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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Doug Self Preamp from Linear Audio #5
Doug Self Preamp from Linear Audio #5
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Old 16th July 2018, 12:42 PM   #1061
hadihf is offline hadihf  Pakistan
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Default regulator

I think a 78L12 should perfectly work as it is driving just four relays at a time with 12mA each, that makes 48mA total and if used to drive an input select LED then 50mA.

Last edited by hadihf; 16th July 2018 at 01:00 PM.
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Old 16th July 2018, 03:24 PM   #1062
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by diyralf View Post
Tantals are very good, but cause a lot of problems in old age. (Shorts etc.).
Tants used to have a bad rep' but I don't think that's the case these days.
At the day job I have a significant number of Tants in power applications in the field and have only had problems where they had been fitted the wrong way round by the contract assembly firm.
I should add that the boards in question go back upto six years and previously used Tants extensively in other applications with no significant issues.

Last edited by rmaudio; 16th July 2018 at 03:26 PM.
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Old 17th July 2018, 05:17 AM   #1063
hadihf is offline hadihf  Pakistan
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Quote:
Originally Posted by rmaudio View Post
Tants used to have a bad rep' but I don't think that's the case these days.
At the day job I have a significant number of Tants in power applications in the field and have only had problems where they had been fitted the wrong way round by the contract assembly firm.
I should add that the boards in question go back upto six years and previously used Tants extensively in other applications with no significant issues.
It should be low ESR type in case of this regulator. Those are already very well built.
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Old 17th July 2018, 06:09 AM   #1064
diyralf is offline diyralf
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Quote:
Originally Posted by rmaudio View Post
Tants used to have a bad rep' but I don't think that's the case these days.
At the day job I have a significant number of Tants in power applications in the field and have only had problems where they had been fitted the wrong way round by the contract assembly firm.
I should add that the boards in question go back upto six years and previously used Tants extensively in other applications with no significant issues.

My old tants from 1991 (unused) have all shorts.
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Old 17th July 2018, 08:29 AM   #1065
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by diyralf View Post
My old tants from 1991 (unused) have all shorts.
Fair enough. But I don't think you can extrapolate that to likely failures with current day tantalum capacitors. Of course we'd need to wait a couple of decades to be sure :-)

The other thing is that the alternative is often Al Electrolytics.
Whilst you can get high quality parts of these they do have inherent properties that are less than ideal - loss of capacity with age / temp / voltage / ripple current etc can be significantly worse and they are likely to dry out after a decade or two !
Reliability wise there was the infamous 'Capacitor Rash' affecting Electrolytics some years ago but I wouldn't avoid them now for that reason.

Having said all that - if you get Tants the wrong way round they can end up making a nasty mess on the pcb and quite a smell
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Old 17th July 2018, 09:17 AM   #1066
diyralf is offline diyralf
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I recently had several devices (> 10 years old) that do not work at all anymore. It was also almost impossible to find out where the defect was. After the exchange of all Tants everything worked perfectly again. These things are very annoying.
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Old 18th July 2018, 06:07 AM   #1067
hadihf is offline hadihf  Pakistan
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Default Scratch built DS Preamp

Both 78L12 and TL750L12 should work. Both oscillate w/o caps. 78L12 is easy to use. Just need to solder two 0805 SMD 100n caps between the pads under the PCB.

I suggest to add caps to all builders. This will prolong the life of relays as those are specified to work at 9V. Also nobody wants unwanted oscillators in their HiFi Preamps.

Best Regards
Farooq
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Old 18th July 2018, 08:35 AM   #1068
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by hadihf View Post
I suggest to add caps to all builders. This will prolong the life of relays as those are specified to work at 9V. Also nobody wants unwanted oscillators in their HiFi Preamps.

Best Regards
Farooq
Oscillations to be avoided of course.
But I don't understand linking the use of capacitors in a voltage regulator circuit with relay life / voltage ?
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Old 18th July 2018, 10:51 AM   #1069
hadihf is offline hadihf  Pakistan
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Originally Posted by rmaudio View Post
Oscillations to be avoided of course.
But I don't understand linking the use of capacitors in a voltage regulator circuit with relay life / voltage ?
w/o capacitors no regulation. Around 15V to relays with 17V input.
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Old 19th July 2018, 10:29 AM   #1070
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by hadihf View Post
w/o capacitors no regulation. Around 15V to relays with 17V input.
Yes - of course you need the regulator to be working properly in any case.

78L12 won't necessarily oscillate without capacitors if the power source is near it but I always place input caps and also output caps - not strictly necessary but reduces noise and improves impulse response. Generally SMT X7R 100n right by the regulator and some tens of uF electrolytics or tantalum also.
Also diodes from output to oinout to protect against load discharge.

Can't remember last time had a problem with a 78xxx type regulator (Well I can but that's what happens when you get the footprint back to front ! Bottom View on the datasheet )
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