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.
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It should be low ESR type in case of this regulator. Those are already very well built.
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
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
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
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 ?
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
)Doug Self Preamplifier Kits
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Forooq,
From your description I think about the only way that you can accomplish what you describe is to reverse the wiring on pins 1 & 3 on the pots.
I am guessing that you are not using PCB solder mounted pots but rather chose to use panel pots with wire between them and the PCB.
If that is the case simply swap the wires now on pins 1 & 3. I invite others to comment.
Pcb's ordered - glad there was some left!
I was pleased to find that Carl still had some pcbs available when I enquired a few days ago.
I decided to built the preamp for use with my dual TDA1541A balanced Dac with Sowter 9545 I/V transformers and IanCanada's I2S to Simultaneous interface. (almost finished)
I did once have a Quad 34 preamp driving a 405-2 and Martin Logan Aeon hybrid electrostatic speaker and found Quad's unusual "Ambler" tilt tone controls more useful than the usual Baxandall type. (which date from 1952)
I once had the commonly held view that tone controls were a no no and I still hold this view of the basic Baxandall type. However, now my Aeons are in a small space where they tend to bass heaviness, and with my age related high frequency hearing loss, I have realised that Doug Self's tone control design is just what I need to drive the Quad & Aeons.
I plan to dispense with the input capacitors + R2/R4 and change R5/6 to 3k3 as they will become the transformers' secondary load resistors. The load is reflected to the primary at the step up ratio (5:1) squared resulting in it seeing about 100R (in parallel with the existing 100r I/V resistors.)
I will probably also reduce the preamp gain since the 405-2 is more sensitive than modern power amps.
Ian
I was pleased to find that Carl still had some pcbs available when I enquired a few days ago.
I decided to built the preamp for use with my dual TDA1541A balanced Dac with Sowter 9545 I/V transformers and IanCanada's I2S to Simultaneous interface. (almost finished)
I did once have a Quad 34 preamp driving a 405-2 and Martin Logan Aeon hybrid electrostatic speaker and found Quad's unusual "Ambler" tilt tone controls more useful than the usual Baxandall type. (which date from 1952)
I once had the commonly held view that tone controls were a no no and I still hold this view of the basic Baxandall type. However, now my Aeons are in a small space where they tend to bass heaviness, and with my age related high frequency hearing loss, I have realised that Doug Self's tone control design is just what I need to drive the Quad & Aeons.
I plan to dispense with the input capacitors + R2/R4 and change R5/6 to 3k3 as they will become the transformers' secondary load resistors. The load is reflected to the primary at the step up ratio (5:1) squared resulting in it seeing about 100R (in parallel with the existing 100r I/V resistors.)
I will probably also reduce the preamp gain since the 405-2 is more sensitive than modern power amps.
Ian
Thanks Carl,
Yes reversing will defiantly solve the problem. I am just curious why this is happening.
Since nobody seems to have time to answer my query, been experimenting on my own. So far changing the caps to polarized has no effect on frequency control pots rotation.
In my case still has to turn both pots clockwise to 'decrease' frequency instead of increasing, I have checked pots are wired correctly as per schematic.
Best Regards
Fatooq
Yea, I still have a few kits left. The kit amounts to ...
#1) the main PCB
#2) the 5 x 1 IO PCB,
#3) Power supply PCB (120v but can be easily modded to 230v)
#4) and 2 (hard to find) OEM quad RCA phono connector blocks
All of the parts to build can be purchased from Mouser & Digikey
Please check your in box for a note containing the details.