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Old 25th March 2013, 01:15 PM   #21
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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.

Last edited by gianmarco; 25th March 2013 at 01:20 PM.
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Old 25th March 2013, 01:54 PM   #22
picbuck is offline picbuck  United States
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<< Hooking an ohmmeter across speaker terminals is meaningless. >>

Hold it! Correcting myself, here.

Regardless of anything else, if an ohmmeter across the speaker terminals shows any kind of continuity then the speaker is OK. That's barring mechanical damage, of course.
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Old 25th March 2013, 02:33 PM   #23
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A friend of mine told me that if some turns of the coil are fused together, than the resistance is lower... Is this wrong?
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Old 25th March 2013, 03:36 PM   #24
picbuck is offline picbuck  United States
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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."

Last edited by picbuck; 25th March 2013 at 03:39 PM. Reason: clarity
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Old 25th March 2013, 03:36 PM   #25
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by gianmarco View Post
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.
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Old 25th March 2013, 08:47 PM   #26
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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
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Old 25th March 2013, 09:57 PM   #27
JMFahey is offline JMFahey  Argentina
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Oh, I see.
But I think you can buy the original Velleman kit in Italy.
Will you design your own PCB?
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Old 25th March 2013, 11:26 PM   #28
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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?
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Old 26th March 2013, 02:18 AM   #29
JMFahey is offline JMFahey  Argentina
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The Velleman circuit has short circuit protection ... something *many* (most?) posted here do not
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.
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Old 26th March 2013, 04:12 AM   #30
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ok after many hours of working I have the first drawing of the pcb on protoboard, tomorrow I will post the pic.
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