[dviswa]

Thanks BrokenEnglish, steinchen. I think I found it. There are a few different options.
Digi-Key Part Number ED7310-ND is one.

 

[Glassman]

how are your buffers comming around guys?

just wanted to let you know that today I've finaly received AD744 for my PPA and boy you all really owe trying them to yourself! this opamp is a special one in the sense that it has so called compensation pin available, which internally connects to a point between input and output circuitry of the opamp, so that after some trivial modifications you can use it as an output to the diamond buffer, skipping entirely the opamp's own output stage.. it works perfectly stable with my latest buffers and really pushes the PPA even further!

 

[bg4533]

Glassman,
Wanna post instructions on how to do this for those of us that don't have a clue.

 

[motherone]

Glassman,

I'm a big fan of the AD744/746 (the dual version). I have a 746 running in an audio alchemy DAC and it sounds great. Specwise, it's very similar to the 627/637, but has slightly poorer noise performance, and some better specs elsewhere (If I recall correctly).

Great chip, though! I still need to put my buffers together.. Since I'm going to be swapping out my Elantecs, I thought that I would get a second PPA board just so I could have a PPA with the old buffers and a PPA with the Diamond Buffers.

Please post the details of your 744 mods.. I'd be interested in giving them a try (hell, I really like the chip WITH the output circuitry.. I'd love to see how it sounds without it!)

 

[rickcr42]

Quote:

I'm a big fan of the AD744/746 (the dual version).

the "original" jung multiloop amp used this baby along with the AD811.

There is also a pdf for download out there from an old Audio Amatuer (now called Audio Xpress) article that uses this combination in a full feature preamp,the Valkyrie.Some nice layouts/power supply/bypassing ideas in the article.

STILL a valid and fine sounding design though out of fashion with the "gotta be new' crew.

Old does not always mean bad because good sound is timeless

 

[Sovkiller]

We found another OPamp recently, that is supposed to perform even better, and do not need the compnesation pin mode, I'm waiting for the order to arrive...they need to be mounted in BD though, no big deal, I will try it soon and will report the results....this is incredible, upgraditis never ends....

The OPA637 is similar to the AD744 in sound as a regular OPAmp, but using the compensation pin you skip one step, and the sound is completelly different....cleaner and crystal clear.....

 

[rickcr42]

Quote:

We found another OPamp recently, that is supposed to perform even better, and do not need the compnesation pin mode, I'm waiting for the order to arrive...they need to be mounted in BD though, no big deal, I will try it soon and will report the results....this is incredible, upgraditis never ends....

that is the thing man.

"supposed to sound better" and upgraditis is a detriment to music by being more equipment-centric rather than geared towards music appreciation and actual listening to the song instead of the chip.

Upgraditis means you are going past the music and listening to "parts" which for me is the cart leading the horse.i have damn near every new ADI chip that has come out in the last few years and I still roll back time and go with the "comfortable shoes" chips.
nothing new has so far caused me to change my mind and is either a variant of what came before but in an unmanagable package (SOT etc) or brings nothing new to the plate worth tossing out the known.Good yes.Better no.

I mostly use the old and familiar if I use an IC at all and my only beef is when they stop being available in the DIP package or are discontinued.Then I have to scramble to scoop up a bunch before they are all gone because I HATE having to do a redesign for a standard gainblock,each withs its own layout peculiaraties and bypassing schemes

If I did have a wish list though it would be for the new opamp layout,the new ADI pin designators which make far more sense for audio use,in an old DIP Style package for easier use and plug in capability without an adapter from microscopic to "old mans eyes" and "all thumbs" size

 

[Glassman]

just like Sov says, crystal clear were the words that immediately came to my mind when hearing them for the first time, in the first seconds..


so, what do we need to do? basicaly three things:

1) disconnect Class A biasing current sources by removing R9 in case of PPA v1.0 or R10 if you have PPA v1.1 revision (these are the same 1k resistors just different names for v1.0 and v1.1)

2) short pins 5 and 6 of the opamp sockets, the easiest way is to do a solder bridge from the underside..

3) bend out pin 6 of the AD744 opamps before you insert them into the sockets.. (prevent pin 6 from touching pin 6 hole in opamp socket!)

and that's it! enjoy

 

[BrokenEnglish]

Quote:

Originally Posted by Sovkiller We found another OPamp recently, that is supposed to perform even better, and do not need the compnesation pin mode, I'm waiting for the order to arrive...they need to be mounted in BD though, no big deal, I will try it soon and will report the results....this is incredible, upgraditis never ends....

hehe... i'm pretty sure, you're speaking of that tempting little highspeed piece, i talked about with xtreme lately..

...unfortunately the dip8-versions are reserved for military use only. looking forward to your thumbs up, al!

Quote:

The OPA637 is similar to the AD744 in sound as a regular OPAmp, but using the compensation pin you skip one step, and the sound is completelly different....cleaner and crystal clear.....

tempting... very tempting....

glassman... please... /edit: ah... the instructions are there... thanks!

 

[motherone]

Glassman,

Just assembled my buffers, disassembled a ton of stuff from my PPA (out go a bunch of Vishay S102's.. Ugh!) and installed my buffers. They definitely rock. Thanks for putting this thing together for us!

Mike

 

[hypophysis]

I moded my PPA yesterday as described by glassman.
The sound is very good, but I have a problem with noise, hum and buzzing. When I turn the PPA on it's silent but after some seconds there's really loud noise and and it also starts buzzing. The buzzing can be modulated when I put my hand over the case (not even touching it). When the buffers get warm the noise decreases and after about 5 minutes of loud music listening all the noise disappears almost completely.
When I put an Intersil instead of the diamond buffer into ground channel, the amp is dead silent at all times.
Did anyone discover similar problems? How can I solve this?

 

[Sovkiller]

Quote:

Originally Posted by hypophysis I moded my PPA yesterday as described by glassman. The sound is very good, but I have a problem with noise, hum and buzzing. When I turn the PPA on it's silent but after some seconds there's really loud noise and and it also starts buzzing. The buzzing can be modulated when I put my hand over the case (not even touching it). When the buffers get warm the noise decreases and after about 5 minutes of loud music listening all the noise disappears almost completely. When I put an Intersil instead of the diamond buffer into ground channel, the amp is dead silent at all times. Did anyone discover similar problems? How can I solve this?

Do you have the input grounded to the case??? It seems that you have a grounding problem there...

 

[hypophysis]

Quote:

Originally Posted by Sovkiller Do you have the input grounded to the case??? It seems that you have a grounding problem there...

I've tried to to this a few minutes ago. I have doobooloo's 'crystal' PPA with acrylic front an backpanels in a small lansing case. Its very hard to contact the case to input ground, because the volume pot nut is isolated from the metal case. I have soldered a wire through a input ground pad that has now contact to the bottom case frame, but it's only touching it, and maybe I should screw it to the frame.
But there is not only ground hum an buzzing, but also loud white noise within the first minutes. When I put an Intersil into the ground channel it's always totally silent. If it is a grounding problem why do I only have it with the diamond buffer in ground channel?

 

[Sovkiller]

Quote:

Originally Posted by hypophysis I've tried to to this a few minutes ago. I have doobooloo's 'crystal' PPA with acrylic front an backpanels in a small lansing case. Its very hard to contact the case to input ground, because the volume pot nut is isolated from the metal case. I have soldered a wire through a input ground pad that has now contact to the bottom case frame, but it's only touching it, and maybe I should screw it to the frame. But there is not only ground hum an buzzing, but also loud white noise within the first minutes. When I put an Intersil into the ground channel it's always totally silent. If it is a grounding problem why do I only have it with the diamond buffer in ground channel?

The white noise seems like the amp is oscilating, try ferrites on the input and output, or maybe a cap from each input to ground, choose 1000pF or the like....(also you could try the OPA627 on all 3 channels, the bandwith for this one is lower and it is less prone to oscilate...But you will loose the compensation pin mod goodness.)

 

[hypophysis]

Quote:

Originally Posted by Sovkiller The white noise seems like the amp is oscilating, try ferrites on the input and output, or maybe a cap from each input to ground, choose 1000pF or the like....(also you could try the OPA627 on all 3 channels, the bandwith for this one is lower and it is less prone to oscilate...But you will loose the compensation pin mod goodness.)

I already have OPA627 on all channels. But I agree that this could be oscillation. The noise morphs from white noise to buzzing and buzzing changes frequeny an volume. Sounds really weird.
My PPA is fully breadboarded, maybe all these sockets between PCB and parts cause the oscillation. Maybe I should desolder these IC sockets and solder the resistors, the 100pf cap and the buffers directly to the PCB. But my soldering skills are not like doobooloo's and I am afraid of damaging the amp.