[ppl]

The Replacement of the IC buffers on the PPA v1.0 with the discrete component Buffers introduced on the V2 allow for a mode of operation not possible with the HA5002 IC Buffers in the V1.0. The Discrete component buffer in the V2 boosts an ultra low input Bias current and this makes operation from high resistance sources such as a volume control possible while obtaining Low DC offset. The clever mind would instantly think of the possibility of using the output stage all on it’s own without any op amps and thus Drastically reduce the number of active components in the signal path.

If your application requires no voltage gain because your source puts out plenty of output voltage for your listening level and you don’t require the Bass boost feature then perhaps this configuration is for you. The PPA’s output buffers supply the current to drive the Load. And thus you have a purely discrete component 100% feedback free unity gain current stage that will accurately follow the input.

Assuming you PPA V2 is already assembled and you simply wish to mod your amp for this configuration then simply remove all three op amps from there sockets. Also remove R10 so as to disable the op amp Cascode Bias as you don’t know longer need it. Jumper pin 6 to pin 3 on all three op amp sockets that used to contain the op amp this connects the volume control wiper to the op amp output and thus to the buffers input. This completes the modification connect power measure DC offset and if all is well proceed to connect you headphones and listen.

If you are building from the start and plan on this unity gain configuration as your PPA then you do not need to install any op amp components or there related power supply circuitry just the resistors going to the op amp output R11 and the resistors on the volume control side of the op amp input R1, R2, R3 on the gain channels and R1 on the ground channel jumper pin 3 to pin 6 as described above on each op amp and your ready to test and play. The volume control will work just as if it normally would and DC offset is a constant 1-15 mV Typical at any volume position.

You will have a better performing and IMHO a lot better sounding version of this
http://www.stereophile.com/amplifica...54/index1.html

 

[dsavitsk]

This basic premise seems to get used in the GC world quite a bit. Here is a SS version (scroll down to where it says "The Buffer"), and a Tube one too. In fact, I think I proposed it a few weeks ago

Edit: I also drew this up a while back as a possible circuit to use in a buffered passive pre. It is essentially just the buf634 datasheet. Looking at it again, I think the feedback resistor should be a bit lower. Also, you would want a pot right before it. Also, I am not sure what the current draw would be, but if it is low enough, one could just use a tle2426 instead of the first buf634.

I remember reading the Corey Greenburg article when it was published, and have been interested in doing it ever since. Mine (based on the discreet SS one above, is almost done.) I am actually building one from Holco/PRP resistors, and one from Kiwame to see if there is a difference.

-d

 

[rickcr42]

Full circle !

I have stopped using opamps years ago unless it is a must do and now the PPL amp comes full circle from all IC to opamp/discrete to all discrete !

Welcome to my world man

 

[ppl]

Quote:

Originally Posted by dsavitsk This basic premise seems to get used in the GC world quite a bit. Here is a SS version (scroll down to where it says "The Buffer"), and a Tube one too. In fact, I think I proposed it a few weeks ago Edit: I also drew this up a while back as a possible circuit to use in a buffered passive pre. It is essentially just the buf634 datasheet. Looking at it again, I think the feedback resistor should be a bit lower. Also, you would want a pot right before it. Also, I am not sure what the current draw would be, but if it is low enough, one could just use a tle2426 instead of the first buf634. I remember reading the Corey Greenburg article when it was published, and have been interested in doing it ever since. Mine (based on the discreet SS one above, is almost done.) I am actually building one from Holco/PRP resistors, and one from Kiwame to see if there is a difference. -d

yes it was your previous post that reminded me of the ability of the PPA2.0 to do exacly what you requested so i presented this as a seperate enity so as to be easy to search for in the future.

with regard to IC buffers i have not found a currently available buffer that will operate from sources impedances above 10K without large DC offset, The last ones available that would are the BUF03 as used in the Stereophile artical and the LH-0033 and LH-0063 series of fet input buffers. the last one i played with an EL2004CG cost me $35.00 Each and is what i used in place of the BUF-03 http://www.alldatasheet.co.kr/datash...EC/EL2004.html

The LH-0063 series is http://www.alldatasheet.co.kr/datash.../LH0063CK.html

The LH-0033 Series http://www.alldatasheet.co.kr/datash...C/LH0033C.html

man what a Blast in the past these Chips are but like all good things must come to an end and so have these and nurmerious other really good Buffers Like the EL-200X series we loved so much.

 

[xtreme4099]

yup yup ... code amps are all discrete rickster! btw the v2 is very smooth and detailed with mod, most detailed id say, but me, i need it to go loud as ******, which is why i havent modded mine yet ... but maybe the mod itch will come back... sometime later.

 

[rickcr42]

Quote:

man what a Blast in the past these Chips are but like all good things must come to an end and so have these and nurmerious other really good Buffers Like the EL-200X series we loved so much.

the LH0033 and 66 are the only monolithic buffers in my system.If modern specs were the only benchmark then they fall far short in the idling current to output current area,speed,distortion,rise time,etc- but if sound quality is the measure then they are right there.
The purity of the internal schematic is also something special and as close to a discrete "module" as an I.C. gets.

Years ago National Semiconductor had a factory in my town and I lucked out by obtaining someones "stash" of parts but sadly my supply has finally run out and I am keeping what's left for me.One stereo headphone buffer,one stereo line driver (the 0033s) and one stereo pair mounted on a pine board with the factory heatsinks (0063) and barrier strip terminations for the buffer pins-to-world hookup

 

[Megaptera]

Has anyone tried this yet? I've got the parts on the way to do it, since between the efficiency of my MS-2s and Athenas, and the gain on my Gainclone, I'd like to be able to use more than 40% of my pot's range.

 

[Megaptera]

Well, I've put one together like this, and I've run into a bit of a problem: There's a pretty nasty buzz that I'm pretty sure is a grounding issue. Chassis is at signal ground, pot housing is grounded, dc offset is ~15mV, etc. -- what's new to me is that if I short signal ground to one of the power supply caps (the vent area, at least), the noise disappears. When I do this, I can tell that the amp sounds great, but obviously that's not a real solution.

I assume the problem is not with the caps, but with the ground, since the noise disappears if I touch any of the nine electrically-unconnected cap vents. I haven't given up trying to figure it out myself yet, but does anyone have an idea what the problem might be?

 

[ppl]

did you remove the class a bias resistor R10 and is this a V2 PPA V1's with the IC buffers will not work in this mode.

 

[Megaptera]

It is a V2 -- I reused a few components (including the power caps) from my V1 but it's a new amp. And since I was starting it as a new build I just never bothered installing R10 in the first place. It probably is something as simple as forgetting to install some vital component but I've looked over the board half a dozen times already without seeing anything obvious missing.

 

[Megaptera]

Got it fixed. I'd completely spaced on the fact that the TLEs set the virtual ground that the input ground gets tied to (and not just the opamp's power rails), so once I tossed one on and connected it, all was good. I'm just starting to really listen to it, but I like it a lot so far.

 

[ppl]

Quote:

Originally Posted by Megaptera Got it fixed. I'd completely spaced on the fact that the TLEs set the virtual ground that the input ground gets tied to (and not just the opamp's power rails), so once I tossed one on and connected it, all was good. I'm just starting to really listen to it, but I like it a lot so far.

That would have been my next question is at least one TLE installed. I amglad you got iy working. Maybe some more folks will try this and report on how it works out in there systems and what it sounds like.

 

[Megaptera]

Thanks for your help, PPL -- I was a bit reluctant to mention what the problem was, since it's so obvious, but hopefully someone else will learn from my embarassing mistakes

One question left, though: since the low-current section only consists of a single TLE to set the virtual ground, would it benefit from the isolation JFETs?

Into Day 2 of listening, it's a definite step up from my PPA v1, even with the Larocco diamond buffers. I can't A/B them since I used a number of parts from the v1 but there are a few minor problems I'd been hearing that have disappeared with the upgrade.

If anyone's thinking of trying this I'd be happy to help with part selection and the like. It's really impressed me so far and I'd encourage anyone building one for efficient headphones to give it a try.

 

[ppl]

Quote:

Originally Posted by Megaptera Thanks for your help, PPL -- I was a bit reluctant to mention what the problem was, since it's so obvious, but hopefully someone else will learn from my embarassing mistakes One question left, though: since the low-current section only consists of a single TLE to set the virtual ground, would it benefit from the isolation JFETs? Into Day 2 of listening, it's a definite step up from my PPA v1, even with the Larocco diamond buffers. I can't A/B them since I used a number of parts from the v1 but there are a few minor problems I'd been hearing that have disappeared with the upgrade. If anyone's thinking of trying this I'd be happy to help with part selection and the like. It's really impressed me so far and I'd encourage anyone building one for efficient headphones to give it a try.

That's OK Im Embarresed that i often times put LED's in Backwards. You Are correct jowever in that its allways good if somone elce can avoid the same mastakes, so while to Error is humnan. Oh and one more thing (I see Dead Transistors)

Yes use a pair of isolation Jfets and a real low value IDSS type like a 2N5484 is good since the current drain is way low only uAmps

 

[xtreme4099]

currently testing this configuration ... very detailed balanced sound more so than any opamp ive heard--- in the ppav2 ... of course the volume is decreased because of the no gain thing .. but its the purest most detailed sound your gonna get outta of the ppav2 ... ppl is working is currently working on getting a switch to go from opamp gain to noopamp no gain ... with a flip of a switch. quite cool indeed.