Re-design stage monitor after a big failure.

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The coil resistance is: 3,8/3,9 ohms (4,1 - 0,2 of shorted probes)

With no thinking about I went to the shop and bought the stuff to build the one from velleman! The big cost is the transformer, 24-0-24 about 45€, the rest is about 40€ to all (included cable connectors).

I bought a pre-drilled pcb, for some components the holes are a little too small, but with a mini-driller I will fix it.
 
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<< if some turns of the coil are fused together, than the resistance is lower... Is this wrong >>

Of course it's not wrong. Some coils (of many) fused = resistance changes, sure.

However, it's not a highly likely situation. I'd very much expect total failure before I'd expect a partial short. There's such a thing as ignoring the probable in favor of the interesting.

Even so, it seems I must correct myself again. This time adding a qualifier.

"...if an ohmmeter across the speaker terminals shows any kind of continuity then the speaker is probably OK."
 
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The coil resistance is: 3,8/3,9 ohms (4,1 - 0,2 of shorted probes)

With no thinking about I went to the shop and bought the stuff to build the one from velleman! The big cost is the transformer, 24-0-24 about 45€, the rest is about 40€ to all (included cable connectors).

I bought a pre-drilled pcb, for some components the holes are a little too small, but with a mini-driller I will fix it.

Fine, good choice.
I have some doubts.

1) price: Velleman Discrete Power Amplifier 200W Kit and DISCRETE POWER AMPLIFIER 200W - K8060 - VELLEMAN KIT ask for 13 British Pounds (GBP) + VAT, around 15 GBP final , which is less than 40 €.
In USA they ask for U$38 at Velleman Price List and U$33 at K8060 : Velleman DISCRETE POWER AMPLIFIER 200W: Designnotes.com
Pure curiosity, does not affect amp quality of course.

2) this one is more important: did you buy the original Velleman PCB ?
I find it strange that "for some components the holes are a little too small,"
Beware that *some* components , such as "snap-in" big filter capacitors *must* fit tightly, that's what "snap" implies, for better mechanical strength.
If you open those holes, capacitor legs are held only by solder but are not "grabbed" by the PCB and in a future date may (will) crack solder, a very common problem, much more in Musical Instrument amplification which travels a lot.
The proper way to mount them is to push them in as far as they will go by hand, then invert the pcb , caps on the table, and gently push thepcb around each leg, you'll hear them "snap" and slide in all the way.
After you've done this to all, solder them.

3) the VC resistance sounds reasonable.
If overheated, rather than fuse together the VC wires burn the adhesive and unglue from the coil former and each other.
If yours wirks and sounds "clean", it's fine.
Mind you, it *might* have been reconed by the guy who took a dead Laney passive monitor and turned it into an active one.
I sometimes do such things, make one working product out of 2 or 3 broken ones, by taking the good parts from each.
Not bad if done properly.

In your case, they took a good cabinet, speaker, an excellent transformer and heatsink, but fit a too powerful power amp, and with a terrible PCB.

What you are building now is much more balanced.
 
Nope, is not the original velleman PCB, is a protoboard, with also each component bought single. For that reason I didn't buy the snap-it connectors, I bought some screw clamp, that fit perfectly with the dimension of the holes in the protoboard. the only thing that don't fit are the 4 diodes and the trimmer.

Maybe if i took the velleman I could spend less but, if you add shipping to italy you have almost the same cost. I spent more or less 35€ for the components and 45 for the transformer
 
Yes, I will try, on paper and then on protoboard. Because I want to make it the smallest, to fit in the board also a circuit to handle balanced audio coming from a balanced out of a mixer. I read also about some "protection" circuits, and maybe not to waste money and time i think i need to add some of them. Don't you think so?
 
The Velleman circuit has short circuit protection ... something *many* (most?) posted here do not :rolleyes:
As of speaker protection with relays and such, 95% of amps don't have it, yet are used everywhere.
I'd build and use it as is.
After all it's a "simple" application: inside a powered box, directly connected to the speaker, etc.
If at some later date you want some add-ons, you can build them if you wish, but first concentrate on building a working amp.
 
Good!!!

By the way, I had suggested Velleman among many other possibilities (most in USA or EBay) to make you easy and cheap to get the kits, within Europe and paying in Euros, local postage.

Just in case I contacted Vellemen Europe, asking for an Italian Distributor.
I guess now it's too late, but for any future doubt (yours or from any Italian DIY), this is their answer, which just arrived:

Buongiorno,
siamo stati contattati da nostro fornitore Velleman in qualità di loro distributori per l'Italia.
Per qualsiasi informazione su prodotti, disponibilità e prezzi potete consultare il nostro sito internet Futura Elettronica srl - Home Page oppure contattarci telefonicamente

cordiali saluti
--

Clara Landonio
Futura Elettronica srl
Via Adige 11, 21013 Gallarate (VA)
Tel: 0331799775 (4 linee R.A.)
Fax: 0331792287
Cod. Fisc. / P.Iva: 10918280156
Reg. Imp. di VA n. 10918280156
Capitale Sociale: Euro 60.000,00 I.V.
Internet: Futura Elettronica-Home Page
 
Thank you for the tip, by the way, yes it's late :) Today I re-create the design of the pcb starting from the one I made yesterday, the result is a circuit 10cm large and 6,5 cm high. Not bad, I think I can even make it larger and shorter. Now it fit almost perfectly onto the heatsink.

EDIT:
GRRR :) 21... not bad, add few shipping euros, maybe it cost about 28/30€... I paid it around 35 with protoboard. Still not bad :)

Please :D help me to justify my shopping ahah.
 
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hello everyone, this is the last version of the PCB, can you please tell me your opinion about it? each hole is 1,27mm from the next one. No values nor name inserted due to time issues. I'm worried about the lines on the right that go to the second transistor and the little bc547 in the heatsink.

An externally hosted image should be here but it was not working when we last tested it.


EDIT: bigger image

EDIT2: There is a track missing, the - pole of the first big capacitor on the left. No worry, I simply forget.
 
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1) Didn't check connectivity, way too time and brain consuming.
Plus you can do it better by using the "highlight net" command, net by net.
After you have rechecked it a couple times, forget it, go to sleep/visit your girlfriend/watch Lazio Vs Milan/whatever.
Next day recheck it, with a fresh mind.
Small errors often "hide in plain sight".

2) basically looks good, but go over it again and *thicken* (a lot) important current carrying tracks, add copper where it's useful, etc.
Did you design a 2 layer PCB?
Try to reduce "top" tracks to minimum and then replace last unavoidable few with wire links, much easier to home make.

Just as an example, here's one of mine, you'll see that I used thicker tracks and added rectangular fills (you can add polygons), this is a 2x15W TDA2030 amplifier and single rail PSU :
 

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1) Actually I did use (if I understand what you mean) the highlight net, the component are all aligned with the holes in the protoboard. Tomorrow I will recheck it and also improve, because I removed the huge main diodes and bought a smaller (only in dimensions, current and voltage are the same) diode bridge. This reduce the tracks between diodes that don't need to be thickened and leave more space to thick the other.

2) I have few unavoidable top tracks to jump over some lines, with the new diode bridge I will remove 2 of them, reaching the total of 3 Top tracks (or jumper if you want).

I can see your example that is very good, remember that I will not use custom made pcb, I will use a stripboard pre-drilled with thousand of holes.

Do you think a 1mm large, solid tin track (due to long drops of tin over more pcb holes) is enough?
 
1) Actually I did use (if I understand what you mean) the highlight net, the component are all aligned with the holes in the protoboard.
Good. I was just reminding you of that tool to ease checking connectivity.
Now I understand you will not etch a PCB but use something similar to Veroboard ("Protoboard" normally means the plastic, solderless, push-in experimenter's board).

2) I have few unavoidable top tracks to jump over some lines
Yes, of course, a few jumpers are almost unavoidable.
I thought you were going to home make and etch a 2 layer PCB.
Not impossible, of course, but requires practice.

Do you think a 1mm large, solid tin track (due to long drops of tin over more pcb holes) is enough?
1mm is fine for most but not all, and it has those copper-robbing holes, but you can pull a single strand or "whisker" from regular cable and use it to reinforce the track.
It holds lots more tin, thanks to capillarity, and bridges the holes.
Not necessary everywhere but on the higher current tracks.
 
Ok, thanks for the advice.

by the way, I figure out that I don't know what "highlight net" is, what kind of program do you use to draw the PCB? i use FidoCadJ

I checked FidoCad.
Looks nice, but it's a standard general purpose CAD package, which has some electronics symbols , the same way most have architectural symbols, but it's not a dedicated PCB package.
In fact, they claim: There is no netlist concept behind the drawings:(

Highlight net is a useful tool: you click on any part pin and *everything* connected to it, including tracks, becomes bright fluo green.
Helps a lot to avoid forgetting some connection.
But if you don't have it, just check twice (or more ;) )

As of the balanced line driver, I wouldn't worry.
We are in the Music Instrument World, not the Ultra Fi one.
Any mixer or keyboard out can drive dozens of meters of shielded audio cable with no problems.
 
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