juggling parts

On Tuesday, November 16, 2021 at 2:48:29 AM UTC+11, jla...@highlandsniptech=
nology.com wrote:
> On Mon, 15 Nov 2021 15:15:25 GMT, Jan Panteltje=20
> <pNaOnSt...@yahoo.com> wrote:=20
>=20
> >On a sunny day (Sun, 14 Nov 2021 14:22:45 -0800) it happened=20
> >jla...@highlandsniptechnology.com wrote in=20
> ><ss23pgp37oil6tqvi...@4ax.com>:=20
> >=20
> >>When I see a schematic full of trimpots, it's a sure bet that the=20
> >>author doesn't understand things.=20
> >=20
> >=20
> >In the older days trimpots were common for opamp offset compensation in =
many precision circuits.=20
> >Not sure if modern opamps still have offset errors?
>
> Some have a few uV offset and a few nV/degc drifts.=20

Every last op amp has built-in thermocouples and built-in thermal gradients=
, There's always a few microvolts of thermocouple potential and it varies w=
ith heat dissipation.

>But we cal things  out in automated test, and save the cal table in flash,=
 so don't need  pots. Sometimes we even cal out tempcos, which takes longer=
 but nobody  is standing around watching.=20

Which is worth doing, if you are producing in volume. What the Review of Sc=
ientific Instruments reports are one-off and short series instrument design=
s used to solve specific scientific problems.

> Turning trimpots to tweak tempcos is for masochists.

But writing an elaborate program to do it for you is also time consuming - =
it's quicker to twiddle a few trimpots by hand if there are only ever going=
 to be a few of them

> >>The Review Of Scientific Instruments is full of trimpots. And diffamps.=
 And current mirrors.=20

And John Larkin doesn't seem to like designing them into his own circuits,
=20
> >Its the same with variable inductors, radios used to be full of those, n=
ow everything is done in silicon.rtl-sdr USB stick as example.=20

Not always.

https://www.tdk-electronics.tdk.com/inf/80/db/fer/rm_10.pdf

Note the screw-in adjuster on page 8. If you really do need to change the i=
nductance of an inductance made with an RM10 core, this is one long-establi=
shed way of doing it. There are bigger cores and bigger adjusters if you ne=
ed more inductance, and different core materialsif you need higher frequenc=
ies.

--=20
Bill Sloman, Sydney

On 16/11/2021 02:49, jlarkin@highlandsniptechnology.com wrote:
> On Mon, 15 Nov 2021 23:07:34 +1100, Chris Jones
> <lugnut808@spam.yahoo.com> wrote:
> 
>> On 15/11/2021 16:34, whit3rd wrote:
>>> On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:
>>>> On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
>>>
>>>>> I have space on this one for a few more 0603s. It's inefficient to
>>>>> load a reel onto the pick-and-place just for one resistor.
>>>
>>>> Pots are your enemy...
>>>
>>> When mailorder is slow, and you have a triangle file and carbon comp
>>> resistor in play, it's time to declare armistice or maybe even peace.
>>>
>>> Remember, after filing the notch, to use some nail  polish for
>>> sealing that surface...  or  job it out to a cosmetology shop.
>>>
>>
>> Barbarian, using a triangle file, think of the mechanical stress
>> concentration begging it to snap in half. Use a round chainsaw
>> sharpening file or round needle file at least! I'd even consider
>> drilling a few small holes part way through it would be more humane.
>>
> 
> I haven't seen a carbon comp resistor in years.

The only good use I can think of for them is absorbing large pulses of 
energy in a very short time, as the heat would be deposited throughout a 
larger mass than the mass of a thin or thick film.

On Sun, 14 Nov 2021 10:27:20 -0800, jlarkin@highlandsniptechnology.com
wrote:

<snip>
>>What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?
>
>Trimpots are expensive and need manual turning. DACs are automated and
>can have cal factors stored in cal tables. I'm using 16-bit DACs and
>there are no 16-bit trimpots.
>
>Some of my customers absolutely forbid trimpots, which I think is
>extreme. Once in a while they make sense. They say that if there's a
>pot, their techs will turn it.
>

If the tech doesn't have access to the cal table, that DAC's not doing
the work of a trimpot.

RL

On Tuesday, November 16, 2021 at 9:54:14 AM UTC-4, legg wrote:
> On Sun, 14 Nov 2021 10:27:20 -0800, jla...@highlandsniptechnology.com=20
> wrote:=20
>=20
> <snip>
> >>What I do not get is: you sell expensive things in low quantity and try=
 to save on a trimpot?=20
> >=20
> >Trimpots are expensive and need manual turning. DACs are automated and=
=20
> >can have cal factors stored in cal tables. I'm using 16-bit DACs and=20
> >there are no 16-bit trimpots.=20
> >=20
> >Some of my customers absolutely forbid trimpots, which I think is=20
> >extreme. Once in a while they make sense. They say that if there's a=20
> >pot, their techs will turn it.=20
> >
> If the tech doesn't have access to the cal table, that DAC's not doing=20
> the work of a trimpot.=20

Sometimes it's better to not give the tech access.  It's not unusual for an=
 adjustment to be needed one time at the factory to account for tolerances.=
  Field repair is often at the board level, so no field replacement of anyt=
hing that would impact that trim setting.  People may whine about "the cost=
" and "the convenience", but the manufacturer sets the procedures to facili=
tate repair to a known state with factory tolerances.=20

--=20

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

In article <3ud7pg1ajig89gc8jshk6cp0kg45fn37m3@4ax.com>, 
legg@nospam.magma.ca says...
> 
> On Sun, 14 Nov 2021 10:27:20 -0800, jlarkin@highlandsniptechnology.com
> wrote:
> 
> If the tech doesn't have access to the cal table, that DAC's not doing
> the work of a trimpot.
> 
> RL

Regardless of the topic, the headline has just reminded me of something 
the film critic Barry Norman once said on TV. He was commenting on a 
mention in a film of "pocket billiards". He just said that he didn't 
realise it was competitive!

On Tue, 16 Nov 2021 22:42:52 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

>On 16/11/2021 02:49, jlarkin@highlandsniptechnology.com wrote:
>> On Mon, 15 Nov 2021 23:07:34 +1100, Chris Jones
>> <lugnut808@spam.yahoo.com> wrote:
>> 
>>> On 15/11/2021 16:34, whit3rd wrote:
>>>> On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:
>>>>> On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
>>>>
>>>>>> I have space on this one for a few more 0603s. It's inefficient to
>>>>>> load a reel onto the pick-and-place just for one resistor.
>>>>
>>>>> Pots are your enemy...
>>>>
>>>> When mailorder is slow, and you have a triangle file and carbon comp
>>>> resistor in play, it's time to declare armistice or maybe even peace.
>>>>
>>>> Remember, after filing the notch, to use some nail  polish for
>>>> sealing that surface...  or  job it out to a cosmetology shop.
>>>>
>>>
>>> Barbarian, using a triangle file, think of the mechanical stress
>>> concentration begging it to snap in half. Use a round chainsaw
>>> sharpening file or round needle file at least! I'd even consider
>>> drilling a few small holes part way through it would be more humane.
>>>
>> 
>> I haven't seen a carbon comp resistor in years.
>
>The only good use I can think of for them is absorbing large pulses of 
>energy in a very short time, as the heat would be deposited throughout a 
>larger mass than the mass of a thin or thick film.
>

AoE X-chapters, p 26, has some great data about exploding various
resistors. The carbon comps win for short pulses, below about 1
millisecond.

I always assumed that 50 ohm cc's were best for high frequency
termination, but the cheap carbon film resistors are about as good.
Surface-mount thick films are better than either... less lead
inductance.



-- 

Father Brown's figure remained quite dark and still; 
but in that instant he had lost his head. His head was
always most valuable when he had lost it.



  

On Tue, 16 Nov 2021 08:56:07 -0500, legg <legg@nospam.magma.ca> wrote:

>On Sun, 14 Nov 2021 10:27:20 -0800, jlarkin@highlandsniptechnology.com
>wrote:
>
><snip>
>>>What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?
>>
>>Trimpots are expensive and need manual turning. DACs are automated and
>>can have cal factors stored in cal tables. I'm using 16-bit DACs and
>>there are no 16-bit trimpots.
>>
>>Some of my customers absolutely forbid trimpots, which I think is
>>extreme. Once in a while they make sense. They say that if there's a
>>pot, their techs will turn it.
>>
>
>If the tech doesn't have access to the cal table, that DAC's not doing
>the work of a trimpot.
>
>RL

It's preventing him from mucking with something he doesn't understand
and doesn't have the equipment to calibrate. Besides, some products
have a hundred cal factors.

If something in a signal chain is broken, twiddling pots will break
more things. We rarely use trimpots, and then only to tweak gain in
GHz-range amplifiers.



-- 

Father Brown's figure remained quite dark and still; 
but in that instant he had lost his head. His head was
always most valuable when he had lost it.



  

On Tue, 16 Nov 2021 07:40:30 -0800, jlarkin@highlandsniptechnology.com
wrote:

>On Tue, 16 Nov 2021 08:56:07 -0500, legg <legg@nospam.magma.ca> wrote:
>
>>On Sun, 14 Nov 2021 10:27:20 -0800, jlarkin@highlandsniptechnology.com
>>wrote:
>>
>><snip>
>>>>What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?
>>>
>>>Trimpots are expensive and need manual turning. DACs are automated and
>>>can have cal factors stored in cal tables. I'm using 16-bit DACs and
>>>there are no 16-bit trimpots.
>>>
>>>Some of my customers absolutely forbid trimpots, which I think is
>>>extreme. Once in a while they make sense. They say that if there's a
>>>pot, their techs will turn it.
>>>
>>
>>If the tech doesn't have access to the cal table, that DAC's not doing
>>the work of a trimpot.
>>
>>RL
>
>It's preventing him from mucking with something he doesn't understand
>and doesn't have the equipment to calibrate. Besides, some products
>have a hundred cal factors.
>
>If something in a signal chain is broken, twiddling pots will break
>more things. We rarely use trimpots, and then only to tweak gain in
>GHz-range amplifiers.

If it's not meant to be adjusted, then sot fixed parts are more a 
suitable analog comparison. A trimpot would be an unjustified 
vulnerability, simply from a reliability and cost standpoint.

I'm finding that that programmable part are increasingly dominant in 
non-repairability situations, so It rankles when the equation is 
made to an impractical analog equivalent.

RL

On Tue, 16 Nov 2021 11:23:59 -0500, legg <legg@nospam.magma.ca> wrote:

>On Tue, 16 Nov 2021 07:40:30 -0800, jlarkin@highlandsniptechnology.com
>wrote:
>
>>On Tue, 16 Nov 2021 08:56:07 -0500, legg <legg@nospam.magma.ca> wrote:
>>
>>>On Sun, 14 Nov 2021 10:27:20 -0800, jlarkin@highlandsniptechnology.com
>>>wrote:
>>>
>>><snip>
>>>>>What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?
>>>>
>>>>Trimpots are expensive and need manual turning. DACs are automated and
>>>>can have cal factors stored in cal tables. I'm using 16-bit DACs and
>>>>there are no 16-bit trimpots.
>>>>
>>>>Some of my customers absolutely forbid trimpots, which I think is
>>>>extreme. Once in a while they make sense. They say that if there's a
>>>>pot, their techs will turn it.
>>>>
>>>
>>>If the tech doesn't have access to the cal table, that DAC's not doing
>>>the work of a trimpot.
>>>
>>>RL
>>
>>It's preventing him from mucking with something he doesn't understand
>>and doesn't have the equipment to calibrate. Besides, some products
>>have a hundred cal factors.
>>
>>If something in a signal chain is broken, twiddling pots will break
>>more things. We rarely use trimpots, and then only to tweak gain in
>>GHz-range amplifiers.
>
>If it's not meant to be adjusted, then sot fixed parts are more a 
>suitable analog comparison. A trimpot would be an unjustified 
>vulnerability, simply from a reliability and cost standpoint.
>
>I'm finding that that programmable part are increasingly dominant in 
>non-repairability situations, so It rankles when the equation is 
>made to an impractical analog equivalent.
>
>RL

We do polynomial calibrations all the time. Try that with trimpots!




-- 

Father Brown's figure remained quite dark and still; 
but in that instant he had lost his head. His head was
always most valuable when he had lost it.



  

On 2021-11-16 16:35, jlarkin@highlandsniptechnology.com wrote:
> On Tue, 16 Nov 2021 22:42:52 +1100, Chris Jones
> <lugnut808@spam.yahoo.com> wrote:
>
>> On 16/11/2021 02:49, jlarkin@highlandsniptechnology.com wrote:
>>> On Mon, 15 Nov 2021 23:07:34 +1100, Chris Jones
>>> <lugnut808@spam.yahoo.com> wrote:
>>>
>>>> On 15/11/2021 16:34, whit3rd wrote:
>>>>> On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:
>>>>>> On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
>>>>>
>>>>>>> I have space on this one for a few more 0603s. It's inefficient to
>>>>>>> load a reel onto the pick-and-place just for one resistor.
>>>>>
>>>>>> Pots are your enemy...
>>>>>
>>>>> When mailorder is slow, and you have a triangle file and carbon comp
>>>>> resistor in play, it's time to declare armistice or maybe even peace.
>>>>>
>>>>> Remember, after filing the notch, to use some nail  polish for
>>>>> sealing that surface...  or  job it out to a cosmetology shop.
>>>>>
>>>>
>>>> Barbarian, using a triangle file, think of the mechanical stress
>>>> concentration begging it to snap in half. Use a round chainsaw
>>>> sharpening file or round needle file at least! I'd even consider
>>>> drilling a few small holes part way through it would be more humane.
>>>>
>>>
>>> I haven't seen a carbon comp resistor in years.
>>
>> The only good use I can think of for them is absorbing large pulses of
>> energy in a very short time, as the heat would be deposited throughout a
>> larger mass than the mass of a thin or thick film.
>>
>
> AoE X-chapters, p 26, has some great data about exploding various
> resistors. The carbon comps win for short pulses, below about 1
> millisecond.
>
> I always assumed that 50 ohm cc's were best for high frequency
> termination, but the cheap carbon film resistors are about as good.
> Surface-mount thick films are better than either... less lead
> inductance.
>
>
>

I've tried several low-value resistors for high-frequency matching pads
and terminations. SMD 1206 resistors tend to be too capacitive, and the
similar-sized MELFs are too inductive. It's easier to gimmick the MELFs,
so that's what I tend to choose when it matters.

Jeroen Belleman