Hello,


I have an old amplifier I am using in a project and I wish to upgrade the
power supply capacitors. I need some help in determining a safe value, or
guidlines to follow when choosing a higher value. The amplifer is an Audio
Reflex ARA-335. I have never heard of this name before but it appears to be
an early 80's built amplifier (2 chan). It seems to be built with high
quality parts...almost all the pots and swithches are made by Alps and the
sound is great.

Anyway...the supply capacitors are 50V 4700uF. I cannot find any
documentation on this amplifier so I do not even know how many watts/channel
it is. Any recomendations would be greatly apprieciated!

Jerry Lynds

Anyway...the supply capacitors are 50V 4700uF. I cannot find any
documentation on this amplifier so I do not even know how many
watts/channel
it is. Any recomendations would be greatly apprieciated!

The obvious thing to do would be replace them with fresh 4700-uF 50-volt
capacitors.

You could go to somewhat more uF (like 10,000) without appreciably changing
the way the circuit works, and it might give you slightly better regulation
on high-power peaks, which I assume is your goal.

"Jerry Lynds" wrote in message
news:rbNBf.194671$OU5.132815@clgrps13...
Hello,


I have an old amplifier I am using in a project and I wish to upgrade the
power supply capacitors.

why? what do you need to accomplish?

I need some help in determining a safe value, or
guidlines to follow when choosing a higher value.

the safe thing is to replace with identical values.
when re-engineering a product you need to consider the values in each stage
and how they will be affected. worst case, fire. less worse case, blown
fuses or burnt parts.

The amplifer is an Audio
Reflex ARA-335. I have never heard of this name before but it appears to
be
an early 80's built amplifier (2 chan). It seems to be built with high
quality parts...almost all the pots and swithches are made by Alps and the
sound is great.

Anyway...the supply capacitors are 50V 4700uF. I cannot find any
documentation on this amplifier so I do not even know how many
watts/channel
it is. Any recomendations would be greatly apprieciated!

Jerry Lynds



lets assume that your DC supply is +/- 35 V @no load. then assume the peak
output voltage is 30 V @ normal load. that would make the output about 21
Vrms. if the load is 8 ohms it works out to about 55 W/ch. of course if the
output devices (transistors or ICs) are not rated for that it wont be.

the AC line fuse value may assist in guessing output power. if its a 1 amp
fuse you know that input power is less then 120 watts (assuming 120 Vac
line) therefore total output power will be less then that.

the safe thing is to replace with identical values.
when re-engineering a product you need to consider the values in each
stage
and how they will be affected. worst case, fire. less worse case, blown
fuses or burnt parts.

Explaining that a little mo If you replace the capacitors with much
larger ones, the inrush current when you first turn the amplifier on may be
enough to blow fuses. I suggested that a 2x increase would probably do no
harm, but don't just put gigantic capacitors in place of modest-sized ones.

Having said that... There is little reason to suppose the amplifier needs
new capacitors unless the old ones are starting to increase in resistance
(which typically happens if the amp. has been unused for several years;
regular use keeps capacitors young). Increasing the capacitors might give
you a *tiny* bit better performance at high power, or it might make no
difference at all. Assuming the capacitors are in good condition, they have
no effect on sound when the amplifier isn't bumping into high-power limits.

On Wed, 25 Jan 2006 15:55:03 GMT, "Jerry Lynds"
wrote:

I have an old amplifier I am using in a project and I wish to upgrade the
power supply capacitors. I need some help in determining a safe value, or
guidlines to follow when choosing a higher value. The amplifer is an Audio
Reflex ARA-335. I have never heard of this name before but it appears to be
an early 80's built amplifier (2 chan). It seems to be built with high
quality parts...almost all the pots and swithches are made by Alps and the
sound is great.

Excuse the obvious question. But if the sound is "great", why mess
with it? If there IS a problem, replace the caps with ones of the
same spec. If you've caught audiophool disease, paint your CDs green
or buy some magic cables. At least that won't risk breaking an amp
which currently sounds "great".

OK...seems I have set myself up for some critism...I'll accept that. Perhaps
I have developed "audiophool disease" and most likely have had it since I
have owned my first piece of stereo equipment.

I am not an electronic technition, nor do I claim to be. I have never had
any training and that is obvious. But, I do have a huge interest in
electronics and I do try to learn and in a safe way...ie my post. It was my
aim to increase the power reserve to a greater amount for more demanding
bass notes at higher volumes...without getting into anything beyond
replacing the supply capacitors with beefier ones. It has been some time
since I really looked at this topic, but I do remember a general guidline
saying not to exceed an increase of more that 2X...but I wanted to make
sure. Would it have made an aprieciable difference? I don't know...that was
my experiment for my ears and/or perception of what "good" sound is. There
was never a need to do this; just a curiosity.

To follow up with TimPerry's post...I measured DC +/- 35 Volts and the AC
line fuse is 250V @ 3.5V.

The transformer is a decent size and the power suppy fuses are rated at 250V
@ 6 amps.


Thanks for the help...sorry if this was a lame question.

Jerry

"Jerry Lynds" wrote in message
news:rbNBf.194671$OU5.132815@clgrps13...
Hello,

I have an old amplifier I am using in a project and I wish to upgrade the
power supply capacitors. I need some help in determining a safe value, or
guidlines to follow when choosing a higher value. The amplifer is an Audio
Reflex ARA-335. I have never heard of this name before but it appears to
be
an early 80's built amplifier (2 chan). It seems to be built with high
quality parts...almost all the pots and swithches are made by Alps and the
sound is great.

If the sound is "great," then why are you mesing with it?

Stuart Welwood
6 sigma

Jerry Lynds wrote:

OK...seems I have set myself up for some critism...I'll accept that. Perhaps
I have developed "audiophool disease" ...

Nah. You're desire to replace the caps is based on physics and
engineering. There are circumstances where beefing up the power supply
will improve sound, and larger caps is one way to do that.

I'm just not sure that this is one of those circumstances. My advice is
that if it sounds great as it, leave it alone.

//Walt

"Walt" wrote in message
...
Jerry Lynds wrote:

OK...seems I have set myself up for some critism...I'll accept that.
Perhaps
I have developed "audiophool disease" ...


having it isn't so bad... just so it doesn't spread too much


Nah. You're desire to replace the caps is based on physics and
engineering. There are circumstances where beefing up the power supply
will improve sound, and larger caps is one way to do that.

I'm just not sure that this is one of those circumstances. My advice is
that if it sounds great as it, leave it alone.

//Walt


i recall that i once modified a home stereo to work from 12V dc. it sounded
great too! but it was such a hassle to try to adjust volume and tuning when
it was in the back seat....

"Jerry Lynds" wrote in message
news:SpbCf.112126$m05.65460@clgrps12...
OK...seems I have set myself up for some critism...I'll accept that.
Perhaps
I have developed "audiophool disease" and most likely have had it since I
have owned my first piece of stereo equipment.

I am not an electronic technition, nor do I claim to be. I have never had
any training and that is obvious.

it's a reason why care must be taken when advise is given.

But, I do have a huge interest in
electronics and I do try to learn and in a safe way...ie my post. It was
my
aim to increase the power reserve to a greater amount for more demanding
bass notes at higher volumes...without getting into anything beyond
replacing the supply capacitors with beefier ones.

you kind of have the right idea but underestimate the magnitude needed to
create a significant improvement.
i just bought another 2400W amplifier today. it will help me by increasing
my ability to power subwoofers without clipping or distortion at higher
volumes.

It has been some time
since I really looked at this topic, but I do remember a general guidline
saying not to exceed an increase of more that 2X...

that's the trouble with general gidelines: mom said to always wear clean
underwear but what if you have to go to the hospital at the end of the day?


but I wanted to make
sure. Would it have made an aprieciable difference? I don't know...that
was
my experiment for my ears and/or perception of what "good" sound is. There
was never a need to do this; just a curiosity.

i wonder about stuff too. like how come mashed avocados get a fancy name
like guacamole but spuds only are called mashed potatos?
why arn't pickles called pickled cukes?


To follow up with TimPerry's post...I measured DC +/- 35 Volts and the AC
line fuse is 250V @ 3.5V.


hummm 35 volts? i guess i made a lucky guess
i'm assuming that's 3.5A
allowing for starting surges and line fluctuations i would guess an Imax of
1.5 to 2.5A



The transformer is a decent size and the power suppy fuses are rated at
250V
@ 6 amps.



Thanks for the help...sorry if this was a lame question.

Jerry
it just basic power supply considerations.

since we don't know, if we want to find the output power we have to measure
it.
a typical setup would involve an 8 ohm resister @ 100 W or larger (AKA power
soak or dummy load), an oscilloscope (and/or distortion meter), a
calculator, a signal generator.

a tone is fed into the input and the gain is increased until the output as
observed on the 'scope starts to flatten (distort) back down the gain, take
the peak to peak reading and calculate the power at test frequency. if you
brave you can try it at a 4 ohm load, making sure to test only briefly
(consumer stuff doesn't usually like being driven at 100% continuously).

another test is to look at the DC supply with the 'scope while it it being
driven hard. if the "ripple" (the waveform floating on the DC) is large it
time to replace the big capacitors.

my feeling is that you have a fairly potent vintage amplifier the might be
capible of pushing 100 watts per channel or more into a 4 ohm load, but it
is just a guess based on the info so far provided.

my prediction is that no matter how much C you add you will detect zero
improvement at 'normal' listening levels and any measurable improvement when
operated at peak power will be largely indistinguishable by ear from the way
it was before. this is assuming that the original caps are good.

"Jerry Lynds" wrote in message
news:SpbCf.112126$m05.65460@clgrps12...
OK...seems I have set myself up for some critism...I'll accept that.
Perhaps I have developed "audiophool disease" and most likely have had it
since I have owned my first piece of stereo equipment.

I am not an electronic technition, nor do I claim to be. I have never had
any training and that is obvious. But, I do have a huge interest in
electronics and I do try to learn and in a safe way...ie my post. It was
my aim to increase the power reserve to a greater amount for more
demanding bass notes at higher volumes...without getting into anything
beyond replacing the supply capacitors with beefier ones. It has been some
time since I really looked at this topic, but I do remember a general
guidline saying not to exceed an increase of more that 2X...but I wanted
to make sure. Would it have made an aprieciable difference? I don't
know...that was my experiment for my ears and/or perception of what "good"
sound is. There was never a need to do this; just a curiosity.

To follow up with TimPerry's post...I measured DC +/- 35 Volts and the AC
line fuse is 250V @ 3.5V.

The transformer is a decent size and the power suppy fuses are rated at
250V @ 6 amps.


Thanks for the help...sorry if this was a lame question.

Jerry

A +/- 35 volt (70 volts) rail is typical of an amp in the 50 watt range at 8
Ohm load. It would clip at around 70 watts. Of course, this considers the
amp can put all the voltage and current to use and the supply is stiff. You
can calculate by this formula:

Po = .25 (Vs - 2 Vcesat)^2 / 2 Load

For a typical amp, Vcesat can estimated about 2 volts (voltage drop across
transistors at saturation)
Po is the max output just before clipping
Vs is the supply voltage (at full output, both channels driven, expect Vs to
drop.
Load is the speaker's impedance
The formula is for single ended amps. Remove the .25 for bridge amps.
John

To follow up with TimPerry's post...I measured DC +/- 35 Volts and the AC
line fuse is 250V @ 3.5V.


hummm 35 volts? i guess i made a lucky guess
i'm assuming that's 3.5A
allowing for starting surges and line fluctuations i would guess an Imax
of
1.5 to 2.5A


Yes....that was a typo...

But anyway...That about wraps this topic up for me so thanks for all of your
replies. I really don't think I will bother...but wanted to look into the
option since I have it all torn apart...

For curious minds...this is an old amp with a front face smothered with
about 12 switches and knobs. With the exception of the pots, I never change
a setting for things like loudness, subsonic filter, tape dubbing etc...so I
am removing all unused settings and hard wiring them directly to the main
board. All components not used like the phono board and mic/headphone have
been removed. The pre-amp stage has been moved to the rear to save the
bass/trebble controls but rarely used so out of sight but intact. The front
has been given a new metal plate (overlaid on top of the old and mounted via
the rack mount holes) now complete with only a power switch and a volume
control, and a centre mounted Blue backlit 40x4 LCD (also why the pre-amp
stage had to go to the rear). So, the amp will be hooked to my computer to
display mp3 tag info like artist and track name, time remaining...anything
winamp can generate including a 40 band graphic EQ. So..this is my project
and the reason for taking this thing apart in the first place...Cheers

Jerry

On Thu, 26 Jan 2006 19:09:50 -0500, "TimPerry"
wrote:


i recall that i once modified a home stereo to work from 12V dc. it sounded
great too! but it was such a hassle to try to adjust volume and tuning when
it was in the back seat....

What was the point of car hi-fi if you weren't in the back seat with
her too?

On Fri, 27 Jan 2006 05:23:51 GMT, "Jerry Lynds"
wrote:

For curious minds...this is an old amp with a front face smothered with
about 12 switches and knobs. With the exception of the pots, I never change
a setting for things like loudness, subsonic filter, tape dubbing etc...so I
am removing all unused settings and hard wiring them directly to the main
board. All components not used like the phono board and mic/headphone have
been removed. The pre-amp stage has been moved to the rear to save the
bass/trebble controls but rarely used so out of sight but intact. The front
has been given a new metal plate (overlaid on top of the old and mounted via
the rack mount holes) now complete with only a power switch and a volume
control, and a centre mounted Blue backlit 40x4 LCD (also why the pre-amp
stage had to go to the rear). So, the amp will be hooked to my computer to
display mp3 tag info like artist and track name, time remaining...anything
winamp can generate including a 40 band graphic EQ. So..this is my project
and the reason for taking this thing apart in the first place...Cheers


Until you mentioned the LCD I was quite impressed at your quest for
sonic improvement :-)

You LOOK at your amplifier?

Laurence Payne wrote:

On Fri, 27 Jan 2006 05:23:51 GMT, "Jerry Lynds" wrote:

...a centre mounted Blue backlit 40x4 LCD (also why the pre-amp
stage had to go to the rear). So, the amp will be hooked to my computer to
display mp3 tag info like artist and track name, time remaining...anything
winamp can generate including a 40 band graphic EQ. So..this is my project
and the reason for taking this thing apart in the first place...Cheers

Until you mentioned the LCD I was quite impressed at your quest for
sonic improvement :-)

You LOOK at your amplifier?

What did it for me is that he's all geeked about sound and he's
listening to mp3s.

//Walt

Laurence Payne wrote:

Until you mentioned the LCD I was quite impressed at your quest for
sonic improvement :-)

My quest for sonic improvement of a pair of Sansui B55's included
removing their display board.


Kind regards

Peter Larsen


--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************

"Walt" wrote in message
...
Laurence Payne wrote:

On Fri, 27 Jan 2006 05:23:51 GMT, "Jerry Lynds" wrote:

...a centre mounted Blue backlit 40x4 LCD (also why the pre-amp
stage had to go to the rear). So, the amp will be hooked to my computer
to display mp3 tag info like artist and track name, time
remaining...anything winamp can generate including a 40 band graphic EQ.
So..this is my project and the reason for taking this thing apart in the
first place...Cheers

Until you mentioned the LCD I was quite impressed at your quest for
sonic improvement :-)

You LOOK at your amplifier?

What did it for me is that he's all geeked about sound and he's listening
to mp3s.

//Walt


Man...some of you guys are a bunch of assholes. You guys are taking this way
to seriously and I never said my intention to do all this was to re-design
this amp into a thing of sonic pefection. In fact, this whole thing started
around the interest of PIC programming and finding something cool to
intergrate it into. I don't think my interest in home audio and PIC/LCDs
warrents me being labeled as being "all geeked about sound". I think you
guys have to look at how you are...my post seems to have turned into more of
a way for some of you to compete with one another to see who can best answer
a question and then get so far off topic you don't even know what I was
asking. To me, the only thing I hear is a bunch of old geeks mumbling in a
nerdish ramble making digs at someone who looked to this group for some
honest advice. Up until now, I felt quite comfortable drawing on the
resources of this group to expand an interest. If anything, it is assholes
like you that deter people from wanting to learn or pursue ideas.

Do I look at my amplifier? What is it to you? Jesus...for your info this
amplifier is going to be used in my garage and hooked into an old
computer...For the amount of work I am putting into this thing you are damn
straight I am going to look at it. I will be able to view directories and
song/track info from the LCD in the amplifer and thus, will not need a
monitor. I never once mentioned I was so critical of audio reproduction as
you guys seem to be. I want to be able to drive this amp fairly hard for
what it is so that explains my "interest" in increasing the power supply
capacitors...

I think perhaps some of you should maybe ask some more questions and lay off
the digs...or just don't reply at all. Not everyone is as sophisticated and
knowledgeable as you...

Jerry Lynds wrote:

Man...some of you guys are a bunch of assholes. You guys are taking this way
to seriously and I never said my intention to do all this was to re-design
this amp into a thing of sonic pefection. In fact, this whole thing started
around the interest of PIC programming and finding something cool to
intergrate it into. I don't think my interest in home audio and PIC/LCDs
warrents me being labeled as being "all geeked about sound".

Don't take the word "geek" the wrong way. I'd describe anybody who
opens up the case on their otherwise perfectly working gear to fiddle
with it a "geek". It's not meant to be pejorative. I've been known to
be pretty geekful myself at times.

Sorry if I hurt your feelings. Usenet can be a tough place, and I can
be a prick sometimes. You've been pretty civil, so it's not really fair
to tease you for asking a serious question.

So, let me try re-stating what I was trying to say, but this time
without the snark:

I didn't realize that you were using this amp to listen to mp3s. If
that's the case, and you're looking to improve the sound of your system,
the way to get the most improvement is to focus on the source material,
not the caps in the amp. MP3's are mid-fi at best, and fiddling with
the amp is not going to help much as long as you're listening to
aggressively bit-rate reduced audio.

I know that's not what you asked. But it's my opinion, worth every
penny you've paid for it.

//Walt

But anyway...That about wraps this topic up for me so thanks for all of
your
replies. I really don't think I will bother...but wanted to look into the
option since I have it all torn apart...


you may want to consider adding a small fan to aid cooling. i used to use
one on a unit of about that size. i used a low noise muffin type. it
depends on a lot of factors like how hard you are going to run it whether
the fan will be a constructive addition. keeping the final transistors cool
is an aid to long life.

i recall that i once modified a home stereo to work from 12V dc. it
sounded
great too! but it was such a hassle to try to adjust volume and tuning
when
it was in the back seat....

What was the point of car hi-fi if you weren't in the back seat with
her too?

this was back when stock radios were mono and the more desirable ones had
mechanical pushbuttons. the speaker was a single oval shaped speaker (5x7?)
in the front dash.

having a stereo with 2 Jenson 6x9 with whizzer cones "trunk" mounted in the
rear deck was COOL.