Lee S wrote:What rectifier? We are using AC aren't we?
simon wrote:Simple CRC. 5V Hammond filament tx into bridge into 4700uF - 0.1R - 4700uF.
My gut instinct is also to put one in each wire, though I can't see why it would make any difference either. Of the few amps I've built the AC filament voltages have been spot on, this is the first time it's been out. I'm going to Maplins shortly, shame they don't do anything suitable. If the 0.1Rs don't fettle it, it's looking like a special order to Farnell in the New Year.
do people think there a sonic downside to this with dht amps ?
Even just giving my view on this is a complex thing, normally I would say increasing the supply resistance would be a bad thing, except, having a higher resistance, may reduce the Q of the supply and prevent overshoot. It may also work out better, as the higher resistance may lead to a less strict bass response, which giving a particular amp/speaker/room/ear combination may be a good or a bad thing.
So I think for me the answer is "depends"
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
The additional two nominally 0.1R resistors dropped the voltage from 5.48V to 5.22V. Paralleling a pair of nominally 0.47Rs instead gave 5.07V. I guess the values of the resistors are so small the tolerances of the resistors will be important. A little job for the new year I think.
the thing is Simon as you reduce the voltage to the filaments they pull less current so the predicted value estimated from the current drawn originally is always out. It's exactly the same when calculating cathode bias resistor. It's like chasing a fighter plane, it shifts parameters as you go after it.
That's why it's best to adjust everything empirically.
Hadn't thought about it like that Paul, makes perfect sense now you say it.
I've managed to bodge it with various resistors I have - paralleling some, series others - and I've got 5.04V and 5.07V which will do me for now. What's interesting is that laid back sound that the amps had developed which I really didn't like has disappeared now I've got the filament voltage up from 4.4V to 5V. I think 5.5V might have been best of all, but I'm trying not to think about that. Burning up KRs prematurely would make them very expensive indeed...
I feel a lot happier about my humble efforts now I know I'm trying to outwit fighter pilots.
And so you should. Actually making something is a major achievement.
I have been outside in the cold and the rain making some Open back boxes for my newly arrived Supravox woofers. I decided to keep them seperate and make fullrange driver baffles to sit on top. That way I can try the lowther pm7a's against the aer mk1's and against anything else I care to try.
When I've got speakers sorted I'll have to find a new hobby. (imagine four rolling about on the floor emoticons and insert here).
Hmm, they're an expensive option but ultimately may give superior results. I'm weighing up options at the moment, and the Supravox are contenders, depends what I can find. Good luck integrating them.
Had Mum & Dad round for tea yesterday evening. The amp was burbling away in the background playing some jazz. Suddenly Mum piped up,
"ooh! hasn't it got a lovely tone Stephen"
Oh dear
Steve.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Had Mum & Dad round for tea yesterday evening. The amp was burbling away in the background playing some jazz. Suddenly Mum piped up,
"ooh! hasn't it got a lovely tone Stephen"
Oh dear
Steve.
I think you're miss-reading what she said Steve, secretly she's a hard-core be-bop jazz buff and commenting on the Selmer Series 3 Sax tone She probably let being uber-cool slip out and was hoping you wouldn't notice...