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Old 18th April 2012, 12:07 PM   #521
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The left hand side of the 470Rs (into the Regs) should be connected to the left hand side of the 22Ks.

Then there is a simple series 22K and LED across each rail.

Cliff
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Old 1st July 2012, 06:20 PM   #522
goody75 is offline goody75  United States
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I have a question about identifying/quantifying source impedance.

Specifically, I'm trying to figure out if the source impedance (Rs) seen at the input pin (pin 3) of the opamps in the Yuanjng Gainclone is effected by the upstream 22Kohm input resistor or if it's simply the output impedance of the source device.

For example, if I have a DAC w/ a very low output impedance (<100ohms), will the opamp see the impedance of the source device as something close to 100ohms or will it see an Rs much closer to the 22K input resistor?

Last edited by goody75; 1st July 2012 at 06:26 PM. Reason: expanding on an idea
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Old 5th July 2012, 02:48 AM   #523
yuhjeng is offline yuhjeng  United States
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Hi everyone, I too have just finished wiring up the yuanjing 3886 from ebay. The only mod I did was moving the 7812 and 7912 off the board and mounted them somewhere else with heat sinks. I used 30.5-0-30.5 transformer from a dead receiver. The main heat sink remained warm but not hot during the first few hours of light listening.

To my surprise, there was no hum and no hiss at all. I am happy.
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Old 27th October 2012, 10:36 PM   #524
goody75 is offline goody75  United States
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Default Lifted Trace

Hopefully this thread isn't so old now that everyone has died off

After waaaay to long, I am getting close to finishing this amp but along the way I lifted a trace on one of the op amp power supply rails and I'm hoping someone can help me with a fix.

The pin I lifted is the ground pin for the electrolytic cap on the positive rail of one of the op amps. I think the best way to fix it is to run a wire to a ground pin on another component on the board. Does it matter where I connect it?

It looks to me like the best option is the the 0.1uF op amp PS cap next to it (it's in parallel with the lifted trace cap). The smoothing cap is also very close. Another option could be to wire it to the corresponding pin on the other channel.

I appreciate any guidance on this since I don't want to kill myself or the amp.
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Old 27th October 2012, 10:46 PM   #525
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Wire it close to the 100nF capacitor.
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Old 28th October 2012, 08:57 AM   #526
AndrewT is online now AndrewT  Scotland
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Electrolytic capacitor:
Is it an MF decoupling capacitor?
Then it must be connected directly to it's partner. The two decoupling caps must be connected together.
Similarly where two HF decoupling caps are fitted these too must be directly connected together.
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Old 28th October 2012, 01:02 PM   #527
goody75 is offline goody75  United States
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AndrewT,
Yes. The lifted trace is on the electrolytic decoupling cap (positive rail). Can you please clarify what you mean by partner? Do you mean the electrolytic on the neg rail of the same opamp (next to the lifted trace cap)? the electrolytic on the pos rail of the other opamp?
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Old 7th November 2012, 06:01 PM   #528
Mihkus is offline Mihkus  Estonia
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All these chinese kits are with fake ic's/trans, junkyard shitty and blown parts
I bought TDA8920BTH shitty but expensive board, when i reached +-28v dc both 35v "Elna" caps blew also the ic went extremely hot until blew, then i bought new ic removed all these
nasty looking screw terminals and added pins, desoldering the ic was easy but it dint really went well, both output tracks got damaged so i had to use copper foil to make new ones...
After that everything worked very well, at 12v it puts out around 4-5wmax without clipping
at 28-30 and at 4 ohms it does put out 100w with ease.
Fake parts and junk parts are in use, if u buy the board and you have original IC laying around its totally worth it still, boards have very good quality.
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Old 2nd February 2013, 04:26 PM   #529
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Hey guys,

Quick question.

I'm looking for new potentiometers for my lm3886x2 (Jim's Audio).

Currently I have two 50K 1/4W. I want to try 10K or 25K. What is a suitable power rating for these? Is 1/10W too small? Should I try to find a 1/4W?
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