Resistors measure 10 ohms on each of R16 and R17
.6V DC between amp ground and RCA shields. Grounding the shield does not change amp's output at all.
The hum is not being supplied from the source. Mini amp on the source RCAs is clean. Speaker output has the hum when driving a load. I'm now calling it sort of like a 'trumpet' effect with a 400hz input frequency.
.6V DC between amp ground and RCA shields. Grounding the shield does not change amp's output at all.
The hum is not being supplied from the source. Mini amp on the source RCAs is clean. Speaker output has the hum when driving a load. I'm now calling it sort of like a 'trumpet' effect with a 400hz input frequency.
With no RCAs connected and no jumper, what is the resistance between the main ground and the RCA shield?
If you listen to the output of the signal source with the mini amp, do you hear a hum?
If you listen to the output of the signal source with the mini amp, do you hear a hum?
280ohms from ground to rca shields with the amp powered off. 10.2M ohms with the amp powered on.
Mini amp against the signal source and no hum. No hum when reading the RCA input cables in both connected and disconnected states. Hum is coming in somewhere after the RCAs.
Mini amp against the signal source and no hum. No hum when reading the RCA input cables in both connected and disconnected states. Hum is coming in somewhere after the RCAs.
Side note: Gettig back to the PC275, the small 8 pin opAmp (2068D) makes a considerable change FOR THE WORSE in the right channel's noise level when I touch it with my finger, but nothing on te left channel. Whats the best way to test this opAmp? Seems every which way theres too high a voltage for the miniAmp. I reviewd datasheet for pinouts. Also, the PC2150 has all of the same opamps as the PC275.
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If you were not touching the legs of the 2068, I'd suspect that it's defective but I don't know how it's being used. All of the op-amps that I've seen that were sensitive to touch were defective. This is very rare. I've only seen it a few times in 20+ years.
Have you ever heard of an amp picking up FM broadcast? I'm sure yes though. I remember a friend's jeep 10 years ago picking up a tower on top of a water tank while parked under it. I thikn he had a Fosgate or Hifonics amp. Not sure.
Picture around the PC275's 2068D. Coincidentally the PC2150 has a 2068D and its quiet when I touch it.
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I'm making a Mouser shopping list to fix up the PC275. The .22om resister near the output transistor I fried yesterday... Is it a metal oxide type? 2W or 3W?
Current Parts list for the PC275:
1x 513-NJM2068D
3x 610-2N6491
3x 660-MOSX3CT631RR22J or 660-MOX2CT631RR22J
I'd like to take more stabs at fixing the PC2150 before putting this order in. I dont know what else I can try for tracking down the trumpet 'hum' for parts replacement.
Current Parts list for the PC275:
1x 513-NJM2068D
3x 610-2N6491
3x 660-MOSX3CT631RR22J or 660-MOX2CT631RR22J
I'd like to take more stabs at fixing the PC2150 before putting this order in. I dont know what else I can try for tracking down the trumpet 'hum' for parts replacement.
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I think I'm probably best off having both of these amps on the bench at the same time. Theres a lot of similarities between them, and maybe one can help fix the other. I'll set them up and report!
Heres a great video showing how the PC2150 sounds like a 'trumpet' at 400hz under a small load.
PPC PC275 :: VIDEO0002.mp4 video by unclemeat2010 - Photobucket
PPC PC275 :: VIDEO0002.mp4 video by unclemeat2010 - Photobucket
It sounds like it's clipping.
On the driver boards, measure the resistance between the endpoints of the resistors (overlaid) on the driver boards.
http://www.bcae1.com/temp/ppidriverboardresistoroverlay01.swf
On the driver boards, measure the resistance between the endpoints of the resistors (overlaid) on the driver boards.
http://www.bcae1.com/temp/ppidriverboardresistoroverlay01.swf
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Cool picture. Both driver boards measure 100 Ohms as your picture discribes where to measure in two locations for each board. According to your pictured resistors that sounds about right - 100 Ohms.
Taking a step back for a moment hear. When you had me test the large blue caps near the driverboard I thought I did something a little wrong.
At a very low volume while the terminal output-speakers are trumpeting, I connected shield of miniamp to unbridged output, then the probe to the blue caps.
From ne side (Closest the L channel fets) I hear the trumpeting tone through the mini amp on both caps no matter which channel the shield is touching on the terminals.
If I touch the other side of the cap - twards the middle of the PCB, I still get trumpeting through the Mini amp, but what also happens is invertly my test speakers press and bottom out. I actually blew one of the stock test speakers up last night... See if this chart makes any sense
Taking a step back for a moment hear. When you had me test the large blue caps near the driverboard I thought I did something a little wrong.
At a very low volume while the terminal output-speakers are trumpeting, I connected shield of miniamp to unbridged output, then the probe to the blue caps.
From ne side (Closest the L channel fets) I hear the trumpeting tone through the mini amp on both caps no matter which channel the shield is touching on the terminals.
If I touch the other side of the cap - twards the middle of the PCB, I still get trumpeting through the Mini amp, but what also happens is invertly my test speakers press and bottom out. I actually blew one of the stock test speakers up last night... See if this chart makes any sense
Term Cap Lead MiniAmp Speaker Bottoms out
Left C50 Fet Side Trumpets no
Left C51 Fet Side Trumpets no
Right C50 Fet Side Trumpets no
Right C50 Fet Side Trumpets no
Left C50 Center PCB Trumpets no
Left C51 Center PCB Trumpets Left - Yes
Right C50 Center PCB Trumpets Right - Yes
Right C51 Center PCB Trumpets no
At a very low volume while the terminal output-speakers are trumpeting, I connected shield of miniamp to unbridged output, then the probe to the blue caps.
From ne side (Closest the L channel fets) I hear the trumpeting tone through the mini amp on both caps no matter which channel the shield is touching on the terminals.
If I touch the other side of the cap - twards the middle of the PCB, I still get trumpeting through the Mini amp, but what also happens is invertly my test speakers press and bottom out. I actually blew one of the stock test speakers up last night... See if this chart makes any sense
Taking a step back for a moment hear. When you had me test the large blue caps near the driverboard I thought I did something a little wrong.
At a very low volume while the terminal output-speakers are trumpeting, I connected shield of miniamp to unbridged output, then the probe to the blue caps.
From ne side (Closest the L channel fets) I hear the trumpeting tone through the mini amp on both caps no matter which channel the shield is touching on the terminals.
If I touch the other side of the cap - twards the middle of the PCB, I still get trumpeting through the Mini amp, but what also happens is invertly my test speakers press and bottom out. I actually blew one of the stock test speakers up last night... See if this chart makes any sense
Term Cap Lead MiniAmp Speaker Bottoms out
Left C50 Fet Side Trumpets no
Left C51 Fet Side Trumpets no
Right C50 Fet Side Trumpets no
Right C50 Fet Side Trumpets no
Left C50 Center PCB Trumpets no
Left C51 Center PCB Trumpets Left - Yes
Right C50 Center PCB Trumpets Right - Yes
Right C51 Center PCB Trumpets no
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For the PC275, you mind taking a look at this video? it shows the 2068D opamp behaving irratically from human touch. What are your thoughts on it? Replace it? I'm thinking yes, but you said this effect is extremely rare case.
The left channel is clean, the right channel is very noisy.
Also, the PC2150 has the same opamp and does nothing when touched.
PPC PC275 :: VID_20101021_153633.mp4 video by unclemeat2010 - Photobucket
Also this one using dDVM probe.
PPC PC275 :: VID_20101021_155746.mp4 video by unclemeat2010 - Photobucket
Thank you
The left channel is clean, the right channel is very noisy.
Also, the PC2150 has the same opamp and does nothing when touched.
PPC PC275 :: VID_20101021_153633.mp4 video by unclemeat2010 - Photobucket
Also this one using dDVM probe.
PPC PC275 :: VID_20101021_155746.mp4 video by unclemeat2010 - Photobucket
Thank you
LOL I just watched that first video again. Ever play Operation? Thats what the miniamp sounds like when I touch 2068D opamp.
OK. Added to the parts list. I'll put the PC275 aside for awhile and start concentrating on the PC2150. If you think the signal is clipping, thats peculiar but I dont doubt it. The setup actually sounds very good at high volume in the car running my single 12. I keep the gain at no more than 1/4 the way up and my HU has 5v output. The system sounds very clean and compact. Not slobbery or anything. The amp and sub always have plenty of room for big punch and I never go over that volume level.
That being said its not all a happy story in my car. At very low volumes I can hear the trumpeting sound coming out of the sub. Raising the volume may be masking the clipping but I'm sure its not getting eliminated. I want to avaiod clipping the sub with this amp at all costs due to how I'm currently overpowering the sub's RMS rating.
I've heard stories about those driverboards failing. I think by default and because of minimum orders Im going to order an extra 2068 and opAmps for the PC2150. They dont cost much so its no big deal, and I wont feel bad if I just toss or dont use them.
Now, since we think its clipping; but then again high volumes dont seem to carry just a low volume clip. is there anyway I can bypass the majority of the pre-amp controls and get the RCA somehow connected after all the sound processor stuff? Like connect the RCAs closer to the high voltage side without frying anything? If the problem still exists there then its not the sound processing side. Also its equal on both channels so something in the middle might be the cause; or just both channels degraded at the same time.
That being said its not all a happy story in my car. At very low volumes I can hear the trumpeting sound coming out of the sub. Raising the volume may be masking the clipping but I'm sure its not getting eliminated. I want to avaiod clipping the sub with this amp at all costs due to how I'm currently overpowering the sub's RMS rating.
I've heard stories about those driverboards failing. I think by default and because of minimum orders Im going to order an extra 2068 and opAmps for the PC2150. They dont cost much so its no big deal, and I wont feel bad if I just toss or dont use them.
Now, since we think its clipping; but then again high volumes dont seem to carry just a low volume clip. is there anyway I can bypass the majority of the pre-amp controls and get the RCA somehow connected after all the sound processor stuff? Like connect the RCAs closer to the high voltage side without frying anything? If the problem still exists there then its not the sound processing side. Also its equal on both channels so something in the middle might be the cause; or just both channels degraded at the same time.
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Are you sure that the mini amp has not been damaged when you touched it to high voltage points?
Is the battery possibly dead?
Did you try the woofer on each channel of the amp to see if the noise was present in the vehicle?
There's no practical way to modify the circuit.
Is the battery possibly dead?
Did you try the woofer on each channel of the amp to see if the noise was present in the vehicle?
There's no practical way to modify the circuit.
The mini amp is still working very well. I've been making sure nothing over about .25v has hit its input for longer than a second. The components inside the mini appear to be in execlent condition. In the last video the mini is only recieving .015v AC from the speaker outputs even when Im touching the opamp. It still sounds perfectly fine over the PC275's left channel, as well as plain input RCAs. I know it seems like it might be excessivly amplified with my phone but its really not that loud - I think my phone's mic must be very very sensitive, and yes I probably did turn it up a bit louder so the phone could pick it up better. At any volume level on the mini, the 2068D opAmp makes a noisier right channel when touched. The 9v in the mini is a lithium and still reading 8.9v.
I've also been topping off the 12v (6A) motorcycle battery for ~30 minutes every night and its been reading good voltage the whole time. Its $75 battery so its holding its own. Its good enough to sit all winter and start a motorcycle without needing a charge.
For the PC2150...
Unfortunately the 12" woofer makes noise on either R/L or in bridged configuration, and do my bench test speakers and the miniamp.
Dang. I'll just have to keep looking for the clipping source. Nothing comes to mind?
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