carpenter said:
Uhm... Where's my skill in turning my 25-turns Vishay trimmer and reading from the tester? 😀
It's very, very sensitive... A bunch of degrees results in 2-3 mV variation, if someone's using single-turn pots I think is having a really hard time adjusting the DC offset.
Giacomo
Another question: Is the recommended bias per device now 0.53 ampere or 0.43 ampere ? In the latest service manual it is 0.53, but I have have as well a version with 0.43 in it?
And second question: If I measure across the source resistors (0.5 ohm) of the 9240 and of the 240, I get two different values, on typicically is 0.200V, while the other is 0.220 V. Do you found the same true ?
And second question: If I measure across the source resistors (0.5 ohm) of the 9240 and of the 240, I get two different values, on typicically is 0.200V, while the other is 0.220 V. Do you found the same true ?
Blitz said:
I'm very interested in this one too. I read that the correct BIAS should match with 250mV across those resistors... Then I set it that way, and I have very HOT heatsinks (not measured yet). Now Blitz' question is makin' me think about it: is 250 mV wrong, should I stay within 200-220?
Giacomo
I adjusted my bias up to 280 mv to achieve a sink temp of 50 deg C. I read papa tell that the 50 deg was the magic number to shoot for. 
Blitz said:
giacomo_pagani said:
question for current - as much output mosfets are happy ........ meaning on excessive temperature of die , or dissipation ..... what comes first ;
considering writing of you both, in your case(s) temperature will come first .
so - taking in account Papa's "skin burning test" ........ fry them 'till fingers can stay on heatsinks ; then stop , or even back up a little .
nota bene - if Magura try to tell ya something about these issues - do not even read ..... he like them toasty
regarding 23V6 vs. 22V ............ naah ....... don't even bother .... 😉
Blitz said:
I will not comment on the bias per fet. As I typically use heatsinks from the scrapyard, and these can vary a bit wrt thermal properties, I tend to use a bias that gives me a heatsink temperature of ~45 - 50 degrees C.
As source resistors have a tolerance as well. Did you check the resistor values? 5% tolerance and 2 resistors on the extremes can give you the situation presented.
Blitz said:
The RC has some time constant and works like a high pass filter at very low frequencies. Generally, the sound is cleaner upto about 500Hz, as a result of CRC filters. They also seem to remove the bright edge in the higher frequencies. Finally the caps on board the amp-boards play a very important role in "voicing" the amp.
Did Jensen state what value the L is so that you can calculate the filter? If anything it must be much smaller compared to a discrete CLC filter, probably by several orders of magnitude.
I believe for all practical purposes you should consider the Jensens to be single caps, so you have now converted from a CRC filter to a simple C filter and are comparing the two, this may explain most of the sound difference. What you could off course try is building a CRC with the Jensens in the second position.
Hi,
I also use the 4 poles Jensen caps but I parallel them. Pls. see the faq notes from Jensen Caps. There are some comments about paralleling caps.
https://audio.jensencapacitors.com/faq/
Best Regards
S K
I also use the 4 poles Jensen caps but I parallel them. Pls. see the faq notes from Jensen Caps. There are some comments about paralleling caps.
https://audio.jensencapacitors.com/faq/
Best Regards
S K
That's a good hint. I will play around with it...As I understand you use Jensen's as well ? Did you realize a burn-in-effect and took it long ?
Samuel Jayaraj said:
OK...that is a lot sounding like what I am missing right now, some of the charme / smoothness is gone and some bright egde in the trebles are introduced...
diferent Mosfets
Hello,
interposed question:
I have a lot of IRF9540 and IRF540. Can I use this devices instead of IRFP9240 / IRF240 in the F4 ?
( I'm not sure but I belief somebody said that the Devices even have the same DIE inside with just another package)
Greetings from Germany,
Andreas
Hello,
interposed question:
I have a lot of IRF9540 and IRF540. Can I use this devices instead of IRFP9240 / IRF240 in the F4 ?
( I'm not sure but I belief somebody said that the Devices even have the same DIE inside with just another package)
Greetings from Germany,
Andreas
x540 is quite different from the x240 series, not the same die for sure. Probably some minor value modifications are necessary, and good matching will be even more important than with the x240's.
- Klaus
- Klaus
At a little over 13W of dissipation each, i've been a bit surprised as yet no one has posted IRF630/9630.
I've used Fairchild's TO220 for the A75 (shivers, that's fifteen help me gawd years ago), "papa's got the same die in a brand new pig bag" as the intended IRF230-9230/31 TO3 combo for Pyjama-P and Spaced-Out Normy's amp.
630/9630s are like 25cts each nowadays.
I've used Fairchild's TO220 for the A75 (shivers, that's fifteen help me gawd years ago), "papa's got the same die in a brand new pig bag" as the intended IRF230-9230/31 TO3 combo for Pyjama-P and Spaced-Out Normy's amp.
630/9630s are like 25cts each nowadays.
jacco vermeulen said:
naah .........
even 530/540 with cousins are good enough
there are numerous possibilities around these numbers ........ if someone is cheapskate as Jaccovitty and ZM .......
Yeah, some must suffer, as we didn't all get a couple of tubes of matched IRF144 with best regards from Santa 😀
Magura 🙂
Magura 🙂