Tír Na HiFi

They're lovely cases

abraxalito wrote: ↑Wed Jul 12, 2017 7:31 amI think probably the only one that worked first time

ah.. i thought it was only me that happened to

looking forward to the pics

was there a schematic for the gain stage somewhere or did i dream there was?

I was talking about sharing the gain stage schematic, however I've not listened to it enough to offer it as a recommendation yet. I'll do that after I've compared it with the step-up trafo and it hasn't been completely clobbered...

abraxalito wrote: ↑Wed Jul 12, 2017 1:24 pm I was talking about sharing the gain stage schematic, however I've not listened to it enough to offer it as a recommendation yet. I'll do that after I've compared it with the step-up trafo and it hasn't been completely clobbered...

assume your inputting from a j327 type buffer or "hot buffer" so output impedance will be very low and the 10:1 step up will have the best chance of working and sounding good?

think this is will be a very interesting comparison to see if there's more to transformers than psrr

Yes, right on, I'll be driving this trafo from a CCS-loaded MOSFET buffer with plenty enough classA current to saturate the trafo. Just done some preliminary calculations, I reckon I can just get the secondary on a PQ2625 core with some very fine wire (0.06mm). That'll be a centre-tapped secondary which can handle up to 20VRMS so good to try with a balanced higher power version of this amp if I can find a case which can absorb all the heat....

abraxalito wrote: ↑Wed Jul 12, 2017 2:19 pm Yes, right on, I'll be driving this trafo from a CCS-loaded MOSFET buffer with plenty enough classA current to saturate the trafo. Just done some preliminary calculations, I reckon I can just get the secondary on a PQ2625 core with some very fine wire (0.06mm). That'll be a centre-tapped secondary which can handle up to 20VRMS so good to try with a balanced higher power version of this amp if I can find a case which can absorb all the heat....

this is the yoke ive been using for the hot stuff

https://www.modushop.biz/site/index.php ... uct_id=226

assume 8 mosfets per channel for balanced ?

is there a way to do balanced with the gain stage?

Here's where I've gotten to with my prototype step-up transformer.

Core is PQ2625, primaries are is 2 * 303 turns using 0.11mm wire (ideally would be 0.15mm but I was too lazy to go looking for the right size). Secondaries are 2 * 3030 turns 0.06mm.

Primary inductance ~ 660mH @ 50Hz with 1V drive. Input capacitance ~ 24nF @20kHz. Primary DCR 27ohm, secondary 1.1kohm.

With such a high input capacitance I think it was a mistake to create two secondaries, I'll not make a 'double duty' trafo rather a simple 1:10 and see if we can get that capacitance down.

<later> 2nd generation effort more promising - single primary 0.21mm 7.8ohms, single secondary 0.09mm 500ohms. Input capacitance ~12nF @20kHz. I'll make a second one like this...

I made a few more measurements of the transformers and plugged them into LTspice to see how we get on. Turns out that the leakage inductance is a critical parameter because it resonates with the input capacitance of the amp, forming a low-pass filter. With an input capacitance of 270pF (estimated from the two TK13E25Ds in parallel) plus 120pF for the trafo's self-capacitance we get an uncomfortably low turnover frequency from these trafos (leakage L about 1mH). I shall try it with the lowish band limitation to see how it sounds, the best solution I think will be to add an input buffer to the amp with a much lower capacitance FET - the Crss is quite non-linear in the TK13E25Ds, strongly dependent on gate-drain voltage.

You da man!

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By adding an input buffer to the amp you mean putting a low crss fet between the traffic secondaries and the TK13E25Ds?
If so won't that raise its output impedance?

Edit

Doh,......

It buffers it further
Yea u da man