Want to build my first amp

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#181
Hey Jens,

That's really cool. Hoping to have similar success with mine. It will probably take at least a week for my heatsinks to arrive from Austrailia.

I suppose I could do some testing without them.

Got a question about the copper plate for my filter cap ground plate. Is there a minimum thickness this should be? Anyone know what this would be?

Thanks, Terry
 
#183
Actually, Rod says this in his construction documents:

Apply power at +/15V from a suitable supply - do not connect the amplifier directly to the main power supply for the initial test, and do not attach a speaker !.

The voltage across each 100 ohm resistor should be no more than about 2V, and the amplifier's output voltage should be close to zero volts. If these conditions are not met, then there is a fault in your assembly. If everything is ok, the safety resistors may be removed and you may connect a speaker and signal source, and verify that the amp works without distortion. Remember that there is no heatsink, so any signal test must be kept very brief, even with a low voltage.
Click to expand...

I probably won't do this anyway since I'd just have to stop right afterwards anyway and that would be tough to do. :bawling:

Now, does anyone know how thin the copper plate can be?

Thanks, Terry
 
#184
Actually, Rod says this in his construction documents:

Apply power at +/15V from a suitable supply - do not connect the amplifier directly to the main power supply for the initial test, and do not attach a speaker !.

The voltage across each 100 ohm resistor should be no more than about 2V, and the amplifier's output voltage should be close to zero volts. If these conditions are not met, then there is a fault in your assembly. If everything is ok, the safety resistors may be removed and you may connect a speaker and signal source, and verify that the amp works without distortion. Remember that there is no heatsink, so any signal test must be kept very brief, even with a low voltage.
Click to expand...

I probably won't do this anyway since I'd just have to stop right afterwards anyway and that would be tough to do. :bawling:

Now, does anyone know how thin the copper plate can be?

Thanks, Terry
 
#185
Terry,

If I remember correctly, you wanted to use the plate to hold the caps in place. This will probably give you the minimum thickness, based on your requirements for physical strength. Such a copper plate can carry A LOT of current without problems, and will not likely be any electrical problem, in my oppinion.

As for testing the amp, I agree with BobEllis. I would NEVER test the amp without the power devices mounted on a heat sink or a faiely big block of metal.

Heat sinks are designed to have the air flow remove the heat. For your short term test, a simple, big block of metal will have sufficient heat capacity to keep things cool. Without the metal block, the output devices will die quickly.

Speaking of testing... what kind of measuring equipment do you have (or have access to)?

Jennice
 
#186
Jennice said:
Terry,

If I remember correctly, you wanted to use the plate to hold the caps in place. This will probably give you the minimum thickness, based on your requirements for physical strength. Such a copper plate can carry A LOT of current without problems, and will not likely be any electrical problem, in my oppinion.

As for testing the amp, I agree with BobEllis. I would NEVER test the amp without the power devices mounted on a heat sink or a faiely big block of metal.

Heat sinks are designed to have the air flow remove the heat. For your short term test, a simple, big block of metal will have sufficient heat capacity to keep things cool. Without the metal block, the output devices will die quickly.

Speaking of testing... what kind of measuring equipment do you have (or have access to)?

Jennice
Click to expand...


Hi Jens,

OK I won't do any testing until I get the heatsinks and get them mounted. I'm not on a time schedule here.🙂

For testing I only have a couple of multi meters and a variac.
I haven't even found the 100ohm 5V resistors yet. I can't believe how happless these electronic stores are about replentishing their supplies. So many empty hooks. Seems like almost every part I need is always missing. When I ask them why, I get "It must be a popular value". I just thinks they don't bother with them because they don't make enough money off of them.

I'll tell this though, when I find a store that keeps their stock up, they will get all my business.😉

Blessings, Terry
 
#187
A popular value... YEah RIGHT! 🙄

More likely they don't sell it often (no wonder if it's not in stock), so they don't want to occupy storage and money with it. That's what >I< think.

On to a more positive subject to conclude this working week: If you consider doing more DIY auio stuff, and your budget allows, you my want to consider buying an oscilloscope. It's a really handy tool, especially if you can work the switches properly. 😀
It doesn't need to be something fancy - any 2 chnnel, 10-20MHz thing should do fine for this purpose.

Jennice
 
#188
Yes I would like to have a scope. Man, those things are costly though. I wish I knew more about them. There are quite a few on ebay, but not knowing enough about them, I don't know what is a good deal and what is not.

I do plan on doing more DIY stuff, providing this one turns out succesful. 😀

Hopefully I will plan better on the next one and not spend so much money foolishly. I think I bought a new truck for UPS on this one.:xeye:

As far as the componants being out of stock, the hook is there on the rack, so it's not like it would take up any extra room. 😉

Blessings, Terry
 
#189
Terry,

I don't know if it gives you any mental support, but I have a hard time keeping DIY budget also. :cannotbe:

I started out as a child, and had my first real stereo set at the age of 7. Our neighbours thought it was madness to give an expensive (at the time) pair of amplifier and tape deck to a 7 year old, but the amp still exists, and the tape deck was sold as partial trade-in for a Yamaha, which was since replaced by Denon's top model.
Over time I started to be curious as to what was inside the boxes, and pulling defect products apart to learn about the components.
I built my first "real" hi-fi amplifier before attending the engineering academy. Countless kits and circuits went before that.

However, my g/f isn't too keen on my hobby taking up too much space, so when we moved, I organized an electronic cupboard, which contains my scope, some multimeters, some Brüel & Kjaer equipment (old, but still useable) and all my boxes with "stuff".
At the front of the table is my current project on a scrap heat sink and spare power transducers, for testing the PCB circuit.
It just played 50W into a 2 ohm load (car speaker) until it rattled and fell, scraping the wooden floor. Oh, well... the price one pays for a hobby. :cannotbe:

I'll upload the pic to my server before long, and call it "cupboard".

Jennice
 
#191
Thanks for the pic Jens,

A little tough to view with it on it's side though.:xeye:
Maybe you could reload it the right way up?

You've got some cool tools there fella.

I know about damaging things with the hobby. I am having new Corian countertops put our kitchen next week due to a stray soldering iron ruining her formica tops. :hot:

I'm pretty sure I will not be allowed to do any soldering at that counter any longer. 😀

That's OK, I'm building a new shed so I can get some of the stuff out of the garage so I can get to my work counter again. Better lighting there anyway.

Blessings, Terry
 
#197
OK I'm ready to do some initial tests of my p101 boards. In the instructions it say this;

For testing, you will need two 100 Ohm 5W resistors, and a signal source. Before power is first applied, temporarily install the 100 Ohm "safety" resistor in series with each DC supply line to the board. You must also connect the power ground connection to each end of the PCB - there are two connections labelled P-GND, and both must be connected as shown below with an insulated wire link. Make sure that the bias pot is set to minimum resistance. Measure it with an ohmmeter to make sure that it really is at minimum.

Apply power at +/15V from a suitable supply - do not connect the amplifier directly to the main power supply for the initial test, and do not attach a speaker !.

The voltage across each 100 ohm resistor should be no more than about 2V, and the amplifier's output voltage should be close to zero volts. If these conditions are not met, then there is a fault in your assembly. If everything is ok, the safety resistors may be removed and you may connect a speaker and signal source, and verify that the amp works without distortion. Remember that there is no heatsink, so any signal test must be kept very brief, even with a low voltage.
Click to expand...

Here's my question.

When it says "The voltage across each 100 ohm resistor should be no more than about 2V", do I measure the down side to the 100ohm resistor to ground? Also, it mentions a signal source. Do I need to be feeding it a signal for this test?

Another question. Since I don't own a 15V power supply but do own a variac, can I use the main power supply and just run it at 15V using the variac?

Thanks, Terry
 
#198
NO !

still4given said:
OK I'm ready to do some initial tests of my p101 boards. In the instructions it say this;



Here's my question.

When it says "The voltage across each 100 ohm resistor should be no more than about 2V", do I measure the down side to the 100ohm resistor to ground? Also, it mentions a signal source. Do I need to be feeding it a signal for this test?

Another question. Since I don't own a 15V power supply but do own a variac, can I use the main power supply and just run it at 15V using the variac?

Thanks, Terry
Click to expand...

Hi,
without following this thread except your last post I assume
your 15V power supply I guess it is refering to Direct Current. The Variac provide you Alternate Current.

The Butcher😀
 
#199
Hi,
without following this thread except your last post I assume
your 15V power supply I guess it is refering to Direct Current. The Variac provide you Alternate Current.

The Butcher
Click to expand...


I'm not suggesting that I connect the variac to the board. I intend to connect the variac to my PSU and adjust it so that the PSU is putting out +/- 15V. I suppose that I would then be using my amps PSU as a variable power supply. I want to make sure that is OK to do.

Blessings, Terry
 
#200
still4given said:
OK I'm ready to do some initial tests of my p101 boards. In the instructions it say this;



Here's my question.

When it says "The voltage across each 100 ohm resistor should be no more than about 2V", do I measure the down side to the 100ohm resistor to ground? Also, it mentions a signal source. Do I need to be feeding it a signal for this test?

Another question. Since I don't own a 15V power supply but do own a variac, can I use the main power supply and just run it at 15V using the variac?

Thanks, Terry
Click to expand...




Terry:

you need to measure straight across the 100ohm resisto r, of which you should have 1 in series with your +ve and -ve rails,

i drew another pic quickly to be sure..



test1.JPG



And yes you can use the variac , no probs.


ALSO to remember: make sure the bias pot is wound right down, (should be anti clockwise if you put it in exactly has Rod shows it in the photo) , double check with a meter! , measure between the centre pin on the pot to both the outside pins and make sure they are BOTH 0ohm (one is allways going to be 0ohm as its linked to the inside pin)


and lastly, no you don't need a signal source for that particular test thee should be nothing on the input.

once youre sure that is correct, measure the DC voltage between the speaker out and Ground to make sure its virtually 0v , then you can connect a test speaker and a source


another quick tip, i allways measure the voltage at the INPUT terminals aswell just incase theres a weird fault putting a voltage at the terminals that could blow up your source. better to be safe than sorry
 
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