Thanks, but to be universally usable, a solution would need to be found for the transistors: I had to test tens of 2N3866 and 2N5583 to find to pairs having a Vceo>50V. There are probably better, more modern substitute, but they would need to be found and tested before committing to a PCB
It was proposed by Nico Ras:
https://www.diyaudio.com/community/threads/can-you-improve-these-amplifiers.400560/post-7441066
https://www.diyaudio.com/community/threads/can-you-improve-these-amplifiers.400560/post-7441066
I was looking around for fast outputs that are current production, meet your requirements, low and behold, Sanyo parts that Onsemi did not axe,
2SA2222AG and 2SC6082 might do the job, both in stock at Mouser.
2SA2222AG and 2SC6082 might do the job, both in stock at Mouser.
They are quite hefty, maybe a bit too much: their Cob is comprised between 85 and 115pF, which risks to be problematic. In fact, I switched from BD139/140 to RF transistors for precisely that reason
They look ideally suitable. If you are willing to part with a pair, fix your conditions
Today, I have received a nice little parcel:
Not only did it contain 5 pairs of BFQ, but a board named "nanoDSP" was also included.
Koen, you have some explaining to do!
Thanks a lot for generosity anyway.
Now, I will need to graft these racing beasts into my amplifier: due to their higher speed, the stabilization measures will probably have to be adapted
Not only did it contain 5 pairs of BFQ, but a board named "nanoDSP" was also included.
Koen, you have some explaining to do!
Thanks a lot for generosity anyway.
Now, I will need to graft these racing beasts into my amplifier: due to their higher speed, the stabilization measures will probably have to be adapted
the nanodsp is a project I once did, I have a whole box of boards made, equally collecting dust like the BFQ's. pls give me yr email adress, and I send you the doc package how to built a project with that. for example 2CH XO balanced in balanced out with limiters and EQ etc. or stereo unbalanced XO 4ch out. there is room for rca in and out or XLR balanced in and out. 2 color led and volume control included.
I haven't read the whole thread, but maybe under
https://www.diyaudio.com/community/...eled-in-place-of-one-output-transistor.61627/
you will find some additional hints.
Is the mentioned peak immediately in left of the falling edge near on ft of the whole amp stage ? In real life or while CAD simulation (e. g. ORCAD) ?
If the character of the frequency response is similar to those red line from attachment (consequence of not correct MM cartridge loading) then the oscillation potential (ring ring) around 200MHz is very great due not good phase margin - go to
https://skills.microchip.com/introduction-to-operational-amplifiers/691882
As long it is only by simulation some experiments with base stopper resistors could help.
If this peak is only in real life, PCB-layout isn't good enough, because some parasitic and unwanted inductors and capacities are occur. I recall to an article in ELRAD (German issue) concerning optimize PCB layouts for that kind of amplifiers. Unfortunately I don't know the associated issue (month/year) but I think late 80s or early 90s. Main feature here was, that the copper tracks of both voltage rails and GND rail was as close as possible (and not - as often to observe - pos. rail at the top edge and neg. rail at the bottom edge.
Attachments
The problems are now solved, and they were mostly caused by local instabilities. Abandoning output-inclusive compensation was also a factor. The squarewave response had always been clean, even when VHF oscillations were superimposed.
There are now stoppers everywhere, even in the collectors of the transistors. Most are probably superfluous, but now that I have landed on a stable design, I do not want to tinker again: it is not a commercial design, and it doesn't need to be streamlined by pruning useless components.
My next challenge is to make it work with the super-fast transistors that Basreflex was kind enough to send me.
There are now stoppers everywhere, even in the collectors of the transistors. Most are probably superfluous, but now that I have landed on a stable design, I do not want to tinker again: it is not a commercial design, and it doesn't need to be streamlined by pruning useless components.
My next challenge is to make it work with the super-fast transistors that Basreflex was kind enough to send me.
"Abandoning output-inclusive compensation was also a factor."
That is what I intended to show in posting #109
That is what I intended to show in posting #109
Indeed, but it didn't do the trick all by itself: in sim, the amplifier remained stable with OIC, and on my prototype I tried the conventional compensation without the other mods, and it remained unstable
