DIY Audio Projects Forum

Some good electrical safety tips: http://tubelab.com/Safety.htm

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

$12 at Home Depot - there's no excuse for not using a GFCI - it will plug in to any grounded outlet:

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Stephen

When testing a newly built project I always use the in series 100 watt light bulb, it guarantees that if there is a fault you will not create a huge explosion, and if the line voltage shorts to the case the bulb will light up.

Also always using a three prong plug with the ground lug mounted directly to the chassis can also save you. NEVER have one hand on the chassis, or any grounded surface while working with live voltages, YOU become the direct path to ground.

Some people have problems with grounded equipment so they don't bother grounding it, there are ways of wiring your chassis to prevent ground loops and noise.

The articles in this thread I found very useful: viewtopic.php?f=9&t=979

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My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

• Project Page - Mini 12AU7 Tube Preamplifier
• Support/Questions - Mini 12AU7 Tube Preamp thread

thank you for making this section ebbe. i am somewhat new to dc electric circuits. as a musician i have had a long love affair with tube/valve amplifiers. i have been reading books trying to learn more about the subject. at the same time i am experimenting with old tube equipment and reading on this board about trying one of the diy projects.

in the opening safety bullet points posted, you mentioned draining the large filter caps using a resistor. in the book on tube amps i have, the procedure given is to make a contact between chassis and the cap using a large insulated screwdriver. this will make a scary sounding pop. it seems your suggestion is safer and less scary. could you run through exactly how you make contact between resistor, chassis and capacitor? what materials used and so forth? thanks.

i plan on trying to tackle the headphone tube amp first when i can catch up with my bills enough to buy the things i need for that project.

i did want to make a suggestion to you or any of the senior members of the site. i have seen many floor type, stomp boxes for sale to guitar players that supposedly "imitate" the sound of a tube amp. i've never tried one and can guess that they probably sound just like a solid state box trying to imitate a tube amp. but it got me thinking....is it possible to make a small battery operated pre-amp that could be activated similarly with a stomp switch and could be used the same way but actually using one or two tubes? something along the line of the headphone tube amp project i mentioned above?

thanks agan. i will post more questions as they come up. c

Ok Connie, I'm back from Dreamhack and answering your question.

1: For the discharging of caps I just hold the two "legs" of the resistor against the poles of the cap, in other words: the resistor is connected in parallel over the cap. I use a 10K Wire-wound ceramic resistor rated for 10W and hold it there for a few seconds (10-20) you should probably go up in resistance for higher voltages, so far I've only been at 350V or so, go up to a 100K for higher voltages and as stated if your not sure the cap is fully discharged, get you're multimeter out and voltage-test. Voltage testing saves lives, equipment and prevents generally bad experiences. (I'm a bit paranoid about this as I'm fresh out of high-school for domestic electricity and I'm moving on to high-voltage distribution-lines in half a year.) This technique gives a slow discharge instead of a short and it works on amps that don't have a grounded chassis like wood or plastic. Theoretically if you have a filter cap with a big enough voltage and charge it could result in a ugly mark on both your chassis and screw-driver as the arc will melt the metal like an arc-welding-torch.

2: If I understand what you've written correctly you want to build an amp with a tube pre-stage and a solid-state power-stage, I don't see any reason why this would not work but bare in mind that tubes usually (some work at low and some are actually made for low voltages) work at higher voltages so you would need a transformer between pre and power or high-voltage transistors in the power-stage and OPTs, otherwise what I think you're getting at now while I'm writing is to use tubes like for example the ECC series where most work at low voltages too, again I don't see any reason this would not work but I'm out on very thin ice here as I'm a newbie myself and I lack sufficient experience with tubes too be sure, I would be happy if some of our more seasoned members looked at this.

Also, welcome aboard the audio-boat, I hope you have a nice time with us and would like to stay.

/Ebbe

P.S. Smiley to make my posts look less wooden in an attempt to seem like a less boring person than I actually am ->

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"I've done this a thousand times befo..." on not voltage testing before getting to work.
"I'm gonna take my time on the next amp....." on First tube project.

thanks ebbe.

that answers it pretty well. your english is superb. ok, now back to more practical matters. i have been trying to educate myself about electronic circuits using an online course called "all about circuits. com" i'm basically following what any first year student would learn about the subject. i can only get so far each day because i hate reading for too long on the computer. that means the learning curve is long. in the meantime i want to learn practical knowledge with real equipment and hands on experience. old tube electronics are easy to come by for free so i have found some old stereo equipment to start. the reason i chose that, as well as my interest in the first place, is loving tube amps for playing guitars of various types through. so i have two questions today. the first is easy.

1.) beginner book....could you, or anyone else, recommend a good student book on electronic circuits/electronics that i might be able to find cheap so i don't have to keep reading on the computer(also good as reference...)

2.) practical experience...two of the tube amps i have acquired work to some degree. probably have not been used in years and brought them up to power on a variac. the older of the two is an amp with a tuner and no preamp. the second is an amp with tuner and preamp. they both probably need new filter caps from what i can gather from an amp troubleshooting book i have. the third amp i have is really gorgeous. it is 100w motorola from 1955. i will post pics later...i started bringing it up to power on the variac. about halfway through the travel of the dial, a loud hum started to come out of the speakers. it increased with the power. i stopped because it was too loud and not a good sound. i tried again slowly after checking all connections and replaced the speakers. i checked to see if any of the tubes were microphonic and switched out one but that did not fix it. i looked underneath the chassis for any obvious component failure but could find none. same problem.

so, the question is, what would be my next step?

Sorry for the late reply,

1. I can't really help you here unless you read swedish. I'll ask around though.

2. I would replace all the electrolytic caps since they are probably dried out.

/Ebbe

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"I've done this a thousand times befo..." on not voltage testing before getting to work.
"I'm gonna take my time on the next amp....." on First tube project.

That hum of yours connie mack is likely a bad ground or a bunch of dried out electrolytics, replace all of them in the power supply look for bad soldering and then try it again, take some pics if you can and make a thread about it, I really want to see this beast!

The hum could also be that you do not have an input load hooked up, hook up an preamp and see if it goes away then, I have an old Heathkit amplifier that gives an awful loud oscillating hum when there is nothing connected to it.

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My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700

• Project Page - Mini 12AU7 Tube Preamplifier
• Support/Questions - Mini 12AU7 Tube Preamp thread

Hey guys, members and guests .

I've thought it would be useful to post some practical tips and hints for the interested beginners.
We all have started with little projects somehow and sometime.. We also had to pay our lessons and
wasted money or time on stuff we didn't need. That's the way of learning and collecting experience.

For saving your time and money, i post some tips and hints to give a good start.

Some warm words before i begin:
Please take care of your health. This subject is already posted in this thread, but I want to say it again!
Some projects include mains wiring. Mains-wiring can be lethal or cause serious injuries.
Please be sure that you know what you do. If you are not in common with this subject, learn the basics for
mains-wiring first. Collect experience with healthy, non lethal LOW VOLTAGE projects first.
Be sure that you use fuses if recommended. Protect yourself against body shortings to ground.
Put rubber mats between you and the earth (the earth you stand on). Put your electric tools and the circuit on rubber mats.


At the top of beginning... Think twice before you start anything!

First think about the purpose of your project. Think about - what you want to build.
Pick yourself a simple and easy project and gather useful informations about the project / schematic and what it will give to you.
Ask your mates or the Forum members if you are not sure where to start with your project.
There is nothing more frustrating than a non useful and wasted project, lying around somewhere in the corner.

DIY is a LOT of FUN, if you have picked a usefull project - successfully built by your own hands. A project that fits your needs.

This Forum is a nice place where you can ask for help and support (if possible, because we all are only humans).
You can also ask for suggestions, if you need some informations to get a start.


Now you have picked your project and you want to begin? Let's go!

Stop - not that fast...
Make sure you have all the tools and materials you need. I think you don't want to drive to your local e-shop again and again,
just because you've forgotten to buy solder or something else you need... No - that's not a joke.

Write a Partlist or a Plan of what you need for your project before you start to build your circuit. Make sure that you can get
your components at your local store or online and take a look at the shipping costs. Order local if possible - even online.
I tend to order 1 or 2 components (from each) more than i need for my projects. This, because if i break a component,
i have it on spare. Tread the components like a virgin . I want to say that it's not a good idea to bend a resistor leg 10
times until it breaks. DIY is more expensive if you have to pay double the shipping costs when you have to rebuy components.

All stuff together now?

OK - now you're a lucky guy and your iron is hot... What now?? Unplug the iron!

Before you start soldering a rat's nest think about the layout. Again - make a layout drawing or a components plan.
Depending on your project, you got a schematic - with much luck also a ready component / layout plan.
If not - draw a plan. Many projects are done on "Veroboards" (aka pad-per-hole boards or prototype boards).
Other projects are based on etched PCBs. "Ready for use" (DIY) PCBs usually come with a component plan.
A good example is this project: NP-100v12 - Rogers' Headamp.
Rogers provides PCBs for DIY etching. This boards come with a component plan and also a "Bill of Materials" (List of needed components).
Such a project makes the DIY as easy as possible. You only have to etch and drill the boards - Thanks a lot Rogers!
(OK - you'll need some practice for etching PCBs, but that's way easier than drawing a complete layout).

Now - in the case your project is based on a schematic only - without any other plans - you should first think about a usable layout.
Take your schematic and your partslist and create a layout from the schematic. First place / draw the components on a papersheet,
and and try to draw the connections (junctions) with a erasable pencil. Using this method, you will easily be able to replace and
redraw the position of the components, until you have a usable and good result. A good result is having the components close to
each other, without a lot of crossed leads / rails or wires. Straight from one part to the other with a low count of rails. Resistors
(in example) can be placed to cross over a rail on the "solder side". Same as larger capacitors or long lead axial components.

A drawn (or print out / copied) layout is the most important thing as you won't have any chance to keep a layout in mind!
You need it to place the components, to solder them at the right place and to build the junctions / rails.
This are the most efforts on DIY electronics, indeed, but the only way to get a good result. No plan - no amp.


OK - you have the components, the tools you need, your PLAN... That's a good start .

Now you should be ready to start. Use the plan to stuff the circuit boards or maybe your point-to-point "air" wiring.
Place the parts and connect them like you need them. Story long - short. The circuit is built up now .

All connections are made and... ahh - Time to check the circuit! Time to Check it twice!
Follow all the connections on the schematic (start in one corner) and compare them with your creation.
Investigate all connections - until you are sure that you didn't spot any miswirings.
Take a look at the semiconductor devices, active and passive components like ICs, Diodes, polarity of capacitors,
Regulator pins, Transistor pins (polarity / pinout). Most of the issues with non-working circuits are wrong placed ICs,
regulators, caps and such things. Keep a eye on this to prevent any possible problems.
Are all connections really connected? No junction missing or shorted? CHECK IT - twice!.


Time to fire up the project...

All is checked, ought to be fine - what now?
Do a first "burn down" test. Power up the circuit, using the proper power supply and take a look on the components.
If nothing starts to burn or crackle - well done!
If you already own a DMM (multimeter tool) measure the electrical pathes and control them again.
Some circuits / projects come with "voltage measuring values". This are voltages & currents, drawn on the schematic
for final circuitry testings. When the measurments are fine - Congrats - you've got a running project .


Now - i hope this lines were understandable (readable) and useful. I hope that it all makes sense to you.
Long story short, if you put some efforts on your preparations, your DIY should come out fine.

Have fun .


ps - still learning english *oh my*

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Tom,

Your English is very good - I thought it was your native language - you write as well or better than most Americans.

This is what happens when you don't plan how the circuit will be laid out and where the wires will be placed:




It's been coined "3D wiring". Although it was fast to construct, it's not the ideal. I don't think my amp would sell for a very good price if anyone were to look inside! The outsides look beautiful, but the inside wiring leaves something to be desired. Compare that with Ben's latest amp. They make mine look like a joke. (But mine DO work!) If I had more time I'd do it right. My advice is "make the time" or "take your time and do it right". I need to go back and clean up both of the amps above.

Also - Use wire that holds a bend!!! The fine standing and thick insulation of the wire I bought prevented it from holding a bend. Next time I'm using wire with heavier strands and thinner insulation. Teflon seems to work well and is very thin and flexible. Cloth insulation seems to work well too, and the retro look of cloth adds character to the amp IMHO. I'm tempted to use solid wire for my next amp. As long as it's not subjected to repeated bending it should last forever and hold it's shape perfectly.

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Stephen