JC-1's vs Pass Labs X350.5

[CP-Mike]

I'm trying to decide between these two amps for my 2-channel system that will eventually become a 5-channel system. I've heard many many great things about the JC-1's on this forum and elsewhere, and I've heard great things about the X350.5 elsewhere. However, I've read of two people who compared them both in their own systems and ended up going with the Pass Labs. I can get a pair of JC1's for a little less than the X350.5, but let's just say that price is not a factor. Have any of you auditioned/used both? Any opinions?

[nicholtl]

Oh god, this is a tough comparison... Personally, I don't know which route I'd go either.

[Peter Nielsen]

Apples to oranges in my opinion. You're comparing monoblocks with a stereo amp. No doubt, both amps are great choices.

Some things to consider:

The X350.5 draws the same idle current and puts out the same heat as a pair of JC1 monoblocks in HIGH BIAS. If heat dissipation is a concern (e.g. less than stellar air conditioning available), the JC1s let you drop the bias so that the heat output is reduced by 50%.

The JC1s can be placed next to the speakers since they're monoblocks. You're probably going to have to spend more on longer speaker cables for the X350.

Anyway, I would say it really boils down to the question: Do you want a stereo amp or mono blocks?

If you're considering a stereo amp, have a look at the Musical Fidelity kW 750. That's a sweet sounding stereo amp!

Peter

[CP-Mike]

As far as form factor goes, I really don't care one way or another. Monoblocks would be nice because it'd be easier/cheaper to add a third for my center channel and some stereo amp for the rears when I finally go 5-channel, but other than that, the differences are negligible. I'd rather put my amps on some sort of vertical stand/rack, as having amps on the floor next to my speakers would look cluttered in my setup. I don't have that much floorspace in the front of my living room, due to sub, speakers, TV, and electronics. If I got an amp rack it'd have to go off on the side of the room.

Nooo, not another amp to research! Just when I think I have my choices narrowed down, I get another suggestion.

[CP-Mike]

What if I asked you to compare the JC-1's to the X250.5? Obviously the JC1's have more total power available, but the 250.5 has more power in pure class-A mode...35W vs 25W. Which one sounds more smooth? What about dynamics? Any opinions from those that have heard both?

Also, what is up with the damping factor of the JC-1's? The Parasound website says ">1200 at 20 Hz". Damping factor is a ratio of load impedance to output impedance. WTF does 20 Hz have to do with anything? It seems to me like Parasound is trying to fudge/conceal their calculations for damping factor...

[Pieter]

Damping factor is a ratio of load impedance to output impedance. WTF does 20 Hz have to do with anything?

And the load impedance varies with...?

[Peter Nielsen]

Mike,

When talking specifications, I have a few questions myself:

Pass Labs specifies 20A max current for the 350.5. What's up with that? The JC1 delivers 135A. The Musical Fidelity can deliver a whopping 250A (!). The Pass Labs 20 Ampère specification seems odd in comparison...

Also, I find it strange that Pass Labs doesn't clearly specify what the wattage in 4 ohms and 2 ohms is. (At least I could not find this info, although I searched for it). These figures are IMPORTANT, especially for us with 4 ohm speakers.

Peter

[Peter Nielsen]

And the load impedance varies with...?

A loudspeaker's load impedance varies with... you guessed it... FREQUENCY :B

Peter

[Peter Nielsen]

Also, what is up with the damping factor of the JC-1's? The Parasound website says ">1200 at 20 Hz". Damping factor is a ratio of load impedance to output impedance. WTF does 20 Hz have to do with anything? It seems to me like Parasound is trying to fudge/conceal their calculations for damping factor...

On the contrary. They are very upfront about at what frequency their specified figures apply. Most manufacturers don't mention the frequency.

The output impedance of most amplifiers is frequency dependent. You can of course say that for solid-state amps, the frequency has little or no meaning. (However, for amps with output transformers, like tube amps, specifying the frequency is important as the damping factor will vary with frequency in these amps). See this page

Peter

[CP-Mike]

Right, I know that for a given speaker, impedance varies by frequency. One speaker's impedance at 20 Hz could be much different from another's at 20 Hz. So, quoting their damping factor in terms of a frequency is BS. They could have tested it on a speaker that, at 20 Hz, has an astronomically high impedance, thus boosting their damping factor, and impressing people who make purchases based on numbers in a spec sheet. If they were really forthcoming, they would have published the impedance they used to calculate the damping factor. 20 Hz is meaningless without knowing the speaker it is associated with.

I'm confused by that current rating also. 20 amps is pretty low by comparison. The way they state it is weird too: "Output Current: Maximum plus, minus approx. 20amps". Are they saying it's plus or minus 20 amps? Or are they just throwing in the "plus, minus" for fun and it means nothing? The only reason I can think of as to why it's so low compared to other amps is that current output depends on load impedance. For Parasound and MF, they may be quoting their current output at a 2 ohm load.

Let's do some math to reality check some numbers. Assuming Pass Labs is quoting their current output at 8 ohms (seeing as everything else on the spec sheet is in terms of an 8 ohm load), then their max output potential should follow P = VI. 350 = V*(20 A), Vmax = 17.5 volts. That sounds pretty high. Or is it?

Assuming Parasound is quoting their current output at 8 ohms, and taking their 8 ohm output power rating, we get 400 = V*(135 A), Vmax = 2.96 volts. That sounds pretty low. If we recalculate for 2 ohms, 1200 = V*(135 A), Vmax = 8 volts.

I don't know jack about amplifier design, but it seems like the Pass amp favors sending out a higher potential and the Parasound favors high current. Is one design better or worse than the other? Does it matter? Am I missing something with my oversimplified calculations?

In the owner's manual, it states that "the amplifiers are unconditionally stable into any speaker load. If you need high power for difficult loads and want to retain the qualities of the finest low power Class A amplifiers, the X.5 Series is a logical choice. [compared to their other amplifier lines]". So I'm sure it will be able to handle our 4-ohm speakers, but I want to find out if it doubles power into half impedance loads

I'm going to e-mail Pass with these and a few other questions, like the rated power at 4 ohms.

[Peter Nielsen]

So, quoting their damping factor in terms of a frequency is BS.

We're of course talking about the impedance WITHOUT speaker. Quoting the damping factor is something you HAVE to do with a tube amp or with ANY amp that has an output transformer or any other component or design that causes a "built-in" output impedance.

Quoting it for a solid-state amp is more of a courtesy thing, since it usually is meaningless, as the damping factor stays the same in the audible frequency range.

The fact that Parasound quotes the figure for a specific frequency, could possibly indicate that they warrant this specification for all shipped units.

"Output Current: Maximum plus, minus approx. 20amps". Are they saying it's plus or minus 20 amps? Or are they just throwing in the "plus, minus" for fun and it means nothing?

I also found that strange. It really is nonsense. Granted, the output voltage and current will swing between positive and negative when measured to the neutral ground...

It sounds like a sales person wrote down something an Engineer told him in order to shut up :B

Vmax = 17.5 volts. That sounds pretty high. Or is it?

Not at all. Vmax is usually in the ~100V range for powerful amps like these.

I don't know jack about amplifier design, but it seems like the Pass amp favors sending out a higher potential and the Parasound favors high current.

The speaker impedance/resistance determines what the voltage and current will be.

If the amp is able to send out a high voltage, then you can drive high impedance speakers. For instance, if you want 1000W out of a 8 ohm speaker, the amp must be able to output U=sqrt(P*R), I=sqrt(P/R). In this case 89.4 V and 11.2 A.

If the amp is able to send out a high amperage, then you can drive low impedance speakers. For instance 1000W in a 2 ohm speaker yields 44.7 V and 22.3 A.

Now, a realistic case is that a very "difficult" speaker may go VERY low in impedance for certain frequencies. Also, remember that the amplifier power demand will increase when resistance drops. An amp that is normally 250W in 8 ohms will need to be able to deliver 500W in 4 ohms, 1000W in 2 ohms or a whooping 2000W in 1 ohm. Likewise, this means that the amp needs to be able to deliver a current of 31.6 A if your speaker goes down to 2 ohms or a whooping 44.7 A if your speaker impedance goes as low as 1 ohm...

Is one design better or worse than the other? Does it matter? Am I missing something with my oversimplified calculations?

Yes, you're not realizing all the aspects. VOLTAGE is required only to achieve the nominal power at the highest rated impedance. CURRENT is required to sustain the increased power demand as the impedance goes down.

You could argue that the BEST design is an amp that can deliver power correctly down to 1 ohm (or even down to 0.5 ohms). Krell is one of the manufacturers that provide amps like this (the Class A and Reference series).

Check out the 300cx stereo amp or 350Mcx monos. Either one might fit your needs... (Just FWIW, I see that Krell specifies 138V peak voltage for these units. It's nice to have that in the specs too!)

Peter

[CP-Mike]

Huh. Good info, Peter. So, by the numbers, the Pass amp sucks pretty hard compared to the JC-1. Although, getting 600 watts out of 4 ohms (which is double the "max recommended" power rating of my speakers) only requires 12 amps.

Oh, that brings up another question. How come speakers "dip lower" than their minimum impedance, if the purpose of "minimum impedance" is to say that the speakers will not go below this impedance, so if your amp can handle this minimum impedance, it will safely handle the speakers. It would seem to me that having a speaker that says minimum 3.5 ohms impedance that really goes down to 1 ohm is inviting disaster in the way of a fried amplifier.

I forgot about those P = (V^2)/R and P= (I^2)R formulas. That's what I needed. So how does the JC-1 get to 130 amps? If it's max power for 8 ohms is 400 W, that implies 7 A max at 8 ohms. Likewise, 800 W at 4 ohms implies 14 A, and 1200 W at 2 ohms implies 25 A. The only way you'd get to 130 A is if your resistance was super super low, about 0.15 ohms. That conceivably could be little more than the resistance of speaker wire. What kind of speakers can dip that low?

[CP-Mike]

Don't Krells have the reputation of sounding very "forward", or "bright", or whatever you want to call it? I'm looking for that tube-like smoothness and warmth.

[Peter Nielsen]

Huh. Good info, Peter. So, by the numbers, the Pass amp sucks pretty hard compared to the JC-1.

Yeah, maybe in theory but not in practice. There is nothing wrong with Pass Labs amps. They are excellent amps.

Much of this is really numbers and completely theoretic...

Oh, that brings up another question. How come speakers "dip lower" than their minimum impedance

A speaker has a nominal (=typical) impedance. It does not say that it won't go lower. How low it goes totally depends on your speaker design.

that says minimum 3.5 ohms impedance that really goes down to 1 ohm is inviting disaster in the way of a fried amplifier.

A fried amplifier is not the result. The result is distortion. The amp won't fry. It simply won't be able to deliver the correct signal to the speaker. It does not sound 100% right. Whether you can hear this distortion or not is another story. Those that can hear it, usually refer to the phenomenon as "lack of dynamics".

So how does the JC-1 get to 130 amps?

I believe this is a purely theoretical figure that comes from the use of 18 output transistors, each rated @ 15A. Each rail (positive/negative) has 9 transistors, which gives a maximum current capacity of 9*15 = 135 Amps.

about 0.15 ohms. That conceivably could be little more than the resistance of speaker wire.

A decent speaker cable should have no more resistance than 0.01 ohm (10 milliohms). A "great" speaker cable no more than 1 milliohm (0.001 ohm).

What kind of speakers can dip that low?

It very much depends on the construction.
See this article. To name one specific type of speaker, I would say that electrostatic speakers in general are notorious for low impedance.

Peter

[CP-Mike]

Both my speakers (PSB) and B&W have minimum impedance ratings in addition to nominal impedance ratings. Maybe others too, but those are the only ones I looked at that closely.

[VikingP]

Hi,

Just wanted to add a few things that might help.

First, you must take into account that these amps are biased in class A, but after a certain point, they get into B, so the max power will not be into A anymore. When it will be into class A, the output power for 4 ohms impedance will be half of that for an 8 ohms impedance, so for class A biasing, you'll never have 2x the output power into 1/2 the impedance, but 1/2 the output power. For Class B, it's another story.
Taking what you mentioned earlier, about the Pass having 35W in class A and 25W for the JC-1, it must imply that the Pass power supply is just as robust, if not more then the JC-1's, since it's in class A that the higher stress is put on the PS (since the current drawn by the outputs is at a maximum).
As for the specs, most of the time, those specs are there for marketing purposes, and most of the time, they misrepresent the "truth" (would you be able to imagine 130A into a 14 AWG, or even 10 AWG speaker wire? an electric extinguisher is required ). As for damping, remember that what wire gauge and length you put in between your amp and speaker will greatly affect damping.
Having said all that, the Pass amplifier definitely does not suck, and Nelson Pass' designs are among the best out there IMHO.
Really, it all comes down to listening to both, since each person's sonic appreciation of an amplifier differs (I actually think that the Krells have a superb low end and mid, but can be surpassed in the highs).

Paul

[CP-Mike]

Having said all that, the Pass amplifier definitely does not suck

Nope, it definitely doesn't suck. My statement above was tongue-in-cheek, because numbers do not a good-sounding-amplifier make.

[CP-Mike]

I live in an audio/video void. There's not many dealers in my area, and of course no dealers for the kind of stuff that I want to audition. Unless I can hear both amps side-by-side in the same system, I will not audition either of them. My sonic memory is not long enough to compare stuff that I heard more than 10 minutes ago. I also don't want a crappy room or a speaker that I don't like adversely coloring my opinions. I'd rather try to see if someone else HAS heard both amplifiers and what their opinions are.

Numbers don't make a good sounding amplifier, but what about the slew rate? Since the slew rate on the JC-1 is almost triple that of the X350.5, wouldn't that indicate that the JC-1 is a more dynamic amp? Meaning, it can go from silence to a crescendo, like an orchestra hit, with less distortion? Wait, slew rate describes the rate of change in potential across the output terminals...does potential have more to do with frequency than loudness? Sonically, what kind of sound would require a high slew rate?

[CP-Mike]

First, you must take into account that these amps are biased in class A, but after a certain point, they get into B, so the max power will not be into A anymore. When it will be into class A, the output power for 4 ohms impedance will be half of that for an 8 ohms impedance, so for class A biasing, you'll never have 2x the output power into 1/2 the impedance, but 1/2 the output power. For Class B, it's another story.

Paul, for some reason what you're saying here just registered in my brain. So let me get this straight: If you've got 20 W of class-A going into 8 ohms, you have 1.58 amps and 12.6 volts. Then you switch to a 4-ohm load, suddenly the amplifier only provides 10 W, with 1.58 amps and 6.3 volts? I don't see how this works. Why is the current kept constant when going from 8 ohms to 4 ohms?

But after doing some quick Google research, I found that you are indeed correct. For an amplifier in pure class-A mode, current is constant, regardless of load. Must be something unique to class-A operation.

[Peter Nielsen]

would you be able to imagine 130A into a 14 AWG, or even 10 AWG speaker wire?

Sure. We're talking about transients of 0.01 seconds here. 10 AWG wire can handle 135A for that short a time.

When you were kid, did you ever do the dangerous thing to short a car battery with a thin wire? That gives you about 250 Amp (or much more) current. If you did, you will remember that it actually took a second or two for the wire to melt down. Nothing will happen in 0.01 seconds...

Peter

[Peter Nielsen]

Paul, for some reason what you're saying here just registered in my brain. So let me get this straight: If you've got 20 W of class-A going into 8 ohms, you have 1.58 amps and 12.6 volts. Then you switch to a 4-ohm load, suddenly the amplifier only provides 10 W, with 1.58 amps and 6.3 volts? I don't see how this works. Why is the current kept constant when going from 8 ohms to 4 ohms?

That's because idle bias current is totally independent of the speaker load.

The idle current I is constant. P=(I^2)*R. Since R is halved when you go down from 8 to 4 ohms, then P will of course be halved from 20W to 10W too.

Just think about this: Imagine for a second that it WOULD be dependent on the speaker impedance; What would happen if you disconnect the speaker? Would it suddenly stop running in class A completely, or would it provide infinite power in class A... :??

Peter

[CP-Mike]

I would think if you disconnect the speaker you'd have an open circuit. Unless you short the wires. Then I would expect the amp to dump as much current as it could provide, before blowing the fuse/breaker.

it actually took a second or two for the wire to melt down

LOL... I don't know what's so funny, maybe the way you said it, but I got a huge laugh out of that. It's like, "it didn't happen THAT quick, it actually took a few seconds for catastrophic failure to occur". I understand your point, although I have never engaged in such a past-time, I just thought your wording and imagined delivery were funny.

[VikingP]

Sure. We're talking about transients of 0.01 seconds here. 10 AWG wire can handle 135A for that short a time.

My bad, I actually thought 135A continuously ops:

When you were kid, did you ever do the dangerous thing to short a car battery with a thin wire? That gives you about 250 Amp (or much more) current. If you did, you will remember that it actually took a second or two for the wire to melt down. Nothing will happen in 0.01 seconds...

:lol: never tried that one... but sounds interesting

Must be something unique to class-A operation

It's also why class A amps use so much power, and need to dissipate so much heat.

It's a bummer that you can't listen and compare them, but both should definitely sound fantastic.
Good luck with your purchase, and let us know how it turns out.

Paul

[Peter Nielsen]

It's a bummer that you can't listen and compare them, but both should definitely sound fantastic.

All the amps discussed here sound fantastic. (Pass Labs, Parasound JC1, Musical Fidelity kW 750, and Krell Class A).

Cost was the main reason I went with the JC1s. Similar monoblocks from any of the three other manufacturers mentioned cost the double, or more. To boot, Brent Huskins gave me a really good deal on the JC1s.

Krell is my #1 choice if cost is no object.

Peter

[CP-Mike]

No doubt Brent is the go-to guy for Parasound gear. Regardless of what amp I buy, I'm 95% sure I'll be buying a C2 from him. You can find similar amazing deals on other manufacturers' stuff, you just have to do some looking and schmoozing/haggling.

Peter, why do you have such high regard for Krell? I'm just curious. I've read very mixed reviews of their stuff. Personally I think their processors could look a lot nicer, considering how much one pays for their stuff.

[Peter Nielsen]

Mike, I should problably be more clear: It's the Krell power amplifiers that I like, more precisely the Krell Class A series (cx and Mcx series amplifiers).

I have mixed feelings about the rest of the Krell gear. For instance, I really can't see myself spending the money they ask for one of their high end preamps. If I spend that much money on a preamp, it will probably be on a Meridian 861.

Oh, and I agree about the looks of the Krell preamps, CD transports, etc. They're in need of some serious cosmetic overhaul IMHO. The power amps are beautiful though...

Peter

[CP-Mike]

Yikes, that Meridian costs quite the pretty penny. My first and second cars cost less than that. Looks pretty darn awesome though. Maybe if I'm a REALLY good boy until Christmas, Santa will bring me one. :yesnod:

[Peter Nielsen]

The G68 is more affordable... I'm playing with the idea of upgrading my C2 to a G68 at some point...

Peter

[CP-Mike]

Ooh, that one looks like a winner. Something I could potentially afford, to boot!

[Peter Nielsen]

Methinks that Brent should start selling Meridian :B :T

Not only does Meridian have awesome and super-versatile Preamps, they also have corresponding CD/DVD transports that are equally awesome...

My first encounter with Meridian was in 1983 (500-series). Sure, it was ridiculiously expensive back then (especially to a 15-year old). Today, I can still acknowledge that they're expensive, although I would strike the word "ridiculous". After all, even today Meridian offers features that other manufacturers can only dream of...

It bothers me a bit that the C1/C2 is based on a 3rd party design that Parasound really does not have any "control" over...

Peter

[krellfan]

Peter,

Have you compared a Krell FPB MCx to the JC1? The JC1 seems like an excellent amp for the $$$. John Curl and I used to work in the same company but I never met him since he left right before I joined the company.
I am currently using three Krell FPB 350Mcx amps in my HT system.

[slayer]

"It bothers me a bit that the C1/C2 is based on a 3rd party design that Parasound really does not have any "control" over..."



What are you talking about Peter? I've never heard this before.

[Peter Nielsen]

Randy,

The C1/C2 is based on the TITAN platform from Vinci Labs in Finland (formerly Flextronics Finland Oy). See: http://www.vincilabs.com/

If you upgrade the software you will notice that the update program is called "TitanUpdater.exe". The back of the C1/C2 also says "Made in Finland", so there is no question about these facts :B

Peter

[slayer]

Never heard of them. I just went through their whole site. Thanks for the link. It sounds like they OEM for several companies. Did you read the specs on the new Titan? Sounds nice. I'm curious who else they manufacture for. This is typical for a majority of the companies. They find a platform that they like, and have that company OEM their models for them but built with certain features and changes that they want.
Outlaw states on their site clearly that it is a modified Sherwood Newcastle P-965.
I think the companies that design, manufacture, and sell their own products are the ones that demand a kings ransom. Meridian, Theta...

[J.H.]

Question I have been on that website before. Can you buy the Sound-1 or the Titan themselves? Or is it just a platform used to make other processors not an actual processor? Thanks J.H.

[Peter Nielsen]

I think the companies that design, manufacture, and sell their own products are the ones that demand a kings ransom. Meridian, Theta...

King's Ransom or not... I don't know. I'm getting SERIOUSLY interested in the Meridian 861. I really like the fact that they honor the "early adopters", i.e. the 861 is hardware upgradeable to a very high extent... To boot, it has all the features you could dream of. The price is really very reasonable when you think about it. When you buy a Meridian 800-series, you buy it to keep it for 10 years. (I'd like to keep my stuff for 20 years, but I guess 10 years is a reasonable lifespan for a PrePro and DVD)

Personnally, I think that Meridian has what it takes to keep me happy when it comes to the PrePro and DVD... (The saving starts... :B )

Peter