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Messages - J M Fahey
Pages: 1 ... 136 137  139 140 ... 181
« on: February 16, 2010, 06:19:19 PM »
Now that you built it, just play.
Watch for funny smells, smoke, too hot cases, do not wait for molten plastic.
Touch them every 5 minutes.
If you find them unbearably hot, forget them; if they are only warm after an hour or two, you got lucky.
« on: February 15, 2010, 04:12:18 PM »
Rather than only the transistor overheating (which also happened), eventually it shorted and that track passed 10 times what it was designed for.
*That* burnt it.
There's something else, although they will *never* recognize it to you, many try to "repair" the amp with a higher value fuse, or even some cigarette paper or bypassing it.
It never blows, so some part of the amp must, to stop that overcurrent.
Either that, or your house burns.
I've made and sold over 10000 amplifiers (in 40 years) and obviously I backup them, both under guarantee and years afterwards.
When the original fuse blows, and there's no foul play, that's to say, the original type and value is used (as all amps state clearly written on user manuals and back panels), 90% of them only have output transistors blown, sometimes only one, the board looks virginal.
I use regular (fast) blow fuses and always supply an extra one or two taped to the power cable, so it's always there if needed.
Sometimes amps come with no fuse at all (they pull the incriminating evidence) but with burnt tracks, wire resistors no simply "cut" but when open show sizable balls of molten wire, grey cracked solder, resistors burnt beyond recognition, cracked transistors, the full horror show.
All those used way oversized fuses.
I'm starting to include hidden in-transformer picofuses just because of that.
So now you can imagine what might have happened there.
« on: February 15, 2010, 02:12:58 PM »
Out of curiosity I searched a little, can't believe you must pay those incredible prices, maybe you got a little confused with exchange rates.
DigiKey NORWAY offers in its page :http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=786735&k=transformer%2024V%2030VA
eight transformers, all dual primary (115/230) , 24V center tap secondary, from 30VA 11.5Euro , 36VA 13.6Euro, 43VA 15.25 Euro, and so on, up to 175VA 32Euro. 1 Euro approx. 1.20U$S
The transformers are exported from US warehouses, but *they* pay all Customs duties, you have to pay VAT (like on a Norsk product) which I guess will be around 10%.
Shipping is free on orders over 65 Euro, it shouldn't be that expensive for your order, unless you ask for express next day delivery.
What strikes me as odd is that if you can have a Canadian made highest quality transformer (Hammond), shipped all the way from the US, for such a price, a Norwegian supplier can't charge you more than that.
« on: February 14, 2010, 11:56:16 PM »
If you already have them, try them
, what can you loose?.
Power a TDA2030, hook a speaker and some preamp, even a 1 transistor job will do, or an LM386 used as a preamp, don't remember the project name but somebody will post it ..... and have fun ....
Watch/smell for smoke/melting varnish though, just in case.
After 1/2 hour practice at high levels, you can trust them.
Don't you have a mail order electronics shop in Norway?
Can't you buy from the UK or France , Holland, Belgium, Italy?
What's the E.U. useful for?
Post any shop links you have, and good hunting.
« on: February 13, 2010, 11:02:24 PM »
First of all, pamper those Jensens.
If they are 50 year old Alnicos, original never reconed, they are worth a lot.
Sell them on EBay for a good price, buy a couple higher power new ones, and pocket the change.
Problem is, the original ones stand 15W maximum, they won't stand 50W between them.
Well, *maybe*, but why take unnecessary chances?
Just to be sure, post whatever is written on them, Jensen used paint and rubberstamps to mark various codes on the frame, at unusual places.
The idea of a future TL072 (dual op amp) is to add some tone control, another channel, whatever.
« on: February 13, 2010, 08:45:02 PM »
I'll draw the schematic and the little board needed (uses 1 TL072) and post it here for anybody who needs to bridge a couple chipamps (any of them, from LM386 to TDA7294)
Check tomorrow night.
PS: I'll include it's own mini PSU fed from the main +/-B
« on: February 13, 2010, 08:33:56 PM »
Start with one TDA2030 to practice (anyway 15W are more than enough for the garage), search for a 12+12V, 25VA to 50VA, that's to say 12+12V , from 1A to 2A.
That *can't* cost $80 !!!
The 12+12VAC will give you 16+16VDC , which are fine.
Those Laptop chargers sound interesting, but are weird pieces of equipment and doubt you can really get them for $2, at least the working kind variety.
Shadowy characters can sell you a "charging brick" and send you .... a finely wrapped *real* brick.
, if you get what I mean.
« on: February 13, 2010, 08:24:09 PM »
A 12+12V 2A transformer is fine, a 3 A is better.
Use a TDA2040 or 2050 instead, the pinout is the same but they are beefier.
Something I often see in practice amps, is to add a stamp-size mini-board, ,just with the TDA20xx pins , so the power chip can be mounted away from the front board, usually bolted to the chassis or to a better heatsink.
You can use the EPE board and only add the little adapter.
You might even solder wires to the "floating" pins but it's unprofessional
In that case heat shrink insulate chip wiring or sparks will fly.
Keep the chip close, if possible wires no more than a couple inches, four maximum, for stability.
I'll build one as-is to test, and if good (I think so) I'll adapt it for a 30W TDA2050 , separate volume controls and a simple tone control.
Will also use a TL072 (dual op amp) instead the single TL081, the price is the same
Anyway the project is great as-is.
Those speakers you mention will turn it into a serious amp.
« on: February 13, 2010, 07:04:22 AM »
Hi Ed, let's go step by step.
To begin with, *maybe* somebody has a schematic, but for the time being we'll have to do without one.
Neither the first time to do that, nor the last.
You don't tell us what the problem is, nor whether the output stage is a chip or discrete, what the main V+ and V- (if applicable) are, etc.
7411 strikes me as a date code, please tell us the total list of chips you have there, power transistors, if any, etc., and post all that is readable on each of them, even if some letter or number is too faint, it's still a guide.
The preamp voltages are reasonable, on the DIP8: -12V on pin 4 and +12V on pin 8 suggest a standard dual op amp; the 14 pin is trickier: normal quad op amps use V+/V- on pins 4/11(TL074 pinout) , some old amps used RC4136 with V+/V- on pins 11/7, but yours baffles me, so look at it in the sun with your best glasses and try to read whatever you can.
PS: +1 on asking you to avoid all caps on text.
« on: February 12, 2010, 09:35:00 PM »
Then that's the problem, lin pots start too fast.
Use an Audio/A curve/Logarithmic 22k pot.
« on: February 12, 2010, 09:29:23 PM »
Cool project !!!!!!!!!!!
And it is EPEMag indeed!!
The link is: http://www.epemag3.com/index.php?option=com_docman&task=doc_download&gid=184&Itemid=38
You do not need to modify much, as it is it's better for bass than for guitar.
1) use a slightly beefier power transformer: 12+12VAC, 25 to 40 V.A.
2) use a good audio woofer, 8" or 10" (or 12" if you dare), 4 ohms
3) that heat sink/dissipator is skimpy, try to mount there a somewhat larger, finned one
4) the left side of the board is supported by the jacks and pot; fix something for the right side.
A larger sheet aluminum heat sink, bolted to the front panel, can do double duty as extra support
It's so cool that I'll build one just for fun.
The microphone idea is amazing. British ingenuity at its best.
« on: February 12, 2010, 10:42:23 AM »
Both essentially the same topics have been merged into one, to avoid clutter.
All questions and answers are here, ordered by time.
« on: February 12, 2010, 10:31:38 AM »
Fully agree about your Ramrod idea.
If you can build a somewhat larger box for it, even better; you said you won't be carrying it around much.
When I said "Loud" I did not mean "upgrading" to a 50 or 100W amp, but to let loose the one you have now.
I'm sure you are very annoyed at the buzzy thin sound you have now, and most "solutions" consist in heavily cutting the top end, which will kill the buzz, but also sparkle, definition, the works, and not adding needed bass.
Your Ramrod or equivalent "serious" guitar speaker will give you a much better tone, and using the amp "loud" as , say, above 6 or 7, will clip the annoying peaks *without* cutting definition.
To lower power somewhat, you can buy an 8 ohm speaker which will lower your power to about 15W.
Anyway, good tone requires certain minimum levels, the best 1W amp in the world may *record* excellent but your ears will think otherwise.
As far as OpAmps, diodes, etc., the maximum has already been squeezed from them.
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