Nelson Pass design Adcom GFA 5500 & 5800
Greg Brown
essentially the same except for power (200W@8ohms vs 250W). Has
anybody heard the gfa 5500 and would they say its similar to the 5800?
Does the 5500 have fans to cool the mosfets? (fans make some noise)
I think their other mosfet amps don't have many of the features of the
top 2, eg, 3 power transformers, 20 mosfets/chan, etc. but are an
improvement over bi-polars.
--
Internet: gbr...@va.med.umich.edu
Jim Miglino
I have not compared the two but I did audition the 5500 in my system.
It is a sweet amp. Very powerful and smooth. However it does not
have the front to back depth nor is it as detailed as the McCormick
dna .5 delux which I ended up purchasing. It was not at all like my
GFA-555 (1986 vintage), though. No hard highs in my system and much
more open.
Note there is a price difference but I think for $995 you can't beat
it.
My systems at the time
Denon DCD-2700
Conrad pv10a
B&W 804's
Tara prime cables.
Jim
Scythebill
speakers about 14 feet from my listening position and cannot hear the
fan(perhaps I'm a bit deaf). Anyway, it is not bothersome. I really
like the amp. It is a big improvement over their previous amps-much
smoother, fabulous dynamics and bass, marvelous sound stage(at least
in my system). My system: Thiel 3.6s, PAV preamp, AQ Quartz
interconnects, Cardas Quadlink speaker cable, Adcom 700 DAC, PD 65
transport, AA DTI pro 32.
nny...@ny.ubs.com
Posted for a friend:
I have been experiencing a maddening intermittent problem with a 5800.
The amp buzzes (not the fans). It doesn't come through the speakers
and it's not constant but it is loud. This is the third amp; Adcom
and Park Ave Audio very graciously took back the first two. They came
out and tested the line and could find nothing wrong with the line but
said that they think that there is some sort of harmonic distortion
affecting the transformer. Has anyone else experienced this?
wwr...@chmc.org
I have had similar results when plugging equipment into poor quality
electrical circuits. What I mean is something like old house wiring
etc. Usually it would happen with something that wanted to draw some
current, like your amplifier. Even if the circuits check out they
could be the problem. I put in dedicated circuits. The breakers and
outlets are still 15amp type but I used 10 gauge wire. This resolved
the problem for me. Try taking the amp to someone elses house,
preferably someone not on the same electrical transformer as you. If
you know anyone with a dedicated circuit that would be a good test.
It almost sounds like a power factor problem.
Dave Platt
>The amp buzzes (not the fans). It doesn't come through the speakers
>and it's not constant but it is loud. This is the third amp; Adcom
>and Park Ave Audio very graciously took back the first two. They came
>out and tested the line and could find nothing wrong with the line but
>said that they think that there is some sort of harmonic distortion
>affecting the transformer. Has anyone else experienced this?
Here's what I've heard (it may or may not be entirely accurate):
One thing which can cause power-amp transformer to buzz, is an
"unclean" powerline waveform. In particular, amps which use toroidal
power transformers can be particularly prone to buzzing if the
powerline waveform is nonsymmetrical. The asymmetry cause the
waveform to have a net DC component, this results in a net DC current
flow through the primary winding of the toroid, and the toroid core
saturates. Other types of transformer (the common EI-core with
laminated sections) don't saturate as easily when faced with a net DC
current flow, and aren't as prone to buzzing.
You can also get buzzing if there are abrupt changes in the powerline
voltage (i.e. if it isn't a clean sinewave, but instead changes voltage
abruptly).
The commonest reason for the powerline having a nonsymmetric or uneven
voltage waveform is that certain appliances may draw current from the
line in an asymmetrical or intermittent fashion.
The most common evildoers, in my experience, are triac-type light
dimmers. Triac circuits are used both in wall-mounted dimmer controls,
and in the built-in dimmers on many halogen light fixtures. When an
incandescent light is dimmed with a triac, the bulb doesn't draw any
current from the line during the initial part of the power waveform
(when the voltage is rising up from 0 volts). When the voltage reaches
a specific threshold, the triac switches on, and the bulb begins drawing
current (often an ampere or more) within a fraction of a millisecond.
The current being drawn by the bulb causes the voltage at the outlet to
drop slightly. This sudden decrease in voltage is "seen" by any other
component on the same circuit, and can result in a sudden change in the
current flowing through an amp's transformer - this can make the
transformer core move slightly, and creates a buzz.
"Bulb saver" diodes are another source of problems. These are sometimes
installed in light sockets to increase the lifetime of the bulbs - they
act as half-wave rectifiers, reducing the total voltage applied to the
bulb filament, dimming the bulb, and greatly increasing its life. They
cause problems because each bulb so equipped draws current during only
half of the powerline waveform - this introduces harmonic distortion
onto the power line, and can lead to an asymmetrical voltage as seen by
other appliances on the circuit, and thus leads to transformer core
saturation and buzzing.
Certain other appliances or audio components may draw power from the
line in an ill-behaved fashion, and cause transformer buzzing. They
don't have to be in the same room, or even in the same house - in
principle, they could be anywhere on the same secondary circuit (that
is, hooked up to the same power-pole transformer) and still affect
your amplifier.
Remedies: if possible, find the appliance or light which is drawing
current in an evil fashion, and either turn it off, get rid of it, or
repair it. If a cheap triac light dimmer is causing the problem,
don't use it to dim the lights when you're listening to the stereo.
Or, replace it with a higher-quality triac dimmer (the good ones have
inductive "chokes" which limit the sudden current surge which occurs
120 times a second, thus reducing radio-frequency interference and
perhaps reducing transformer buzzing). An even better solution is to
remove the triac dimmer, and replace it with a Variac dimmer (a
variable transformer) - these are more expensive, but don't generate
the sudden current spikes (and don't make the lightbulb filaments
"sing" the way a triac dimmer does).
If you've got lightbulb-life-extending diode disks in your lights, get
rid of them (they're actually a money-loser in the long run - you'll
save money on lightbulbs, but spend far more on additional electricity
to make up for the reduced efficiency of bulbs run at below-normal
voltage).
Last-ditch solutions may include running a dedicated 20-amp circuit
for your stereo, or installing a large isolation transformer between
the wall outlet and your amp. Both of these are expensive remedies.
--
Dave Platt dpl...@3do.com
USNAIL: The 3DO Company, Systems Software group
600 Galveston Drive
Redwood City, CA 94063
Richard Bass
> I have been experiencing a maddening intermittent problem with a
> 5800. The amp buzzes (not the fans). It doesn't come through the
> speakers and it's not constant but it is loud. This is the third
> amp; Adcom and Park Ave Audio very graciously took back the first
> two. They came out and tested the line and could find nothing wrong
> with the line but said that they think that there is some sort of
> harmonic distortion affecting the transformer. Has anyone else
> experienced this?
Sorry to hear that someone else is having the problem with the
GFA-5800 that I have had. I called Adcom when I got mine and was
given the brush off. I found that if I removed all of the halogen and
flourescent bulbs in the house the problem went away. None of my
other amplifiers exhibit the hum when installed in my system. I feel
that an amplifier should be able to perform properly in an average
home environment. The GFA-5800 definitly has a design or part
problem. The halogen and flourescent bulbs have been reinstalled and
the GFA-5800 is now idle on a shelf. I might add that I was contacted
by Adcom recently regarding the a potential fire hazard in my GFA-6000
amplifier. When I returned this amplifier to them I mentioned the
problem with the GFA-5800 and was again given the brush off. This
frustrated me and I sent several e-mails regarding the GFA-5800. They
finally responded and stated that they would accept the GFA-5800 if I
wished to return it. I have not done so because, as a matter of
principle, I feel they should to pay shipping for a unit that in my
estimation was defective from day one. I might add that the GFA-5800
is not the best sounding amplifier that I have (understatement). This
comment comes from a person that believes he cannot usually hear much
difference in amplifiers.
Dick Bass
Richard Bass
> Posted for a friend:
>
> I have been experiencing a maddening intermittent problem with a 5800.
> The amp buzzes (not the fans). It doesn't come through the speakers
> and it's not constant but it is loud. This is the third amp; Adcom
> and Park Ave Audio very graciously took back the first two. They came
> out and tested the line and could find nothing wrong with the line but
> said that they think that there is some sort of harmonic distortion
> affecting the transformer. Has anyone else experienced this?
Sorry to hear that someone else has experienced the same problem as I
had with the GFA-5800. When I first received my unit I call Adsom and
was given the brush off. Later I found that removing all of the
halogen and flourscent bulbs in the house caused the problem to
disappear. I have tried other amplifiers on the same AC circuit and
they did not exhibit the problem. I put the bulbs back in and the
GFA-5800 on the shelf. The sound of this amplifier was not up to par.
This is an understatement that is coming from a person who does
believe there much difference in the sound of amplifiers. Last month
Adcom recalled the GFA-6000 amplifier that I had due to potential fire
hazard. When I contacted them about this amp, I mentioned the toroid
hum problem the GFA-5800 and was again brushed off. I sent several
emails to Adcom and they agreed to look at the GFA-5800 if I would
send it in. I have not done so because, as a matter of principle, I
do not believe that I should incur shipping expense for an amplifier
that either has as a design flaw or was defective from the time I
received it. An amplifier, in my opinion, should be useable in an
average home enviromnment.
Dick Bass
wwr...@chmc.org
> Sorry to hear that someone else is having the problem with the
> GFA-5800 that I have had. I called Adcom when I got mine and was
> given the brush off. I found that if I removed all of the halogen and
> flourescent bulbs in the house the problem went away. None of my
> other amplifiers exhibit the hum when installed in my system. I feel
> that an amplifier should be able to perform properly in an average
> home environment. The GFA-5800 definitly has a design or part
> problem.
Someone in this thread mentioned that the 5800 uses a torroidal
transformer. It is my understanding that these transformers are
popular because stray field emmisions are greatly reduced. However,
one thing they are not good at is rejecting line noise. They will
pass any noise right through the power supply. Regular transformers
are much better in this regard. I wonder if a transformer
substitution might solve this particular problem??
nny...@ny.ubs.com
>nny...@ny.ubs.com writes:
>> I have been experiencing a maddening intermittent problem with a 5800.
>> The amp buzzes (not the fans).<stuff deleted>
>It almost sounds like a power factor problem.
I'm pretty sure that is the power; the amp checked out fine at Adcom
and at Park Ave. What is a "power factor" problem?
Adam Bernardi
> I have been experiencing a maddening intermittent problem with a 5800.
> The amp buzzes (not the fans). It doesn't come through the speakers
> and it's not constant but it is loud. This is the third amp; Adcom
> and Park Ave Audio very graciously took back the first two. They came
> out and tested the line and could find nothing wrong with the line but
> said that they think that there is some sort of harmonic distortion
> affecting the transformer. Has anyone else experienced this?
That's interesting, I have an Adcom GSP-560, their Dolby decoder/amp.
When I first got it about two years ago, it buzzed like crazy. After
a few months it went away. Either that or it burned those frequencies
out of my eardrums!
dave marceau
:> nny...@ny.ubs.com writes:
:>> I have been experiencing a maddening intermittent problem with a 5800.
:>> The amp buzzes (not the fans).<stuff deleted>
: >It almost sounds like a power factor problem.
it sounds like the potting in the transformer may be shot. i recently
bought a used forte 3 which has a similar buzz. i took the cover off
to reset the bias current and realized it was a physical buzz from the
transformer. i haven't decided whether to repot the transformer or buy
a new lower voltage transformer and change it to a model four. it has,
however, abated to some extent as i've used the amp.
regards,
dave
Richard Bass
> wwr...@chmc.org wrote:
>> nny...@ny.ubs.com writes:
>>> I have been experiencing a maddening intermittent problem with a
>>> 5800. The amp buzzes (not the fans).<stuff deleted>
>>It almost sounds like a power factor problem.
> I'm pretty sure that is the power; the amp checked out fine at Adcom
> and at Park Ave. What is a "power factor" problem?
I have had the same problem with the GFA-5800. The transformer has a
mechanical hum that seems to be excited by slight noise on the AC
line. The problem may be that the windings on the toroid are not
secure. As I stated in a previous post, removal of halogen and
flourescent bulbs in my house eliminated the problem. Also, no other
amplifier on the same AC circuit has ever exhibited the problem,
including those with toroid transformers. I never returned mine to
Adcom partly because they never gave me any satisfaction that they
could solve the problem. It comes as no surprise the amplifier
checked out fine at your dealer and at Adcom if they did not replicate
the noise on the AC line. An amplifier, in my opinion, should be able
to perform quietly even with some noise on an AC line. All AC lines
have noise and the manufacturer of the amplifier should design the
amplifier to operate quietly when used with normal household
appliances and lights. Again, the only amplifier I have ever had this
problem with is the 5800. I don't know what a "power factor" is.
Perhaps someone could enlighten both of us on what this kind of
problem is and why it causes hum in toroid transformers.
Dick Bass
k...@interport.net
>I have had the same problem with the GFA-5800. The transformer has a
>mechanical hum that seems to be excited by slight noise on the AC
>line. The problem may be that the windings on the toroid are not
>secure. As I stated in a previous post, removal of halogen and
>flourescent bulbs in my house eliminated the problem. Also, no other
>amplifier on the same AC circuit has ever exhibited the problem,
>including those with toroid transformers. I never returned mine to
>Adcom partly because they never gave me any satisfaction that they
>could solve the problem. It comes as no surprise the amplifier
>checked out fine at your dealer and at Adcom if they did not replicate
>the noise on the AC line. An amplifier, in my opinion, should be able
>to perform quietly even with some noise on an AC line. All AC lines
>have noise and the manufacturer of the amplifier should design the
>amplifier to operate quietly when used with normal household
>appliances and lights. Again, the only amplifier I have ever had this
>problem with is the 5800.
A friend of mine just picked up the 5800. Though the fan noise was a
bit of a surprise at first, he has experienced no transformer hum
whatsover. I know that his AC line is NOT dedicated and knowing
LILCO's reputation for "dirty power", I'm fairly certain that his
lines are afflicted with noise as well. Your speculation about power
line noise may still me correct as he is using the ACE-515 line
conditioner. Maybe that's the difference...maybe not. You might want
to get your dealer to lend you one or try another brand like the
Chang, Power Wedge or Tice (lots more money for the latter 3). BTW,
the fan noise is inaudible with music playing, even at fairly low
volume.
Good luck.
Ken
nny...@ny.ubs.com
> I have been experiencing a maddening intermittent problem with a
> 5800. The amp buzzes (not the fans).<stuff deleted>
The culprit has been discovered. It was the humidifier! It seems this
amp is sensitive to noise that the humidifier creates on the ac line.
Turn off the humidifier and the buzz is gone. Thanks for everyone's
input.
James