Toshiba MOSFETs with a twist

[abraxalito]

Doesn't light my fire as I've had enough of hearing the PSU and from inspection I'd guess the PSRR's rather poor. It'll likely be more efficient than an SE classA though. I noticed some on DIYA were building that circuit with 2SK2013 - those look to be fairly low gm transistors, almost as low as the now defunct laterals in TO220 (Hitachi 2SK213/J76) but with higher parasitics.

[nige2000]

I guess these are all variations of the pass f5
In my case my f5 version improved substantially
Using the battery supply so yea psrr is likely poor

Any thoughts on a class a power amp circuit maybe something with super psrr I can build and compare with what I got

[jkeny]

I guess these are all variations of the pass f5
In my case my f5 version improved substantially
Using the battery supply so yea psrr is likely poor

Any thoughts on a class a power amp circuit maybe something with super psrr I can build and compare with what I got

I think Richard's initial idea was to upscale that hotbuffer into a low power (20W) buffer USING 4 TK13E25D MOSFETS but I don't know if that is still his intent? It would also need voltage gain.

There is another very interesting approach using mosfets as followers as current gain devices - Susan Parker's Zeus amplifier
It's not SE but push pull & uses an input transformer as voltage gain device & output transformer (along with MOSFETs) as current gain stage. It's also a high PSRR design & said to sound wonderful but this should be taken to another thread if we want to discuss?

[nige2000]

think if i were to use transformers id like to use them with a good step down probably 5:1 or greater
maybe it was the ones i was using but at anything under 2:1 in comparison to 5:1 and greater seemed to be a loss noticeable in tautness in bass notes and in resolution

so in which case id need to add gain to input signal say x10 and use a 5:1 transformer at the front of that zeus amp,
id be interested in that, id guess the transformers wont be cheap

[jkeny]

OK, let's move Susan Parker Zeus mosfet amplifier to a separate thread so as not to confuse this one too much
Already there are 3 topics being discussed on this thread & although related it can get confusing for readers:
- headbuffer using high gm mosfets uncovered by Richard
- TDA1387 I/V stage using same mosfets
- mosfet linebuffer using TO220 version mosfet

Richard might want to combine discussion of his mosfet linebuffer in the Zeus thread or keep it here - it's his choice?

[abraxalito]

I guess these are all variations of the pass f5
In my case my f5 version improved substantially
Using the battery supply so yea psrr is likely poor

Right - you could also have tried with the step-down OPT and I guess you'll get more improvement. The primary purpose of the OPT is PSRR enhancement.

Any thoughts on a class a power amp circuit maybe something with super psrr I can build and compare with what I got

As John said, the TK13E25D buffer can be extended to whatever output power is needed by paralleling via the output capacitors. I reckon 4 buffers (so 8 transistors total) would do fine for around 20W. The heatsinking does need to be substantial due to the max 25% efficiency - so with 20W output power the idle dissipation is 80W. There's another even heavier duty Toshiba MOSFET that I'm intending to try which will halve the number of transistors required.

[abraxalito]

so in which case id need to add gain to input signal say x10 and use a 5:1 transformer at the front of that zeus amp,
id be interested in that, id guess the transformers wont be cheap

Transformers for that needn't be expensive, can be DIY'd on ferrite cores. Maybe I'll talk more on the Zeus thread about that amp.

I think there's a trade-off between amount of input voltage gain and step down ratio at output - in theory when the PSRR's sufficient we'd not need any OPT so the experiment is to see where the sweetspot is. With classAB chip amps the PSRR's lousy to begin with which is why trafos work such magic, however when a design's built from the ground up for high PSRR then I reckon the trafo should have little to no effect. But we do need to verify this in practice as there may be secondary effects the transformer has - like EMI reduction for example.

[jkeny]

There's another even heavier duty Toshiba MOSFET that I'm intending to try which will halve the number of transistors required.

What figure of merit in the mosfet spec is important for choosing these high power mosfets - the high gain Yfs plot was the FOM for the low signal mosfets for headbuffer - Is it the same here? We might be able to help in searching for alternatives with this info?

Maybe you can just give us your reading of the Yfs plot for the TK13E25D

YfS.jpg (50.22 KiB) Viewed 534 times

[abraxalito]

What figure of merit in the mosfet spec is important for choosing these high power mosfets - the high gain Yfs plot was the FOM for the low signal mosfets for headbuffer - Is it the same here? We might be able to help in searching for alternatives with this info?

The parasitic capacitances are relevant too, in the I/V stage discussion I figured a good FoM was the gm divided by the Crss. This is just a first approximation as some FETs in some applications will be dominated by the input capacitance (as is the Zeus) rather than the reverse feedback capacitance.

Maybe you can just give us your reading of the Yfs plot for the TK13E25D

I made some estimates of the gm below 1A as that info isn't shown in the plot. I got about 2.2S @ 300mA in a direct measurement. I also make measurements of Zout in amps to infer what the gm is, I shall try that with my hot buffer and report back.

[jkeny]

Ok, thanks,
Are the OptiMos-3 mosfets usable (dirt cheap) as they have an in-built diode between drain & source?

This one, IPD060N03 - N-channel mosfet TO252 device, transconductance 67S

transconductance.jpg (40.74 KiB) Viewed 517 times

Crss.jpg (70.87 KiB) Viewed 517 times