The Holy Grail Follower Output Stage

[lhquam]

Congratulations. It is amazing how much power supply and ground noise can be affected by seemingly insignificant layout and wire changes.

 

[william2001]

About to mount these up and run some wires. Fortunately won't need to drill and tap anything, with some already existing "UMS" holes. PS is +/-28.5V unloaded so we'll see where that ends up. I set the gain at 4.7x since I have a tube preamp that's still part of the action.

 

[lhquam]

Those are mighty power supplies. ZM would be happy with them.
Will they attach by umbilical?

 

[gary s]

In the picture of the 2 loaded boards in post #502, each board is loaded with C7 and R16 - am I correct in saying the instructions are to only load these on 1 channel?

 

[lhquam]

You can load both boards, but attach RCAgnd to GndR on one PCB and RCAgnd to Gnd one the other.
IKf the power supplies are totally independent from one another, it is possible to avoid the ground loop issue. I can supply an appropriate wiring diagram.

 

[gary s]

Thanks for the reply, I think it might be a wise move to post your wiring diagram - that night help a lot of builders,

 

[william2001]

Those are mighty power supplies. ZM would be happy with them.
Will they attach by umbilical?

Just big monoblocks. Chassis salvaged from a scrap heap and re-purposed. I've shared multiple pictures and commentary in other threads (i.e. ZM's SS R.3), and don't want to clutter and derail this nice thread going into detail on those. Overkill PS not so much for the big capacitance... more for the ultra low ESR on the final C. If I like it, it will feed the next big thing (HGF Mk2 "now even Holier!", and the next one after that, and so on... Or maybe a sip from this Holy Grail really is the End Game, and I just sell everything else and retire...

 

[william2001]

each board is loaded with C7 and R16

I have monoblocks and built the PCB's with all options.. may or may not route ground through there. Or even use the built-in opamp front end forever, we'll see.

 

[gary s]

OK, good luck with the build and the testing.

 

[lhquam]

If the power supplies are independent, wire the ZD25-Mini PCBs as though they were two mono block amplifiers in a single chassis.

 

[gary s]

Do you have a similar diagram where only one PSU is used to supply both channels - maybe it is your manual?

Thanks for the mono diagram.

 

[gary s]

Yes, just had a look in the manual, and the wiring diagram is there for a stereo chassis with 1 PSU - so all options seem to be covered, thanks again for your great work on the amp. It is on my list as the next one to start.

 

[william2001]

People kinda like pictures so here's a shot of Ch. #2 for one final Iq / DC offset checkout before final assembly and transport to the listening room.

 

[Analogico]

My source for FETs was the EBay seller Polida Electronics Ltd. For $14.99 + $5.00 shipping you can order 5 pairs of FQA28N15+FQA36P15.

A word of warning
I ordered a set of 10 MOSFETs (28N15) from this eBay seller. When I saw the image (see below) posted by @myleftear I was quite confident that I could receive potentially genuine MOSFETs, but unfortunately the articles I received seem obviously counterfeit.
Apparently, the seller may have genuine FETs as well as fake ones.
In other words, buying from this seller seems to be a game of chance.
Do business with this seller at your own risk!

@myleftear MOSFETs (which I assume @lhquam got from Polida's store)


MOSFETs I received from Polida (visual inconsistency between the various items is significant)


For reference genuine onsemi 28N15 MOSFET

 

[myleftear]

@Analogico thanks for the word of caution. I hope this won't be so.
I fully trusted lhquam when I jumped on the wagon. And as they were measured, I'm still confident they're what they ought to be. Of course I hope they are...

 

[Analogico]

@myleftear
Yours look genuine (despite the legs appearing to have been 'refurbished') and correspond to the image that Polida's store shows, mine simply don't.

Polida's store image

 

[Gyuri]

Polida?
I'm not saying that he is selling fake parts on purpose. Maybe he doesn't even know what he's doing. (I hope.)
But I bought here definitely fake Toshiba 2SJ313 and 2SK2013
parts.

 

[TungstenAudio]

Measuring the Mosfets received could answer some questions.

 

[myleftear]

Measuring would indeed. I should have to, ahem!, learn to howtodothat... finally!

 

[Vunce]

Why take a chance with fakes when they are readily available from trusted sources. Search them out😉