Re: Arcam Alpha 3 Alpha3 Distortion Problem

[Norbert Hahn]

"Uwe Surojegin" > wrote:

>Hello Folks,
>I'm servicing an Acram Alpha 3 amplifier. The amp gives clear and nice sound
>up to a volume of around 11 o'clock on the volume potentiometer. Above 12
>o'clock the amplifier gives a "bad" distortion on both channels.
>Has anyone an idea what that that could be?

The problem could be caused by oscillation. Have you checked the
amp with a o'scope?

Norbert

[Uwe Surojegin]

Hi again,
I have not checked the amp with a scope - I dont have one. But, in general
.... it could well be that the amp is going into clipping already. I'm not
very familiar with the Alpha 3 model. Maybe someone could give me input
about his experience(s) with the Alpha 3 model. Would appreciate it.
P.S. I'm running the amp into an 8 Ohm speaker system. So the impedance
could not be the reason.

Rgds
Uwe

"Norbert Hahn" > schrieb im Newsbeitrag
...
> "Uwe Surojegin" > wrote:
>
> >Hello Folks,
> >I'm servicing an Acram Alpha 3 amplifier. The amp gives clear and nice
sound
> >up to a volume of around 11 o'clock on the volume potentiometer. Above 12
> >o'clock the amplifier gives a "bad" distortion on both channels.
> >Has anyone an idea what that that could be?
>
> The problem could be caused by oscillation. Have you checked the
> amp with a o'scope?
>
> Norbert
>

[Tim Schwartz]

Uwe,
You should be able to get specs at Arcam's website, www.arcam.co.uk.

Regards,
Tim Schwartz
Bristol Electronics


Uwe Surojegin wrote:
>
> Hi again,
> I have not checked the amp with a scope - I dont have one. But, in general
> ... it could well be that the amp is going into clipping already. I'm not
> very familiar with the Alpha 3 model. Maybe someone could give me input
> about his experience(s) with the Alpha 3 model. Would appreciate it.
> P.S. I'm running the amp into an 8 Ohm speaker system. So the impedance
> could not be the reason.
>
> Rgds
> Uwe
>
> "Norbert Hahn" > schrieb im Newsbeitrag
> ...
> > "Uwe Surojegin" > wrote:
> >
> > >Hello Folks,
> > >I'm servicing an Acram Alpha 3 amplifier. The amp gives clear and nice
> sound
> > >up to a volume of around 11 o'clock on the volume potentiometer. Above 12
> > >o'clock the amplifier gives a "bad" distortion on both channels.
> > >Has anyone an idea what that that could be?
> >
> > The problem could be caused by oscillation. Have you checked the
> > amp with a o'scope?
> >
> > Norbert
> >

[John Dawson]

Hi there Uwe,

The amplifier's volume control feeds the power amps directly if you
use the direct switch. At full volume setting it will only take about
300 millivolts to clip the amplifier, so it looks to me like your
source voltage is higher than that (a CD player perhaps, which can
deliver 2 volts at full output?). So my best guess is that Tim is
correct and there is nothing wrong with the amplifier. Send me your
fax number and I'll have someone fax over the circuit if you are still
stuck.

John Dawson (Arcam)

Tim Schwartz > wrote in message >...
> Uwe,
> You should be able to get specs at Arcam's website, www.arcam.co.uk.
>
> Regards,
> Tim Schwartz
> Bristol Electronics
>
>
> Uwe Surojegin wrote:
> >
> > Hi again,
> > I have not checked the amp with a scope - I dont have one. But, in general
> > ... it could well be that the amp is going into clipping already. I'm not
> > very familiar with the Alpha 3 model. Maybe someone could give me input
> > about his experience(s) with the Alpha 3 model. Would appreciate it.
> > P.S. I'm running the amp into an 8 Ohm speaker system. So the impedance
> > could not be the reason.
> >
> > Rgds
> > Uwe
> >
> > "Norbert Hahn" > schrieb im Newsbeitrag
> > ...
> > > "Uwe Surojegin" > wrote:
> > >
> > > >Hello Folks,
> > > >I'm servicing an Acram Alpha 3 amplifier. The amp gives clear and nice
> sound
> > > >up to a volume of around 11 o'clock on the volume potentiometer. Above 12
> > > >o'clock the amplifier gives a "bad" distortion on both channels.
> > > >Has anyone an idea what that that could be?
> > >
> > > The problem could be caused by oscillation. Have you checked the
> > > amp with a o'scope?
> > >
> > > Norbert
> > >

[Uwe Surojegin]

Hi there John,
first of all: Many thanks for all the input and help. Second: My fax number
is: +49-7541-26060
I checked my CD player output: Very low voltage, not nearly close to 300 mV.
Of course, I had to replace the volume poti (was broken, originally I guess
20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this could
certainly not be the case. Other parts have been checked already ... but
still not really satisfied. Other high-end freaks which are familiar with
this unit tell me that the clipping would be tolerated around 2 o'clock -
but not before. So, I'm still trying to double-check my circuit etc and the
AC - DC sources, diodes and capacitors. I'll keep you posted.

Uwe

"John Dawson" > schrieb im Newsbeitrag
om...
> Hi there Uwe,
>
> The amplifier's volume control feeds the power amps directly if you
> use the direct switch. At full volume setting it will only take about
> 300 millivolts to clip the amplifier, so it looks to me like your
> source voltage is higher than that (a CD player perhaps, which can
> deliver 2 volts at full output?). So my best guess is that Tim is
> correct and there is nothing wrong with the amplifier. Send me your
> fax number and I'll have someone fax over the circuit if you are still
> stuck.
>
> John Dawson (Arcam)
>
> Tim Schwartz > wrote in message
>...
> > Uwe,
> > You should be able to get specs at Arcam's website, www.arcam.co.uk.
> >
> > Regards,
> > Tim Schwartz
> > Bristol Electronics
> >
> >
> > Uwe Surojegin wrote:
> > >
> > > Hi again,
> > > I have not checked the amp with a scope - I dont have one. But, in
general
> > > ... it could well be that the amp is going into clipping already. I'm
not
> > > very familiar with the Alpha 3 model. Maybe someone could give me
input
> > > about his experience(s) with the Alpha 3 model. Would appreciate it.
> > > P.S. I'm running the amp into an 8 Ohm speaker system. So the
impedance
> > > could not be the reason.
> > >
> > > Rgds
> > > Uwe
> > >
> > > "Norbert Hahn" > schrieb im Newsbeitrag
> > > ...
> > > > "Uwe Surojegin" > wrote:
> > > >
> > > > >Hello Folks,
> > > > >I'm servicing an Acram Alpha 3 amplifier. The amp gives clear and
nice
> > sound
> > > > >up to a volume of around 11 o'clock on the volume potentiometer.
Above 12
> > > > >o'clock the amplifier gives a "bad" distortion on both channels.
> > > > >Has anyone an idea what that that could be?
> > > >
> > > > The problem could be caused by oscillation. Have you checked the
> > > > amp with a o'scope?
> > > >
> > > > Norbert
> > > >

[Norbert Hahn]

"Uwe Surojegin" > wrote:

>I checked my CD player output: Very low voltage, not nearly close to 300 mV.

Only a very few CD players have such low output voltage, unless they
have a volume control.

>Of course, I had to replace the volume poti (was broken, originally I guess
>20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this could
>certainly not be the case.

The volume control of my amp is located in the feed back loop, thus
its value is important. Replacing a 20 kOhm potentiometer with a
50 kOhm type would influence stability.

But I don't know your amp so it can be a different problem. OTOH you may
simple connect a resistor in parallel to the volume pot (47 kOhm are a
good start) and check if the distortion/oscillations are gone.

HTH
Norbert

[Uwe Surojegin]

Hi Norbert,
I connected already a 33K Ohm resistor parallel to the poti. I'll keep you
posted ... next steps are with oszilloscope to check the AC and DC voltage
from the transformer and so on....

Uwe


"Norbert Hahn" > schrieb im Newsbeitrag
...
> "Uwe Surojegin" > wrote:
>
> >I checked my CD player output: Very low voltage, not nearly close to 300
mV.
>
> Only a very few CD players have such low output voltage, unless they
> have a volume control.
>
> >Of course, I had to replace the volume poti (was broken, originally I
guess
> >20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this could
> >certainly not be the case.
>
> The volume control of my amp is located in the feed back loop, thus
> its value is important. Replacing a 20 kOhm potentiometer with a
> 50 kOhm type would influence stability.
>
> But I don't know your amp so it can be a different problem. OTOH you may
> simple connect a resistor in parallel to the volume pot (47 kOhm are a
> good start) and check if the distortion/oscillations are gone.
>
> HTH
> Norbert
>

[Uwe Surojegin]

Hi John, Hi all,
many thanks for all your input. Specially to John from Arcam who faxed me
the circuit diagram!!! If this amp is not going to work any more ... I
probably consider another ARCAM because of the excellent support !!!
First of all: The 12 o'clock clipping would not worry me if the output would
be adequate at 11. It's somehow not very loud.
FYI: I replaced the 50K Ohm volume potentiometer with an 20K Ohm. No
improvement. The CD player output I checked again: Its acutally close to 2,5
V !!! So that could be a reason. I double-checked with a scope and a 50Hz
squared input signal, 3V. Going close to 12 ... the reading at the CD
chinch input ! already showed clipping with the scope !!! Strange!!! And
actually all the way through the amp section. Next steps I will do is
checking on the capacitors etc. If this aint gonna help ... -> bonfire :)
I'll keep you posted.

Uwe

"Uwe Surojegin" > schrieb im Newsbeitrag
...
> Hi Norbert,
> I connected already a 33K Ohm resistor parallel to the poti. I'll keep you
> posted ... next steps are with oszilloscope to check the AC and DC voltage
> from the transformer and so on....
>
> Uwe
>
>
> "Norbert Hahn" > schrieb im Newsbeitrag
> ...
> > "Uwe Surojegin" > wrote:
> >
> > >I checked my CD player output: Very low voltage, not nearly close to
300
> mV.
> >
> > Only a very few CD players have such low output voltage, unless they
> > have a volume control.
> >
> > >Of course, I had to replace the volume poti (was broken, originally I
> guess
> > >20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this
could
> > >certainly not be the case.
> >
> > The volume control of my amp is located in the feed back loop, thus
> > its value is important. Replacing a 20 kOhm potentiometer with a
> > 50 kOhm type would influence stability.
> >
> > But I don't know your amp so it can be a different problem. OTOH you may
> > simple connect a resistor in parallel to the volume pot (47 kOhm are a
> > good start) and check if the distortion/oscillations are gone.
> >
> > HTH
> > Norbert
> >
>
>

[Tim Schwartz]

Uwe,

Have you measured the output power into 8 ohm loads? This will tell you
if there is any fault in the amp. As I said earlier, this is a low power
amp, and you might be asking too much of it. If it is delivering rated
power at clipping, you need to expect less volume or get a more powerful
amp.

Regards,
Tim Schwartz
Bristol Electronics

Uwe Surojegin wrote:
>
> Hi John, Hi all,
> many thanks for all your input. Specially to John from Arcam who faxed me
> the circuit diagram!!! If this amp is not going to work any more ... I
> probably consider another ARCAM because of the excellent support !!!
> First of all: The 12 o'clock clipping would not worry me if the output would
> be adequate at 11. It's somehow not very loud.
> FYI: I replaced the 50K Ohm volume potentiometer with an 20K Ohm. No
> improvement. The CD player output I checked again: Its acutally close to 2,5
> V !!! So that could be a reason. I double-checked with a scope and a 50Hz
> squared input signal, 3V. Going close to 12 ... the reading at the CD
> chinch input ! already showed clipping with the scope !!! Strange!!! And
> actually all the way through the amp section. Next steps I will do is
> checking on the capacitors etc. If this aint gonna help ... -> bonfire :)
> I'll keep you posted.
>
> Uwe
>
> "Uwe Surojegin" > schrieb im Newsbeitrag
> ...
> > Hi Norbert,
> > I connected already a 33K Ohm resistor parallel to the poti. I'll keep you
> > posted ... next steps are with oszilloscope to check the AC and DC voltage
> > from the transformer and so on....
> >
> > Uwe
> >
> >
> > "Norbert Hahn" > schrieb im Newsbeitrag
> > ...
> > > "Uwe Surojegin" > wrote:
> > >
> > > >I checked my CD player output: Very low voltage, not nearly close to
> 300
> > mV.
> > >
> > > Only a very few CD players have such low output voltage, unless they
> > > have a volume control.
> > >
> > > >Of course, I had to replace the volume poti (was broken, originally I
> > guess
> > > >20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this
> could
> > > >certainly not be the case.
> > >
> > > The volume control of my amp is located in the feed back loop, thus
> > > its value is important. Replacing a 20 kOhm potentiometer with a
> > > 50 kOhm type would influence stability.
> > >
> > > But I don't know your amp so it can be a different problem. OTOH you may
> > > simple connect a resistor in parallel to the volume pot (47 kOhm are a
> > > good start) and check if the distortion/oscillations are gone.
> > >
> > > HTH
> > > Norbert
> > >
> >
> >

[Uwe Surojegin]

Hi Tim,
many thx for your input. You're absolute right. I'm probably asking too much
:)
I connected a Denon CD player with variable output (0 - 2V) and somehow the
problem was nearly solved. The other thing I did, I kicked out the 50K Ohm
volume poti and replaced it with a 22K (original 20K). That already helped.
Next steps are an Alps 20K Ohm volume poti to have the original setup. I
looked like that the 50K poti influenced the "seperator capacitor" to the
power amp :(
Right now, I'm satisfied so far ... although that the Alpha 3 is a little
bit weak :)
Best wishes and many thx again from Germany to England !!! Great support
folks.
Regards Uwe
"Tim Schwartz" > schrieb im Newsbeitrag
...
> Uwe,
>
> Have you measured the output power into 8 ohm loads? This will tell you
> if there is any fault in the amp. As I said earlier, this is a low power
> amp, and you might be asking too much of it. If it is delivering rated
> power at clipping, you need to expect less volume or get a more powerful
> amp.
>
> Regards,
> Tim Schwartz
> Bristol Electronics
>
> Uwe Surojegin wrote:
> >
> > Hi John, Hi all,
> > many thanks for all your input. Specially to John from Arcam who faxed
me
> > the circuit diagram!!! If this amp is not going to work any more ... I
> > probably consider another ARCAM because of the excellent support !!!
> > First of all: The 12 o'clock clipping would not worry me if the output
would
> > be adequate at 11. It's somehow not very loud.
> > FYI: I replaced the 50K Ohm volume potentiometer with an 20K Ohm. No
> > improvement. The CD player output I checked again: Its acutally close to
2,5
> > V !!! So that could be a reason. I double-checked with a scope and a
50Hz
> > squared input signal, 3V. Going close to 12 ... the reading at the CD
> > chinch input ! already showed clipping with the scope !!! Strange!!! And
> > actually all the way through the amp section. Next steps I will do is
> > checking on the capacitors etc. If this aint gonna help ... -> bonfire
:)
> > I'll keep you posted.
> >
> > Uwe
> >
> > "Uwe Surojegin" > schrieb im Newsbeitrag
> > ...
> > > Hi Norbert,
> > > I connected already a 33K Ohm resistor parallel to the poti. I'll keep
you
> > > posted ... next steps are with oszilloscope to check the AC and DC
voltage
> > > from the transformer and so on....
> > >
> > > Uwe
> > >
> > >
> > > "Norbert Hahn" > schrieb im Newsbeitrag
> > > ...
> > > > "Uwe Surojegin" > wrote:
> > > >
> > > > >I checked my CD player output: Very low voltage, not nearly close
to
> > 300
> > > mV.
> > > >
> > > > Only a very few CD players have such low output voltage, unless they
> > > > have a volume control.
> > > >
> > > > >Of course, I had to replace the volume poti (was broken, originally
I
> > > guess
> > > > >20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this
> > could
> > > > >certainly not be the case.
> > > >
> > > > The volume control of my amp is located in the feed back loop, thus
> > > > its value is important. Replacing a 20 kOhm potentiometer with a
> > > > 50 kOhm type would influence stability.
> > > >
> > > > But I don't know your amp so it can be a different problem. OTOH you
may
> > > > simple connect a resistor in parallel to the volume pot (47 kOhm are
a
> > > > good start) and check if the distortion/oscillations are gone.
> > > >
> > > > HTH
> > > > Norbert
> > > >
> > >
> > >

[Uwe Surojegin]

Hi again,
looks like everything got solved. It certainly looks like I'm asking too
much :) On other speakers (> 90 db) the Alpha 3 works not too bad. My
speakers offer only about 86 db (1W/1m). Right now, all of the important
electronic parts have been replaced - works fine now. Although I would have
been pleased with a little bit more power. BUT, the sound is very "british"
(like it), warm and "analog". Many thx again to all, many thx for all your
input.

Best rgds
Uwe
"Tim Schwartz" > schrieb im Newsbeitrag
...
> Uwe,
>
> Have you measured the output power into 8 ohm loads? This will tell you
> if there is any fault in the amp. As I said earlier, this is a low power
> amp, and you might be asking too much of it. If it is delivering rated
> power at clipping, you need to expect less volume or get a more powerful
> amp.
>
> Regards,
> Tim Schwartz
> Bristol Electronics
>
> Uwe Surojegin wrote:
> >
> > Hi John, Hi all,
> > many thanks for all your input. Specially to John from Arcam who faxed
me
> > the circuit diagram!!! If this amp is not going to work any more ... I
> > probably consider another ARCAM because of the excellent support !!!
> > First of all: The 12 o'clock clipping would not worry me if the output
would
> > be adequate at 11. It's somehow not very loud.
> > FYI: I replaced the 50K Ohm volume potentiometer with an 20K Ohm. No
> > improvement. The CD player output I checked again: Its acutally close to
2,5
> > V !!! So that could be a reason. I double-checked with a scope and a
50Hz
> > squared input signal, 3V. Going close to 12 ... the reading at the CD
> > chinch input ! already showed clipping with the scope !!! Strange!!! And
> > actually all the way through the amp section. Next steps I will do is
> > checking on the capacitors etc. If this aint gonna help ... -> bonfire
:)
> > I'll keep you posted.
> >
> > Uwe
> >
> > "Uwe Surojegin" > schrieb im Newsbeitrag
> > ...
> > > Hi Norbert,
> > > I connected already a 33K Ohm resistor parallel to the poti. I'll keep
you
> > > posted ... next steps are with oszilloscope to check the AC and DC
voltage
> > > from the transformer and so on....
> > >
> > > Uwe
> > >
> > >
> > > "Norbert Hahn" > schrieb im Newsbeitrag
> > > ...
> > > > "Uwe Surojegin" > wrote:
> > > >
> > > > >I checked my CD player output: Very low voltage, not nearly close
to
> > 300
> > > mV.
> > > >
> > > > Only a very few CD players have such low output voltage, unless they
> > > > have a volume control.
> > > >
> > > > >Of course, I had to replace the volume poti (was broken, originally
I
> > > guess
> > > > >20K Ohm) and replaced it with a 50K Ohm Alps potentiometer. So this
> > could
> > > > >certainly not be the case.
> > > >
> > > > The volume control of my amp is located in the feed back loop, thus
> > > > its value is important. Replacing a 20 kOhm potentiometer with a
> > > > 50 kOhm type would influence stability.
> > > >
> > > > But I don't know your amp so it can be a different problem. OTOH you
may
> > > > simple connect a resistor in parallel to the volume pot (47 kOhm are
a
> > > > good start) and check if the distortion/oscillations are gone.
> > > >
> > > > HTH
> > > > Norbert
> > > >
> > >
> > >