[ppl]

WELL.... AFTER HAVING TO REMOVE THE BOARDS FROM THE CASE TO OPTIMIZE MY bUFF-634 x3 AND opa-637 AMP I DECIDED TO GO FUTHER AND ADD MODIFICATIONS THAT WILL ASO IMPROVE ALL MY PORTABLE AMP VARRIENTS.....

THESE INCLUDE ....RAISING THE cURRENT SOURCE FROM 1 MA TO 2mA nITICEABLE IMPROVERMENT BUT NOT SUBSTANTIAL JUST SUBTILE. tHEN IN ORDER TO LOWER THE IMPEDANCE UPON THE INPUT OF THE CAPACITENCE MULTIPLIER CIRCUITS I WOULD NEED TO ADD SOMTHING MORE THAN THE 100Uf CAP ORIGELALY USED AND NO ROOM FOR LARGER CAPS. wELL THE tle 2426 TO THE RESCUE WILL OFFER A LOW IMPEDANCE UP TO THE POINT THE 100UF CAP KICKS IN. AND IT CAN BE PLACED UPON THE EXSISTING BOARD JUST BY DRILLING HOLES OUT FOR IT AND LOCATING THE PART CLOSE TO THE OTHER CIRCUITRY AND wOW A PART TAKING UP THE SPACE OF A TO-92. THIS REDUCED THE RIPPLE REJECTION BELOW 100 hZ. BY ANOTHER 30Db ALWAYS GOOD SO NOW WERE LOOKING AT A TOTAL OF OVER 100 Db.

bUT FUTHER IMPROVEMENT CAN BE HAD BY ADDING JUST (2) MORE PARTS AND EXCHANGING (4) RESISTORS WITH (4) 40 mA CURRENT SOURCE CONNECTED jFETS. A pAIR OF lOW POWER bUFFERS FORM INDIVDUAL VIRTUAL GROUND DRIVERS FOR EACH CHANNELS OPAMP. tHE cURRENT SOURCE REPLACES THE 10 OHM sUPPLY LINE RESISTORS SO AS TO OFFER A hIGH IMPEDANCE FROM THE OUTPUT OF THE cAPACITENCE mULTIPLIER'S tHIS COMBO ADDED ANOTHER 20 dB IF REJECTION OR ISOLATION AND THAT IS ALSO BETWEEN OPAMPS. dUAL MONO ON A bUDJET MABY hA.

tHE SONIC RESULT OF ALL THIS IMPROVED THE APPARENT SPEED THIS MAY BE BECAUSE THE OPAMP WAS NOW OPERATING FRON A FAST SUPPLY NOT BOGED DOWN BY THE 15k CAP UPON THE OUTPUT OF THE CAPACITENCE MULTIPLIER. tHE eL-2001 bUFFER I USED HAS A FLAT AND LOW OUTPUT IMPEDANCE LESS THAN 10 OHMS UP TO 30mhZ. EASALY WITHIN THRV RANGE OF AN opa-627. OR IF YOU WILL AN ad-824 BUT I THINK I WOULD GO WITH THE 180 hHZ. el-2002 FOR AN 825. bUT BACK TO THE SOUND NOT ONLY WAS THE TRANSIENTS VERRY QUICK BUT SOUNDSTAGE IS ABOUT 50% GREATOR tHIS IS A REAL TREET.mIDRANGE ASPECHILY VOCALS TOOL ON AN INTIMATENCY I HAVE NOT HEARED FOM MOST ANY AMP LET ANONE A PORTABLE. SO wILL cLOSE FOR NOW.

nOTE I WILL CONTACT HANSON AND SEE IF HE CAN PUT UP THIS NEW VERSION ALONG WITH MY OTHERS.

 

[Trap]

Interesting, the first inverted case posting I have ever seen.

 

[hsnam]

ppl,
i don't have time to build one, but you can email the schematics to the following address, and i'll put it up my iDisk:
hyn2001@med.cornell.edu

 

[ppl]

Trap: and you seen it hear first.....

hanson thanks but it will be some time before i get the docs done. Still Tweeking this Circuit. But so far i like.

 

[ppl]

After speending the weekend away and listening to this upgraded amp i felt uncomfortable with the Dip Buffers tack soldered upon the Bottom of the board with the Top of the Chips package toutching the Chass and thus adding unwanted stress. well i got out some BUF-634U SMT Buffers This part has the same pinout as an opamp and the SMT case fit into a hole on the Bottom of the Argut sockets i used for the opamps. the SMT buffer and it's assoeated 47K SMT resistors fit into that space like a glove. Now i have a Dip socket with it's own virtual ground driver included. You C-MOY amp Builders worring about space should try this. I now feel comfident that the assembly will hold up plus looking unmodified except the Transistors replacing the origenal 10 ohm resistors in series with the Opamp supply lines. gess it is time to make another amp board for this incorperation of my latest thinking on Keeping the Power suppl ultra quiet. BTW this all only added 2 MA to the total amps Current drain. it was about 1 ma but the BUF-634's (Low Bandwidth Mode) draw three times the Current of the EL-2001's.

 

[erix]

This sounds very cool!

I would love to see a pic of this setup, or any other smt to dip socket rig Headwizers and Head-Fi-ers have come up with.

Any chance?

ok,
erix

 

[ppl]

I do not have a good quality Digital camra but i may bev able to get some pictures from a frend that has a great one then will post Pictures of this amp. and the Inside Circuitry.

 

[ppl]

I now have also tried this mod with the AD-825 and the results are evean Better than thay were with the OPA-627 & 637's. The Midrange is Brought right up on the 825 the tendency to Accuate Sibelense is compleatly Gone Since the EL-2008's are no more I am investigating parralell EL-2001's so far This is the Best of all me Amp Desigs. and onyl 36MA quesent Current Drain. Not bad for an Amp using (5) BUF-634's (2) AD-825's (8) EL-2001's Plus an LED and the Current sources. By powering the OPamps in this way made the Bass loudness less than it was But still Plenty Good also alot Tighter, Maby to Mutch so. The High frequency Reproduction of the 2001's are Better than evean the 2008's But it takes (4) el2001's to Drive Grados and Sonys Well. Anyone who thinks the MDR-V6 is not amp sensitive is full of S*^%. These cans will be Under dampened or over dampened depending upon what is Driving them and a Balance is Needed with these cans. What sounds great on the Grado's are OverDampened with the Sony's Ie 2008. and Less than 250 Ma of output Current from the amp will make the MDR-v6's sound Bright and Thin.

 

[jude]

Quote:

Originally posted by ppl Anyone who thinks the MDR-V6 is not amp sensitive is full of S*^%.

ppl,

I don't know too much about the DIY neck of the woods, but I agree with you on this statement. I also feel the V6's can benefit greatly from use with an amp that's a good match.

 

[ppl]

JUDE: I hear all the time about the V6's Being so sensitive that thay do not need an amp and Having Lived With These for years and the 7506's for almost a year I can say that YES Not only do these Cans need an amp thay are also very paticular about what Kind of amp powers them. Not enought Output Current and the Bass is Fat and in some cases Boomy. Drive them with a High Current Low outImpedance Amp and Thay Bass gets Week and the Highs overpowering. So these Cans DO indeed require an amp made just just them. Now the MDR-V600 is Like the Grado's Lots of output Current to Get The Control out of them. and While the V600's may not be the Best Cans in the world Thay are still popular so People using them should give good consideration to what powers them. Now an easy to Drive Can is my Koss PRO 4AA as long as thay get enought voltage thay dont really intereact with the source like most other cans do in fact these cans worke great with OTL tube amps.