My "audiophile" LM3886 approach - Page 427 - diyAudio
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Old 9th January 2014, 04:34 PM   #4261
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To varun21,
Some versions of MyRef use pin 8 on the LM318n. Check your pcb if pin 8 is connected. TL071 pin 8 = nc
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Old 10th January 2014, 08:18 AM   #4262
AndrewT is offline AndrewT  Scotland
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measure the output offset from the speaker output terminal to the main audio ground on the PCB.
If the relay is triggered to OFF the speaker return is isolated and you can't use it to reference to the zero volts.
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Old 11th January 2014, 04:50 AM   #4263
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@mark: Yes pin 8 is connected to the PCB and goes to R39 and R43. So apparently TL071c works without compensation while LM318n is either faulty or needs some custom compensation? (Pls note: I'm using TL071-"C" if that matters.)

@andrew: I do all my measurements from the power ground (0v rail). With TL071c it works and gives .005v.

I've got some new LM318n s and I'm planning to plug them into the socket. Should I go ahead?
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Old 18th January 2014, 04:46 PM   #4264
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Finally plugged in LM381n and yes it did have some stability issue. Sometimes it click in and I can play. But at other times I switch on and it comes on for a fraction of a sec and then goes off (relay). When it works it does have a HF oscillation (something 13-14KHz and above).

But I'm so glad I was pleasantly surprised by my DIY make-shift speakers living up to myref. I always thought my 3-way speakers would just sound dull without the tone controls of ESP project 97. Plugged in the TL071c again and I just sat right in the middle of the two for several hours and played out all my favs. The myref has a very clear, detailed image and sounds just like inside a movie hall or better. I feel as if I'm out there in the live.

The paint on the enclosure will dry by tomorrow and then once inside, the shield of the enclosure will hopefully reduce or rectify the oscillation of the myref.

From the looks of it, these look trash and those are some of the cheapest drivers I bought with my pocket money 15yrs back. But for now, my new 2-way speaker project is on indefinite hold.

DSC_0888-as-Smart-Object-1.jpg
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Old 19th January 2014, 05:59 AM   #4265
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So I turned it off and went for a break. When I returned, I switched on the mains with shivering hands (it's biting cold here). And I saw a spark on the PCB. The only switch I have currently is the AC mains. And then no sound. The relay clicks in though.

Upon microscopic inspection I saw that the PCB has some kind of a fuse built-in. Is it ok to jump it and try again?

Photos from a blank PCB (I have 4 extras). Click for larger version.

_DSC2017-as-Smart-Object-1.jpg

_DSC2017-as-Smart-Object-1-100.jpg
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Old 19th January 2014, 10:32 AM   #4266
AndrewT is offline AndrewT  Scotland
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repair the break.
test via your bulb tester.
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Old 19th January 2014, 04:50 PM   #4267
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Thanks AndrewT.

I jumped the breaks with solder. I put in the bulb tester and turned it on. The LED came on and the relay clicked.

If I remember correctly: I measured 0V at speaker gnd terminals (well the positive rail read 25.6VDC from there so they were not disconnected, suggesting that the relay was engaged). But this is if I remember correctly.

And no sound. Speakers felt dead.

I'm supplying 19VAC and getting 25.6VDC on the rails. I'm also using a TL071c instead of LM318 (they were blown and I'll only put in new ones once I've put this in it's enclosure).

The only way to turn on this thing now is to touch the Pin 1 of TL071c with a screwdriver etc. That somehow seems to engages the relay and turn on the speakers? This is contradictory to my measuring 0VDC on speaker gnd terminals.

What else should I try?
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Old 20th January 2014, 05:49 AM   #4268
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Thats not a fuse. You can change the fuction of the pcb. If it worked without then they probely need to be left as is. Are you still using shunts on your supply? This is not the way to get a stable supply. As the current increases the voltage decreases (Relais on relais off relais on.......). I think this amp needs 24Vac if only for the relais (30Vdc).
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Old 20th January 2014, 07:05 AM   #4269
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I use transformer 25-0-25, but i have Omron 8A-24V, can I use it?
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Old 20th January 2014, 07:51 AM   #4270
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Hi Mark,

I bought 4 PCBs and one assembled piece from a chinese vendor. I saw a spark while turning it on (it played fine for hours earlier), and then I verified with my multimeter that the spark-gap fuse was in fact blown. When soldered it came right on but I'm using a blulb tester in series now. And apparently now it's too low a voltage. I'm planning to raise it to 22VAC and the primary in series with a 100W bulb. I'm currently connecting 4 ohm speakers.

My broken PCB had that gap/fuse blown (looked just like a shorted blown out metal). On the new pcb that was a 0 ohm, conducting joint.

thedeath0212: You should be able to use it provided it is actually a 24 - 0 - 24 and NOT a 24 - 0.
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