[mitru78]

well, i guess it's time i chimed in here. i've had this little amp for about a month now, and have been using it nonstop with my Zu'd K271s, RnB Diamond IC, and Aiwa AM-F80 MD player...

and I'm digging this bugger! it packs a fair amount of punch.

it opens up the soundstage dramatically, as opposed to plugging the K271s directly into the line/headphone out on the MD player. it adds some clarity, and just generally tightens up the sound all around.

i threw a couple OPA2107's into it but things got a bit crunchy at moderate -to-high volumes. i've got a some AD8397ARZ chips, but am waiting on order from Brown Dog before i can toss 'em in.

it's a great little amp!

 

[Andrea]

Elephas, yup, you confused "chips" with "caps", never mind. Mine has Wima caps too, and DC jack, but the standard gain (gain of 7.8) as the idea of a low gain with subsequent ample rotation of the volume pot gives me some sort of... claustrofobia. Eeeh, what can I say

mitru78, that's sweet news

I don't think the OPA2107 is well suited for the task here, due to its comparatively low output current. The AD8397's I have as well, but the amp's builder told me that the non-standard dimensions of the browndog dip to so8 adapters would make them unusable in his amp (though, I wonder if perhaps just one of them, to replace only the buffer op amp ...?). Instead, the single to double dip browndog would fit without problems at least for the gain opamp (as he also said that the DC jack, if present, would get in the way of it if using one of these for the closer opamp to the jack). I have a few ones, AD843's and BUF634's on top, to try if I manage.

Note that the AD8397 has a higher input bias current than the other opamps. This means that you'd want to check the offset voltage on the output to know if things are entirely safe ...

 

[mitru78]

yeah, i'd not figured out what i'd do just yet if the BrownDog SO8/DIP + AD8397 setup managed to work out well.

i obviously would prefer to just take the opa2227's out and pop another set of DIP opamps in; all without any adapters or tweaks.

could you recommend any easy swaps, Andrea? you mention the AD843, and BUF634. are you suggesting AD843 --> IC1 and BUF --> IC2 ?


let us know what you come to find after a bit of listening/toying.

 

[Andrea]

Eh, it's a bit tricky. You need 'dual' DIP op amps, then. And the AD843, 845, 744, and BUF634, are all 'single' chips.

For the gain chip you can find good ones that are both DIP and dual (and faster than the OPA2227, though it's to be seen whether they sound any better): AD823, OPA2134 for instance would be direct substitutes.

For the buffer chip, the matter is more complicated: finding a double DIP op amp that has good output current. There's the AD8056, but again it's only SMD. But before I do anything myself, I'll first have to make sure what the exact configuration is -- if it's a typical gain + buffer configuration (with a 'jung multiloop' feedback network, the builder told) or perhaps one with the two op amps 'in parallel' (which is what I thought at first). Oh, and FIY, I know the schematic includes class-A biasing resistors too, though even this is not 'flaunted' on the ebay page.


Wow, this stuff can be (pleasantly?) mind-boggling

 

[Andrea]

Quote:

Originally Posted by mitru78 let us know what you come to find after a bit of listening/toying.

Yup, 'course I will

 

[Andrea]

Inspecting the spare circuit board the builder added in my package to compensate for unavailable priority shipping, I realized that it's a true op amp + buffer configuration (with jung multiloop), the second op amp (the one closer to the DC jack) playing the buffer part. Which makes it definitely easier to do a BUF634 tweak, as all you'd need would be this double DIP adapter (and remove or place elsewhere the DC jack

).


edit- Ouch, I forgot that listening is delayed to the week end since I caught a mild flu that can still be so much disturbing to headphone listening.

 

[kramer5150]

Quote:

Originally Posted by Andrea Inspecting the spare circuit board the builder added in my package to compensate for unavailable priority shipping, I realized that it's a true op amp + buffer configuration (with jung multiloop), the second op amp (the one closer to the DC jack) playing the buffer part. Which makes it definitely easier to do a BUF634 tweak, as all you'd need would be this double DIP adapter (and remove or place elsewhere the DC jack ). edit- Ouch, I forgot that listening is delayed to the week end since I caught a mild flu that can still be so much disturbing to headphone listening.

WOW!! He gave you a spare unstuffed PCB? in addition to the amp? Thats pretty good

This thread is evil!!!... just brutal!! I'm completely happy with my govibeII, now that I modded it to fit in a smaller serpac case.

Garrett

 

[Andrea]

-edited-

 

[dokebi]

Nice.

 

[Andrea]

Quote:

Originally Posted by dokebi Nice.

Alright now.

 

[sxr71]

Quote:

Originally Posted by mitru78 well, i guess it's time i chimed in here. i've had this little amp for about a month now, and have been using it nonstop with my Zu'd K271s, RnB Diamond IC, and Aiwa AM-F80 MD player... and I'm digging this bugger! it packs a fair amount of punch. it opens up the soundstage dramatically, as opposed to plugging the K271s directly into the line/headphone out on the MD player. it adds some clarity, and just generally tightens up the sound all around. i threw a couple OPA2107's into it but things got a bit crunchy at moderate -to-high volumes. i've got a some AD8397ARZ chips, but am waiting on order from Brown Dog before i can toss 'em in. it's a great little amp!

I've found that things can get crunchy even with the OPA2227s that come with the amp if you go past the "1 o'clock" mark on the volume knob. That's part of the reason I experiemented with extra voltage. With 27v it doesn't get crunchy until you hit 5 o'clock or thereabouts (which I can only hold for a second or two before I blow out my head). I really think that extra voltage transforms this amp even with the stock op-amps.

 

[Andrea]

So besides changing the buffer op amp, if in my amp the capacitors are really 470uF 16V, I'll power it with a 24V wall wart as I'd thought.

Right now I'm undecided if I'll use 2 AD825 or 2 AD8610 for the buffer stage, or modify the circuit for a single AD8397.

 

[Andrea]

Quick update:

just to say that the amp, even untouched

, sounds great!


The HD595 is so happy (in every way) with it notwithstanding its 50 ohms, that, especially when driving a high impedance like that of the HD650, I guess things wouldn't get any much better substituting true buffers to buffering opamps.


Nonetheless, I plan to order some single dual DIP to double single DIP

browndog adapters in order to try both two AD843 (which is better than two AD825 I believe) and two BUF634 as output buffers.

 

[Andrea]

Wanna know the result of all my naive upgrading fervour? I don't feel like upgrading the Zero anymore. It's good enough as it is.

 

[Andrea]

Ok, no, that was being too drastic.

I'm actually waiting for the browndogs to fit 2 AD744K + 2 BUF634 in there.