The Last Amplifier Project - Pass Labs X600.5 Monoblocks

DarqueKnight

Over the past few years I have been evaluating higher powered amps (and saving coins) to replace my Parasound Halo JC 1 monoblocks. My research kept leading me back to the Pass Labs X600.5 monoblocks. I will take delivery of a pair next week.

Specs:

600 watts into 8 ohms (400 watts for JC 1)
1200 watts into 4 ohms (800 watts for JC 1) (my modified SDA SRS 1.2TL's are 4 ohm equivalent speakers)
Class A watts: 80 (compared to the JC 1's 29 watts class A)
Weight: 132 pounds (64 pounds JC 1)









The X600.5 is taller than the JC 1's, but has approximately the same size footprint, so it will easily fit in the same cabinet space. The X600.5 idle heat sink temperature is only a little more than the JC 1's (122 degrees F compared to 118 degrees F). If everything works out, the JC 1's will be traded in.

I'm hoping the X600.5's will be great compliments for my Pass XP-30 line stage preamp and Pass XP-25 phono preamp. I actually was planning to make this purchase next year, but the dealer (Reno HiFi) made me an offer I could not refuse.

headrott

Oh boy Ray! Can I come over!?

nooshinjohn

But for these beauties I would make an exception. Congrats man. I cannot wait to read your review.:cool:

monepolk

Very nice, enjoy!

DarqueKnight

headrott wrote: »

Oh boy Ray! Can I come over!?

Sure. I could use some help unpacking and setting up those beasts, plus I need help setting up blind tests, lest I be accused of imagining performance improvements:razz:

nooshinjohn wrote: »

Tubes Rule!!!

Tubes rule? But...but...but...Nelson said he designed the X600.5 to have the sweetness, air, layering, and sound staging of the best high end tube designs, yet with the bass slam, articulation and detail of the best high end solid state designs. We'll see.

zingo

Very nice, and I would hope that system would have good synergy... :cheesygrin:

Dawgfish

Those are freaking amazing! Honestly I'd give my left one to hear the big boy SDAs and that much super high quality amplification! Listening to them is probably going to be a religious experience. Congrats!

pitdogg2

I'm so jealous

bobsauto49

That's a pretty set-up! Beautiful Amps!

falconcry72

Those could definitely fit the bill as "Last" amplifiers. There's not a whole of gear I'd say that about. Congrats, man!:cheesygrin:

NJPOLKER

Hey Ray

I can see all is going well and happy to see your spending money on good things.

It seems to me the weakest link in your system is the 1.2tl's. Can that be true?????

Like all the others here I really have enjoyed reading your reviews/findings and look forward to your thoughts on your new power plant.

Drenis

Impressive, period.

thsmith

Congrats !

Toolfan66

Awesome!!!

Congrats Ray!!

DarqueKnight

NJPOLKER wrote: »

It seems to me the weakest link in your system is the 1.2tl's. Can that be true?????

Yes, that could be true.

I keep expecting to reach "the wall" whereby differences in high performance gear can no longer be perceived, but I have not reached it yet. The 1.2TL's have "grown" along with my electronics upgrades. If the 1.2TL's were still in their stock form, then yes, they would be a weak link. I still continue to audition speakers...patiently waiting for that magical moment when a new pair speakers entices me to replace my hot-rodded 1.2TL's.

On the surface, it might seem inefficient to run a 20+ year old pair of speakers with top of the line electronics and cables. It is no more inefficient than taking a 20+ year old Porsche and updating its engine and other components and ending up with a car that is the equal in many respects, and is the superior, in some respects, of contemporary sports cars.

When you crack open many of today's-well regarded high end speaker designs, sometimes you find exotic drivers and custom crossover components, but often you find high quality, but off the shelf, parts. It is how those off the shelf parts are implemented in the speaker design that makes the magic happen. When you crack open my 23 year old SDA SRS 1.2TL's, you find:

1. Audioquest 15 gauge solid core premium quality wiring,
2. premium capacitors, which are designed to minimize electrical and mechanical noise,
3. premium resistors, which are designed to minimize electrical and mechanical noise,
4. premium inductors, which are designed to minimize electrical and mechanical noise,
5. a custom designed and extensively vibration damped crossover circuit board, with over-sized, heavy-weight copper traces,
6. damped driver baskets and drivers and tweeters tightly coupled to the baffle board with steel retaining rings.

How many modern high end speaker designs have all of that, or even half of that?

Even more important than all of the physical design improvements is the patented SDA interaural crosstalk cancellation circuit. The purpose of stereo reproduction is to recreate a three dimensional illusion of a musical performance. No other speaker in existence does that as well as SDA's, with their wide and stable sweet spot and panoramic sound stage.:biggrin:

Conradicles

Very nice amps! Have fun!

EndersShadow

Hey Ray... you have a problem though now...

You cant end every review with:

Someday when I am more dedicated to audio than I am now....

I think "someday" has arrived

txcoastal1

Can't wait for the deatails...'cause know shows or explains the details like you

those are beasts

Big Dawg

Beautiful amps, Ray, congrats.

heiney9

I think you will be very happy and as good as the JC1's are...........I predict you will like the X600.5's even better.

H9

[Deleted User]

Ray,
Congrats on the amps, a beast with beauty for sure! I look forward to your review, as always.

Halen

NJPOLKER

DarqueKnight wrote: »

Yes, that could be true.

I keep expecting to reach "the wall" whereby differences in high performance gear can no longer be perceived, but I have not reached it yet. The 1.2TL's have "grown" along with my electronics upgrades. If the 1.2TL's were still in their stock form, then yes, they would be a weak link. I still continue to audition speakers...patiently waiting for that magical moment when a new pair speakers entices me to replace my hot-rodded 1.2TL's.

On the surface, it might seem inefficient to run a 20+ year old pair of speakers with top of the line electronics and cables. It is no more inefficient than taking a 20+ year old Porsche and updating its engine and other components and ending up with a car that is the equal in many respects, and is the superior, in some respects, of contemporary sports cars.

When you crack open many of today's-well regarded high end speaker designs, sometimes you find exotic drivers and custom crossover components, but often you find high quality, but off the shelf, parts. It is how those off the shelf parts are implemented in the speaker design that makes the magic happen. When you crack open my 23 year old SDA SRS 1.2TL's, you find:

1. Audioquest 15 gauge solid core premium quality wiring,
2. premium capacitors, which are designed to minimize electrical and mechanical noise,
3. premium resistors, which are designed to minimize electrical and mechanical noise,
4. premium inductors, which are designed to minimize electrical and mechanical noise,
5. a custom designed and extensively vibration damped crossover circuit board, with over-sized, heavy-weight copper traces,
6. damped driver baskets and drivers and tweeters tightly coupled to the baffle board with steel retaining rings.

How many modern high end speaker designs have all of that, or even half of that?

Even more important than all of the physical design improvements is the patented SDA interaural crosstalk cancellation circuit. The purpose of stereo reproduction is to recreate a three dimensional illusion of a musical performance. No other speaker in existence does that as well as SDA's, with their wide and stable sweet spot and panoramic sound stage.:biggrin:

Beautiful

Exactly what I was hoping or thinking your findings would be. Another true to life testament on the potential of Polk SDA's Kind of makes me want to take a trip down to New Jersey and pick up my SDA SRS2's right now!!

Thanks for your response and congratulations on another job well done.

hochpt21

Weight: 132 pounds (64 pounds JC 1)

:eek:

Those are beautiful.

steveinaz

I believe you have found the holy grail! Very nice.

D_M

DK,

You mind listing the amps you have evaluated? I'm just curious about your journey. Thanks.

cstmar01

Very cool and congrats! Always have wanted to get my ears on a full Pass system like that. Look forward to your impressions on it!

DarqueKnight

EndersShadow wrote: »

Hey Ray... you have a problem though now...

You cant end every review with:

Someday when I am more dedicated to audio than I am now....

I think "someday" has arrived

No, I'm not there yet. There is always something "better" around the corner.:cool:

D_M wrote: »

DK,

You mind listing the amps you have evaluated? I'm just curious about your journey. Thanks.

A discussion, with pictures, can be found in this thread from 2008:

Higher-Power-Amplification-For-SDA-SRS

You can see that this has been on my mind for a while. I had narrowed my choices to the Bryston 28BSST2 and the X600.5. The 28BSST2 offered more power (1000 wpc into 8 ohms) and costs 13% less than the X600.5, but the 28BSST2 is optimized for 8 ohm speakers. I was not fully confident about its performance with my 4 ohm 1.2TL's. The 28BSST2's output goes down to 900 wpc into 4 ohms. The X600.5 "doubles down" to 1200 wpc at 4 ohms.

I have attached spreadsheets which compare the JC 1 to the X600.5 and to the 28BSST. Specs can be misleading if you don't know the design specifics. For example, the JC 1 has a slew rate of 130 V/usec compared to the X600.5's mere 50 V/usec. That might lead some to believe that the JC 1 is the faster, more agile and more nimble amplifier. Nelson Pass explained the X600.5's lower slew rate this way:

"In the X600.5 the symmetric voltage gain stage will peak out at about 100 mA. We also take advantage of balanced output stages (halving the slew requirement), and last but not least, we bias the amplifiers high."

EndersShadow

DarqueKnight wrote: »

No, I'm not there yet. There is always something "better" around the corner.:cool:

LOL, I agree to disagree.....

Whats left Raife? Re-wiring your connection from your house directly to the power station :biggrin:..

Cause thats about all I can think of.....

DarqueKnight

EndersShadow wrote: »

LOL, I agree to disagree.....

Whats left Raife? Re-wiring your connection from your house directly to the power station :biggrin:..

Cause thats about all I can think of.....

I can think of a few things:

1. Dedicated, fully acoustically treated listening room.
2. Dedicated transformer from the power company to isolate my house from the power grid's noise.
3. Separate, audio grade breaker box for audio and video AC circuits.
4. Commercial grade AC regenerators.
5. Whole-house surge suppression.
6. And things like this:






Pass Labs X1000.5
1000 wpc into 8 ohms.
2000 wpc into 4 ohms.

:cool:

unc2701

DarqueKnight wrote: »

You can see that this has been on my mind for a while. I had narrowed my choices to the Bryston 28BSST2 and the X600.5. The 28BSST2 offered more power (1000 wpc into 8 ohms) and costs 13% less than the X600.5, but the 28BSST2 is optimized for 8 ohm speakers. I was not fully confident about its performance with my 4 ohm 1.2TL's. The 28BSST2's output goes down to 900 wpc into 4 ohms. The X600.5 "doubles down" to 1200 wpc at 4 ohms.

They're both balanced designs, so they will both have the same issues with low impedence loads. The difference being that Bryston always under-rates their amps.
http://www.stereophile.com/content/bryston-28b-sst-monoblock-power-amplifier-measurements

The Pass is spec'd at 1% THD; from Stereophile's results, had you cranked the Bryson until you hit 1%, you would get 1300 watts into 8 ohms and 1800 watts into 4 ohms.

I'm not aware of a class A/AB amplifier that truly "doubles down"; manufactures just manipulate the THD at which they report wattage to give the appearance of doubling down. The good news is that at 600 watts into 8 ohms, it'll be far better than the 1% THD reported.

In any case, they're both beasts and I'm sure you'll get plenty of enjoyment from the Pass.

DarqueKnight

unc2701 wrote: »

They're both balanced designs, so they will both have the same issues with low impedence loads. The difference being that Bryston always under-rates their amps.
http://www.stereophile.com/content/bryston-28b-sst-monoblock-power-amplifier-measurements

The Pass is spec'd at 1% THD; from Stereophile's results, had you cranked the Bryson until you hit 1%, you would get 1300 watts into 8 ohms and 1800 watts into 4 ohms.

My understanding is that the 28BSST2 can do 1000 watts continuous into 8 ohms, but not 1800 watts continuous into 4 ohms. My understanding is that the X600.5 ratings are for continuous power at 8 and 4 ohms. The 28BSST2 manual (pg. 4) lists 900 watts continuous into 4 ohms. Regarding the Stereophile review, which I had previously read, it is important to note that:

"Into 4 ohms, the Bryston clipped at 1800W (29.5dBW, 117.5V wall voltage), though it couldn't maintain its high power into 2 ohms, delivering 1050W (24.2dBW, 116V wall voltage)."

The following quote is from the X600.5 manual (pg. 7):

"The Pass Laboratories X600.5 is optimized for loads nominally rated at 4 ohms and above. You can run the amplifiers into a lower nominal impedance without difficulty, and we are not aware of a speaker on the market that presents unusual difficulty with these amplifiers."

unc2701 wrote: »

I'm not aware of a class A/AB amplifier that truly "doubles down"; manufactures just manipulate the THD at which they report wattage to give the appearance of doubling down. The good news is that at 600 watts into 8 ohms, it'll be far better than the 1% THD reported.

Thank you for your insights. Pass is also known for conservative power ratings. I sent your comments to Pass Labs. I will post their response here.

unc2701 wrote: »

I'm sure you'll get plenty of enjoyment from the Pass.

We'll see.