REVIEW: Lisa III prototype - new portable amp by Phil Larocco

[amb]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif so swapping opamps isn't a matter of dropping a new one in, you'd need to re-wire the opamp pins

Yep, you cannot swap the opamps with other models without some circuit board hacking.

The AD744 is unique in that the comp pin connection is just prior to its internal output stage, and Phil took the output from there and substituted an external discrete output stage. Other opamps don't have this feature and that "comp" pin is either NC (no connection) or serve some other function. Althougha few other opamps also has a "comp" pin, they are wired internally to a place where it cannot be used in this way.

To roll opamps in this amp, you'd have to hack the PCB to use the opamp's traditional output pin instead, but this kinda' defeats the design.

By the way, this is not the first time the AD744 is used in this manner. In addition to a PPAv2 mod that Phil had published some time back, I've seen an old Adcom preamp with a similar design.

 

[Sovkiller]

Quote:

Originally Posted by wakeride74 /img/forum/go_quote.gif Nice write-up Skylab! Sounds like a promising amp indeed... I'll have to pick one up... I'm always looking for more bass I hope Phil does produce a version that uses Li-Ion battery and a gain switch... that would really add value IMO, especially given the direction portable and transportable amps are moving. Any idea if one could roll some AD797's in there? Have you compared it to the new TTVJ Millet Hybrid yet? Despite the background noise issue I had with that amp its sound was pretty damn impressive IMO.

The AD744 used by Phil is the best OPamp for that configuration, and it is used, as many had stated, in a different way bypassing the internal buffer, by using the componnet pin. There are not too many Opamps like this one, with a component pin, that you can do that, again this is a the best OPamp for that configuration, you will not get a better sound out of any other...the amp was designed around that OPamp configuration...

 

[amb]

Quote:

Originally Posted by Sovkiller /img/forum/go_quote.gif The AD744 used by Phil is the best OPamp for that configuration, and it is used, as many had stated, in a different way bypassing the internal buffer, by using the componnet pin ...

Just a little nit pick... The "Comp" pin is short for compensation, not component. This is pin 5 of the opamp, and is usually not used on other single-channel opamps. The original intended use is for (optionally) adding an external capacitor across pins 5 and 8 to increase the total compensation capacitance. Doing so allows the opamp to drive a more capacitive load and have additional margin of stability at or near unity gain, but at the expense of reduced bandwidth and slew rate. See the AD744 datasheet for details. Note that the datasheet has a simplified schematic (figure 28) showing where pin 5 is internally connected.

 

[Sovkiller]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Just a little nit pick... The "Comp" pin is short for compensation, not component. This is pin 5 of the opamp, and is usually not used on other single-channel opamps. The original intended use is for (optionally) adding an external capacitor across pins 5 and 8 to increase the total compensation capacitance. Doing so allows the opamp to drive a more capacitive load and have additional margin of stability at or near unity gain, but at the expense of reduced bandwidth and slew rate. See the AD744 datasheet for details. Note that the datasheet has a simplified schematic (figure 28) showing where pin 5 is internally connected.

I just saying what he told me, maybe we both make the same mistake while calling the pin....LOL...

About the slew rate and bandwidth, well we sometime go insane with that and actually we go far far above of what we actually need, to the point that sometimes stability is an issue...not sure in this particular case, but sometimes to cut the bandwidth a little bit, is not a bad practice, we do not need it anyway as those OPamp we usually use, are not even or audio but for video freqs....

 

[GreenLeo]

Thank you for the information. Does it means that a 4 channel will be better than a 3 channel amp? Also does it means that a Xin IV amp is a 4 channel amp?

 

[Remitrom]

Amb. Thanks for explaining the technical side of LISA III. You certainly know
Even a newby like me could hear the caracteristic black Quiet background the
Third Ground Channel Provides In Amb amps as well as LISA III. (at head-fest 07) I was honored to have you share your space with Lisa & I.
Your hospitality and everyone else's involved it Head-fest 07 made
Lisa"s debu truly Awesome.
LISA WILL BE AT the SEATLE MEET May 27 for Public listening

 

[gregeas]

Will a metal case be an option? Any idea of the dimensions? I would kill for an amp with a similar footprint to the Benchmark DAC1...

 

[Skylab]

The LISA III will be sold in a metal Hammond case. The wood one above is just the prototype.

 

[GlorytheWiz825]

Just found this thread. Excited about the initial reviews.

Keep up the good work Skylab!

 

[Remitrom]

Da Gusta Bus Non es Des Bu Tan Dum

Hey my latin is lousy, but that is supposed to mean....

" There is no acounting for taste"

If you would like to REVIEW LISA YOURSELF no obligation, just pay shipping to next reviewie.. there will soon be a place to sign up...

 

[wakeride74]

Just thought I'd update Skylabs thread based on the discussion for a Li-Ion battery. Based on Big Poppa's review it appears that the Expedition will have a built in battery (I'm assuming it is a Li-Ion?) that will give about 60hrs of play time per charge. Not sure how long it will need to recharge or what options we will have for wall warts (for those not opting for the $300 PSU).

Quote:

Originally posted by: Big Poppa With the built in rechargeable battery I was told it would last 60+ hours on a charge.

Also it appears as if things are getting close (I know this is not news but...) and as is the case with many amps the last thing remaining is enclosures!

Quote:

by Remitrom on Fri Jul 06, 2007 3:49 pm I still have not located my crystal ball, but I feel I can make an educated guess now. I expect to be shipping Lisa by the end of this month! (July 07). The basic Lisa III will cost US $500. and will come in a Hammond enclosure (black or silver) OR a strait grain Wood box! (redwood or possibly Myrtle). Thats rite, no extra for a woody! Lisa does not need a metal case for ground because Phil put a full double copper ground plane in the PCB board. (no RF interferance) There is a $50. premium for the expedition. Wood cases made from Maple burl, Myrtle burl, Mullberry and other exotics will also demand a premium. (to be determined individualy) Power supply will cost US $300. If you have already requested a power supply you will get it with your Lisa in July. Those that post a power supply request now require one month lead time. ALL TRIAD AUDIO products come with a customer satisfaction Guarantee or your money back. Your Ears Are In For A TREAT! Sincerly Brad Taylor

Also Phil appears to be trying to decide on the best gain setting or possibly a gain switch. http://www.triadaudio.net/phpBB3/viewtopic.php?f=3&t=6

I can't wait to get mine! I've already sent Ken at ALO some messages about a short right angle RCA to mini... something that would make a short loop to one side to keep cable clutter down.

 

[V-Duh]

Has anyone seen photos of "almost ready" production models - aluminum or wood?

 

[Tantra]

Quote:

Originally Posted by Skylab /img/forum/go_quote.gif ...the Lisa III is also going to be BIG - maybe too big to be compared to other portable amps.

If something can't be put in the pocket of a man's jeans, then it isn't portable...

 

[wakeride74]

Quote:

Originally Posted by Tantra /img/forum/go_quote.gif If something can't be put in the pocket of a man's jeans, then it isn't portable...

It's being listed as a "transportable" like the XP-7, Headroom Desktop, etc. Perfect for those of us that bring a backpack to work.

Lunch - check!
sunglasses - check!
DAP - check!
IC - check!
Lisa - check!
Cans - check!

 

[V-Duh]

Depends on your genes!

Anything you can lift is transportable - just need a big backpack and a big desk.

Quote:

Originally Posted by Tantra /img/forum/go_quote.gif If something can't be put in the pocket of a man's jeans, then it isn't portable...