30 Jul
2016
30 Jul
'16
10:24 p.m.
Since I acquired a Coco Orchestra 90 unit awhile back, and I am trying
to find the source of some humming in my system when the Orch 90 unit is
operational, I looked at the schematic:
http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Orchest…
(page 109 of the PDF)
I understand the ROM, the resistor ladders, and the latches, but analog
is not my strong suit. I made my way through the op-amp design, but I
am stumped on one component (actually three)?
C7,C9, and C10
They look like electrolytic polarized caps, but are NP (non polarized),
with no '+' on the schematic.
Can someone shed light on what these are and where you would find them
(or if they can safely be replaced with another kind of capacitor)? I
will admit I've never seen mention of these before now.
Are they "bipolar"?
http://www.digikey.com/product-detail/en/nichicon/UVP1H010MDD/UVP1H010MDD-N…
Or, are they called something else now?
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
30 Jul
30 Jul
10:37 p.m.
Jim,
These are non-polarized (or bi-polar) electrolytics. An example is the following digikey
part number: 493-12697-3-ND
You can always whip one up out of your junk box - just put 2 normal (polarized)
electrolytic in series with the polarities alternating (for example, connect the two
positives together). Each capacitor has to be twice the value of the result - so for
example, to replace a 1uF 50v non-polarized, you can put two 2uF in series.
Hope this helps.
Ian
On Jul 30, 2016, at 10:24 PM, Jim Brain <brain at
jbrain.com> wrote:
Since I acquired a Coco Orchestra 90 unit awhile back, and I am trying to find the source
of some humming in my system when the Orch 90 unit is operational, I looked at the
schematic:
http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Orchest…
(page 109 of the PDF)
I understand the ROM, the resistor ladders, and the latches, but analog is not my strong
suit. I made my way through the op-amp design, but I am stumped on one component
(actually three)?
C7,C9, and C10
They look like electrolytic polarized caps, but are NP (non polarized), with no
'+' on the schematic.
Can someone shed light on what these are and where you would find them (or if they can
safely be replaced with another kind of capacitor)? I will admit I've never seen
mention of these before now.
Are they "bipolar"?
http://www.digikey.com/product-detail/en/nichicon/UVP1H010MDD/UVP1H010MDD-N…
Or, are they called something else now?
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
---
Filter service subscribers can train this email as spam or not-spam here:
http://my.email-as.net/spamham/cgi-bin/learn.pl?messageid=3CDFF5C056DF11E69…
1 Aug
1 Aug
12:30 a.m.
On 7/31/2016 12:37 AM, Ian McLaughlin wrote:
Jim,
These are non-polarized (or bi-polar) electrolytics. An example is the following digikey
part number: 493-12697-3-ND
You can always whip one up out of your junk box - just put 2 normal (polarized)
electrolytic in series with the polarities alternating (for example, connect the two
positives together). Each capacitor has to be twice the value of the result - so for
example, to replace a 1uF 50v non-polarized, you can put two 2uF in series.
Hope this helps.
Ian
Thank you (and Chuck) for the response.
I guess it brings up more questions for me:
* Why would Tandy spec such a cap in the design?
* As I look at the specifications of the design, it looks like the
rest of the design assume mac .250W of power on the audio line
(given the selection of resistor networks and other parts) . I
noticed the Digikey unit you referenced has 17mA of ripple current
capability. I realize audio is not truly a ripple current, but the
disparity between 17mA and 250mW seems like a problem... (Again, my
analog is severely rusty, so maybe I am looking at this wrong. I
spent all night trying to find a way to determine the power of a R2R
ladder given 5V logic and 8mA output drive of the 74ls374 IC, to no
avail, so maybe I am looking at this wrong)
o you'd think with the prevalence of R2R ladder logic, someone
would have whipped up a power calculator, if nothing else, to
determine the wattage of the resistors in the R2R, but I came up
empty... I'll have to either calculate it longhand by summing
all of the currents or sim it; not sure I can assume that since
the effective impedence is 10K, the amperage would be .5mA @ 5V
and thus the power would be 2.5mW
Sometimes, I wish I'd cared more about analog in college...
Jim
1:03 a.m.
It's pretty simple, really.
Non-polar caps are used in locations where they must pass AC. Film caps (of
various constructions) are practical until the values exceed a few uF. Once
you need more than a few uF of non-polar capacitance, it's time to look at
NP electrolytics, as they are the cheapest route to a large-ish value
without the polarity issue.
Film caps (in the 63-350V range) are available in values as large as 10uF,
22uF, 47,uF and even 100uF - or more. But those are usually high-priced
specialty audio parts, for things like speaker crossovers and output
coupling caps in some audio preamp circuits.
A non-polar electrolytic is nothing more than a pair of normal (polar)
electrolytics, with the negative (-) leads tied together. There is no
difference between a (nominal) 10uF non-polar and a pair of 22uF polars
tied neg to neg.
Pos to pos works just as well, but it's just not the standard for a very
good reason.. think about how a standard electrolytic cap case is built &
sealed..
On Mon, Aug 1, 2016 at 2:30 AM, Jim Brain <brain at jbrain.com> wrote:
On 7/31/2016 12:37 AM, Ian McLaughlin wrote:
Jim,
These are non-polarized (or bi-polar) electrolytics. An example is the
following digikey part number: 493-12697-3-ND
You can always whip one up out of your junk box - just put 2 normal
(polarized) electrolytic in series with the polarities alternating (for
example, connect the two positives together). Each capacitor has to be
twice the value of the result - so for example, to replace a 1uF 50v
non-polarized, you can put two 2uF in series.
Hope this helps.
Ian
Thank you (and Chuck) for the response.
I guess it brings up more questions for me:
* Why would Tandy spec such a cap in the design?
* As I look at the specifications of the design, it looks like the
rest of the design assume mac .250W of power on the audio line
(given the selection of resistor networks and other parts) . I
noticed the Digikey unit you referenced has 17mA of ripple current
capability. I realize audio is not truly a ripple current, but the
disparity between 17mA and 250mW seems like a problem... (Again, my
analog is severely rusty, so maybe I am looking at this wrong. I
spent all night trying to find a way to determine the power of a R2R
ladder given 5V logic and 8mA output drive of the 74ls374 IC, to no
avail, so maybe I am looking at this wrong)
o you'd think with the prevalence of R2R ladder logic, someone
would have whipped up a power calculator, if nothing else, to
determine the wattage of the resistors in the R2R, but I came up
empty... I'll have to either calculate it longhand by summing
all of the currents or sim it; not sure I can assume that since
the effective impedence is 10K, the amperage would be .5mA @ 5V
and thus the power would be 2.5mW
Sometimes, I wish I'd cared more about analog in college...
Jim
30 Jul
30 Jul
10:55 p.m.
On 07/30/2016 10:24 PM, Jim Brain wrote:
Since I acquired a Coco Orchestra 90 unit awhile back,
and I am
trying to find the source of some humming in my system when the Orch
90 unit is operational, I looked at the schematic:
http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Orchest…
Can someone shed light on what these are and where you
would find
them (or if they can safely be replaced with another kind of
capacitor)? I will admit I've never seen mention of these before
now.
Electrolytic caps have different characteristics (they actually act
somewhat akin to diodes) in the reverse direction. Often, what's done
is to construct a non-polar cap by taking two capacitors of double the
capacitance in series with like poles forming the connection. You can
also run into nonpolar caps used in AC power circuits as PF adjustment,
motor starting/run etc. with special construction (i.e. oil dielectric).
However, the small values that I see in the schematic would seem to
suggest that plain old film caps (polyester/polypropylene) will do the
job just fine.
FWIW,
--Chuck
2834
days inactive
2835
days old
4 comments
4 participants
participants (4)
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brain＠jbrain.com -
cclist＠sydex.com -
drlegendre＠gmail.com -
ian＠platinum.net