Need recommendations for bench power supply (guitar amp prototyping) - Page 1
Forum section: electronics / beginners

author: Crush
author_rank: Contributor
timestamp: July 19, 2012, 09:07:01 pm
content: Hi,I would like to make guitar amps that use vacuum tubes that power speakers.I understand that theses boards require transistors. Both input and output.But in my lab environment I need to practice on a breadboard like the pick below and wanted know what kind of power setup I need.Thanks

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2012, 10:09:16 pm
content: Quote from: Electroalek on July 19, 2012, 09:59:10 pmAs has been stated before, an ATX PSU is not a good bench supply. Especially cheap ones.Their regulation is poor, ripple can be quite high, and cross-load regulation is extremely poor. They also cannot supply much of any current on negative rails (and many don't even have the -5V rail).

author: madires
author_rank: Super Contributor
timestamp: July 19, 2012, 10:10:51 pm
content: Quote from: Electroalek on July 19, 2012, 09:59:10 pmLooks more likely to be 6.3V for filament and 300V for anodes.

author: Monkeh
author_rank: Super Contributor
timestamp: July 19, 2012, 10:14:42 pm
content: Quote from: madires on July 19, 2012, 10:10:51 pmYes, DIYing a 300VDC PSU is far from a good idea for a beginner.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: July 19, 2012, 10:28:43 pm
content: Quote from: Electroalek on July 19, 2012, 09:59:10 pmIf you are beginner i would highly recommend not to recommend at all...As far as the topic concerned, you should have fairly specific power requirements for an amplifier, sowhy not make a dedicated PSU rightaway. For instance the one you intend to be using in the final product?

author: Crush
author_rank: Contributor
timestamp: July 19, 2012, 10:47:42 pm
content: Quote from: Monkeh on July 19, 2012, 10:09:16 pmYes that's why I was asking.I've learned in life not to start hobby's on the cheap because it wastes time when learning real craft can be achieved for just a little bit more cost. If you want to brew beer, I'd recommend to go right into all grain brewing with kegs, don't waste time on extracts or other 'beginner' methods.. they will waste your valuable time and money and you'll brew bad beer. You need to put your time and effort on learning the 'real' skill of making 'real' beer.. not making fake beer.I'd prefer not to 'home brew' bench tools like power supplies because I know what the outcome will be. I'm ordering a Hakko soldering iron with good quality core wire. Breadboard with solid 22awg tin wires non crimped. That's all I have so far. But I'm buying these things because I know the problems that will happen if the right breadboard wire isn't purchased. I read all about it and am trying to avoid those mistakes.So that's why I wanted a proper bench setup.. Obviously I'm not a professional so don't need the best stuff, but I just wanted to someone to recommend a brand or something that is 'acceptable' or 'meet my needs' and 'won't let me down'. I have no idea what I need for the type of things I'll be interested in doing. That's why I'm asking. I've asked on other forums, searched videos, and I have a hunch that people really don't know the answer. All I've heard is 9 volts is 'more than you need' for most project. Guitar amps plug directly into the wall. There's no 6v plug like other electronic household items or guitar pedals.. That's all the info I can give.

author: Crush
author_rank: Contributor
timestamp: July 19, 2012, 10:55:57 pm
content: Quote from: Short Circuit on July 19, 2012, 10:28:43 pmI'd like to play around with various designs and such. I would also like to add low pass/high pass filters, eq boosts, etc.Don't the power supplies sit on the bench and you turn the knob to the power you need?Or is designing guitar amps a special case?

author: madires
author_rank: Super Contributor
timestamp: July 19, 2012, 11:26:33 pm
content: Quote from: Crush on July 19, 2012, 10:55:57 pmUsing vacuum tubes is a special case since it involves high voltages. Please do yourself a favour and stay away from high voltages until you know what you're doing. There are some special low voltage vacuum tubes but they're not practical for guitar amps. Start with transistors!Regarding a bench/lab power supply I recommend one of the inexpensive standard units providing 0-30V and 0-3A.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: July 19, 2012, 11:38:28 pm
content: Actually, I hardly use voltage setting of my lab power supplies, current limiter is much more important.That's because I add a power supply circuit quite early in the design stage, so the input voltage does not really matter anymore.But what I do is not very relevant for your applicationHowever for your amp experiments, things are not that much different. Most small-signal stuff with transistors and opamps can be powered from the 'classic' +/-9~15V. You can use some symmetric lab power supply for that purpose, or a simple PSU like Electroalek suggested (2nd suggestion), or just a couple of 9V batteries. I guess it depends on the amount of time you intend to be playing with this stuff, and your budget.Ok, reading back, the advise to your question is above; get a symmetric power supply. So you can play with audio circuits, without having to worry about DC biasing of your signals.After a bit googling, a pure symmetric PSU seems quite rare. I'm quite sure Elektor has published a few designs in the 80's end 90's, but I cannot find them.Nowadays alternative seems to get a dual channel PSU (2x 30V/3A is very common) with tracking feature, likehttp://nl.farnell.com/tenma/72-8690/power-supply-bench-2-x-32v-3a/dp/1836056?in_merch=true&MER=i-9b10-00001422(quite cheap) orhttp://nl.farnell.com/aim-tti-instruments/pl303qmd/psu-dual-30v-3a/dp/1510524(versatile).When it comes to the tube amp stuff, things get a bit different, and also more dangerous. Adjustable power supplies with tube amp ranges are not very common. And personally I would not want to have live banana wires carrying many 10's of mAmps at 300-500V accross my working area anyway... That's what I had in mind with the comment regarding a more integral build of amplifier stuff and power supply; so that all lethal stuff is somewhat shielded by the chassis.

author: Crush
author_rank: Contributor
timestamp: July 20, 2012, 12:42:17 am
content: But why do they sell these tube kits to mainstream users and what about the picture of the guy with the breadboard working with tubes?

author: ivan747
author_rank: Super Contributor
timestamp: July 20, 2012, 12:51:04 am
content: Avoid the ATX power supply for audio applications at all costs! They are very noisy and unstable, they might introduce oscillation to your circuit or noise.You probably need a dual polarity power supply. Or two supplies in series. +/-15V could be fine because op-amps are usually powered at these voltages.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: July 20, 2012, 01:55:07 am
content: The tube kit builds on the included chassis. And I'm sure it comes with step by step instructions that allow a safe assembly process.Chassis + instructions will ensure the builder will never be in contact with hot circuits.The breadboard scenario is probably just another I-have-done-this-a-thousend-times-without-problem kind of guy.Conveniently forgetting that he got bitten by a 300VDC line every now and then, non remembering he did actually fry some of those IC's by accidentily connecting a high-voltage to one of its pins (probably blaming it on dodgy devices afterwards), or ignoring the circuits that did not work because of the leakage currents through the breadboard (which is probably just rated for 30VDC or thereabout).Or maybe he really knows what he is doing and doing it safely, at least from the human safety viewpoint.However, when somebody still has to ask a forum what PSU is needed, then this person is far from ready to do that by himselfNo offence intended, just trying to keep you alivePersonally, if I would want to experiment with tube circuits, I would pick a simple metal box to use as chassis, punch or drill some holes for the tube sockets, install a bunch of these old-skool terminal strips, and keep all high voltage stuff inside that box.

author: ivan747
author_rank: Super Contributor
timestamp: July 20, 2012, 02:07:29 am
content: I would love to get into this sort of guitar audio stuff. It looks quite lucrative. How did you get started?

author: DrGeoff
author_rank: Frequent Contributor
timestamp: July 20, 2012, 03:21:31 am
content: Decent tube guitar amps are expensive to make. You need a good output stage, which uses expensive tubes, and the output transformer is also expensive. I've seen a few pretend tube naps that used a 12ax7 in a preamp and a solid state output to save costs, but it does not quite sound the same as an all tube design.

author: Crush
author_rank: Contributor
timestamp: July 20, 2012, 08:55:34 am
content: oh well I tried.. I guess I'll have to go to a third forum to find users who are more knowledgeable on a very easy, electronics 101 type of question.And as far as the safety Sally's go, they should learn about electricity. Go back to beginners electricity 101 instead of calleing me one. The typical lightning bolt contains 1 billion volts and contains between 10,000 to 200,000 amperes of current. 1 in 7 people die from getting hit.And no I would never put those pc power supplies near the amp. Might as well put FM tansmitter and RCA jacks also if I was going to ruin the testing. That's why I asked about a testing environment.

author: madires
author_rank: Super Contributor
timestamp: July 20, 2012, 10:59:06 am
content: Quote from: Crush on July 20, 2012, 08:55:34 amA current of just 50mA is already deadly. Safety regulations over here require proper isolation for >50V AC and >120V DC. It doesn't need to be a lightning to knock you off your feet. Please checkhttp://en.wikipedia.org/wiki/Electric_shockbefore complaining about safety Sallys.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 20, 2012, 11:47:19 am
content: Quote from: Crush on July 19, 2012, 09:07:01 pmSorry,but your first posting doesn't show any basic understanding of what you are wanting to do.Re-read it & see if it makes any sense to you!I gave you a sensible answer in your other thread,assuming you had a bit more knowledge.To answer the question:(1)Yes,some"tube"amplifiers also use transistors,normally in the input circuits.In this kind of amplifier,the output power devices are vacuum tubes.Many tube amplifiers do not use any solid state devices,other than in the power supply,in fact some traditionalists refuse to use any semiconductors at all.(2) The kind of "breadboard" in the picture is designed for prototyping discrete semiconductor & IC circuits & is notappropriate for tube circuits due to insufficient insulation & the size of components normally used in such circuits.Historically,(in the 1920s),tube circuits were built on wooden bases which in some cases were real breadboards out of the owner's kitchen,& in others were specially made,with tube sockets & other components mounted on the board with screws,& connections made,initially with nuts & bolts,& later with point to point soldered connections.Problems arose due to lack of shielding of sensitive circuits,which led to the metal "chassis"type of construction,with wiring under the chassis.There were some Printed Circuit Board tube devices built in the late1950s,early 1960s,but problems with heat damage to the board arose,& most tube construction stuck with the chassis.(3) I have seen,& used, about three bench power supplies suitable for vacuum tube use,in a working lifetime in TV & radio Broadcasting,a fair part of that time in Transmitter sites using mainly tube equipment.In tube equipment,it is common to build the power supply into the amplifier,as it is difficult to know in advance the power requirements of every piece of equipment you will build.If you look at the kit amplifier photo,the big transformer is probably a power transformer.Serious solid state amplifiers also use built in power supplies.Bench power supplies have only come to prominence since the almost complete replacement of tubes by solid state.Some supplies go up to around 50V,many much lower,at various current ratings.(4)Re your comments about"not starting a hobby on the cheap".Many years ago,I decided to become a Surf fisherman,so I bought the best equipment.I found out that I didn't know how to cast,so I hardly ever got the bait out far enough to catch anything,& spent most of my time untangling line & disputing ownership of the bait with seagulls.If I had found somewhere that taught casting,I would have been OK,but no,I persevered,& got worse,rather than better,all because I was too stubborn!If I had started out "on the cheap", sitting on a jetty with a handline,or a flick rod,I would have caught fish,& probably still be a fisherman,but I wanted to "do it all" from the outset,grew disenchanted,& gave up!

author: Bored@Work
author_rank: Super Contributor
timestamp: July 20, 2012, 03:54:03 pm
content: Quote from: Crush on July 20, 2012, 08:55:34 amBy, by, and don't let the door hit you on your way out.

author: T4P
author_rank: Super Contributor
timestamp: July 20, 2012, 06:42:19 pm
content: Quote from: Crush on July 20, 2012, 08:55:34 amGoodbye and not let karma hit you outside~This is the main point i make across about tubes! HOT NON-LINEAR INEFFICIENT AND DANGER!

author: vk6zgo
author_rank: Super Contributor
timestamp: July 21, 2012, 01:18:12 am
content: Is it just me,or are we having a rash of beginners who start multiple threads about virtually the same thing?They don't all stomp off like 13 year olds when they don't get the answer they wanted,like Crush did,but it's still annoying,& I wish they'd stop!

author: Short Circuit
author_rank: Frequent Contributor
timestamp: July 21, 2012, 03:49:27 am
content: Don't bother to much. They bring some vividness to the forum. If everybody would think and work like us old guys, the forum would not exist at all. After all, we were raised and educated to go and search for answers in datasheets, application notes, libraries. Sharing of knowledge did not really exist back then, except face 2 face or you would have to be really devoted and decide to write a book or magazine article. The fun thing about internet is that it allows to flush some snippets of your knowledge or thinking without going through the obligation of finishing it to something publishable. And no big deal if the topic starter feels offended, the question and answers will remain for quite some time, possibly being of benefit of some other readers sometime in the future.

author: David Aurora
author_rank: Frequent Contributor
timestamp: July 21, 2012, 05:23:51 am
content: Quote from: Crush on July 20, 2012, 08:55:34 amWow. You're an ass.If you're asking "electronics 101" questions, and two forums have already told you you're barking up the wrong tree, are you starting to wonder if maybe you don't know even roughly what the hell you're doing?The bit that really sticks out to me was this:QuoteWell, if you don't have faith in your skills to work on the simplest, most fundamental part of every guitar amp, you probably shouldn't be building one yet.As for your lightning bolt thing, 1 in 7 doesn't sound too good to me. Would you get on a plane if 1 in 7 crashed? Moron.

author: Psi
author_rank: Super Contributor
timestamp: July 21, 2012, 07:52:16 am
content: Quote from: Electroalek on July 19, 2012, 10:19:18 pmWhat happens when you accidentally short it out?nevermind, you'll find out

author: SeanB
author_rank: Super Contributor
timestamp: July 21, 2012, 08:09:01 am
content: Normally shorting an ATX supply will result in the tracks on the device under test fusing. Most will happily supply 100A plus into a short, but only for a second or two until they either do overcurrent protection or blow the power switches as the loop tries to do a 110% power cycle, or they get driven to punch through from thermal stress.I have seen PC motherboards catch fire due to a short, and the supply was happy to keep on cooking the board until the chipset on board shut down.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 21, 2012, 07:03:33 pm
content: Quote from: vk6zgo on July 21, 2012, 01:18:12 amSummer school-holidays in the Northern Hemisphere.