sci.electronics.repair - 25 new messages in 4 topics - digest

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Today's topics:

* Mixing 4 audio channels to 3? - 19 messages, 8 authors
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
* Thoughts on this little oddity, anyone ...? - 4 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
* Hot electrolytics - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
* What Are the Cylyndrical Objects You Often See on Audio, USB, etc, Cables? -
1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/ab1226e8296518ed?hl=en

==============================================================================
TOPIC: Mixing 4 audio channels to 3?
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
==============================================================================

== 1 of 19 ==
Date: Wed, Nov 9 2011 10:19 am
From: moroney@world.std.spaamtrap.com (Michael Moroney)

DaveC <invalid@invalid.net> writes:

>> Your drawing is wrong; signal goes to the inverting (-) inputs and the
>> Vcc/2 reference goes to the non-inverting (+) inputs.
>> JF

>Thanks guys. Fixed:

><http://i44.tinypic.com/r1k8qa.jpg>

>All else looks good?

You still have the signal go to the non-inverting input. The way the
schematic is, U1-U3 will throw their output hard to a rail or oscillate
with positive feedback from R13-R15.

>Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
>designs. Values for these?

I worry that the RC time constant would have the reference be not at the
1/2 way point while C8 charges on powerup. I don't see a C9. Might do
something not so good to the subwoofer.

== 2 of 19 ==
Date: Wed, Nov 9 2011 10:43 am
From: DaveC

> You still have the signal go to the non-inverting input.

The current version of the drawing has signal going to the inverting input

>> Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
>> designs. Values for these?

> I worry that the RC time constant would have the reference be not at the
> 1/2 way point while C8 charges on powerup.

Suggestions?

> I don't see a C9.

That means you're not looking at the right version of the drawing. Copy &
paste this into a browser:

<http://i44.tinypic.com/r1k8qa.jpg>

> Might do something not so good to the subwoofer.
> [M. Moroney]

Suggestions?

Thanks.

== 3 of 19 ==
Date: Wed, Nov 9 2011 10:52 am
From: spam@spam.com (Don Pearce)

On Wed, 9 Nov 2011 09:07:15 -0800, DaveC <invalid@invalid.net> wrote:

>> Your drawing is wrong; signal goes to the inverting (-) inputs and the
>> Vcc/2 reference goes to the non-inverting (+) inputs.
>> JF
>
>Thanks guys. Fixed:
>
><http://i44.tinypic.com/r1k8qa.jpg>
>
>All else looks good?
>
>Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
>designs. Values for these?
>
>Thanks.

What does U4 do?

== 4 of 19 ==
Date: Wed, Nov 9 2011 10:53 am
From: dplatt@radagast.org (Dave Platt)

In article <0001HW.CADFF34300E39070B038C9DF@news.eternal-september.org>,
DaveC <newsgroups> wrote:

>> Your drawing is wrong; signal goes to the inverting (-) inputs and the
>> Vcc/2 reference goes to the non-inverting (+) inputs.

Agreed.

>Thanks guys. Fixed:
>
><http://i44.tinypic.com/r1k8qa.jpg>
>
>All else looks good?

>Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
>designs. Values for these?

I'd eliminate C9. Some op amps aren't able to drive capacitive loads
without exhibiting instability.

If you do want some noise reduction on your reference, I'd add a
small decoupling resistor (say, 47R) between U4 and C9, and perhaps
use another .1 uF for C9. If you're using a good low-noise op amp,
you can probably just omit the filtering here and feed U4's output
directly to your "common".

I'd also recommend decoupling your 16-volt power supply, with a .1 uF
located as close as practical to the V+/V- pins of each op amp.

Remember to get the polarities of C1-C7 correct when you install them
(+ to the op-amp side, - to the outside world).

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

== 5 of 19 ==
Date: Wed, Nov 9 2011 12:08 pm
From: DaveC

> I'd eliminate C9. Some op amps aren't able to drive capacitive loads
> without exhibiting instability.

OK, done.

> If you're using a good low-noise op amp,
> you can probably just omit the filtering here and feed U4's output
> directly to your "common".
>
> I'd also recommend decoupling your 16-volt power supply, with a .1 uF
> located as close as practical to the V+/V- pins of each op amp.

Sound like basic good advice. :-)

> Remember to get the polarities of C1-C7 correct when you install them
> (+ to the op-amp side, - to the outside world).

I presumed that such coupling caps should be non-polar. No?

Thanks.

== 6 of 19 ==
Date: Wed, Nov 9 2011 12:10 pm
From: Bob E.

> What does U4 do?

Provides a Vcc/2 local "ground" so I can use these op amps with a single
supply voltage.

== 7 of 19 ==
Date: Wed, Nov 9 2011 12:13 pm
From: DaveC

> I'd also recommend decoupling your 16-volt power supply, with a .1 uF
> located as close as practical to the V+/V- pins of each op amp.

Since the V- pin is already PS ground, I need decouple caps only on the V+
pins, yes?

== 8 of 19 ==
Date: Wed, Nov 9 2011 12:13 pm
From: NT

On Nov 9, 5:07 pm, DaveC <inva...@invalid.net> wrote:
> > Your drawing is wrong; signal goes to the inverting (-) inputs and the
> > Vcc/2 reference goes to the non-inverting (+) inputs.
> > JF
>
> Thanks guys. Fixed:
>
> <http://i44.tinypic.com/r1k8qa.jpg>
>
> All else looks good?
>
> Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
> designs. Values for these?
>
> Thanks.

First you can replace C1-5 with 1uF each. Replace C8 with 220uF, and
omit U4 & C9 entirely.
You dont want to use a 50k pot followed by a 10k load (R5-12). I'd go
with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.

== 9 of 19 ==
Date: Wed, Nov 9 2011 12:31 pm
From: DaveC

> First you can replace C1-[4?] with 1uF each. Replace C8 with 220uF, and
> omit U4 & C9 entirely.

Leave C5-7 as is?

> You dont want to use a 50k pot followed by a 10k load (R5-12).

Teach this man to fish: why don't I want to use 50K pot & 10K load
combination?

> I'd go
> with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.
> NT

"adjusting" means replace those with 100K's also?

Thanks.

== 10 of 19 ==
Date: Wed, Nov 9 2011 12:32 pm
From: spam@spam.com (Don Pearce)

On Wed, 9 Nov 2011 12:10:19 -0800, Bob E. <bespoke@invalid.tv> wrote:

>> What does U4 do?
>
>Provides a Vcc/2 local "ground" so I can use these op amps with a single
>supply voltage.

More useful to let it oscillate as a square wave generator at 100kHz
or so, and rectify the output into a negative 15V rail. That way you
can run the op amps the way they are meant to be run.

== 11 of 19 ==
Date: Wed, Nov 9 2011 12:49 pm
From: Stuart

In article <4ebae303.100219082@news.eternal-september.org>,
Don Pearce <spam@spam.com> wrote:
> >Provides a Vcc/2 local "ground" so I can use these op amps with a single
> >supply voltage.

> More useful to let it oscillate as a square wave generator at 100kHz
> or so, and rectify the output into a negative 15V rail. That way you
> can run the op amps the way they are meant to be run.

KISS

--
Stuart Winsor

Only plain text for emails
http://www.asciiribbon.org

== 12 of 19 ==
Date: Wed, Nov 9 2011 12:53 pm
From: Stuart

In article <3quqo8-5e3.ln1@radagast.org>,
Dave Platt <dplatt@radagast.org> wrote:
> I'd eliminate C9. Some op amps aren't able to drive capacitive loads
> without exhibiting instability.

It's largely redundant anyway.

--
Stuart Winsor

Only plain text for emails
http://www.asciiribbon.org

== 13 of 19 ==
Date: Wed, Nov 9 2011 1:16 pm
From: DaveC

> More useful to let it oscillate as a square wave generator at 100kHz
> or so, and rectify the output into a negative 15V rail. That way you
> can run the op amps the way they are meant to be run.
>
> d

Suggest a circuit...?

Thanks.

== 14 of 19 ==
Date: Wed, Nov 9 2011 1:16 pm
From: dplatt@radagast.org (Dave Platt)

In article <0001HW.CAE01DBF00081152B01849DF@news.eternal-september.org>,
DaveC <newsgroups> wrote:

>> Remember to get the polarities of C1-C7 correct when you install them
>> (+ to the op-amp side, - to the outside world).
>
>I presumed that such coupling caps should be non-polar. No?

No need for that. You're going to have an 8-volt bias sitting on each
cap (half of your supply voltage), and the audio signals that they see
will only be a volt or two, peak-to-peak, so the caps will always be
polarized in the direction I indicated.

It's entirely usual and standard practice to use polar electrolytics
in this sort of situation. If you want to get fancy I'm sure you
could find an exotic 'lytic (like one of the new solid-electrolyte
types), but I see no need for that in this application.

You *could* use nonpolar 'litics if you have them around, but as
they're usually more expensive I don't see the point.

== 15 of 19 ==
Date: Wed, Nov 9 2011 1:18 pm
From: dplatt@radagast.org (Dave Platt)

>> I'd also recommend decoupling your 16-volt power supply, with a .1 uF
>> located as close as practical to the V+/V- pins of each op amp.
>
>Since the V- pin is already PS ground, I need decouple caps only on the V+
>pins, yes?

Good practics is to put the bypass caps as close to the IC leads as is
practical, and run short traces (or wires) to the IC pins.

I wasn't suggesting one bypass cap from V+ to ground and another from
V- to ground... since you're using a single-sided supply and V- is DC
ground, that would be redundant (as you have noted).

== 16 of 19 ==
Date: Wed, Nov 9 2011 1:44 pm
From: NT

On Nov 9, 8:31 pm, DaveC <inva...@invalid.net> wrote:
> > First you can replace C1-[4?] with 1uF each. Replace C8 with 220uF, and
> > omit U4 & C9 entirely.
>
> Leave C5-7 as is?

1uF

> > You dont want to use a 50k pot followed by a 10k load (R5-12).
>
> Teach this man to fish: why don't I want to use 50K pot & 10K load
> combination?
>
> > I'd go
> > with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.
> > NT
>
> "adjusting" means replace those with 100K's also?
>
> Thanks.

that would work

== 17 of 19 ==
Date: Wed, Nov 9 2011 2:20 pm
From: John Fields

On Wed, 09 Nov 2011 20:32:36 GMT, spam@spam.com (Don Pearce) wrote:

>On Wed, 9 Nov 2011 12:10:19 -0800, Bob E. <bespoke@invalid.tv> wrote:
>
>>> What does U4 do?
>>
>>Provides a Vcc/2 local "ground" so I can use these op amps with a single
>>supply voltage.
>
>More useful to let it oscillate as a square wave generator at 100kHz
>or so, and rectify the output into a negative 15V rail. That way you
>can run the op amps the way they are meant to be run.

---
Amen to that!

The beauty parts are that it doesn't need to be regulated, it only
needs to be smooth enough so that its ripples don't bump into the
output's low peaks, and it gets rid of all those damned coupling caps
and their frequency response killing reactances.

I was going to suggest that, since the mixer is going to be external
to the amp, he use a couple of wall-warts to get the dual supplies,
but I like your solution a lot better. :-)

--
JF

== 18 of 19 ==
Date: Wed, Nov 9 2011 2:45 pm
From: DaveC

> No need for that. You're going to have an 8-volt bias sitting on each
> cap (half of your supply voltage), and the audio signals that they see
> will only be a volt or two, peak-to-peak, so the caps will always be
> polarized in the direction I indicated.
>
> It's entirely usual and standard practice to use polar electrolytics
> in this sort of situation. If you want to get fancy I'm sure you
> could find an exotic 'lytic (like one of the new solid-electrolyte
> types), but I see no need for that in this application.
> ...
> Dave P.

I'm learnin'! Thanks for the explanation. I'll use standard aluminum 'lytics
here, connected as noted.

Dave C.

== 19 of 19 ==
Date: Wed, Nov 9 2011 2:45 pm
From: DaveC

> I was going to suggest that, since the mixer is going to be external
> to the amp, he use a couple of wall-warts to get the dual supplies,
> but I like your solution a lot better. :-)

Enough to suggest a nice circuit? ;-)

Thanks,
Dave

==============================================================================
TOPIC: Thoughts on this little oddity, anyone ...?
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
==============================================================================

== 1 of 4 ==
Date: Wed, Nov 9 2011 10:35 am
From: "Gareth Magennis"

"Gareth Magennis" <sound.service@btconnect.com> wrote in message
news:6pzuq.19921$na5.14751@newsfe08.ams2...
>>> That reminds me- does anybody unnderstood what Carver's "power steering"
>>> was supposed to be or mean in their amps?
>>>
>>
>>
>> Probably refers to "rail-switching" where higher voltage power supply
>> rails are switched in on demand. (during musical peaks).
>>
>> Has several advantages including being able to get away with a smaller
>> power transformer and smaller heat sinks. Reduces power dissipation at
>> idle and at low power.
>>
>> It's said that such amps can sound nasty - not sure I've ever noticed
>> that.
>>
>> Mark Z.
>
> The Carver PM1.5 had both the triac and inadequate transformer, and rail
> switching. High rail was + and - 125v IIRC.
>
>
>
> Gareth.

Er, actually I seem to recall now being corrected on that figure once before
by Mr Allison, and it is slightly less? 117?

Gareth.

== 2 of 4 ==
Date: Wed, Nov 9 2011 11:07 am
From: Klay_Anderson

According to the manual:

"CONSTANT POWER SWITCH Set the rear panel slide switch to match the impedance of the speakers used. Use the combined impedance value if you are connecting speakers in series or parallel. Choose the nearest match if the value is not exactly 4 or 8 ohms. Note that no damage will be done if the switch is left in the wrong position. However, you may not benefit from the full capability of the amplifier.
􏰀 Constant power explained The typical amplifier is optimised to produce full power into 4 ohms and therefore considerably less into 8 ohms. The PA Series features a unique facility that ensures you get full power output into either 4 or 8 ohm speakers. It does this by reconfiguring the power supply for optimum current (4 ohms), or voltage (8 ohms)."

Perhaps this is why. They also have the ability through switches to delegate signal to the individual amps for mains and monitors.

== 3 of 4 ==
Date: Wed, Nov 9 2011 2:19 pm
From: "Phil Allison"

"Cydrome Leader"

>> ** Bob Carver was an expert at coming up with high falutin' names for
>> various clever dodges he used to save weight and cost.
>>
>> His " Magnetic Field " amps were nothing of the kind. They simply
>> employed
>> a triac based voltage regulator in the AC supply to improve the
>> regulation
>> factor of a ridiculously small iron transformer.
>
> Hmm, was anybody in the 70s not obsessed with triac pre-regulation in all
> sorts of power supplies?

** What drugs are you on ?

Carver amps were the virtually the only ones to use the idea and the first
( M400) came out in the early 1980s.

( Yamaha made a version and sold about 5. )

... Phil

== 4 of 4 ==
Date: Wed, Nov 9 2011 2:29 pm
From: "Phil Allison"

"Gareth Magennis"

>
> The Carver PM1.5 had both the triac and inadequate transformer, and rail
> switching. High rail was + and - 125v IIRC.

** No rail switching as such, just diode steering.

The regulated DC rails were +/- 23, +/- 55 +/- 80 and +/- 125.

... Phil

==============================================================================
TOPIC: Hot electrolytics
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Nov 9 2011 12:04 pm
From: John Robertson

N_Cook wrote:
> How much is down to conflict between power supply designer and EMC
> compliance bod?
> Designer: I want convection vent holes here, here and here, through the
> shielding
> EMC bod: No way, I can let you have a few holes here and thats your lot
>
> Just repaired an LCD monitor, probably started failure with ESR'd caps then
> ohmic zener and eventually blown backlight inverter pair of transistors and
> blown fuse. Plenty of holes top, side and bottom of the shield on the
> digital processing side but only holes at the top on the ps side. So air
> comes in on the colder side at bottom rises to the top by about mid board
> and little or no air traversing the hottest section, that whole section in a
> dead-zone in more ways than one, brilliant
>
>

Any cap with shrinking plastic film is ready to be replaced. Figure out
what circuit it is in and find either a low ESR or low Inductance (or
both) cap to replace the poorer original one.

We put fans on any LCD screens that we install in any sort of cabinet.

It would be nice if tiny fans were installed by the manufacturers...

John :-#(#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

==============================================================================
TOPIC: What Are the Cylyndrical Objects You Often See on Audio, USB, etc,
Cables?
http://groups.google.com/group/sci.electronics.repair/t/ab1226e8296518ed?hl=en
==============================================================================

== 1 of 1 ==
Date: Wed, Nov 9 2011 2:02 pm
From: "hrhofmann@att.net"

On Nov 9, 11:10 am, Jeff Liebermann <je...@cruzio.com> wrote:
> On Wed, 9 Nov 2011 10:32:26 -0500, Nelson <nel...@nowhere.com> wrote:
> >What are those cylindrical objects you often see surrounding the cable
> >on USB, Audio, Firewire, etc cables?
>
> Regulatory repellents. They're attached by the manufacturer to keep
> the FCC off their back by limiting the amount of RFI/EMI sprayed by
> their equipment.
>
> >I am assuming they are some kind
> >of passive RF interference filter.
>
> Yep. Under the nearly impossible to remove plastic cover lies a heart
> of powdered oxidized iron.
>
> >How do they work?
>
> Quite well. If an FCC Enforcement Burro inspector approached, all one
> needs to do is wave the lumpy cable at the inspector, and he will
> vanish into a smog of legalese.
>
> >How effective are they?
>
> 100% successful. I haven't seen an FCC inspector for many years.
>
> >I am having trouble with interference with an audio cable connected
> >from a computer to a TV and was wondering if a cable with one of these
> >doo-dads would be worth the $.
>
> Oh well. You finally decided to disclose what you're trying to
> accomplish, so I guess I'll have to provide a reasonable answer.
>
> I assume the computah generated interference is trashing the picture
> on the TV or is being heard on the TV audio. What channel is the TV
> watching? If it's channel 3/4 from some kind of set top box, you
> might find it more useful to simply avoid the RF problem and rewire
> your TV setup to use a non-RF input. HDMI, DVI, component video,
> S-video, and component video inputs should all be present on the back
> of your unspecified model TV.
>
> If you're only using the TV for computer audio, you could also
> eliminate the problem by purchasing a set of "computah speakers" for
> about $30. The speakers inside most TV's are fairly disgusting.
>
> If none of these alternatives seem useful, you can purchase clamp on
> ferrite filters.
> <http://www.delevan.com/web/PDF/Suppressors/Cable/BFseries/Page%20118_...>
> Radio Shock carries some:
> <http://www.radioshack.com/product/index.jsp?productId=3012599>
> <http://www.radioshack.com/product/index.jsp?productId=2103222>
> or you can just cannibalize the ferrite beads off an old cable. For
> audio, just about anything will work. Bigger is better and running
> multiple turns through the core is even better:
> <http://www.stevelarkins.freeuk.com/computer_interference.htm>
>
> Gotta run... good luck.
>
> --
> Jeff Liebermann je...@cruzio.com
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

Do what Jeff says. As past predident of the IEEE EMC Society, I have
used many ferrite beads to reduce interference levels to meet FCC
requirements. There are cylidrical beads for round cables and flat
beads for ribbon cables. If you scrap almost any piece of electronic
equipment, you can scrounge a ferrite bead or several.

But, there are different compositions of ferrite to cover the whole
frequency band, so the first bead you try might not be the one you
need. If you told us a little bit more about what your setup is and
what the interference is and where and what you turn off to clear the
problem, we might be able to give you a lot more help

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