 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
216.232.207.152
Working on getting a 46 going to audition as a possible driver . Ocillation keeps the LT from going into stable regulation . The LT data sheet gives details on bypassing with Tantalum caps for a voltage reg but nothing on CC use. Just fried one cap, would like to avoid doing another. . .
Other questions here too, like re: that following the sheet literally means you're shunting regulator noise into the cathode of the tube. . .It doesn't seem like something we'd want to do.
Doing searches on the Forums I couldn't find a single reference to this.
Is anybody bypassing the LT 108- terminals in their circuits. No? Either way, can you give details?
Web searches don't turn up schematics of circuits with this reg. I guess you have to know where to look. . . . .`,;^)
Thanks !
Follow Ups:
I think you are refering to the cap on the output pin to ground? I can't see how this would shunt noise into the cathode as it is in effect parallel to it. I don't like a capacitor in this position but for totally different reasons.Anyway, the chip does not like an inductive load on the output. The capacitor is there to stabalize the regulator loop. Without it it is very likely to oscillate. It does not like low ESR caps on the output either since the regulator itself has a slightly inductive output impedance with rising frequency. So using very high quality low ESR caps here might even worsen the case.
The chip does not know if it's being used as a current or as a voltage regulator, it is still just regulating voltage internally. It just wants to see a capacitive load on the output to function properly. A lot of these one-chip regulators do.
In short, I'm not a fan of these regulator chips because they are noisy and prone to oscillation. The only thing they have going for them is that they are easy to use. I much prefer a discrete two-transistor or fet design. A little harder to build but much better results.
I don't understand why the cap fried. Perhaps it has the wrong voltage rating?
Well , this laugh's on me. I assumed that the caps were non polar. It's pure luck that the three other caps I had in the circuit didn't blow too.
Anyway, right after I first posted, I tried the data sheet suggested arrangement for greater ripple rejection. with 10uF in , 20uF out, and 150uF Aluminum 'lytic on the adjust pin. It's probably as quiet as it will get in this breadboard arrangement but it clearly has lost some of the magic it had yesterday in its much simpler setup (Though it has slightly more bottom end).
I'll keep looking at other possibilities, I'd like to try an LR filter with a choke and the filament, also LC etc. . .
Thanks for your reply - Any chance of getting you to say more about your disrete two transistor or FET designs?
Thanks
IanPS. Just gave it another go with L in place of the R in what was a CRC > Reg filter. Sounded bad, then good, then started that scratchy crackle that signals unhappy chips. . . . . .
Hmmm, what to try next? `,;^)
Ja, those tantalums can fail pretty violently!I got the regulator from a book, don't remember which one. I'll try to look it up. You will probably enjoy the discussion on clarisonus.com weblog and the link below.
. . ..It's amazing how much smoke they can pack into those little blobs. `,;^)Thanks for the point to Clarisonus . While we're looking at pages you might like this one for your library.
Yah, If you can find anything on your discrete circuits it would be great if you'd post.
Thanks
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
