A21 and class A...?

**Peter Nielsen** · 04 April 2005, 07:25 Monday

Originally posted by jonia

anyone know at what power output the amplifier switches from class A to AB ?

Supposedly at 4 Watts/channel in 8 ohms.

Peter

**Actiman** · 04 April 2005, 15:25 Monday

Hi Jonia,

Welcome to the forum!

You sure have nice equipment! (I'm referring to the amplifier :lol

Thanks for the nice picture!

Bye,
Acti

**Hirogen** · 04 April 2005, 17:53 Monday

Originally posted by Peter Nielsen

Supposedly at 4 Watts/channel in 8 ohms.

Peter

Are you sure? If my memory serves me well I think I've read some time ago that the A51 switches to class AB at 6 Watts. Since the A21 is its 2-channel peer it would make sense this amp switches also at 6 Watts.

However, it would be nice if someone could confirm this; I couldn't find it with a quick scan through the manual.

**Peter Nielsen** · 04 April 2005, 18:47 Monday

Originally posted by Hirogen

Are you sure? If my memory serves me well I think I've read some time ago that the A51 switches to class AB at 6 Watts. Since the A21 is its 2-channel peer it would make sense this amp switches also at 6 Watts.

However, it would be nice if someone could confirm this; I couldn't find it with a quick scan through the manual.

In an old post I remember writing that the A51 does 6W/channel for a total of 30W in Class A. This is unverified info I got from some place on the net. However, now that I own the A51 and JC1s, I'm pretty sure that the source of this info is wrong. I don't believe that the A51 can idle at 5*6W. It is just not realistic when comparing my A51 to one of my JC1 monoblocks. The JC1 runs noticably warmer than the A51 in low-bias (10W) mode. In high-bias (25W) mode, the JC1 gets so hot in a few hours, that you burn your fingers! The JC1 cooks and the A51 is still cold in comparison...

My conclusion is that the 5 channels of the A51 combined idle at no more than 10 Watts. Since the A51 does have the additional 5th heat sink on the back, it is likely that it idles at 2 watts/channel (but runs a tad cooler than a low-bias JC1 thanks to the 5th heat sink).

In another post, somebody claimed that the A21 does "8 Watts in Class A". Assuming the the A21 is running about as hot as the A51, then 4 W/channel is likely (for a total of 8W). If it runs noticably cooler than the A51, then assume less - maybe 2W/channel... (Disclaimer: I have never used an A21. Maybe Chris could comment on this. I noticed that his rack features the A21 on bottom, which implicates it possibly runs cooler. Chris, please comment!)

Peter

**Chris D** · 04 April 2005, 23:24 Monday

Well, one would assume that since the A51 and A21 run the same wattage, but the A51 has 2.5 times more channels, the A51 would run considerably warmer. Yes, that's why I chose to install the A21 on the bottom of my rack, and the A21 above it. I've noticed that the A51 does indeed run warmer than the A21, but not really as much more as I would have guessed. I guess part of it could be that I have my A21 driving my rear speakers of my 7.1 setup, which doesn't get nearly the amount and volume of signals that the front channels do.

I've also noticed that the A51 is NOT just a 5-channel version of the A21 with the same construction. Yes, they're very similar, and yes, they have equal 250 wpc outputs. But the A21 adds a few things, and I wouldn't be surprised if it has some construction slightly above the A51, but not nearly at the level of the JC1. The JC1 is really in its own class. Sorry that I don't know technical engineering details.

Jonia, welcome to the Guide and Club Parasound. Congrats on the new equipment! :banana:

**jonia** · 05 April 2005, 00:54 Tuesday

Thank you for your answers.... if the A21 runs in class A to say 4 watts per channel in 8 ohms, what is the situation when running 4 ohm speakers? Is it capable to run in class A to 8 watts then?

And does any of you know at what approx. soundpressure one could get at 4-8 watts per channel? Is this normal listening or is it very low? I would say 70 dB to 80 dB is rather normal listening....

I have speakers running at 4 ohms...
A picture of my multichannel system:

**bhuskins** · 05 April 2005, 04:28 Tuesday

Chris...Put your A21 on your L/R mains...you'll thank me later.

Brent Huskins
Media Design

**MichiganMike** · 05 April 2005, 05:34 Tuesday

The review of A51 and A21 at audioholics.com (http://www.audioholics.com/productre...Amplifier.html) suggests 8 watts in Class A. See following quote:

"One of the most noteworthy operational functions of the Parasound A 21 and A 51 amplifiers are their Class A-A/B operation. The input and driver stages operate in pure Class A meaning that the transistors are turned on full all of the time. In essence there are two banks of transistors in the output stage, one of which is devoted to positive voltage and the other devoted to negative voltage. The point where the positive output transistors turn on while the negative transistors turn off (and vice versa) can cause nasty higher-order odd harmonic distortion (3rd, 5th, 7th, 9th, etc.) for which even very small amounts have been demonstrated as a primary cause of listening fatigue. In these Parasound amplifiers both the positive and negative transistors for each channel are always fully on – the definition of Class A operation - up to 8 watts output per channel. So, for the first 8 Watts of power, which exceeds the typical average power requirements for music, the output transistors are always on. For greater than 8 Watts, the transistors are in class A/B operation where they are partially on when they're not up for duty and fully on when they are up for duty."

**Hirogen** · 05 April 2005, 05:39 Tuesday

Originally posted by Chris Dotur

I guess part of it could be that I have my A21 driving my rear speakers of my 7.1 setup, which doesn't get nearly the amount and volume of signals that the front channels do.

Could you tell me why you set it up this way? It would be more logical to me to connect the A21 to the 2 front speakers and the A51 to the 5 surrounds, especially when you suspect that the A21 may be using somewhat better quality components inside. I mean you do listen to stereo sources sometimes don't you?

edit: aah, Brent beat me to it. 8O

Btw Chris, maybe you could contact your sources at Parasound and have this Class A question (for both the A21/A51) answered once and for all.

**jonia** · 05 April 2005, 05:48 Tuesday

8 watts in class A, is that 16 watts in class A when using 4 ohm speakers?

**Peter Nielsen** · 05 April 2005, 07:18 Tuesday

Originally posted by jonia

8 watts in class A, is that 16 watts in class A when using 4 ohm speakers?

No, I don't think so. I'm pretty sure it's still 8 watts total. Unfortunately Parasound doesn't even tell us what the case is with the JC1 in 4 ohms. All the specs say is 10W/25W in 8 ohms...

Peter

**Peter Nielsen** · 05 April 2005, 07:20 Tuesday

Originally posted by Chris Dotur

I've noticed that the A51 does indeed run warmer than the A21, but not really as much more as I would have guessed.

That confirms my guess. The A21 has a higher per-channel bias current than the A51. The A21 will probably do close to 4 watts per channel in Class A.

(FWIW, when comparing the Class A heat dissipation NO SIGNAL should be applied. The amps should idle. Class A always runs the amp at full Class A power. I.e. a 25W class A amp will run at 25W regardless if there's music or not. If you apply a signal, you may inadvertedly cross the Class AB switch boundary and the comparison is ruined.)

Originally posted by Chris Dotur

I've also noticed that the A51 is NOT just a 5-channel version of the A21 with the same construction. Yes, they're very similar, and yes, they have equal 250 wpc outputs. But the A21 adds a few things, and I wouldn't be surprised if it has some construction slightly above the A51

Absolutely correct! And as Brent already pointed out, hurry up and put the A21 on your main speakers. That's where it belongs. :wink:

Peter

**nicholtl** · 05 April 2005, 13:08 Tuesday

Yup, I switched out my mains from being run off the A51 to strictly the A21, and there was quite a marked improvement in all departments of industry buzzwords.

**Peter Nielsen** · 05 April 2005, 13:29 Tuesday

Originally posted by MichiganMike

The review of A51 and A21 at audioholics.com (http://www.audioholics.com/productre...Amplifier.html) suggests 8 watts in Class A.

While 8 watts probably is correct, the statement "8 watts/channel" must be wrong. (This would mean the A21 idles at 16 watts). The JC1 has only one channel, and at 10 watts, it idles hotter than the A21/A51.

Peter

**MichiganMike** · 05 April 2005, 17:25 Tuesday

Originally posted by Peter Nielsen

While 8 watts probably is correct, the statement "8 watts/channel" must be wrong. (This would mean the A21 idles at 16 watts). The JC1 has only one channel, and at 10 watts, it idles hotter than the A21/A51.

Peter

Peter, I am not certain that apparent relative temperature between amplifiers with different designs, different layouts and different number of channels is necessarily going to be a good indication of how many watts in Class A. To directly compare you would need to run a controlled experiment, remove other heat sources in each amplifier and have the same conditions for heat transfer (convection, external temperature, heat sink radiational surface, etc.). For example, the manual recommends at least 6 inches clearance above the A51 and three inches to the sides. If there was less clearance or poorer air flow with one amp than another, this may affect relative temperatures. If one is above the other in a rack, even with proper spacing, heat rises so the differential temperature across the heat sinks may be diminished in the unit higher in the rack and the temperature of the heat sink may be somewhat higher even for two identical amps.

I am not an electrical engineer, so I will defer to the experts on circuit design to address the Class A operation. One of the reviewers of the A21/A51 at audioholics.com is an electrical engineer and the other is a mechanical engineer with ISF training, so they both know more than I do about the field. However, I have no idea how they checked their facts.

Audioholics.com has a discussion forum linked to the A21 and A51 review. That may be another place to ask questions on their Class A operation.

**Peter Nielsen** · 05 April 2005, 18:15 Tuesday

Originally posted by MichiganMike

Peter, I am not certain that apparent relative temperature between amplifiers with different designs, different layouts and different number of channels is necessarily going to be a good indication of how many watts in Class A.

I agree 100%. Between two brands, it would be impossible to draw conclusions like this. However, the JC1, A21, and A51 are all similar enough to do it thanks to the identical steel case and heatsinks. (The cases are identical, except for the A51 that provides a 5th sink on the back).

I'm absolutely sure Parasound would have made the JC1 do more than 25W in Class A if they could. They even had to provide a bias switch to let the user select a "cool" 10W mode (which still runs hotter than the A51 and A21).

I'm pretty confident that the A21 will do no more than 4W Class A/channel. However, anyone is welcome to prove me wrong! :T

I'm also sure that the Audioholics guy didn't verify the fact, since this would be pretty difficult and involve disassembling the amp. Maybe it's just a simple misunderstanding. Parasound told him "8 Watts" and he incorrectly assumed it was per channel. (Mishaps like this happens when an engineer talks to a sales person :B) Now, if they had included the JC1 in their test, they probably would have come to the same conclusion as I, and realized that there is no way the A21 idles at 16W in Class A.

Doing a Google search on "Class A" heat dissipation provides a lot of valuable info! Spend some time reading this, get hold of an A21/A51 and JC1, and you will most likely come to the same conclusion I did. If not, then post your facts here. I'm an electrical engineer by education (MSEE), but my work the past 10 years is in the field of computer science, so I could be wrong, especially since I'm by no means an expert in audio amplifier design...

Peter

**jonia** · 06 April 2005, 01:22 Wednesday

Howcome Parasound doesn't state the effect in class A in the manual? That could be interesting for some nerds... like myself....

And if we conclude that the A21 is capable of 4 watts/channel in 8 ohm (and let's say the same in 4 ohm), is that enough to run in pure class A when listening to music at "normal" listening levels, say at 70-80 dB soundpressure?

Thank you for all your replys!

**Chris D** · 06 April 2005, 01:59 Wednesday

Actually, my "contacts" at Parasound are everybody else's contacts too. I've probably shot the breeze with everybody in the company at one time or another, but others have too, and posted about it. Richard Schram, the president, even takes time to talk to consumers about some things. So if anyone wants the full info, go ahead and give them a call! Just check out the "Contact Info" thread at the top of Club Parasound that I made. Sorry, I got a lot on my plate right now, and wouldn't be able to call for a while myself.

Brent/Hirogen/nicholt/Peter - Actually, we had a discussion thread about this a while ago here in Club Parasound, earlier towards the beginning, whether it was better for a A21/A51 combo to use the A21 for rears or front mains. I'd have to dig up the discussion. I'll try the swap and put the A21 on the mains and see if I notice a difference.

**Hirogen** · 06 April 2005, 06:46 Wednesday

Chris, (or anybody else)

I looked in the contact info thread and since it's not there I was wondering if there isn't some kind of generic e-mail address available? (e.g. support@parasound.com) I'd rather e-mail than call since I'm in Europe.

I got one address but that's a personal address of someone who works at Parasound and the last time I used it I got no reply.

If you find it please add it to the contacts thread as well.

Thanks.

**Peter Nielsen** · 06 April 2005, 07:12 Wednesday

Originally posted by jonia

And if we conclude that the A21 is capable of 4 watts/channel in 8 ohm (and let's say the same in 4 ohm), is that enough to run in pure class A when listening to music at "normal" listening levels, say at 70-80 dB soundpressure?

That very much depends on what speakers you're using. At 4 watts, a pair of efficient horn speakers (e.g. 104dB/1W/1m) may give you 103.3 dB at 10' listening distance while inefficient speakers like my Maggies (85dB/1W/1m) will only give 84.3 dB...

SPL Calculator

Peter

**Chris D** · 06 April 2005, 11:33 Wednesday

Hirogen, thanks for pointing that out. I haven't even looked at the contact thread for a very long time. It's service@parasound.com

Updated now. I need to update the other locked threads too.

**Hirogen** · 06 April 2005, 13:17 Wednesday

Originally posted by Chris Dotur

Hirogen, thanks for pointing that out. I haven't even looked at the contact thread for a very long time. It's service@parasound.com

Updated now. I need to update the other locked threads too.

Thanks Chris, I've sent them an e-mail.

**Chris D** · 06 April 2005, 21:40 Wednesday

Hirogen--where are you located, anyway?

**jonia** · 08 April 2005, 01:12 Friday

My speakers run at 4 ohms, and have a sensitivity of 91 db/1w/1m .

From this I guess that my speakers are capable of 97 db/4 watt/1m.... (double the effect gains 3 dB soundpressure).

So, my listeningposition is about 3,5 meters from the speakers, I don't know how many dB's that are lost on the way... but that can't be more than 10 dB, can it? So, that means I could expect pure class A operation at normal listening levels (between 70-80 dB).

Anyone have comments on this?

And another question...
How loud do you guys normally listen to music and movies? I have a problem because I listen to movies very loud... and I can't really do anything with it... I love watching movies loud and I always crank up the volume more than I should... Even though I know i shouldn't... Typically listening levels are in the area 85-90 dB from my center channel (dialogs), that gives me readings of more than 100 dB in explosions and other action-scenes...
The question is if this is dangerous for my ears.....

**Peter Nielsen** · 08 April 2005, 07:17 Friday

Originally posted by jonia

Anyone have comments on this?

Click the "SPL Calculator" link in my previous post. It takes you to a calculator that lets you calculate the exact figures at the specified distance... At 12' (~3.6m), your speakers could output 88.8 dB if placed away from the wall and as much as 94.8 dB if placed in the corners of the room.

Peter

**Hirogen** · 08 April 2005, 08:06 Friday

Originally posted by Peter Nielsen

Click the "SPL Calculator" link in my previous post. It takes you to a calculator that lets you calculate the exact figures at the specified distance... At 12' (~3.6m), your speakers could output 88.8 dB if placed away from the wall and as much as 94.8 dB if placed in the corners of the room.

Peter

Peter, thanks for posting that link to the SPL calculator, interesting and bookmarked.

Chris, I'm from the city where anything goes ... Amsterdam, in The Netherlands.

**Hirogen** · 11 April 2005, 08:43 Monday

Okay I received an answer to my e-mail from a Parasound tech. Somebody put this in the FAQ please.

Question: At what poweroutput (above how many Watts) does the A51 and A21 switch from Class A to Class AB ? Please specify if this is per channel and at how many Ohms this is.

Answer:

The A51 delivers 2 watts per channel into 8 ohms and 1 watt into 4 ohms.

The A21 delivers 5 watts per channel into 8 ohms and 2.5 watts per channel into 4 ohms.

The results may vary slightly due to bias levels and parts tolerances - AC mains voltage will also affect levels.

**Peter Nielsen** · 11 April 2005, 10:04 Monday

Originally posted by Hirogen

The A51 delivers 2 watts per channel into 8 ohms and 1 watt into 4 ohms.

The A21 delivers 5 watts per channel into 8 ohms and 2.5 watts per channel into 4 ohms.

Aha! My educated guess and conclusion about the A51 being 2W per channel was right-on! :B

When thinking about the 4 ohm wattage, I feel stupid. Since the idle current is constant, the wattage can very easily be calculated using Ohm's laws: P=I*R :bash:. Now that we know the wattage at 8 ohms, we can conclude that the idle current is 0.5A for the A51, 0.79A for the A21 and 1.77A for the JC1.

Of course this means that the JC1 will only produce 12.5W in 4 ohms or only 5W in low-bias mode :roll:

Peter

**Peter Nielsen** · 11 April 2005, 17:38 Monday

Chris, with this info in mind, your A21 needs to be on top!!!

Both the A21 and A51 have identical idle power when combining all the channels in the amp. However, the A51 has 5 heatsinks, 4 radiating to the sides and one to the back. The A21 puts the same power in 4 heat sinks on the sides.

Ideally the unit that runs the hottest should go on top. Considering this, the A21 should go on top of the A51, since its heat dissipation capability is lower than the A51's (four heat sinks vs. five).

Peter

**nicholtl** · 11 April 2005, 20:49 Monday

Hey Pete,

In my experience, while the A51 has more heatsinks, after heavy multichannel music playing, or a DVD movie, the A51 is always atleast twice as hot as my A21 (which runs the mains)?

That's why I keep my A51 on a shelf a foot above my A21.

**Chris D** · 11 April 2005, 22:54 Monday

Ah... for me, I'm not going to swap my A21 and A51 in my rack. Way too heavy and too much work to do the swap at this point. Maybe the next time I move and take apart the whole rack anyway!

**nicholtl** · 12 April 2005, 00:06 Tuesday

Oh come on, Chris! A little excercise never hurt anyone! =)

A21 and class A...?

A21 and class A...?

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