Warbler; Mos/Schade MOS/SIT choke loaded follower power amp

[Zen Mod]

These are not really my Cup of Tea, but there are few Greedy Boyz gnawing me about this...... so finally

as usual - basic pics in this post

I did forgot any pics taking apparatus today, going to my Workshop, so didn't took in vivo pics of T -Bed; will do that tomorrow when doing SIT ( two iterations of it) arrangement and tests

with this one - name of the game is to get trouble free and steady Iq setting, while having all variations named in title, by wish

EDIT on 16.07.2022. - Revised schematic and measurements, starting from post #30

 

[Zen Mod]

as seen on schematic - projected (negative) rail voltage is around 35Vdc; projected Iq is in range of 3A to 3A2, using IXYS Puck MOS, or same in Scade config, or Tokin Puck SIT

2SK2087C - rail can be lower , Iq in range of 2A

Ben Mah did play with several iterations of choke loaded amps, so he's a guy with best xperience which ready made chokes are good

All I have now of chokes ( no intention to chase better ones, too many amps) are two pcs of so-so similar cannibalized Microwave Owen xformers; while inductivity is OK ( 200mH), their Rdc is catastrophic - slightly under 2R

So, graphs I'm going to show are up to 10W and no more - due to two reasons:

- my THD measuring apparatus is good (amp input signal department) up to [email protected] voltage swing and I wasn't in the mood to work on that further
-had a setup with 30Vdc rail; lazy to make necessary changes on T-Bed for more

So, with proper rail voltage, proper loading choke ( Rdc much lower), you can expect to see lower THD at 5W and 10W levels, and you can expect steady [email protected], taking in account that SE Follower isn't PL XA25, cruising near max power all day long


again, test setup - 30Vdc rail, Iq 3A


so, for start, straight MOS iteration, 8R load

 

[Zen Mod]

same - straight MOS, 4R load

 

[Zen Mod]

Schade MOS , load 8R

as is normal with Scade arrangement, thing always get interesting above 10KHz or so, but that's nature of the Beast; there are different ways of doing it, Papa did show his trick with input xformer in Singing Bush predecessor amp - BAF 2015 .... anyway, 101 way of skinning virtual Cat

 

[cubicincher]

Looks interesting! Nice work!
Cheers
Dirk

 

[Zen Mod]

Schade MOS, 4R load

 

[Zen Mod]

tomorrow will set THF51 and 2SK2087C and post meausurements

and some pics of Funny Beast in action

 

[codyt]

Time to update the list!

 

[Zen Mod]

in fact, I believe there is a way of doing it even better, mostly thinking of better Iq stability in dynamic domain

stiffer Iq with large signals and much faster recovery

oh well, can't always end with what's drawn on first napkin, sometimes second one is better



in short, out with optocoupler, in with current mirror

Warbler postponed to final version, whichever one ends as one

 

[Ben Mah]

I have a different taste in tea than Zen Mod. I like my choke loaded followers.

The only brand of chokes that I have tried is Hammond. They are made in Canada and I buy them from Mouser, who has them shipped to the USA and then they ship them back to me in Canada.

The Hammond chokes that I use in my amps as load are the 193V and the 159ZC. The 193V is rated at 150mH 3.0A 1.0 Ohm DCR. I use it in my 2SK180 follower. The 159ZC is rated at 60mH 2.0A 0.7 Ohm DCR. I use it in my 2SJ28 follower. I am very happy with the performance of these two amplifiers.

Zen Mod has specified 60mH 5A 0.47 Ohm RDC. As far as I know Hammond does not have a choke that meet those numbers. However I would venture to guess that the 193V would do the job.

 

[Zen Mod]

oh yeah, specification on schm is utter wish, say - data which I will give to my custom winder

however, tomorrow will check Hammond catalog and say what I have to say ........ most certainly confirming what you already said, but just to recollect my own memory

 

[Zen Mod]

will proceed with this one

 

[Vix]

So it could be named Super-Mofo?
As to microwave oven transformers, I played a bit with them while building Mofos.
And yes, the problem with the 220 V ones we have in Europe is too high Rdc (I measured almost 3 ohms).
But then, I counterproductive/counterintuitive idea crossed my mind:
Two MW xformers in parallel? That would halve their inductance (self shot in the leg), but it would also halve their Rdc, making them somewhat usable, at twice the bulk/weight (or even four of them in parallell/series, but that would be a double overkill)...
But, since I can obtain them cheaply at a jukyard, maybe it makes sense...

 

[Zen Mod]

all roads are leading to Rome



yes, if having enough inductivity in each, you can parallel them to obtain lower Rdc

in many cases, cheapskate/dumpster diver approach is giving enormous joy

ZM, Omnidumpsterdiver

 

[dimkasta]

A PCB suggestion if I may

The screw pads are going to be very prone to lifting if you take into consideration the increased temperature and the strain of the screws. Even with washers. Some reinforcement with vias would increase their strength

 

[Zen Mod]

tnx, easy to do and I probably will ..... and small vias can be filled with solder prior to mounting

though, it didn't show as critical, yet ....... and I saw plenty of same arranged pads in really critical equipment

remember that screw holes are big vias itself

 

[Zen Mod]

in fact, I believe there is a way of doing it even better, mostly thinking of better Iq stability in dynamic domain

stiffer Iq with large signals and much faster recovery

oh well, can't always end with what's drawn on first napkin, sometimes second one is better



in short, out with optocoupler, in with current mirror

Warbler postponed to final version, whichever one ends as one

which means that Choked Singing Bush (yeah, SB with choke in place of Mu follower, thus needing full biasing mech. at SIT side) is going to benefit from same change

I already have pcbs for Choked one, dunno, maybe even for 6 months , simply didn't had brain (ppl usually are saying - time) to put it on bench

oh well, Life is Good

 

[dimkasta]

and I saw plenty of same arranged pads in really critical equipment

Critical equipment is probably tightened with torque wrenches
Perhaps a note on the assembly guide for greedy paws to not use the grip of death while tightening these

 

[Zen Mod]

you're right

- I paid my dues - have TW for M3 and M4, and using them

- Indeed ....... Assembly of Japanese Bicycle Require Great Peace of Mind; so, Regular Greedy Boy must be aware of one thing first - peanut brain size of Might ZM is allowing just that much of Assembly Manual ...... if you see that your chain is slipping, that doesn't mean that Mighty ZM sent you chain too big ......

 

[claudio52]

In the Lundahl chokes the core is an audio C-core. For my choke loaded I used the LL2733. With the coils in parallel: 100 mH - 3.4 A - 0.85 Ohm DCR.
Only 1.35 Kg!