ack's system - end of round 1

On the 810LP, see this http://www.whatsbestforum.com/showt...-Spectral-Gear&p=205362&viewfull=1#post205362

The A90's output is just too low for it?!?

Hi Andrew, thanks for your kind comments. So a few things:

1) Yes, timbre is of utmost importance to me; anything but, and I am not really reproducing music in its most fundamental form; surely, there are plenty of other factors too (body, image size, resolution, etc), they just come in behind timbre

2) Related to that, the modified XP-25 (not only the line filters & shields, but also the removal of the loading capacitors), along with the MIT MA-X cable, additional shielding on the cable (not shown in the pictures) and arm, result in exceptional timbre fidelity. Thus, when tamed, the XP-25 is an exceptional phono; but, not for the timid. I must emphasize that it was only after installing the MA-X phono cable that the entire phono chain went in the direction I wanted it; therefore, it feels like that this bridge/interface is extremely critical, meaning that there can be significant signal losses and noise pick-up by a not-so-good phono cable

3) Still related to timbre, the DMA-400RS monos with the updated driver board, plus a new (2014) version of the 30SS S2 preamp I got recently, are also responsible for said timbre qualities (and more) - while keeping in mind that nothing is really perfect. Therefore, this is really testament to the XP-25's sound quality *potential* as well

4) "not self deluding" - yes, all of this stuff is just "things" to me; nice things, but things nonetheless. It's important to me to be able to see the good and the bad attributes of a design, in order to help form an opinion and potentially determine direction. I am really only loyal to my money and Symphony Hall

5) I have high hopes for the upcoming Spectral phono, due out before I turn 90, I assume But at the moment, I am not clamoring for it

6) These modified Logans have very little to do with what came out of the factory. The biggest gain came after replacing the crossover caps (panel and woofer - they are two different crossovers, like your ex Prodigies); I have not touched the power supply. But it's also true that the Mundorf foil inductors brought in much lower series impedance (at the very least) than the originals. At one point I thought about completing just one speaker in order to easily compare with the other, but just the cap replacement in the panel in one was so dramatic (especially with overtone decay) that it was pointless to do any further A/B testing. And between the two crossovers, the most dramatic gain eventually came in the bass section - truly night and day

7) I have heard your CLX a couple of times and I wish I could fit them in my room; I am not really familiar with its crossover, but from pictures I have seen, I would probably be looking to modify it too. The support frame would also be an issue for me. Also curious about your ribbon supertweeter - years ago I was looking at using one as well; it turned out everything but the panels were responsible for the darker system character back then

8) Apparently, Spectral with stats isn't all that unusual - I have sold two amplifiers in the past to Logan owners, who claimed they got the idea from other friends of theirs

I am curious about your Japanese tube amps - what are they? I love the tube device for its linearity and extremely wide bandwidth...

Thanks again

audioarcher said:

I found this nice little tutorial on shielding online if anyone is interested. http://www.learnemc.com/tutorials/Shielding02/Practical_Shielding.html

Click to expand...

Beautiful, thanks! Just about the perfect article for the uninitiated. I would add a couple more data points to complete the picture: materials with very high permeability, like mu-metal, are far superior for magnetic shielding, and are thus used in what we call Zero-Gauss chambers (using layers and layers of said materials; think room within a room). By contrast, low-permeability materials, like the XP-25's aluminum (permeability ~= to air's), effectively leave the circuit board totally exposed. Finally, when working with such materials, make sure they are not bent out of shape too much - i.e. avoid creases, otherwise, in order to fix those, you need to re-anneal the material in a hydrogen atmosphere within a high-temperature furnace.

Nice, though couldn't find any info on the tube versions... So the other thing I wanted to mention is that noise has dropped to the point I can easily hear the faint pre-echo that some LPs have before the start of a track, from the speakers at regular listening levels - the pre-echo is usually audible when using headphones with the volume cranked up, or from CDs. This is a good noise threshold to have, and I am sure others with more capable systems reached that level years ago.

An example of such an LP with pre-echo is this Speakers Corner re-issue

ack's analog rig shield

Here's a video of the completed analog rig shield I have implemented, mu-metal+copper foil throughout and routed to ground - as others have attested, the drop in noise and resulting improvement is simply staggering... a clear example of form following function.

I mean business No the tuner is dead quiet; unplugging or removing it makes no difference; it's an exceptionally well-shielded tuner. BTW, I recently added a Shunyata Defender to the same circuit with the tuner, phono and panels - and what a significant improvement that brought; e.g. there was some residual noise from the panels' power supply if you were to stick your ear on them - like hashies - with no music playing, but no more... tiny but important improvements.