B&B/Aphex Hybrid Op Amps

Hi All!
I came across some un-potted B&B Hybrid modules. They have the same footprint as the 990/2520. Just doing some preliminary testing, they measure and sound as good as the 990 in a MCI 636 @ 55dB gain that has the Hardy retrofit installed. At the bench they have no problem driving a 150 ohm load and distortion is very low at .01%
I replaced the LM356 with 5534A's as a sort of an upgrade, although
the LM356 works good too.

I know the benefits of building a discrete op amp, (noise) but has anybody
considered using a hybrid instead of a discrete? I would want to
add short circuit protection and a few other little goodies to the circuit
but the idea is there.

Schematic here:http://www.nashaudio.com/public/B&BOpAmp.pdf

Comments welcome!

> I would want to add short circuit protection

It is current-limited. Base of Q101 connects to bottom of R144 via three diodes. D103 roughly matches Q101 Vbe drop. So if drop in R144 wants to exceed about two diode-drops, base of Q101 is clamped. 1.4V/2.7R= 0.5 Amps max current. No instant-death for these transistors, altho the power dissipation in a sustained short could hurt. Assuming you apply your short on the far side of R146, and drive only with AC (so each device is off half the time), and +/-18V supply, about 3 Watts heat, twice the MJE180's naked rating, but easily handled on a scrap of metal.

> has anybody considered using a hybrid instead of a discrete?

Perhaps you are the first?

[quote author="rlaury"]I would want to
add short circuit protection and a few other little goodies to the circuit
but the idea is there.

Comments welcome![/quote]

Hi,

Since you went 5534 already it might be fun to see if pulling some current from the opamp (instead of entering the diode-stack midpoint) noticably improves things.

Like:



IIRC the Neve BA640 does this as well, and if that one doesn't use bootstrapping as well then there are others that do it.


While I guess this is all about small differences, most of them likely hardly noticable (we'd better make music, spend time with GF or go to pub instead of pondering these details), it'd still be nice to see what topology would make 'the definitive hybridTM'. The off-midpoint can cost headroom and will increase I_quiescent somewhat, but apart from that I'm wondering if there are reasons not to do it like that.

Bye,

Peter

FWIW:




bigger version:
http://www.twin-x.com/groupdiy/albums/userpics/10640~0.jpg

Apparently, the "oldfart" NE5534 can be hacked really "truly deeply madly" into. Not only by adding ABclass followers, but also with turning off/replacing the whole input stage and the output stage as well. A true hackintosh.

some more info here:
http://www.diyaudio.com/forums/showthread.php?postid=457320#post457320
http://www.diyaudio.com/forums/showthread.php?postid=612461#post612461
http://www.diyaudio.com/forums/showthread.php?s=&postid=675703&highlight=#post675703
http://www.diyaudio.com/forums/showthread.php?postid=706907#post706907


the "follower" with ccs's:
http://ipodstudio.com/cms/media/lisa_ii_schematic_complete_1.pdf

Hey
What was the 10640 power amp used in?
Was it a module?

RonL

[quote author="rlaury"]Hey
What was the 10640 power amp used in?
Was it a module?

RonL[/quote]
It's from the Neve 33609J... looks like a module indeed. For some reason AMS-Neve don't list that model (/file: 33609J.pdf) anymore.
Elsewhere in that 33609J-manual they call it by its probably better known name BA640.

Bye,

Peter

Hey
Looks interesting.
Thanks!

[quote author="rlaury"]Looks interesting.[/quote]
It looks like this one has all the various 'goodies' on board:
(1) output-protection (as described by PRR above for the other circuit),
(2) pulling DC from the opamp and
(3) bootstrapping to lessen the AC-load the IC-opamp sees.

But would it make for 'the definitive hybridTM' ? Or in D.Self-speak, 'the blameless hybrid' ? Anything we still can blame '10640' for ?

Bye,

Peter

blaming
a) bootstrapping (versus ccs active loading) is usually described as "coloring" and "detail-hiding"
b) there's apparently much more possible to do with 5534, see above post. There were also schems posted on diyaudio which incorporated 2sk389 frontend. Similar method is described in nat. an-222 for lm318


One can also use the compensation pin5 to bypass the 5534 internal output stage and use his own class-A or AB output stage, as described in links I posted before. (maybe too much)

Thanks tv for the response.

[quote author="tv"]blaming
a) bootstrapping (versus ccs active loading) is usually described as "coloring" and "detail-hiding"[/quote]
Might that be the influence of the electrolytic cap or is it thought to be caused by the bootstrapping-technique itself already ?

b) there's apparently much more possible to do with 5534, see above post. There were also schems posted on diyaudio which incorporated 2sk389 frontend. Similar method is described in nat. an-222 for lm318

Click to expand...

Had a quick look, but these measures seem are all noise-related. With a hybrid like this (output-stage with BJTs added) it'll be more likely though that we're already further down the chain, where noise doesn't matter much anymore.

For a one-opamp-does-it-all box it might be good/fun/overkill/necesary to give that IC-opamp both stuff in front and after of course.


Bye,

Peter

hey sinchronicity :grin:
(.. it's european weekend "morning")

yep "one chip (+3 trannies if 2sk389 accounts for one) does it all" (with feeling)
from my reading sofar the 5534 is __the_only__ chip in existence that lets you do this (but I ain't no expert at that)

it might be very interesting if "best brains" here took a plunge at this? maybe around the lsk389 and bc639/640 or some BD pair (or aclass w/o output protection)?

BUT (warning!!!) I also read in many places that for best "tone" they have to be signetics/phillips chips. personally I have a couple ti's (I think) chips in a bag, so far I only spotted that 5534's are a little quieter and "centered" than some other opamps..

@bootstrapping: from what I read there's always a time-constant present when bootstrapping. I'd use bootstrapping for coloring purposes (in fact I did that in some distortion generators !!! ). When going for cleanliness, I'd use ccs active loads (the 2-bjt configuration) like in this circuit:

(pimped-up jlh a-class amp)

[quote author="tv"]hey sinchronicity :grin:
(.. it's european weekend "morning")[/quote]
Hi again,

I can't see where you're located, but I bet you're not in Europe, otherwise you wouldn't have written Philips as Phillips :twisted: :thumb:

yep "one chip (+3 trannies if 2sk389 accounts for one) does it all" (with feeling)

Click to expand...

Sorry, 'with feeling' ?

(or aclass w/o output protection)?

Click to expand...

It's indeed weekend here, and no coffee yet, so in this I probably falsely read that you're saying class-A and the diode-type protection won't go together ? If a fault develops it's always possible to clamp the voltage across Re, but you might have meant something else... or I must indeed switch from tea to coffee now.

BUT (warning!!!) I also read in many places that for best "tone" they have to be signetics/phillips chips. personally I have a couple ti's (I think) chips in a bag, so far I only spotted that 5534's are a little quieter and "centered" than some other opamps..

Click to expand...

No problem, have these. Coincidentally I got an old studio RIAA-pre in yesterday, using socketed NE5534AP TI-stuff, so a mental note was made then to try a swap with Philips-ones.

Bye,

Peter

[quote author="tv"]@bootstrapping: from what I read there's always a time-constant present when bootstrapping. I'd use bootstrapping for coloring purposes (in fact I did that in some distortion generators !!! ). When going for cleanliness, I'd use ccs active loads (the 2-bjt configuration) like in this circuit:
[/quote]
Hmm, would that time-constant be the reason ?
DC-bootstrapping exists, probably those 'sonic objections' vanish if it was done DC-wise ?

Thanks for adding circuit.

Bye,

Peter