[philodox]

Quote:

Originally Posted by bg4533 OPA637/627 Things are a bit too smooth and less dynamic than I wanted. Detail is improved, but not quite as much as I expected.

I'm no expert, but maybe you should consider changing your opamps to AD8020/AD8010?

 

[Earwax]

Quote:

Originally Posted by sanaka I hope the more knowledgable will chime in here, but I think the ground channel buffer(s) 'override,' orincrease, or, uh, buffer, the 20mA limitation of the TLE. Otherwise it would be quite rediculous, wouldn't it? Peace, Sanaka

I thought the idea was for the caps to supply what the TLE can't handle directly?

I should have checked to see if the power supply was becoming unbalanced under load before I pulled the TLE out.

 

[bpribadi]

Quote:

Originally Posted by setmenu The best mod I can think of for the Pimeta is to ditch the Buf 634's and replace them with Intersil HA 5002's Setmenu

Is the HA-5002 sounds superior than the BUF634? Do you mind to elaborate how the HA-5002 sound compare to BUF634?

 

[Heady]

Hmm.. very interesting, I found my pimeta clone with AD8620 to be very dynamic and detailed. Of course, the design I used do have a slight difference in that I used an OpAmp as a buffer after the TLE and the capacitors are NOT rails to ground but rail to rail.

 

[setmenu]

Quote:

Originally Posted by bpribadi Is the HA-5002 sounds superior than the BUF634? Do you mind to elaborate how the HA-5002 sound compare to BUF634?

It is a while since i did a back to back comparison.
When I first built the Pimeta I was not too keen on the sound, finding the
sound a little 'veiled' and the bass a bit off.[for my own tastes]
Raising the 634 quiescent current [bandwidth pin] improved things but the
overall character still seemed to remain.
I then noted that the well thought of PPA amp used different buffers, the
HA5002's so I gave them a try and found the sound opened up and the bass
became more natural sounding, to my ears a night and day improvement..
No doubt some here would still prefer the 634, but they are not my bag at all,
I cannot imagine ever again wanting to use these buffers in an audio application.


Setmenu

 

[skyskraper]

what other buffers can be rolled pin for pin in to the pimeta????

 

[guzzler]

Just the BUF634. Monolithic buffers aren't like opamps, in that there isn't a standard pin out for them. When I have a little bit of time, I might look at discrete buffers for the PIMETA, but it might not be worth the effort...

g

 

[skyskraper]

ah well

i just thought it might be another way to waste my precious time

 

[Earwax]

My guess right now, is that with the TLE in place the buffers were never really getting into wide bandwidth mode. Now, using resistor divider, they can draw all the current they want and actually operate in wide bandwidth.

I really wish I'd done some current measurements before the change.


[edit]
I should also point out that the reason I was able to get away with this trick is that I've got a 24V power supply so I didn't have to care if the rail splitter isn't perfectly accurate. It's probably a bad idea for 9V batteries or even 12V wall warts.

 

[tangent]

Quote:

Now, using resistor divider, they can draw all the current they want

Ohm's Law tells you this is bogus. You can't "draw all the current you want" from a resistor. You will get a voltage drop across it, which in the case of the virtual ground means you shift the ground point around.

In any case, current limiting is not a problem for the TLE in the PIMETA. The only currents it has to manage are down in the microamps range! The heavy load is handled by the ground channel.

As for the buffer change, yes, going to HA-5002s should improve things a lot. The BUF634 does indeed have a politeness to it. The reason I chose the BUF634 for the PIMETA is its low current consumption. This is primarily a portable amplifier design, so low current draw is important. The PPA, by contrast, is "portable" only in a very limited sense, so we can get away with using the 5002s.

 

[setmenu]

Tangent is correct, but if one is prepared to use a battery pack comprised of AAA nimh cells reasonable run times can be had in a portable setup.
I use the 5002 in a portable setup but singles rather than stacks, so 3 of these will draw about 24ma + whatever your chosen opamps use.
I get run times around 13 hours.
So it can be reasonably practical if one is not after smallest/lightest amps.

And one other point, the 5002 has no built in short circuit protection!


Setmenu

 

[Earwax]

I'm sure Tangent is right, other smart people are also happily using TLEs in their amp designs.

Yet, I hear a difference.

 

[SHLim]

Have anyone notice this post?
http://www4.head-fi.org/forums/showthread.php?t=91443
Will Xin new discovery of double buffer double caps apply here?
Wonder if this will work for PPA?


Sam

 

[Madcat05]

Glad to see some more interest in the pimeta.

I going to be doing some upgrades to mine soon. Including a Par Metal case, a DC jack, Class A bias, Wima caps and a stepped attenuator too.

 

[bg4533]

Quote:

Originally Posted by Madcat05 Glad to see some more interest in the pimeta. I going to be doing some upgrades to mine soon. Including a Par Metal case, a DC jack, Class A bias, Wima caps and a stepped attenuator too.

As someone who just built a rather high end Pimeta I suggest you consider a PPA. I have never heard a PPA, but I am currently wishing I would have built one.

Don't listen to me though as I don't really know what I want. Well, I want everything....on a college students budget. I am looking for something that is warm and "thick", a tube amp I think.