Polymorph

Hi Guys,

I decided to add the LM386 amplifiers to my Mockingboard that I posted
about a few weeks ago. Prior to adding the amplification, the board
was working fine with powered speakers. This might be another case of
"if it aint broke, don't fix it", but I wanted to hear the difference
the amplifiers would make, and I had already bought them as well, so
the temptation was too strong. ;-)

I completed the amplifier add-on and have got it working as such, but
with *heaps* of bus noise being output. I can play music, and I know
the amplifiers are obviously working as the sound is loud even on un-
powered speakers. The trouble is, as soon as I turn on the Apple II, I
can hear fairly loud bus noise.

Now I've used the circuit as described in the AY-3-8910 data manual
which can be seen here:
http://apple2.sytes.net/Mockingboard...nterfacing.jpg

From analysis of the high resolution scans of the Mockingboard V1 on
the ReactiveMicro site, this circuit appears to be very similar to
what is on the Mockingboard V1. Is there anything obviously wrong
with the circuit above?

Another thing I've noticed is that the Mockingboard V1 has some
additional 0.1uF capacitors on the +5V line going into the AY-3-8910
and 6522 chips. Could the absence of these capacitors be responsible
for the noise I'm hearing?

I've gone over the additional amplifier circuitry that I added, and
everything appears to be wired correctly. Remember, the rest of the
circuit was working fine (albeit without amplification).

Is anything else I should check to eliminate the bus noise?

Any help would be greatly appreciated!

Cheers,
Mike

Osgeld

On Aug 28, 8:35*pm, Polymorph <mike.a.steph...@gmail.com> wrote:
> Hi Guys,
>
> I decided to add the LM386 amplifiers to my Mockingboard that I posted
> about a few weeks ago. Prior to adding the amplification, the board
> was working fine with powered speakers. This might be another case of
> "if it aint broke, don't fix it", but I wanted to hear the difference
> the amplifiers would make, and I had already bought them as well, so
> the temptation was too strong. *;-)
>
> I completed the amplifier add-on and have got it working as such, but
> with *heaps* of bus noise being output. I can play music, and I know
> the amplifiers are obviously working as the sound is loud even on un-
> powered speakers. The trouble is, as soon as I turn on the Apple II, I
> can hear fairly loud bus noise.
>
> Now I've used the circuit as described in the AY-3-8910 data manual
> which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>
> From analysis of the high resolution scans of the Mockingboard V1 on
> the ReactiveMicro site, this circuit appears to be very similar to
> what is on the Mockingboard V1. Is there anything obviously wrong
> with the circuit above?
>
> Another thing I've noticed is that the Mockingboard V1 has some
> additional 0.1uF capacitors on the +5V line going into the AY-3-8910
> and 6522 chips. Could the absence of these capacitors be responsible
> for the noise I'm hearing?
>
> I've gone over the additional amplifier circuitry that I added, and
> everything appears to be wired correctly. Remember, the rest of the
> circuit was working fine (albeit without amplification).
>
> Is anything else I should check to eliminate the bus noise?
>
> Any help would be greatly appreciated!
>
> Cheers,
> Mike

nothing looks offensive, although the 386 is an especially noisy chip
in the first place, the 0.1uf caps going to the digital chips are
decoupling caps, they keep bouncy power from effecting the chips
(false triggers and whatnot) and they should not have any effect on a
analog output

what happens if the amp is powered externally?

Polymorph

On Aug 29, 1:47*pm, Osgeld <osg...@cheesefactory.us> wrote:
> On Aug 28, 8:35*pm, Polymorph <mike.a.steph...@gmail.com> wrote:
>
>
>
>
>
> > Hi Guys,
>
> > I decided to add the LM386 amplifiers to my Mockingboard that I posted
> > about a few weeks ago. Prior to adding the amplification, the board
> > was working fine with powered speakers. This might be another case of
> > "if it aint broke, don't fix it", but I wanted to hear the difference
> > the amplifiers would make, and I had already bought them as well, so
> > the temptation was too strong. *;-)
>
> > I completed the amplifier add-on and have got it working as such, but
> > with *heaps* of bus noise being output. I can play music, and I know
> > the amplifiers are obviously working as the sound is loud even on un-
> > powered speakers. The trouble is, as soon as I turn on the Apple II, I
> > can hear fairly loud bus noise.
>
> > Now I've used the circuit as described in the AY-3-8910 data manual
> > which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>
> > From analysis of the high resolution scans of the Mockingboard V1 on
> > the ReactiveMicro site, this circuit appears to be very similar to
> > what is on the Mockingboard V1. Is there anything obviously wrong
> > with the circuit above?
>
> > Another thing I've noticed is that the Mockingboard V1 has some
> > additional 0.1uF capacitors on the +5V line going into the AY-3-8910
> > and 6522 chips. Could the absence of these capacitors be responsible
> > for the noise I'm hearing?
>
> > I've gone over the additional amplifier circuitry that I added, and
> > everything appears to be wired correctly. Remember, the rest of the
> > circuit was working fine (albeit without amplification).
>
> > Is anything else I should check to eliminate the bus noise?
>
> > Any help would be greatly appreciated!
>
> > Cheers,
> > Mike
>
> nothing looks offensive, although the 386 is an especially noisy chip
> in the first place, the 0.1uf caps going to the digital chips are
> decoupling caps, they keep bouncy power from effecting the chips
> (false triggers and whatnot) and they should not have any effect on a
> analog output
>
> what happens if the amp is powered externally?

Thanks, I'll give that a try tonight and see what happens.

One thing that has occurred to me just now is that the resistors I've
used are all 0.5 Watt. The addition of the amplifier would be causing
the output to go greater than 0.5 Watts now would it not? Could this
be the cause of the noise? Should I replace all resistors with 1 Watt
(or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?

Cheers,
Mike

Osgeld

On Aug 29, 12:20*am, Polymorph <mike.a.steph...@gmail.com> wrote:
> On Aug 29, 1:47*pm, Osgeld <osg...@cheesefactory.us> wrote:
>
>
>
> > On Aug 28, 8:35*pm, Polymorph <mike.a.steph...@gmail.com> wrote:
>
> > > Hi Guys,
>
> > > I decided to add the LM386 amplifiers to my Mockingboard that I posted
> > > about a few weeks ago. Prior to adding the amplification, the board
> > > was working fine with powered speakers. This might be another case of
> > > "if it aint broke, don't fix it", but I wanted to hear the difference
> > > the amplifiers would make, and I had already bought them as well, so
> > > the temptation was too strong. *;-)
>
> > > I completed the amplifier add-on and have got it working as such, but
> > > with *heaps* of bus noise being output. I can play music, and I know
> > > the amplifiers are obviously working as the sound is loud even on un-
> > > powered speakers. The trouble is, as soon as I turn on the Apple II, I
> > > can hear fairly loud bus noise.
>
> > > Now I've used the circuit as described in the AY-3-8910 data manual
> > > which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>
> > > From analysis of the high resolution scans of the Mockingboard V1 on
> > > the ReactiveMicro site, this circuit appears to be very similar to
> > > what is on the Mockingboard V1. Is there anything obviously wrong
> > > with the circuit above?
>
> > > Another thing I've noticed is that the Mockingboard V1 has some
> > > additional 0.1uF capacitors on the +5V line going into the AY-3-8910
> > > and 6522 chips. Could the absence of these capacitors be responsible
> > > for the noise I'm hearing?
>
> > > I've gone over the additional amplifier circuitry that I added, and
> > > everything appears to be wired correctly. Remember, the rest of the
> > > circuit was working fine (albeit without amplification).
>
> > > Is anything else I should check to eliminate the bus noise?
>
> > > Any help would be greatly appreciated!
>
> > > Cheers,
> > > Mike
>
> > nothing looks offensive, although the 386 is an especially noisy chip
> > in the first place, the 0.1uf caps going to the digital chips are
> > decoupling caps, they keep bouncy power from effecting the chips
> > (false triggers and whatnot) and they should not have any effect on a
> > analog output
>
> > what happens if the amp is powered externally?
>
> Thanks, I'll give that a try tonight and see what happens.
>
> One thing that has occurred to me just now is that the resistors I've
> used are all 0.5 Watt. The addition of the amplifier would be causing
> the output to go greater than 0.5 Watts now would it not? Could this
> be the cause of the noise? Should I replace all resistors with 1 Watt
> (or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?
>
> Cheers,
> Mike

half watt resistors are really overkill (but not doing any harm) the
wattage rating of a resistor is not how much you can pass though it,
but how much energy it can dissipate before breaking, with the current
and voltages involved your more than ok

the issue is there is noisy power, your amplifying it (just like the
hum of a guitar amp) so you are looking to remove it or filter it
out...

I dont know how you have this constructed, if its soldered together,
trial and error could be a big PITA, that is why I suggested running
it off of a separated power supply first, you could also increase the
value of the 300pf capacitor or omit it and the 500 ohm resistor, as
that is not usually seen on basic applications of the amp

it also could be coming from the passive mixer since its taking 3
inputs and running them through a voltage divider to ground

dunno I am not an analog electronics guru

Polymorph

On Aug 29, 3:34*pm, Osgeld <osg...@cheesefactory.us> wrote:
> On Aug 29, 12:20*am, Polymorph <mike.a.steph...@gmail.com> wrote:
>
>
>
>
>
> > On Aug 29, 1:47*pm, Osgeld <osg...@cheesefactory.us> wrote:
>
> > > On Aug 28, 8:35*pm, Polymorph <mike.a.steph...@gmail.com> wrote:
>
> > > > Hi Guys,
>
> > > > I decided to add the LM386 amplifiers to my Mockingboard that I posted
> > > > about a few weeks ago. Prior to adding the amplification, the board
> > > > was working fine with powered speakers. This might be another case of
> > > > "if it aint broke, don't fix it", but I wanted to hear the difference
> > > > the amplifiers would make, and I had already bought them as well, so
> > > > the temptation was too strong. *;-)
>
> > > > I completed the amplifier add-on and have got it working as such, but
> > > > with *heaps* of bus noise being output. I can play music, and I know
> > > > the amplifiers are obviously working as the sound is loud even on un-
> > > > powered speakers. The trouble is, as soon as I turn on the Apple II, I
> > > > can hear fairly loud bus noise.
>
> > > > Now I've used the circuit as described in the AY-3-8910 data manual
> > > > which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>
> > > > From analysis of the high resolution scans of the Mockingboard V1 on
> > > > the ReactiveMicro site, this circuit appears to be very similar to
> > > > what is on the Mockingboard V1. Is there anything obviously wrong
> > > > with the circuit above?
>
> > > > Another thing I've noticed is that the Mockingboard V1 has some
> > > > additional 0.1uF capacitors on the +5V line going into the AY-3-8910
> > > > and 6522 chips. Could the absence of these capacitors be responsible
> > > > for the noise I'm hearing?
>
> > > > I've gone over the additional amplifier circuitry that I added, and
> > > > everything appears to be wired correctly. Remember, the rest of the
> > > > circuit was working fine (albeit without amplification).
>
> > > > Is anything else I should check to eliminate the bus noise?
>
> > > > Any help would be greatly appreciated!
>
> > > > Cheers,
> > > > Mike
>
> > > nothing looks offensive, although the 386 is an especially noisy chip
> > > in the first place, the 0.1uf caps going to the digital chips are
> > > decoupling caps, they keep bouncy power from effecting the chips
> > > (false triggers and whatnot) and they should not have any effect on a
> > > analog output
>
> > > what happens if the amp is powered externally?
>
> > Thanks, I'll give that a try tonight and see what happens.
>
> > One thing that has occurred to me just now is that the resistors I've
> > used are all 0.5 Watt. The addition of the amplifier would be causing
> > the output to go greater than 0.5 Watts now would it not? Could this
> > be the cause of the noise? Should I replace all resistors with 1 Watt
> > (or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?
>
> > Cheers,
> > Mike
>
> half watt resistors are really overkill (but not doing any harm) the
> wattage rating of a resistor is not how much you can pass though it,
> but how much energy it can dissipate before breaking, with the current
> and voltages involved your more than ok
>
> the issue is there is noisy power, your amplifying it (just like the
> hum of a guitar amp) so you are looking to remove it or filter it
> out...
>
> I dont know how you have this constructed, if its soldered together,
> trial and error could be a big PITA, that is why I suggested running
> it off of a separated power supply first, you could also increase the
> value of the 300pf capacitor or omit it and the 500 ohm resistor, as
> that is not usually seen on basic applications of the amp
>
> it also could be coming from the passive mixer since its taking 3
> inputs and running them through a voltage divider to ground
>
> dunno I am not an analog electronics guru

Yeah, its soldered together. Details are on my website as to how I
constructed it:
http://apple2.sytes.net/Mockingboard/

It has been modified since those photo's to accommodate the
amplifiers. I took a couple of quick shots of the card as it is now.
The image links are:
http://apple2.sytes.net/Mockingboard...kingboard1.jpg
http://apple2.sytes.net/Mockingboard...kingboard2.jpg

One thing I forgot to mention is that I had originally wired the
LM386's using the +5V line (as all the other chips are), however, I
noticed that the Mockingboard V1 (and original Mockingboards) used the
+12V line, so I changed to using that; with the 12V wired to a 220uF
cap going to ground (as per the Mockingboard V1). However, after doing
this, the results sound exactly the same. :-(

I'll try rigging up an external power source and see what happens.

Thanks for your help!

Cheers,
Mike

Michael J. Mahon

On 8/28/2010 10:34 PM, Osgeld wrote:
> On Aug 29, 12:20 am, Polymorph<mike.a.steph...@gmail.com> wrote:
>> On Aug 29, 1:47 pm, Osgeld<osg...@cheesefactory.us> wrote:
>>
>>
>>
>>> On Aug 28, 8:35 pm, Polymorph<mike.a.steph...@gmail.com> wrote:
>>
>>>> Hi Guys,
>>
>>>> I decided to add the LM386 amplifiers to my Mockingboard that I posted
>>>> about a few weeks ago. Prior to adding the amplification, the board
>>>> was working fine with powered speakers. This might be another case of
>>>> "if it aint broke, don't fix it", but I wanted to hear the difference
>>>> the amplifiers would make, and I had already bought them as well, so
>>>> the temptation was too strong. ;-)
>>
>>>> I completed the amplifier add-on and have got it working as such, but
>>>> with *heaps* of bus noise being output. I can play music, and I know
>>>> the amplifiers are obviously working as the sound is loud even on un-
>>>> powered speakers. The trouble is, as soon as I turn on the Apple II, I
>>>> can hear fairly loud bus noise.
>>
>>>> Now I've used the circuit as described in the AY-3-8910 data manual
>>>> which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>>
>>>> From analysis of the high resolution scans of the Mockingboard V1 on
>>>> the ReactiveMicro site, this circuit appears to be very similar to
>>>> what is on the Mockingboard V1. Is there anything obviously wrong
>>>> with the circuit above?
>>
>>>> Another thing I've noticed is that the Mockingboard V1 has some
>>>> additional 0.1uF capacitors on the +5V line going into the AY-3-8910
>>>> and 6522 chips. Could the absence of these capacitors be responsible
>>>> for the noise I'm hearing?
>>
>>>> I've gone over the additional amplifier circuitry that I added, and
>>>> everything appears to be wired correctly. Remember, the rest of the
>>>> circuit was working fine (albeit without amplification).
>>
>>>> Is anything else I should check to eliminate the bus noise?
>>
>>>> Any help would be greatly appreciated!
>>
>>>> Cheers,
>>>> Mike
>>
>>> nothing looks offensive, although the 386 is an especially noisy chip
>>> in the first place, the 0.1uf caps going to the digital chips are
>>> decoupling caps, they keep bouncy power from effecting the chips
>>> (false triggers and whatnot) and they should not have any effect on a
>>> analog output
>>
>>> what happens if the amp is powered externally?
>>
>> Thanks, I'll give that a try tonight and see what happens.
>>
>> One thing that has occurred to me just now is that the resistors I've
>> used are all 0.5 Watt. The addition of the amplifier would be causing
>> the output to go greater than 0.5 Watts now would it not? Could this
>> be the cause of the noise? Should I replace all resistors with 1 Watt
>> (or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?
>>
>> Cheers,
>> Mike
>
> half watt resistors are really overkill (but not doing any harm) the
> wattage rating of a resistor is not how much you can pass though it,
> but how much energy it can dissipate before breaking, with the current
> and voltages involved your more than ok
>
> the issue is there is noisy power, your amplifying it (just like the
> hum of a guitar amp) so you are looking to remove it or filter it
> out...
>
> I dont know how you have this constructed, if its soldered together,
> trial and error could be a big PITA, that is why I suggested running
> it off of a separated power supply first, you could also increase the
> value of the 300pf capacitor or omit it and the 500 ohm resistor, as
> that is not usually seen on basic applications of the amp
>
> it also could be coming from the passive mixer since its taking 3
> inputs and running them through a voltage divider to ground
>
> dunno I am not an analog electronics guru

But I expect your diagnosis is correct--the noise is coming from
the +5v power bus, plus any "ground bounce" on the ground lines.

The Apple +5v supply is quite noisy for any audio application.
I expect that your experiment with a (quiet) external supply will
produce results very similar in S/N to your amplified speakers.

The easiest solution for deriving quiet power from the Apple bus
is to use the +12v line, and regulate it down to, say, +8v for the
386's. Also add an RC decoupling circuit to the +12v line prior to
the voltage regulator--say, a 22 ohm series resistor and a 100uF
cap to ground, to reduce high-frequency noise. The regulator should
do a good job attenuating the low-frequency supply noise.

For the AppleCrate II, I built an outboard audio processor powered
by the 'Crate. I regulated the +12v down to +8 for the 386's, and
further regulated the +8 down to +5 for the "quiet" +5 supply for
the 17 1-bit DACs and the opamps.

BTW, if you were unsatisfied with the noise levels with externally
powered speakers, you'll need to begin by using a large decoupling
capacitor from +5v to ground--at least 50uF for starters. It's easy
to try this out for effect by connecting and disconnecting one end
of the capacitor while listening to the output with no sound being
generated.

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page: http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."

Polymorph

On Aug 30, 5:54*pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> On 8/28/2010 10:34 PM, Osgeld wrote:
>
>
>
>
>
> > On Aug 29, 12:20 am, Polymorph<mike.a.steph...@gmail.com> *wrote:
> >> On Aug 29, 1:47 pm, Osgeld<osg...@cheesefactory.us> *wrote:
>
> >>> On Aug 28, 8:35 pm, Polymorph<mike.a.steph...@gmail.com> *wrote:
>
> >>>> Hi Guys,
>
> >>>> I decided to add the LM386 amplifiers to my Mockingboard that I posted
> >>>> about a few weeks ago. Prior to adding the amplification, the board
> >>>> was working fine with powered speakers. This might be another case of
> >>>> "if it aint broke, don't fix it", but I wanted to hear the difference
> >>>> the amplifiers would make, and I had already bought them as well, so
> >>>> the temptation was too strong. *;-)
>
> >>>> I completed the amplifier add-on and have got it working as such, but
> >>>> with *heaps* of bus noise being output. I can play music, and I know
> >>>> the amplifiers are obviously working as the sound is loud even on un-
> >>>> powered speakers. The trouble is, as soon as I turn on the Apple II,I
> >>>> can hear fairly loud bus noise.
>
> >>>> Now I've used the circuit as described in the AY-3-8910 data manual
> >>>> which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>
> >>>> *From analysis of the high resolution scans of the Mockingboard V1on
> >>>> the ReactiveMicro site, this circuit appears to be very similar to
> >>>> what is on the Mockingboard V1. Is there anything obviously wrong
> >>>> with the circuit above?
>
> >>>> Another thing I've noticed is that the Mockingboard V1 has some
> >>>> additional 0.1uF capacitors on the +5V line going into the AY-3-8910
> >>>> and 6522 chips. Could the absence of these capacitors be responsible
> >>>> for the noise I'm hearing?
>
> >>>> I've gone over the additional amplifier circuitry that I added, and
> >>>> everything appears to be wired correctly. Remember, the rest of the
> >>>> circuit was working fine (albeit without amplification).
>
> >>>> Is anything else I should check to eliminate the bus noise?
>
> >>>> Any help would be greatly appreciated!
>
> >>>> Cheers,
> >>>> Mike
>
> >>> nothing looks offensive, although the 386 is an especially noisy chip
> >>> in the first place, the 0.1uf caps going to the digital chips are
> >>> decoupling caps, they keep bouncy power from effecting the chips
> >>> (false triggers and whatnot) and they should not have any effect on a
> >>> analog output
>
> >>> what happens if the amp is powered externally?
>
> >> Thanks, I'll give that a try tonight and see what happens.
>
> >> One thing that has occurred to me just now is that the resistors I've
> >> used are all 0.5 Watt. The addition of the amplifier would be causing
> >> the output to go greater than 0.5 Watts now would it not? Could this
> >> be the cause of the noise? Should I replace all resistors with 1 Watt
> >> (or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?
>
> >> Cheers,
> >> Mike
>
> > half watt resistors are really overkill (but not doing any harm) the
> > wattage rating of a resistor is not how much you can pass though it,
> > but how much energy it can dissipate before breaking, with the current
> > and voltages involved your more than ok
>
> > the issue is there is noisy power, your amplifying it (just like the
> > hum of a guitar amp) so you are looking to remove it or filter it
> > out...
>
> > I dont know how you have this constructed, if its soldered together,
> > trial and error could be a big PITA, that is why I suggested running
> > it off of a separated power supply first, you could also increase the
> > value of the 300pf capacitor or omit it and the 500 ohm resistor, as
> > that is not usually seen on basic applications of the amp
>
> > it also could be coming from the passive mixer since its taking 3
> > inputs and running them through a voltage divider to ground
>
> > dunno I am not an analog electronics guru
>
> But I expect your diagnosis is correct--the noise is coming from
> the +5v power bus, plus any "ground bounce" on the ground lines.
>
> The Apple +5v supply is quite noisy for any audio application.
> I expect that your experiment with a (quiet) external supply will
> produce results very similar in S/N to your amplified speakers.
>
> The easiest solution for deriving quiet power from the Apple bus
> is to use the +12v line, and regulate it down to, say, +8v for the
> 386's. *Also add an RC decoupling circuit to the +12v line prior to
> the voltage regulator--say, a 22 ohm series resistor and a 100uF
> cap to ground, to reduce high-frequency noise. *The regulator should
> do a good job attenuating the low-frequency supply noise.
>
> For the AppleCrate II, I built an outboard audio processor powered
> by the 'Crate. *I regulated the +12v down to +8 for the 386's, and
> further regulated the +8 down to +5 for the "quiet" +5 supply for
> the 17 1-bit DACs and the opamps.
>
> BTW, if you were unsatisfied with the noise levels with externally
> powered speakers, you'll need to begin by using a large decoupling
> capacitor from +5v to ground--at least 50uF for starters. *It's easy
> to try this out for effect by connecting and disconnecting one end
> of the capacitor while listening to the output with no sound being
> generated.
>
> -michael
>
> NadaNet 3.1 for Apple II parallel computing!
> Home page: *http://home.comcast.net/~mjmahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."

Michael,

As I mentioned in a separate post, I had originally wired the LM386's
to +5V, but then checnged to using the +12V line in the exact same way
as on the Mockingboard V1 (and presumably the original Mockingboards).
But after doing the switch to 12V, I heard little or no difference.

But I plan on rigging up a 9V battery as the power source to see if
that eliminates the noise.

If that fails, I'll probably ditch the suggested schematic from the
AY-3-8910 manual, and just implement what I see on the Mockingboard
V1.

Thanks for the help.

Cheers,
Mike

Michael J. Mahon

On 8/30/2010 5:25 PM, Polymorph wrote:
> On Aug 30, 5:54 pm, "Michael J. Mahon"<mjma...@aol.com> wrote:
>> On 8/28/2010 10:34 PM, Osgeld wrote:
>>
>>
>>
>>
>>
>>> On Aug 29, 12:20 am, Polymorph<mike.a.steph...@gmail.com> wrote:
>>>> On Aug 29, 1:47 pm, Osgeld<osg...@cheesefactory.us> wrote:
>>
>>>>> On Aug 28, 8:35 pm, Polymorph<mike.a.steph...@gmail.com> wrote:
>>
>>>>>> Hi Guys,
>>
>>>>>> I decided to add the LM386 amplifiers to my Mockingboard that I posted
>>>>>> about a few weeks ago. Prior to adding the amplification, the board
>>>>>> was working fine with powered speakers. This might be another case of
>>>>>> "if it aint broke, don't fix it", but I wanted to hear the difference
>>>>>> the amplifiers would make, and I had already bought them as well, so
>>>>>> the temptation was too strong. ;-)
>>
>>>>>> I completed the amplifier add-on and have got it working as such, but
>>>>>> with *heaps* of bus noise being output. I can play music, and I know
>>>>>> the amplifiers are obviously working as the sound is loud even on un-
>>>>>> powered speakers. The trouble is, as soon as I turn on the Apple II, I
>>>>>> can hear fairly loud bus noise.
>>
>>>>>> Now I've used the circuit as described in the AY-3-8910 data manual
>>>>>> which can be seen here:http://apple2.sytes.net/Mockingboard...nterfacing.jpg
>>
>>>>>> From analysis of the high resolution scans of the Mockingboard V1 on
>>>>>> the ReactiveMicro site, this circuit appears to be very similar to
>>>>>> what is on the Mockingboard V1. Is there anything obviously wrong
>>>>>> with the circuit above?
>>
>>>>>> Another thing I've noticed is that the Mockingboard V1 has some
>>>>>> additional 0.1uF capacitors on the +5V line going into the AY-3-8910
>>>>>> and 6522 chips. Could the absence of these capacitors be responsible
>>>>>> for the noise I'm hearing?
>>
>>>>>> I've gone over the additional amplifier circuitry that I added, and
>>>>>> everything appears to be wired correctly. Remember, the rest of the
>>>>>> circuit was working fine (albeit without amplification).
>>
>>>>>> Is anything else I should check to eliminate the bus noise?
>>
>>>>>> Any help would be greatly appreciated!
>>
>>>>>> Cheers,
>>>>>> Mike
>>
>>>>> nothing looks offensive, although the 386 is an especially noisy chip
>>>>> in the first place, the 0.1uf caps going to the digital chips are
>>>>> decoupling caps, they keep bouncy power from effecting the chips
>>>>> (false triggers and whatnot) and they should not have any effect on a
>>>>> analog output
>>
>>>>> what happens if the amp is powered externally?
>>
>>>> Thanks, I'll give that a try tonight and see what happens.
>>
>>>> One thing that has occurred to me just now is that the resistors I've
>>>> used are all 0.5 Watt. The addition of the amplifier would be causing
>>>> the output to go greater than 0.5 Watts now would it not? Could this
>>>> be the cause of the noise? Should I replace all resistors with 1 Watt
>>>> (or higher) resistors, or are the 0.5 Watt ones I'm using sufficient?
>>
>>>> Cheers,
>>>> Mike
>>
>>> half watt resistors are really overkill (but not doing any harm) the
>>> wattage rating of a resistor is not how much you can pass though it,
>>> but how much energy it can dissipate before breaking, with the current
>>> and voltages involved your more than ok
>>
>>> the issue is there is noisy power, your amplifying it (just like the
>>> hum of a guitar amp) so you are looking to remove it or filter it
>>> out...
>>
>>> I dont know how you have this constructed, if its soldered together,
>>> trial and error could be a big PITA, that is why I suggested running
>>> it off of a separated power supply first, you could also increase the
>>> value of the 300pf capacitor or omit it and the 500 ohm resistor, as
>>> that is not usually seen on basic applications of the amp
>>
>>> it also could be coming from the passive mixer since its taking 3
>>> inputs and running them through a voltage divider to ground
>>
>>> dunno I am not an analog electronics guru
>>
>> But I expect your diagnosis is correct--the noise is coming from
>> the +5v power bus, plus any "ground bounce" on the ground lines.
>>
>> The Apple +5v supply is quite noisy for any audio application.
>> I expect that your experiment with a (quiet) external supply will
>> produce results very similar in S/N to your amplified speakers.
>>
>> The easiest solution for deriving quiet power from the Apple bus
>> is to use the +12v line, and regulate it down to, say, +8v for the
>> 386's. Also add an RC decoupling circuit to the +12v line prior to
>> the voltage regulator--say, a 22 ohm series resistor and a 100uF
>> cap to ground, to reduce high-frequency noise. The regulator should
>> do a good job attenuating the low-frequency supply noise.
>>
>> For the AppleCrate II, I built an outboard audio processor powered
>> by the 'Crate. I regulated the +12v down to +8 for the 386's, and
>> further regulated the +8 down to +5 for the "quiet" +5 supply for
>> the 17 1-bit DACs and the opamps.
>>
>> BTW, if you were unsatisfied with the noise levels with externally
>> powered speakers, you'll need to begin by using a large decoupling
>> capacitor from +5v to ground--at least 50uF for starters. It's easy
>> to try this out for effect by connecting and disconnecting one end
>> of the capacitor while listening to the output with no sound being
>> generated.
>
> Michael,
>
> As I mentioned in a separate post, I had originally wired the LM386's
> to +5V, but then checnged to using the +12V line in the exact same way
> as on the Mockingboard V1 (and presumably the original Mockingboards).
> But after doing the switch to 12V, I heard little or no difference.

The critical thing is adding the extra bypassing and the voltage
regulator (7808, for example) to prune the noise from the power bus.

> But I plan on rigging up a 9V battery as the power source to see if
> that eliminates the noise.
>
> If that fails, I'll probably ditch the suggested schematic from the
> AY-3-8910 manual, and just implement what I see on the Mockingboard
> V1.

The original Mockingboard was also pretty noisy, so don't think that
will cure the problem!

It's quite possible that your card has always had a fair amount of
background digital noise, and that the 386's are just amplifying it.
(Did you have the treble control turned down on your powered speakers?)

To get reasonably quiet audio out of an Apple II will require good
filtering on all supplies--including the +5v which powers the source
of the audio signal.

Extra bypassing may help, but the ultimate solution is to double
regulate down from the +12v to get quiet +5v for the 8910's.

You may also want to increase the value of the capacitors shunting
the input to the 386's. That will roll off the high frequencies,
attenuating the most annoying noise and making the sound richer
and less shrill (a big issue with squarewave sound generation).

> Thanks for the help.

You're welcome--I hope you get it working to your satisfaction!

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page: http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."

Polymorph

To: Michael J. Mahon
Michael J. Mahon wrote:
>
> The original Mockingboard was also pretty noisy, so don't think that
> will cure the problem!
>
> It's quite possible that your card has always had a fair amount of
> background digital noise, and that the 386's are just amplifying it.
> (Did you have the treble control turned down on your powered speakers?)
>
> To get reasonably quiet audio out of an Apple II will require good
> filtering on all supplies--including the +5v which powers the source
> of the audio signal.
>
> Extra bypassing may help, but the ultimate solution is to double
> regulate down from the +12v to get quiet +5v for the 8910's.
>
> You may also want to increase the value of the capacitors shunting
> the input to the 386's. That will roll off the high frequencies,
> attenuating the most annoying noise and making the sound richer
> and less shrill (a big issue with squarewave sound generation).
>
>> Thanks for the help.
>
> You're welcome--I hope you get it working to your satisfaction!
>


OK, so I bit the bullet today and un-did all of the amplification
circuit and put things back to how they were before (as described on my
web site).

I found the noise from the LM386's unacceptable. I tested the LM386's in
isolation (with no input signal) with only power and ground wired up as
per the Mockingboard V1 (i.e. with the 12V line attached to a 220uF
filter capacitor) and the noise was the same as noted previously.

I notice that I have LM386N-1 chips as opposed to the Mockingboard V1's
LM386N-3 chips, but I don't think this would make any difference from
reading the specs (slightly different voltage tolerance and output
IIRC). So I have no idea how they've got the Mockingboard V1 to not
produce the noise I was getting. The only thing I can think of is that I
noticed that the power and ground rails on the Mockingboard V1 are
thicker. Could using thicker wire for power and ground have reduced the
noise I was getting? I'm not going to try it, but would be interested to
hear thoughts on this.

Without the LM386's in place, I can crank the volume/treble/base up to
maximum on my powered speakers and I can only then just faintly hear
noise when no music is playing.

Based on my findings, anyone looking to make a Mockingboard, my
recommendation is to forget the LM386's and look to another chip, or do
what I did and just forget amplification altogether and run it with
amplified speakers.

Cheers,
Mike

--

Mike Stephens
Central Coast, Australia

Find my Apple II projects online at:
http://apple2.sytes.net/

Michael J. Mahon

On 9/4/2010 2:28 AM, Polymorph wrote:
> To: Michael J. Mahon
> Michael J. Mahon wrote:
>>
>> The original Mockingboard was also pretty noisy, so don't think that
>> will cure the problem!
>>
>> It's quite possible that your card has always had a fair amount of
>> background digital noise, and that the 386's are just amplifying it.
>> (Did you have the treble control turned down on your powered speakers?)
>>
>> To get reasonably quiet audio out of an Apple II will require good
>> filtering on all supplies--including the +5v which powers the source
>> of the audio signal.
>>
>> Extra bypassing may help, but the ultimate solution is to double
>> regulate down from the +12v to get quiet +5v for the 8910's.
>>
>> You may also want to increase the value of the capacitors shunting
>> the input to the 386's. That will roll off the high frequencies,
>> attenuating the most annoying noise and making the sound richer
>> and less shrill (a big issue with squarewave sound generation).
>>
>>> Thanks for the help.
>>
>> You're welcome--I hope you get it working to your satisfaction!
>>
>
>
> OK, so I bit the bullet today and un-did all of the amplification
> circuit and put things back to how they were before (as described on my
> web site).
>
> I found the noise from the LM386's unacceptable. I tested the LM386's in
> isolation (with no input signal) with only power and ground wired up as
> per the Mockingboard V1 (i.e. with the 12V line attached to a 220uF
> filter capacitor) and the noise was the same as noted previously.
>
> I notice that I have LM386N-1 chips as opposed to the Mockingboard V1's
> LM386N-3 chips, but I don't think this would make any difference from
> reading the specs (slightly different voltage tolerance and output
> IIRC). So I have no idea how they've got the Mockingboard V1 to not
> produce the noise I was getting. The only thing I can think of is that I
> noticed that the power and ground rails on the Mockingboard V1 are
> thicker. Could using thicker wire for power and ground have reduced the
> noise I was getting? I'm not going to try it, but would be interested to
> hear thoughts on this.

Thicker isn't so much the issue, but a ground plane might help.

If noise is entering through the power bus, then neither wire nor
a ground plane will make any difference.

If the noise is originating in the 386's, then *nothing* will help,
except fixing the 386's. ;-) It is possible that the 386's are
oscillating at a very high (inaudible) frequency, and that is the
source of the noise. Decoupling close to the 386 and care to reduce
coupling between the input and output are important. It is also
useful to use a high-frequency "snubbing" ciruit across the output
(which is otherwise dominated by the LC circuit of the speaker coil).

Many 386 circuits show a 10 ohm resistor and a 0.05uF capacitor,
connected in series, shunting the output to ground. I don't recall
if your circuit has this or not, but it's worth a try.

It's worth keeping in mind that the 386 has a high gain, so good
analog circuit layout techniques are in order to prevent oscillation.

For diagnostic purposes, try building up a 386 amplifier on a separate
piece of perfboard, powered by a known quiet source--like a battery.
Then see how it sounds. If the noise is still present, then you have
a bad 386 (or very high standards ;-).

I would expect this 386 amp to be sufficiently quiet, and then you
can hook it up to your board and see if the noise is on the input.
If it isn't, then cleaning up the Apple +12v is the only thing
that needs to be done. If the noise *is* on the input, then the
problem isn't the 386 stage at all.

> Without the LM386's in place, I can crank the volume/treble/base up to
> maximum on my powered speakers and I can only then just faintly hear
> noise when no music is playing.

That's good. That bodes well for getting a 386 stage to work, too.

> Based on my findings, anyone looking to make a Mockingboard, my
> recommendation is to forget the LM386's and look to another chip, or do
> what I did and just forget amplification altogether and run it with
> amplified speakers.

From a practical point of view, running with amplified speakers makes
a lot of sense--they're about the only game in town these days. ;-)

The 386's provide for headphone use, though, and that may be enough
reason to include them.

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page: http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
tool--and it's seriously underused."