I have a Precision Power A600 which is giving me a scratchy "static" sounding noise on the left channel. The noise is there almost all the time and does not go away if I unplug the RCA input cables, and also the volume of the noise is not affected by the gain control on the amp. I still hear it just the same if I turn down the gain all the way.
The channel still functions when the audio inputs are connected, and the output sounds OK except that there is always this fixed level of noise present.
I checked out the board to make sure there weren't any obvious broken solder joints near the inputs, and everything looks OK. None of the components look burnt or damaged.
I've noticed that there are quite a few PPI experts in this forum, so I'm hoping someone can help me track down this issue or suggest someone competent who could fix it.
Thanks very much for your help!
Bryan
The channel still functions when the audio inputs are connected, and the output sounds OK except that there is always this fixed level of noise present.
I checked out the board to make sure there weren't any obvious broken solder joints near the inputs, and everything looks OK. None of the components look burnt or damaged.
I've noticed that there are quite a few PPI experts in this forum, so I'm hoping someone can help me track down this issue or suggest someone competent who could fix it.
Thanks very much for your help!
Bryan
Thanks for your suggestion. All of the large resistors seem to check out OK with the multimeter. The RCA shield is common for both input channels, so would that mean the problem is elsewhere?
Here is a link to a picture of the board, hoping it may be helpful:
http://www.bitbytes.com/bsl/a600.jpg
Thanks,
Bryan
Here is a link to a picture of the board, hoping it may be helpful:
http://www.bitbytes.com/bsl/a600.jpg
Thanks,
Bryan
Another idea... I came across a discussion on another forum in which a guy had a similar problem with a Kenwood car amp. It turned out to be a bad opamp introducing a crackling noise into just one of four channels.
Could that be the case here? I believe there are two opamps in this A600 unit, both having part #47833 9224 M10. This cross-references to a Fairchild KA4558 on Mouser's part site. Is this the correct replacement part? These are fairly cheap and would be easy to replace.
Or is there a better part that I should use? This discovery led me to read a bunch of opamp discussions here on diyAudio, and it seems to be common for people to replace opamps with higher quality parts to improve sound quality.
Any help would be greatly appreciated.
Thanks,
Bryan
Could that be the case here? I believe there are two opamps in this A600 unit, both having part #47833 9224 M10. This cross-references to a Fairchild KA4558 on Mouser's part site. Is this the correct replacement part? These are fairly cheap and would be easy to replace.
Or is there a better part that I should use? This discovery led me to read a bunch of opamp discussions here on diyAudio, and it seems to be common for people to replace opamps with higher quality parts to improve sound quality.
Any help would be greatly appreciated.
Thanks,
Bryan
Hi
I assume that all of your problems come from bad solder joints. I used to fix a lot of broken amplifiers throughout all sizes and price-ranges. Almost all amplifiers had bad solder jobs in common.
If it was the OP-amp, you could use the 4558. You can also use a TL072 (Dual) or a TL084 (quad) for Audio purposes.
But I would start first to resolder all solder joints. Even if they look good. In 2 out of 5 cases I didn´t have to replace parts in broken amps, I just had to resolder everything, or broken parts were caused by bad solder joints.
If there still is a fault then, you can be sure that it is not a bad solder joint and start testing parts.
If you can power up the amplifier on your workbench, use a voltmeter to check the power-transistors base voltage while the RCA inputs are shortened. You should read smthg. around 0,5 -0,6V. If there is a higher voltage (e.g. 1,3V) something in the pre-amps of the power-amplifier is broken.
I once had a Crunch V4004 amplifier that had a steady loud noise on one channel, even w/o inputs connected. There a bad solder joint somewhere caused the amplifier to run @ 3V rms all the time.
sdoom
I assume that all of your problems come from bad solder joints. I used to fix a lot of broken amplifiers throughout all sizes and price-ranges. Almost all amplifiers had bad solder jobs in common.
If it was the OP-amp, you could use the 4558. You can also use a TL072 (Dual) or a TL084 (quad) for Audio purposes.
But I would start first to resolder all solder joints. Even if they look good. In 2 out of 5 cases I didn´t have to replace parts in broken amps, I just had to resolder everything, or broken parts were caused by bad solder joints.
If there still is a fault then, you can be sure that it is not a bad solder joint and start testing parts.
If you can power up the amplifier on your workbench, use a voltmeter to check the power-transistors base voltage while the RCA inputs are shortened. You should read smthg. around 0,5 -0,6V. If there is a higher voltage (e.g. 1,3V) something in the pre-amps of the power-amplifier is broken.
I once had a Crunch V4004 amplifier that had a steady loud noise on one channel, even w/o inputs connected. There a bad solder joint somewhere caused the amplifier to run @ 3V rms all the time.
sdoom
I re-soldered the entire underside of the board, and I also replaced both op amps. Problem is still there.
I found a better way to describe the noise: it's a scratchy static noise with an occasional "popping popcorn" type of noise. The static is almost constant while the popcorn noise comes and goes.
Bryan
I found a better way to describe the noise: it's a scratchy static noise with an occasional "popping popcorn" type of noise. The static is almost constant while the popcorn noise comes and goes.
Bryan
Hi again,
ok, resoldering didn´t solve the problem, but I assume it will let the amplifier run for another 5 years or more
Is the sound like a whining sound or more like noise (like a TV set when the there is a bad carrier) . It could be a bad capacitor .
use a voltmeter to check all OP-Amps if they have proper supply voltage. That should be around +/- 15V (usually generated with 2 Zener-Diodes)
Try to follow the curcuit board lines from the pre-amps to the power amplifer. Usually this goes from the last OP-Amp to a 1k - 10k resistor and a 1µF -10µF Capacitor (all in series) to the power-amplifier section. If you find those connection, you can disconnect it (e.g. take out the capacitor) and power up the unit .
The power-amplifier section now runs without the preamps and filters. If the sound/noise is still there, the fault is within the power-amplifier itself. If it is quiet, the problem is in the pre-amps or filters.
BTW: When you power up the amplifer on your workbench, don´t use a high-current fuse. 5A will do. Also add a 2Ohm / 10W power-resistor in between the +12V wire. This is to protect the amplifier if anything would ever go wrong. ( If a short would appear inside the amplifier, the high current draw would cause the voltage to drop @ the resistor, thus shutting down the amplifier)
ok, resoldering didn´t solve the problem, but I assume it will let the amplifier run for another 5 years or more
Is the sound like a whining sound or more like noise (like a TV set when the there is a bad carrier) . It could be a bad capacitor .
use a voltmeter to check all OP-Amps if they have proper supply voltage. That should be around +/- 15V (usually generated with 2 Zener-Diodes)
Try to follow the curcuit board lines from the pre-amps to the power amplifer. Usually this goes from the last OP-Amp to a 1k - 10k resistor and a 1µF -10µF Capacitor (all in series) to the power-amplifier section. If you find those connection, you can disconnect it (e.g. take out the capacitor) and power up the unit .
The power-amplifier section now runs without the preamps and filters. If the sound/noise is still there, the fault is within the power-amplifier itself. If it is quiet, the problem is in the pre-amps or filters.
BTW: When you power up the amplifer on your workbench, don´t use a high-current fuse. 5A will do. Also add a 2Ohm / 10W power-resistor in between the +12V wire. This is to protect the amplifier if anything would ever go wrong. ( If a short would appear inside the amplifier, the high current draw would cause the voltage to drop @ the resistor, thus shutting down the amplifier)
An externally hosted image should be here but it was not working when we last tested it.
I also thought R33 didn't look too good, but it seemed to measure the same resistance as the one for the other channel (just below and to the right, on the picture). Tonight I'll remove it from the board and test it out of the circuit. Maybe the reading I was getting was via some other path on the board.
Back to the topic of op amps, is the 4558 the correct "original" part for this amp? Or is there are better choice? It seems like quite a few people replace op amps with better ones to improve sound quality. Just curious about this.
And can you tell me what is the 6-pin chip just to the right of the two op amps? The part number didn't yield any results when I tried to find information.
Thanks,
Bryan
Back to the topic of op amps, is the 4558 the correct "original" part for this amp? Or is there are better choice? It seems like quite a few people replace op amps with better ones to improve sound quality. Just curious about this.
And can you tell me what is the 6-pin chip just to the right of the two op amps? The part number didn't yield any results when I tried to find information.
Thanks,
Bryan
OP-Amp: The TL072 is a good replacement part. Some people overhere replace the 4558 in their cheaper amplifiers with it.
It ´s THD is ~ 0,003 % and the noise is just 18 nV/√Hz Typ at 1 kHz for example.
Do you mean the small black thing ? I think that´s not a chip , it looks like a resistor-network.
It ´s THD is ~ 0,003 % and the noise is just 18 nV/√Hz Typ at 1 kHz for example.
Do you mean the small black thing ? I think that´s not a chip , it looks like a resistor-network.
TO-3: I removed and tested R33, it seems fine and measures 1.6 ohms which matches the same resisitor on the other channel.
sdoom: The chip I'm referring to is the third of three small square chips all in a row. The far right one has 3 pins per side. Part number is "4N 25 305 S TK4".
What are the small "vertical" boards used for? They are labeled on the circuit board as U1 and U7.
Thanks again for all your help so far!
Bryan
sdoom: The chip I'm referring to is the third of three small square chips all in a row. The far right one has 3 pins per side. Part number is "4N 25 305 S TK4".
What are the small "vertical" boards used for? They are labeled on the circuit board as U1 and U7.
Thanks again for all your help so far!
Bryan
troll5501 said:
U1 and U7 are discrete diff-amps. It may be possible that the board for the left channel is bad. I have seen that before, too. The problem with those is that they have resistors that are integrated into the traces so only caps and xistors had to be soldered on.
The 6-pin IC is 4N25. It is a opto-isolator for the muting circuitry.
the TL072 is as crappy of an opamp as you can find. Yes, there are worse, but also, there are much better. Most people upgrade to Burr-Brown ops(OP275, OP2134), both of those are cost effective replacements that will sound much cleaner than the TL072. I like the Analog Devices AD823 opamps. I believe they can accept up to +/-18V, but are not that cost effective when you replace every one in your system(at around $4.30/each). I replaced about 30 in my old system, years ago, and I loved the new sound. I made my Tube Drivers sound even better than stock.
As for R33, it is common that they discolor like that, without opening, but it also would be indicative of high-frequency oscillations as that resistor is coupled to ground through a capacitor. If you can, put a scope on it and check that channel. You can test the amp, without the cover, as long as there is no load on it. Just keep checking the regulators to be sure they are not getting too warm.
Another thing I thought of this morning, do you get static when adjusting the gain pot?
Re: To-3
There are differences. Not that extreme and you may be able to get away without modding the power supply. The A open-loop is about 20dB higher on the BB part, so you might have to make some feedback-loop adjustments. It is important to have an oscope handy to verify that the part does not oscillate after the change. Check out the datasheets below:
TL072
OPA2134
IMPALAMAN1 said:
There are differences. Not that extreme and you may be able to get away without modding the power supply. The A open-loop is about 20dB higher on the BB part, so you might have to make some feedback-loop adjustments. It is important to have an oscope handy to verify that the part does not oscillate after the change. Check out the datasheets below:
TL072
OPA2134
My A600.2 has static or scratchiness that accompanies certain frequencies in music, such as horns. I sent it to the amp lab, and just got it back from Ethan. No luck. They couldn't find the source of the problem.
I'm probably going to just use it as a bass amp because I'm pretty sure I won't hear any of that static on low frequencies but haven't had a chance to confirm it. Actually, I suspect that despite the amp's age, it was like this the whole time I owned it. But I never knew because I used only use it as an as a bass amp before.
Anyway, I'm thinking after some time I'll try spending another couple hundred bucks on another try with this guy instead
Auto Repair Cranston Rhode Island, Custom Audio, Hydro Dipping.
Old school car audio restorations - Cranston, Rhode Island | Facebook
he seems to be having a lot of success and a good reputation
I'm probably going to just use it as a bass amp because I'm pretty sure I won't hear any of that static on low frequencies but haven't had a chance to confirm it. Actually, I suspect that despite the amp's age, it was like this the whole time I owned it. But I never knew because I used only use it as an as a bass amp before.
Anyway, I'm thinking after some time I'll try spending another couple hundred bucks on another try with this guy instead
Auto Repair Cranston Rhode Island, Custom Audio, Hydro Dipping.
Old school car audio restorations - Cranston, Rhode Island | Facebook
he seems to be having a lot of success and a good reputation
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