[AtomBoy]

I'm looking at the Hybrid Tube/MOSFET amp by Erno Borbely. There's an article here:

http://www.borbelyaudio.com/pics/405borbely2506.pdf

I'd like to do a low-buck point to point version.

It looks like all the transistors and MOSFETs are tough to get. I've found them on specalty sites for around $10 ea, but I'm thinking there's got to be an equivalent in the Mouser catalog for a buck or something.

Here's the list of suspects:

Q2 - 2SA872 (Hitachi (now Renesas) - Silicon PNP - complimentary pair with Q5 - 2SC1775)

Q3 - 2SJ79 (Hitachi - Silicon P-Channel MOSFET - complimetary pair with Q4 - 2SK216) or 2SJ313 (Toshiba - complimentary pair with Q4 - 2SK2013)

Q4 - 2SK216 or 2SK2013

Q5 - 2SC1775

I've spent a couple of hours with Google and haven't found any clues for equivalents. I spent a while looking at the datasheets, but I don't have the skillz yet to figure out how to pick an equivalent.

EDIT: http://www.bdent.com/ has the parts for sane prices!

 

[Pars]

If BDent doesn't have them, check www.mcmelectronics.com. Grab the datasheets and pay attention to the gain ranges as the Toshiba transistors are typically offered in 2-3 gains. Make sure for any complimentary pairs that supplier gives you the same range for both, otherwise you might have problems.

 

[rickcr42]

The borbely is not a PP output but a SE Class-A Mosfet stage with a CCS so the pairs do not have to be matched,just get close.

The main thing you want to look out for is a high gate capactance which will turn the SE stage into a Low Pass filter if too high.Other than that similiar gain but V/A rating can be higher

 

[Crowbar]

Can the output stage be made a follower, so the tube does all the voltage gain, while still retaining DC coupling throughout? I realize, of course, that the feedback will then have to go to the opposite side.
I'm also thinking of making this balanced output, for rewired headphones (with balanced input of course). Also, is 6DJ8 OK for the tube?

 

[gsteinb88]

Quote:

Originally Posted by Pars If BDent doesn't have them, check www.mcmelectronics.com. Grab the datasheets and pay attention to the gain ranges as the Toshiba transistors are typically offered in 2-3 gains. Make sure for any complimentary pairs that supplier gives you the same range for both, otherwise you might have problems.

mcm is the same company as newark FYI. Anything one has the other should have.

 

[Crowbar]

Quote:

Originally Posted by gsteinb88 mcm is the same company as newark FYI. Anything one has the other should have.

Er, it's been a year since he posted. I'm sure he's found them by now.

 

[Pars]

And Newark does not carry them. Strangely, even though MCM is part of the same company, they do not carry much of what Newark does and vice versa. They both kinda suck to order from, btw... expect high shipping costs and HUGE packaging for small parts.

 

[gsteinb88]

Yea, i know about newark and that, only order from them when i have to. Didnt notice that the thread was a year old, just that there was a new post today.

 

[Crowbar]

Anyway, back to my question:

Quote:

Originally Posted by Crowbar Can the output stage be made a follower, so the tube does all the voltage gain, while still retaining DC coupling throughout? I realize, of course, that the feedback will then have to go to the opposite side. I'm also thinking of making this balanced output, for rewired headphones (with balanced input of course). Also, is 6DJ8 OK for the tube?

[Edit:] I simulated the amp and the MOSFET actually does no voltage gain. I wonder if that's as good as a follower then.
Also, trying to set it as follower by replacing with a N-channel and moving feedback to the other input does give output but with DC offset; not sure how to do it right.

 

[Crowbar]

Oh wait... as Rescue Toaster pointed out to me in the IRC channel, it actually IS a follower... LOL
(the current sink provides high AC impedance below)

He also pointed out that C4 carries all the signal current... so would capacitor nonlinearities in this power supply cap seriously affect the signal?