[ScottMayo]

By doubling the input decoupling cap, the 20hz drop is now only 0.25db (versus 0.9db). Yeah, it is very good but can anyone hear the diff?

I'm told (haven't tried it) that a simple test device for this sort of thing is a Buttshaker or similar device. Maybe you won't hear a 0.5db difference, but your bottom will know.  

Anyway, getting to +/- 0.1db from 15Hz to 50kHz isn't really about the ears. At least not at 20Hz. What's it's about, to me, is being able to notice a problem and being able to flatly say, "well I know the amp is flat and I know the wire is neutral, so let's start with..."

When you are tuning a room, it's nice to know what gear is on your side and which gear isn't. At 0.25db down, you're almost there.   I'm very intrigued by an amp that's lightweight, packs some power and is razor flat, 15-50. Just the tool for helping evaluate a room - and driving my sub in between.  

[mlawson66]

Well, 1dB is 26% difference in power. It is also defined as the following: "One decibel is close to the Just Noticeable Difference (JND) for sound level"
Check out the link. You can hear the difference 1 dB makes. http://www.phys.unsw.edu.au/~jw/dB.html The sound files just use white noise but they do illustrate that you don't have to be an audiophile to hear 1 dB difference in signal. It is a fun site.

I'm very happy with my NuForce amps and look forward to trying one with a larger cap (or more caps) on the input. Should make for a real "butt shaker"  

Yeah, I agree with Scott. It is more a peace of mind thing.

[ctviggen]

I always thought that 3db was about a minimum threshold for hearing.  But it's actually frequency related. See here:

http://www.phys.unsw.edu.au/~jw/dB.html

Also, white noise has all frequencies, so it's not a real good indicator for certain things, such as low frequencies.  If you're curious, play a 20Hz tone and increase the sound until you get a 1 dB increase using a RS SPL meter. Personally, I can barely hear 20 Hz at all.  30Hz, I can hear.  20 Hz?  I don't think I can, even when the RS meter tells me that I should.

[mlawson66]

Yep, after listening to the sound samples from the link mentioned above again,  I sure can't distinguish .25 dB but 1 dB is pretty obvious.

Doubling the decoupling cap sounds like a winner!  

Jason, how does this effect the higher frequencies?

[mlawson66]

I always thought that 3db was about a minimum threshold for hearing.  But it's actually frequency related. See here:

http://www.phys.unsw.edu.au/~jw/dB.html

Also, white noise has all frequencies, so it's not a real good indicator for certain things, such as low frequencies.  If you're curious, play a 20Hz tone and increase the sound until you get a 1 dB increase using a RS SPL meter. Personally, I can barely hear 20 Hz at all.  30Hz, I can hear.  20 Hz?  I don't think I can, even when the RS meter tells me that I should.

Sorry about that Bob. Thast last message got posted before I saw your post. Yeah, we would have to use a frequency generator and a pure tone in the frequency range in question to do a true empirical test. My hearing is probably not what it used to be. Too much motorcycle riding without ear plugs and too much bass in the HT system. Yeah, that and I think Seattle might be close enough to John C's monument to massive bass system that my hearing might have been effected.  

Yeah, I wonder if 1 dB is distinguishable with the seat of the pants?   We will have to try this at home this evening.

[doug s.]

...Yeah, I wonder if 1 dB is distinguishable with the seat of the pants? We will have to try this at home this evening....

i suspect it is, if yure listening to test tones really carefully.  w/music, i somehow think it would be a lot harder to hear.  not sure it would be worth modifying an amp to have 0.65db higher response at 20hz, if the mfr sez it will negatively impact the midrange.  mebbe bigger caps w/small bypass caps is the way to do it?

doug s.

[ctviggen]

Well, the only reason I posted this was because I have a CD of test tones (actually, I now have about 5 CDs of test tones) that go from 20 Hz to 1 kHz in certain increments.  I've used these to test my many different versions of my system (before I got ETF, that is).  When I would test at 20Hz, the RS meter would say a certain dB level, and I could tell somewhat that something was playing, but the higher test tones (I think the next higher was about 30 Hz) were way more audible to me even though the RS meter might be registering about the same dB level.  So, a 1db change at 1kHz may be audible, but you might have to have a 5db change at 20Hz for the same effective loudness increase, depending on your hearing.

[mlawson66]

...Yeah, I wonder if 1 dB is distinguishable with the seat of the pants? We will have to try this at home this evening....

i suspect it is, if yure listening to test tones really carefully.  w/music, i somehow think it would be a lot harder to hear.  not sure it would be worth modifying an amp to have 0.65db higher response at 20hz, if the mfr sez it will negatively impact the midrange.  mebbe bigger caps w/small bypass caps is the way to do it?

doug s.

Hey Doug, I agree that we wouldn't want to jeopardize mids and highs for a flatter response on the bottom octaves. The only reason the question came up is that I'm using 2 of them to drive the subs on my RM30s because these amps have excellent dampening (> 4000) and are particularly clean in the lower frequencies (no 60 or 120 Hz noise at all!). The awesome guys at NuForce have graciously offered a modification to their amps to bring up the response in the lower frequencies for those of us that are using these amps to drive subs. Yep, if I was running these on a full range speaker, I would definitely leave well enough alone.  

In fact, I'm still debating whether I will bother with this mod or just hold out for some Larger Subs. If I leave these guys stock, they are more versatile and as the system evolves, they can used in other ways/systems. I do still intend to replace the HT amp with NuForce amps. This weekend we will do a side to side comparison between an RM30-MW bi-amped with 2 channels of Son of Ampzilla and an RM30-MW driven by 2 NuForce Reference 9s.

As for bipassing caps, they do make for a larger package but a sweeter sound. In all my home grown headphone amp projects I've use multicap http://www.capacitors.com/catalogs/multicap_3.html caps and can attest to their sonic qualities. I haven't had the opportunity to try Auricaps or TRT caps in anything I've built yet. I leave that for the pros like Brian C...

[mlawson66]

Well, the only reason I posted this was because I have a CD of test tones (actually, I now have about 5 CDs of test tones) that go from 20 Hz to 1 kHz in certain increments.  I've used these to test my many different versions of my system (before I got ETF, that is).  When I would test at 20Hz, the RS meter would say a certain dB level, and I could tell somewhat that something was playing, but the higher test tones (I think the next higher was about 30 Hz) were way more audible to me even though the RS mete ...

Bob, those CDs sound like they would come in handy. Where did you find them?

I'm obsessed with my system but I guess the most of us are...  

[KJ]

Depending on the capabilities of your system, you can purchase a test tone generator online for about $25.00.  Since I use the pre-out functionality of my receiver to front the signal, I just installed the software on my laptop, hooked up a USB cable between the two and was off and running.  You can set what Hz tone you want to hear, how long, etc.  Comes in handy, and it has a free 30-day trial.

-KJ

[mlawson66]

Awesome! Thanks KJ. My wife is just going to shake her head   "Too many gadgets for you."  

[ctviggen]

I would go the test tone generator route, as KJ suggested.  I have several CDs that have things like phase reversal (which, sadly, I cannot tell which phase is better), imaging tests (they take the microphone and walk from the back of a church to the front, then to the left and right, etc.), and a whole bunch of other tests. If you want more info, let me know.

[JoshK]

I find those test CDs to be really really useful.  Phase is a strange one and it is hard to say what is absolutely correct as many albums switch phase throughout the album, from track to track. Some DACs have phase switches.  

Of the three phase test tracks I have, two of them I can definitely tell the difference and one I can't.  Oddly enough, the one I can't tell the difference has some horns in it and I was a horn player for quite a few years.  The other two I thought were mildly obvious.

[mlawson66]

I'll have to get some of those CDs. In the mean time, I've got a couple software signal generators compiled and working on the mac mini. I'm in the process of making some test CDs but I'll have to get the real deal at some point.

Anyway, I just wanted to give an update. I've had the NuForce amps burning for about a week. One of them is running full range on an LRC. I've got to say, that one is breaking in nicely. The dynamics are awesome. Lots of instant power. I really do like the presentation on these amps. I'm just dying to do try the RM30 full range expirement. Well, good night all...

[doug s.]

marchand electronics (www.marchandelec.com) has sound generating stuff on-line for free doqnload.

http://marchandelec.com/fg.html

they also sell a retail $250 sinewave generator.  and the best crossovers at anywhere near a reasonable price, imo.

i would certainly recommend vmps subs to anyone - i certainly think the pair of vmps larger subs i have are the greatest!    if you have a smaller room, i am certain the original or dedicated subs will be yust as good.  now, if i can only get my personal mess straightened out enuff to set up my subs again.  

doug s.

[CornellAlum]

A larger works great in small rooms, I should know, I have both!  Just one though, two might be neighbor-really unfriendly!

[doug s.]

A larger works great in small rooms, I should know, I have both!  Just one though, two might be neighbor-really unfriendly!

if i were in a smaller room & had to choose between one larger & two originals or dedicated's, i would go for the pair of smaller subs.  i strongly prefer a pair of subs over a single sub for 2-channel audio.

regards,

doug s.

[mlawson66]

Nice digs Doug! Good taste in music too. Thanks for the signal generator link. I'm having a little trouble being totally objective with the RM30-MW NuForce vs Son of Ampzilla test as the Reference 9s have a bit more gain (1.5 dB) than the SoA so I'll have to make a recording to compensate for this. Very subjective initial impressions are as follows:

The SoA sounds a tad deeper on the bass but maybe not as controlled. The NuForce is very articulate in the bass and midbass. The NuForce also seems warmer and more forward in the mids and highs. The SoA is more liquid and laid back. I want to compensate for the gain difference before I give a full review. I might break down and get some software that will let me record JC's reference tracks with one channel at 1.5 dB higher than the other. (By the way, thanks John for the cool reference cuts CD. You have excellent tastes. )

Anyway, both of these amps are excellent. Initial impressions tip the hat to the SoA for finesse and the NuForce gets major kudos for control, especially in the midbass to bass. The full on review is still to come.

I think that a pair of dedicated subs will be the answer for the bottom octave or two on the bass. Now I just have to be creative and figure out how to fit all that into my living room. I'm running out of wall! Well, if I can stand waiting long enough, I can replace that behemoth big screen projection tv for something that will sit on top of a couple of larger subs I'll be in nirvana!