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#1
Posted to rec.audio.high-end
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Adcom 535 acting up
My adcom 535 II has started exhibiting hum and scratchy noise. I
isolated it from my other components and it still does the same the with nothing connected. It's doing it on both channels but one channel is a bit worse that the other. Which is a bit annoying since the amp is two independent amps in one box. I'm suspecting the electrolytics in the power supplies. When I play around with them it affects the scratchiness. I don't have a schematic for this amp but it looks like the power supplies are basic unregulated rectifier/ capacitor arrangements. I'm thinking I should replace all 4 electrolytics. I was browsing the newark selection and it looks like I could raise the size a bit and still fit in the space. The original ones are 6800uf at 63v. There are a number of 8200uf that will fit. The lead spacing is a bit of a chore since the originals are a lot wider that today's typical 10 or 12mm. Any suggestions on my diagnosis or on bumping up the size? |
#2
Posted to rec.audio.high-end
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Adcom 535 acting up
On Jul 23, 9:42*am, jamesgangnc wrote:
My adcom 535 II has started exhibiting hum and scratchy noise. *I isolated it from my other components and it still does the same the with nothing connected. *It's doing it on both channels but one channel is a bit worse that the other. *Which is a bit annoying since the amp is two independent amps in one box. I'm suspecting the electrolytics in the power supplies. *When I play around with them it affects the scratchiness. *I don't have a schematic for this amp but it looks like the power supplies are basic unregulated rectifier/ capacitor arrangements. I'm thinking I should replace all 4 electrolytics. *I was browsing the newark selection and it looks like I could raise the size a bit and still fit in the space. *The original ones are 6800uf at 63v. *There are a number of 8200uf that will fit. *The lead spacing is a bit of a chore since the originals are a lot wider that today's typical 10 or 12mm. Any suggestions on my diagnosis or on bumping up the size? My scope shows a noticable sawtooth at 60hz on the power supply output. Looks like there are a some .22 film capacitors on the power supply board as well. I would think they would be filtering out the scrathchy/static sort of noise I'm getting. I suppose it's possible that the power supply caps explain my hum while the static sort of noise is a different problem. There are several small electrolytics on the amp boards as well. Anyone got a schematic for one of these amps they could share? |
#3
Posted to rec.audio.high-end
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Adcom 535 acting up
On Jul 23, 12:02*pm, jamesgangnc wrote:
On Jul 23, 9:42*am, jamesgangnc wrote: My adcom 535 II has started exhibiting hum and scratchy noise. *I isolated it from my other components and it still does the same the with nothing connected. *It's doing it on both channels but one channel is a bit worse that the other. *Which is a bit annoying since the amp is two independent amps in one box. I'm suspecting the electrolytics in the power supplies. *When I play around with them it affects the scratchiness. *I don't have a schematic for this amp but it looks like the power supplies are basic unregulated rectifier/ capacitor arrangements. I'm thinking I should replace all 4 electrolytics. *I was browsing the newark selection and it looks like I could raise the size a bit and still fit in the space. *The original ones are 6800uf at 63v. *There are a number of 8200uf that will fit. *The lead spacing is a bit of a chore since the originals are a lot wider that today's typical 10 or 12mm. Any suggestions on my diagnosis or on bumping up the size? My scope shows a noticable sawtooth at 60hz on the power supply output. *Looks like there are a some .22 film capacitors on the power supply board as well. *I would think they would be filtering out the scrathchy/static sort of noise I'm getting. *I suppose it's possible that the power supply caps explain my hum while the static sort of noise is a different problem. *There are several small electrolytics on the amp boards as well. *Anyone got a schematic for one of these amps they could share? I guess it would be easier to use rec.audio.tech Its hard to believe the caps would not filter with no signal input. I would first check all connections including crimps. I don't like crimps. greg |
#4
Posted to rec.audio.high-end
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Adcom 535 acting up
On Thu, 23 Jul 2009 06:42:17 -0700, jamesgangnc wrote
(in article ): My adcom 535 II has started exhibiting hum and scratchy noise. I isolated it from my other components and it still does the same the with nothing connected. It's doing it on both channels but one channel is a bit worse that the other. Which is a bit annoying since the amp is two independent amps in one box. I'm suspecting the electrolytics in the power supplies. When I play around with them it affects the scratchiness. I don't have a schematic for this amp but it looks like the power supplies are basic unregulated rectifier/ capacitor arrangements. I'm thinking I should replace all 4 electrolytics. I was browsing the newark selection and it looks like I could raise the size a bit and still fit in the space. The original ones are 6800uf at 63v. There are a number of 8200uf that will fit. The lead spacing is a bit of a chore since the originals are a lot wider that today's typical 10 or 12mm. Any suggestions on my diagnosis or on bumping up the size? Increasing the value of the caps won't hurt as long as they have sufficient voltage rating, but don't expect any "improvement" in the sound. And yes, the hum and the fact that the problem is in both channels is indicative of power supply problems. But the scratchy sound is somewhat puzzling. I've never heard of that particular problem being caused by leaky filter caps before, but I guess it IS possible. If you have an oscilloscope. I'd look at the "B+" across both the power supply's output as well as across the filter caps. There is a possibility that the power supply is regulated and if it is, the regulator circuitry will be after the filter caps and before the power supply output to the amp circuit boards. I would suspect regulation for the source of the scratchy sound before I would suspect the filters. They generally just cause hum. Of course, if the Adcom's PS is unregulated....... |
#5
Posted to rec.audio.high-end
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Adcom 535 acting up
On Thu, 23 Jul 2009 09:02:13 -0700, jamesgangnc wrote
(in article ): On Jul 23, 9:42*am, jamesgangnc wrote: My adcom 535 II has started exhibiting hum and scratchy noise. *I isolated it from my other components and it still does the same the with nothing connected. *It's doing it on both channels but one channel is a bit worse that the other. *Which is a bit annoying since the amp is two independent amps in one box. I'm suspecting the electrolytics in the power supplies. *When I play around with them it affects the scratchiness. *I don't have a schematic for this amp but it looks like the power supplies are basic unregulated rectifier/ capacitor arrangements. I'm thinking I should replace all 4 electrolytics. *I was browsing the newark selection and it looks like I could raise the size a bit and still fit in the space. *The original ones are 6800uf at 63v. *There are a number of 8200uf that will fit. *The lead spacing is a bit of a chore since the originals are a lot wider that today's typical 10 or 12mm. Any suggestions on my diagnosis or on bumping up the size? My scope shows a noticable sawtooth at 60hz on the power supply output. Looks like there are a some .22 film capacitors on the power supply board as well. I would think they would be filtering out the scrathchy/static sort of noise I'm getting. I suppose it's possible that the power supply caps explain my hum while the static sort of noise is a different problem. There are several small electrolytics on the amp boards as well. Anyone got a schematic for one of these amps they could share? I looked online and while I found a couple of places that can supply schematics and service manuals for this puppy, they all want $$$. While I'd like to help you out here, I my desire to help a fellow audiophile doesn't extend to out-of-pocket expenses. 8^) Sorry. OTOH, the sawtooth looks like it could be a rectifier bridge with one diode gone bad. Usually, bad filters just exhibit high amplitude sinosoidal ripple on them, not sawtooth waves which usually indicate extreme differentiation. The .22 ufd caps are there for high-frequency bypass if they are across the filter caps. If they leak, I wouldn't expect to see any noticeable performance problems. If they short, you'd get the capacitor-as-fuse effect and there would be physical signs of damage. Small caps like that (especially if they use a plastic film as the dielectric) don't usually go bad over time, so unless you have some real reason to suspect them, I would ignore those. |
#6
Posted to rec.audio.high-end
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Adcom 535 acting up
jamesgangnc wrote:
My scope shows a noticable sawtooth at 60hz on the power supply output. Are you sure it's 60 Hz and not 120 Hz? What kind of amlitude is the square wave? If it's relatively small, i.e. even a couple of volts or less, I'd guess that the caps are relatively OK. Looks like there are a some .22 film capacitors on the power supply board as well. I would think they would be filtering out the scrathchy/static sort of noise I'm getting. Nope. I'd bet good money the scratchy noise is not coming from the power supply. There's not a lot there that would give rise to such (with one exception, see later on). Not only that, but these amp designs tend to have pretty reasonable power supply rejection ratios, so the amout of scratchy noise would have to be pretty fierce on the power supply to make it audible. I suppose it's possible that the power supply caps explain my hum while the static sort of noise is a different problem. Yup. Anyone got a schematic for one of these amps they could share? You've got more data gathering to do before you HAVE to have a schematic. Here are some questions to explo 1. Is the noise identical in both channels? If so, look at whatever is common between the two. If not, is the noise different in both channels or only present in one? 2. Can you make the noise different (better, worse, different) by banging the chassis or tapping boards or components? If so, look for loose connections, solder joints or broken compoenents. 3. Is the noise immediately audible on startup and doesn't change with time? Is the noise absent on first startup and then slowly starts to increase (over a few seconds or many minutes)? If so, look for something that's temperature dependent, like a leaky transistor or capacitor or even a connection that might be loose and heat-sensitive. Get a can of circuit cooler spray and spray individual components until the noise goes away for a little bit. 4. Try wiggling wires and connections. Does the noise change, get better or worse? If so, you have a loose connection. Tighten everything down, clean connectors, etc. This kind of step-buy-step diagnosis can very quickly isolate the problem down to an individual component or components. At that point, a schematic may be a luxury rather than a necessity. -- +--------------------------------+ + Dick Pierce | + Professional Audio Development | +--------------------------------+ |
#7
Posted to rec.audio.high-end
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Adcom 535 acting up
"jamesgangnc" wrote in message
My scope shows a noticable sawtooth at 60hz on the power supply output. I've got a scope with 1 mv sensitivity. Negligable amounts of noise on filter caps is "noticable". Got a number? Power amp output stages generally have 100 dB power supply noise rejection at low frequencies. *Some* hum and noise on the main filter caps is normal. You could have a broken/cold solder joint in the grounding system of the amp. If there are two independent amps, they don't have a lot in common. But, a chassis ground might be one of them. |
#8
Posted to rec.audio.high-end
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Adcom 535 acting up
On Jul 24, 9:35*am, "Arny Krueger" wrote:
"jamesgangnc" wrote in message My scope shows a noticable sawtooth at 60hz on the power supply output. I've got a scope with 1 mv sensitivity. Negligable amounts of noise on filter caps is "noticable". Got a number? Power amp output stages generally have 100 dB power supply noise rejection at low frequencies. *Some* hum and noise on the main filter caps is normal. You could have a broken/cold solder joint in the grounding system of the amp. *If there are two independent amps, they don't have a lot in common. But, a chassis ground might be one of them. Lots of good comments, thanks guys. I'll take another look at the saw tooth on the power lines. I did not take the time to figure out it's exact amplitude or frequency. I just noted that my scope settings were in the range to suggest it was low frequency and not just a few millivolts. It was a quick check before I left for work. I just hooked the scope leads up to one of the power out lines and turned it on. My reporting it was 60hz was jumping to a conclusion. My bad. I see nothing that looks like any sort of regulation in this amp. There are a few extra discretes atrtached to the heat sinks on the sides so it's possible that there is some sort of regulation directly on the amp boards. Might be that the preamps are supplied with regulated power while the output transistors are unregulated. I think I might have seen that sort of setup on other adcom circuits. This model is about as close to two completely independent amps as you could get. The power supply is on one board at the middle rear of the chassis but it is two power supplies. There are two power transformers connected to it with everthing duplicated on the two sides of the board. The amp boards are on each side of the chassis and are also practically mirrors of each other. The scratchy noise is on both channels but it is not identical. Given that there is hardly any common components makes it a bit strange. There are a number of wire wraps on the pwer supply. I have encountered age related issues with wire wraps in other amps. (I have a sx-1250 that had a low output problem on one channel that was fixed by simply soldering the wire wraps. That amp has the output transistors connected to the main board with wire wraps.) This adcom does not have any wire wraps in the output circuitry but there are some on the power supply board. And a few on indicator leds. No hard in soldering those. I think the next step for me is to check the rectifier bridges for shorts. Replace the filter caps since they are 20 years old anyway. Solder all the wire wraps. And then see where I stand. If I still have a problem I will try messing around with some of the components on the amp boards to see if that has an impact. The unit does share a common ground throughout and one side of each output channel is at ground. I have not checked to see if one side of the input is ground but expect it is. The power cord does not connect to the mains ground. There definitely could be something to the ground issue idea. |
#9
Posted to rec.audio.high-end
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Adcom 535 acting up
jamesgangnc wrote:
I see nothing that looks like any sort of regulation in this amp. If you're saying this because of the phrase "power supply relection," it's not the same thing as "power supply regulation." Most modern amplifiers have the ability to isolate the output signal from variations and noise on the power supply as an intrinsic property of the amplifier. There are a few extra discretes atrtached to the heat sinks on the sides so it's possible that there is some sort of regulation directly on the amp boards. Nope, likely not relevant even if they were there. Might be that the preamps are supplied with regulated power while the output transistors are unregulated. Again, not relevant to power supply rejection nor, I suspect, to your problem. The scratchy noise is on both channels but it is not identical. Given that there is hardly any common components makes it a bit strange. There are a number of wire wraps on the pwer supply. I think the fact that the noise is not identical eliminates the power supply as a prime suspect. I have encountered age related issues with wire wraps in other amps. (I have a sx-1250 that had a low output problem on one channel that was fixed by simply soldering the wire wraps. That amp has the output transistors connected to the main board with wire wraps.) This adcom does not have any wire wraps in the output circuitry but there are some on the power supply board. And a few on indicator leds. No hard in soldering those. I think the next step for me is to check the rectifier bridges for shorts. Why do you suspect shorts in the bridge? Shorts would lead to, among otherb things, overheating of the filter caps at a minimum. Do you have that symptom? Replace the filter caps since they are 20 years old anyway. I wouldn't unless I knew they were bad. DOing so might fix the problem, but not necessarily because the caps were bad, but becase a connection was bad. Solder all the wire wraps. I wouldn't touch them unless I KNEW they were bad. And mechanically flezing the wires and see what happens to the noise would tell you that. And then see where I stand. If I still have a problem I will try messing around with some of the components on the amp boards to see if that has an impact. I suggested a dignostic method that is cheap, easy and could well elinminate all sorts of dead ends. Try it. But I would not haul out the soldering iron unless I had a component holding a smoking gun. The unit does share a common ground throughout and one side of each output channel is at ground. I have not checked to see if one side of the input is ground but expect it is. The power cord does not connect to the mains ground. There definitely could be something to the ground issue idea. Uh, that's a SAFETY issue, not a noise issue. -- +--------------------------------+ + Dick Pierce | + Professional Audio Development | +--------------------------------+ |
#10
Posted to rec.audio.high-end
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Adcom 535 acting up
Sonnova wrote:
OTOH, the sawtooth looks like it could be a rectifier bridge with one diode gone bad. Usually, bad filters just exhibit high amplitude sinosoidal ripple on them, not sawtooth waves which usually indicate extreme differentiation. The .22 ufd caps are there for high-frequency bypass if they are across the filter caps. If they leak, I wouldn't expect to see any noticeable performance problems. If they short, you'd get the capacitor-as-fuse effect and there would be physical signs of damage. Small caps like that (especially if they use a plastic film as the dielectric) don't usually go bad over time, so unless you have some real reason to suspect them, I would ignore those. Any unregulated power supply, or regulated one before the regulator, will have a sawtooth waveform. The filter caps charge up through a fairly low impedance (the diodes) and then discharge through a higher one (the actual amplifier circuit). DEAD as opposed to poor filter caps result in simple rectified sine waves. Since you've got a scope, use it aggressively. Those things can make the blind see. Doug McDonald |
#11
Posted to rec.audio.high-end
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Adcom 535 acting up
"jamesgangnc" wrote in message
I see nothing that looks like any sort of regulation in this amp. That is typical. The scratchy noise is on both channels but it is not identical. Given that there is hardly any common components makes it a bit strange. There are a number of wire wraps on the pwer supply. I have encountered age related issues with wire wraps in other amps. (I have a sx-1250 that had a low output problem on one channel that was fixed by simply soldering the wire wraps. That amp has the output transistors connected to the main board with wire wraps.) This adcom does not have any wire wraps in the output circuitry but there are some on the power supply board. And a few on indicator leds. No hard in soldering those. Go for it! I think the next step for me is to check the rectifier bridges for shorts. Unlikely, as shorted power supply diodes always blow fuses and the like. Open diodes is more likely. Replace the filter caps since they are 20 years old anyway. Don't jump to conclusions. Solder all the wire wraps. Agreed. The unit does share a common ground throughout and one side of each output channel is at ground. I have not checked to see if one side of the input is ground but expect it is. There might be some low value resistors in that path, or the path may be through one circuit board. The power cord does not connect to the mains ground. Normal. There definitely could be something to the ground issue idea. Please keep us informed! |
#12
Posted to rec.audio.high-end
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Adcom 535 acting up
On Fri, 24 Jul 2009 17:26:57 -0700, Arny Krueger wrote
(in article ): "jamesgangnc" wrote in message I see nothing that looks like any sort of regulation in this amp. That is typical. The scratchy noise is on both channels but it is not identical. Given that there is hardly any common components makes it a bit strange. There are a number of wire wraps on the pwer supply. I have encountered age related issues with wire wraps in other amps. (I have a sx-1250 that had a low output problem on one channel that was fixed by simply soldering the wire wraps. That amp has the output transistors connected to the main board with wire wraps.) This adcom does not have any wire wraps in the output circuitry but there are some on the power supply board. And a few on indicator leds. No hard in soldering those. Go for it! I think the next step for me is to check the rectifier bridges for shorts. Unlikely, as shorted power supply diodes always blow fuses and the like. Open diodes is more likely. Yep. Replace the filter caps since they are 20 years old anyway. Don't jump to conclusions. Yes. If the ripple is just a few millivolts, the problem is unlikely to be the filter caps. Besides modern electrolytic caps don't really go bad like the old ones from the 50's and 60's used to do. I don't mean to to infer that they NEVER fail, but it's much more rare than it it used to be. And if the caps aren't bad, you'd gain nothing by increasing their value. Solder all the wire wraps. Agreed. The unit does share a common ground throughout and one side of each output channel is at ground. I have not checked to see if one side of the input is ground but expect it is. There might be some low value resistors in that path, or the path may be through one circuit board. That's usual in so-called dual-mono designs. One channel is grounded directly and the other through a 1 to 5 Ohm resistor, The power cord does not connect to the mains ground. Normal. There definitely could be something to the ground issue idea. Please keep us informed! |
#13
Posted to rec.audio.high-end
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Adcom 535 acting up
"Sonnova" wrote in message
Replace the filter caps since they are 20 years old anyway. Don't jump to conclusions. Yes. If the ripple is just a few millivolts, the problem is unlikely to be the filter caps. Besides modern electrolytic caps don't really go bad like the old ones from the 50's and 60's used to do. I don't mean to to infer that they NEVER fail, but it's much more rare than it it used to be. And if the caps aren't bad, you'd gain nothing by increasing their value. Actually, something like a volt of ripple on the filter caps can be OK. Under heavy load it may increase to several volts. Mr. Pierce's comments about the power supply noise rejection of power amps is correct and relevant. |
#14
Posted to rec.audio.high-end
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Adcom 535 acting up
On Sun, 26 Jul 2009 11:06:04 -0700, Arny Krueger wrote
(in article ): "Sonnova" wrote in message Replace the filter caps since they are 20 years old anyway. Don't jump to conclusions. Yes. If the ripple is just a few millivolts, the problem is unlikely to be the filter caps. Besides modern electrolytic caps don't really go bad like the old ones from the 50's and 60's used to do. I don't mean to to infer that they NEVER fail, but it's much more rare than it it used to be. And if the caps aren't bad, you'd gain nothing by increasing their value. Actually, something like a volt of ripple on the filter caps can be OK. Under heavy load it may increase to several volts. Yes, but I was just repeating what the OP said. He's the one who mentioned that the sawtooth he saw was but "a few millivolts". Mr. Pierce's comments about the power supply noise rejection of power amps is correct and relevant. Yep. |
#15
Posted to rec.audio.high-end
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Adcom 535 acting up
On Jul 26, 5:40*pm, Sonnova wrote:
On Sun, 26 Jul 2009 11:06:04 -0700, Arny Krueger wrote (in article ): "Sonnova" wrote in message Replace the filter caps since they are 20 years old anyway. Don't jump to conclusions. Yes. If the ripple is just a few millivolts, the problem is unlikely to be the filter caps. Besides modern electrolytic caps don't really go bad like the old ones from the 50's and 60's used to do. I don't mean to to infer that they NEVER fail, but it's much more rare than it it used to be. And if the caps aren't bad, you'd gain nothing by increasing their value. Actually, something like a volt of ripple on the filter caps can be OK. Under heavy load it may increase to several volts. Yes, but I was just repeating what the OP said. He's the one who mentioned that the sawtooth he saw was but "a few millivolts". Mr. Pierce's comments about the power supply noise rejection of power amps is correct and relevant. Yep.- Hide quoted text - - Show quoted text - Actually what I said was "not just a few millivolts". As it turns out it's about 2/10's of a volt in the ripple. Not a whole lot more than a few millivolts though. And it is 60hz. With it at idle current shouldn't the output be pretty close to flat? |
#16
Posted to rec.audio.high-end
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Adcom 535 acting up
jamesgangnc wrote:
Actually what I said was "not just a few millivolts". As it turns out it's about 2/10's of a volt in the ripple. Not a whole lot more than a few millivolts though. And it is 60hz. With it at idle current shouldn't the output be pretty close to flat? 0.2 volts is not a lot of ripple. And, no, at "idle current," it's still pulling a fair amount of current out of the power supply, possibly on the order of several hunddred milliamps, so, without real regulation, it's likely to exhibit the sawtooth waveform on the power supply as you describe. However, the 60 Hz frequency gives me pause: it would expect they are doing sull-wave rectificationm and if your report is accurate, then it suggests an imbalance of some sort on the power supply. Do all four supplies exhibit the same waveform? -- +--------------------------------+ + Dick Pierce | + Professional Audio Development | +--------------------------------+ |
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