Nick wrote: ↑Mon May 23, 2022 2:50 pm
You are putting big (150R) resistors in the power supply again. Just saying.
I don’t see what else I can do. I am severely constrained by the size of the chassis, and the chokes I have, have an even higher DCR than the resistors and are only specced for 50mA so would be saturating at the current the EL34s are pulling. The corner frequency for that stage (150R with 100uF) is 10.6Hz which may or may not be a problem; I don’t know, and that is perhaps the
real problem.
It is highly probable, nay almost certain, that I misunderstood something fundamental, twenty years ago about power supplies and have carried it with me, like a lead backpack for all that time, making the same mistakes time and again and not understanding why I’m mistaken, or what I should be doing differently to resolve such issues.
This I’m afraid is what is so disheartening about this game, or to put it more accurately, the maths involved with it. I don’t know. Maybe I learn something from a book, apply it diligently, carefully working out the answers, but the maths doesn’t fit the situation, so that’s not what you need. I’ve worked hard, but not smart. This is one reason why I decided to stop with all this, get the NVA thing out, tweak it up and be satisfied with that. I’d just had enough of making no progress.
For example, Morgan Jones goes deeply into cascaded RC section filters to remove noise efficiently from power supplies, referring to ‘Cathode Ray’ and his tables giving suggestions for the minimum number of sections that will achieve a noise level of -ndB. Is this what I’m doing here? latching onto something, then using it in the wrong context?
All I know is that the supply is essentially silent. I cannot hear any hum whatsoever at the speaker, even with an ear inside the bass driver.
It was the same at school. Teacher would teach, I would think I was diligently carrying out the instructions, be pleased with a job well done, then the work would come back covered in red ink. When, quite naturally, I asked what I’d done wrong, more often than not, the answer would be, ‘you’re at a Grammar school lad! If you don’t get something this simple, I suggest you take yourself off to the Secondary Modern tout suite!’ usually said in front of a class full of sniggering kids.
So….I need to understand what is wrong with the supply I’ve built and why? because clearly I’m using learned information that is not applicable to the situation and not understanding
why it doesn't apply at that point in the circuit, but somewhere else it does.
I could do with getting this valve amp power supply business sorted out in my head once and for all, or I’ll simply give up again, which would be a shame, as this particular amplifier really
does stir up deep emotions. In that respect at least, nothing else has ever come close.