Hi guys,
I am new here and I am going to start with a fairly simple (I think) question. I would like to build an amplifier for my A2 level Product design project, maybe a 10 or 20 watt amp. To start with though, I would just like to make a really simple 1/2 watt guitar amp to get some understanding in my head. I have done some basic electronics before and I have had a go at this (see attachment) however I have not had any sound out of it. Some people I have spoken to said the input impedance was too low and that it needs an output stage.
Am I going in the right direction with this? What do I need to do to make it work? Is there a better simple amp that anyone can think of, bearing in mind that, if only for this first one, I would like to avoid chips and use discrete components to get a better understanding.
Thanks in advance peoples for any help.
Callum
That stage is good as a signal preamplifier but does not deliver power, so it can't drive a speaker.
Try this, it's as simple as can get:
(http://www.circuitdiagram.org/images/simple-transistor-audio-amplifier-250mw.GIF)
You can proto board it first, and later build it on perfboard or veroboard.
Thanks man! I will give that one a go :)
Callum
Right I have been trying some stuff out just on the basic circuit whist I am waiting for some more bits to arrive. I have a question now to do with the biasing potential divider circuit. I was trying to bias it with roughly 3V (that's about enough right?) and I used a 22k and a 47k to start with (will alter them for impedence later) wich gave me just less than 3V when I calculated it from a 9V supply, and worked out about right in practice. However, When i added the transistor in, the drop across the lower went to the 0.7Veb and the upper resistor went to the remaining 8V ish. Now I know the transistor set the 0.7V itself, but why does this then alter the divider voltages? I know this is a simple question, but I can't work this one out -_-
Any suggestions would be great,
Cheers, Callum
Not clear, please draw the schematic you actually built and measured voltages.
Although I would start with the original schematic, as published, and later start modifying.
I think I have solved this one, I was looking at it the wrong way :)
Quote from: Calx
I would like to build an amplifier for my A2 level Product design project, maybe a 10 or 20 watt amp.
Being on the other side of the planet I first had to do a bit of research to understand what "A2 level Product design" is, and after wandering around the AQA site (where they never did get around to explaining what "AQA" stands for) I gather that this is a module in the English General Certificate of Education Advanced Levels, what some would call Matriculation, the end of Secondary schooling with possible university entrance next.
Quote from: AQA
---
Summary
This specification is designed to encourage candidates to:
develop a broad view of design and technology
develop their capacity to design and make products
appreciate the complex relations between design, materials, manufacture and marketing.
AS outline
At AS level candidates develop an understanding of a broad range of materials, with emphasis on the life cycle of products, manufacture and final disposal. This specification also considers the broader issues for the designer including the environmental sustainability of products and consumer safety:
Unit 1: (PROD1) Materials, Components and Application
Unit 2: (PROD2) Learning Through Designing and Making.
A2 outline
At A2, the specification offers candidates the opportunity to further develop the knowledge and practical skills from AS. Candidates will continue to develop a body of coursework alongside an understanding of the processes and procedures of commercial production and manufacture:
Unit 3: (PROD3) Design and Manufacture
Unit 4: (PROD4) Design and Making Practice.
---
As it happens I had a lifetime in the design, manufacture and service of industrial electronics while moonlighting as a musician and music/theater tech building and repairing guitar amps and sundry showbiz-related gear.
If you haven't already an early task is to go out and see what is already available as a "10 or 20 watt" guitar amp. Call this basic market research, checking out what such a product looks like, what potential customers and users expect.
I started by Googling "10 to 20 watt guitar amplifier" and having a look at the images that brought up.
The first thing to notice is that this got 1.6 million hits including some very heavyweight names such as Fender, Behringer, Ashton and many lesser knowns, at prices ranging from $50 to $1500. So the first message here is that while this is an interesting design project, and you should end up with a guitar amp out of it, you can forget about getting rich quick by taking the industry by storm - there are many thousands out there ahead of you.
If you are going to build any guitar amplifier some of the things that you must consider include;
- features and facilities
- inputs and outputs (how many? what levels/connectors? headphones?
- effects
- controls
- speaker size
- the box or case it is going to go in (head and cab or combo?)
- the chassis metalwork to hold the amp electronics and front panel
- the printed circuit board (for ease of manufacture, and rework/repair)
- discreet components or IC's?
- heatsinks and cooling
- power supply, power mains safety (and approvals in different markets CE, C-tick, UL ...)
- ease of assembly
- ease of disassembly and repair
- finish, styling, dress
- costs, "price point"
...and lots of associated details besides. Many of the above are inter-active meaning that the process of design can have a lot of circularity and backtracking as various factors are traded off against each other during product development.
One particular amp stood out, the Marshall Lead 20, simply because I could find the circuit, and external and internal pix that help illustrate the reality of the design process.
Quote from: marketing
---
Vintage Marshall Lead 20 (Model 5002) 20-Watt 1x10 Guitar Amp in Excellent Condition, made in England, serial number U41410. Features a 10" Celestion G10L-35 speaker. The Marshall Lead 20 is 17" tall, 18 1/2" wide, 9 1/2" deep, and weighs about 28 pounds.
Buy the Marshall Lead 20 Model 5002 Guitar Amp 1x10" Celestion for 199.00!
---
The external and internal views of this amp are attached below.
Here are some different takes on the same idea (not related to each other);
(http://4.bp.blogspot.com/_bXU7O6Ba3kg/Sqa6nbbeYjI/AAAAAAAAAv8/vWFPNuFeCjQ/s320/10+-+20Watt+Guitar+Amplifier.gif)
Jade Hot Shot
(http://imgc.classistatic.com/cps/blnc/120410/066r1/393147l_20.jpeg)
ESP
(http://wiringschematic.net/wp-content/uploads/2012/04/p10_fig22.gif)
Marshall Lead 20 circuit
(http://www.drtube.com/schematics/marshall/5x02.gif)
Some things to think about.
Dear Roly. First of all thanks for your investigation and detailed explanation.
Real Pro :tu:
That said, I think that calx is not going to take the Industry by storm (not an easy task even for heavyweights such as Fender and Marshall), but simply trying to comply with some School Project requirements.
Which is good.
Don't know the time constraints involved.
If calx has, say, 30 days to present a working project and, probably, a working prototype, I guess the design should be kept very basic and to the point.
Something quite standard which can be finished in such a short time, without endless tweaking (which might take *years*, not kidding).
Dear calx, can you please tell us more about your project requirements?
Time?
*Must* it be built into a finished box, "ready to sell", or can it be made out of several boards, a transformer, maybe an L shaped front panel, everything bolted to some wooden board and with everything visible?
I have seen many such projects shown in school "science fairs".
Yea, thanks Roly for doing all the research, you now probably know more about the course than I do! I had been interested in basing it loosely on a Marshall as my current amp is a Marshall 100watt, so that info on Marshall practice amps is really helpful.
In terms of the project, we will have approx 6 months worth of lessons and the work I can put in in personal study periods and my own time, so the deadline is not too tight. It does need to look like a finished product so it will need to be in a cabinate - I am going for a combo design - but I am not too worried about the cabinate construction as I have made something similar in the past and have some experience in this kind of thing. The circuitry is the bit that I have to learn about before construction as this is the area I am least experienced in.
There is no brief as we have "free rein" to make what we want, as long as it is within the capabilities of the workshop.
Thanks again guys,
Callum
JM - I posted part of the course requirements that Calx is doing because it's actually a bit daunting. This is somewhat up-market on a Science Fair project and more like the sort of project that engineering students at uni or senior college have to turn in.
What is being asked of Calx is not just to create a going guitar amp (he already has one of those) but to demonstrate that he understands how to engineer a product for manufacture, something I'm sure you will agree is of a rather different order.
He's not going to put his design into production, but he has to go through the motions and produce a design package that could potentially be then taken to cabinet makers, metalwork shops, and PCB suppliers. I say "daunting" because I have been through this process many times and it always looks easier than it actually is - as you say "tweeking", or even getting serious bugs out, can take years.
{A company building a prison in my home state of Victoria just went broke, partly because the windows and doors they ordered from China were the wrong size, and as somebody said, having doors that fit seems pretty basic to a prison.}
Given that he has a deadline in about six months it is going to need a heavy application of the KISS principle just to get there. {Calx; "KISS" stands for "Keep It Simple - Stupid", take the line of least resistance and don't get adventurous, pick the simple and obvious for each step, e.g. no in-built fuzz box.}
Calx; I notice that your course syllabus places some stress on drawing and sketching. I can't tell you how important I think this is. You are going to need to produce drawings of your cabinet, chassis, and PCB layout, and before you get to the final stage there may be quite a bit of horse-trading, e.g. you can't get the transformer or heatsink you wanted and what you can get is a different shape with different mounting holes. So expect to produce several versions of each, and here "version control" becomes vital; all drawings should have a title block showing all the normal guff, but some sort of version number is vital, particularly if you are going to be discussing drawings with people on-line, to make sure that we are literally all on the same page.
I use a date group for this function, so today is 120522 and if there is more than one drawing a day (we hope) a 24-hour time group as well, and since we are all in very different time zones you need to specify GMT/CUT because you are on GMT, I am some 10 hours ahead, and I'm guessing that JM for example is some hours behind. So 120522-1203GMT should be a serial number that leaves no doubt which is the latest revision.
The honest designer will tell you that there is very little that is new under the Sun, and that most of us (very quietly) operate on the motto "plagiarise and hybridise". In this particular project you don't have to worry about being sued for copyright, and imitation is not only the sincerest form of flattery, it is also building on the valuable experience of others.
So generally I'd take the Marshall Lead 20 as an "inspiration", since it represents exactly your aim having gone through exactly the process of preparation for manufacture you are supposed to put your design through.
Most commercial small amp designs are crippled at birth by being ... well ... small. At the 10-20 watt power level I'd suggest that you consider using a 12-inch speaker and allowing for a sealed enclosure of at least 50 litres (that's about root(2) cubic foot); you imitate the simple U-shaped chassis with front, back and floor ('tho you may want to use separate front and back panel sections to allow finish such as anodizing, painting, silk-screen printing of control legends, and so on), and the floor might need tabs at each end to secure the chassis.
You don't want it to look too much like a clone of a Marshall either, so I'd be inclined to make it a bit narrower and taller, but your cab size should be driven by what sizes of timber are locally available that minimise cutting and working. Here again your will find you produce a lot of sketches and drawings of different arrangements until you find one that satisfies the largest number of conditions.
It will also not be hard to improve on the Marshall heatsinking arrangements and use a rear-mounted heatsink that can actually get rid of some heat.
I normally build my amps out of individual components, like this Marshall, but in your case I think you should give serious consideration to using an integrated chip amp where you can pretty well use the circuit off the data sheet, bolt it to the heatsink, and worry about other things - such as the preamp.
An important point to keep in mind with any amp build is to keep the mains wiring well away from all the other wiring. This is mainly for safety considerations, partly to stop main-carried electrical noise getting in to your amp circuits, and partly because such segregation is required for type approval in just about every potential market; and consideration of such legal pitfalls should be one of the critical things your instructors should be looking for in your design.
I am willing to provide whatever assistance I can, but ultimately it is down to you to understand your course requirements and fulfill them. Six months may seem like a long time now but you will be horribly surprised how quickly it will evaporate. Murphy's Law states that things always take longer and cost more than expected (doubly true for software projects), so getting in early leaves you with some "lead time" up your sleeve when something goes wrong - and it will. I look forward to you posting your initial design ideas.
Thanks again, you sound pretty experienced in this field, what is it you do?
I have an appreciation for the pace at which the time seems to run out from completing GCSE and AS levels in this subject, and I fully agree that the KISS principal, which I already try to use in a lot of projects, definitely applies here - some sound advice I think. Can you recommend any cheap/free software for the design (and maybe testing) of schematics?
I have had some good fortune though. I was at a guitar lesson last night and told my tutor about the project, as he used to be an electrical engineer, and he had an old Carlsbro amp in his attic. The amp itself does not work but there are still a lot of components that can be used on my project like the power transformer etc, which I am still trying to find the rating of. The best part is the 12 inch Celestion speaker that was with it, so he has probably saved me £30 - £40 in parts there because this was a freebie!
I will do some research and let you know what comes up. In the meantime, do you know of a source of preamp schematics for inspiration/reproduction as I have a book with some fairly simple power amp schematics, however the preamp is proving harder to find.
Thanks again,
Callum
Also, what is this an schematic of (http://wiringschematic.net/wp-content/uploads/2012/04/p10_fig22.gif) ?
What are the input/output ratings and stuff?
Thanks
calx see here http://sound.westhost.com/project10.htm . check out the rest of the site as well. A wealth of info! :)
I will check that site out. Can that circuit just use a guitar input or does it need a line level input from a preamp? That's the bit i'm struggling with - something that I can plug my guitar in one end and have it power a decent speaker at the other. All I seem to be finding are power amps that require a line level input - obviously more than a guitar can give. I'm sure I must be missing the blindingly obvious... :-[
By the way, I just built that circuit in the first reply to this thread and had no luck, I used 2n3904's and a2n3906 instead of the ones in the schematic, as that is what I have, and I subsituted the 1k8 resistor for a 2k2 as again, that was just what I had. Other than that, It was the same so do they matter? I will come back to it tomorrow withn a fresh head, and make sure I haven't protoed it wrong.
Thanks again.
just to add something to that last comment, I have seen this: http://sound.westhost.com/project27b.htm
The 100Watt amp here is probably more than I want but the Preamp schematic is what I was interested in. This uses op amps, which I am not set against I just fancied using discrete components as I said before. Is this a good example of a preamp? Can a similar thing be done as well using discrete components, or would that be over-complicating the process?
Thanks, Callum
It's an excellent preamp.
First proto board it, then design a PCB (or use perfboard/veroboard) and build it.
I guess you have access to some metal fabrication shops at school, make a "C" or "U" shaped aluminum chassis. at least 18Ga (1mm) or over.
Easy to work with and no worrying about rust.
Couple that preamp with some TDA2030/50 or LM1875 amp and you are done.
Download and learn to use Bancika's DIY Layout Creator, an impressive tool.
http://www.softpedia.com/get/Others/Home-Education/DIY-Layout-Creator.shtml
I prefer the Windows version, because a lot of people used it and you can learn by looking at their designs.
There's an advanced Java based version which works under *any* Operating System, but it's not as popular and does not open the earlier examples.
Ok, thanks,
So you reckon OpAmps are the way to go for the preamp?
And that looks like it will be helpful, I will download it and try it out!
Thanks again :D
I am a retired electronics tech and spent a large slice of my life designing, building and servicing industrial and bio-med electronics. I've also moonlighted as a muso (keys and guitar) and music/theater tech/soundie/lighting operator since I was a teenager.
Free circuit modeling/drafting software? Sure, Google LTSpice. There is also a strong Yahoo users group. A word of caution about circuit modeling - the ultimate model is a hardware prototype; it automatically includes all the stray resistances and coupling capacitances that cause trouble.
I have no experience of it, but I've been looking at the LM3886 chip amp which seems to already have a lot of community support for guitar amp applications, builds to look at, people's problems to learn from, printed circuit layouts to be informed by. It's quite a bit more powerful than your intended 20 watts, but when it comes to guitar amps it's wise to have some reserve up your sleeve (particularly heatsinking).
The guitar teacher is a double hit because the old amp provides you with a testbed and some bits, and your guitar teacher being experience in electronics and locally accessible to actually look at your problems (and you will have problems) is very valuable indeed.
What is the model number/name of the Carlsbro amp?
The circuit I attached is from Rod Elliot's excellent ESP site and you will find a related guitar preamp there that is well worth a close look;
http://sound.westhost.com/project27.htm (http://sound.westhost.com/project27.htm)
Like the one I posted from Rod's project 27, project 10 requires a preamp. There is a good reason why guitar amps of the 20 watt class aren't Class-A, and that this one is for the audiophiles.
It is fairly normal that the master volume control is at the point of transition between the preamp and the main or power amp, and that the signal voltage level at this point is typically around 1 volt, or "line level".
This means (generally) that pre and main amps can be fairly easily mix-and-matched. Take a look back at one of the circuits I linked to above and you will see a simple preamp that uses a couple of FET's and very simple top-cut "tonestack". If you go for a dig on the net you will be spoiled for choice, but Rod's Project 27 preamp would be hard to beat.
I see JM has mentioned some other chip main amps which you should investigate. As part of your project you should note the different IC's and circuits that you investigate, and why you decided for/against them.
There is no reason why you couldn't go with a transistor preamp, but these days even a fairly "ordinary" op-amp such as the TL07x is pretty damn good and easy to use, and you can go up-market to pin compatible things such as the LM833 which is still almost free to buy and close to perfect, or there are other "ultra" specialist audio op-amps which are not quite free and so perfect they make your eyes water (but are a bit of overkill amplifying guitar which has a typical output level in the hundreds of millivolts, not microvolts, coming via a thrash-metal stomp box :lmao:).
Thanks, I downloaded LTSpice and it looks pretty good, will have a play around to learn how it works but doesn't look too complex.
The Carlsbro is the colt 45Watt lead (I think) have't found model number but from what I can gather this is it.
So that preamp is a good bet then :) Can they both be run off the same power transformer? As one is 15v and the other 20v.
Thanks again guys :)
Callum
A Google search turns up three different Carlbro Colt 45's; L/ead, B/ass, and K/eyboard. I'll bet there are only minor differences.
Since this amp is rated for quite a bit more power then you intend there are likely to be various useful bits for prototyping, not least the power supply (which may actually be a bit too high in voltage for your needs). A pic or two of the chassis insides would be helpful.
As for your preamp power supply, it is normal to derive that from the main amp supply via a regulator of some sort, often a simple zener diode.
You should be developing a list of preamp and main amp options to explore, and gathering datasheets of suitable chip amps and IC's used in your options (e.g. TL07x series op-amps), the TDA2030/50 and LM1875 chip amps suggested by JM, get catalogs from Farnell, RS Components &c, and have a look at what is available in the way of power transformers, bigish electrolytic caps, and hardware such as jack sockets, and dress stuff like knobs and case corners.
You should be developing your first conceptual drawings of what it might generally look like externally and internally, and how the various parts might go together.
I still sketch a lot using pencil and paper, but I also have a favorite drafting programme, an old thing called EasyTrax which is professional abandonware and free, originally intended as a PCB layout programme which it still does well, and also useful for more general drawing. But everyone has their own taste and some people think highly of Eagle (for example). I don't, but whatever floats your boat and gets you results. If you are going to get a PCB done you need to identify your local suppliers and find out what format they like artwork to be submitted in, and be influenced by that. Ditto for any metalwork, panel designs, and so on.
Tried LTSpice, thats a nice little program :)
I will put some pics up here tomorrow, some of the components have been robbed already, but mostly intact. Don't know if It works but I believe there is a little reverb unit in there too.
I will do some research over the weekend into parts and cost and stuff which will influence which schematics I go for (as well as complexity :L), and I will start putting some stuff down on paper as to the structural and aesthetic design. As JM says, the metalwork facilities at school, and at home (in the process of making a 125cc Kart with a mate) should make the chassis not too much of a problem.
I have a fairly firm Idea in my head of what I want it to look like - Similar to Marshalls in terms of size and stuff but I think I fancy a white vinyl/Tolex covering as this should help the amp stand out from the crowd a bit! (even if it doesn't sound great) Get some credit in the course for branding/packaging so I think my brand will be "White Noise" - you heard it here first when it is a multinational audio company! haha, well gotta have ambition :)
Had a look on ESP at some of the power supplies there and I reckon for the 20 Watt, an 18 - 0 - 18 transformer with the supply design provided should give the approx. 25V required.
Thanks again, I will keep you posted.
Callum
Hello Calx,,
I assume you refer to the 20 Watt Class A Amp on ESP site?
It has no safety overload protection, it wastes a lot of power, it runs hot which *Generally* means it will die early. Good luck,, you will need it. :lmao:
If You want it to work without hassle DON"T go near Class A. :trouble
Leave all that silly stuff for the HiFi freaks to debate. :duh :duh
When it comes to Guitar Amps Class of operation is meaningless BS (pardon the swear words)
Good Guitar sound is all about tone shaping not class of power stage (the difference will never be heard by the masses)
IMO less than 30 watts is a waste of land fill.
(Unless of course you only wish to hold bedroom rock concerts) :P
If the supply transformer in the Carlsbro delivers 35-0-35 VDC then just purchase an LM3886 power chip and that will leave time to focus on the preamp.
I have one running from 36-0-36 supply and although it will never impress hifi geeks it does a darn fine job for guitar power stage.
The preamp BY FAR will be where the time is spent. As most of the tone tricks happen there. Get it wrong and no amount of fancy class A drivle will solve it.
Yeah,, repeating Roly's Q,, What model Carlsbro?
It maybe worth saving.
Phil.
+1 on what Phatt said -
I know your were leaning toward discrete components but really, go with LM3886 (or something similar) and say you "rationalized" it as being the most efficient, cheapest, least complex way to build the power amp - get some project points there. :tu:
Like he said, focus on the pre-amp to get that right and pop in the LM3886 (with appropriate power supply) and away you go!
Jim
Ok, like I say, I believe the amp is the Carlsbro is the colt lead 45, here are some pics of it.
Does anyone know of where I can get a decent schematic of a power amp with the chip?
Thanks again, all help is greatly appreciated:)
Callum
Quote from: Calx
I think my brand will be "White Noise"
I like it. :tu:
Wot Phil said about Class-A. +1
Except for anything below 30 watts only being suitable for land fill, I agree with Phil and Spud.
Personally I'm not all that taken with all-in-one chip amps and I couldn't see myself going that way for a guitar amp - HOWEVER - what Spud says is right. Looking at it from a
manufacturers point of view chip amps are a very attractive option when you consider how much messing about they save on a production line, and that's what we have to keep in mind here with this project.
Quote from: Calx
Calx> Does anyone know of where I can get a decent schematic of a power amp with the chip?
GIYF (http://www.catb.org/jargon/html/G/GIYF.html)
I'm going to look in a minute, but it is normal with most IC's that the data sheet contains a representative circuit, and many manufacturers simply follow this; so do what I am about to do, go to;
http://www.alldatasheet.com/ (http://www.alldatasheet.com/)
...and download the .PDF data sheets for the LM3886, the TDA2030/50 and LM1875 chips that JM suggested, and have a good meditate on them. {you have to click to view, wait for it to come up locally in your PDF viewer, then name and save to your datasheets folder}.
Put that speaker in a plastic bag before it grows a fur overcoat from drill swarf. Once a tiny bit of swarf finds its way inside to the pole gap you can just about chuck it as a hopeless cause; otherwise it might be useful.
Google the transformer manufacturer name and type number - you might get lucky and find its spec. The voltage rating of the two big blue electros will give you a clue to the secondary voltage.
You will notice that Carlsbro have used the chassis as a heatsink for the output pair. This is a clue as to why this amp is junk. Using the chassis as a heatsink, particularly a steel chassis as this appears to be, is one "saving" too far, and a short path to amp history.
Real heatsinks are made from ali and have fins mounted
vertically where air can
freely circulate past them, and
that doesn't mean boxed up inside the cab. Guitar amps tend to get used on stage under hot lights and they need to be designed conservatively for heat flow. Whatever the nominal output wattage, you are going to have to get rid of at least as much as waste heat, and on-stage ambient of 40 degrees C are not uncommon.
Notice that the more significant controls have larger knobs.
Yes, that is a spring reverb tank. By all means save it for a project, but I council against trying to include reverb (or any Fx) in your design - you have enough on your plate already.
The Carlsbro sure is a filthy mess, but it looks complete to me and this is the sort of thing I refurbish and bring back to life, so I wouldn't wreck it. It may be useful to provide power generally, and a preamp for testing your mains amp, a main amp for testing your pre - maybe. The thing is, clean it up and have a look at how a manufacturer has created an amp similar to your intent.
I'm on it!
I figured when I checked it over that using the chassis as a heatsink wasn't the greatest idea and it is, I believe, the power amp section that has gone.
I will clean it up and continue with the research and then when my last exam is over with (at the end of the week) I will start with some more serious design and maybe ordering some parts.
GIYF - I like it, I get your point :)
Once again, thanks for your help and I will keep you informed this week as to any decisions and stuff:)
Callum
Re *First pic*.
I'd being injecting a signal into that connector on the left a fair chance the psu and power stage may even still work.
Fire it up with the light build limiter and see how it comes up. :tu:
I'd say the preamp section is cactus, I keep that stuff for spare parts to build prototypes.
Roly has years more experience than most of us so in His hands I have no doubt it would be fixed. 8)
Yes a lot of gear has been built only using the thin case for heat sinking.
I found and old BSR Fender Bass rig years back that had melted the plastic back panel into and unreadable mess halfway slid off the metal back panel.
At that time I was still learning and had not seen much of the designs and how they where made but even with my limited understanding blind freddy could see that a bigger heat sink was needed. :loco
Just blew me away that a Name like Fender could sink that low. :trouble
I was able to save it by sandwiching a 4mm plate of alloy along the back to help.
No more issues.
*****Word of caution;
I hope you don't have plans on building electronic gear on (What looks like) a Steel welding bench? :o
Phil.
Just curious:
is *this* what you are getting into?
http://en.wikipedia.org/wiki/Design_and_technology
OK, I will try out the power stage and see what happens.
It does seem that a lot of the larger companies are as much if not more interested in cost and ease of manufacture than longevity. I guess if things lasted forever then they would never sell any new stock, totally wrong but you can kinda see why it happens.
Yes that is roughly the course I am studying - I have done some form of DT for 6 years but the A level course goes more into the manufacturing processes and material theory etc than just simply "build a CD rack". I intend to study \mechanical/electronic engineering at university, so an electronics based project would seem to make sense.
The metal surface of the bench is just a 2mm sheet steel. It is completely removable and is there as you suggested to turn a regular work bench into a welding table. I would remove the top before any electronics, it is just 3/4 inch ply underneath. Out of interest, would a metal bench be likely to damage components?
Cheers, Callum
Quote from: calx on May 26, 2012, 04:47:04 PM
OK, I will try out the power stage and see what happens.
The metal surface of the bench is just a 2mm sheet steel. It is completely removable and is there as you suggested to turn a regular work bench into a welding table. I would remove the top before any electronics, it is just 3/4 inch ply underneath. Out of interest, would a metal bench be likely to damage components?
Cheers, Callum
Damage to components will be the least of your problem when you are DEAD. 8|
Steel is highly conductive one small mistake which you will likely never see coming and you are history.
I once read a comment Re electricity;
"Don't mess with anything you can't outrun"
You may need to catch up on safety issues before playing with this stuff. :tu:
Yes swarf and grinding grit and sensitive electronics don't generally mix well.
Again both are conductive and one flick of swarf in the wrong place and it all goes bang when you power it up.
I work on a wooden bench standing on a 20mm thick off cut of rubber conveyer belt.
All metal jewelry and stuff comes off before the power goes on.
Never work on electrical stuff without shoes on your feet.
Phil.
Awww, come on Phil, that's only a bit of bird poo; a good dust and a bit of a wash with some metho and it would be good as new (however it is a bit of a distraction from the main game here, but has already provided one salutary lesson about chassis heatsinking).
Not just Fender. Lots of people who should have known better have fallen into this hole - see my Gibson G-20 repair story (and let's not mention Savage).
I'd say at a guess that the two missing power supply fuses imply that the output stage is boofed, but again that's just everyday bread and butter.
Calx - see;
http://www.ozvalveamps.org/solidstateamprepair.htm (http://www.ozvalveamps.org/solidstateamprepair.htm)
Quote from: CalxIt does seem that a lot of the larger companies are as much if not more interested in cost and ease of manufacture than longevity.
Oh you got that dead right, but far from selling new stock to old customers they actually end up trashing their own reputation.
And wot Phil said about electrical safety and metalworking gunge.
just one of many such you should read and take to heart;
http://www.ozvalveamps.org/safety.htm (http://www.ozvalveamps.org/safety.htm)
I will be sure to bear this stuff in mind :o
Hi Callum
That Carlsbro amp is like likely to have a USA made Accutronics reverb tank in it also, which could be usefull for future projects.
If the amp has a Celestion speaker, it is likely a replacement from the original (unless it's a more modern Carlsbro GLX or something, in which case they might come with them) If it's from the 70's/early 80's, then the original speaker would more likely to have been made by either Fane or Mackenzie, which are great brithish speakers and highly sought after. These were often unbranded or labelled with the Carlsbro name 'Powertone'.
I had alot of discussions with one of the engineers from the Carlsbro factory in the UK, who also used to run (a now defunct) Carlsbro website, where you could date the amps and there were forums, etc.
Another little known fact about Carlsbro, is that they took over production of H&H amps about 2-3 years after that company started. So most H&H amps are technically Carlsbros. One goes for big bucks, the other next to nothing. I have 3 Carlsbro amps from the 70's that i got for under £20 each.
Anyway, good luck with your project!
Paolo