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AR3a/AS103a speakers and the Heathkit AR1500 receiver



 
 
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  #1  
Old October 3rd 06, 12:45 AM posted to rec.audio.high-end
[email protected]
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Posts: 2
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

A previous poster stated that the Heathkit AR1500 and AR3a are a poor
combination. This is true if you listen at any level other than quiet.

A couple of years after introduction, the AR1500's output amplifiers
were updated and the AR1500A was born. The AR1500A has specific
circuits that limit clipping and other distortion when it is driving
low imperance speakers at high levels. It is possible to modify the
AR1500's output amplifiers to include this improvement; you'd have to
go to a Heathkit users groups to obtain that information.

Driving AR3a's hard with an unmodified AR1500 produces a lot of
"clipped sine waves" that will blow the mid-range driver. If you don't
want to burnout the mid-range, but want to turn the volume up, add a 1
ohm resistor in series with each mid-range. This will change the
mid-range balance, but that's better than burning out the driver.

The AR3a was sold in kit form as the Heathkit AS103a.

Let me know if you have any questions.

Ads
  #2  
Old October 5th 06, 03:18 AM posted to rec.audio.high-end
Jerry
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Posts: 115
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

> wrote in message ...
> A previous poster stated that the Heathkit AR1500 and AR3a are a poor
> combination. This is true if you listen at any level other than quiet.


Rolf, I have an AR-3a and an AR1500 and they seem to work together fairly
well. I don't know about "quiet" as that is a relative term.

My den is quite small and my normal listening level is less than 1 watt, but
occasionally I'll listen at levels higher.

> A couple of years after introduction, the AR1500's output amplifiers
> were updated and the AR1500A was born. The AR1500A has specific
> circuits that limit clipping and other distortion when it is driving
> low imperance speakers at high levels. It is possible to modify the
> AR1500's output amplifiers to include this improvement; you'd have to
> go to a Heathkit users groups to obtain that information.


Rolf, any chance you have the schematic for the power amp on the "a"
version. If I could see the "a", I could document the differences.

I would think you'd really have to to be driving the speakers hard to get
anywhere near clipping. My guess is the heavy current drain forces the rail
voltages way down, and this allows even modest signals to clip. Only real
solution is to "beef up" the power supply.

> Driving AR3a's hard with an unmodified AR1500 produces a lot of
> "clipped sine waves" that will blow the mid-range driver. If you don't
> want to burnout the mid-range, but want to turn the volume up, add a 1
> ohm resistor in series with each mid-range. This will change the
> mid-range balance, but that's better than burning out the driver.


Well, Rolf, I've done just the opposite. I've taken all the pots out of the
AR-3a circuit and this significantly INCREASES the sensitivity of the
mid-range and tweeter. (Frankly, I'm a little surprised that the mid is
most susceptible to clipping damage. People on the AR forum worry far more
about the tweeters.)

In any event, "clipping" is no longer an issue for me. I'm now bi-amping my
AR-3a's. My AR1500 drives only the woofers. I have a nice little 30 watt
Kenwood powering the mid-range and tweeter. The Kenwood has rail voltages
of 40 volts!

With the pots out AND the fundamentals greatly reduced, it's hard to get
peak voltages of 3 volts going to the mid-range and tweeter. I mean, at 3
volts I can barely stand the volume.

Now, there is no question that at the same time that I have 3 volt peaks in
the Kenwood, the peak voltages in the AR1500 are much, much higher. I can't
see any clipping, but even if there were some, the mid and tweeter are
totally isolated from that amp.

> The AR3a was sold in kit form as the Heathkit AS103a.
>
> Let me know if you have any questions.
>


Rolf, if you have an AR1500 and a set of AR-3a's, I'd strongly recommend you
try a bi-amping experiment. Not only will you protect your mids and
tweeters, but there is a significant tightening of the bass that results.

Regards,
Jerry
  #3  
Old October 6th 06, 12:27 AM posted to rec.audio.high-end
[email protected]
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Posts: 2
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Jerry wrote:
> > wrote in message ...
> > A previous poster stated that the Heathkit AR1500 and AR3a are a poor
> > combination. This is true if you listen at any level other than quiet.

>
> Rolf, I have an AR-3a and an AR1500 and they seem to work together fairly
> well. I don't know about "quiet" as that is a relative term.
>
> My den is quite small and my normal listening level is less than 1 watt, but
> occasionally I'll listen at levels higher.
>
> > A couple of years after introduction, the AR1500's output amplifiers
> > were updated and the AR1500A was born. The AR1500A has specific
> > circuits that limit clipping and other distortion when it is driving
> > low imperance speakers at high levels. It is possible to modify the
> > AR1500's output amplifiers to include this improvement; you'd have to
> > go to a Heathkit users groups to obtain that information.

>
> Rolf, any chance you have the schematic for the power amp on the "a"
> version. If I could see the "a", I could document the differences.
>
> I would think you'd really have to to be driving the speakers hard to get
> anywhere near clipping. My guess is the heavy current drain forces the rail
> voltages way down, and this allows even modest signals to clip. Only real
> solution is to "beef up" the power supply.
>
> > Driving AR3a's hard with an unmodified AR1500 produces a lot of
> > "clipped sine waves" that will blow the mid-range driver. If you don't
> > want to burnout the mid-range, but want to turn the volume up, add a 1
> > ohm resistor in series with each mid-range. This will change the
> > mid-range balance, but that's better than burning out the driver.

>
> Well, Rolf, I've done just the opposite. I've taken all the pots out of the
> AR-3a circuit and this significantly INCREASES the sensitivity of the
> mid-range and tweeter. (Frankly, I'm a little surprised that the mid is
> most susceptible to clipping damage. People on the AR forum worry far more
> about the tweeters.)
>
> In any event, "clipping" is no longer an issue for me. I'm now bi-amping my
> AR-3a's. My AR1500 drives only the woofers. I have a nice little 30 watt
> Kenwood powering the mid-range and tweeter. The Kenwood has rail voltages
> of 40 volts!
>
> With the pots out AND the fundamentals greatly reduced, it's hard to get
> peak voltages of 3 volts going to the mid-range and tweeter. I mean, at 3
> volts I can barely stand the volume.
>
> Now, there is no question that at the same time that I have 3 volt peaks in
> the Kenwood, the peak voltages in the AR1500 are much, much higher. I can't
> see any clipping, but even if there were some, the mid and tweeter are
> totally isolated from that amp.
>
> > The AR3a was sold in kit form as the Heathkit AS103a.
> >
> > Let me know if you have any questions.
> >

>
> Rolf, if you have an AR1500 and a set of AR-3a's, I'd strongly recommend you
> try a bi-amping experiment. Not only will you protect your mids and
> tweeters, but there is a significant tightening of the bass that results.
>
> Regards,
> Jerry


October 5, 2005 update from Rolf:

Both versions of the AR1500's output amplifier have a current limiting
circuit to protect the amplifier's power transistors (Motorola MJ802's)
from burning out. For the original AR1500, the circuit limited the
current too soon when driving low impedance speaker like the AR3a. The
AR1500A added a modification (resistors and capacitors only) that
limited the response time of the current limiters. In effect, the new
current limit circuit let short high-current transients through (which
don't heat up the MJ802's enough to cause trouble) and only limited the
current for non-transients.

With the original AR1500 power amplifier, the too fast-acting current
limiting circuit introduced "harmonics" not in the original signal; at
high sound levels these harmonics have enough energy to burn-out the
mid-range drivers.

I have both versions of the AR1500, a pair of AR3a's (the kit version
Heathkit sold as AS103) and a pair of AS101's (the kit version of the
Altec Lansing Valencia). (The AR1500 and AR3a's were my dad's.) I
modified the power amplifier of the original AR1500 many years ago, and
unforunately no longer have the instructions.

The only problem I've had with the AR1500A was the need to replace the
front panel bulbs more frequently than I want to. I added silicone
grease into the bulbs' sockets, and the bulbs now last much longer (due
to better heat transfer away from the bulbs).

I also spray painted the inside of the AR1500A's cabinet flat black,
this reduces the internal heat of the receiver.
  #4  
Old October 6th 06, 07:29 PM posted to rec.audio.high-end
Peter Wieck
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Posts: 2,418
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Jerry wrote:

> My den is quite small and my normal listening level is less than 1 watt, but
> occasionally I'll listen at levels higher.


Jerry:

There are a lot of misconception to do with "volume", and especially as
it relates to "watts".

At one watt average, with moderately dynamic source, you will need at
least a 100-watt amp to get clean peaks absolutely without clipping.
But you already know this. Put another way, a speaker with an 86dB @
1-watt SPL, a 30-watt amp simply will not cut it, even bi-amped at
anything above a very moderate volume. Agreed, mostly one listens at a
very moderate volume. But not always.

Components of the vintage of your Heath more-or-less send straight DC
into the speaker when driven to clipping. And depending on the source
(where, as it usually happens most of the signal is at the mid-range),
that could be a lot of the time and pretty rapidly fatal to your
speakers.

Again, put another way, it is (Very typical of vintage SS amps)
amplifiers of low power that burn speakers, not high power. Almost any
well-made speaker can handle normal signal at very high power, well
beyond their nominal ratings, for brief periods. Even the very best
conventional PM speakers will fry in short order when fed DC. I think
this is what the OP was trying to convey.

Those of us who dabble in tube equipment tend to ignore this simple
truth as output transformers will not pass DC, so clipping is much
softer and relatively harmless (to the speaker, that is). Also why
those of us who have high-powered amps (tube or SS) also tend to ignore
this as there is enough headroom in any case to minimize consequences
from clipping.

Bi-Amping, even as you have applied it will create some advantages if
very carefully managed. But the real-world difference between a 30 watt
amp and two 30-watt amps split is limited in this *particular*
application given that at any given moment about 75% of your signal
will be at/within the midrange, and if you include the tweeter, that
goes to about 90%, at least as it applies to the need for headroom. I
would very strongly suggest that you make it your mission in Audio to
beg, borrow or steal a well-made high-powered amplifier (200W/RMS/CH @
4 ohms or better) and re-evaluate your position.

Enjoy the results in any case.

Peter Wieck
Wyncote, PA
  #5  
Old October 7th 06, 12:18 AM posted to rec.audio.high-end
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Posts: 402
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Peter Wieck wrote:
>


Some misconceptions:

> There are a lot of misconception to do with "volume", and especially as
> it relates to "watts".
>
> At one watt average, with moderately dynamic source, you will need at
> least a 100-watt amp to get clean peaks absolutely without clipping.


A peak-to-average ratio of 20 dB: moderate??

> Components of the vintage of your Heath more-or-less send straight DC
> into the speaker when driven to clipping.


Some pathological cases do, the vast majority don't.

> Again, put another way, it is (Very typical of vintage SS amps)
> amplifiers of low power that burn speakers, not high power.


This has been pretty thoroughly debunked elsewhere, check
out Rane's application notes on apolifier clipping and tweeter
life.

> Those of us who dabble in tube equipment tend to ignore this simple
> truth as output transformers will not pass DC, so clipping is much
> softer and relatively harmless


That tubes clip more softwly has almost nothing whatsoever to do
with the fact that the output transformers do not pass DC. The
clipping is software for two reasons:

1. The upper end gain transfer characteristics of the tube do not
change as abruptly when limiting is reached,

2. The conbination of the tube's HF bandwidth, the transformer's
HF bandwidth and the overall circuit's HF bandwidth can suppress
some of the higher harmonics resulting from clipping.
  #6  
Old October 7th 06, 04:47 AM posted to rec.audio.high-end
Jerry
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Posts: 115
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

"Peter Wieck" > wrote in message
...
> Jerry wrote:
>
> > My den is quite small and my normal listening level is less than 1 watt,

but
> > occasionally I'll listen at levels higher.

>
> Jerry:
>
> There are a lot of misconception to do with "volume", and especially as
> it relates to "watts".
>
> At one watt average, with moderately dynamic source, you will need at
> least a 100-watt amp to get clean peaks absolutely without clipping.
> But you already know this. Put another way, a speaker with an 86dB @
> 1-watt SPL, a 30-watt amp simply will not cut it, even bi-amped at
> anything above a very moderate volume. Agreed, mostly one listens at a
> very moderate volume. But not always.


Peter, please remember that the 30 watt amp is driving strictly the mid and
tweeter. Further, this amp sees greatly reduced fundamentals, so the
voltage swings are NOTHING like what a single amp would experience. When
playing music at levels I can just barely stand (somewhere around 10 -20
watts), PEAK output voltages in this amp are LESS than 7 volts.

Now, one reason for that low output voltage is that I removed those blasted
pots from the AR xover circuit. This netted a huge gain in sensitivity on
just those drivers. So I must compensate by reducing volume or the
mid/tweeter will overpower the woofer. To give you a feel ... the average
voltage swings in the woofer amp are 5 times higher!

Based upon all of the above, there is just no way that peak output voltage
could ever get to the 40 volt rails in the mid/tweeter amp. Further, rail
drop will be minimal given the low current drain of the mid and tweeter.

Peter, please remember that I don't have the fundamentals going through that
30 watt amp and this significantly changes the game and the math.

> Components of the vintage of your Heath more-or-less send straight DC
> into the speaker when driven to clipping. And depending on the source
> (where, as it usually happens most of the signal is at the mid-range),
> that could be a lot of the time and pretty rapidly fatal to your
> speakers.


Even if this is the case, (and I doubt that because I measured the filter
caps and they are just fine), the mid and tweeter will never see the impact
of the clipped waves and resulting harmonics in the woofer amp. Further,
neither will the woofer as it's internal xover will reject those harmonics.

Peter don't forget that the Heath amp sees reduced harmonics as well. Now
this reduction is NOT as great as the reduction of fundamentals in the 30
watt amp, but still there is a significantly less harmonics "riding on
fundamentals" than what a single amp would see.

> Again, put another way, it is (Very typical of vintage SS amps)
> amplifiers of low power that burn speakers, not high power. Almost any
> well-made speaker can handle normal signal at very high power, well
> beyond their nominal ratings, for brief periods. Even the very best
> conventional PM speakers will fry in short order when fed DC. I think
> this is what the OP was trying to convey.


Peter, if we drove this 30 watt amp to the 40 volts rails, clipping would be
the least of our problems. Both the mid and the tweeter would be smoking
long, long before. With the fundamentals removed, the impact of stacking 40
volt rails on top of 40 volt rails in the Heath is equivalent to a 750 watt
amp. Now this is from the vantage point of the mids/tweeters. (The woofer
still sees the same 100 watt amp with but even it "goes further" without the
harmonics.)

> Those of us who dabble in tube equipment tend to ignore this simple
> truth as output transformers will not pass DC, so clipping is much
> softer and relatively harmless (to the speaker, that is). Also why
> those of us who have high-powered amps (tube or SS) also tend to ignore
> this as there is enough headroom in any case to minimize consequences
> from clipping.


Peter, you can ignore it, but the truth is that I have far, far more
headroom than you with your "brute" ss amp. You must pass fundamentals
with harmonics on top through that amp. Further, you still have the pots
"sucking up power" in your AR-3a's and this also contributes to a reduction
in headroom.

> Bi-Amping, even as you have applied it will create some advantages if
> very carefully managed. But the real-world difference between a 30 watt
> amp and two 30-watt amps split is limited in this *particular*
> application given that at any given moment about 75% of your signal
> will be at/within the midrange, and if you include the tweeter, that
> goes to about 90%, at least as it applies to the need for headroom. I
> would very strongly suggest that you make it your mission in Audio to
> beg, borrow or steal a well-made high-powered amplifier (200W/RMS/CH @
> 4 ohms or better) and re-evaluate your position.


Peter, are you saying that 75% of the signal STRENGTH is going to the
mids/tweeters? This is totally incorrect and I have a dual channel scope
to prove it. Less than 25% of the voltage swings are going to the
mid/tweeter amp. Then if we integrated the signals to compute power, once
again the real power is in the woofer amp ... BY A LOT! It's not even
close.

I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8 ohms).
Why in heavens name would I want a mere 200 watt amp. That would be going
backwards.

Regards,
Jerry
  #7  
Old October 7th 06, 03:29 PM posted to rec.audio.high-end
Peter Wieck
external usenet poster
 
Posts: 2,418
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Jerry wrote:
> I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8 ohms).
> Why in heavens name would I want a mere 200 watt amp. That would be going
> backwards.
>


Jerry:

Pulling the pots from the AR3(a) is about the first thing that should
be done, they were barely functional when-new. So we are 100% agreed
there. But per any of the several web-sites dedicated to these speakers
(Layne, Vintage, et.al.) this gives only about a 3dB gain (assuming
otherwise good pots) over the pots in the max (theoretically
straight-wire) position.

And, as to the "equivalent" of a 750 watt amp, _ALL_ I am suggesting is
that unless you have tried the brute-force amp and rejected it as being
unsatisfactory as compared to your present set-up, you REALLY SHOULD
try it. The results may well be revealing. At the very least they will
endorse your present position.

Yeah, a good part of the stuff I listen to regularly does have a 20dB
P/A, the room is fairly large, and I do like to run at a moderately
high volume... trumpets like that. And even the solo human voice with
an orchestral background likes that.

Peter Wieck
Wyncote, PA
  #8  
Old October 7th 06, 06:22 PM posted to rec.audio.high-end
John Stone
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Posts: 117
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

On 10/6/06 10:47 PM, in article , "Jerry"
> wrote:

> Now, one reason for that low output voltage is that I removed those blasted
> pots from the AR xover circuit. This netted a huge gain in sensitivity on
> just those drivers. So I must compensate by reducing volume or the
> mid/tweeter will overpower the woofer. To give you a feel ... the average
> voltage swings in the woofer amp are 5 times higher!


I thought all your bi-amping adventures were done with the purpose of not
altering the original design of your AR3a's. Well, now that you're in there
changing things around, I'm wondering if you did anything to compensate for
the removal of those pots from the circuit. They place a 16 ohm load across
the mid and tweeter crossover circuits, and that load forms part of the
filter network. Did you put a fixed 16 ohm resistor in the circuit in their
place? If not, you've certainly altered the crossover responses and
consequently, the speaker response. (I can't wait to see whether you're
going to agree with this). I'm also trying to figure out how you got such a
huge gain in sensitivity by removing the pots. Turned all the way up, the
mid and tweeter are directly connected to the crossover outputs, so the pot
is out of the circuit other than presenting a parallel 16 ohm load. Unless
those were the world's most defective pots-and you would have easily been
able to tell from the intermittent operation-then I don't see where you're
picking up all the sensitivity from.
I'm also amazed at how much work you've gone through to deviate from the
original design intent of the AR3a's. If it was me, I would put them back to
stock and sell them. They still bring decent money. Then I would invest in
some real DIY loudspeaker building using the much more robust and better
performing loudspeaker components that are available today. You could then
tweak to your heart's desire without the worry of blowing fragile drivers
that are no longer available. You seem like the type that loves to
experiment. Why limit yourself to such old technology that will never reach
today's performance levels no matter what you do?
  #9  
Old October 7th 06, 08:21 PM posted to rec.audio.high-end
Peter Wieck
external usenet poster
 
Posts: 2,418
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

John Stone wrote:

> I thought all your bi-amping adventures were done with the purpose of not
> altering the original design of your AR3a's.


John, the various mod sites noted emphasize the need for a fixed
resistor in place of the pot, simply bypassing the adjustable function.
Yes, *maybe* get them out of the circuit, no, do not alter the overall
function of the circuit.

http://layneaudio.hypermart.net/AR3aXorig.gif shows the OEM crossover
arrangement. One may either bypass the wiper directly to the 0-ohms
position, or remove the pot inserting a 16-ohm resistor and tying the
correct leads at the 0-ohm position.

(above link courtesy Layne Audio)

Classic Speaker Pages:

http://www.classicspeakerpages.net/a...ar-3a/ar3a.htm

All sorts of information and suggestions.

Peter Wieck
Wyncote, PA
  #10  
Old October 8th 06, 02:39 AM posted to rec.audio.high-end
Jerry
external usenet poster
 
Posts: 115
Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Peter Wieck wrote on 10/7/2006:

> Jerry wrote:
> > I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8

ohms).
> > Why in heavens name would I want a mere 200 watt amp. That would be

going
> > backwards.
> >

>
> Jerry:
>
> Pulling the pots from the AR3(a) is about the first thing that should
> be done, they were barely functional when-new. So we are 100% agreed
> there. But per any of the several web-sites dedicated to these speakers
> (Layne, Vintage, et.al.) this gives only about a 3dB gain (assuming
> otherwise good pots) over the pots in the max (theoretically
> straight-wire) position.


Hmmm, 3db seems low, but could be right. I should have, but didn't measure
before and after. In any event, a 3db reduction in power is equivalant to
cutting the power to the mids/tweeters in HALF. That is, I now send half as
much power to the mids/tweeters and get the same SPL. This equates to a
terriffic gain in headroom and issures clipping in the mid/tweeter amp will
never happen.

Peter, you never told me you removed the pots from your AR-3a's!

You can't do this, Peter, and mainain the proper sound balance UNLESS you
compensate with fixed resistance in the xover. So, Peter, what mod did you
perform upon your 3a's?

> And, as to the "equivalent" of a 750 watt amp, _ALL_ I am suggesting is
> that unless you have tried the brute-force amp and rejected it as being
> unsatisfactory as compared to your present set-up, you REALLY SHOULD
> try it. The results may well be revealing. At the very least they will
> endorse your present position.


Alas, I can't do this anymore. With the pots out, there is no way to power
my AR with a single amp and maintain any semblance of balance between the
energy sent to the woofer and that sent to the mids and tweeters. And I'm
NOT putting those pots back in the circuit. I itched for three days the
last time I opened those boxes.

Peter did you ever look at your audio signal on a scope to see the height of
the transients? I look fairly often and I've never seen peak voltages as
high as you describe.

Regards,
Jerry
 




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