps.You want NOT non linear but switched mode, SMPS.Voltage multipliers like Crockoff-Walton have very high Zo and only for ma/ua loads and HV.A simple flyback or boost conv is the simple solution.As years of experience and lots of special lab equip and components are needed to make an offline SMPS, suggest:1/ Fast and simple: Buy off the shelf SMPS to your specs.2/ DIY/Learn: Read and research flyback and boost converters, with isolated output .Learn to specify and wind transformersChoose SMPS control ICDesign PSUAcquire all parts,Test equip:100 MHz 2..4 ch scope10x voltage probesCurrent probe if possible1:1 mains isolation trsfVariacwind and test transformerBuildDebug.Perhaps a few months and $1000 equipment...You will learn a lot!Jon

author: JohnG
author_rank: Frequent Contributor
timestamp: January 24, 2023, 03:42:39 pm
content: Quote from: T3sl4co1l on January 23, 2023, 08:12:09 pmThanks for this! It's a clever idea. It's either ultra-audiophile or ultra-audio-blasphemy, not sure which.I went from tubes to Class D after I realized I could not educate my family out of putting things like CDs on my restored Dynaco ST-70. Also, it had terrible bass with my speakers at the time.John

author: Martinn
author_rank: Frequent Contributor
timestamp: January 24, 2023, 05:51:35 pm
content: Quote from: TomJPartin on January 23, 2023, 05:57:28 pmIIRC Jon posted a link to a free (limited to two windings) transformer design software recently, this might help you getting started.- Martin