Hi all!
Finally, I took time during my hollydays to build my FX8 boards.
Thanks everybody here for this thread. It took me time as I am learning....
Next step is to build my PSU.
Maybe I should use a toroidal transformer instead a SMPS
Unfortunately 24V-0-24V looks hard to find in France (and expensive)
Is it possible to use a 2 wires toroid transformer (24V-24V)? Is the neutral wire important?
Any suggestions for french or european people?
Finally, I took time during my hollydays to build my FX8 boards.
Thanks everybody here for this thread. It took me time as I am learning....
Next step is to build my PSU.
Maybe I should use a toroidal transformer instead a SMPS
Unfortunately 24V-0-24V looks hard to find in France (and expensive)
Is it possible to use a 2 wires toroid transformer (24V-24V)? Is the neutral wire important?
Any suggestions for french or european people?
the "0" is NOT a Neutral wire. It is the centre tap.
You can use 0-25, 0-24Vac dual secondary, or 24-0-24Vac centre tapped secondary.
You could also use 0-22, 0-22Vac, or 22-0-22Vac, or 0-25, 0-25Vac, or 25-0-25Vac.
They are all close enough. That gives you 6 choices.
Try RS, Rapid, Farnell, CPC
You can use 0-25, 0-24Vac dual secondary, or 24-0-24Vac centre tapped secondary.
You could also use 0-22, 0-22Vac, or 22-0-22Vac, or 0-25, 0-25Vac, or 25-0-25Vac.
They are all close enough. That gives you 6 choices.
Try RS, Rapid, Farnell, CPC
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You can use transformer without centre tap but you nee double voltage 48vac.
Attachments
You can use any similar transistors and with this psu you don't need DC protect but you need separate psu for each channel.
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Thanks Mile I have a giant 2x100V (1000va) transformer leaving around
May be I will use the on coil for a general +\-50vpower supplier
A 100Vac coil will give you ~ 140V to 150Vdc that would split into ~±75Vdc power supply.
Alternatively you could rewind the secondaries. Big transformers have few turns (expect 1.5T to 2T/volt) so are not too difficult to rewind.
Another alternatively.
If you can identify the centre point of the two existing windings, you can tap into them and attach output leads to create 100Vac centre tapped secondaries. This does not require any rewinding. Just take off the outer insulation tape and reapply after the centre taps are added.
Alternatively you could rewind the secondaries. Big transformers have few turns (expect 1.5T to 2T/volt) so are not too difficult to rewind.
Another alternatively.
If you can identify the centre point of the two existing windings, you can tap into them and attach output leads to create 100Vac centre tapped secondaries. This does not require any rewinding. Just take off the outer insulation tape and reapply after the centre taps are added.
Center tapped 25vac transformers rated for 250va or higher are very standard fare and should be available in Europe. Either EI style or toroidal can work. You need approx +/-35v DC. SMPS is an excellent option as well and Connexelextronic is a good supplier there. PSU for a class AB amp is the single most expensive item. Once you have one - you can build many amps to try out with that supply. So think of it as a baseline cost to play - like having a set of speakers.
Tried Farnell (France)?
This transformer was salvaged from a PA amplifier
Strange is that filter capacitors working voltage was 100V!
Two SicSafco 10000uf\100V
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Hi xrk971,
thank you for your answer,
Maybe it is fine if I invest in a toroidal transformer.
and yes, maybe with free postage farnell is fine.
I found these models:
VTX-146-300-125 MULTICOMP, Transformateur toroïdal, 54mm x 125mm, 300 VA, 2 x 25V, 6 A, Châssis, VTX Series | Farnell element14 France
MCTA250/25 MULTICOMP, Transformateur toroïdal, 250 VA, 2 x 25V, 5 A, Panneau, MCTA Series | Farnell element14 France
MCTA300/25 MULTICOMP, Transformateur toroïdal, 300 VA, 2 x 25V, 6 A, Panneau, MCTA Series | Farnell element14 France
I don't really know the difference between the two series (VTX/MCTA), but maybe the VTX is suitable?
Maybe can you help me to choose ?
Then I would like to build a preamp, maybe I am going to begin with a PX6, I think I red a post somewhere from APEX to output 18V DC from 35V, so maybe it is a good start.
Do you think 250VA is sufficient to work or should I invest in 300VA?
Many thanks
More VA is always better if you can afford it - it lets you play high current amps like class A later on. I use 250va and works fine for most of my class AB projects. I have a big 300VA but that is being saved for a special amp one day.
These amps are circa 30dB gain and I find that I don't need a pre-amp at all. Especially if you have a standalone DAC, it can probably drive more than 1.2v - which is about what is needed to hit clip one of these 35v rail amps.
These amps are circa 30dB gain and I find that I don't need a pre-amp at all. Especially if you have a standalone DAC, it can probably drive more than 1.2v - which is about what is needed to hit clip one of these 35v rail amps.
Is F8 topology totally different? Looks like a complementary input rather than LTP:
Reminds me of the earlier 50mm FX8 layout you did:
50mm FX8 was a cute little thing...
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F8 is CFA topology with diamond buffer input stage, yes it is totally diferent.
Ok, kind of like VSSA with CCS's and BD drivers - cool. Which post is schematic on?
Edit: found it...
This looks like fun. Sort of along lines of my CFH7 amp but with latFETs rather than hexFETs?
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