Mosfet amplifiers including Susan Parker Zeus amplifer

User avatar
Fran
Site Admin
Posts: 4141
Joined: Sat Jan 16, 2010 10:03 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by Fran »

They're lovely cases
Do or do not, there is no try
nige2000
Posts: 4253
Joined: Thu Feb 14, 2013 10:47 am
Location: meath

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by nige2000 »

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?
sd card player, modded soekris dac, class a lifepo4 amp or gb class a/b amp, diy open baffle speakers based on project audio mundorf trio 10's
abraxalito
Posts: 230
Joined: Fri Sep 16, 2016 11:05 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by abraxalito »

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...
nige2000
Posts: 4253
Joined: Thu Feb 14, 2013 10:47 am
Location: meath

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by nige2000 »

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
sd card player, modded soekris dac, class a lifepo4 amp or gb class a/b amp, diy open baffle speakers based on project audio mundorf trio 10's
abraxalito
Posts: 230
Joined: Fri Sep 16, 2016 11:05 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by abraxalito »

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....
nige2000
Posts: 4253
Joined: Thu Feb 14, 2013 10:47 am
Location: meath

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by nige2000 »

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
Image
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?
sd card player, modded soekris dac, class a lifepo4 amp or gb class a/b amp, diy open baffle speakers based on project audio mundorf trio 10's
abraxalito
Posts: 230
Joined: Fri Sep 16, 2016 11:05 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by abraxalito »

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...
abraxalito
Posts: 230
Joined: Fri Sep 16, 2016 11:05 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by abraxalito »

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.
stepuptrafos.jpg
stepuptrafos.jpg (108.05 KiB) Viewed 543 times
jkeny
Posts: 2387
Joined: Sun Jan 17, 2010 9:37 pm

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by jkeny »

You da man!

Sent from my XT1033 using Tapatalk

www.Ciunas.biz
For Digital Audio playback that delivers WHERE the performers are on stage but more importantly WHY they are there.
nige2000
Posts: 4253
Joined: Thu Feb 14, 2013 10:47 am
Location: meath

Re: Mosfet amplifiers including Susan Parker Zeus amplifer

Post by nige2000 »

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
sd card player, modded soekris dac, class a lifepo4 amp or gb class a/b amp, diy open baffle speakers based on project audio mundorf trio 10's
Post Reply