[jamesgangnc[_3_]]

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?

[jamesgangnc[_3_]]

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?

[g]

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

[Sonnova]

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.......

[Sonnova]

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.

[Dick Pierce[_2_]]

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 |
+--------------------------------+

[Arny Krueger]

"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.

[jamesgangnc[_3_]]

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.

[Dick Pierce[_2_]]

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 |
+--------------------------------+

[mcdonaldREMOVE TO ACTUALLY REACH [email protected]]

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

[Arny Krueger]

"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!

[Sonnova]

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!

[Arny Krueger]

"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.

[Sonnova]

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.

[jamesgangnc[_3_]]

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?

[Dick Pierce[_2_]]

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 |
+--------------------------------+