Amplitude do not look high, if scope is right 1,2v peak to peak, so its not power supply related ,probably oscillation. Can you check output of ic103, ic 303 , also their power supply? Also check if ground to their circuits is not broken.
My mistake.
What's the DC voltage on all 3 terminals of Q519?
On Q101?
Anything in the MHz range is likely just noise.
What's the DC voltage on all 3 terminals of Q519?
On Q101?
Anything in the MHz range is likely just noise.
Amplifiers are not designed to operate in the MHz range. Sometimes, noise in the audio output circuit can be too high for the circuit to get the outputs turned off quickly enough causing an increase in current draw. This can be seen when driving 20kHz signals into some amps at high enough levels. Higher frequencies can do it at very low levels. I may be proven wrong but I think he said 3 amps did the same thing.
I think there's some kind of oscillation , when rca ground got connected, and amplifier is unable to amplify that correctly, causing higher current draw and output devices heating . Is ic 101-301 power supply voltages good and clean ?
Unless something has changed, the amp works perfectly when signal is injected into Rx06 for any of the 4 channels. That's why I was trying to troubleshoot the circuit before that.
RCA shield not grounded
Q519
E 15v
C 15.6v
B 15.6v
Q101
B 15v
C 15v
E 15v
RCA shield grounded
Q519
E 14.8v
C 15.4v
B 15.5v
Q101
B 5.2v
C 10.6v
E 4.6v
Clean at 15v dead on, but if you ground the rca shield - there is the same noise like at the speaker terminals on the aux +-15vcc, at the rails...everywhere.
It does, but the sinewave is a distorted ....like the noise is riding on the wave...i'll take a picture...give me a sec.
If you ground the scope probe with the short grounding clip to the non-bridging speaker terminal for the channel you're testing, do you still have the same level of noise?
Same. It's the same even with main gnd....but if I ground the scope probe directly at the rca shield I do have a clean sinewave and my current draw goes back to normal 0.5A.
I think the scope and my lab power supply does NOT share a mains common ground. If i'm not using the gnd clip attached to the scope probe, i cannot measure anything. I'm not 100% sure how is the electrical in this building done.
I think the scope and my lab power supply does NOT share a mains common ground. If i'm not using the gnd clip attached to the scope probe, i cannot measure anything. I'm not 100% sure how is the electrical in this building done.
So, do you still think there is a problem with the amp?
If you're using a switching power supply for your bench supply radiated noise could be getting into the system (if the supply voltage looks clean).
If you're using a switching power supply for your bench supply radiated noise could be getting into the system (if the supply voltage looks clean).
So, do you still think there is a problem with the amp? - yes, idle current draw jumping 6 times when grounding the rca shields does not seem normal. Outputs are heating a lot with no load. Should I measure the bias current with the RCA shield grounded to the main gnd ?
I've just tried it with an AGM battery which is totally isolated from anything electrical in my house, still the same noise and distortion.
(if the supply voltage looks clean) - it is clean.
"If you're using a switching power supply for your bench supply radiated noise could be getting into the system " - this is the only amp I think i've seen doing this.
I've just tried it with an AGM battery which is totally isolated from anything electrical in my house, still the same noise and distortion.
(if the supply voltage looks clean) - it is clean.
"If you're using a switching power supply for your bench supply radiated noise could be getting into the system " - this is the only amp I think i've seen doing this.
You're grounding the RCAs directly at the amp. What if you ground it at the source and run 20 feet of RCA to the amp?
Do the other two amps that are identical do something similar?
Do the other two amps that are identical do something similar?
What if you ground it at the source and run 20 feet of RCA to the amp? More noise will be picked up, I guess ?!
And having in mind how much electronic stuff there is in a modern car, how shitty (sorry) are sometimes the installs from the factory, and this all being in one big giant closed electrical system, not good. I do sometimes installs for friends... I've had many noise issues when a cheap Xenon or LED headlight system was installed in the car...
Do the other two amps that are identical do something similar? Yeah, they are the same board, caps, transistors, and so on, just the heatsink is a little bit different and they behave the same...
And having in mind how much electronic stuff there is in a modern car, how shitty (sorry) are sometimes the installs from the factory, and this all being in one big giant closed electrical system, not good. I do sometimes installs for friends... I've had many noise issues when a cheap Xenon or LED headlight system was installed in the car...
Do the other two amps that are identical do something similar? Yeah, they are the same board, caps, transistors, and so on, just the heatsink is a little bit different and they behave the same...
I think you need to try to simulate the expected install conditions (20ft of patch cord, can't assume) to know if there is a problem that needs to be resolved. That's why I suggested grounding at the source and running the patch cord.
Is your signal source plugged into a charger?
What if you insert a resistor (try various values up to about 1k) in the ground jumper?
Is your signal source plugged into a charger?
What if you insert a resistor (try various values up to about 1k) in the ground jumper?
Can you also measure current, how many millianperes passes through wire , with which you connect rca ground to 12v ground. There must be few milliamperes, from q101 and similar from other channels.
P.s. try to short ground not directly, but through a 1uf film capacitor. Q101 etc would not operate, but interesting if current will still increase.
P.s. try to short ground not directly, but through a 1uf film capacitor. Q101 etc would not operate, but interesting if current will still increase.
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1. No. I usually use a totally isolated source, like a phone or laptop running on a battery only.
2. Doesn't this circuit also use a small cap in parallel with the resistor when separating the primary and secondary ground ?