There are no potentiometers besides the gain and qbass control on this pcb and are quiet. The noisyest switchs are the ones for the crossover network and they make pops and crackles when pressed which is a different sound than the buzzing right channel. Should these be replace?
I'm also going to get some new RCA input jacks.
Swapping op-amps isn't as simple as it may seem. Sometimes op-amps that are more expensive are actually more finicky and cause all sorts of problems. If you absolutely have to try other op-amps, get the amp working 100% with the originals and then swap in the more expensive ones. Don't expect any audible improvement from any substitute op-amps.
It's possible that each op-amp processes audio from both channels. If you drive signal into only the left channel, you can see which op-amp outputs have audio on them.
There are no op-amps outputs in parallel with other outputs.
It's possible that each op-amp processes audio from both channels. If you drive signal into only the left channel, you can see which op-amp outputs have audio on them.
There are no op-amps outputs in parallel with other outputs.
This list so far
The list of parts starts to grow. Does the PPI PC2150 use the same opAmps as the PC275? If I'm ordering parts I might as well save on the shipping
LM837N Quad Operational Amplifier (National)
Item: A10784 Price: $0.45 $1.35
2N6491 PNP Silicon Power Transistor
Item: G14777 Price: $1.00 $3.00
2N6488 Power Transistor (Pkg of 3) (ST)
Item: G14201 Price: $1.00 $1.00
MPSA06 NPN General Purpose Transistor
Item: G43198 Price: $0.10 $1.00
MPSA56 PNP Amplifier Transistor (Pkg of 10)
Item: G14614 Price: $0.99
The list of parts starts to grow. Does the PPI PC2150 use the same opAmps as the PC275? If I'm ordering parts I might as well save on the shipping
Item: A10784 Price: $0.45 $1.35
Item: G14777 Price: $1.00 $3.00
Item: G14201 Price: $1.00 $1.00
Item: G43198 Price: $0.10 $1.00
Item: G14614 Price: $0.99
I tried them first. I could not find Digikey nor Mouser to have the LM837N. Then www.goldmine-elec-products.com doesnt sell to many resistors but their transistor pricing seems best. :/
I was doing some more noise testing with the mini amp, and did what you said - Had only 1 RCA conected at a time, and metered the outputs of the opAmps. All 12 opAmp outputs are clean 6 on the Right and 6 on the Left. This time I had the mini amp shield connected to a pad in very close proximity to the opamps.
Oh btw and this probably should have been mentioned very early on - the right channel worsens if I hook up 4ohm speakers to the terminals on the bench. When the speakers are hooked up even the opAmp right side has signs of noise.
What else can I test after the opAmps with the mini amp?
Oh btw and this probably should have been mentioned very early on - the right channel worsens if I hook up 4ohm speakers to the terminals on the bench. When the speakers are hooked up even the opAmp right side has signs of noise.
What else can I test after the opAmps with the mini amp?
OK I'm sure this thread is getting out of control... I moved work benches, and since my wife is tired of hearing the mini-amp screel, I've not moved to using headphones with it. With the new setup my mini amp is actually picking up an over the air radio station when I attach the leads to the right channel. Its FM broadcast station 105.1 in Atlanta - a local country radio station.
The left channel does not do this.
The left channel does not do this.
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If you short the center conductor of the input RCA jack to the shield of the RCA jack, does it stop the radio station from playing through?
If you touch any of the op-amps, does it change the way the station plays through?
Do you hear the radio station on any op-amp output with the mini amp?
If you touch any of the op-amps, does it change the way the station plays through?
Do you hear the radio station on any op-amp output with the mini amp?
Shorting the input RCA jack conductor to shield does not stop the radio station from playing (Perhaps I need to call them to tell them -stop broadcasting - LOL)
I dont hear the radio station over any of the opAmp outputs. Touching the opAmps does not change any sound while I have the miniAmp connected to right terminal outputs.
If I touch cap C73 I get a lot of static and the radio station seems to diminish. If I touch any of the output transistors from UB, Q45, Q46, Q47, Q50, Q51, Q52 the radio station noise changes slightly but does not go away. If gently touch any caps ~1 inches from the 8 pin IC; 20680/JRC/6005B the sound changes.
All this is without RCAs connected
I dont hear the radio station over any of the opAmp outputs. Touching the opAmps does not change any sound while I have the miniAmp connected to right terminal outputs.
If I touch cap C73 I get a lot of static and the radio station seems to diminish. If I touch any of the output transistors from UB, Q45, Q46, Q47, Q50, Q51, Q52 the radio station noise changes slightly but does not go away. If gently touch any caps ~1 inches from the 8 pin IC; 20680/JRC/6005B the sound changes.
All this is without RCAs connected
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I'm leaning twards giving up on this thing. Does anyone offer service for fixing amp on here? I dont want to sound cheap but I dont want to spend too much on it which is why I'm on a DIY forum. Getting back to the PC2150, it sounds good enough but not as clean as the PC275's left (good) channel. I think it may need tunup service as well.
I've put the amp back together (minus the one removed left channel output transistor I burnt the other day). It plays fine in my car except for the Right channel buzzing.
I've put the amp back together (minus the one removed left channel output transistor I burnt the other day). It plays fine in my car except for the Right channel buzzing.
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I don't generally take repairs from here but this one seems interesting. If you want to send it to me, read the following very carefully, particularly the part about the return shipping label.
Shipping Instructions and Terms
For the 2150, monitor the audio on either leg of the large blue capacitors. Are both channels clean at that point? Connect the shield of the mini amp to either of the non-bridging speaker terminals.
Shipping Instructions and Terms
For the 2150, monitor the audio on either leg of the large blue capacitors. Are both channels clean at that point? Connect the shield of the mini amp to either of the non-bridging speaker terminals.
OK lets work on the PC2150 for a bit. Its gonna be more difficult but here goes.
I tried a lot of the steps I'd already done on the PC275, the opAmps on the Pc2150 sound dirty with the miniAmp. Touching almost anything on the board does not seem to change the output sound. I dont want to call this amp the same as the PC275 anymore; as the PC2150 is making more of hum or 'ringing' tone out of both channels on the bench with my test speakers. I set the gain low and -12db button controls so that the miniAmp matches the same audible output volume level for the speaker terminal outputs and the input RCAs for testing.
I wasnt sure if you meant the electrolitics near the PS or the two parralel just an inch from the OpAmps, so heres both>
(Near Power supply)
C26 and the cap mirrored on the other side of the coil sound clean
C27 and the cap mirrored on the other side of the coil sound staticy, but they also show up with 37vDC on the dvm.
(Near Opamps)
C50 and C51 both have the humming sound from shield on either L or R non-bridged output.
CR34, Q68, Q69, & Q16, Q17, CR3 right near the caps get warm faster than anything else on the PCB even with heatsync clamped own.
I tried a lot of the steps I'd already done on the PC275, the opAmps on the Pc2150 sound dirty with the miniAmp. Touching almost anything on the board does not seem to change the output sound. I dont want to call this amp the same as the PC275 anymore; as the PC2150 is making more of hum or 'ringing' tone out of both channels on the bench with my test speakers. I set the gain low and -12db button controls so that the miniAmp matches the same audible output volume level for the speaker terminal outputs and the input RCAs for testing.
I wasnt sure if you meant the electrolitics near the PS or the two parralel just an inch from the OpAmps, so heres both>
(Near Power supply)
C26 and the cap mirrored on the other side of the coil sound clean
C27 and the cap mirrored on the other side of the coil sound staticy, but they also show up with 37vDC on the dvm.
(Near Opamps)
C50 and C51 both have the humming sound from shield on either L or R non-bridged output.
CR34, Q68, Q69, & Q16, Q17, CR3 right near the caps get warm faster than anything else on the PCB even with heatsync clamped own.
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Are the large 10 ohm resistors near the RCA jacks within tolerance?
Is so, connect the RCA shield ground to the amp's main ground. Before making the connection, confirm that there is not more than a fraction of a volt between the shield and main grounds (no RCAs connected).
Does the amp still hum?
Is the hum you're hearing the sine wave you're feeding into the amp?
Is so, connect the RCA shield ground to the amp's main ground. Before making the connection, confirm that there is not more than a fraction of a volt between the shield and main grounds (no RCAs connected).
Does the amp still hum?
Is the hum you're hearing the sine wave you're feeding into the amp?
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