Toshiba MOSFETs with a twist

[nige2000]

theres 3.5ish v between the tk30j25d gate and v- what sort of cap should i put across it?

Are you asking about improving the PSRR? In which case a cap between gate and v- isn't what I have been suggesting. It would probably improve PSRR but at the expense of worse output impedance.

i must have picked it up wrong, what were u suggesting?

[abraxalito]

If you go back to the original 'hot buffer' schematic you'll see R3 is 10k. Its this resistor which biasses the current source and we need to make this bias current more independent of supply ripple. The way to do that is split it into two Rs, say 4k7s. Then attach the cap between the mid-point of the 4k7s and -v. Best go for at least 100uF, 220uF would be my choice.

[nige2000]

ok got it now
\

\thanks

[nige2000]

need a little more testing but i think is a little softer sounding with that rc, think i prefer it without, its got more balls

[nige2000]

i brought the tk50j30d amp and my battery powered push pull class a amp down to Frans for a bit of cross comparison
played the tk amp for a couple hours we (myself fran,derek) were super happy with the sound could have easily listened to it all night, it was dynamic, aggressive yet free flowing
we weren't expecting the batt amp to be better than it at that stage so we were a bit shocked when we switched over to the batt amp to hear more depth and layers
there are aspects in regards dynamics and attack i think is better
i get the feeling some work on the power supply may help

[randytsuch]

With permission from Richard, I am working on a little pcb for the mosfet hp amp circuit.

Definitely a work in progress, I'm planning to move P1 (input power) to be closer to M1

pwb5.JPG (120.99 KiB) Viewed 727 times

Was made using easyeda, a cloud based tool that seems to work well.

My first PCB, so be gentle lol

I was going to add heatsinks, but they were going to take up too much room so I'm putting the mosfets on the edge of the board.

Randy

[nige2000]

the mosfets might benefit from been further apart they get rather hot?
maybe just run wire?

[randytsuch]

Thanks Nige

I was thinking if you use one large heatsink, it would be better to keep the mosfets on the same side of the pcb.
Since my pcb is rather small, they end up close together.

But yeah, when I build, I can wire up one of the mosfets to add more space between them, that would be easy to do.

Randy

[abraxalito]

i get the feeling some work on the power supply may help

What were you using as power supply for the gain stage? Its highly sensitive to PSU. I haven't found my TK amp particularly PSU-sensitive, but then again it does seem to lack dynamics compared to headphones. Work on power supplies is almost always repaid...

[nige2000]

i get the feeling some work on the power supply may help

What were you using as power supply for the gain stage? Its highly sensitive to PSU. I haven't found my TK amp particularly PSU-sensitive, but then again it does seem to lack dynamics compared to headphones. Work on power supplies is almost always repaid...

i had a few of these lying about audiowind sp-2
http://www.audiowind.com/pdf/A-240LM.pdf
used two of them (just the negative half) for the gain stages

briefly connected up a batt pack for gain stage for a quick haphazard test and got a good lift in sq
that i wasnt overly surprised with,
i tried a batt on the tk13 headphone amp and there was very little improvement
so i was surprised there was a lesser but substantial improvement by powering the tk50 with batt
seemed to be a cleaner sound or a lower noise floor, better decay, reverb etc, dynamics unchanged