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?
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?
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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.
To my surprise, there was no hum and no hiss at all. I am happy.
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.
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.
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.
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.
Hi!
Great thread!
I have one of these boards. Did all the mods exept the power regulator mod.
I put the board in a n Akai ac 3500 l which had a defective power output stage.
Removed the filter caps (fake) and rectifier from the board and the power supply in the Akai and put in two 22000 uF from a Nad amp.
Powerd up, and not a sound. Only a little pop from the speakers when power on.
Power off shows that -power drops fast and +power remains high for a long time.
Only red led on the board lights up.
Suggestions?
I am quite new to this but have some experience with electronics and quite handy with the soldering iron and stuff.
Should i replace the rest of the caps?
I am thinking of connecting it to another signal source as the Akai may be busted.
Great thread!
I have one of these boards. Did all the mods exept the power regulator mod.
I put the board in a n Akai ac 3500 l which had a defective power output stage.
Removed the filter caps (fake) and rectifier from the board and the power supply in the Akai and put in two 22000 uF from a Nad amp.
Powerd up, and not a sound. Only a little pop from the speakers when power on.
Power off shows that -power drops fast and +power remains high for a long time.
Only red led on the board lights up.
Suggestions?
I am quite new to this but have some experience with electronics and quite handy with the soldering iron and stuff.
Should i replace the rest of the caps?
I am thinking of connecting it to another signal source as the Akai may be busted.
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